TWI423742B - Printed wiring board with copper foil and the use of its layered body - Google Patents

Description

Copper foil for printed wiring board and laminated body using the same

The present invention relates to a copper foil for a printed wiring board and a laminated body using the same, and more particularly to a copper foil for a flexible printed wiring board and a laminated body using the same.

Printed wiring boards have developed rapidly over the past half century and are used today in almost all electronic devices. With the increase in the demand for miniaturization and high performance of electronic devices, the high-density mounting of components and the high-frequency of signals have been progressing, and the wiring pattern is required to be fine-grained (fine pitch). (fine pitch)) or high frequency correspondence.

The printed wiring board is usually manufactured by forming an insulating substrate on a copper foil to form a laminated body, and then etching a copper foil surface to form a conductor pattern. Therefore, copper foil for printed wiring boards is required to have good etching properties.

If the surface of the copper foil and the resin are not surface-treated, the copper portion of the copper foil circuit after etching is etched from the surface of the copper foil, that is, gradually spread toward the resin layer (indentation is generated). In general, the "indentation" of the surface on the circuit side is small, and in particular, when a large "indentation" occurs, a copper circuit is short-circuited in the vicinity of the resin substrate to cause a defective product. Here, Fig. 4 is an enlarged photograph of a circuit surface which is an example of a case where a copper circuit is formed and a "crush" occurs in the vicinity of a resin substrate, and a copper circuit is short-circuited in the vicinity of a resin substrate.

This "indentation" must be minimized, but in order to prevent such a gradual expansion of etching, it is also considered to extend the etching time and perform more etching to reduce the "indentation". However, at this time, there will be a problem that when there is a portion having a certain width dimension, the portion will be further etched, so that the circuit width of the copper foil portion is thus narrowed, and the circuit design cannot obtain the desired one. A uniform line width (circuit width), especially in this part (the thinned portion), generates heat and sometimes breaks. In the process of further engraving the fine patterning of electronic circuits, the problems caused by such poor etching are more serious, and it becomes a big problem in circuit formation.

Patent Document 1 discloses a method for improving the above problem, in which a copper foil on the etching surface side is subjected to a surface treatment of a metal or alloy layer having an etching rate slower than that of copper. The metal or alloy at this time is an alloy of Ni, Co, and the like. When the circuit is designed, since the etching liquid is permeated from the resist coating side, that is, from the surface of the copper foil, if a metal or alloy layer having a slow etching rate is directly under the resist, the etching can be suppressed. The etching of the copper foil portion near the metal or alloy layer is performed, and the etching of the other copper foil portions is still performed, so that the effect of reducing the "indentation" and forming a circuit having a more uniform width can be obtained, which can be formed in comparison with the prior art. The steep circuit can be said to have made great progress.

Further, in Patent Document 2, a thickness of 1000 to 10,000 is formed. Cu film, and formed on the Cu film to a thickness of 10 to 300 A Ni film that is slower to etch than copper.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-176242

Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-269619

In recent years, in order to further develop the miniaturization and high density of circuits, it is necessary to have a circuit having a steeper side slope. However, the technique described in Patent Document 1 does not satisfy these requirements.

Further, the surface treatment layer disclosed in Patent Document 1 is required to be removed by soft etching, and further, in the step of processing the surface-treated copper foil with the non-adhesive surface of the resin into a laminate, high-temperature treatment such as resin adhesion is required. This causes oxidation of the surface treatment layer, resulting in deterioration of the etching property of the copper foil.

In the former, in order to shorten the time for removing the etching and to remove it relatively cleanly, it is necessary to make the thickness of the surface treatment layer as thin as possible, and in the latter case, it is necessary to improve or replace it with other materials because of the following problems. This problem is caused by the fact that the copper layer of the substrate is oxidized by heat (generally referred to as "burn marks" due to discoloration), and the coating property (uniformity, adhesion) of the resist is poor or the interface is oxidized at the time of etching. Excessive etching or the like causes problems such as etchability of pattern etching, short-circuiting, and controllability of circuit pattern width.

