JP2011166078A - Flexible printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed wiring board capable of inhibiting breakage of a circuit wiring even if bent with a narrow gap. <P>SOLUTION: The flexible printed wiring board 2 includes an insulating substrate 21, the circuit wiring 22 laminated on the insulating substrate 21 and a coverlay film 23 for covering the circuit wiring 22, wherein expression (1) of 12.5 μm<t<16 μm and expression (2) of 4.33 GPa≤Ea≤9.30 GPa are satisfied, where t refers to a thickness of the insulating substrate 21 and Ea refers to tensile modulus of elasticity of the insulating substrate 21. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flexible printed circuit (FPC) that can be bent with a narrow gap (small radius).

  A flexible printed wiring board is known in which a base film is formed of a polyimide film having a thickness of 12.5 μm or less and an elastic modulus of 4.3 GPa or less (see, for example, Patent Document 1).

JP 2007-208087 A

  In the flexible printed wiring board described above, in order to improve flexibility, the thickness of the base film is reduced and the elastic modulus of the base film is reduced. However, when the flexible printed wiring board is reciprocally slid in a state where the flexible printed wiring board is bent with a narrow gap, a buckling phenomenon occurs and the circuit wiring is disconnected.

  The problem to be solved by the present invention is to provide a flexible printed wiring board capable of suppressing disconnection of circuit wiring even when bent in a narrow gap.

  The flexible printed wiring board which concerns on this invention is a flexible printed wiring board provided with the insulating board | substrate, the circuit wiring laminated | stacked on the said insulating board | substrate, and the coverlay film which covers the said circuit wiring, Comprising: 1) and 2) are satisfied.

12.5 μm <t <16 μm (1) Formula 4.33 GPa ≦ Ea ≦ 9.30 GPa (2) where t is the thickness of the insulating substrate, and Ea is the tensile elastic modulus of the insulating substrate. It is.

  In the above invention, the following expression (3) may be satisfied.

4.70 GPa ≦ Ea ≦ 6.50 GPa (3) Formula In the above invention, the following formula (4) may be satisfied.

  13.50 μm ≦ t ≦ 14.25 μm (4)

  In the present invention, when the flexible printed wiring board satisfies the above formulas (1) and (2), disconnection of the circuit wiring can be suppressed even when the flexible printed wiring board is bent with a narrow gap.

FIG. 1 is a perspective view of a sliding mobile phone according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of the flexible printed wiring board taken along line II-II in FIG. FIG. 3 is a plan view of the flexible printed wiring board according to the embodiment of the present invention. FIG. 4 is a graph showing the results of a slide bending test of an example of the present invention and a comparative example for the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 is a perspective view of a slide type mobile phone according to the present embodiment, FIG. 2 is an enlarged cross-sectional view of the flexible printed wiring board taken along line II-II in FIG. 1, and FIG. 3 is a plan view of the flexible printed wiring board according to the present embodiment. FIG.

  For example, as shown in FIG. 1, the flexible printed wiring board 2 according to the present embodiment is bent at 180 degrees with a small radius R (for example, about 0.75 mm), and the gap G is narrowed. It is incorporated in the mobile phone 1.

  As shown in FIG. 2, the flexible printed wiring board 2 includes an insulating substrate 21, circuit wiring 22, and a coverlay film 23.

  As shown in FIG. 2, the insulating substrate 21 is a layer located on the innermost side in a state where the flexible printed wiring board 2 is bent. The thickness of the insulating substrate 21 is t. The insulating substrate 21 is made of a flexible material such as polyimide, and has a tensile elastic modulus of Ea.

  In the flexible printed wiring board 2 in the present embodiment, the thickness t of the insulating substrate 21 preferably satisfies the following formula (1), and more preferably satisfies the following formula (4).

12.5 μm <t <16 μm (1) Formula 13.50 μm ≦ t ≦ 14.25 μm (4) In this embodiment, the tensile elastic modulus Ea of the insulating substrate 21 is expressed by the following Formula (2). It is preferable to satisfy | fill, and it is still more preferable to satisfy | fill following (3) Formula.

