JP2014090041A - Printed wiring board - Google Patents

Abstract

To provide a printed wiring board capable of effectively suppressing the occurrence of disconnection and cracks even when bent at a curvature radius of 0.5 mm or less.
A base material, a first conductive layer formed on the base material, and a first conductive layer formed on the base material so as to cover the first conductive layer are used. A first insulating layer; a second insulating layer formed on the first insulating layer; and a second conductive layer formed on the second insulating layer; Provided is a printed wiring board characterized by satisfying the following formulas (I) and (II) when the Young's modulus of the layer 30 is Ei1 and the Young's modulus of the second insulating layer 40 is Ei2.
Ei1 <Ei2 (I)
10 MPa <Ei2 <500 MPa (II)
[Selection] Figure 1

Description

  The present invention relates to a printed wiring board.

  A printed wiring board that is bent and used at a predetermined radius of curvature is known (for example, see Patent Document 1).

JP 2011-222664 A

  However, in the above prior art, it is possible to bend with a relatively large radius of curvature, but when bent at a radius of curvature close to zero, specifically, a radius of curvature of 0.5 mm or less. However, there is a problem that disconnection and cracks occur.

  The problem to be solved by the present invention is to provide a printed wiring board capable of effectively suppressing the occurrence of disconnection and cracks even when bent at a radius of curvature of 0.5 mm or less.

[1] A printed wiring board according to the present invention is a printed wiring board used by being bent, and covers a base material, a first conductive layer formed on the base material, and the first conductive layer. A first insulating layer formed on the substrate, a second insulating layer formed on the first insulating layer, and a second conductive layer formed on the second insulating layer. When the Young's modulus of the first insulating layer is Ei1 and the Young's modulus of the second insulating layer is Ei2, the following formulas (I) and (II) are satisfied.
Ei1 <Ei2 (I)
10 MPa <Ei2 <500 MPa (II)

[2] In the above invention, the following formula (III) can be satisfied.
1 MPa <Ei1 <100 MPa (III)

[3] In the above invention, when the Young's modulus of the second conductive layer is Ec2, the following formula (IV) can be satisfied.
100 MPa <Ec2 <1000 MPa (IV)

  [4] In the above invention, the glass transition temperature of the first insulating layer can be lower than the glass transition temperature of the second insulating layer.

  [5] In the above invention, a third insulating layer formed on the second insulating layer so as to cover the second conductive layer is further provided, and the surface roughness Ra of the third insulating layer is 0.1 μm. <Ra <10 μm.

  [6] In the above invention, an additional layer may be further provided on the surface of the substrate opposite to the surface on which the first conductive layer is formed.

  According to the present invention, when the Young's modulus Ei1 of the first insulating layer and the Young's modulus Ei2 of the second insulating layer satisfy the above formulas (1) and (2), Even when bent at a radius of curvature of 0.5 mm or less, the occurrence of disconnection and cracks can be effectively suppressed.

FIG. 1 is a cross-sectional view of a printed wiring board 1 according to the present embodiment. FIG. 2 is a cross-sectional view of the printed wiring board 1 according to the present embodiment in a bent state. FIG. 3 is a cross-sectional view of a printed wiring board 1a according to another embodiment. FIG. 4 is a graph showing the results of a tensile test of an insulator film formed from the insulator paste used in the examples and comparative examples. FIG. 5 is a graph showing the results of a tensile test of a conductor film formed using the conductor paste used in Examples and Comparative Examples. FIG. 6 is a graph showing the results of resistance values of the second conductor layer 50 in the examples and comparative examples during the bending test.

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

  FIG. 1 is a cross-sectional view of a printed wiring board 1 according to this embodiment, and FIG. 2 is a cross-sectional view of the printed wiring board 1 according to this embodiment in a folded state.

  The printed wiring board 1 of the present embodiment is a substrate of an input device capable of touch input that employs a so-called capacitance method. When incorporated in an electronic device or the like, as shown in FIG. It is used in a bent state under the condition of 0.5 mm or less, in particular, a curvature radius of 0.3 mm or less, and a curvature radius of substantially zero. The printed wiring board 1 of the present embodiment can be used in various electronic devices, but more specifically, is preferably used as a touch pad substrate of a laptop personal computer.

  As shown in FIG. 1, the printed wiring board 1 of the present embodiment includes a base material 10, a first conductive layer 20, a first insulating layer 30, a second insulating layer 40, a second conductive layer 50, And a third insulating layer 60.

<Substrate 10>
As shown in FIG. 2, the substrate 10 may be made of a flexible material so that the printed wiring board 1 can be bent with a curvature radius of 0.5 mm or less. Although not particularly limited, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc., because it is excellent in flexibility and inexpensive, and therefore can reduce the product cost. It is preferable to comprise.

<First conductive layer 20>
The first conductive layer 20 is a conductive layer formed in a predetermined pattern on the substrate 10. The first conductive layer 20 is usually formed by screen-printing a conductive paste containing conductive particles and a binder resin and then curing the conductive paste.

