JP2007080938A - Multilayer printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer wiring board with an excellent bend characteristic even if roughening processing is applied to a conductor circuit surface. <P>SOLUTION: The multilayer printed wiring board 70 includes a flexure 71 composed of two sheets of single-sided flexible printed wiring boards 20, 20 stacked via an interlayer adhesive agent 40. Roughening processing is applied to the conductor circuit surface 13 of each of the two sheets of the single-sided flexible printed wiring boards 20, 20 of the flexure 71. The conductor circuit surface 13 of the one single-sided flexible printed wiring board 20 of the two sheets faces the side of the other single-sided flexible printed wiring board 20, while the conductor circuit surface 13 of the other single-sided flexible printed wiring board 20 faces a side opposite to the one single-sided flexible printed wiring board 20. Further, the multilayer printed wiring board may be constituted in such a way that the two sheets of the single-sided flexible printed wiring boards are stacked so that their conductor circuit surfaces face each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer printed wiring board having a conductor circuit surface subjected to a roughening treatment.

Flexible printed wiring boards are thin and have excellent flexibility, and are used in various electronic devices. Among them, a flexible printed wiring board used for a hinge part of a folding cellular phone or a PDA terminal is required to have high repeated bending characteristics.
When manufacturing a multilayer substrate, it is known to roughen the copper foil surface for the purpose of improving interlayer adhesion. Further, it is generally known that the roughening treatment forms a roughened shape by micro-etching the copper foil circuit surface with a chemical solution of sulfuric acid / hydrogen peroxide. In the case of a multilayer substrate having a cable portion, a roughening process is also applied to the inner FPC cable portion in order to obtain a close contact portion of the multilayer portion.

For example, Patent Document 1 has a structure in which two single-sided CCLs are bonded to each other through an adhesive, and the adhesive is opened only at a bent portion. According to this structure, it is possible to realize a rigid-flex multilayer substrate having a high bending characteristic equivalent to that of a single-sided CCL, although it has a double-sided plate structure.
In Patent Document 2, in a rigid-flex multilayer substrate, a flexible layer extending from a rigid portion has a conductor circuit only on one side, and a flexible layer in the rigid portion inner layer has a conductor circuit on both sides. This structure makes it possible to provide a rigid-flex multilayer substrate having high bending resistance.
In Patent Document 3, in a rigid-flex multilayer substrate, by providing an opening in the insulating resin layer of the flexible part, stress concentration at the boundary between the rigid part and the flexible part can be prevented, and high reliability is obtained for repeated bending. .
Japanese Patent Laid-Open No. 7-312469 JP 2003-258426 A JP 2004-319962 A

  When the copper foil circuit surface (conductor circuit surface) is roughened, irregularities are formed on the surface of the copper foil (conductor), and minute cracks are likely to occur. Since this grows into a macro crack due to repeated bending and leads to circuit disconnection, the bending characteristics are remarkably deteriorated by the roughening treatment. However, in the above-mentioned known documents, no mention is made of the case where the conductor circuit surface of the bent portion is subjected to a roughening process, and further, no influence or causal relationship on the bending characteristics is shown.

  This invention is made in view of the said situation, Comprising: Even if it is a case where a roughening process is given to the conductor circuit surface, it aims at providing the multilayer printed wiring board which has a favorable bending characteristic. .

  In order to solve the above-mentioned problem, the present invention is a multilayer printed wiring board having a bent portion composed of two single-sided flexible printed wiring boards laminated via an interlayer adhesive, and the two single-sided surfaces of the bent portion The conductor circuit surface of the flexible printed wiring board is subjected to a roughening treatment, and the conductor circuit surface of one of the two flexible printed wiring boards faces the other one side of the flexible printed wiring board, and the other Provided is a multilayer printed wiring board characterized in that the conductor circuit surface of the single-sided flexible printed wiring board faces the side opposite to the one-sided flexible printed wiring board.

  Further, the present invention is a multilayer printed wiring board having a bent portion composed of two single-sided flexible printed wiring boards laminated via an interlayer adhesive, the conductor of the two single-sided flexible printed wiring boards at the bent portion Provided is a multilayer printed wiring board characterized in that the circuit surface is roughened and the two single-sided flexible printed wiring boards are laminated so that the respective conductor circuit surfaces face each other. .

In the multilayer printed wiring board of the present invention, a multilayer part in which printed wiring boards are laminated is provided at both ends of the bent part, and the two single-sided flexible printed wiring boards of the bent part are not at the bent part. It is preferable to be joined.
The multilayer part may be configured such that one or more other printed wiring boards are laminated. The other printed wiring board may be a rigid printed wiring board or a flexible printed wiring board.

