CA1157622A - Polysulfone surfaced laminated blanks - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A blank and method for its manufacture which blank is useful in the preparation of printed circuit boards.
The blank comprises an insulating substrate, typically impregnated with an epoxy resin and with reinfo???? fiber glass. Superimposed and adhered to at least one surface of the substrate is a high temperature thermoplastic polymer film or sheet having a substantially uniform thickness between about 10 and about 500 microns. The thermoplastic polymer surface can be chemically treated to activate it and facilitate subsequent deposition of an adherent film of electrolessly deposited metal thereon. The circuits formed by such deposition are uniform, have excellent adherence of a conductor pattern to the thermoplastic polymer surface, have excellent electrical properties and resist heat in continuous use or when soldered.

Description

11~i7~ 2 ~ ,~
~CJ198~ !l Il . . . ,.
.~ Il .
1 1 BACKGRO~UND OF T~ INVENTION
1. Field of the Invention ; 3 ¦ This invention relates in general to a blank and 4 I a method of its manufacture, the blank being suitable for S use in the manufacture o printed circuit boards. More particularly, the present invention relates to a blank 7 comprised of an insulating substrate having a thin, high .~ temperature, ther~oplastic polymer sheet or film superimposed and adhered to at leas~ one surface thereof and a method of its manufacture.
lL 2 Description of-the Prior ~rt . . . .
12 Printed circui~ boards generally comprise an 13 electrically insulating substrate associated with one or more 14 electrically conducti~e circuit patterns. Typically, the insulating substrate comprises a synthetic resin co~position 16 reinforced with non-conductive fibrous materials, for exa~ple, 17 fibrous glass sheets or papers or webs or ~ats of glass fibers 18 in either woven or unwoven form, or cellulose paper sheets; the 19 electrically conductive circuit pattern may be a metal such as copper, nickel, cobalt, gold, sil~er or the like.
21 The use of insulating substrates to prepare printed 22 circuits by electroless deposition techniques is well known.
23 For example, in the preparation of such printed circuits, 24 adhesion of a copper conductor pattern to an insulating plastic support or base has been obtained by high pressure, 26 high temperature lamination of copper foil to the base. After 27 the lam$nation, the copper conductor pattern is established by 28 etching away most of the copper to lea~e ehe desired conductor ~ 29 1 pattern. Frequently before etching, it is also necessary to J~ 30 ;l electroplate additional copper to establish interconnections ';. ,....... . '

-2~

;

~' , ~ : -; ~ ~
'' ' ~-198 ~ 7~Z ( 7 ,';'~ . . ~' '.~ .
1 between separate layers of etched conductor patterns. ~o 2 overcome adhesive tifficulties and waste of ~opper associated ¦ with the techniques of lamination of copper foil and etching . 4 1 conductor patterns described hereinabove, the use of adhesi~es ,,; 5 ¦ have been proposed in U.S. patents 2,699,424 and 2,699,425, ¦ both to ~ieter and also in U.S. patent 3,052,957 to Swanson.
These adhesives are receptive to and can be coated with a thin 8 electroless metal film before the conductors are formed by 9 electroplating. The adhesive, in the form of a film, then may be cross-linked and thermoset. These techniques have not been 11 widely adopted because the adhesion of the conductor to the 12 ¦¦ insulating substrate is generally poor, i.e., 0.7 newtons/~m 13 !I conductor width. Generally, the printed circuit industry 14 1 requires at least 1.4 newtons/mm. U.S. patent 3,625,758 to Stahl et al. discloses thermosetting a rubber-resin film before L6 electrolessly depositing a metal in order to improve adhesion.
17 The insulating resinous film layer adhered to the base has uni-1 18 formly distributed therein particles of a resin or rubber 19 oxidizable and/or degradable by suitable oxidizing chemicals.
The peel strengths achieved according to the techniques of 21 U.S. patent 3,625,758 are, in general, excellent, i.e., 3.5 22 newtons/mm.
23 The Stahl et al. technique has been successfully 24 employed in the printed circuits industry for a number of ~'~ 25 years. Its main deficiency has been surface resistance. The 26 surface resistance of printed circuits employing the techniques - 27 disclosed in the above-mentioned U.S. patent 3,625,758 have ; 28 been as low as 5000 megohms when conditioned according to ASTM
29 D618-61 Procedure C and measured on an insulation resistance ; I pattern as shown in IPC Test Method Number 5.8.1 (April, 1973)

- 3- . i -:
. ' ~, ' .

11~762Z
(Institute for Interconnecting and Packaging Electronic Circuitry, 1~17 Howard St-reet, Evanston, Illinois 60202);
reinforced, epoxy resin impregnated substrates typically have a surface resistance of about 100,000 megohms. As circuits have become more complex and conductors spaced closer together, low surface resistance becomes a problem.
The prior art adhesive techniques can also be better understood by the type of substrates used. Organic coatings and materials whose surfaces may be provided with electroless metal deposits having commercially acceptable adhesion, that is, peel strengths of at least 1.2 newtons/mm of width, have heretofore fallen into two distinct categories according to the method of preparing them and the requisite chemical treat-ment for insuring sufficiently adherent electroless metal plating on them.
A first type includes such products as the adhesives disclosed in the aforementioned U.S. patent No. 3,625,758 and epoxy/phenolic blends with synthetic elastomers. Materials of this first type typically contain a dispersed phase of synthetic rubber such as butadiene or acrylonitrile butadiene copolymers with a matrix of materials such as epoxy/phenolic blends. The material of the dispersed phase of such substrates ; is readily degraded by oxidizing agents, such as chromic or permanganate solutions, while the matrix phase is less reactive to such agents. Following the oxidation treatment, the sub-strate surface is microporous, resulting in greatly increased `- surface area. The substrate surface also has been transformed from hydrophobic to hydrophilic and is suitable for further processing in known electroless metal plating procedures.

. .
, "
.: .: . :

, ;
' ~
'' ' :

!
-198 ( ~ ~j7 6 ~

11 .

1 ,' Substrates of this type, i e., hetero~eneous, dlc-2 ¦¦ persed phase-matrix phase materials, have pseviously been 3 ¦I prepared by mAsticating prepoly~ier of the dispersed or

4 ¦I reacti~e phase material in solvent down to the desired molecular

5 ¦ L weight or chain length, and then blending the masticated

6 prepolymer with the continuous phase or matrix phase materials

7 in copious amounts of solvent. Such substrate materials

8 ¦ normally comprise from 65 to 80 weight percent solvent prior to

9 ¦ their application to base substrates as coatings, and,

10 ¦ following solvent evaporation, typically comprise about 60

11~, weight percent of unsaturated rubber as the dispersed phase and

12 1l about 40 weight percent of a thermosetting plastic matrix.
~; 13 ~¦ A second general type of resinous substrates, such 14 ~¦ as epoxy and polysulfone, includes materials having homogeneous 5 i¦ single phase. Forming a microporous surface on such substrates 6 1I requires a ~andatory step preceding oxidation; polar and strained 17 1! sites that are selecti~ely attacked in the oxidation steps ~Nst j 18 ll be created, usually by contacting the homogeneous substrate with 19 1 a strong organic solvent, to permit preferential attack at these ¦ sites. This process of swelling the surface with an organic 21 ¦ solvent prior to attack by oxidizing agents has become known 1 22 as the "swell and etch" technique.
23 In the "swell and etch" technique, the surface of a ~ 24 glass reinforced epoxy resin impregnated laminate i9 first : 2s treated with a solvent and then with a strong oxidizer, e.g., 26 ¦ chromic acid, to etch away part of the surface and produce a 27 ¦ microporous, hydrophilic surface suitable for adherent 28 ¦1l electroless metal deposition~ This technique by itself did 29 'j not give acceptable surface resistance because the oxidation !! coul~ be deep enough to allow contamination of the glass c;oth .
_ 5 _ ~: .

~ 762Z . ic C-198 l, . :
. ,i, ~ .
.. .

1 laminate core. To avoid this problem, manufacturers of glass 2 cloth reinforced epoxy resin impregnated laminates have produced 3 special grades of laminates with thick, epoxy resin "butter 4 coates" over the glass fibers. Using such grades of laminates, it has been possible to produce printed circuits with bond ,~ ,6 -strengths of 1.1 newtons/mm and an insulation resistance of .s.~,, ~qc,l~ ~S
' 7 100,000 ff~ge~m~,. However, the variation of the cure of the 8 epoxy "butter coat" from one manufacturer to another and from 9 lot to lot of the same manufacturer requires the process to be ! :
redefined for each lot. For this reason, attempts to achieve 11 commercial production have not been successful. A further 12 disadvantage of this process is the failure of the bond in large j

13 areas of exposed metal during soldering. !
'4 It is also well known that plas~ics may be electro^
plated for the decorative arts by chemically conditioning them 16 in strong oxidizing acids, e.g., chromic. Among the plastic 17 materials that have been successfully plated are acrylonitrile-18 butadiene-styrene copolymers, polyphenylene oxides, polysulfones, lg polycarbonates and nylon. The majority of these plastics are ' -not suitable for printed circuit board applications because they 21 cannot resist the temperature of soldering, i.e,, about 260C. I :
22 For example, acrylonitrile-butadiene-styrene has been proposed 23 for use as a film in the manufacture of printed circuit boards 24 but was not suitable because when used in typical process in-the manufacture of circuit boards, its bond stren~th was only 26 1 newtonjmm and the printed circuit board could not withstand 27 soldering temperatures.
28 Molded polysulfones have been used in very limited 29 quantities as printed circuit base material, but only in lligh frequency applications where the low dielectric constant and .
; ~ . - 6 - .

