JP2007036098A - Printed wiring board and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board and a manufacturing method therefor which give a circuit both adhesion and bending characteristics. <P>SOLUTION: A silver foil circuit surface coated with a cover lay or an inter-layer adhesive is subjected to microetching and turned into a rough surface with a roughness Rz of 0.5 μm or lower, or a surface roughness Ra of 0.5 μm or lower. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printed wiring board and a method for manufacturing the same.

Since flexible wiring boards are thin and excellent in flexibility, they are incorporated in various electronic devices. In particular, a flexible wiring board used for a hinge portion of a folding cellular phone, a PDA terminal, or the like is required to have high bending resistance.
When manufacturing a flexible wiring board, a coverlay (CL) is affixed on the copper foil of a copper clad laminated board (CCL) for protection of the copper foil surface. In a multilayer substrate, a coverlay or an interlayer adhesive may be attached. Conventionally, in order to improve the interlayer adhesion between the copper foil and the coverlay or the interlayer adhesive, the copper foil surface may be subjected to a roughening treatment. Here, the roughening treatment is to form an uneven shape on the surface of the copper foil.

Patent Documents 1 and 2 are documents relating to the surface roughness of the copper foil surface on the side bonded to the insulating substrate. Patent Document 1 describes a rolled copper foil having a surface oil pit depth of 2.0 μm or less formed by cold rolling. Patent Document 2 describes a flexible metal foil laminate in which polyimide as a substrate material is laminated on the surface of a metal foil with a small surface roughness Ra of about 0.2 μm or less.
In addition, there are Patent Documents 3 to 6 as documents relating to the surface roughness of the copper foil. In Patent Document 3, in order to facilitate the formation of a fine circuit, the Rz of the surface in contact with the thermosetting adhesive or the electrically insulating resin is 3 μm or less, and the nickel content in the surface treatment layer is 0.2 g / A flexible printed wiring board using a copper foil of m ² or less is described. Patent Document 4 describes a laminated board for a flexible printed circuit board in which Rz of a surface (M surface) on which a copper foil is bonded is 0.5 to 3.0 μm in order to improve migration resistance. Patent Document 5 discloses a method of manufacturing a multilayer wiring board in which Rz is 0.1 to 5.0 μm by physically roughening the surface of a copper foil for the problem that the adhesive strength deteriorates when left at high temperature or when moisture is absorbed. Is described. In Patent Document 6, in order to prevent the occurrence of cracking, peeling, and swelling of the insulating layer in a severe heat cycle test, the average depth of the irregularities formed by the roughening of the conductor layer is set to 10% or more of the wiring metal thickness. A multilayer circuit board is described.
Patent Documents 7 and 8 are documents relating to the bending characteristics of flexible wiring boards. Patent Document 7 describes a flexible printed circuit board in which the surface of a metal foil layer on a base film is roughened by an electrolytic plating method in order to improve the adhesive force and flexibility between the metal foil and the coverlay. In Patent Document 8, in order to form a good through hole in a multilayer part formed by laminating a hard printed wiring board material on a part of a flexible printed wiring board material, a roughening treatment is applied to the copper foil in the part that becomes the multilayer part. A method for manufacturing a printed wiring board is described, in which a hard printed wiring board material is laminated without interposing a film cover lay to improve adhesion to a prepreg.
JP 2001-58203 A JP 2001-270036 A JP 2003-86936 A JP 2003-133666 A JP 2003-332485 A Japanese Patent Laid-Open No. 11-330695 JP 2003-209351 A Japanese Patent No. 3155565

  Conventionally, it has been known to roughen the surface into a concavo-convex shape in order to improve the adhesion of the conductor circuit surface. In addition, micro-cracks are likely to occur due to surface roughening, and the cracks grow into larger cracks (macro cracks) due to repeated bending, leading to circuit disconnection. It is known to decline. Therefore, a roughening technique that achieves both circuit adhesion and bending characteristics has been desired.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the printed wiring board which can make the contact | adhesion power and bending characteristic of a circuit compatible, and its manufacturing method.

In order to solve the above problems, the roughness Rz of the copper foil circuit surface roughened by microetching is 5.0 μm or less, and a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface. A printed wiring board characterized by the above is provided. The roughness Rz is preferably 28% or less of the thickness of the copper foil.
In the present invention, the surface roughness Ra of the copper foil circuit surface roughened by microetching is 0.5 μm or less, and a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface. A printed wiring board characterized by the above is provided.