  According to the configuration of the present invention, the adhesion of the conductor circuit surface is improved by the roughening treatment, and the conductor circuit surface subjected to the roughening treatment of the flexible printed wiring board in the bent portion located outside during bending is bent. It can be bent so as to face the center direction (inner side). As a result, it is possible to reduce a load on the rough surface of the roughened shape of the conductor circuit surface and to manufacture a multilayer printed wiring board having excellent bending characteristics.

The present invention will be described below with reference to the drawings based on the best mode.
FIG. 1 is a sectional view schematically showing a multilayer printed wiring board according to a first embodiment of the present invention. The multilayer printed wiring board 70 includes an inner layer substrate 30 composed of two flexible printed circuit boards (FPCs) 20 and 20 laminated via an interlayer adhesive 40, and an interlayer on the outer surface of the FPCs 20 and 20. Outer substrates 50 and 50 made of Rigid Printed Circuit (RPC) laminated with an adhesive 60 are provided.

Here, the multilayer printed wiring board 70 includes a bent portion 71 and multilayer portions 72 and 72 provided at both ends (left and right ends in FIG. 1). The interlayer adhesives 40 and 60 and the RPCs 50 and 50 are It is provided only in the multilayer portions 72 and 72. That is, in the multilayer portions 72, 72 according to this embodiment, four printed wiring boards are joined via an interlayer adhesive, and RPC50 / interlayer adhesive 60 / FPC20 / interlayer adhesive 40 / FPC20 / interlayer adhesive 60 / The RPC 50 is stacked in this order. As described above, since the bent portion 71 constituted by the FPCs 20 and 20 becomes a flexible portion, and the multilayer portion 72 becomes a rigid portion by stacking the RPCs 50, the multilayer printed wiring board 70 of this embodiment is a rigid-flex multilayer substrate ( RF substrate).
Note that the number of printed wiring boards stacked in the multilayer sections 72, 72 is not particularly limited in the present invention.

  Of the four printed wiring boards, the two FPCs 20, 20 constituting the inner layer substrate 30 are drawn out as bent portions 71. In the bent portion 71, it is preferable that the two FPCs 20, 20 are not provided with the interlayer adhesive 40 to be a non-joined portion 41, and by forming a hollow structure with the non-joined portion 41, 2 of the bent portion 71. The bending and expansion / contraction of the FPCs 20 and 20 caused by bending between the FPCs 20 and 20 are absorbed by the sliding of the FPCs 20 and 20, and thus the bending resistance at the bending part 71 can be improved.

  In the example shown in FIG. 1, the example in which the RPC is provided as the outer layer substrate is shown. However, the present invention is not particularly limited to this, and the configuration of the bent portion 71 can be achieved even when the FPC is laminated as the outer layer substrate. Since it becomes the same, the effect of this invention can be acquired. In addition, the inner layer substrate 30 according to this example shows an example in which the two FPCs 20 and 20 drawn out as the bent portion 71 are joined with the interlayer adhesive 40 without the intervention of another substrate. However, the present invention is not limited to this, and another FPC or RPC may be laminated between the two FPCs 20 and 20 drawn out as the bent portion 71. In some cases, the outer layer substrate may be omitted, and a multilayer flexible printed wiring board (multilayer FPC) composed entirely of two layers of FPC may be used.

  In the present invention, the roughening process is performed on the conductor circuit surface 13 of the FPC 20. The method of roughening treatment is not particularly limited, but, for example, a microetching method can be suitably used. As the etching solution used in microetching, when the conductor layer 12 is a copper foil, a sulfuric acid / hydrogen peroxide-based chemical solution is preferable. The degree of roughening of the conductor circuit surface 13 depends on the material and thickness of the conductor layer, the degree of required bending characteristics, etc., but is set within an appropriate range for the purpose of improving the adhesion of the conductor circuit surface. For example, the roughening amount converted by the weight method is preferably about 1.5 μm (for example, 0.5 to 3.0 μm).

  FIG. 2 shows an example of a manufacturing procedure of the FPC 20 in which the conductor circuit surface 13 is roughened. Using a single-area layer plate (single-sided CCL) 10 having a conductor layer (for example, copper foil) 12 on one side of the insulating substrate 11, a part of the conductor layer 12 was circuit-formed as shown in FIG. Thereafter, the conductor circuit surface 13 is roughened as shown in FIG. Further, as shown in FIG. 2 (c), a coverlay (CL) 21 is laminated on the roughened conductor circuit surface 13 and cured, whereby the roughened conductor circuit surface 13 of the single-sided CCL 10 is obtained. The FPC 20 protected by the coverlay 21 can be manufactured.