~, , ` `- . . --, . .
, .
;
.
, ' ' . ~, ~' ' ' , : . ,`' - ~57~ZZ
dissipa-tion factor of the polysulfone is required. Circuit base materials consisting of polysulfone have not achieved wide usage because of the extreme processing difficulties and the high price of the resin system. In processing molded polysulfone bases for use as printed circuit substrates, it is necessary to anneal or stress relieve a minimum of 2-4 hours;
6-8 hours is preferred. These laborious steps are required two or more times during a cycle. Over-annealing the poly-sulfone materials also must be avoided to prevent embrittlement thereof or other dileterious effects.

. ~ .

ms/ ''` ~ 7 ~
.
, ' '. . . ' . .

....

S7~iZZ

SUMMARY OF THE INVENTION

To achieve the foregoing objects, and in accordance with its purpose, as embodied and broadly des-cribed, the present invention provides an improved blank and method for its preparation, an improved metal clad insulating substrate and method of its manufacture, im-proved methods of producing printed circuit boards em-ploying the improved blanks and the improved circuit boards ; 10 formed thereby. AS Will be clear from the following des-cription, there is used in the manufacture of circuit boards of this invention certain blanks containing a thin surface layer of a thermoplastic resin with an aromatic backbone, .

.~ : mab/~

: : .
:' ';.~ ,.' ~ .:

,.

:
,. : ' .

~ ~7~2Z

By "B-Stage", as used throughout the speci-f:ication and claims, is meant that condition of a composi-tion where some but not all of the active molecules are cross-linked and the composition is still softened by heat.
By "C-Stage", as used throughout the speci-fication and claims, is meant that condition where a com-position has substantially reached the final stage of poly-merization where cross-linking becomes general and the composition assumes a thermoset, is substantially insol-uble and infusable.
The laminated blanks of the present inven-tion and methods of their preparation represent an improve-ment over the insulating substrates heretofore employed.
The methods of this invention utilize thermoplastic, organic~ high temperature polymers as the surface layer(s) of a blank. The surface layer has a thickness above about 10 micronsj preferably above about 25 microns, and most preferably above about 50 microns; the thickness of the polymer surface layer is below about 500 microns, mab/~
.. .. . . .

, ~

..

C-198 "` ~ 7~;i~2 ~c 1~ ~ ?

1 preferably below about 125 microns and most preferably below 2 about 75 microns. One or ~ore plies of a thermoplastic polymes 3 is superimposed and laminated onto one or more plies of a "B-Stage", resin impregnated reinforcement, such as glass, 5 1 cloth or paper, under heat and pressure to form a rigid 6 1 printed wiring board substrate. An advantage of this invention 7 ¦ is that it eliminates the problems associated with the prior 8 art methods of coating glass cloth surface sheets to yield a 9 "C-Staged" laminate exhibiting a 25-50 micron epoxy "butter coat"
or "resin-rich" layer.
The present invention provides a simple and 12 economical method of preparing (blanks) insulating substrates 13 having substantially planar surfaces which surfaces may be

14 adapted to receive a layer or pattern of conductive ~etal by electroless deposition techniques. In one aspect, this 16 invention relates to an insulating substrate suitable for use 17 in printed circuits and the method of its preparation which 18 method comprises:
19 providing thermoplastic films or sheets having a substantially uniform thickness between about 10 and about 500 21 microns, the thermoplastic material having an aromatic backbone 22 that does not liquify or decompose at a temperature of 245C
23 after five seconds exposure at the temperature;
24 providing a fibrous sheet or web impregnated with a 2S ¦ thermosettable resin or plies of the impregnated fibrous sheets 26 ¦ or webs;
27 superimposing at least one of said films or sheets .
28 on at least one of said plies of thermosettable resin impregna~ed 29 fibrous sheets or webs; and consolidating, preferably between planar press plates, ., . ~ . .
; ; ' ~ ! .. .

,~
,; '' ~ ' :. ' ` ~ '' ., , llS76Z2 the assembly so produced and curing the thermosettable resin by heating under pressure.
In another aspect, this invention relates to a blank suitable for use in printed circuits which comprises:
an insulating substrate having adhered to a surface thereof or opposite surfaces thereof a thermoplastic organic high temperature polymer having a thickness between about 10 and about 500 microns, the polymer having an aromatic backbone that does not liquify or decompose at a temperature of 245C
10 after five seconds exposure at the temperature.
In still another aspect, this invention relates to a laminate and the method of its preparation as subsequently described herein which laminate comprises the blank as described hereinabove and further including a layer of an electro-conductive metal superimposed on and adhered to the polymer surface layer(s).
The surface layer of polymer film serves as an adhesive means between the electroconduc.tive metal layer and the reinforced thermoset substrate. Consequently, to laminate a metal to a reinforced polyester substrate, for example, a metal film and 20 thin thermoplastic film may be pressed togther with a reinforced polyester substrate to bond the three together or the thermo-plastic film surface of the blank may be treated with an oxidizing media or a plasma to produce a hydrophilic surface receptive to subsequent metallization.
In another aspect, this invention relates to a multi-layer printed circuit board and method of its preparation which method comprises the steps of:
providing an insulating substrate having a circuit pattern adhered to at least one surface thereof;
applying a.layer of polysulfone film over the circuit , ms/ f t~

~ ~ .
., ,.~ .

';, ,-198 '( ~ ~ ~7~2Z . .~
I
.. I
., l pattern(s);
2 treating the polysulfone surface(s) with a solvent and 3 oxidizing agent to render said sur ace(s) microporous and 4 hydrophilic; and electrolessly depositing a metal onto the treated 6 surface (6) .
7 Any thermosettable resin known for use in preparing 8 insulating substrates for printed circuits may be employed in 9 applicants' method and blank provided it or they produce, together 10 with the other materials employed, the desired properties in the 11 finished substrates. Exa~ples are allyl phthalate, furane, allyl 12 resins, glyceryl phthalates, silicones, polyacrylic esters, 13 phenol-for~aldehyde and phenol-furfural copolymer, alone or 14 I co~pounded with butadiene acrylonitrile copolymer or acrylonitrile butadiene-styrene copoly~ers, ureaformaldehyde, melamine-16 formaldehyde, modified methacrylic, polyester and epoxy resins.
17 Phenol-formaldehydes may be used if requirements of use are not 18 s~ringent. Epoxy resins are preferred when stringent properties 19 are required~ For impregnating the fibrous sheets or webs utilized in applicants' methods, the thermosettable resin may be 21 employed in any convenient form and manner, but a varnish is 22 preferably employed wherein the resin is dispersed or dissolved 23 in a suitable medium. The weight of resin so~ids in the varnish 24 is not generally critical, but it is selected to achieve epoxy glass cloth composites comprising about 35 to 70Z, e.g., about 26 35 to about 55% resin solids by weight.
27 The insulating base of this invention need not be 28 organic. Thus, ~t could be made o~ inorganic insulating 29 materials, e.g,., inorganic clays and minerals such as ceramic, C ~'~o~ ~ ~ n~ ~
ferrite, c~.~v.rn~ , glass, glass bonded mica, steatite and ~K ~ r ~ ~ n v ~ ~

, ~ ... . _ .: - . . ~ .
. .

... .
, :
.. ..

., , , . . :

the like.
Suitable thermoplastic film materials are high temperature thermoplastic polymers having an aromatic back-bone and which do not liquify or decompose at a temperature of about 245C after five seconds exposure at such a tem-perature. Examples include polycarbonate, polysulfone having the following recurring unit:

~, .
"' ~~ ]

polyethersulfone having the following recurring unit:
~e} {}
d ; polyphenylsulfone;
polyphenylene oxide; and Noryl thermoplastic resin (Noryl is a trade mark for a molding and extruding resin based on ;' phenylene oxide technology and commercially available from General Electric Co., Polymer Products Operation, Pittsfield, Massachusetts).
~ 20 As can be seen in the structural formula set - forth hereinabove, each aromatic unit in the polysulfone ~ is linked to its neighbor by an -SO2- sub-stituent, called a sulfone linkage. Similarly, each aromatic unit in the polyethersulfone is linked to its neighbor by an -SO2- substituent at one end, and an -O- substituent ~ at the other end, called an ether linkage. Eurthermore, it i~' also can be seen that each substituent is separated by four .,~1 -~ carbon atoms of the aromatic unit; i.e. para substitution.