Further, the surface treatment layers disclosed in Patent Document 1 and Patent Document 2 are formed using Ni or Co, but this causes a concern that Ni or Co may adversely affect the electronic device due to its magnetic properties.

In view of the above, it is an object of the present invention to provide a copper foil for a printed wiring board which is excellent in etchability when formed into a circuit pattern and which is suitable for fine pitch, and which can satisfactorily suppress magnetic properties, and a laminated body using the same.

As a result of intensive studies, the present inventors have found that a coating layer containing at least one of platinum, palladium, and gold can be formed by providing a specific amount of metal adhesion on the side of the copper foil which is not adjacent to the resin. The circuit on the side of the circuit has an inclination angle of 80° or more. Thereby, it is possible to form a circuit that can sufficiently correspond to the miniaturization and high density of circuits in recent years.

In one aspect of the present invention, which has been completed based on the above findings, there is provided a copper foil for a printed wiring board comprising a copper foil substrate and a coating layer covering at least a portion of a surface of the copper foil substrate, and the coating The layer contains at least one of platinum, palladium and gold, and the platinum adhesion amount in the coating layer is 1050 μg/dm ² or less, the palladium adhesion amount is 600 μg/dm ² or less, and the gold adhesion amount is 1000 μg/dm ² or less.

A printed wiring board according to the present invention with a copper foil embodiment, the coating weight of the platinum-based coating layer is 20 ~ 400μg / dm ^2, a deposition amount of palladium 20 ~ 250μg / dm ^2, the amount of adhesion of gold 20 ~ 400μg /dm ² .

A printed wiring board according to the present invention of another embodiment of a copper foil, the adhesion amount of platinum-based coating layer is 50 ~ 300μg / dm ^2, a deposition amount of palladium 30 ~ 180μg / dm ^2, the amount of adhesion of 50 to gold 300 μg/dm ² .

In still another embodiment of the copper foil for a printed wiring board of the present invention, the printed wiring board is a flexible printed wiring board.

According to still another aspect of the present invention, a method for forming an electronic circuit includes the steps of: preparing a rolled copper foil or an electrolytic copper foil composed of the copper foil of the present invention; and preparing the coated layer of the copper foil as an etched surface. a step of laminating a copper foil and a resin substrate; and a step of etching the layered body with an aqueous solution of ferric chloride or copper chloride to remove a portion not requiring copper to form a copper circuit.

According to still another aspect of the present invention, a laminate comprising a laminate of a copper foil and a resin substrate of the present invention is provided.

According to still another aspect of the invention, there is provided a laminate comprising a laminate of a copper layer and a resin substrate, comprising a coating layer of the invention comprising at least a part of a surface of the copper layer.

In one embodiment of the laminate of the present invention, the resin substrate is a polyimide substrate.

In still another aspect of the invention, there is provided a printed wiring board using the laminate of the invention as a material.

According to the present invention, it is possible to provide a copper foil for a printed wiring board which is excellent in etchability and which is suitable for fine pitch and which can satisfactorily suppress magnetism when a circuit pattern is formed, and a laminate body using the same.

(copper foil substrate)

The form of the copper foil substrate which can be used in the present invention is not particularly limited, and it is typically used in the form of a rolled copper foil or an electrolytic copper foil. Usually, an electrolytic copper foil is produced by electrically analyzing copper from a copper sulfate plating bath to copper on a titanium or stainless steel drum, and the rolled copper foil is repeatedly produced by plastic working and heat treatment using a calender roll. Rolled copper foil is often used for applications requiring flexibility.

As the material of the copper foil substrate, in addition to high-purity copper such as toughened copper or oxygen-free copper which is generally used as a conductor pattern of a printed wiring board, for example, copper doped with Sn, copper doped with Ag, and, if added, may be used. A copper alloy such as Cr, Zr or Mg, or a copper alloy to which a Cason copper alloy such as Ni or Si is added. In addition, in the present specification, when the term "copper foil" is used alone, a copper alloy foil is also included.

The thickness of the copper foil substrate which can be used in the present invention is also not particularly limited as long as it is appropriately adjusted to be suitable for the thickness of the printed wiring board. For example, it may be about 5 to 100 μm. However, in the case of forming a fine pattern, it is 30 μm or less, preferably 20 μm or less, and typically about 5 to 20 μm.

