Cover lay and printed wiring board

Abstract

To provide a coverlay capable of securing adhesion between wiring and an adhesive layer even after being held at a high temperature.SOLUTION: The coverlay includes a resin film, an adhesive layer, and at least one gas barrier layer. The resin film has a first main surface and a second main surface opposite to the first main surface. The adhesive layer is disposed on the first main surface. Each of the at least one gas barrier layer is disposed at least either between the first main surface and the adhesive layer or on the second main surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a coverlay and a printed wiring board. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2021-091873 (Patent Document 1) describes a printed wiring board. The printed wiring board described in Patent Document 1 has a support layer, a conductor disposed on a main surface of the support layer, and an insulating layer disposed on the main surface of the support layer so as to cover the conductor. The insulating layer is, for example, a coverlay having an adhesive layer disposed on the main surface of the support layer so as to cover the conductor, and a resin film layer disposed on the adhesive layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-091873 Summary of the Invention [Problem to be solved by the invention]

[0004] When the printed wiring board described in Patent Document 1 is kept in a high-temperature (e.g., 150°C) environment, the surface of the conductor may be oxidized. If the surface of the conductor is oxidized, it is difficult to ensure adhesion between the conductor and the adhesive layer, even if a highly heat-resistant material is used for the adhesive layer.

[0005] The present disclosure provides a coverlay that can ensure adhesion between wiring and an adhesive layer even after being held at high temperatures. [Means for solving the problem]

[0006] The coverlay of the present disclosure includes a resin film, an adhesive layer, and at least one gas barrier layer. The resin film has a first main surface and a second main surface opposite the first main surface. The adhesive layer is disposed on the first main surface. Each of the at least one gas barrier layer is disposed at least either between the first main surface and the adhesive layer or on the second main surface. [Effects of the Invention]

[0007] The coverlay of the present disclosure can ensure adhesion between the wiring and the adhesive layer even after being held at high temperatures. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a coverlay 100. [Figure 2A] FIG. 2A is a cross-sectional view of a coverlay 100 according to the first modification. [Figure 2B] FIG. 2B is a cross-sectional view of the coverlay 100 according to the second modification. [Figure 3] FIG. 3 is a cross-sectional view of the printed wiring board 200. [Figure 4] FIG. 4 is a manufacturing process diagram of the printed wiring board 200. [Figure 5] FIG. 5 is a cross-sectional view of printed wiring board 300. [Figure 6A] FIG. 6A is a microscope image of the top surface of wiring 60 of Sample 1 after being held at high temperature. [Figure 6B] FIG. 6B is a microscope image of the top surface of wiring 60 of Sample 2 after being held at high temperature. [Figure 6C] FIG. 6C is a microscope image of the top surface of wiring 60 of Sample 3 after being held at high temperature. [Figure 7A] FIG. 7A is a graph showing the change over time in peel strength between wiring 60 and adhesive layer 20 in Sample 1 when held at 150°C. [Figure 7B] FIG. 7B is a graph showing the change over time in peel strength between wiring 60 and adhesive layer 20 in sample 2 when held at 150°C. [Figure 7C] FIG. 7C is a graph showing the change over time in peel strength between wiring 60 and adhesive layer 20 in sample 3 when held at 150°C. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) A coverlay according to an embodiment includes a resin film, an adhesive layer, and at least one gas barrier layer. The resin film has a first main surface and a second main surface opposite the first main surface. The adhesive layer is disposed on the first main surface. Each of the at least one gas barrier layer is disposed at least either between the first main surface and the adhesive layer or on the second main surface. The coverlay of (1) above can ensure adhesion between the wiring and the adhesive layer even after being held at high temperatures.

[0011] (2) In the coverlay of (1) above, the at least one gas barrier layer may be a single gas barrier layer. The single gas barrier layer may be disposed between the first main surface and the adhesive layer. The coverlay of (2) above can prevent cracks from occurring in the gas barrier layer.

[0012] (3) In the coverlay of (1) above, the at least one gas barrier layer may be a single gas barrier layer. The single gas barrier layer may be disposed on the second main surface.