In the present invention, the copper foil circuit surface is roughened by microetching so that the roughness Rz is 5.0 μm or less, and then a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface. A method for manufacturing a printed wiring board is provided. The roughness Rz by the microetching is preferably 28% or less of the thickness of the copper foil.
In the present invention, the copper foil circuit surface is roughened by microetching so that the surface roughness Ra is 0.5 μm or less, and then a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface. A printed wiring board manufacturing method characterized by the above.

  According to the present invention, it is possible to manufacture a printed wiring board having both bending characteristics, adhesion, and heat resistance.

The present invention will be described below based on the best mode.
A printed wiring board to which the present invention is applied has a flexible portion used for bending. As such a printed wiring board, a single layer flexible substrate (FPC), a flexible multilayer substrate in which only two layers of FPC are laminated, a rigid substrate (on one side or both sides of an FPC serving as an inner layer substrate) Examples thereof include a rigid flex multilayer substrate (RF) in which other substrates such as RPC) are stacked.

In general, the flexible part includes a copper clad laminate (CCL) in which a copper foil is laminated as a conductor layer on one or both sides of a flexible insulating substrate (base film), and a circuit formed on the copper foil of the copper clad laminate. It consists of a coverlay laminated on the circuit for protection. In the case of a multilayer substrate, a coverlay or an interlayer adhesive may be stuck on the copper foil circuit surface.
As the copper foil, either a rolled copper foil or an electrolytic copper foil may be used. Although the thickness of copper foil is not specifically limited, For example, it is 9-36 micrometers.
As a coverlay, what provided the adhesive bond layer on the single side | surface of films of insulating resin, such as a polyimide (PI), can be used, for example. The adhesive used for attaching the coverlay is not particularly limited, and examples thereof include epoxy-based, rubber-based, acrylic-based, and polyimide-based adhesives.

  When the surface of the circuit is roughened to improve the adhesion between the circuit and the coverlay or interlayer adhesive, cracks grow from the irregularities on the surface, leading to disconnection of the circuit. To do. Therefore, in the present invention, when the roughening process is performed on the circuit surface of the copper foil, an optimum range is defined for the roughness Rz or the surface roughness Ra. Thereby, it is possible to manufacture a printed wiring board having both bending characteristics, adhesion and heat resistance.

Therefore, in the first invention, the surface of the copper foil circuit is roughened by microetching, and the roughness Rz of the copper foil circuit surface is set to 5.0 μm or less, more preferably 4.0 μm or less. Here, the roughness Rz is an average roughness of 10 points, and specifically, 5 points are selected in descending order from the top of the mountain, and 5 points are selected in order from the bottom of the valley, and the average of the peak height and valley depth is calculated. It is. Further, the roughness Rz is preferably 28% or less, more preferably 22% or less of the thickness of the copper foil.
If the roughness Rz of the copper foil circuit surface exceeds the above upper limit, the bending characteristics deteriorate, which is not preferable. In addition, the roughness Rz of the copper foil circuit surface is preferably 1.0 μm or more for adhesion and heat resistance (prevention of peeling).

  In the second invention, the copper foil circuit surface is roughened by micro-etching so that the surface roughness Ra of the copper foil circuit surface is 0.5 μm or less, more preferably 0.4 μm or less. Here, the surface roughness Ra is an arithmetic average roughness, and the reference length l is extracted from the roughness curve in the direction of the average line, and the absolute values from the average line of the extracted portion to the roughness curve are summed. The average value. If the surface roughness Ra of the copper foil circuit surface exceeds the upper limit, the bending characteristics are deteriorated, which is not preferable. Further, for the adhesion and heat resistance (prevention of peeling), the surface roughness Ra of the copper foil circuit surface is preferably 0.1 μm or more.

  In the present invention, the surface of the copper foil circuit surface is roughened by microetching, and the conditions are adjusted so that the roughness Rz or the surface roughness Ra is within the above-mentioned range. Then, a coverlay or an interlayer adhesive is laminated on the roughened copper foil circuit surface. This makes it possible to manufacture a printed wiring board that has both bending characteristics, adhesion, and heat resistance. The microetching can be performed, for example, by a sulfuric acid / hydrogen peroxide blackening alternative method. Micro-etching is preferable because it can be performed at a lower cost and has higher productivity than roughening plating, electrolytic plating, and blackening treatment.

Hereinafter, the present invention will be specifically described based on test examples.
In this test example, a plurality of printed wiring board samples having different roughness Rz or surface roughness Ra of the copper foil circuit surface of the inner layer FPC are manufactured, and a bending test, a peel test, and a reflow heat test are performed on the printed wiring board. Went.
FIG. 1 shows the structure and manufacturing process of a printed wiring board 60 as a sample. As shown in FIG. 1E, the printed wiring board 60 is a rigid flex multilayer board with a cable having a cable portion 61 made of only FPC.