~ - 13 -X mab/ cJ~

. ` . `

-..................................... ` ` .. "

~57~22 Certain grades of these thermoplastics in molded sheets, rods and/or film forms can be treated to render the surfaces of these materials receptive to adherent metal deposition.
These materials have been used widely in the decorative, auto-motive, electronic component, medical appliance, food processing and dairy equipment industries. For illustrative purposes, the following discussion will be directed to certain grades of polysulfone (commercially available from Union Carbide Corportion, 270 Park Avenue, New York, New York 10017 under the trade mark UDEL). It is known that the various grades of polysulfone are characterized ~y toughness, low creep, and long term thermal and hydrolytic stability, including years of continuous service in boiling water or steam, and in air in excess of 150C, with little change in properties. Polysulfones qualify for Under-writers' Laboratories Thermal Index ratings of 150C; they maintain their properties over a temperature range from -100C
to above 150C. They have a heat deflection temperature of about 174C at 264 psi (1.8MPa) and about 181C at 6 psi (41KPa). Long term t~ermal aging at 150 - 200C has little effect on the physical or electrical proPerties of polysulfones.
Polysulfone may be prepared by the nucleophilic sub-stitution reaction between the sodium salt of 2,2-bis (4-hydroxy-phenyl) propane and 4,4'-dichlorodiphenyl sulfone. The sodium phenoxide and groups are reacted with methyl chloride to terminate the polymerization. This controls the molecular weight of the :
polymer and contributes to thermal stabilityO
- The chemical structure of polysulfone is characterized by the diaryl sulfone grouplng. This is a highly resonating structure, in which the sulfone group tends to draw electrons from the phenyl rings. The resonance is enhanced by having .' , ~
ms/~ f~ 14 -.
. .

!: , .

' ' . ~ ' 3L~57~22 oxygen atoms para to the sulfone group. Having electrons tied up in resonance imparts excellent oxidation resistan oe to polysulfones Also, ; the sulfur atom is in its highest state of oxidation. m e high degree of resonanoe has two additional effects: it increases the strength of the bonds involved and fixes this grouping spatially into a planar con-figuration. mis provides rigidity to the polymer chain, which is retained at high temperatures.
m e ether linkage imparts some flexibility to the poly~er chain, giving inherent toughness to the material. m e sulfone and ether linkages connecting the benzene rings are hydrolytically stable. m erefore, as indicated previously hereinabove, polysulfones are resistant to hydrolysis and to aqueous acid and alkaline environments.
Suitable g~àdes ~fpolysulfone according to the present invention include an unfilled grade such as the P-1700 series which is used for injection molding or extrusion; a higher molecular weight series for extrusion applications, such as the P-3500 series; and a mineral filled ; polysulfone useful for plating applications such as the P-6050 series (the P-1700, P-3500 and P-6050 series all being polysulfones identified by the trade mark UDEL ànd commercially available from Union Carbide Corporation, .'A 20 270 Park Avenue, New York, New York 10017).
Polycarbonates are linear, low-crystalline, high molecular weight (about 18,000) polymers in which the linking elemsnts are carbonate ; radicals. Polycarbonates possess a co~bination of very useful propsrties r' ~ including: (1) very high impact strength (16 ft.-lb./in. notch) oo~bined with good ductility, (2) exoellent dimensional stability oombined with low water absorption (0~35~ immersed in water at room tem~erature; boiling ~- water immersion doe s not cause dimensions to alter by more than 0.001 in/in), .
~` (3) high heat distortion tem~erature of , "s~ ~
~ - 15 -:., y~
` ms/ ~~`r'J~

., . .

~L57~i~2 about 135C, (4) superior heat resistance showing excellent resistance to thermal oxidative degradation, and (5) good electrical resistan~e.
Polyphenylene oxide may be prepared via oxidative coupling of phenols. B~ oxidative coupling is ~eant a reaction of oxygen with active hydrogens from different monomers to produce water and a di~erized molecule. If the monomer has two active hydrogens, oxidative coupling continues resulting in polymerization. The polymer structure of polyphenylene oxide is characterized by a high degree of symmetry, no strongly polar groups, rigid phenylene oxide backbone, a high glass transition temperature (21C) and no other observable transitions in the range of -273C to 210C.
Polyphenylene oxide possesses a combination of useful properties including: (1) a temperature range between about -180C and ~; a~out 180C, (2) excellent hydrolytic stability, (3) dimensional stability with very low water absorption, low creep and a high modulus, (4) excellent dielectric properties over a wide range of temperatures (-180C to 180C).
It is believed that a polyphenylene oxide based thermD~lastic ;~ resin (NORYL*) would also be a suitable high temperature thermoplastic polymer useful in the present invention. Noryl thermoplastic resin is a tough, rigid material which maintains its mechanical properties over a wide temperature range. It also exhibits excellent dimensional stability with low creep and low moisture absorption. Noryl thermDplastic resin exhibits excellent hydrolytic stability.
~- ~ The laminated thermoplastic polymer films of this ~ invention provide a high performance adhesive means suitable for - printed circuit application with reliable properties and per-formance superior to that obtainable with the resin-rich b ~
'. '~
* trade mark .

~' ` ' ' ' ' s~ z -198 ., il ' .

1l, and rubber thermoset adhesive blends of the prior ar~. The ¦ thermoplastic film surface(s) of the blanks of this inventio~
3 have a substantially uniform thickness and can be chemically 4 treated by techniques known in the art to achieve excellent adhesion of subsequent deposits of electroless metal during the manufacture of printed circuit boards.
71 It is generally known that these high te~perature 81 polymers, specifically polysulfones, when used by themselves 9¦ in greater thickness than the extruded films require prolonged 10¦1 secondary annealing bakes to prevent stress cracking. Typical recommendations for annealing conditions are two to four hours 12 l¦ and up to nine hours at 170~C prior to processing. An additional 13 ll extended annealing cycle is required after machining the . 14 ,¦ material prior to etching the surface for subsequent metal ; 15il depositions. The advantages of using rigid molded polysulfone 16~¦ are limited to those users who have stringent electrical require-17~¦ ments at high frequency applications. In such cases, the poly-,~, 18 11 sulfone material is ideally suited but requires that the laboriou 19l annealing steps be performed in order to render these materials . 201 processable. However, as subsequently described herein, annealin ,, 21 ' and production of the blank and/or laminate of this invention ` . 22 , occur simultaneously in one step. It has been found that when 23¦ the thermoplastic polymer films of this invention, such as 24 ~ polysulfone, were laminated to an insulating substrate according 25~ to the present invention, the thermoplastic polymer films are i` 2~1 stress relieved during the laminating cycle. This eliminates .
271 the need for the previously mentioned laborious and time 281 consuming secondary annealing steps.
-~ 29 ! According to a method of applicants' invention, the blank is formed by arranging impregnated plies of the insulating : .

. ' ', ' - .

: ' ' ,' ~

,-198 Ij ` ~ ~15762~;

11 i 1 substrate and extruded thermoplastic film o~ sheets in the form 2ii of the laminate and laminating the same under heat and pressure, ¦
3 1l for example, at 160C and 1.4 ~a. up to 60 minutes. The 4 ¦¦ lamination step can be carried out in a conventional press 5¦¦ using conditions ~nown for preparin~ ther~osettable resin . 6 11 impregnated laminates with substantially planar surfaces. A
I ' suitable cure cycle is 10-60 minutes at 120-1~0C and 8 1.5 to 10 MPa. -9 Although the blank of this invention has been described hereinabove in conjunction with an extruded, high 11~ temperature thermoplastic polymer used in a press lamination 12i procedure, other methods.of manufacturing the blank of this ¦
13, invention may be employed. For example, a laminated insulatin~ ¦
14l substrate may be dipped into a polysulfone adhesive to build up lSI a layer of polysulfone on its surface(s) by drying steps or an 16¦ ex,ended high temperature, thermoplastic film Day be laminated 17, to an insulating substrate employin~ polysulfone as an adhesive.
18l, It is well known that a 2-S percent solution of polysulfone in 19 methylene chloride can be used to achieve a strong bond at ~i 20 room temperature. A polysulfone film, for example, may be clad 21¦ to an insulating substrate by dipping the film and substrate in 22l the polysulfone-methyle.ne chloride solution, air drying for lS
` 23 seconds, and then assembling them in a jig and placing them ~ 24 under a pressure of about 500 psi for 5 minutes.
-:~ 25 ¦ After removal from the press plates or the like ~- 26 ¦ employed in the lamination step described hereinabove, the '` 27 li blank thus formed may be employed in the manufacture of printed ; 20 1,¦ circuit boards which comprise an insulatinR base material. In i-' 29'l another preferred embodiment, a thin metal film mav be supcr-:` 30~ imposed on one or more surfaces of the blank and adhered thereto , .. ! ' ,. . .
~, ,~ .