  As the conductive particles to be included in the conductive paste, those made of various metals such as silver and various conductive materials such as carbon can be used. As the conductive particles, the average particle diameter D50 is 1 μm <D50. <10 μm is preferably used. By using a conductive particle having an average particle diameter D50 in the above range, when the printed wiring board 1 is bent at a radius of curvature of 0.5 mm or less, the first is formed in the bent portion. When a microcrack occurs when the conductive layer 20 is pulled, the propagation of the microcrack in the first conductive layer 20 can be prevented. Thereby, the effect of suppressing the disconnection of the first conductive layer 20 can be further enhanced.

  The binder resin contained in the conductor paste is preferably a thermosetting resin that is cured by heat, and examples thereof include polyester resins, epoxy resins, and urethane resins. Among these, polyester resins A resin is particularly preferred.

In the present embodiment, the first conductive layer 20 preferably has a Young's modulus Ec1 [MPa] satisfying the following formula (1), and the breaking elongation Bc1 [%] satisfies the following formula (2). It is preferable to satisfy.
100 MPa <Ec1 <1000 MPa (1)
Bc1 ≧ 10% (2)

  The Young's modulus Ec1 and the breaking elongation Bc1 of the first conductive layer 20 are the same as the conditions for forming the first conductive layer 20 using, for example, a conductor paste for forming the first conductive layer 20. It can be measured by performing a tensile test in accordance with JIS K7127 using the film-like molded body produced as described above.

In the present embodiment, the Young's modulus Ec1 and the breaking elongation Bc1 of the first conductive layer 20 are, for example, the content ratio of the binder resin contained in the first conductive layer 20 or the binder resin contained in the first conductive layer 20. It can be controlled by adjusting the type of the image.
Specifically, when the content ratio of the binder resin in the first conductive layer 20 is increased, the Young's modulus Ec1 tends to decrease accordingly, and the breaking elongation Bc1 tends to increase. On the other hand, when the content ratio of the binder resin is decreased, the Young's modulus Ec1 tends to increase accordingly, and the breaking elongation Bc1 tends to decrease. Furthermore, as the glass transition temperature (Tg) of the binder resin is lower, the Young's modulus Ec1 tends to be lower and the breaking elongation Bc1 tends to be higher, while the glass transition temperature (Tg) of the binder resin is higher. The higher the modulus, the higher the Young's modulus Ec1, and the lower the elongation at break Bc1. Similarly, as the content ratio of the soft segment in the binder resin increases, the Young's modulus Ec1 tends to decrease, the breaking elongation Bc1 tends to increase, and as the plasticizer increases, the Young's modulus increases. Ec1 tends to be low, and the breaking elongation Bc1 can tend to be high. Therefore, in this embodiment, the Young's modulus Ec1 and the breaking elongation Bc1 of the first conductive layer 20 can be controlled by appropriately adjusting these conditions.

<First insulating layer 30>
The first insulating layer 30 is an insulating layer formed on the base material 10 so as to cover the first conductive layer 20 formed in a pattern. The first insulating layer 30 is formed by a method of laminating a film of an insulating resin, or a method of screen-printing an insulating paste containing an insulating resin and then curing it. Although it does not specifically limit as insulating resin, The photocurable resin hardened | cured with an ultraviolet-ray, an electron beam, etc. is preferable, for example, an ultraviolet curable urethane acrylate resin etc. are mentioned. The first insulating layer 30 may contain an inorganic filler such as silica, mica, clay, talc, titanium oxide, calcium carbonate, aluminum hydroxide, and magnesium hydroxide as necessary.

In the present embodiment, the first insulating layer 30 preferably has a Young's modulus Ei1 [MPa] satisfying the following formula (3), and the breaking elongation Bi1 [%] satisfies the following formula (4). It is preferable to satisfy.
1 MPa <Ei1 <100 MPa (3)
Bi1> 100% (4)

  In the present embodiment, the Young's modulus Ei1 and breaking elongation Bi1 of the first insulating layer 30 are set such that, for example, when the first insulating layer 30 is formed using an insulator paste, the first insulating layer 30 is By performing a tensile test in accordance with JIS K7127 using a film-like molded body produced in the same manner as the conditions for forming the first insulating layer 30 using the insulating paste for forming. Can be measured.

In the present embodiment, the Young's modulus Ei1 and the breaking elongation Bi1 of the first insulating layer 30 are included in, for example, the content of the insulating resin included in the first insulating layer 30 or the first insulating layer 30. It can be controlled by adjusting the type of insulating resin.
Specifically, when the content ratio of the insulating resin in the first insulating layer 30 is increased, the Young's modulus Ei1 tends to decrease accordingly, and the breaking elongation Bi1 tends to increase. On the other hand, when the content ratio of the insulating resin is decreased, the Young's modulus Ei1 tends to increase accordingly, and the breaking elongation Bi1 tends to decrease. Further, as the glass transition temperature (Tg) of the insulating resin is lower, the Young's modulus Ei1 tends to be lower and the breaking elongation Bi1 tends to be higher, while the glass transition temperature (Tg) of the insulating resin is higher. ) Is higher, the Young's modulus Ei1 tends to be higher, and the breaking elongation Bi1 tends to be lower. Similarly, as the content ratio of the soft segment in the insulating resin increases, the Young's modulus Ei1 tends to decrease, the breaking elongation Bi1 tends to increase, and as the plasticizer increases, the Young's modulus Ei1 tends to decrease. The rate Ei1 tends to be low, and the breaking elongation Bi1 can tend to be high. Therefore, in this embodiment, the Young's modulus Ei1 and the breaking elongation Bi1 of the first insulating layer 30 can be controlled by appropriately adjusting these conditions.

