DE2453788A1 - METHOD OF MANUFACTURING CIRCUIT PANELS WITH PRINTED CIRCUITS - Google Patents

Description

Your sign Your message Our sign Day Your Ref. Your letter .Our Ref. Date L / p 7989 12th

Applicant: Litton Industries, Inc.,
360 North Crescent Drive, Beverly Hills, California 90210, USA

Process for the production of circuit boards with printed circuits

The invention relates to the manufacture of circuit boards with printed circuit and with plated through Interconnections, with at least one inner metallic layer being provided which acts as a heat sink.

It has been found that circuit components associated with printed circuit boards in electronic Devices are attached, in many cases generate an extraordinarily high amount of heat that must be dissipated, to prevent damage or destruction of the circuit components, the circuit board, or both. To the As a remedy, circuit boards have been manufactured that have a metallic layer, usually a thin plate, which is inserted into the body of the circuit board, i. H. between insulating layers is embedded. These metallic layers or plates act as heat sinks, but usually form

509821/0741

Account: Bayerische Vereinsbank (bank code 750 200 73) 5 804 248 Postscheckkonto Munich 893 69-801

Place of jurisdiction is Regensburg

- 2 - L / p 7989

not part of an electrical circuit and must therefore be electrical to the circuits on the circuit board to be isolated. Printed circuit boards with such heat sinks are, for example, from US patents 3 259 8o5, 3 296 o99 and 3 514 538 known.

Furthermore, circuit boards have been developed with printed Circuit diagrams are provided on each of the two larger surfaces of such a plate. Plated through electrical connections formed through the plate to a point on one of the two larger surfaces with a corresponding Connect point on the other larger face of the circuit board. In most cases these form appropriate places on each side of a part of the circuit diagram in the form of circuit conductors, in some 'cases however, such a plated-through connection can have a connection with a circuit line on one and the other connect the other of the two larger surfaces of the circuit board.

Furthermore, multilayer, plated-through circuit boards are known in electronics, which have a large number of intermediate circuit _{rails which are embedded in the body of the circuit board (} and then the plated-through connections can optionally be one or more of the locations of the intermediate circuit diagrams with one or both of the larger surfaces The design of the circuit rails is of course a function of the electrical circuit that is to be implemented by a circuit board, and is made as a master copy when it is created. A detailed description of single-layer and multi-layer circuit boards with plated-through connections can be found in US patents 2 872 391, 2 9o7 925 and 3 219 749.

If you combine the principle of the plated-through circuit board with the principle of circuit boards with heat sinks, one is faced with the problem that interconnections are provided that must be plated through, d. H.,

509821/0741

where there is no electrical contact to the inner metallic Layer or plate, which represents the heat sink, is made, since such contact leads to an undesirable electrical Short circuit would lead. It was thus necessary to put insulating areas inside the heat sink on each of the Provide places where a plated connection should be formed. This problem is in the past has been solved by the fact that relatively large holes plated through the heat sink at the points of the intended Connection were made that separate from it Plastic materials were provided that fit exactly into this larger holes fit that a washer was placed in each of the holes, which then a bolt in the proportionately have formed a larger hole, and that a relatively smaller hole was then drilled through the disc. The relationship the moderately smaller hole made in this way through the bolt had inner surfaces of insulating material which when plating these surfaces, the interconnections through the circuit board at the selected locations on the circuit board have formed. From the above it can be seen that the insertion of the usually circular disks in the usually circular, relatively larger holes are quite cumbersome, time consuming and therefore expensive was because the washers had to be individually inserted into each hole to form the insulating bolt that was required was so that a suitable plated through circuit board with a heat sink could be obtained.

From the following detailed description of the invention it will be seen that a method has been developed by that all bolts are simultaneously formed in place within the relatively larger holes of the sheet or plate that will be the heat sink. The formation of the bolts in place is achieved through the use of slack Achieved material that is introduced into all holes of a heat sink at the same time, such a loose material the Has the property that it is permanently solid, electrical forms conductive material. This special feature of the

509821/0741

-4- L / p 7989

Find enables all of the holes to be filled with such loose material in a single step. That loose Material is preferably finely divided solid material e.g. B. Thermosetting plastic, when the holes are filled, the metal layer, which then becomes the heat sink, is subjected to a treatment, e.g., heat and pressure, with it the filler material in place; d. H. inside the holes, solidifies and forms the bolts. Many other steps which form part of the process of the present invention are carried out in a conventional manner, albeit this special feature of the invention enables different steps to be combined into one step, as further is explained below.