Although the material of the single area layer board 10 is not specifically limited, For example, the insulating base material 11 is insulating materials, such as a polyimide, The copper clad laminated board (CCL) which the conductor layer 12 consists of copper foil is mentioned. An adhesive (not shown) may be provided between the insulating substrate 11 and the conductor layer 12, but a two-layer material (the insulating substrate 11 and the conductor layer 12 are directly integrated without an adhesive). Are particularly preferred. As the copper foil, either a rolled copper foil or an electrolytic copper foil may be used, and a metal foil other than copper may be used as long as the characteristics are not hindered.
Examples of the coverlay 21 include those in which an adhesive layer 23 is provided on one side of a flexible insulating base material 22 made of a resin such as polyimide. The adhesive is not particularly limited, and examples thereof include epoxy, rubber, acrylic, and polyimide.

  In the multilayer FPC 30 and the RF substrate 70 of the first embodiment of the present invention, the conductor circuit surface 13 of one FPC 20 of the two FPCs 20 and 20 faces the other FPC 20 side, and the conductor circuit surface 13 of the other FPC 20. Faces the opposite side of one FPC 20. Here, the direction of the conductor circuit surface 13 of the single-sided FPC 20 having the conductor layer 12 on one side of the insulating base material 11 is the direction from the side facing the insulating base material 11 of the conductor layer 12 toward the conductor circuit surface 13 side. Means. Accordingly, in the example shown in FIGS. 1 and 3, the conductor circuit surface 13 of the FPC 20 in the drawings is directed downward, the conductor circuit surface 13 of the upper FPC 20 faces the lower FPC 20 side, and the lower side. The conductor circuit surface 13 of the FPC 20 is directed to the side opposite to the upper FPC 20.

  In order to laminate the multilayer FPC 30 so that the direction of the conductor circuit surface 13 of the FPC 20 is the above-mentioned direction, two FPCs 20 shown in FIG. 2C are prepared, and the interlayer adhesive 40 is interposed as shown in FIG. Then, the adhesive may be cured by laminating in the predetermined direction. Further, in order to provide the non-joint portion 41 in the bent portion 71, it is only necessary to prepare an opening (window opening process) by removing the portion of the interlayer adhesive 40 corresponding to the bent portion 71 prior to lamination. . The interlayer adhesive 40 is not particularly limited, and examples thereof include epoxy, rubber, acrylic, and polyimide.

In order to fabricate the RF substrate 70 shown in FIG. 1, there is a method of stacking the outer layer substrate 50 and processing the outer shape by, for example, the procedure shown in FIG.
As shown in FIG. 4A, outer layer substrates 50 and 50 are laminated on the upper surface of the upper FPC 20 and the lower surface of the lower FPC 20 of the multilayer FPC 30 shown in FIG. Here, the outer layer substrate 50 is a single-sided RPC in which a conductor layer (for example, copper foil) 52 is laminated on one side of a rigid insulating base 51. The copper foil used as the conductor layer 52 may be either a rolled copper foil or an electrolytic copper foil, and may be a metal foil other than copper as long as the characteristics are not impaired. The interlayer adhesive 60 is not particularly limited, and examples thereof include epoxy, rubber, acrylic, and polyimide.

  After the outer substrate 50 is stacked, through holes (TH) 61 are drilled and plated layers (TH plating) 62 are applied as shown in FIG. A plated through hole penetrating the FPCs 20 and 20 is formed. Circuits (not shown) are formed on the conductor layers 52 and 62 on the outer substrate 50. After forming the circuit, it is also preferable to provide a resist (not shown) on the surface of the conductor layer 52 as an insulating protective layer for protecting the outer layer circuit.

  After forming the circuit on the outer layer substrate 50, the portion (removal portion) 73 corresponding to the bent portion 71 of the outer layer substrate 50 is peeled and removed by the outer shape processing of the outer layer substrate 50 as shown in FIG. 4C. The removal portion 73 is removed from the bent portion 71 of the inner layer substrate 30 by previously forming a slit or a half cut groove on the boundary line between the removal portion 73 of the outer layer substrate 50 and the portion corresponding to the multilayer portion 72. The operation of peeling the portion 73 is facilitated, which is preferable.

