Printed Circuit Board

Abstract

To provide a printed circuit board where connection failure can be prevented.SOLUTION: A printed circuit board comprises: a base film 11 made of an insulator; a conductor pattern 12 formed on a surface of the base film 11; an insulative cover film 14 covering the conductor pattern 12; a circuit part 10a where a circuit is formed by the conductor pattern 12; and a pad part 10b where part of the conductor pattern 12 is exposed from the cover film 14 so as to form a bonding pad 16. The pad part 10b has rigidity higher than that of the circuit part 10a.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a printed circuit board. [Background technology]

[0002] FPC (flexible printed circuit) boards are configured with a copper foil pattern and the like formed on a base film made of resin, and have low rigidity. Regarding wire bonding to such FPC boards, for example, Patent Document 1 proposes a technique in which a reinforcing material is attached to the back surface of the FPC board, and the FPC board is supported by this reinforcing material for wire bonding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5877595 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if a reinforcing material is attached to the back side of the FPC board, the rigidity of the FPC board itself remains low. In particular, if the pad part where the bonding pad is formed is mainly composed of a resin with a low elasticity modulus, the bonding pad may sink during wire bonding, causing the load from the capillary to escape, resulting in a connection failure.

[0005] In view of the above, an object of the present invention is to provide a printed circuit board capable of suppressing the occurrence of connection defects. [Means for solving the problem]

[0010] request request 1In the invention described in the above, the printed circuit board comprises a base film (11) made of an insulator, a first conductor pattern (12) formed on the front surface of the base film, an insulating first cover film (14) covering the first conductor pattern, a second conductor pattern (17) formed on the rear surface of the base film, an insulating second cover film (19) covering the second conductor pattern, a circuit section (10a) in which a circuit is formed by the first conductor pattern or the second conductor pattern, and a pad section (10b) in which a part of the first conductor pattern is exposed from the cover film and a bonding pad (16) is formed, and the second conductor pattern is formed over the entire pad section. It is formed only partially in the circuit area. There are.

[0011] By forming the conductive pattern over the entire pad portion in this manner, the rigidity of the pad portion is increased, which reduces sinking of the bonding pad during wire bonding and suppresses the occurrence of connection failures.

[0012] Note that the reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of an FPC board according to a first embodiment. [Diagram 2] 1 is a cross-sectional view showing a state in which bonding wires are connected to a semiconductor chip. [Diagram 3] 1 is a cross-sectional view showing how bonding wires are connected to an FPC board. [Figure 4] FIG. 11 is a cross-sectional view of a comparative example. [Diagram 5] FIG. 11 is a cross-sectional view of an FPC board according to a second embodiment. [Figure 6] FIG. 11 is a cross-sectional view of an FPC board according to a third embodiment. [Figure 7] FIG. 11 is a cross-sectional view of an FPC board according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0015] (First embodiment) The first embodiment will be described below. As shown in Fig. 1, an FPC board 10 of this embodiment includes a base film 11, a conductive pattern 12, an adhesive layer 13, a cover film 14, and a metal plating layer 15.

[0016] The base film 11 is made of an insulating material such as polyimide, and is used as a substrate for forming the conductor pattern 12 and the like. The conductor pattern 12 is formed on the surface of the base film 11, and is made of a conductive material such as copper foil. The conductor pattern 12 corresponds to a first conductor pattern. A circuit is formed on the front and back surfaces of the base film 11 by the conductor pattern 12 and a conductor pattern 17 described below. FIG. 1 is a cross-sectional view along a signal line formed by the conductor pattern 12.

[0017] The adhesive layer 13 is formed so as to cover the conductive pattern 12. The adhesive layer 13 is for adhering the cover film 14 to the conductive pattern 12, and is made of an insulator such as epoxy resin. The adhesive layer 13 corresponds to a first adhesive layer. The cover film 14 is for protecting the conductive pattern 12, and is made of an insulating material such as polyimide. The cover film 14 corresponds to a first cover film.