According to the invention, in a method for producing circuit boards with a printed circuit and with plated through Connections between corresponding points of Stromkrexsschienen on the two main surfaces and with one at least inner metallic layer, which acts as a heat sink, suggested that within holesr ^ through the metallic layer at the aforementioned points a sufficient amount of loose material is solidified so that A permanently fixed, electrically insulating bolt connection, essentially filling a hole, is provided in place and that on each surface and isolated from each surface a circuit diagram with plated through Connections at the aforementioned points is formed through at least some of the bolt connections. So the invention proposes the use of loose, preferably finely divided material, which in permanent solid insulating material can be solidified so that holes are filled by the metallic layer.

In a further embodiment of the invention it is proposed that the filling of the holes and the solidification of the loose Material is carried inside the holes with a base that is temporarily attached to the bottom of the metallic Layer is applied and that then the base

609821/0741

_ 5 - ^L / P ⁷⁹⁸⁹

is removed. The finely divided, solid material is expedient a thermoplastic material, e.g. B. a thermosetting material that is inside the holes by Applying heat and / or pressure is solidified, for example using a heating press with upper and lower panels; the temporarily applied base can represent the lower plate.

According to a particular embodiment of the invention comprises creating a circuit diagram creating a Isolation coating on each of the two surfaces of the metallic layer and the subsequent production of the two Circuit diagrams, namely one circuit diagram on each surface, using masking and etching techniques. The holes are taken through at least some of the bolt connections and the surfaces that define the holes are plated in such a way that the plated-through connections before, ■ at the same time or after the production of the circuit diagrams formed on the two surfaces will. If the metallic layer is an aluminum sheet, an insulating coating can be applied to each of the two Surfaces include an anodizing treatment performed at some stage prior to the manufacture of circuit bills on the performed on both surfaces of the aluminum sheet. On the other hand, according to the present invention, an insulating coating can be formed on each of the two surfaces of the metallic layer, with each side of the metallic Layer one of two layers of plastic is connected, and then the circuit diagrams on the insulating coverings using masking and etching techniques and forming the plated-through connections.

The invention also relates to a circuit board printed circuit, which has been produced by a method as explained above.

509821/0741

- 6 - L / p 7989

Before a detailed description of the invention and various Embodiments should be noted that the invention is explained with reference to a circuit board provided with printed circuits on two sides, d. H. one Printed circuit board in which a circuit is provided on that of the two major surfaces and there is only a metallic layer or plate inside the body of the circuit board. The principle However, the present invention can readily be transferred to multilayer circuit boards; H. on circuit boards with internal circuit diagrams and also on circuit boards with more than one internal heat sink. Although in relation to the plated-through connections a plating of inner surfaces of the holes by bolt connections through the. Circuit board formed therethrough is shown, plating can be completed so that solid pillars be formed inside the holes, inside each can other conventional technique for forming interconnections can be used.

The invention is explained below in conjunction with the drawing on the basis of various exemplary embodiments. the Drawings show:

Fig. 1 (a) to (<&) schematically a sequence of process steps as they are used in the production of a clad Circuit board are used with a heat sink according to the present invention,

Fig. 2 (a) to (c) schematically shows another embodiment of the method according to the invention, and

Fig. 3 (a) to (c) another embodiment of the invention, in which various process steps are combined into a single step.

In Fig. L (a) a metallic layer, e.g. For example, a metal plate Io is shown in cross section with holes 12 which have been produced (e.g. drilled or etched) from one of the two main surfaces to the other. As known in practice _}

609821/0741 BATH ORIGINAL

- 7 - L / p 7989

A large number of holes must be made through a circuit board in order for the circuit board to be used for an electronic Circuit is usable. Although any metallic composition of the layer Io can be used the preferred metal is aluminum because it is lightweight and has good thermal conductivity owns. The aluminum plate Io may have a thickness of about 0.15 cm, but any thickness will usually be chosen according to the design parameters of the circuit that is created on the finished circuit board. The choice of material used and the thickness of the plate Io are, however not critical.

In Fig. 1 (b) is the filling of the holes 12 in the plate Io shown with loose material; this loose material is for example a thermoplastic, especially a thermosetting plastic material, which is especially partially hardened and which is then often referred to in the art as a B-stage thermoplastic material, e.g., epoxy. As in Fig. L (b) shown, the plate Io is on a detachable b £ s set, which is shown schematically by a plate 14; the holes are made with thermoplastic material 16, preferably a B-stage epoxy resin and a second plate 18 is placed in a suitable manner on the holes, if the holes are filled.