  In the multilayer printed wiring board according to the first embodiment, the conductor circuit surfaces 13 of the two FPCs 20 and 20 laminated as described above are roughened, and the conductor circuit surfaces 13 have the same orientation. The FPCs 20 and 20 are laminated so that when the bent portion 71 of the multilayer printed wiring board 70 is bent in one direction, the conductor circuit surface 13 of the conductor layer 12 is bent as shown in FIG. Can be bent toward the center direction (inner side). For this reason, the adhesive force of the adhesive on the roughened conductor circuit surface 13 can be improved, and stress concentration on the rough surface of the conductor circuit surface 13 can be reduced or suppressed. As a result, the load on the conductor circuit surface 13 due to bending can be reduced, and both the resistance to bending (inhibition of circuit disconnection) and heat resistance (inhibition of peeling) can be exhibited, and excellent characteristics can be obtained. .

  On the other hand, in the multilayer printed wiring board 100 shown in FIG. 11, the FPCs 20 and 20 are laminated on the inner layer substrate 110 (see FIG. 12) so that the conductor circuit surface 13 is on the outer side. When the bent portion 101 of the wiring board 100 is bent, the conductor circuit surface 13 that has been subjected to the roughening process faces the outside of the bend, so that stress is concentrated on the roughened irregularities, resulting in a large load on the bent portion 101. Therefore, it breaks at an early stage starting from the unevenness where stress is concentrated.

As a bending test when the bent portion 71 of the multilayer printed wiring board 70 is bent in one side direction, there are a sliding method shown in FIG. 5 and a one-side bending method shown in FIG.
The slide method shown in FIG. 5 is a method based on the bending resistance test of JIS C 5016 8.6. The center portion of the printed wiring board to be the sample 81 is bent, and one end 81a of the sample 81 is attached to the fixed frame 82. The other end 81b is fixed to the sliding rod 83, and the distance between the fixed frame 82 and the sliding rod 83 is kept constant, and the sliding rod 83 is reciprocated to the left and right at a predetermined stroke (movement distance). This is a method of repeatedly bending the central portion of the.

  Further, in the one-side bending method test shown in FIG. 7, the central portion of the printed wiring board serving as the sample 91 is wound around the mandrel 92 in an α shape as shown in FIG. ), One end 91a of the sample 91 is fixed, and the other end 91b is bent in a range of 0 ° to 180 °. According to such a bending test, it is possible to perform a test that accurately simulates the bending of the hinge portion of the folding mobile phone.

Next, a second embodiment of the multilayer printed wiring board according to the present invention will be described.
FIG. 8 is a sectional view schematically showing a multilayer printed wiring board according to the second embodiment of the present invention. The multilayer printed wiring board 70 </ b> A includes an inner substrate 30 </ b> A composed of two flexible printed circuit boards (FPCs) 20 and 20 laminated via an interlayer adhesive 40, and an interlayer on the outer surface of the FPCs 20 and 20. Outer substrates 50 and 50 made of Rigid Printed Circuit (RPC) laminated with an adhesive 60 are provided.

Here, the multilayer printed wiring board 70A has a bent portion 71 and multilayer portions 72, 72 provided at both ends (left and right ends in FIG. 8). The interlayer adhesives 40, 60 and the RPCs 50, 50 are It is provided only in the multilayer portions 72 and 72. That is, in the multilayer portions 72, 72 according to this embodiment, four printed wiring boards are joined via an interlayer adhesive, and RPC50 / interlayer adhesive 60 / FPC20 / interlayer adhesive 40 / FPC20 / interlayer adhesive 60 / The RPC 50 is stacked in this order. As described above, the bent portion 71 formed of the FPCs 20 and 20 becomes a flexible portion, and the multilayer portion 72 becomes a rigid portion by stacking the RPCs 50. Therefore, the multilayer printed wiring board 70A of this embodiment is a rigid-flex multilayer substrate ( RF substrate).
Note that the number of printed wiring boards stacked in the multilayer sections 72, 72 is not particularly limited in the present invention.

  Of the four printed wiring boards, the two FPCs 20 and 20 constituting the inner layer substrate 30 </ b> A are drawn out as the bent portions 71. In the bent portion 71, it is preferable that the two FPCs 20, 20 are not provided with the interlayer adhesive 40 to be a non-joined portion 41, and by forming a hollow structure with the non-joined portion 41, 2 of the bent portion 71. The bending and expansion / contraction of the FPCs 20 and 20 caused by bending between the FPCs 20 and 20 are absorbed by the sliding of the FPCs 20 and 20, and thus the bending resistance at the bending part 71 can be improved.