(Materials used)
As the copper clad laminate 10 (CCL), a flexible structure in which copper foils 12 and 13 are laminated on both sides of a flexible base material 11 and the flexible base material 11 and the copper foils 12 and 13 are directly integrated without using an adhesive. A two-layer material was used. Here, the flexible substrate 11 was polyimide (PI) with a thickness of 25 μm, and the copper foils 12 and 13 were rolled copper foil with a thickness of 18 μm.
As the coverlay 20 (CL), a flexible substrate 21 provided with an adhesive 22 on one side thereof was used. Here, the flexible substrate 21 was made of polyimide (PI) having a thickness of 25 μm, and the adhesive 22 was made of an epoxy system having a thickness of 25 μm.
As the interlayer adhesive 40 (ADH), an adhesive sheet having a thickness of 40 μm was used.
As the outer layer substrate 50, RPC in which a copper foil 52 was laminated on one side of a rigid base material 51 was used. Here, the rigid base 51 was made of 150 μm thick glass epoxy resin (glass fiber braided and hardened with epoxy resin), and the copper foil 52 was made of 18 μm thick electrolytic copper foil.

(Manufacturing process)
First, as shown in FIG. 1A, circuits (not shown) are formed on the copper foils 12 and 13 on both sides of the copper clad laminate 10. Further, the circuit surfaces 12a and 13a of the copper foils 12 and 13 are micro-etched and roughened by using a sulfuric acid / hydrogen peroxide blackening alternative method. In addition, when producing the sample of the comparative example which did not process the roughening process, implementation of this roughening process is abbreviate | omitted.

Next, as shown in FIG.1 (b), the coverlays 20 and 20 are each laminated | stacked on the circuit surfaces 12a and 13a of the copper foils 12 and 13 of the copper clad laminated board 10, and the adhesive agent 22 side is copper clad laminated. It superposes on the copper foils 12 and 13 side of the board 10 and bonds them together by hot pressing or the like (CL cure).
By the above, the flexible substrate (inner layer FPC) used as the inner layer board | substrate 30 of the printed wiring board 60 is formed.

  Next, as shown in FIG. 1C, outer layer substrates (RPC) 50 and 50 are laminated on both surfaces of the inner layer substrate 30 with an interlayer adhesive 40 interposed therebetween. Further, a circuit (not shown) is formed on the copper foil 52 on the surface of the outer layer substrate 50.

  Next, as shown in FIG. 1 (d), the outer layer substrate 50 is peeled off by the outer shape processing of the outer layer substrate 50 to expose the inner layer substrate 30. As shown in FIG. 1 (e), the exposed inner layer substrate 30 becomes the cable portion 61, and the portions where the outer layer substrate 50 is left on both sides of the cable portion 61 are the three layers of the inner layer substrate 30 and the outer layer substrates 50 and 50. The multilayer portions 62 and 62 are formed by stacking and integrating the substrates.

(Test conditions)
In the bending test, in accordance with JIS C 5016 8.6, a sample is attached to a bending tester, and the sample is reciprocated at a constant speed while current is passed through the conductor pattern of the sample to measure the resistance value. The number of bendings was measured when it was recognized that the resistance value increased and the circuit was broken. For the number of bendings, an average value of 10 samples having the same roughness or surface roughness was used as a measurement value. The bending radius when the sample was bent repeatedly was 2.5 mm.

  In the peel test, in accordance with JIS C 6471 8.1, the copper foil of the sample was peeled in the direction of 90 ° with respect to the copper foil removal surface at a pulling speed of 50 mm / min in a normal temperature environment, and the obtained peeling was performed. From the load, the peel strength (N / cm) was calculated based on JIS C 5016 8.1.6.

  In the reflow heat resistance test, pretreatment is performed using JEDEC (Joint Electron Engineering Engineering Council; a joint committee of the National Electrical Manufacturers Association (NEMA) and the Electronic Industries Association of Japan (EIA)) Level 1 standard (temperature 85 ° C., relative humidity 85% RH). In this environment, a heat absorption treatment of 168 hours was performed, and then heating at 230 ° C. or higher (peak temperature was 250 ° C.) was continued for 30 seconds, and this heating was repeated three times. The presence or absence of peeling after heating (O: no peeling, x: occurrence of peeling) was tested.