[0018] A part of the conductor pattern 12 is exposed from the adhesive layer 13 and the cover film 14. A metal plating layer 15 made of a metal such as Au (gold) is formed on the surface of this exposed part so as to cover this part. The conductor pattern 12 exposed from the adhesive layer 13 and the cover film 14 and the metal plating layer 15 form bonding pads 16 for connecting the FPC board 10 to an IC chip or the like. A part of the FPC board 10 in which a circuit is formed by the conductor pattern 12 covered with the cover film 14 and a conductor pattern 17 described later is referred to as a circuit section 10a, and a part in which the bonding pads 16 are formed is referred to as a pad section 10b.

[0019] In addition to the base film 11 and the like, the FPC board 10 includes a conductor pattern 17, an adhesive layer 18, and a cover film 19. The conductor pattern 17 is formed on the back surface of the base film 11, and is made of a conductive material such as copper foil. The conductor pattern 17 corresponds to the second conductor pattern. The adhesive layer 18 is formed so as to cover the conductor pattern 17. The adhesive layer 18 is for adhering the cover film 19 to the conductor pattern 17, and is made of an insulator such as epoxy resin. The adhesive layer 18 corresponds to the second adhesive layer. The cover film 19 is for protecting the conductor pattern 17, and is made of an insulating material such as polyimide. The cover film 19 corresponds to the second cover film.

[0020] An adhesive layer 20 is formed on the surface of the cover film 19 opposite to the base film 11. The adhesive layer 20 is made of an insulator such as epoxy resin. The adhesive layer 20 corresponds to a third adhesive layer. The cover film 19 is adhered to a reinforcing plate 30 by the adhesive layer 20. The reinforcing plate 30 supports the FPC board 10 from the back side during wire bonding, and is made of a metal such as SUS.

[0021] In this manner, the occurrence of connection failures is suppressed by supporting the FPC board 10 with the reinforcing plate 30. In this embodiment, in order to further suppress the occurrence of connection failures, the rigidity of the pad portion 10b is made higher than the rigidity of the circuit portion 10a.

[0022] Specifically, in the circuit section 10a, there are a mixture of a portion where the conductor pattern 17 is formed to configure a desired circuit, and a portion where the conductor pattern 17 is not formed and an adhesive layer 18 is attached to the rear surface of the base film 11. In contrast, in the pad section 10b, the conductor pattern 17 is formed over the entire pad section 10b. That is, below the bonding pad 16, the entire rear surface of the base film 11 is covered with the conductor pattern 17, which has a higher elastic modulus than the adhesive layer 18.

[0023] The FPC board 10 having such a configuration is manufactured, for example, as follows. First, a base film 11 having a conductor layer formed on the entire front and back surfaces is prepared, and the conductor layer on the front surface side is patterned into a desired shape by etching using a resist to form a conductor pattern 12. Then, a cover film 14 having an adhesive layer 13 formed on one side is attached to the conductor pattern 12 and the surface of the base film 11 exposed from the conductor pattern 12. At this time, the portion of the conductor pattern 12 that will become the bonding pad 16 is exposed. After that, a metal plating layer 15 is formed by electrolytic plating or the like on the portion of the conductor pattern 12 exposed from the cover film 14. This forms the bonding pad 16.

[0024] Furthermore, the conductor layer on the back surface side of the base film 11 is patterned into a desired shape by etching using a resist to form the conductor pattern 17. Then, a cover film 19 having an adhesive layer 18 formed on one surface is attached to the conductor pattern 17 and the back surface of the base film 11 exposed from the conductor pattern 17. Thereafter, the outer shape of the FPC board 10 is formed into a desired shape by die cutting or the like, and an adhesive layer 20 is applied to the back surface of the cover film 19, and the cover film 19 is adhered to the reinforcing plate 30.