  In the example shown in FIG. 8, the example in which the RPC is provided as the outer layer substrate is shown. However, the present invention is not particularly limited to this, and the structure of the bent portion 71 is also provided when the FPC is laminated as the outer layer substrate. Since it becomes the same, the effect of this invention can be acquired. Further, the inner layer substrate 30A according to this example shows an example in which the two FPCs 20 and 20 drawn out as the bent portion 71 are joined with the interlayer adhesive 40 without any other substrate being laminated. The invention is not particularly limited to this, and another FPC or RPC can be laminated between the two FPCs 20 and 20 drawn out as the bent portion 71. In some cases, the outer layer substrate may be omitted, and a multi-layer FPC composed of two FPC layers as a whole may be used.

  In the present invention, the roughening process is performed on the conductor circuit surface 13 of the FPC 20. The method of roughening treatment is not particularly limited. For example, a method of micro-etching the circuit surface using a sulfuric acid / hydrogen peroxide type chemical solution can be suitably used. The manufacturing method of the FPC 20 in which the conductor circuit surface 13 is roughened is the same as the method described above with reference to FIG. 2 for the multilayer printed wiring board 70 of the first embodiment. Omitted.

  In the multilayer FPC 30A and the RF substrate 70A according to the second embodiment of the present invention, the conductor circuit surfaces 13 and 13 of the two FPCs 20 and 20 are laminated so as to face each other. Here, the direction of the conductor circuit surface 13 of the single-sided FPC 20 having the conductor layer 12 on one side of the insulating base material 11 is the direction from the side facing the insulating base material 11 of the conductor layer 12 toward the conductor circuit surface 13 side. Means. Therefore, in the example shown in FIGS. 8 and 9, the direction of the conductor circuit surface 13 of the upper FPC 20 in the drawings is downward, the direction of the conductor circuit surface 13 of the lower FPC 20 is upward, and the conductor circuit of the upper FPC 20 The surface 13 faces the lower FPC 20 side, and the conductor circuit surface 13 of the lower FPC 20 faces the upper FPC 20 side.

In order to laminate the multilayer FPC 30A so that the direction of the conductor circuit surface 13 of the FPC 20 is the above-mentioned direction, two FPCs 20 shown in FIG. 2 (c) are prepared, and the interlayer adhesive 40 is interposed as shown in FIG. Then, the adhesive may be cured by laminating in the predetermined direction. Further, in order to provide the non-joint portion 41 in the bent portion 71, it is only necessary to prepare an opening (window opening process) by removing the portion of the interlayer adhesive 40 corresponding to the bent portion 71 prior to lamination. . The interlayer adhesive 40 is not particularly limited, and examples thereof include epoxy, rubber, acrylic, and polyimide.
Further, the method for manufacturing the RF substrate 70A shown in FIG. 8 is the same as the method described with reference to FIG. 4 for the RF substrate 70 of the first embodiment, and redundant description is omitted here.

  In the multilayer printed wiring board of the second embodiment, the conductor circuit surfaces 13 of the two laminated FPCs 20 and 20 are roughened as described above, and the conductor circuit surfaces 13 face each other. Since the FPCs 20 and 20 are laminated on each other, when the bent portion 71 of the multilayer printed wiring board 70A is bent, the conductor circuit surface 13 of the FPC 20 located on the outside at the time of bending is bent regardless of which direction is bent. It can be bent so as to face the center direction (inner side) of bending. For this reason, the adhesive force of the adhesive on the roughened conductor circuit surface 13 can be improved, and stress concentration on the rough surface of the conductor circuit surface 13 can be reduced or suppressed. As a result, the load on the conductor circuit surface 13 due to bending can be reduced, and both the resistance to bending (inhibition of circuit disconnection) and heat resistance (inhibition of peeling) can be exhibited, and excellent characteristics can be obtained. .

  As a bending test when the bent portion 71 of the multilayer printed wiring board 70A is bent in both directions, there is a bending method in both directions shown in FIG. In the both-side bending method test, the central portion of the printed wiring board to be the sample 91 is wound around the mandrel 92 in an α shape as shown in FIG. 10A, and one end 91a of the sample 91 is fixed. 10 (b), the other end 91b of the sample 91 is bent in a range of −180 ° to 180 °, or the other end 91b of the sample 91 is 0 ° to 360 ° as shown in FIG. 10 (c). It bends within the range. According to such a bending-type bending test, it is possible to perform a test that accurately simulates the bending of the hinge portion of the folding-type electronic device in both directions.