The arrangement of Fig. 1 (b) is then subjected to a consolidation treatment, e.g. B. a "heat treatment, at a exposed to an elevated temperature of about 177 ° C for the material 16 to set in place; H. inside the holes, solidified.

After completion of the consolidation script, after removal of the plates 14 and 18 (as shown in Fig. Ic) and after To cool down, bolts 2o have been formed where the holes 12 were present in FIG. 1 (a) and these bolts are now permanently strong, especially when partially cured, thermosetting plastic material has been used.

509821/0741

- 8 - L / p 7989

Using the arrangement of FIG. 1 (c), a printed circuit board is now the desired one Kind of created as shown in Fig. L (d). The steps to do this are to put insulating layers 22 on each of the major surfaces of the plate Io. This can be done by conventional means using layers of glass fiber reinforced Epoxy resin known as PREPREG that is applied to the two major surfaces and exposed to heat and pressure expediently using a laminating press. Then relatively smaller holes 24 are made through the bolts 20 and also through the insulating layers 22, preferably drilled, and the circuit bars 26, 28 are applied to the insulating layers 22 in a conventional manner. This can be done using conventional plating, masking and etching techniques, as sufficiently described in the literature are. As shown in Fig. 1 (b), an arbitrarily chosen, simplified cross-section of circuit diagrams can be used for circuit conductors 26 and 28 on the two main surfaces, also the plating 3o on the inner surfaces of the holes 24 through the bolts 2o, whereby these platings 3o through the holes form part of the entire circuit diagram that is thus extends over both main surfaces and includes the plated-through connections 3o.

. According to a modified embodiment of the method according to Fig l (a) to 1 (d), the two insulating layers 22 of Figure l (d) ^v instead that they v prepared in the vorbesehriebenen manner / ground -. The result of a treatment of the Layer Io that becomes the heat sink when the selected material is subjected to such a treatment, resulting in the creation of an insulating surface. In the case of aluminum, the known anodizing process can be used. According to this modified embodiment, the sheet or plate Io can be anodized at any stage during the process, but prior to the application of the circuit diagram 26 and 28 of FIG. 1 (d). Thus the plate Io according to FIG. 1 (a) can already be anodized. Obviously, the presence of the insulating coating, which is produced in the anodizing step, affects the production of

509821/0741

- 9 - L / p 7989

Bolts not in the manner described. On the other hand, the anodizing can be carried out in the case of the layer or plate Io according to FIG. 1 (c) be, d. H. following the formation of the bolts 2o, even following the drilling of the relatively smaller ones Holes through the bolts 2o; However, the anodizing must be carried out on the surfaces before the circuit diagrams 26, 28 are produced and achieved through the relatively smaller holes 24 therethrough.

It should also be noted that plating through the holes that extend through the bolts and plating the Circuit wires on the two main surfaces in separate Steps or in a single step and in any order of these steps can be carried out.

Following the explanation of the embodiment of the invention, which is shown schematically in Fig. 1, it is pointed out that that the term "loose material", as it is to be understood in the present application, includes any material, which is not solid at normal temperature ranges and is not a gas. In other words, the invention proposes the Suggests the use of material that is either a paste or that can be written on so that it can flow freely in the In contrast to solid or gaseous substances. So can any of these materials, provided that it is capable of is to get himself either through special treatment or in some cases without such ^ he ^ treatment if it is a certain time is left long / solidify, a permanently strong dielectric Material. From the description of these materials of the present invention, it will be seen that a large number of products meets the requirements that are necessary to form the bolts 2o on the spot. Although in the above description of the method according to FIGS. 1 (a) to 1 (d) -i »reference to thermoplastic, preferably thermosetting Plastics has been taken, the invention is not limited to the use of these materials. For example Commercially available paste-like materials can be used, v / ie they in the construction industry

50982 1/07 41

and are used for repair purposes, e.g. B. so-called Synthetic wood, to name just one class of examples. Many of these materials have a tendency to work with the Time to harden while others require heating and many require drying} all these examples are encompassed by the present invention.