(Test Example 1)
In the above manufacturing process, the roughness Rz of the circuit surfaces 12a and 13a of the copper foils 12 and 13 is 1.0 μm (6%), 2.0 μm (11%), 3.0 μm (17%), 4.0 μm (22 %), 5.0 μm (28%), 6.0 μm (33%), 7.0 μm (39%), and 8.0 μm (44%). A sample of the printed wiring board 60 was prepared. The roughness Rz is a value measured by observing the circuit surface with a laser microscope, and the percentage in parentheses after the roughness Rz indicates the ratio of the roughness Rz to the thickness of the copper foil in%. Value. Further, an untreated sample (Rz = 0 μm) was produced by omitting the roughening treatment.

  Bending test (measurement of the number of bendings of the cable part), peel test (measurement of the peel strength between the copper foil circuit surface and the coverlay), and the cable part of each sample of the manufactured printed wiring board, and A reflow heat resistance test (inspection for peeling between the copper foil circuit surface and the coverlay) was performed. The results are shown in Table 1 and FIG.

  From the results of Table 1 and FIG. 2, when a roughening process is performed on the circuit surface of the FPC in a printed wiring board having a bending cable portion, the roughness Rz is 5.0 μm or less (28% or less of the conductor thickness), More preferably, it was found that when the roughness Rz is 4.0 μm or less (22% or less of the conductor thickness), good bending characteristics are maintained. Also, by making the roughness Rz 1.0 μm or more (6% or less of the conductor thickness) by the roughening treatment, it has a higher peel strength than the untreated product (roughness Rz = 0 μm) and is reflow heat resistant. Since the coverlay is not peeled even in the test, it can be said to be an excellent printed wiring board having both bending characteristics, adhesion and heat resistance.

(Test Example 2)
In the above manufacturing process, the surface roughness Ra of the circuit surfaces 12a and 13a of the copper foils 12 and 13 is 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, A roughening process was performed so as to be 0.8 μm, and samples of the printed wiring board 60 having respective surface roughness Ra were produced. The surface roughness Ra is a value measured by observing the circuit surface with a laser microscope. Further, an untreated sample (Ra = 0 μm) was produced by omitting the roughening treatment.

  Bending test (measurement of the number of bendings of the cable part), peel test (measurement of the peel strength between the copper foil circuit surface and the coverlay), and the cable part of each sample of the manufactured printed wiring board, and A reflow heat resistance test (inspection for peeling between the copper foil circuit surface and the coverlay) was performed. The results are shown in Table 2 and FIG.

  From the results of Table 2 and FIG. 3, when a roughening process is performed on the circuit surface of the FPC in a printed wiring board having a bending cable portion, the surface roughness Ra is 0.5 μm or less, more preferably the surface roughness Ra. It was found that when the thickness was 0.4 μm or less, good bending characteristics were maintained. In addition, by making the surface roughness Ra 0.1 μm or more by roughening treatment, it has a higher peel strength than an untreated product (surface roughness Ra = 0 μm), and the coverlay can be peeled off even in a reflow heat test. Since it does not occur, it can be said that it is an excellent printed wiring board having both bending characteristics, adhesion and heat resistance.

  The present invention can be used for manufacturing a printed wiring board to be incorporated in various electronic devices.

It is sectional process drawing which shows an example of the manufacture procedure of (a)-(e) printed wiring boards. It is a graph which shows an example which shows the relationship between the roughness Rz of a copper foil circuit surface, the frequency | count of bending, and peel strength. It is a graph which shows an example which shows the relationship between surface roughness Ra, the frequency | count of bending, and peel strength of a copper foil circuit surface.

Explanation of symbols

12, 13 ... Copper foil, 12a, 13a ... Circuit surface, 20 ... Coverlay, 60 ... Printed wiring board.

Claims (6)

  Printed wiring characterized in that the roughness Rz of the copper foil circuit surface roughened by microetching is 5.0 μm or less, and a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface Board.   The printed wiring board according to claim 1, wherein the roughness Rz is 28% or less of a thickness of the copper foil.   The surface roughness Ra of the copper foil circuit surface roughened by microetching is 0.5 μm or less, and a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface. Wiring board.   Printed wiring characterized in that the copper foil circuit surface is roughened by micro-etching so that the roughness Rz is 5.0 μm or less, and then a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface. A manufacturing method of a board.   The method for manufacturing a printed wiring board according to claim 4, wherein the roughness Rz is set to 28% or less of the thickness of the copper foil in the microetching.   The copper foil circuit surface is roughened by micro-etching so that the surface roughness Ra is 0.5 μm or less, and then a coverlay or an interlayer adhesive is laminated on the copper foil circuit surface. A method for manufacturing a wiring board.

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