Coverlay film, printed wiring board, method for manufacturing coverlay film, and method for manufacturing printed wiring board

Abstract

This coverlay film is provided with: an insulation film that has a first principal surface and a second principal surface, which is a surface opposite the first principal surface; an adhesive layer that is disposed on the first principal surface and is formed from an uncured adhesive; and a separator that is disposed on the adhesive layer. The thickness of the insulation film is 2-15 μm. The thickness of the adhesive layer is 10-50 μm.

Description

Coverlay film, printed wiring board, method for manufacturing coverlay film, and method for manufacturing printed wiring board

[0001] The present disclosure relates to a coverlay film, a printed wiring board, a method for manufacturing a coverlay film, and a method for manufacturing a printed wiring board. This application claims priority to Japanese Patent Application No. 2022-059505, filed on March 31, 2022. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] For example, as described in Japanese Patent Laid-Open No. 2019-116619 (Patent Document 1), a coverlay film includes an insulating film and an adhesive layer. The insulating film is made of a material that is electrically insulating and flexible. The adhesive layer is disposed on a main surface of the insulating film.

[0003] Japanese Patent Application Laid-Open No. 2019-116619

[0004] The coverlay film of the present disclosure includes an insulating film having a first main surface and a second main surface opposite the first main surface, an adhesive layer disposed on the first main surface and formed of an uncured adhesive, and a separator disposed on the adhesive layer. The insulating film has a thickness of 2 μm or more and 15 μm or less. The adhesive layer has a thickness of 10 μm or more and 50 μm or less.

[0005] Fig. 1 is a cross-sectional view of a coverlay film 100. Fig. 2 is a manufacturing process diagram of the coverlay film 100. Fig. 3 is a cross-sectional view of a printed wiring board 200. Fig. 4 is a manufacturing process diagram of the printed wiring board 200.

[0006] [Problem to be Solved by the Present Disclosure] The coverlay film is attached to a printed wiring board. More specifically, the printed wiring board has a base film and a conductive pattern disposed on a main surface of the base film. The coverlay film is disposed on the main surface of the base film so that the adhesive layer covers the conductive pattern.

[0007] If the thickness of the adhesive layer is small, it becomes difficult to fill the gap between the adjacent conductive pattern portions with the adhesive layer when the distance between the adjacent conductive pattern portions becomes small.If the thickness of the insulating film is large, it becomes difficult to thin the printed wiring board to which the coverlay film is attached.

[0008] The present disclosure has been made in view of the above-described problems of the conventional art. More specifically, the present disclosure provides a coverlay film that can reduce the thickness of a printed wiring board while improving the embedding ability of an adhesive layer between adjacent conductive pattern portions.

[0009] Effect of the Present Disclosure The coverlay film of the present disclosure makes it possible to reduce the thickness of a printed wiring board while improving the embedding ability of an adhesive layer between adjacent conductive pattern portions.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] (1) A coverlay film according to an embodiment includes an insulating film having a first main surface and a second main surface opposite the first main surface, an adhesive layer disposed on the first main surface and formed of an uncured adhesive, and a separator disposed on the adhesive layer. The insulating film has a thickness of 2 μm or more and 15 μm or less. The adhesive layer has a thickness of 10 μm or more and 50 μm or less.

[0012] The coverlay film of (1) above makes it possible to reduce the thickness of the printed wiring board while improving the embedding property of the adhesive layer between adjacent conductive pattern portions.

[0013] (2) The coverlay film of (1) above may further include a protective film. The protective film may be disposed on the second main surface.

[0014] The coverlay film of (2) above can suppress damage to the insulating film, and the coverlay film of (2) above can improve the handleability of the coverlay film.

[0015] (3) In the coverlay film of (2) above, the peel strength of the protective film relative to the insulating film may be greater than the peel strength of the separator relative to the adhesive layer.

[0016] According to the coverlay film of (3) above, it is possible to peel the separator from the adhesive layer without peeling the protective film from the insulating film.

[0017] (4) In the coverlay films of (1) to (3) above, the thickness of the adhesive layer may be greater than the thickness of the insulating film.

[0018] (5) In the coverlay films according to (1) to (4), the insulating film may have a thickness of 2 μm or more and 13 μm or less, and the adhesive layer may have a thickness of 20 μm or more and 50 μm or less.