All of the aforementioned materials have in common that when the plate 10 with holes on the temporary base 14 is put on (Pig. Ib), these materials can be introduced into the holes in a single step. In the event of of finely divided solid material can be covered over the entire plate and the excess material simply removed wiped off the top surface. In the case of a paste, this can be pushed into the holes using a blade or like a tool are smeared. If the loose material is a liquid, e.g. B. a liquid thermoplastic Material that has been added with a hardener can be used to fill the holes by that the plate 10 is immersed in liquid or covered with liquid, the undesired excess being wiped away is, and by subjecting the plate to a solidification process, which always depends on the type of selected depends on loose material.

Another embodiment of the invention is shown in FIG. In the process step shown in Fig. 2 (a) the plate or layer 32 which will become the heat sink has already been perforated to give the relatively larger holes in which the bolts are formed. A pile has been molded between the two plates 34 and 36 of a laminating press by adding a glass fiber reinforced epoxy resin layer 38 (PREPREG) was placed on the lower plate 34 of the laminating press, the holes are covered with powdered, Thermosetting material 40 filled, excess material wiped away and a second layer 42 made of glass fiber reinforced Epoxy on top of the board or layer

509821/0741

- 11 - L / p 7989

32 has been ordered. Then when the top platen 36 of the laminating press is lowered to the configuration so described as well as heat and pressure can be applied

-see
readily allows the loose material 4o within the holes to be solidified into a bolt formed in place in each hole, and at the same time the fiberglass reinforced epoxy layers 38 and 42 are bonded to the entire major surfaces of the plate 32 as well as the bolt .

When removing the assembly from the press, look like this the schematic representation in Fig. 2 (b) is shown, represent the coatings, which are made of the glass fiber reinforced epoxy resin layers 38 and 42 are formed, a unitary insulating structure with the solidified material 44 within of the holes.

Thereafter, the relatively smaller holes are drilled through the bolts 44 of Fig. 2 (b), and upon completion of the Conventional steps in creating the circuit diagram can be accomplished using plating, masking and etching techniques a schematic cross section of the finished circuit board will look as shown in Fig. 2 (c). During execution of the method described and illustrated in connection with Figures 2 (a), 2 (b) and 2 (c) needs that loosely The material 4o that forms the bolts 44 in place may not necessarily be a thermoplastic or thermosetting plastic material as the foregoing with regard to the loose material also apply here and for any other embodiment of the invention.

The embodiment according to the invention according to FIGS. 3 (a), 3 (b) and Figure 3 (c) provides a further simplification of the process using a commercially available one Material, which is a layer of glass fiber reinforced, partially hardened, thermosetting plastic material with a metallic, e.g. B. copper layer, which is bonded therewith, forms. As shown in Fig. 3, a lamination

5 0 9 8 21/0741

- 12 - L / p 7989

press dei ^ .rt as mentioned in connection with Fig. 2 is to be used appropriately. A prelaminated layer is first placed on top platen 34 of the press, the one metallic layer 46 with a layer 48 made of glass fiber reinforced Has bound epoxy resin. This material is commercially available, is known and is described in the Circuit board technique widely used. The shift or Plate 50 with relatively larger holes is then placed on top of the prelaminated layer 46, 48 which become holes with loose material 52, preferably made of thermosetting plastic material, which is also known as B-stage plastic material, is filled with excess material if necessary wiped away and a second, pre-laminated layer, which consists of a glass fiber reinforced epoxy resin covering 54 and a copper sheet 56 is put on the upper major surface of the plate 5o as shown in Fig. 3 (a) is.

The top platen 36 of the press is then lowered and the assembly between the platen is subjected to heat and pressure. As mentioned above, the temperature can be around 177 C; a suitable pressure for the mentioned thermosetting materials

2
is in the range of Io kg / cm. It is known that such a treatment is expediently carried out for one hour, but it should be mentioned again that the temperature and pressure and, more generally, the consolidation steps, if such are carried out, depend on the type of loose material selected from which the bolts are attached Shaped on the spot. As mentioned above, a wide range of materials can be selected if the material selected only requires time to cure without special treatment and the relatively long time required to cure the material is not detrimental.

FIG. 3 (b) shows a subsequent process step in which the laminated arrangement according to FIG. 2 is removed from the laminating press

509821/0 7

- 13 - L / p 7989

has been removed, smaller holes 58 drilled or otherwise formed through the solidified material 52 the material 52 forming the bolts 6o at this stage of the process; Fig. 3 (b) also shows that in a Process according to Fig. 3 (a) metal coatings have been formed on the two main surfaces of the arrangement, resulting from the lamination step. This metal overr. trains are then metal pads 46 and 56 in FIG. 3 (b), which are now have been bonded to the plate or layer 5o as a result of the lamination step, as far as the insulating plastic coverings 48 and 54 act as an adhesive.