The copper foil substrate used in the present invention is not particularly limited, and for example, a copper foil substrate which has not been subjected to roughening treatment can also be used. In the past, it is generally the case that the surface roughening treatment is performed by attaching a special surface to the surface with a μm-order unevenness, and the copper foil substrate has a bond with the resin by a physical registration effect. On the other hand, in terms of fine pitch or high frequency electrical characteristics, a smooth foil is preferred, and a roughened foil develops in an unfavorable direction. Moreover, in the case of the copper foil base material which is not roughened, since the roughening process step is abbreviate|omitted, it has the effect of improving economics and productivity.

(construction of the cover layer)

A coating layer is formed on at least a part of the surface of the copper foil substrate opposite to the surface on the subsequent surface of the insulating substrate (the side on which the circuit is to be formed). The coating layer contains at least one of platinum, palladium, and gold. In the case where the coating layer is composed of platinum, the platinum adhesion amount is 1050 μg/dm ² or less, preferably 20 to 400 μg/dm ² , and more preferably 50 to 300 μg/dm ² . In the case where the coating layer is made of palladium, palladium deposition amount of 600μg / dm ² or less, preferably 20 ~ 250μg / dm ^2, more preferably 30 ~ 180μg / dm ^2. In the case where the coating layer is composed of gold, the amount of gold adhered is 1000 μg/dm ² or less, preferably 20 to 400 μg/dm ² , and more preferably 50 to 300 μg/dm ² . When the platinum adhesion amount of the coating layer exceeds 1050 μg/dm ² , the palladium adhesion amount of the coating layer exceeds 600 μg/dm ^{2 ,} and the gold adhesion amount of the coating layer exceeds 1000 μg/dm ² , the initial etching property is adversely affected.

(Manufacturing method of copper foil)

The copper foil for a printed wiring board of the present invention can be formed by a sputtering method. That is, at least a part of the surface of the copper foil substrate is coated by the coating layer by a sputtering method. Specifically, a coating layer is formed on the etched surface side of the copper foil by a sputtering method, and the coating layer is one selected from the group consisting of a platinum group metal having a lower etching rate than copper, gold, and silver. Composition. The coating layer is not limited to being formed by a sputtering method, and may be formed by a wet plating method such as electroplating or electroless plating.

(Manufacturing method of printed wiring board)

A printed wiring board (PWB) can be manufactured according to a usual method using the copper foil of the present invention. An example of a method of manufacturing a printed wiring board is given below.

First, a copper foil and an insulating substrate are bonded together to manufacture a laminated body. The insulating substrate in which the copper foil is laminated is not particularly limited as long as it has characteristics suitable for the printed wiring board. For example, when used for a rigid PWB, a paper substrate phenol resin, a paper substrate epoxy resin, a synthetic fiber cloth can be used. Substrate epoxy resin, glass cloth-paper composite substrate epoxy resin, glass cloth-glass non-woven composite substrate epoxy resin and glass cloth substrate epoxy resin, etc. For FPC, polyester film or poly醯 imine film and the like.

Regarding the bonding method, in the case of using the rigid PWB, the following prepreg is prepared: the resin is impregnated into a substrate such as a glass cloth, and the resin is cured to a semi-hardened state. The surface of the copper foil from the opposite side of the coating layer may be superposed on the prepreg, and heated and pressed to bond the copper foil.

In the case of use in a flexible printed wiring board (FPC), an epoxy-based or acrylic-based adhesive may be used to bond the polyimide film or the polyester film to the copper foil (three-layer structure). Further, a method (two-layer structure) in which an adhesive is not used is exemplified by a casting method in which a polyimine varnish (polyamic acid varnish) which is a precursor of polyimine is applied to copper. The foil is imidized by heating; or the laminate method is applied to the polyimide film, and the thermoplastic polyimide is coated thereon, and the copper foil is laminated thereon and heated and pressurized. In the casting method, it is also extremely effective to apply an anchor coat material such as thermoplastic polyimide under the coating before the coating of the polyimide varnish.