[0019] (6) In the coverlay films of (1) to (5) above, the insulating film may be made of polyimide or liquid crystal polymer.

[0020] (7) A printed wiring board according to an embodiment includes a base film having a third main surface, a conductive pattern disposed on the third main surface, and the coverlay film described above in (1) to (6). The separator is peeled off from the coverlay film. The coverlay film is disposed on the third main surface so that the adhesive layer covers the conductive pattern. The adhesive is cured.

[0021] According to the printed wiring board of (7) above, it is possible to improve the embedding property of the adhesive layer between adjacent conductive pattern portions, while reducing the thickness of the printed wiring board.

[0022] (8) A method for manufacturing a coverlay film according to an embodiment includes the steps of: preparing an insulating film having a first main surface and a second main surface opposite the first main surface, with a protective film disposed on the second main surface; forming an adhesive layer on the first main surface using an uncured adhesive; and disposing a separator on the adhesive layer. The insulating film has a thickness of 2 μm or more and 15 μm or less. The adhesive layer has a thickness of 10 μm or more and 50 μm or less.

[0023] According to the method for producing a coverlay film described above in (8), it is possible to prevent the coverlay film from collapsing during the production process.

[0024] (9) The method for producing a coverlay film according to (8) above may further include a step of peeling the protective film from the insulating film.

[0025] (10) A method for manufacturing a printed wiring board according to an embodiment includes the steps of: preparing a coverlay film having an insulating film including a first main surface and a second main surface opposite the first main surface; an adhesive layer disposed on the first main surface and formed from an uncured adhesive; a protective film disposed on the second main surface; and a separator disposed on the adhesive layer; peeling the separator from the adhesive layer; preparing a base film having a third main surface and on which a conductive pattern is disposed; placing the coverlay film on the third main surface so that the adhesive layer covers the conductive pattern and curing the adhesive; and peeling the protective film from the insulating film.

[0026] According to the method for manufacturing a printed wiring board of (10) above, it is possible to improve the embedding property of the adhesive layer between adjacent conductive pattern portions, while reducing the thickness of the printed wiring board.

[0027] (11) In the method for manufacturing a printed wiring board according to (10) above, the protective film may be peeled off after the coverlay film is placed on the third main surface.

[0028] According to the method for manufacturing a printed wiring board in (11) above, it is possible to improve the handleability of the coverlay film.

[0029] [Details of the embodiment of the present disclosure] Details of the embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description will not be repeated.

[0030] (Coverlay Film According to the Embodiment) A coverlay film according to the embodiment will be described. The coverlay film according to the embodiment is referred to as a coverlay film 100.

[0031] <Configuration of Coverlay Film 100> The configuration of the coverlay film 100 will be described below.

[0032] Fig. 1 is a cross-sectional view of a coverlay film 100. As shown in Fig. 1, the coverlay film 100 has an insulating film 10, an adhesive layer 20, and a separator 30. The coverlay film 100 may have a protective film 40. However, the coverlay film 100 does not have to have the protective film 40.

[0033] The insulating film 10 has a first main surface 10a and a second main surface 10b. The first main surface 10a and the second main surface 10b are end surfaces of the insulating film 10 in the thickness direction. The second main surface 10b is the surface opposite to the first main surface 10a. The insulating film 10 is made of a flexible, electrically insulating material. The insulating film 10 is made of, for example, polyimide. The insulating film 10 may also be made of a liquid crystal polymer. However, the constituent material of the insulating film 10 is not limited to this.

[0034] The adhesive layer 20 is disposed on the first main surface 10 a. The adhesive layer 20 is formed of an uncured adhesive. This adhesive is, for example, an epoxy adhesive. However, the adhesive is not limited to this.

[0035] The thickness of the insulating film 10 and the thickness of the adhesive layer 20 are designated as thickness T1 and thickness T2, respectively. Thickness T1 is 2 μm or more and 15 μm or less. Thickness T2 is 10 μm or more and 50 μm or less. Thickness T2 is preferably greater than thickness T1. Thickness T1 is preferably 2 μm or more and 13 μm or less. Thickness T2 is preferably 20 μm or more and 50 μm or less. Note that thickness T2 is the thickness of the adhesive layer 20 in a dried state in the adhesive layer forming step S2 described below.