[0013] (4) In the coverlay of (1) above, the at least one gas barrier layer may include a first gas barrier layer and a second gas barrier layer, and the first gas barrier layer and the second gas barrier layer may be disposed between the first main surface and the adhesive layer and on the second main surface, respectively.

[0014] (5) In the coverlays (1) to (4) above, each of the at least one gas barrier layer may be made of silicon oxide, a metal material, or DLC.

[0015] (6) The coverlays of (1) to (5) above may further include a separator. The adhesive layer may have a third main surface facing the first main surface and a fourth main surface opposite the third main surface. The separator may be disposed on the fourth main surface.

[0016] (7) A printed wiring board according to one embodiment includes the coverlay described above in (1) to (6), a base film, and wiring. The base film has a fifth main surface. The wiring is disposed on the fifth main surface. The coverlay is disposed on the fifth main surface so that the adhesive layer covers the wiring.

[0017] (8) A printed wiring board according to another embodiment includes a base film, wiring, and a coverlay. The base film has a fifth main surface. The wiring is disposed on the fifth main surface. The coverlay includes an adhesive layer disposed on the fifth main surface so as to cover the wiring, and a resin film disposed on the adhesive layer. After the printed wiring board is maintained at 150°C for 250 hours, the top surface of the wiring includes a first region and a second region having a lower brightness than the first region. The proportion of the top surface of the wiring that is occupied by the second region is 10 percent or less.

[0018] (9) In the printed wiring board of (8) above, the coverlay may have at least one gas barrier layer disposed at least either between the adhesive layer and the resin film or on the resin film.

[0019] (10) In the printed wiring board of (8) or (9) above, each of the at least one gas barrier layer may be made of silicon oxide, a metal material, or DLC.

[0020] (11) In the printed wiring boards of (8) to (10) above, the adhesive layer may contain silicone polyimide.

[0021] [Details of the embodiments of the present disclosure] The details of the embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated. The coverlay according to the embodiment is referred to as coverlay 100, and the printed wiring board according to the embodiment is referred to as printed wiring board 200.

[0022] (Coverlay 100 composition) The configuration of the coverlay 100 will be described below.

[0023] 1 is a cross-sectional view of a coverlay 100. As shown in FIG. 1, the coverlay 100 has a resin film 10, an adhesive layer 20, and a gas barrier layer 30.

[0024] The resin film 10 is made of a flexible, electrically insulating material. The resin film 10 is made of, for example, polyimide. However, the resin film 10 may be made of other materials, such as polyester, polyamideimide, or liquid crystal polymer (LCP). The resin film 10 has a main surface 10a and a main surface 10b. The main surface 10b is the surface opposite to the main surface 10a.

[0025] The adhesive layer 20 is formed of an adhesive. The adhesive layer 20 is formed of, for example, an epoxy adhesive, a polyamide adhesive, an acrylic adhesive, a urethane adhesive, or the like. To ensure high heat resistance, the adhesive layer 20 may be formed of an adhesive containing silicone polyimide (an adhesive containing silicone polyimide as a main component). The adhesive layer 20 is formed of, for example, a material that has a heat resistance of 150°C or higher. The adhesive layer 20 is disposed on the main surface 10a. The adhesive layer 20 has a main surface 20a and a main surface 20b. The main surface 20a faces the main surface 10a. The main surface 20b is the opposite surface to the main surface 20a.

[0026] The gas barrier layer 30 is formed of a material with low oxygen permeability. The gas barrier layer 30 is formed of, for example, silicon oxide, a metal material, or DLC (Diamond Like Carbon). The metal material used for the gas barrier layer 30 is, for example, a material that forms a dense passive oxide film, such as aluminum or titanium, or a metal material that is difficult to oxidize, such as gold, silver, or platinum. The gas barrier layer 30 is disposed, for example, on the main surface 10b. The thickness of the gas barrier layer 30 is defined as thickness T. Thickness T is, for example, 1 μm or less.

[0027] The coverlay 100 may further include a separator 40. The separator 40 is formed of a material that can be easily peeled off from the adhesive layer 20. The separator 40 is disposed on the main surface 20b.