Finally, a finished circuit board as shown in Fig. 3 (c) is obtained by making the circuit diagrams can be obtained from the metal coatings 46 and 56. This happens with each of the exemplary embodiments described here »with Using conventional masking and etching techniques and using a so-called masking material, such as this per se is known. Similarly, the interior surfaces defining the holes 58 of Fig. 3 (b) are plated through as shown in Fig. 3 (c) unless another method of making electrical connections through the bolts 6o is preferred will.

In summary, it can be seen that the special feature for Manufacture of insulating bolts at the point of desired intermediate connections by solidifying loose material A major improvement in the manufacture of printed circuit boards and printed circuit boards in place with heat sinks built into the bodies of the circuit boards. The inventive method is Particularly suitable for series production because once all bolts can be formed at the same time and for other different method steps can be combined into one method step, as explained above became.

509021/0741

Claims (15)

- 14 - L / p 7989 Claims Iy process for the production of circuit boards with printed circuit and plated-through connections between the corresponding sites of Stromkreisschöm.en _au fd _s two main surfaces and at least one inner layer acting as a heat sink, characterized in that within holes through the metallic layer at the a sufficient amount of loose material is solidified in place so that a permanently solid, electrically insulating, essentially a hole filling bolt connection is provided, and that on each surface and isolates from each surface a circuit diagram with plated-through connections at the aforementioned points is formed through at least some of the bolt connections. 2. The method according to claim 1, characterized in that loose material is used which is permanently solid Insulating material can be solidified so that holes are largely filled by the metallic layer. 3. The method according to claim 1 or 2, characterized in that the method steps of filling the holes and solidification of the loose material inside the holes can be carried out with a base that is temporary is applied to the underside of the metallic layer, and that then the base is removed. 4. The method according to claims 1 to 3, characterized in that finely divided, solid material as loose material is used. 5. The method according to claim 4, characterized in that the finely divided solid material is a thermoplastic Material is. 5098 21/0741 - 15 - L / p 7989 6. The method according to claim 5, characterized in that the thermoplastic material is a thermosetting material that is deposited inside the holes by the application of heat and / or pressure is solidified. 7 .. Method according to claims 3 and 6, characterized in that the loose material is a finely divided, partially hardened, thermosetting material, -uad that the solidification is carried out using a heating press with upper and lower plates, and that the temporarily applied Base is the lower plate. 8. The method according to claim 1 ff, characterized in that the drawing up of a circuit diagram the production of an insulating coating on each of the two surfaces of the metallic layer as well as the subsequent production of the two circuit diagrams, one circuit diagram each on each surface, using masking and etching techniques. 9. The method according to claim 8, characterized in that the holes will be made through at least some of the bolt connections and that the surfaces that the holes will set, are plated in such a way that the plated-through connections before, at the same time or after production the circuit diagrams formed on the two surfaces will. 10. The method according to claims 8 or 9, characterized in that that the metallic layer is an aluminum sheet and that the application of an insulating coating each of the two surfaces includes an anodizing treatment, at any stage prior to making the circuit diagrams on the two surfaces of the Aluminum sheet is made. 609 821 / 0741- - 16 - L / p 7989 11. The method according to claims 8 or 9, characterized in that that an insulating cover on each of the two Surfaces of the metallic layer is formed by having one with each side of the metallic layer is connected by two layers of plastic material, and that then the circuit diagrams on the Insulating coatings made using masking and etching techniques and the plated-through connections be formed. 12. The method according to claim 11, characterized in that the layers of plastic material layers of glass fiber reinforced Are epoxy. 13. The method according to claims 11 or 12, characterized in that that a pair of layers of thermoplastic, preferably thermosetting material is used, their each has a metallic reinforcement on one of its sides, and that the electrically conductive circuit diagrams of each metallic reinforcement can be formed using masking and etching techniques. 14. The method according to claims 11, 12 or 13, characterized in that that solidifying the loose material and forming an insulating coating on each of the both surfaces is combined into a single process step in a laminating press. 15. A printed circuit board manufactured by a method according to any one of the preceding claims. 509821/0741 Blank page