4.33 GPa ≦ Ea ≦ 9.30 GPa (2) Formula 4.70 GPa ≦ Ea ≦ 6.50 GPa (3) Formula As shown in FIG. 2, the circuit wiring 22 includes an insulating substrate 21 and a coverlay film 23 ( (To be described later). The circuit wiring 22 is made of a conductive material such as copper.

  As shown in FIG. 3, the circuit wiring 22 is composed of, for example, three wirings, and both ends thereof are exposed from a coverlay film 23 (described later). Note that the number of wirings is not particularly limited.

  Such circuit wiring 22 (wiring) is formed, for example, by etching a single-sided copper-clad laminate (copper foil) by a subtractive process. Note that the circuit wiring 22 (wiring) may be directly formed on the insulating substrate 21 by an additive process.

  In the flexible printed wiring board 2 according to the present embodiment, the circuit wiring 22 is laminated on one (outside) main surface of the insulating substrate 21, but the circuit wiring 22 is laminated on both surfaces of the insulating substrate 21. Also good.

  The coverlay film 23 includes a coverlay adhesive layer 231 and a coverlay insulating layer 232.

  As shown in FIG. 2, the coverlay adhesive layer 231 covers the circuit wiring 22 and bonds the circuit wiring 22 and the coverlay insulating layer 232 (described later). The coverlay adhesive layer 231 is made of an adhesive made of, for example, an epoxy resin.

  As shown in FIG. 2, the cover lay insulating layer 232 is laminated on the cover lay adhesive layer 231 to protect the circuit wiring 22. The coverlay insulating layer 232 is made of a flexible material such as polyimide.

  Further, although not particularly illustrated, the cover lay insulating layer 232 may be laminated with a shield layer made of, for example, an aluminum foil in order to block electromagnetic waves.

  Next, the operation of this embodiment will be described.

  When the flexible printed wiring board is bent, a restoring force is generated to restore the bent state to a flat state. In particular, the smaller the gap at the time of bending, the greater the restoring force. As a result, the frictional force generated between the flexible printed wiring board and a member that supports the flexible printed wiring board (for example, a casing of a sliding mobile phone) also increases.

  Here, when a flexible printed wiring board having a thin insulating substrate and a small tensile elastic modulus of the insulating substrate is bent at a narrow gap and reciprocally slid, the friction force increased as described above. It cannot endure, and a buckling phenomenon easily occurs. When this buckling phenomenon occurs, the circuit wiring may be disconnected in the flexible printed wiring board.

  That is, in the flexible printed wiring board, the flexibility increases as the thickness of the insulating substrate is thin and the tensile modulus of the insulating substrate is small. The bending phenomenon is likely to occur, and as a result, the circuit wiring is easily disconnected.

  Conversely, if the thickness of the insulating substrate is simply increased and the tensile elastic modulus of the insulating substrate is increased, the flexible printed wiring board is less likely to buckle, but the flexibility of the flexible printed wiring board is reduced. .

  On the other hand, in the flexible printed wiring board 2 in the present embodiment, as shown in the above formulas (1) and (2), the upper limit of the thickness t of the insulating substrate 21 and the tensile elastic modulus of the insulating substrate 21. By defining the upper limit of Ea, a decrease in flexibility is suppressed (bending in a narrow gap is possible), the lower limit of the thickness t of the insulating substrate 21, and the tensile elastic modulus Ea of the insulating substrate 21 Therefore, the occurrence of a buckling phenomenon in the reciprocating sliding movement in a state bent at a narrow gap is suppressed.

  The embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  Below, the effect of the present invention was confirmed by examples and comparative examples that further embody the present invention. The following examples and comparative examples are for confirming the effect of suppressing disconnection of circuit wiring in the flexible printed wiring board in the above-described embodiment.

  FIG. 4 is a graph showing the results of a slide bending test of an example of the present invention and a comparative example for the present invention.