[0028] <Modification> 2A is a cross-sectional view of a coverlay 100 according to Modification 1. As shown in FIG. 2A, in the coverlay 100, the gas barrier layer 30 may be disposed between the resin film 10 and the adhesive layer 20. That is, in the coverlay 100, the adhesive layer 20 may be disposed on the main surface 10a with the gas barrier layer 30 interposed therebetween. FIG. 2B is a cross-sectional view of a coverlay 100 according to Modification 2. As shown in FIG. 2B, in the coverlay 100, the gas barrier layer 30 may be disposed between the resin film 10 and the adhesive layer 20 in addition to being disposed on the main surface 10b.

[0029] (Configuration of printed wiring board 200) The configuration of the printed wiring board 200 will be described below.

[0030] 3 is a cross-sectional view of the printed wiring board 200. As shown in FIG. 3, the printed wiring board 200 has a base film 50, wiring 60, and a coverlay 100.

[0031] The base film 50 is made of a flexible, electrically insulating material. The base film 50 is made of, for example, polyimide. The base film 50 has a main surface 50a and a main surface 50b. The main surface 50b is the surface opposite to the main surface 50a. The wiring 60 is made of a conductive material, for example, a metal material. The wiring 60 is made of, for example, copper or a copper alloy. The wiring 60 is disposed on the main surface 50a.

[0032] The coverlay 100 is disposed on the main surface 50a so that the adhesive layer 20 covers the wiring 60. The adhesive of the adhesive layer 20 is cured. Holding the printed wiring board 200 at 150°C for 250 hours is referred to as "high-temperature holding." The peel strength between the adhesive layer 20 and the wiring 60 after high-temperature holding is, for example, 3.4 N / cm or more. Note that 3.4 N / cm is the standard value for peel strength (standard value for initial peel strength) specified in standards for flexible printed circuit boards, such as those of JPCA and IEC. The peel strength between the adhesive layer 20 and the wiring 60 is measured by performing a 90° peel test or a 180° peel test in accordance with IPC-TM-650 2.4.9. A sample to be subjected to the peel test is cut into a strip, and the peel test is performed on the sample using a peel tester (tensile strength tester).

[0033] After being held at high temperature, the top surface of the wiring 60 has a first region and a second region. After being held at high temperature, an oxide of the material contained in the wiring 60, more specifically, copper oxide, is formed in the second region. On the other hand, copper oxide is not formed in the first region. Therefore, the brightness of the second region is lower than the brightness of the first region. After being held at high temperature, the ratio of the area of ​​the second region to the area of ​​the top surface of the wiring 60 is, for example, 10 percent or more. The ratio of the area of ​​the second region to the area of ​​the top surface of the wiring 60 is measured by the following method.

[0034] First, a microscope image of printed wiring board 200 in a plan view is captured. Based on this microscope image, the area of ​​the top surface of wiring 60 is calculated. Second, an appropriate brightness threshold is set for the microscope image captured as described above, and a binarization process is performed. Third, based on the microscope image that has been binarized, the area of ​​the second region is calculated. Then, the area of ​​the second region obtained as described above is divided by the area of ​​the top surface of wiring 60, and this result is multiplied by 100 to obtain the ratio of the area of ​​the second region to the area of ​​the top surface of wiring 60.

[0035] (Method of manufacturing printed wiring board 200) The following describes a method for manufacturing the printed wiring board 200. Fig. 4 is a manufacturing process diagram for the printed wiring board 200. As shown in Fig. 4, the manufacturing method for the printed wiring board 200 includes a preparation step S1 and a coverlay application step S2.

[0036] In the preparation step S1, a coverlay 100 and a printed wiring board 200 are prepared. In the coverlay 100 prepared in the preparation step S1, openings are formed using a mold or the like, and the outer shape is shaped. In the printed wiring board 200 prepared in the preparation step S1, a circuit is formed using wiring 60 formed by etching copper foil. In the coverlay attachment step S2, the coverlay 100 is aligned with the printed wiring board 200 and then attached. In the coverlay attachment step S2, first, the separator 40 is peeled off. Second, the coverlay 100 is positioned so that the adhesive layer 20 faces the main surface 50a. Third, the coverlay 100 is heated while being pressed toward the main surface 50a. This hardens the uncured adhesive layer 20, and the coverlay 100 is attached to the printed wiring board 200. As a result, the structure of the printed wiring board 200 shown in FIG. 3 is formed.