.
' ''' ' ` '' : ' ' '-^

: ' -.

.

to form a laminate. ~157~2 Blanks of the type described hereinabove could be used to prepare one-layer, two-layer and multi-layer printed circuit boards with and without plated through holes in the manner more particularly described hereinafter.
In one method of producing printed circuit boards, a "semi-additive" technique is employed. The insulating blank of this invention is cut to size and holes are prepared therein by drilling, punching, or the like. The surface of the blank is subjected to a pre-etch-solvent attack on an abrasive treatment thereon. It is believed that the surface of the blank may be mechanically roughened before the oxidizing treatment. The mechanical roughening would replace solvent pretreatment. A
typcial mechanical roughening is grit blasting the surface of the blank with a slurry of abrasive particulate matter such as sand, aluminum oxide, quartz, carborundum*, and the like, sized finer than 100 U.S.A. Sieve Series mesh. The solvent attacked ~; board is then mechanically and chemically treated with an oxiding solution to activate the surface of the blank.
A conventional electroless plating process is employed s to deposit a thin conductive layer of copper on the activated surface of the blank and in the holes. A temporary protective coating or resist is employed to silk screen print a circuit pattern having 0.35mm lines; the temporary resist is heat cured~
The circuit pattern is built up by electroplating a metal onto the exposed areas of the substrate. The temporary resist is removed and the thin layer of electroless metal which had been covered by the mask is etched away with an acid. A permanent registered ;~ solder mask is printed onto the blank and heat cured. Then, the blank is wave or dip soldered.

* trade mark - 19 -ms~

~ . ~ ., ~ : :.

~, ~S762Z
Alternatively, the temporary protective coating may be a photoresist. In such a case, the subsequent steps would be photo-imaging and then developing the imaged resist to cure it prior to the electroplating step.
In another method of producing printed circuit boards, a "fully additive" technique is employed. A suitable insulating blank according to the present invention is prepared having a polysulfone, polyethersulfone or polycarbonate surface layer laminated to a suitable insulating base such as an epoxy-resin-fiber glass reinforced base. Holes with a distance betweencenters of about 2.5mm or less typically are formed in the blank at preselected sites. The blank and walls of the holes are surface pretreated by deep etching with a conventional chrome acid oxidizingsolution to prepare the surface of the blank and the walls of the holes chemically and physically. A photo-imaging technique described in U.S. patents 3,772,078; 3,907,621;
3,925,578; 3,930,962; and 3,994,727, all to Polichette et al., is then employed. The blanks and holes are completely coated with an aqueous ultraviolet light reducible, copper complex and dried. An ultraviolet light photoimage is formed by brief-projection or contact printing on the sensitized substrate. The unexposed light reducible coating is washed off and the image is fixed by brief exposure to an electroless "strike" bath to ~provide a permanent background resist leaving the desired circuit ,jlpattern exposed, the pattern having as low as about 0.2mm between lines.
A metal such as copper is electrolessly deposited onto the exposed pattern and in the holes until a circuit is built up to the desired thickness, e.g., about 1-5 mils. (25-125 microns).
The circuit is protected from corrosion by coating it : ~ .

ms/ (`-~`

. ` ~ ~ .. ..
-- .

`-` li,~7 t;,2Z

with rosin lacquer or solder coating the blank.
Unclad blanks of this invention are best provided with an additional surface treatment, e.g., the direct bon-ding retreatment process of U.S. patent No. 3,723,039 to achieve strong adhesion of electroless metal deposits to the blank.
....
This generally comprises treating the blank with a suitable organic or inorganic acid, e.g., chromic or sul-furic acid, or base solution to render it porous. In many cases it is desirable to also treat the surface with an agent, e.g., dimethyl formamide or dimethyl sulfoxide before or during the etching process. The effect of such treatment is -~ to render the surface polar, Suitable solvents and blends thereof for swelling polysulfone in particular include dimethyl formamide, aceto-phenone, chloroform, cyclohexanone~ chlorobenzene, dioxane, methylene chloride and tetrahydrofurane.
-; Dependlng upon the particular surface of the blanks, other ion exchange imparting materials may beutilized to effect the aforementioned temporary polarization reaction. For ex-ample, acidified sodium fluoride, hydrochloric and hydro-fluoric acids, chromic acids, borates, fluoroborates and i~ caustic soda, as well as mixtures thereof, have been found effective to polarize the various synthetic thermoplastic insulating materials described herein.
In one type of proceduce, after treatment with the polarizing agents, the insulating bodies are rinsed so as to eliminate any residual agent, following which they are immersed in a solution containing a wetting agent, the ions of which are base exchanged with the surface of the insulating blank to ~ 21 -rn :~ h J ~i ,~
- ., '~
~' ' i ,, '." '',, :: ,, .

', ~ ~ ,~ :.. ', : ' ' .
' ' , ' , 6~2 9~

1 thereby impart to the b}ank relatively long chained ions which 2 1 also are capable of chemically linking with previous metal ions 3 or ionic complexes containing precious metal ions. Following 4 treatment with the wetting agent, the insulating bodies are rinsed again so as to eliminate the residual wetting agent 6 solution.
7 . In the semi-additive method of producing printed 8 circuit boards, an electroplating technique is employed. A
9 ¦ blank according to ?resent invention is pretreated for about three I to six minutes in a dimethyl formamide solution to promote 11. ! adhesion of metal to the surface of the blank after an etching 12 step. The blank is then-etched for about three minutes at about 13 55C to 65C in a highly oxidizing solution. This changes 14 the surface of the blank from glossy to hazy while providing ¦I sites for chemical linking of the surface of the blank to metal.
16 1 Effective etching (microscopic crazing and cracking) occurs 17 due to the combination of the liquid pretreatment and the 18 ! oxidizer contacting the surface(s) of the blank of this invention 19 'I With dimethyl formamide solution, a low chromic acid may be ¦¦ used. If a high chromic acid were used with dimethyl formamide 21 1¦ solution, macrocrazing would occur destroying both adhesion 22 ¦ and good surface appearance. The etched and pre-treated blank 23 1 is catalyzed by im~ersion in solutions according to U,S~ Pat~
24 4,020,197at ambient te~perature for 1-3 minutes. During such immersions, copper -catalytic sites are deposited over the 26 entire blank including on the walls of holes in the blank in 27 order to catalyze the subsequent deposition of electroless 28 metal.
29 I Electroless metal is then deposited on the activated I surface and in the holes of the blank typically at ambient , ~

~: :

~' ' ~ 1~7622 temperature or about 52C (about 30C for nickel) for about 8 minutes for sufficient metal deposition to make the surface of the blank conductive. Following this step, the metal coated board is imprinted with a desired circuit by a photoresist technique. According to the photoresist technique, a photosensitive coating is applied to the surface of the blank. The photo-senstive coating may be of the type that polymerizes or de-polymerizes on exposure to ultraviolet light. A positive or negative transparency, respectively of the circuit, is then used to form a background resist which in turn outlines a circuit pattern on the blank. Copper or another electroconductive metal is electroplated onto the pattern to a desired thickness such as ,~ 1-5 mils. in about 1/2-2 hours. The pattern may then be solder plated. Contact areas such as edge connectors may be electro-~ plated with noble metals such as gold, silver, etc.
'i r It is believed, however, that polycarbonate is not suitable for the electroless deposition of copper or nickel because the pH of the deposition solutions would be too high for satisfactory results with polycarbonate resins in that particular embodiment.
The acid conditioner typically used for etchingacrylonitrile-butadiene-styrene substrates is satisfactory for polysulfone substrates. A typical composition of this acid on a weight basis:
60% H2SO4, 10% H3PO4, 1% CrO3 and 30% H2O. During etching, the chromium that comes in contact with the pretreated polysulfone surface is reduced from Cr 6 to Cr~3. When most of the chromium .~ .
is reduced, the acid is no longer as effective in improving adhesion of metal coatings. For this reason, it is desirable to . ~ ..
have as much chromium in the acid conditione~ as possible.