<Example 1>
In Example 1, ten samples of flexible printed wiring boards having the same structure as the above-described embodiment were produced. In the sample of Example 1, the insulating substrate is made of polyimide, the circuit wiring is made of copper, the coverlay adhesive layer is made of an adhesive made of an epoxy resin, and the coverlay insulating layer is made of polyimide. .

  In the sample of Example 1, the thickness t of the insulating substrate is 14 μm (design value), the tensile elastic modulus Ea of the insulating substrate is 4.33 GPa, the thickness of the circuit wiring is 12 μm, The tensile modulus of the cover layer is 31.5 GPa, the thickness of the coverlay adhesive layer is 15 μm, the tensile modulus of the coverlay adhesive layer after curing is 2.6 GPa, and the thickness of the coverlay insulating layer is 12.5 μm. The tensile modulus of the coverlay insulating layer was 3.9 GPa.

  In the 10 samples of Example 1, the maximum value of the thickness t of the insulating substrate was 14.25 μm, and the minimum value was 13.50 μm (the same applies to Examples 2 to 4 and Comparative Example 3). ).

  A slide bending test was performed on the sample of Example 1. This slide bending test is performed with one end of the flexible printed wiring board in a state where the flexible printed wiring board is bent substantially 180 degrees with a radius of 0.65 mm (gap G is 1.3 mm) with the insulating substrate inside. Was fixed, the other end was repeatedly reciprocated and the number of reciprocating slide movements when the circuit wiring was disconnected was examined.

  In this slide bending test, the stroke of the reciprocating slide movement was 50 mm, the speed of the reciprocating slide movement was 100 mm / sec, and the intermittent time was 2 seconds each at both ends (positions of 0 mm and 50 mm) of the stroke. The results of Example 1 are shown in Table 1 and FIG.

なお、表１及び図４において「屈曲寿命[回]」とは、回路配線が断線した時の往復スライド移動の回数であり、１０個のサンプルの平均値である。また、表１中の「評価」では、「屈曲寿命[回]」が４万回未満であれば不合格の「×」とし、「屈曲寿命[回]」が４万回以上であれば合格の「○」とし、「屈曲寿命[回]」が８万回以上であれば合格の中でも好ましい「◎」とした（実施例２〜４及び比較例１〜７において同じ）。

In Table 1 and FIG. 4, “bending life [times]” is the number of reciprocal sliding movements when the circuit wiring is broken, and is an average value of 10 samples. Also, in the “Evaluation” in Table 1, if the “bending life [times]” is less than 40,000 times, it is judged as “x”, and if the “bending life [times]” is 40,000 times or more, it is passed. If “flexion life [times]” is 80,000 times or more, “◎” is preferable among the passes (the same applies to Examples 2 to 4 and Comparative Examples 1 to 7).

<Examples 2 to 4>
In Examples 2 to 4, as shown in Table 1, samples having the same structure as Example 1 were prepared except that the tensile elastic modulus Ea of the insulating substrate was 4.70 GPa, 6.50 GPa, and 9.30 GPa, respectively. Ten of each were prepared.

  A slide bending test was performed on the samples of Examples 2 to 4 in the same manner as in Example 1. The results for Examples 2 to 4 are shown in Table 1 and FIG.

<Comparative Example 1>
In Comparative Example 1, ten samples having the same structure as Example 1 were manufactured except that the thickness t of the insulating substrate was 12 μm and the tensile elastic modulus Ea of the insulating substrate was 4.20 GPa.

  A slide bending test was performed on the sample of Comparative Example 1 in the same manner as in Example 1. The results for Comparative Example 1 are shown in Table 1 and FIG.

<Comparative example 2>
In Comparative Example 2, ten samples having the same structure as Example 1 were prepared except that the thickness t of the insulating substrate was 12 μm and the tensile elastic modulus Ea of the insulating substrate was 6.50 GPa.

  A slide bending test was performed on the sample of Comparative Example 2 in the same manner as in Example 1. The results for Comparative Example 2 are shown in Table 1 and FIG.