(Materials used)
The single-sided CCL 10 includes an insulating base material 11 made of polyimide (PI) having a thickness of 25 μm and a two-layer material made of a conductor layer 12 made of rolled copper foil having a thickness of 18 μm (PI and copper foil are interposed with an adhesive). Directly integrated).
As the coverlay (CL) 21, a flexible substrate 22 made of polyimide (PI) having a thickness of 25 μm and having an epoxy adhesive layer 23 having a thickness of 25 μm provided on one side thereof was used.
As interlayer adhesives (ADH) 40 and 60, adhesive sheets having a thickness of 40 μm were used.
As the RPC 50 of the outer layer, a rigid insulating base material 51 is made of glass epoxy (thickness of glass fiber knitted and hardened with epoxy resin) having a thickness of 150 μm, and a conductor made of electrolytic copper foil having a thickness of 18 μm on one side. What laminated | stacked the layer 52 was used.
When the roughening treatment was applied to the copper foil of one side CCL10, a commonly known sulfuric acid-hydrogen peroxide blackening treatment alternative method was used. The amount of roughening (converted by weight method) was 1.5 μm.

(Test Example 1)
In Test Example 1, the rigid-flex multilayer substrate 70 shown in FIG. 1 was manufactured by the method shown in FIGS. In addition, the rigid-flex multilayer substrate as Comparative Examples 1-1, 1-2, and 1-3 was manufactured under the same conditions except for the direction of the FPCs 20 and 20 and the presence or absence of the roughening treatment of the conductor circuit surface 13.
In the first embodiment, as shown in FIG. 13A, two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 is in the same direction, and the conductor circuit surface 13 is roughened. did.
In Comparative Example 1-1, as shown in FIG. 13C, the two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 faces outward, and the conductor circuit surface 13 is roughened. Not configured.
In Comparative Example 1-2, as shown in FIG. 13A, two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 is in the same direction, and the conductor circuit surface 13 is roughened. Not configured.
In Comparative Example 1-3, as shown in FIG. 13C, the two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 faces outward, and the conductor circuit surface 13 is roughened. It was set as the structure made.

Each sample of Test Example 1 was subjected to a bending test and a reflow heat test.
The bending test was performed by the slide method shown in FIG. 5 in accordance with JIS C 5016 8.6. The bending radius of the sample 81 was 10 mm, and the reciprocating speed of the sliding rod 83 was 120 times per minute. For each of the examples and comparative examples, 10 samples having the same configuration were prepared, and the number of bendings until the energization was stopped (disconnected) was measured for each sample. The number of bendings shown in Table 1 is an average value of 10 samples (N = 10).
In the reflow heat test, after pre-treatment (moisture absorption for 96 hours in an environment of temperature 85 ° C. and relative humidity 85% RH), heating at 230 ° C. or higher (peak temperature is 250 ° C.) is continued for 30 seconds. The presence or absence of peeling (○: no peeling, ×: occurrence of peeling) was tested.
Table 1 summarizes the results of the bending test and the reflow heat resistance test according to Test Example 1.

  Comparing Comparative Example 1-1 and Comparative Example 1-2 (comparison of those without roughening treatment), the superiority due to the same orientation of the conductor circuit surface 13 in Comparative Example 1-2 is recognized. Although there is no comparison, Comparative Example 1-3 and Example 1 are compared (comparison between those subjected to roughening treatment), and the advantage of having the same orientation of the conductor circuit surface 13 in Example 1 is the roughening treatment. It was recognized as prevention of a decrease in the number of flexions. That is, in Comparative Example 1-3, the conductor circuit surface subjected to the roughening treatment faces the outside of the bend, so that stress is concentrated on the roughened unevenness, and the load on the bent portion becomes large, and the unevenness where the stress is concentrated. It is thought that it broke early at the starting point. In Example 1, since the conductor circuit surfaces of the two FPCs subjected to the roughening treatment face the inside of the bend, it is considered that the stress load is relatively small and the deterioration of the bend characteristic can be suppressed. It is done. Further, in Comparative Example 1-1 and Comparative Example 1-2, in which there was no roughening treatment, peeling occurred due to insufficient adhesion in the reflow heat test. Therefore, it can be seen that among the samples of Test Example 1, the configuration of Example 1 has the most excellent characteristics.

(Test Example 2)
In Test Example 2, the rigid-flex multilayer substrate 70 shown in FIG. 1 was manufactured by the method shown in FIGS. In addition, the rigid-flex multilayer substrates to be Comparative Examples 2-1, 2-2, and 2-3 were manufactured under the same conditions except for the orientation of the FPCs 20 and 20 and the presence or absence of the roughening treatment of the conductor circuit surface 13.
The configuration of the second embodiment is the same as that of the first embodiment. The configurations of Comparative Examples 2-1, 2-2, and 2-3 are the same as the configurations of Comparative Examples 1-1, 1-2, and 1-3, respectively.