[0036] The separator 30 is disposed on the adhesive layer 20. The separator 30 is formed from a base material that has been subjected to a release treatment. This base material is formed from a resin material such as polyethylene terephthalate, polypropylene, or polyethylene, or from paper. However, the constituent material of this base material is not limited to these. The thickness of the separator 30 is defined as thickness T3. Thickness T3 is, for example, not less than 10 μm and not more than 150 μm.

[0037] The protective film 40 is disposed on the second main surface 10b. The protective film 40 is formed of a resin material such as polyethylene terephthalate. However, the material of the protective film 40 is not limited to this. Although not shown, an adhesive layer may be interposed between the second surface 10b and the protective film 40 to attach the protective film 40 to the second surface 10b.

[0038] The peel strength of the protective film 40 from the insulating film 10 is greater than the peel strength of the separator 30 from the adhesive layer 20. This makes it possible to peel the separator 30 from the adhesive layer 20 without peeling the separator 30 from the insulating film 10. The peel strength of the protective film 40 from the insulating film 10 and the peel strength of the separator 30 from the adhesive layer 20 are measured in accordance with JIS Z 0237:2009.

[0039] <Method for Manufacturing Coverlay Film 100> A method for manufacturing the coverlay film 100 will be described below.

[0040] 2 is a manufacturing process diagram of the coverlay film 100. As shown in Fig. 2, the manufacturing method of the coverlay film 100 includes a preparation step S1, an adhesive layer formation step S2, and a separator arrangement step S3. The adhesive layer formation step S2 is performed after the preparation step S1, and the separator arrangement step S3 is performed after the adhesive layer formation step S2.

[0041] In the preparation step S1, an insulating film 10 is prepared. In the insulating film 10 prepared in the preparation step S1, a protective film 40 is disposed on the second main surface 10b.

[0042] In the adhesive layer forming step S2, the adhesive layer 20 is formed on the first main surface 10a. In the adhesive layer forming step S2, first, an uncured adhesive is applied to the first main surface 10a. Second, the uncured adhesive applied to the first main surface 10a is dried. The uncured adhesive applied to the first main surface 10a is dried by, for example, blowing hot air onto it.

[0043] In the separator placement step S3, the separator 30 is placed on the adhesive layer 20. This results in the manufacture of the coverlay film 100 having the structure shown in Fig. 1. Note that after the separator placement step S3 is performed, the protective film 40 may be peeled off from the insulating film 10.

[0044] (Printed Wiring Board According to the Embodiment) A printed wiring board according to the embodiment will be described. The printed wiring board according to the embodiment is designated as a printed wiring board 200.

[0045] <Configuration of Printed Wiring Board 200> The configuration of the printed wiring board 200 will be described below.

[0046] 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, conductive patterns 61 and 62, and a coverlay film 100.

[0047] The base film 50 has a third main surface 50a and a fourth main surface 50b. The third main surface 50a and the fourth main surface 50b are end surfaces of the base film 50 in the thickness direction. The fourth main surface 50b is the surface opposite to the third main surface 50a. 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 may also be made of a liquid crystal polymer. However, the constituent material of the base film 50 is not limited to this.

[0048] The conductive patterns 61 and 62 are disposed on the third main surface 50a and the fourth main surface 50b, respectively. The conductive patterns 61 and 62 are formed, for example, by a semi-additive method. More specifically, the conductive patterns 61 and 62 each have a seed layer 63, an electroless plating layer 64, and an electrolytic plating layer 65. However, the conductive patterns 61 and 62 may also be formed by a subtractive method.

[0049] The thicknesses of the conductive patterns 61 and 62 are defined as thickness T4 and thickness T5, respectively. Thickness T4 and thickness T5 are, for example, 10 μm or more and 60 μm or less. The distance between two adjacent portions of the conductive patterns 61 is defined as distance DIS1. The distance between two adjacent portions of the conductive patterns 62 is defined as distance DIS2. Distance DIS1 and distance DIS2 are, for example, 5 μm or more and 50 μm or less.

[0050] The seed layer 63 is disposed on the main surfaces (third main surface 50a, fourth main surface 50b) of the base film 50. The seed layer 63 is, for example, a sputtered layer (a layer formed by sputtering). The seed layer 63 is composed of, for example, a nickel-chromium alloy layer disposed on the main surfaces (third main surface 50a, fourth main surface 50b) of the base film 50, and a copper layer disposed on the nickel-chromium alloy layer.