[0037] (Effect of Coverlay 100) The effects of the coverlay 100 will be described below in comparison with a comparative example. The printed wiring board according to the comparative example is designated as printed wiring board 300, and the coverlay according to the comparative example is designated as coverlay 400.

[0038] 5 is a cross-sectional view of printed wiring board 300. As shown in FIG. 5, printed wiring board 300 has a base film 50 and wiring 60, similar to printed wiring board 200. Printed wiring board 300 has a coverlay 400 instead of coverlay 100. Coverlay 400 has resin film 10 and adhesive layer 20, but does not have gas barrier layer 30. In this respect, the configuration of printed wiring board 300 differs from the configuration of printed wiring board 200, and coverlay 400 differs from coverlay 100.

[0039] When the printed wiring board 300 is kept at a high temperature, oxygen in the air diffuses through the coverlay 400 (the resin film 10 and the adhesive layer 20) and reaches the surface of the wiring 60. As a result, the surface of the wiring 60 in the printed wiring board 300 is oxidized.

[0040] On the other hand, in the printed wiring board 200, a gas barrier layer 30 is disposed on at least one of the main surface 10b and between the adhesive layer 20 and the resin film 10. Therefore, even when the temperature is maintained at a high temperature, the gas barrier layer 30 suppresses the diffusion of oxygen in the coverlay 100, making it difficult for oxygen to reach the surface of the wiring 60, and therefore the surface of the wiring 60 is difficult to oxidize.

[0041] FIG. 6A is a microscope image of the top surface of wiring 60 of Sample 1 after being held at high temperature. FIG. 6B is a microscope image of the top surface of wiring 60 of Sample 2 after being held at high temperature. FIG. 6C is a microscope image of the top surface of wiring 60 of Sample 3 after being held at high temperature. Note that in FIGS. 6A to 6C, the acquired microscope images are displayed in grayscale. Coverlay 400 was used for Sample 1, and coverlay 100 was used for Samples 2 and 3. In Sample 2, a gas barrier layer 30 was disposed on main surface 10b, and in Sample 3, a gas barrier layer 30 was disposed between resin film 10 and adhesive layer 20. In Samples 1 to 3, adhesive layer 20 is formed of a silicone polyimide adhesive.

[0042] 6A, in the microscope image of Sample 1, the top surface of the wiring 60 is dark, and an oxide has formed on the entire top surface of the wiring 60. On the other hand, in the microscope images of Samples 2 and 3, although dark spots are observed locally, the top surface of the wiring 60 is whitish overall. As such, it has become clear that if the gas barrier layer 30 is disposed on at least one of the main surface 10b and between the adhesive layer 20 and the resin film 10, oxidation of the surface of the wiring 60 can be suppressed even when the wiring 60 is kept at a high temperature.

[0043] If the surface of the wiring 60 is oxidized, the adhesion between the wiring 60 and the adhesive layer 20 decreases. In the printed wiring board 200, the oxidation of the surface of the wiring 60 is suppressed as described above, so that the adhesion between the wiring 60 and the adhesive layer 20 can be ensured even after being held at high temperatures.

[0044] FIG. 7A is a graph showing the change over time in peel strength between the wiring 60 and adhesive layer 20 in Sample 1 when held at 150°C. FIG. 7B is a graph showing the change over time in peel strength between the wiring 60 and adhesive layer 20 in Sample 2 when held at 150°C. FIG. 7C is a graph showing the change over time in peel strength between the wiring 60 and adhesive layer 20 in Sample 3 when held at 150°C. As shown in FIG. 7A, in Sample 1, the peel strength between the wiring 60 and adhesive layer 20 significantly decreased after 125 hours of holding at 150°C. More specifically, in Sample 1, the peel strength was below 3.4 N / cm (the standard value for initial peel strength) after 125 hours of holding at 150°C.