[0025] The FPC board 10 adhered to the reinforcing plate 30 is connected to an IC chip or the like by a bonding wire. Figures 2 and 3 are diagrams for explaining a wire bonding process for connecting the FPC board 10 and the IC chip 40 adhered to the reinforcing plate 30.

[0026] In the wire bonding process, as shown in Fig. 2, the capillary 50 brings the end of the bonding wire 60 passed through it into contact with the bonding pad 41 on the IC chip 40 and bonds it by applying a load. Then, the capillary 50 moves to above the bonding pad 16 while forming a loop with the bonding wire 60 bonded to the bonding pad 41. Then, the capillary 50 brings the bonding wire 60 near the opening of the capillary 50 into contact with the bonding pad 16 and bonds it by applying a load. In this way, the FPC board 10 is connected to the IC chip 40 by the bonding wire 60 as shown in Fig. 3.

[0027] A comparative example of Fig. 4 will be described. In the FPC board 100 of the comparative example, unlike the FPC board 10 of this embodiment, a circuit is formed on the back side of the base film 11 also in the pad portion 10b. That is, below the bonding pad 16, a portion where the conductor pattern 17 is formed and a portion where the conductor pattern 17 is not formed and an adhesive layer 18 is attached to the back side of the base film 11 are mixed. Therefore, the rigidity of the pad portion 10b is equivalent to that of the circuit portion 10a.

[0028] In the FPC board 100 having such a configuration, when bonding the bonding wire 60 to the bonding pad 16, the pad portion 10b has low rigidity, so that the load from the capillary 50 is released and the bonding pad 16 sinks, which may result in a poor connection.

[0029] In contrast, in this embodiment, the rigidity of the pad portion 10b is made higher than the rigidity of the circuit portion 10a, which reduces sinking of the bonding pad 16 during wire bonding while maintaining the flexibility of the circuit portion 10a, thereby making it possible to suppress the occurrence of poor connection.

[0030] Second embodiment The second embodiment will be described. This embodiment is different from the first embodiment in the method of increasing the rigidity of the pad portion 10b, and is otherwise similar to the first embodiment, so only the differences from the first embodiment will be described.

[0031] 5, in this embodiment, like the circuit portion 10a, the pad portion 10b also has a circuit formed on the back surface side of the base film 11. However, the conductor pattern 17 of the pad portion 10b is formed thicker than the conductor pattern 17 of the circuit portion 10a, which makes the pad portion 10b more rigid than the circuit portion 10a.

[0032] The FPC board 10 having such a configuration can be manufactured, for example, by patterning the conductor pattern 17 in the same manner as in the first embodiment, and then depositing a conductive material on the conductor pattern 17 of the pad portion 10b by using sputtering or the like to thicken the conductor pattern 17. Note that the process on the front side of the base film 11, the adhesion of the cover film 19, the die-cutting process, the adhesion to the reinforcing plate 30, and the like can be performed in the same manner as in the first embodiment.

[0033] In this way, even in a configuration in which a circuit is formed by the conductor pattern 17 in the pad portion 10b, it is possible to increase the rigidity of the pad portion 10b by forming the conductor pattern 17 thick, and the same effect as in the first embodiment can be obtained in this embodiment. Note that, although the conductor pattern 17 of the pad portion 10b is formed thick in this embodiment, the rigidity of the pad portion 10b may be increased by forming the conductor pattern 12 of the pad portion 10b thicker than the conductor pattern 12 of the circuit portion 10a.

[0034] Third embodiment A third embodiment will be described. This embodiment is different from the first embodiment in the method of increasing the rigidity of the pad portion 10b, and is otherwise similar to the first embodiment, so only the differences from the first embodiment will be described.

[0035] 6, in this embodiment, a circuit is formed on the rear surface side of the base film 11 in the pad portion 10b as in the circuit portion 10a. The metal plating layer 15 is formed thicker than in the first embodiment, which makes the pad portion 10b more rigid than the circuit portion 10a. The thickness of the metal plating layer 15 is usually about 3 μm, but by making it 4 μm or more or 5 μm or more, the pad portion 10b can be made more rigid than the circuit portion 10a.