Each sample of Test Example 2 was subjected to a bending test and a reflow heat test.
The bending test was performed by a method of a one-side direction bending method shown in FIG. 7 (one reciprocation in the range of 0 ° to 180 ° is defined as one cycle). The bending radius of the sample 91 was 2 mm, and the bending speed was 1 cycle per second. For each of the examples and comparative examples, 10 samples having the same configuration were prepared, and the number of bendings until the energization was stopped (disconnected) was measured for each sample. The number of bendings shown in Table 2 is an average value of 10 samples (N = 10).
The method of the reflow heat test is the same as in Test Example 1.
Table 2 summarizes the results of the bending test and the reflow heat resistance test according to Test Example 2.

  Comparing Comparative Example 2-1 and Comparative Example 2-2 (comparison of those without roughening treatment), the superiority due to the same orientation of the conductor circuit surface 13 in Comparative Example 2-2 was recognized. Although there is no comparison, Comparative Example 2-3 and Example 2 are compared (comparison between those subjected to roughening treatment), and the superiority due to the same orientation of the conductor circuit surface 13 in Example 2 is roughening treatment. It was recognized as prevention of a decrease in the number of flexions. That is, in Comparative Example 2-3, the conductor circuit surface subjected to the roughening process faces the outside of the bend, so that stress is concentrated on the roughened unevenness, and the load on the bent portion increases, and the unevenness where the stress is concentrated. It is thought that it broke early at the starting point. In Example 2, since the conductor circuit surfaces of the two FPCs subjected to the roughening treatment face the inside of the bend, it is considered that the stress load is relatively small and the deterioration of the bend characteristic can be suppressed. It is done. Furthermore, in Comparative Example 2-1 and Comparative Example 2-2, which had no roughening treatment, peeling occurred due to insufficient adhesion in the reflow heat test. Therefore, it can be seen that among the samples of Test Example 2, the configuration of Example 2 has the most excellent characteristics.

(Test Example 3)
In Test Example 3, the rigid-flex multilayer substrate 70A shown in FIG. 8 was manufactured by the method shown in FIGS. 2 and 9 and the same method as shown in FIG. In addition, the rigid-flex multilayer substrate as Comparative Examples 3-1, 3-2, and 3-3 was manufactured under the same conditions except for the orientation of the FPCs 20 and 20 and the presence or absence of the roughening treatment of the conductor circuit surface 13.
In Example 3, as shown in FIG. 13B, the two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 faces each other, and the conductor circuit surface 13 is roughened. did.
In Comparative Example 3-1, as shown in FIG. 13C, two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 faces outward, and the conductor circuit surface 13 is roughened. It was set as the structure (similar to Comparative Example 1-1) which was not carried out.
In Comparative Example 3-2, as shown in FIG. 13B, the two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 faces each other, and the conductor circuit surface 13 is roughened. Not configured.
In Comparative Example 3-3, as shown in FIG. 13C, two FPCs 20 and 20 are laminated so that the conductor circuit surface 13 faces outward, and the conductor circuit surface 13 is roughened. It was set as the structure (similar to Comparative Example 1-3).

Each sample of Test Example 3 was subjected to a bending test and a reflow heat test.
The bending test was performed by the method of the both-side bending method shown in FIG. 10 (one reciprocation in the range of −180 ° to 180 ° is defined as one cycle). The bending radius of the sample 91 was 2 mm, and the bending speed was 1 cycle per second. For each of the examples and comparative examples, 10 samples having the same configuration were prepared, and the number of bendings until the energization was stopped (disconnected) was measured for each sample. The number of bendings shown in Table 3 is an average value (N = 10) of 10 samples.
The method of the reflow heat test is the same as in Test Example 3.
Table 3 summarizes the results of the bending test and the reflow heat resistance test according to Test Example 3.