[0051] The electroless plated layer 64 is disposed on the seed layer 63. The electroless plated layer 64 is a layer formed by electroless plating. The electroless plated layer 64 is formed of, for example, copper. The electrolytic plated layer 65 is disposed on the electroless plated layer 64. The electrolytic plated layer 65 is a layer formed by electrolytic plating. The electrolytic plated layer 65 is formed of, for example, copper.

[0052] The coverlay film 100 is disposed on the third main surface 50a so that the adhesive layer 20 covers the conductive pattern 61. The coverlay film 100 is also disposed on the fourth main surface 50b so that the adhesive layer 20 covers the conductive pattern 62. In the coverlay film 100 attached to the base film 50, the adhesive constituting the adhesive layer 20 has hardened, and the protective film 40 has been peeled off from the insulating film 10.

[0053] Although the above describes an example in which the conductive pattern 61 and the conductive pattern 62 are respectively arranged on the third main surface 50a and the fourth main surface 50b, the printed wiring board 200 may not have either the conductive pattern 61 or the conductive pattern 62. If the printed wiring board 200 does not have the conductive pattern 61, the coverlay film 100 is not attached to the third main surface 50a, and if the printed wiring board 200 does not have the conductive pattern 62, the coverlay film 100 is not attached to the fourth main surface 50b.

[0054] <Method for Manufacturing Printed Wiring Board 200> A method for manufacturing printed wiring board 200 will be described below.

[0055] 4 is a manufacturing process diagram of the printed wiring board 200. As shown in FIG. 4, the manufacturing method of the printed wiring board 200 includes a preparation step S4, a separator peeling step S5, a coverlay film arrangement step S6, and a protective film peeling step S7. The separator peeling step S5 is performed after the preparation step S4. The coverlay film arrangement step S6 is performed after the separator peeling step S5. The protective film peeling step S7 is performed after the coverlay film arrangement step S6.

[0056] In the preparation step S4, a base film 50 and a coverlay film 100 are prepared. In the base film 50 prepared in the preparation step S4, a conductive pattern 61 and a conductive pattern 62 are arranged on the third main surface 50a and the fourth main surface 50b, respectively.

[0057] In the separator peeling step S5, the separator 30 is peeled off from the adhesive layer 20 in the coverlay film 100 prepared in the preparation step S4.

[0058] In the coverlay film placement process S6, the coverlay film 100 is placed on the third main surface 50a so that the adhesive layer 20 covers the conductive pattern 61, and the coverlay film 100 is placed on the fourth main surface 50b so that the adhesive layer 20 covers the conductive pattern 62.

[0059] In the coverlay film placement step S6, first, the coverlay film 100 is placed on the third main surface 50a so that the adhesive layer 20 covers the conductive pattern 61, and the coverlay film 100 is placed on the fourth main surface 50b so that the adhesive layer 20 covers the conductive pattern 62. Second, the base film 50 to which the coverlay film 100 has been attached is heated and pressurized. This hardens the adhesive that makes up the adhesive layer 20, and the coverlay film 100 is attached to the third main surface 50a and the fourth main surface 50b.

[0060] In the protective film peeling step S7, the protective film 40 is peeled off from the insulating film 10. In this manner, the printed wiring board 200 having the structure shown in Fig. 3 is manufactured. Note that if the protective film 40 has been peeled off from the insulating film 10 after the separator arrangement step S3 has been performed, the protective film peeling step S7 does not need to be performed.

[0061] (Effects) The effects of the coverlay film 100 and the printed wiring board 200 will be described below.

[0062] If the thickness T1 is large, the thickness of the printed wiring board 200 also increases, making it impossible to thin the printed wiring board 200. If the thickness T2 is small, the distance DIS1 (distance DIS2) becomes small, making it impossible to fill the gap between the adjacent conductive patterns 61 (conductive patterns 62) with the adhesive layer 20.

[0063] However, in the coverlay film 100, the thickness T1 is small (specifically, not less than 2 μm and not more than 15 μm) and the thickness T2 is large (specifically, not less than 10 μm and not more than 50 μm). Therefore, with the coverlay film 100, it is possible to reduce the thickness of the printed wiring board 200 while improving the embeddability of the adhesive layer 20 between the portions of the adjacent conductive patterns 61 (conductive patterns 62).