However, with dimethyl formamide as ~.`

. ms/l'`,~?,~
::
.. :
, -.
.
.. . . .
~ ' `!., ' , ~LS~i622 the preconditioner bath, chromic acid contents above about 3% result in macro-crazing and poor adhesion. A preferred acid conditioner for the polysulfone surface(s) is, therefore, (on a weight basis):

55.9% of 96% H2S04, 10.4% of 85-87%, H3PO4, 3% of CrO3 and 30.7% of H20.
In an alternative "fully additive" technique for pro-ducing printed circuit boards, a suitable blank according to the present invention is prepared typically having a distance between hole centers of about 2.5~,m or less. The blank and walls of the holes are activated using known seeding and sensitizing agents such as stannous chloride-palladium chloride, activators. A permanent protective coating or re-sist is screened to produce a permanent background resist leaving the desired circuit pattern exposed, the pattern having spacing as low as about 0.35mm between conductor lines. m e resist is cured and copper is electrolessly deposited on the exposed pattern and in the holes.
` The blank according to the present invention may alter-` nately be catalytic, i.e., having catalytic materials distributed through-o~t its surface during extrusion of the thermDplastic fi~m surface of ~` the blank. In the aforementioned techni~ues for manufacturing printed circuit boards, this would eliminate the need for a separate seeding and sensitizing step. Incorporation of catalytic materials into the surface of the thermoplastic film may be accomplished by the technique disclosed in U.S. patents 3,546,009; 3,560,257; 3,600,330 and example 1 of U.S. patent 3,779,758 (a palladium chloride catalyst). In another embcdiment of the present invention, the high temerature film may be e~ployed as an adhesive means for bonding decorative metallic coatings to plastic, reinforced thermoset substrates.
'' mab/~

'' ' ' ' : ;
, :, .
. ' .' : :

.. . .
Ii ' , , 1 One application, for example, would be rims adapted to hold 2 l' tires such as automobile tires. Reinforced, thermoset polyestes 3 ¦I substrates have been proposed for this purpose but are very 4 j' difficult to pla~e with metals. Standard metallizing techniques 5 ¦' cannot be used effectively since the polyester surface is not 6 ¦¦ oxidizable and electroplatable. The polyester substrates may be 7 li electroplated with a metal layer according to the present inven-8 ¦' tion. Typically, such substrate has been or may be shaped by : 9 ¦ molds. According to this invention, a thermoplastic film is die 10 1 cut, laid into the mold used to form a reinforced wheel rim ~ so that the outer surface of the wheel rim constitutes the 12 i' thermoplastic, and then ~olded to the substrate upon application 13 ¦', of heat and pressure. Alternately, the thermoplastic film J 14 j may be applied under heat and pressure with a shape applicator

15 I to the molded and shaped reinforced, polyester substrate.

16 ' Subsequently, an electroless copper layer may be deposited on

17 ~ the thermoplastic film surface layer of the substrate, followed

18 l! by a layer of electroplated copper approximately 0.3 mils

19 1, thick, a layer of electroplated nickel approximately 0.3 mils

20 1I thick and a layer of chrone approximately 0. 02 mils thick.

21 ¦l Among the materials which may be used as insulating ' 22 - I~ substrates for the blanks and/or laminates of this in~ention 23 ,l are inorganic and organic substances, such as glass, ceramics, 1, ` ~ 24 ¦I porcelain, resins, paper, cloth and the like.
25 ¦l ' For printed circuits, among the materials which 26 ¦I preferably are used as the insulating substrates for the blanks, 27 ~I may be mentioned insulating thermosetting resins, thermoplastic ' 28 1! resins and mixtures of the foregoing, including fiber, e.g., I -1 29 fiberglass, impregnated e~bodiments of the foregoing.
30 ' Included in the thermoplastic resins are acetal ,, .,, . , . ....... . ....... . . ... . -- . . . .y .

:. . : . .
~.

~:1576~
-- resins; acrylics, such as methyl acrylate, cellulosic resins, such as cellulose triacetate, and polycarbonates, polychloro-trifluoroethylene, polyesters and polyimides.
Among the thermosettting resins may be mentioned allyl phthalate; furane, melamine-formaldehyde; phenol formaldehyde and phenolfurfural co-polymers, alone or compounded with butadiene acrylonitrile co-polyers or acrylonitrile-butadiene-styrene co-polymers; polyacrylic esters; silicones; urea formal-dehydes; epoxy resins-; allyl resins; glyceryl phthalates; poly-; 10 esters; and the like.
Porous materials, comprising paper, wood, `fiberglass, ` cloth and fibers, such as natural and synthetic fibers, e.g., ' cotton fibers, polyester fibers, and the like, as well as such materials themselves, may also be metallized in accordance with the teachings herein. The invention is particularly applicable ! to the metallization of blanks having a surface comprised of a high temperature thermoplastic polymer and an insulating substrate ; comprised of resin impregnated fibrous structures and varnish coated resin impregnated fiber structures of the type described.
The blanks will include any insulating material coated with the thermoplastic polymer film form, regardless of shape or thickness, and includes thin films and strips as well as thick substrata. An adhesive layer can be on the blank. The blanks can include metals such as aluminum or steel which are coated with insulating layers of thermoplastic polymers. Where the conductive pattern is only to be on upper and lower sur~fa~c~s - the blank may optionally be coated with extruded thermoplasticfilms.
If the conductive pattern is to include plated through holes it may be preferable to first provide the metal blanks with ~ 30 holes and coat the blank by powder fusing techniques such as ms/

~' ~
- .

- fluidized bed. ~1S76Z2 Typically, the au-tocatalytic or electroless metal deposition solutions for use in depositing electroless metal on the activated surface~s) of the blanks comprise an aqueous solution of a water soluble salt of the metal or metals to be deposited, a reducing agent for the metal cations, and a com-plexing or sequestering agent for the metal cations. The function of the complexing or sequestering agent is to form a water soluble complex with the dissolved metallic cations so as to maintain the metal in solution. The function of the reducing agnet is to reduce the metal cation to metal at the appropriate time.
Typical of such solutions are electroless copper, nickel, cobalt, silver, gold, solutions. Such solutions are well known in the art and are capable of autocatalytically depositing the identified metals without the use of electricity.
Typical o~ the electroless copper solutions which may be used are those described in U.S. patent No. 3,095,309.
Conventionally, such solutions comprise a source of cupric ions, e.g., copper sulfate, a reducing agent for cupric ions, e.g., ` formaldehyde, a complexing agent for cupric ions, e.g., tetra-` sodium ethylenediamine-tetraacetic acid, and a pH adjustor, e.g., sodium hydroxide.
Typical electroless nickel baths which may be used are described in Brenner, Metal Finishing,~Nov.1954, pages 68 to 76. They comprise aqueous solutions of a nickel salt, such as nickel chloride, an active chemical reducing agent for the nickel salt, such as the hypophosphite ion, and a complexing agent, ' such as carboxylic ...

.

ms/ ~J-~: , .: ~

:

acids and salts thereof.
Electroless gold plating baths which may be used are disclosed in U.S. patent 3,589,gl6. They contain an aqueous alkaline solution of a water soluble salt of gold, a : borohydride or amine borane reducing agent, a complexing agent for gold and a small, effective stabilizing amount of a cyanide compound in an amount between about 5 micrograms and 500 milligrams. The pH of the bath will be between about 10 and 1~.
Typical electroless cobalt and electroless silver systems are well known.
A specific example of an electroless copper de-position bath suitable for use will now be described:

N,N,N'-N' tetrakis (2-hydroxy-propyl ethylenediamine) 18 g./l.

CuSO4 2 10 g./l.
Formaldehyde (37% solution) 4 ml./l.

Wetting Agent (GAFAC-RE* 610) 0.01 g./l.
(commercially available from GAF
Corporation)(believed to be a ; phosphate ester of alkylphenol-polyethylene oxide) Sodium hydroxide to desired pH (12-13) Sodium cyanide (NaCN) 25 mg./l.
2-mercapto benzothiazole 10 mg./l.
This bath is preferably operated at a temperature of about 52C, and will deposit a coating of ductile electro-less copper about 35 microns thick in about 18 hours.
Utilizing the electroless metal baths of the type described~ very thin conducting metal films or layers will be laid down on the surface of the blank. Ordinarily, the metal *trade mark - 28 -, ~

mab/ ~

:-198 `
~ 1 5 7 ~ 2 2 !
.i !
1 films superimposed on the surface of the blank by electroless 2 metal deposition will range from 2.5 to 100 microns in thickness, 3 ~, with metal films having a thickness of even less than 2.5 microns¦ -4 1I being a distinct possibility.
5 !! Among its embodiments, the present invention contem-; 6 ! plates metallized blanks in which the electroless metal, e.g., ¦
7 l, copper, nickel, gold or the like, has been further built up by I :
8 1l attaching an electrode to the electroless metal surface and 9 11 electrolytically, i.e., galvanically depositing on it ~ore of the same or different metal, e.g., copper, nickel, silver, gold; j 11 rhodium, tin, all~ys the~eof, and the like. Electroplating 12 I procedures are conventional and well-known to those skilled in 13 the art.
14 For exa~ple, a copper pyrophosphate bath is commer-cially available for operation at a pH of 8.1 to 8.5, a tempera-16 ture of 50C, and a current density of 50 amp./sq. ft. In 17 addition, a suitable acid copper sulfate bath is operated at a 18 pH of 0.6 to 1.2, a temperature of 15-SO~C, and a current 19 l, density of 25 to 70 amp. per sq. ft. and is comprised of:
1 .
20 1i copper sulfate, CuS04-5H2O 60-120 g./l.
21 sulfuric acid, H2S04 160-18 g./l.