When the comparative example 3-1 and the comparative example 3-2 are compared (comparison between those without the roughening treatment), the superiority due to the conductor circuit surface 13 facing each other in the comparative example 3-2 is not recognized. However, when Comparative Example 3-3 is compared with Example 3 (comparison between those subjected to roughening treatment), the advantage of having the conductor circuit surfaces 13 facing each other in Example 3 is a bending over the roughening treatment. Recognized as a prevention of frequency reduction.
That is, since the test condition is bending in both directions, in both Comparative Example 3-3 and Example 3, one of the two sheets has the conductor circuit surface facing the outer side of the bending. However, comparing Comparative Example 3-3 with Example 3, as shown in FIG. 14A, in the configuration of Example 3, the roughened surface from the neutral line 31 (the center line of the material thickness of the bent portion). The distance to 13 is 52 μm, and as shown in FIG. 14B, in the configuration of Comparative Example 3-3, the distance from the neutral line 31 to the roughening surface 13 is 63 μm, and the distance in Example 3 is shorter. For this reason, in Example 3, it is considered that the stress load applied to the roughened surface is relatively small, and the deterioration of the bending characteristics can be suppressed. Further, in Comparative Example 3-1 and Comparative Example 3-2 without the roughening treatment, peeling occurred due to insufficient adhesion in the reflow heat test. Therefore, it can be seen that the configuration of Example 3 has the most excellent characteristics among the samples of Test Example 3.

  The multilayer printed wiring board of the present invention can be suitably used for various electronic devices, electrical devices, etc., and is particularly suitable for applications that require high repeated bending characteristics, such as hinges of folding cellular phones and PDA terminals. It is.

It is sectional drawing which shows an example of the multilayer printed wiring board which concerns on the 1st example of a form of this invention. (A)-(c) is sectional process drawing explaining each process of manufacturing FPC from single-sided CCL. It is sectional drawing which shows the multilayer FPC used as the inner-layer board | substrate of the multilayer printed wiring board of this invention shown in FIG. (A)-(c) is sectional process drawing explaining each process of manufacturing the multilayer printed wiring board shown in FIG. 1 from the inner layer board | substrate shown in FIG. It is a figure explaining the method of the bending test by a slide system. It is sectional drawing which shows the state which the multilayer printed wiring board shown in FIG. 1 bent in the bending part. (A) And (b) is a figure explaining the method of the bending test by the bending method of the one side direction. It is sectional drawing which shows an example of the multilayer printed wiring board which concerns on the 2nd example of a form of this invention. It is sectional drawing which shows the multilayer FPC used as the inner-layer board | substrate of the multilayer printed wiring board of this invention shown in FIG. (A)-(c) is a figure explaining the method of the bending test by the bending method of a both-sides direction. It is sectional drawing which shows the multilayer printed wiring board which concerns on a comparative example. It is sectional drawing which shows the multilayer FPC used as the inner layer board | substrate of the multilayer printed wiring board of the comparative example shown in FIG. (A)-(c) is a fragmentary sectional view which shows the case classification of the direction of the conductor circuit surface of two FPCs which comprise a bending part. It is the elements on larger scale of the bending part explaining the distance from the neutral line of the bending part of a multilayer printed wiring board to the roughening processing surface, (a) shows Example 3 and (b) shows about comparative example 3-3. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 ... Roughened conductor circuit surface, 20 ... Single-sided flexible printed wiring board (FPC), 40 ... Interlayer adhesive, 41 ... Non-joining part, 50 ... Outer layer board | substrate (other printed wiring boards), 70, 70A ... Multilayer printed wiring board, 71 ... bent portion, 72 ... multilayer portion.

Claims (6)

A multilayer printed wiring board having a bent portion composed of two single-sided flexible printed wiring boards laminated via an interlayer adhesive,
The conductor circuit surface of the two single-sided flexible printed wiring boards in the bent portion is subjected to a roughening process, and the conductor circuit surface of one of the two single-sided flexible printed wiring boards is the other single-sided flexible printed wiring. A multilayer printed wiring board, characterized in that the side of the board faces and the conductor circuit surface of the other single-sided flexible printed wiring board faces the opposite side of the one-sided flexible printed wiring board. A multilayer printed wiring board having a bent portion composed of two single-sided flexible printed wiring boards laminated via an interlayer adhesive,
The conductor circuit surfaces of the two single-sided flexible printed wiring boards in the bent portion are subjected to a roughening process, and the two single-sided flexible printed wiring boards are laminated so that the respective conductor circuit surfaces face each other. A multilayer printed wiring board characterized by having   A multilayer part in which printed wiring boards are laminated is provided at both ends of the bent part, and the two single-sided flexible printed wiring boards of the bent part are not joined at the bent part. The multilayer printed wiring board according to claim 1 or 2.   The multilayer printed wiring board according to claim 3, wherein one or more other printed wiring boards are further laminated in the multilayer portion.   The multilayer printed wiring board according to claim 4, wherein the other printed wiring board is a rigid printed wiring board.   The multilayer printed wiring board according to claim 4, wherein the other printed wiring board is a flexible printed wiring board.

Images