[0064] Reducing thickness T1 and increasing thickness T2 may reduce the rigidity of coverlay film 100, making it difficult to handle. In coverlay film 100, protective film 40 is disposed on second main surface 10b, which increases the rigidity of coverlay film 100 and improves the handleability of coverlay film 100.

[0065] Furthermore, by disposing the protective film 40 on the second main surface 10b, damage to the insulating film 10 (for example, surface scratches, dents, tears, burrs, etc.) can be suppressed.

[0066] If the peel strength of the protective film 40 relative to the insulating film 10 is greater than the peel strength of the separator 30 relative to the adhesive layer 20, the separator 30 can be peeled from the adhesive layer 20 without peeling the protective film 40 from the insulating film 10.

[0067] If thickness T1 is reduced and thickness T2 is increased, coverlay film 100 may collapse when adhesive layer 20 is dried with hot air. However, because coverlay film 100 has protective film 40 disposed on second main surface 10b, collapse when adhesive layer 20 is dried is suppressed.

[0068] In printed wiring board 200, thickness T1 is small (more specifically, not less than 2 μm and not more than 15 μm) and thickness T2 is large (more specifically, not less than 10 μm and not more than 50 μm). Therefore, printed wiring board 200 can be made thinner while improving the embeddability of adhesive layer 20 between portions of adjacent conductive patterns 61 (conductive patterns 62).

[0069] 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, not by the above-described embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0070] 10 insulating film, 10a first main surface, 10b second main surface, 20 adhesive layer, 30 separator, 40 protective film, 50 base film, 50a third main surface, 50b fourth main surface, 61, 62 conductive pattern, 63 seed layer, 64 electroless plating layer, 65 electrolytic plating layer, 100 coverlay film, 200 printed wiring board, DIS1, DIS2 distance, S1 preparation step, S2 adhesive layer formation step, S3 separator arrangement step, S4 preparation step, S5 separator peeling step, S6 coverlay film arrangement step, S7 protective film peeling step, T1, T2, T3, T4, T5 thickness.

Claims

1. an insulating film having a first main surface and a second main surface opposite to the first main surface; an adhesive layer disposed on the first main surface and formed of an uncured adhesive; a separator disposed on the adhesive layer; The thickness of the insulating film is 2 μm or more and 15 μm or less, The thickness of the adhesive layer is 10 μm or more and 50 μm or less.

2. Further comprising a protective film; The coverlay film according to claim 1 , wherein the protective film is disposed on the second main surface.

3. The coverlay film according to claim 2 , wherein a peel strength of the protective film relative to the insulating film is greater than a peel strength of the separator relative to the adhesive layer.

4. The coverlay film according to claim 1 , wherein the adhesive layer has a thickness greater than a thickness of the insulating film.

5. The thickness of the insulating film is 2 μm or more and 13 μm or less, The coverlay film according to claim 1 , wherein the adhesive layer has a thickness of 20 μm or more and 50 μm or less.

6. The coverlay film according to claim 1 , wherein the insulating film is made of polyimide or a liquid crystal polymer.

7. A base film having a third major surface; a conductive pattern disposed on the third main surface; The coverlay film according to any one of claims 1 to 6, The separator is peeled off from the coverlay film, the coverlay film is disposed on the third main surface such that the adhesive layer covers the conductive pattern, The adhesive is cured.

8. preparing an insulating film having a first main surface and a second main surface opposite to the first main surface, the second main surface having a protective film disposed on the second main surface; forming an adhesive layer on the first main surface using an uncured adhesive; and disposing a separator on the adhesive layer. The thickness of the insulating film is 2 μm or more and 15 μm or less, The method for producing a coverlay film, wherein the adhesive layer has a thickness of 10 μm or more and 50 μm or less.

9. The method for producing a coverlay film according to claim 8 , further comprising a step of peeling the protective film from the insulating film.

10. A step of preparing a coverlay film including an insulating film including a first main surface and a second main surface opposite to the first main surface, an adhesive layer disposed on the first main surface and formed of an uncured adhesive, a protective film disposed on the second main surface, and a separator disposed on the adhesive layer; peeling the separator from the adhesive layer; providing a base film having a third major surface and a conductive pattern disposed on the third major surface; placing the coverlay film on the third main surface such that the adhesive layer covers the conductive pattern, and curing the adhesive; and peeling the protective film from the insulating film.

11. The method for manufacturing a printed wiring board according to claim 10 , wherein the protective film is peeled off after the coverlay film is placed on the third main surface.