[0036] In this way, even in a configuration in which a circuit is formed by the conductor pattern 17 in the pad portion 10b, it is possible to increase the rigidity of the pad portion 10b by forming the metal plating layer 15 thicker, and the same effect as in the first embodiment can be obtained in this embodiment.

[0037] (Fourth embodiment) A fourth embodiment will be described. This embodiment is different from the first embodiment in the method of increasing the rigidity of the pad portion 10b, and is otherwise similar to the first embodiment, so only the differences from the first embodiment will be described.

[0038] 7, in this embodiment, in the pad portion 10b as well, a circuit is formed on the back surface side of the base film 11, similarly to the circuit portion 10a. The FPC board 10 of this embodiment also includes a reinforcing layer 21 and an adhesive layer 22.

[0039] The reinforcing layer 21 is a layer for reinforcing the pad portion 10b to increase the rigidity of the pad portion 10b, and is formed on the surface of the adhesive layer 18 in the pad portion 10b opposite to the base film 11. The reinforcing layer 21 is made of a metal such as copper, and is insulated from the conductor pattern 17 by the adhesive layer 18.

[0040] The adhesive layer 22 is formed so as to cover the adhesive layer 18 exposed from the reinforcing layer 21 and the reinforcing layer 21. The adhesive layer 22 is for adhering the cover film 19 to the adhesive layer 18 and the reinforcing layer 21, and the cover film 19 is laminated on the surface of the adhesive layer 22 opposite to the adhesive layer 18 and the reinforcing layer 21. The adhesive layer 22 is made of an insulator such as an epoxy resin. In this embodiment, the reinforcing layer 21 is formed on the pad portion 10b, so that the rigidity of the pad portion 10b is made higher than the rigidity of the circuit portion 10a. The adhesive layer 22 corresponds to a second adhesive layer.

[0041] The FPC board 10 having such a configuration is manufactured, for example, as follows. First, the conductor pattern 17 is patterned, and then an adhesive layer 18 is formed by coating so as to cover the conductor pattern 17 and the back surface of the base film 11 exposed from the conductor pattern 17. Then, a reinforcing layer 21 is formed on the surface of the adhesive layer 18 opposite the base film 11 by sputtering or the like, and then a cover film 19 having an adhesive layer 22 formed on one side thereof is attached to the reinforcing layer 21 and the adhesive layer 18 exposed from the reinforcing layer 21. Note that the process on the front surface side of the base film 11, the die-cutting process, and the bonding to the reinforcing plate 30 can be performed in the same manner as in the first embodiment.

[0042] In this way, even in the configuration in which a circuit is formed in the pad portion 10b by the conductive pattern 17, it is possible to increase the rigidity of the pad portion 10b by the reinforcing layer 21, and the same effect as in the first embodiment can be obtained in this embodiment. Note that, although the reinforcing layer 21 is formed over the entire pad portion 10b in FIG. 7, the reinforcing layer 21 may be formed only on a part of the pad portion 10b. Also, the reinforcing layer 21 may be formed on the front surface side of the base film 11.

[0043] (Other embodiments) The present invention is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the claims. The above-described embodiments are not unrelated to each other, and can be combined as appropriate, except in cases where the combination is clearly impossible. In addition, in the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where they are particularly clearly specified as essential or where they are clearly considered essential in principle.

[0044] For example, the present invention may be applied to a single-sided FPC board in which a conductor pattern is formed only on the surface of the base film 11, or a multi-layer FPC board in which a conductor pattern is formed on three or more layers. In the case of a single-sided FPC board, the rigidity of the pad portion 10b can be increased by the configurations of the second to fourth embodiments. In addition, the FPC board 10 may be used without being attached to the reinforcing plate 30.