22 i hydrochloric acid, HCl 1-2 mg.ll.

23 ¦ brighteners and wetting agents optional

24 For printed circuit application, copper deposits for use as the ,1 25 basic conductor material are usually 25um to 70um thick.
. , .
~; 26 I Silver may be deposited galvanically from a cyanide ~ 27 bath operated at a pH of 11.5 to 12, a temperature of 25-35C, `~ 28 and a current density of 5-15 amp,/sq, ft. An illustrative 29 galvanic silver bath is cq~prised of~
silver cyanide, ~ N 50 g./l.

.~ ' ' ~'~ I , .

, ~

.
': : .

-198 ~~ ( ~
,! 1 1 ~ 6 2 ~ !
. , . I
l! I

1 potassium cyanide, RCN 11~ g.~
2 ¦j potassium carbonate, K2C~3 45 g.ll.
3 i! brighteners variable ; 4 il Gold may be deposited galvanically from an acid gold ~;5 li citrate bath at pH 5-7, a temperature of 45-60CC and a current 6 il density of 5-15 amp./sq. ft. An illustrative galvanic gold bath consists of 8 Sodium gold cyanide, NaAu (CN)2 20-30 g.ll.
9 I dibasic ammonium citrate 10 ~¦ (NH4)2C6H5O7 100 g./l.
Nickel can be galvanically deposited at p~ 4.5 to 5.5, 12 ¦ a tenperature of 45~C, and a current density of 20 to 65 amp.lsq.
13 il ft., the bath containing 14 Ii nickel sulfate, NiS04 6H20 240 g./l.
I¦ nickel chloride, NiCL2 6H20 45 g./l.
16 1¦ boric acid, H3BO3 30 g./l.
17 l¦ Tin and rhodium and alloys can be galvanically deposited 18 !I by procedures described in Schlabach et al., Printed and ;19 i Integrated Circuitry, McGraw-Hill, New York, 1963, p. 146-148.
! Other objects and advantages of the invention will 21 be set forth in part herein and in part will be obvious herefrom 22 or may be learned by practice with the invention, the same 23 ! being realized and attained by means of the instrumantalities I;¦ and combinations pointed out in the appended claims.
1 The invention is more fully described hereinafter 26 I with reference to the accompanying drawings which illustrate 27 1, certain enbodiments of the invention and together with the 28 ~ specification serve to explain the principles of the invention.
29 ' Fig. 1-5 illustrate procedures which can be used 30 , to produce printed circuit boards from insulating blanks .

, ~, . . . .
bi I
,1 ! , ' - - - ~ :
. . :
.
-. . ,,. :
. .: . : :.
.

~ I
. I ~

198 `~
5~622 ,....... 1', .
' !i ,~
1 produced in accordance with the teachings herein;
2 !¦ Fig. 6 illustrates a production process apparatus 3 i! for making a blank in a roll to roll fashion following the 4 'i teachings of this invention; and 5 ¦I Fig. 7 illustrates a production process apparatus `~ 6 ¦! for making a blank in a roll application of polysulfone to a ; 7 1 rigid substrate.
8 In the drawings, similar reference numerals are used 9 to represent similar parts.
Referring to Fig. lA, there is shown an insulating blank 10 according to the present invention. The insulating 12 1~! blank 10 comprises a thermoset resin inner core 12 and outer 13 ¦~ surface layers of polysulfone film 14. The core 12 is catalytic 14 1! for deposition of eIectroless metal. The polysulfone film 14 15 lll also is catalytic for electroless deposition. In Fig. lB
16 l,l holes 16 and 18 are drilled through the blank 10. The blank 10 17 ~¦ is then immersed in a pre-etched solvent followed by a chemical `~- 18 'l treatment with an acid etch such as 20 g.ll. CrO3, 350 mg./l.
F~ 19 1~ H2S04, S0 g./l. ~aF at a temperature between 45 and 65DC
¦¦ to expose the catalyst and activate the surface of the blank 10 ~ 21 ¦¦ as shown in Fig. lC. A photoresist 24 is applied (shown in i 22 1I Fig. lD) on a surface of the blank to ~ask areas that will not 23 be subsequently copper plated. Copper is then electrolessly ; deposited, by methods known in the art through the holes 16 and 18 and onto the exposed surfaces of the blank 10 to form a copper ~-¦ 26 ¦¦ conductive pattern 22 about 35 microns thick on the exposed 27 1li surface of the blank and on the walls of the holes 16 and 18 28 il as shown in Fig. lE. The photoresist 24 is then stripped ac .
29 , shown in Fig. lFo A registered solder mask 30 then may be applied over the circuit pattern leaving holes 16 and 18 exposed .

d ' ': ; ~ : ' ' . ~
' '' :~ , ~

-198 (~ `~
?! ~ 15 76z2 1i, ! i ~
1 tFig. lG).
2 ! Fig. 2 illustrates a fully additive method of ?
3 1 producing a printed circuit board. Referring to Fig. 2A there 4 1 is shown an insulating blank 10 according to the present 5 il invention. The insulating blank 10 co~prises an epoxy resin-6 1¦ fiberglass reinforced inner core 12 and outer surface layers of 7 ¦I polysulfone film 14. In Fig. 2B a hole 16 is drilled in the 8 ¦¦ blank. The blank and walls of the hole 16 are surface pre-treated 9 ¦¦ by deep etching with a conventional low chro~e acid etchant such as 11 (on a weight basis): 55.9Z of 96% H2S04, 10.4% of 85-87% H~PO4, ?j 11. ! 3% of CrO3 and 30.7% of H20,.to prepare the surface of the blank 12 !l 10 and the walls of the hole 16 chemically and physically. The 13 1¦ blank lO and hole 16 are then co~pletely coated with an aqueous 14 1¦ ultraviolet light reducible copper complex 20 and dried ~Fig.
ll 2C). An ultraviolet light photo-image is formed by brief projec-' 16 !? tion or contact printing via screen on the sensitized surface 14.1 17 1 The unexposed light reducible coating 20 is washed and the image 18 " 22 is fixed by brief exposure to an electroless "strike" bath - 19 jl as shown in Fig. 2D, leaving the desired circuit pattern exposed.', ~; 20 ! As shown in Fig. 2E, copper is electrolessly deposited onto 21 i the pattern and the hole 16 until a circuit 28 is built up to the¦
22 desired thickness, typically about 1-5 mils. in about 18-20 23 hours.
24 Fig. 3 illustrates an "electroplating" method of produ~ing printed circuit boards. In Fig. 3A there is shown 26 !1 an insulating blank 1~ according to present invention, having 27 j an inner core 12 and polysulfone surface layer 14 as described 28 1! previously herein with respect to Figs. 1 and 2. As illustrated I
I; 29 ! in Fig. 3B, the blank 10 is pre-treatet for about 3-6 minutes I -.. ,, ?
~11 30 ll in a diméthyl formamide solution to pro~ote adhesion of metal ~: .

; -a~?-. _ , :

^ :, .. :::