The laminate of the present invention can be used for various printed wiring boards (PWB), and is not particularly limited. For example, from the viewpoint of the number of layers of the conductor pattern, it can be applied to single-sided PWB, double-sided PWB, and multilayer PWB (three or more layers). From the viewpoint of the type of the insulating substrate material, it can be applied to rigid PWB, flexible PWB (FPC), and rigid-flexible PWB. Moreover, the laminated body of the present invention is not limited to the copper-clad laminate formed by attaching a copper foil to a resin, and may be a metal spray material in which a copper layer is formed on a resin by sputtering or plating. .

The layered body having the structure in which a resist is applied on the surface of the coating layer formed on the copper foil formed on the layered body produced by the above method and covered by the mask is immersed in the etching liquid. A resist pattern is formed by development. In this case, the coating layer composed of one selected from the group consisting of platinum group metals, gold, and silver which are suppressed from etching is located on the copper foil at a position close to the resist portion, and the copper foil on the resist side The etching is performed by etching the copper away from the coating layer at a speed faster than the etching of the vicinity of the coating layer, whereby the etching of the copper circuit pattern is performed substantially vertically. Thereby, the portion which does not require copper can be removed, and then the etching resist is peeled off/removed to expose the circuit pattern.

The etching rate of the coating layer is sufficiently smaller than that of copper with respect to the etching liquid for forming the circuit pattern in the laminated body, and therefore, the effect of improving the etching factor is obtained. As the etching solution, an aqueous solution of copper chloride or an aqueous solution of ferric chloride or the like can be used, but an aqueous solution of ferric chloride is particularly effective. The reason for this is that the etching of the fine circuit takes time, and the etching solution of the aqueous solution of ferric chloride is faster than the aqueous solution of copper chloride. Further, a heat-resistant layer may be formed in advance on the surface of the copper foil substrate before the formation of the coating layer.

[Examples]

The embodiments of the present invention are exemplified below, and are intended to provide a better understanding of the present invention and are not intended to limit the invention.

(Example 1: Examples 1 to 33)

(forming a coating on copper foil)

A rolled copper foil (manufactured by Nippon Steel Co., Ltd. C1100) having a thickness of 12 or 17 μm was prepared as the copper foil substrates of Examples 1 to 21 and Examples 25 to 30. The surface roughness (Rz) of the rolled copper foil was 0.7 μm. Further, an electrolytic copper foil having a thickness of 9 μm which was not roughened was prepared as the copper foil substrates of Examples 22 to 24. The surface roughness (Rz) of the electrolytic copper foil was 1.5 μm. Further, a metal sprayed CCL having a thickness of 8 μm (mangansu made from Nippon Minerals, 0.01 μm on the copper layer side, and a metal adhesion amount Ni of the tie coat layer of 1780 μg/dm ² and Cr of 360 μg/dm ² ) was prepared. The copper foil substrates of Examples 31 to 33.

A thin oxide film adhering to the surface of the copper foil was removed by reverse sputtering, and a target of Au, Pt, and/or Pd was sputtered by the following apparatus and conditions to form a coating layer. The thickness of the coating layer can be varied by adjusting the film formation time. A single system of various metals used for sputtering is used with a purity of 3N.

‧Installation: Batch Sputtering Device (ULVAC, Model MNS-6000)

‧ ultimate vacuum: 1.0 × 10 ^-5 Pa

‧ Sputtering pressure: 0.2Pa

‧Reverse sputtering power: 100W

‧ Sputtering power: 50W

‧ Film formation rate: The film was formed into a film for about 0.2 μm for a certain period of time, and the thickness was measured by a three-dimensional measuring device to calculate the sputtering rate per unit time.

In the above examples, Examples 28 to 30 used the following targets.

‧Target: Au-50% by mass Pd, Pt-50% by mass Pd, and Au-50% by mass Pt

On the surface of the copper foil substrate on the opposite side to the surface on which the coating layer was formed, the thin oxide film adhering to the surface of the copper foil substrate was previously removed by reverse sputtering according to the following conditions, and the target of the Ni and Cr single layer was removed. Sputtering is performed to sequentially form a Ni layer and a Cr layer. The thickness of the Ni layer and the Cr layer can be varied by adjusting the film formation time.