[0045] In the second to fourth embodiments, the conductor pattern 17 may be formed over the entire pad portion 10b as in the first embodiment. In the third and fourth embodiments, the conductor patterns 12 and 17 of the pad portion 10b may be formed thicker than the conductor patterns 12 and 17 of the circuit portion 10a as in the second embodiment. In the fourth embodiment, the thickness of the metal plating layer 15 may be set to 4 μm or more as in the third embodiment. Three or four of the first to fourth embodiments may be combined.

[0046] Furthermore, by increasing the rigidity of the pad portion 10b by using any one or a combination of two or more of the first to fourth embodiments, and then employing the following configuration, the occurrence of poor connection can be further suppressed.

[0047] For example, at least one of the base film 11, adhesive layer 13, adhesive layer 18, and adhesive layer 20 in the entire FPC board 10 is made of a material having an elastic modulus of 1.5 GPa or more, such as epoxy resin. Also, for example, at least one of the base film 11, adhesive layer 13, adhesive layer 18, and adhesive layer 20 in the entire FPC board 10 is formed to have a thickness of 10 μm or less. These thicknesses are usually several tens to several 20 μm, but by reducing this to 10 μm or less, the sinking of the capillary can be further reduced.

[0048] In addition, in each of the above embodiments, the rigidity of the pad portion 10b is set to be higher than the rigidity of the circuit portion 10a, but this is only one example, and the rigidity of the pad portion 10b may be the same as or lower than the rigidity of the circuit portion 10a as long as the occurrence of connection defects can be suppressed. For example, if the conductor pattern 17 is formed over the entire pad portion 10b as in the above first embodiment, even if the rigidity of the pad portion 10b is lower than the rigidity of the circuit portion 10a, it is possible to reduce sinking of the bonding pad 16 and suppress the occurrence of connection defects. [Explanation of symbols]

[0049] 10a circuit section 10b Pad section 11 Base film 12 Conductor Pattern 14 Cover film 16 Bonding Pads 17 Conductor Pattern 19 Cover film

Claims

1. A printed circuit board, A base film (11) made of an insulator; A first conductor pattern (12) formed on the surface of the base film; an insulating first cover film (14) that covers the first conductor pattern; A second conductor pattern (17) formed on the back surface of the base film; an insulating second cover film (19) covering the second conductor pattern; a circuit portion (10a) in which a circuit is formed by the first conductor pattern or the second conductor pattern; a pad portion (10b) in which a part of the first conductor pattern is exposed from the cover film to form a bonding pad (16); The second conductor pattern is formed over the entire pad portion and only partially over the circuit portion.

2. The printed circuit board according to claim 1 , wherein the first conductor pattern or the second conductor pattern is formed to be thicker in the pad portion than in the circuit portion.

3. the bonding pad is composed of the first conductor pattern and a metal plating layer (15) covering a portion of the first conductor pattern exposed from the cover film, 3. The printed circuit board according to claim 1, wherein the metal plating layer has a thickness of 4 [mu]m or more.

4. 4. The printed circuit board according to claim 1, further comprising a reinforcing layer (21) formed on the pad portion and made of metal and insulated from the first conductor pattern and the second conductor pattern.

5. The base film; The first cover film; a first adhesive layer (13) that covers the first conductor pattern and adheres the first cover film to the first conductor pattern; The second cover film; a second adhesive layer (18, 22) that covers the second conductor pattern and adheres the second cover film to the second conductor pattern; At least one of the third adhesive layer (20) that adheres the second cover film to the reinforcing plate (30) is 5. The printed circuit board according to claim 1, which is made of a material having an elastic modulus of 1.5 GPa or more.

6. The base film; The first cover film; a first adhesive layer (13) that covers the first conductor pattern and adheres the first cover film to the first conductor pattern; The second cover film; a second adhesive layer (18, 22) that covers the second conductor pattern and adheres the second cover film to the second conductor pattern; At least one of the third adhesive layer (20) that adheres the second cover film to the reinforcing plate (30) is 6. The printed circuit board according to claim 1, wherein the thickness is 10 [mu]m or less.

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