i7622 l to the surface 14 of ~he blank lO after an etching step. In 2 '¦ Fig. 3C, the blank lO is etched for about three minutes at about 3 1¦ 35C to about 70C in a highly oxidizing solution. This 4 ll changes the surface of the blank from glossy to hazy while S !I providing sites i~ for che~ical linking of the surface of the 6 ,¦ blank 10 to metal, The etched and pre-treated blank 10 is I .
7 i! activated by immersion in a stannous and palladi~m chloride 8 i activator solution which may be at ambient temperature 9 ¦¦ for l to 3 minutes, each, as shown in Fig. 3C. Durin~
,I such immersion, palladium sites 20 are deposited over the ll j entire blank lO, including on the walls of the holes (not shown) ; 12 ~~ in the blank 10 in order to catalyze the subsequent deposition 13 of electroless metal.
14 1 A layer of electroless metal 22 is deposited on , the activated surface 14 and in the holes (not shown) of 16 the blank 10, typically at ambient te~perature for about 8 ; 17 ~I minutes in order to render the surface of the blank electrically 18 I conductive ~as shown in Fig. 3D). In Fig. 3E a desired l9 .i circuit is imprinted by a photoresist technique onto the metal coated blank io. A photo-sensiti~e coating ~ is 21 1 applied to the surface of the blank. The photo-sensitive 22 I coating ~ may polymerize or depolymerize on exposure to 23 1 ultraviolet light. A positive mask ~Kris then used to form 24 ,l a background resist~which in turn outlines a circuit pattern , on the surface of the blank 10 (as shown in Fig. 3E). In ; 26 ~ Fig. 3F copper 28 is electroplated onto the pattern to a deslred 27 thickness such as 25-70~mO In Fig. 3G, the background resist 28 , is stripped and the conductive background filn of copper 29 removed by etching, In Fig. 4, there is shown an additive method for , . : ' ' .
:, :, ,,.: :, :- .~ . ~
~; ' :-198 ., . ,, . I
ii - 1157622 - , ! .
il 1 manufacturing a ~ulti-Layer pri~eed circuit board. In Fig. 4A, 2 ¦ pri~ted circuit pattern 102 is adhered on insulating blank 100.
3 ' A polysulfone film 104 is superimposed and bonded over the printed 4 ¦! circuit pattern 102 (Fig. 4B). A hole 106 is then drilled ! through polysulfone film 104, printed circuit pattern 102 and 6 ll the insulating blank 100 ~Fig. 4C). The surface of the poly-7 ll sulfone film 104 is adhesion promoted via the "swell and etch'`
8 il technique described previously herein. The "swell and etch"
9 ¦I technique also removes smears from the drilled hole edges of the ¦ (copper) circuit pattern 102. The polysulfone film surface 104 is activated by dipping in a palladium and tin solution. In 12 ' Fig. 4D, a photoresist image I10 is imposed on the outer surface 13 of the polysulfone film 104. The exposed film surface 104 and 14 ¦ the hole(s) 106 are electrolessly plated with copper 112 to a 1, thickness of about 35 microns (Fig. 4E). In Fig. 4F, the 16 ,I photoresist image 110 has been stripped providing the multi-17 ¦l layer printed circuit board.
18 1, In Fig. 5, there is shown a semi-additive method of 19 l, manufacturing a ~ulti-layer printed circuitboard. In Fig. 5A, li blank 200 is clad on opposite surfaces with copper 201. An 21 lll interior circuit pattern 202 is etched with a suitable etchant 22 !. and covered with a layer of polysulfone 204 (Fig. 5B). A
23 ¦¦ hole 216 is drilled through the blank 200. The blank 200 is 24 1l adhesion promoted with chromic acid and activated in palladium 1l and tin solution. Then, an electrolessly deposited copper 26 l, film ~ is applied onto the polysulfone surface 204 and in the 27 l hole 216 to a thickness of about 2 microns (Fig. 5C). A
28 ll photoresist image 210 is applied and additional copper 212 is ~ 1-` 29 electroplated to provide a copper layer having a thickness of , about 35 microns (Fig SD). In Fig. 5E,` the photoresist image ,.
.. , ~Q~ ' , ' '- . ' . ' ' ~i .. , f : ~

.. . .
. ~: :
: ' ~ ~ : -:
.,' ~ ' ~ .

11S76~2 ~q 1 1 210 is removed and the copper film 211 under the photoresist j`t 2 ~1 ~ is etched away with a suitable etchant. - - -. 3 l¦ In Fig. 6, there is shown a method for making an 4 ¦¦ insulating blank 10 according to the present invention. There 5 l are shown feed rollers 100, 102 and 104. Uound on roller 100 6 ¦! is a flexible support carrier 106 with a thickness of about 7 li 8 mm., the carrier being woven glass, non-woven glass, dacron, 8 1I rayon, cellulose paper and the like impregnated with resins, 9 il preferably thermoset resins such as epoxy, but high tem~erature 1l thermoplastics, e.g., polyimides and polycarbonates may also be 11 11 used. Wound on feed roller 102 is a thermoplastic film 108 -12 il having a thickness of 1-5 mm. Wound on feed roller 104 is a i 13 1' thermoplastic film having a thickness of about 1-5 n~. The 14 1 thermoplastic film may be polysulfone, polyethersulfone, poly-1S 1! phenylene oxide or polycarbonate.
I . .. .
16 ~1 Also shown are combining-take-up rollers 110 which , -17 il apply heat and pressure to the laminate passing therebetween.
18 1, A temperature of about 160-200~C and a pressure of about 19 I 30-400N/mm is typically applied between rollers~K~. -Exiting li j ~1 from the rollers is a flexible laminated thermoplastic support ¦
21 1¦ carrier which when thermoset becomes the insulating blank li 22 j~ according to the present invention. - i .~; il - !
23 jl In Fig. 7, there is shown a roll application to a .. ...
24 ll rigid substrate, i.e., 1.6 mm. thick epoxy glass cloth 1 25 Ij reinforced laminate. There are shown feed rollers 100, 102 and 26 11 104. Wound on rollers 102 and 104 are respective thermoplastic - 27 I films 108 having a thickness of 1-5 mm. The thermoplastic ; 28 , film 108 may be polysulfone, polyethersulfone, polyphenylene--29 oxide or polycarbonate. Also shown are combining-take-up rollers 110 which apply heat and pressure to the laminate .......... . , . . . ~ _ .
~ . ~
-, -:' :' passing therebetween. A temperature of about 160-200~C and a pressure of about 30-400 N/mm is typically applied between rollers 110. An insulating base 12 passes between rollers ll0 and the thermoplastic film 108 is laminated to opposed surfaces of the base 12 under heat and pressure to form the blank 10 which is severed from the web after exiting from the rollers 110.
Optionally, the insulating base 12 is coated with a polysulfone adhesive comprised of polysulfone dissolved in solvent.
- The following examples illustrate at least one of the best modes of the insulating blanks, printed circuit boards and methods of the present invention as presently understood.
Example 1 8 plies of glass cloth impregnated with 45-55% by weight epoxy resin were placed in a printed circuit lamina~ing press with a sheet of extruded polysulfone film 50~m thick on top and bottom. The extruded polysulfone film was made from Udel* P-1700 polysulfone resin (commercially available from Union Carbide Corporation, Engineering Polymer Division, 270 Park Avenue, New York, New York 10017). A laminating temperature ; 20 of 175C, a pressure of 600 p.s.i. (4.1 MPa) and a dwell time in the hot press of 15 minutes were employed. After 15 minutes, the press was cooled to room temperature and the blank was removed.
The blank was processed into a printed circuit board employing the following steps: (1) Through holes were drilled in the blank; (2) The blank was brushed to remove drilling debris (it is noted that no annealing and/or oven baking was required after drilling); (3) The blank was immersed in dimethyl form-amide-water solution (specific gravity of 0.955-0.965 for 3-6 minutes; (4) The blank was rinsed in hot water for 45 seconds;

;:

- ~ ' *trade mark ms/~

, ,, , ~ : , .. :

;~ ' .
-~ :
:
. .

li5~76ZZ
- (5) The surface of the blank was adhesion promoted at a temperature of 55C for a time period of 7 minutes with the following solution: CrO3 - 20 g/l, H3PO4-100 ml/l, H2SO4-600 ml/l, and FC-98*-0.5 g/l (FC-98* is an anionic perfluoroa~I~yl sulfonate commercially available from 3M Company, Commercial Chemicals Division, St. Paul, Minnesota); ~6) The blank was rinsed in still water; (7) Cr[VI] was neutralized with a solution containing 10~ H2O2 and 15% H2SO4; (8-11) The blank was rinsed with water, immersed successively in 2.5 M HCl, a seeder solution (the seeder solution described in example 1 of U.S. patent 3,961,109 and an accelerator, 5% HBF4; (12) Copper - was electrolessly deposited onto the blank (electroless copper solution is described in U.S. patent 3,095,309) to a thickness of 2.5 microns; (13-14) The copper clad blank was rinsed with water and dried at 125~C for 10 minutes providing a copper clad r blank (as shown in Fig. 3D).
; A printed circuit board was manufactured using such - copper clad blank by techniques well known in the art, i.e., a background resist image was printed, a copper circuit pattern was electroplated using the copper bath described previously herein (page 28), the resist was stripped and the background copper was etched away (See Figs. 3E-3G).
A peel strength of 1.7 N/mm was measured for the printed circuit board. A solder float test was also emplo~ed.
A one-inch square copper pattern (the printed circuit board) produced according to this example was floated on 260~C molten solder for 10 seconds. The sampl~ was removed for examination of potential blisters and/or delamination of the copper pattern (from the blank). No blistering or delamination was detected.
, ~

* trade mark .~. '~
~ ~ ms/ ~ b .

. . . . .
.