‧Installation: Batch Sputtering Device (ULVAC, Model MNS-6000)

‧ ultimate vacuum: 1.0 × 10 ^-5 Pa

‧ Sputtering pressure: 0.2Pa

‧Reverse sputtering power: 100W

‧target:

Ni layer = Ni (purity is 3N)

Cr layer = Cr (purity is 3N)

‧ Sputtering power: 50W

‧ Film formation rate: The film was formed into a film for about 0.2 μm for a certain period of time, and the thickness was measured by a three-dimensional measuring device to calculate the sputtering rate per unit time.

The polyimide film was formed into a side surface on the Ni layer and the Cr layer of the copper foil substrate in the following order.

(1) UVarnish-A (polyimine varnish) manufactured by Ube Industries was applied to a copper foil of 7 cm × 7 cm in a dry body of 25 μm using an applicator.

(2) The resin-attached copper foil obtained in (1) was dried at 130 ° C for 30 minutes under air using a dryer.

(3) The hydrazine imidization was carried out at 350 ° C for 30 minutes in a high-temperature heating furnace in which the nitrogen flow rate was set to 10 L/min.

<Measurement of adhesion amount>

The amount of adhesion of Au, Pd, and Pt in the coating layer was measured by dissolving the surface-treated copper foil sample with aqua regia, diluting the solution, and performing the atomic absorption spectrometry.

(circuit shape formed by etching)

By applying a photosensitive resist to the surface of the coating layer on which the copper foil is formed and performing an exposure process, 10 circuits are printed, and an etching process for removing a portion where the copper foil is not required is performed under the following conditions.

<etching conditions>

‧ Aqueous ferric chloride solution: (37wt%, Baume: 40°)

‧ liquid temperature: 50 ° C

‧ spray pressure: 0.25MPa

(Form a circuit with a pitch of 50 μm)

‧Resist L/S=33μm/17μm

‧Complete circuit bottom (bottom) width: 25μm

‧ Etching time: 10 ~ 130 seconds

(Forming a circuit with a pitch of 30 μm)

‧Resist L/S=25μm/5μm

‧Complete circuit bottom (bottom) width: 15μm

‧ etching time: 30 to 70 seconds

‧ Confirmation of etching end point: The time was changed, etching was performed according to a plurality of standards, and it was confirmed by an optical microscope that copper did not remain between the circuits, and this time was the etching time.

After the etching, the mixture was immersed in an aqueous NaOH solution (100 g/L) at 45 ° C for 1 minute to remove the resist.

<Measurement conditions of etching factor>

The etching factor is used to indicate the ratio b/a of the following a to the thickness b of the copper foil, which indicates the gradual development of the etching (when the depression occurs), and the vertical line from the copper foil and the resin when the circuit is vertically etched. The distance of the indentation length from the intersection of the substrates, the larger the b/a value means that the inclination angle becomes larger, and no etching residue remains, and the depression becomes small. 1 is a photograph showing a surface of a partial circuit pattern, a schematic cross-sectional view in the width direction of a circuit pattern in the portion, and an outline of a method for calculating an etching factor using the schematic. This a is measured from the top of the circuit by SEM observation, and the etching factor (EF = b / a) is calculated. By using this etching factor, it is possible to easily judge whether or not the etching property is good. Further, the inclination angle θ is calculated by calculating the arctangent by using a measured in the above-described order and the thickness b of the copper foil. The measurement range is a circuit length of 600 μm, a 12-point etching factor, and the average value of the standard deviation and the inclination angle θ is used as a result.

(Example 2, Comparative Examples 1 to 3: blank)

A rolled copper foil having a thickness of 12 μm, a thickness of 17 μm, and a thickness of 9 μm was prepared, and the polyimide film was subsequently laminated in the same order as in Example 1. Then, 10 circuits were printed by applying a photosensitive resist and performing an exposure step on the opposite side, and etching treatment for removing a portion not requiring a copper foil was carried out under the conditions of Example 1.