<Comparative Example 3>
In Comparative Example 3, ten samples having the same structure as Example 1 were prepared except that the thickness t of the insulating substrate was 14 μm and the tensile elastic modulus Ea of the insulating substrate was 4.20 GPa.

  A slide bending test was performed on the sample of Comparative Example 3 in the same manner as in Example 1. The results for Comparative Example 3 are shown in Table 1 and FIG.

<Comparative Examples 4-7>
In Comparative Examples 4 to 7, as shown in Table 1, the thickness t of the insulating substrate was 16 μm, and the tensile elastic modulus Ea of the insulating substrate was 4.20 GPa, 4.33 GPa, 4.97 GPa, and 9.30 GPa, respectively. Except for the above, 10 samples each having the same structure as in Example 1 were produced.

  A slide bending test was performed on the samples of Comparative Examples 4 to 7 in the same manner as in Example 1. The results for Comparative Examples 4 to 7 are shown in Table 1 and FIG.

<Discussion>
As shown in Table 1 and FIG. 4, in Comparative Examples 1 to 7, the circuit wiring was disconnected by reciprocating slide movement less than 40,000 times.

  In Comparative Examples 1 and 3 where the thickness t of the insulating substrate is thin and the tensile elastic modulus Ea of the insulating substrate is low, a buckling phenomenon has occurred in the flexible printed wiring board during the slide bending test. Thereby, it is considered that the circuit wiring is disconnected.

  On the other hand, in Comparative Examples 4 to 7 of the insulating substrate, although the buckling phenomenon did not occur in the flexible printed wiring board, the circuit wiring was disconnected by the reciprocating sliding movement of less than 40,000 times. This is considered to be because the thickness t of the insulating substrate is too thick and the flexibility of the flexible printed wiring board is lowered.

  On the other hand, in Examples 1-4, the circuit wiring did not break even when the reciprocating slide movement was performed 40,000 times. From this, the flexible printed wiring board satisfying the following formulas (1) and (2) can achieve both improved flexibility and suppression of the buckling phenomenon, and bends the flexible printed wiring board with a narrow gap (small radius). Even in this case, it can be seen that disconnection of the circuit wiring can be suppressed.

12.5 μm <t <16 μm (1) Formula 4.33 GPa ≦ Ea ≦ 9.30 GPa (2) As described above, t is the thickness of the insulating substrate, and Ea is the thickness of the insulating substrate. Tensile modulus.

  In particular, it can be seen that disconnection of the circuit wiring can be effectively suppressed when the flexible printed wiring board satisfies the following expression (4).

13.50 μm ≦ t ≦ 14.25 μm (4) In Examples 2 and 3, the circuit wiring was not disconnected even when the reciprocating sliding movement was performed 80,000 times. From this, it is understood that the disconnection of the circuit wiring can be more effectively suppressed when the flexible printed wiring board satisfies the following expression (3).

  4.70 GPa ≦ Ea ≦ 6.50 GPa (3)

DESCRIPTION OF SYMBOLS 1 ... Sliding mobile phone 2 ... Flexible printed wiring board 21 ... Insulating substrate 22 ... Circuit wiring 23 ... Coverlay film 231 ... Coverlay adhesive layer 232 ... Coverlay insulating layer

Claims (3)

An insulating substrate;
Circuit wiring laminated on the insulating substrate;
A flexible printed wiring board comprising a coverlay film covering the circuit wiring,
The flexible printed wiring board characterized by satisfy | filling following (1) Formula and (2) Formula.
12.5 μm <t <16 μm (1) Formula 4.33 GPa ≦ Ea ≦ 9.30 GPa (2) where t is the thickness of the insulating substrate, and Ea is the tensile elastic modulus of the insulating substrate. It is. The flexible printed wiring board according to claim 1,
The flexible printed wiring board characterized by satisfying the following formula (3).
4.70 GPa ≦ Ea ≦ 6.50 GPa (3) The flexible printed wiring board according to claim 1 or 2,
The flexible printed wiring board characterized by satisfying the following formula (4).
13.50 μm ≦ t ≦ 14.25 μm (4)

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