[0045] On the other hand, as shown in FIGS. 7B and 7C , in Samples 2 and 3, the peel strength between the wiring 60 and the adhesive layer 20 remained comparable to the initial state even after being held at 150°C for 250 hours. Furthermore, in Samples 2 and 3, the peel strength between the wiring 60 and the adhesive layer 20 decreased only gradually even when the holding time was extended. More specifically, even after being held at 150°C for 1,000 hours, the peel strength remained at the initial value of 10 N / cm or more, with little change. Thus, it was revealed that the presence of a gas barrier layer 30 on at least one of the main surface 10b and the space between the adhesive layer 20 and the resin film 10 can suppress the decrease in peel strength between the wiring 60 and the adhesive layer 20 due to oxidation of the surface of the wiring 60.

[0046] When cracks or the like are formed in the gas barrier layer 30, oxygen passes through the cracks and diffuses into the coverlay 100. Cracks in the gas barrier layer 30 are formed when the coverlay 100 is bent, etc., but when the gas barrier layer 30 is disposed between the resin film 10 and the adhesive layer 20, the occurrence of cracks in the gas barrier layer 30 is suppressed.

[0047] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims rather than the above-described embodiments, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0048] 10 Resin film 10a,10b main surface 20 Adhesive layer 20a,20b main surface 30 Gas barrier layer 40 Separator 50 base film 50a,50b main surface 60 Wiring 100 Coverlay 200 Printed Wiring Board 300 Printed Wiring Board 400 coverlay S1 Preparation process S2 Coverlay application process T Thickness

Claims

1. A resin film; an adhesive layer; At least one gas barrier layer; the resin film has a first main surface and a second main surface opposite to the first main surface, the adhesive layer is disposed on the first major surface; A coverlay, wherein each of the at least one gas barrier layer is disposed at least either between the first main surface and the adhesive layer and on the second main surface.

2. the at least one gas barrier layer is a single gas barrier layer, The coverlay according to claim 1 , wherein the one gas barrier layer is disposed between the first main surface and the adhesive layer.

3. the at least one gas barrier layer is a single gas barrier layer, The coverlay according to claim 1 , wherein the one gas barrier layer is disposed on the second main surface.

4. the at least one gas barrier layer includes a first gas barrier layer and a second gas barrier layer, The coverlay of claim 1 , wherein the first gas barrier layer and the second gas barrier layer are disposed between the first main surface and the adhesive layer and on the second main surface, respectively.

5. The coverlay of claim 1 , wherein each of the at least one gas barrier layer is formed of silicon oxide, a metal material, or DLC.

6. Further comprising a separator, the adhesive layer has a third main surface facing the first main surface and a fourth main surface opposite the third main surface, The coverlay of claim 1 , wherein the separator is disposed on the fourth major surface.

7. The coverlay according to any one of claims 1 to 6; A base film; Wiring, the base film has a fifth major surface; the wiring is disposed on the fifth main surface, The coverlay is disposed on the fifth main surface so that the adhesive layer covers the wiring.

8. A printed wiring board, A base film; Wiring and and a coverlay. the base film has a fifth major surface; the wiring is disposed on the fifth main surface, the coverlay includes an adhesive layer disposed on the fifth main surface so as to cover the wiring, and a resin film disposed on the adhesive layer; After the printed wiring board is maintained at 150°C for 250 hours, the top surface of the wiring includes a first region and a second region having a lower brightness than the first region, A printed wiring board, wherein the second region occupies 10 percent or less of the top surface of the wiring.

9. The printed wiring board according to claim 8 , wherein the coverlay has at least one gas barrier layer disposed at least either between the adhesive layer and the resin film or on the resin film.

10. The printed wiring board according to claim 9 , wherein each of the at least one gas barrier layers is formed of silicon oxide, a metal material, or DLC.

11. The printed wiring board according to claim 8 , wherein the adhesive layer contains silicone polyimide.

Images