(Example 3: Comparative Examples 4 to 6)

A rolled copper foil having a thickness of 12 μm was prepared, and a polyimide film was attached in the same order as in Example 1. Then, in the same manner as in Example 1, each layer of Au, Pd, and/or Pt was formed by sputtering on the surface of the copper foil, and an electric circuit was formed by etching.

The measurement results of Examples 1 to 3 are shown in Tables 1 to 4.

Furthermore, as shown in Fig. 2(b), the cross-sectional shape of the circuit is precisely a trapezoid in which the oblique side is a straight line. In Tables 2 and 4, the inclination angles of the circuits of the examples and the comparative examples are described, but this is merely a value calculated by the definition shown in Fig. 1.

(Evaluation)

(Examples 1 to 33)

Each of Examples 1 to 33 can form a circuit having a large etching factor and no unevenness, and the cross section is approximately rectangular.

2 is a photograph showing a circuit formed according to Embodiment 27 and a cross-sectional photograph thereof.

(Comparative Examples 1 to 6)

Comparative Examples 1 to 3 were unprocessed blanks on the surface of the copper foil, respectively, and a circuit having a rectangular cross section was not formed.

In Comparative Examples 4 to 6, the platinum adhesion amount exceeded 1050 μg/dm ² , the palladium adhesion amount exceeded 600 μg/dm ² or the gold adhesion amount exceeded 1000 μg/dm ² , and thus a circuit having a rectangular cross section was not formed. Here, as an example, FIG. 3 is a photograph showing a circuit formed in accordance with Comparative Example 6.

Fig. 1 is a photograph showing a surface of a partial circuit pattern, a cross-sectional view in the width direction of a circuit pattern in the portion, and an outline calculation method using an etching factor (EF) of the schematic.

Fig. 2 is a photograph showing a circuit formed according to Embodiment 27 and a cross section thereof.

Fig. 3 is a photograph showing the circuit formed in accordance with Comparative Example 6.

Fig. 4 is a magnified photograph of a circuit surface showing an example of occurrence of "indentation" in the formation of a copper circuit and short-circuiting of a copper circuit in the vicinity of a resin substrate.

Claims (9)

A copper foil for a printed wiring board comprising a copper foil base material and a coating layer, the coating layer covering at least a part of the surface of the copper foil base material, and containing at least one of platinum, palladium and gold; and the coating layer The platinum adhesion amount is 1050 μg/dm ² or less, the palladium adhesion amount is 600 μg/dm ² or less, and the gold adhesion amount is 1000 μg/dm ² or less. The patentable scope of application of the first printed wiring board a copper foil for items, wherein the adhesion amount of platinum in the coating layer is 20 ~ 400μg / dm ^2, a deposition amount of palladium 20 ~ 250μg / dm ^2, the coating weight is from 20 to gold 400 μg/dm ² . The patentable scope of the printed wiring board applications, Paragraph 2 using a copper foil, wherein the adhesion amount of platinum in the coating layer is 50 ~ 300μg / dm ^2, a deposition amount of palladium 30 ~ 180μg / dm ^2, the amount of adhesion of 50 to gold 300 μg/dm ² . The copper foil for a printed wiring board according to any one of claims 1 to 3, wherein the printed wiring board is a flexible printed wiring board. An electronic circuit forming method comprising the steps of: preparing a rolled copper foil or an electrolytic copper foil composed of a copper foil according to any one of claims 1 to 3; etching the coating layer of the copper foil And a step of forming a laminate of the copper foil and the resin substrate; and etching the laminate with an aqueous solution of ferric chloride or copper chloride to remove a portion not requiring copper to form a copper circuit. A laminate which is a laminate of a copper foil and a resin substrate according to any one of claims 1 to 3. A laminate comprising a laminate of a copper layer and a resin substrate, comprising a coating layer according to any one of claims 1 to 3, which covers at least a part of the surface of the copper layer. The laminate of claim 6 or 7, wherein the resin substrate is a polyimide substrate. A printed wiring board which is made of a laminate of the sixth or seventh aspect of the patent application.