~lS7622 Example 2 Example 1 was repeated except a laminating pressure of 400 p.s.i. (2.8 MPa) and a dwell time on the laminating press of 1 hour were used. A final peel strength of 2.4 N/mm was measured and a one-inch square copper pattern sample floated in 260 molten solder for more than 10 seconds without blistering or delaminating.
Example 3 Example 1 was repeated except that a laminating pressure of 200 p.s.i. (1.4 MPa) and a dwell time in the laminating press of 5 minutes were employed. After laminating, the blank was stabilized at 160C for 1 hour in a circulating hot air oven to prevent shrinkage and warping during processing.
A final peel strength of 1.9 N/mm was measured.
Example 4 A blank made according to example 1 was used. Following the first 10 steps of example 1, the seeded blank was printed ` with Riston 129 (Ristan 129 is a trade mark for a dry film - photopolymer resist commercially available from E. I. duPont deNemours & Co., Wilmington, Delaware) to leave a desired circuit pattern exposed. The blank was immersed in an accele-:
ration (step 11 of example 1) and electrolessly copper plated (step 12 of example 1) to a thickness of 35 microns.
Example 5 ~, An epoxy glass laminate was clad with 35~m thick copper ;!;' foii top and bottom. A copper circuit was etched in the foil by laminating with Riston 1206 (Riston 1206 is a trade mark ~ which identifies 0.6 mil thick dry film photopolymer commercially !. available from E. I. duPont deNem~urs & Co., Wilmington, Delaware),~exposing ~ - - 38 -'` ~

.

i7622 to ultraviolet light through a negative, developing out the unexposed Riston* 1206 with l,l,l-trichloroethane, etching the copper with ammoniacal cupric chloride and removing the ; remaining Riston 1206 with methylene chloride.
A polysulfone adhesive was prepared by dissolving pellets of Udel P1700 NT polysulfone resin (UDEL P1700 NT is a trade mark which identifies a polvsulfone resin commercially available from Union Carbide Corporation, 270 Park Avenue, New York, New York, 10017) in methylene chloride. The etched panel was dipped in the polysulfone solution and air dried.
A 75~m thick polysulfone foil was laminated to the adhesive coated double sided panel in a press at 175C for 10 minutes at 200 p.s.i. (1.4 MPa).
Through holes were drilled in the panel and the debris was removed by brushing. The panel was converted into a multi-layer printed circuit board following the procedure of example 1 except that the adhesion promotion time was only two minutes.
Example 6 A single layer of epoxy impregnated ~lass cloth was placed between two sheets of 25~m polysulfone foil and laminated in a press at 400 p.s.i. (2.8 MPa) at 175C for ` 10 minutes. This produced a flexible blank useful in the manufacture of printed circuit boards.

.
.

* trade mark > -39-.-- 1 cb/l' :l~
- - . ~ ; ` .
.
` . - :

;' . . ' :~ " ~ ' .: ~. : .

Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A blank suitable for use in the preparation of a printed circuit board by electroless deposition which comprises an insulating substrate having adhered to at least one surface thereof a thermoplastic organic high temperature polymer having a thickness between about 10 and about 500 microns, the polymer having an aromatic backbone that does not liquify or decompose at a temperature of 245°C after five seconds exposure at said temperature, the polymer selected from the group consisting of polysulfone and polyether-sulfone.

2. A blank as defined in claim 1 wherein said polymer is polysulfone.

3. A blank as defined in claim 1 wherein said polymer is polyethersulfone.

4. A blank as defined in claim 1 wherein said insulating substrate is comprised of an organic material.

5. A blank as defined in claim 1 wherein said insulating substrate is comprised of an inorganic material.

6. A blank as defined in claim 5 wherein said inorganic material is selected from the group consisting of inorganic clays and minerals.

7. A blank as defined in claim 4 wherein said organic material is selected from the group consisting of thermosettable resins, thermoplastic resins and mixtures thereof.

8. A blank as defined in claim 7 wherein said insulating substrate further includes a fiber impregnated thermosettable resin.

9. A method of preparing a blank suitable for use in the manufacture of a printed circuit board which method comprises:
providing extruded thermoplastic film or sheets having a substantially uniform thickness between about 1 and 5 mils, the thermoplastic material having an aromatic backbone that does not liquify or decompose at a temperature of 245°C
after five seconds exposure at said temperature;
providing a fibrous sheet or web impregnated with a thermosettable resin or plies of the impregnated fibrous sheets or webs;
superimposing at least one of said films or sheets on at least one of said plies of thermosettable resin impregnated fibrous sheets or webs; and consolidating the assembly so produced and curing the thermosettable resin by heating under pressure.

10. A blank suitable for use in the preparation of a printed circuit board by electroless deposition which comprises:
extruded thermoplastic films or sheets having a substantially uniform thickness between about 1 and about 5 mils, the thermoplastic material having an aromatic backbone that does not liquify or decompose at a temperature of 245°C
after five seconds exposure at said temperature, the thermo-plastic material being an organic high temperature polymer selected from the group consisting of polysulfone and polyethersulfone;
a fibrous sheet or web impregnated with a thermoset resin or plies of the impregnated fibrous sheets or webs;
at least one of said extruded thermoplastic films or sheets laminated onto at least one of said plies of thermoset resin impregnated fibrous sheets or webs.

11. A method as defined in claim 9 wherein said consolidation step takes place at a temperature between about 120°C and about 180°C and a pressure between about 1.5 MPa and about 10 MPa.

12. A method as defined in claim 9 wherein planar press plates are employed in the consolidation step.

13. A blank suitable for use in the preparation of a printed circuit board which comprises an insulating substrate having an epoxy glass and phenolic paper core, said substrate having adhered to a surface thereof or opposite surfaces thereof polysulfone having a thickness between about 10 and about 500 microns.

14. A method of preparing a laminate suitable for use in the preparation of a printed circuit board, which method comprises:
extruding thermoplastic films or sheets having a substantially uniform thickness between about 1 and about 5 mils, the thermoplastic material having a catalyst uniformly therein and having an aromatic backbone that does not liquify or decompose at a temperature of 245°C after five seconds exposure at said temperature;

providing a fibrous sheet or web impregnated with a thermosettable resin or plies of the impregnated fibrous sheets or webs;
superimposing at least one of said films or sheets on at least one of said plies of thermosettable resin impregnated fibrous sheets or webs;
consolidating the assembly so produced and curing the thermosettable resin by heating under pressure;
pretreating the polymer surface with a polar solvent capable of swelling the outer layer of the polymer to promote adhesion of metal to the surface of the polymer after an etching step;
etching the polymer surface in a highly oxidizing solution at a temperature and for a time period sufficient to expose the catalyst; and electrolessly depositing a metal on the exposed catalytic surface of the blank.

15. A method of preparing a laminate suitable for use in the preparation of a printed circuit board, which method comprises:
extruding thermoplastic films or sheets having a substantially uniform thickness between about 1 and about 5 mils, the thermoplastic material having an aromatic backbone that does not liquify or decompose at a temperature of 245°C
after five seconds exposure at said temperature;
providing a fibrous sheet or web impregnated with a thermosettable resin or plies of the impregnated fibrous sheets or webs;

superimposing at least one of said films or sheets on at least one of said plies of thermosettable resin impregnated fibrous sheets or webs;
consolidating the assembly so produced and curing the thermosettable resin by heating under pressure;
pretreating the polymer surface with a polar solvent capable of swelling the outer layer of the polymer to promote adhesion of metal to the surface of the polymer after an etching step;
etching the polymer surface in a highly oxidizing solution at a temperature and for a time period sufficient to provide sites for chemical linking of the polymer surface to a metal;
activating the pretreated and etched surface of the polymer by immersion of the polymer surface in a stannous and palladium solution for a time period sufficient to deposit palladium sites over the surface of the blank; and electrolessly depositing a metal on the activated surface of the blank.

16. A method as defined in claim 14 wherein said polar solvent is dimethyl formamide solution.

17. A method as defined in claim 15 wherein said polar solvent is dimethly formamide solution.

18. A method as defined in claim 15 wherein the oxidizing solution is chromic acid and wherein said electrolessly deposited metal is copper or nickel.

19. A printed circuit board which comprises an insulating base having a separate surface layer comprised of a high temperature thermoplastic film having a thickness between about 10 and about 500 microns, the thermoplastic having an aromatic backbone that does not liquify or decompose at a temperature below about 245°C after five seconds exposure at said temperature, the thermoplastic material being an organic high temperature polymer selected from the group consisting of polysulfone and polyethersulfone, and a metallic circuit pattern adhered to the surface layer of said insulating substrate.

20. A printed circuit board which comprises an insulating base having a core comprised of epoxy resin impregnated fiberglass and phenolic resin impregnated paper and a separate and discrete surface layer comprised of polysulfone having a thickness between about 10 and about 500 microns, and a metallic circuit pattern adhered to the surface layer of said insulating substrate.

21. A method of preparing a multi-layer printed circuit board which method comprises the steps of:
providing a circuit pattern on at least one surface of an insulating substrate;
applying a layer of polysulfone film over the exposed circuit patterns;
treating the polysulfone surfaces with a solvent and oxidizing agent to render said surfaces microporous and hydrophillic; and electrolessly depositing a metal onto the treated surfaces.