  In addition, the first insulating layer 30 exhibits rubber elasticity at room temperature, and therefore, when incorporated into an electronic device, even when bent multiple times, it is possible to effectively suppress the occurrence of plastic deformation. It is preferable that temperature (Tg) is 30 degrees C or less.

<Second insulating layer 40>
The second insulating layer 40 is an insulating layer formed on the first insulating layer 30 described above. Similar to the first insulating layer 30 described above, the second insulating layer 40 is formed by a method of laminating an insulating resin film, or a method of screen-printing and then curing an insulating paste containing an insulating resin. Is done. As insulating resin, the thing similar to the 1st insulating layer 30 mentioned above can be used. Moreover, the 2nd insulating layer 40 may contain the inorganic filler similarly to the 1st insulating layer 30 mentioned above as needed.

In the present embodiment, the second insulating layer 40 has a Young's modulus Ei2 [MPa] that satisfies the following formula (5) and the following formula (6).
Ei1 <Ei2 (5)
10 MPa <Ei2 <500 MPa (6)

  That is, in the present embodiment, the Young's modulus Ei2 of the second insulating layer 40 is greater than 10 MPa and less than 500 MPa, and has a Young's modulus Ei2 higher than the Young's modulus Ei1 of the first insulating layer 30 described above. Shall. According to the present embodiment, by setting the Young's modulus Ei2 of the second insulating layer 40 to satisfy the above formulas (5) and (6), the printed wiring board of the present embodiment as shown in FIG. 1 is bent even under the condition that the radius of curvature is 0.5 mm or less, preferably 0.3 mm or less, more preferably the curvature radius is substantially zero, and the conductive layers 20 and 50 are disconnected or each insulating layer is bent. The occurrence of cracks 30, 40, and 60 can be effectively prevented. The Young's modulus Ei2 of the second insulating layer 40 is preferably 50 MPa <Ei2 <200 MPa.

  In particular, according to this embodiment, by setting the Young's modulus Ei2 of the second insulating layer 40 to satisfy the above formula (5) and the above formula (6), the printed wiring board 1 of the present embodiment has a radius of curvature. When bent at 0.5 mm or less, the deformation amount of the first insulating layer 30 can be relatively increased. As a result, the first insulating layer 30 is greatly deformed, so that the thickness of the first insulating layer 30 is reduced at the bent portion (bent portion), and the thickness of the first insulating layer 30 is reduced. The deformation of the second insulating layer 40, the second conductive layer 50, and the third insulating layer 60 that are located on the outer peripheral side can be suppressed, and the breakage and cracks of these layers can be effectively prevented. It is.

  In this embodiment, the method for satisfying the above formula (5) for the Young's modulus Ei1 of the first insulating layer 30 and the Young's modulus Ei2 of the second insulating layer 40 is not particularly limited. For example, a method of forming the first insulating layer 30 with a glass transition temperature (Tg) lower than the glass transition temperature (Tg) of the second insulating layer 40, or the inclusion of the insulating resin in the first insulating layer 30 Although the method etc. which make a ratio smaller than the content rate of the 2nd insulating layer 40 are mentioned, as shown in FIG. 2, when the printed wiring board 1 of this embodiment was bent by the curvature radius of 0.5 mm or less, The first insulating layer 30 has a glass transition temperature (Tg) lower than the glass transition temperature (Tg) of the second insulating layer 40 from the viewpoint that the effect of suppressing the occurrence of disconnection and cracks in each layer is higher. Preferred method of forming Arbitrariness.

In the present embodiment, the second insulating layer 40 may have any Young's modulus Ei2 satisfying the above formula (5) and the above formula (6), but the breaking elongation Bi2 [%] is represented by the following formula. It is preferable to satisfy (7).
Bi2> 100% (7)

  The Young's modulus Ei2 and the breaking elongation Bi2 of the second insulating layer 40 can be measured, for example, in the same manner as the Young's modulus Ei1 and the breaking elongation Ei1 of the first insulating layer 30 described above. The Young's modulus Ei2 and the breaking elongation Bi2 of the insulating layer 40 are the same as the Young's modulus Ei1 and the breaking elongation Ei1 of the first insulating layer 30 described above, and the content ratio of the insulating resin contained in the second insulating layer 40, It can be controlled by adjusting the type of insulating resin contained in the second insulating layer 40.

  The second insulating layer 40 also has a glass transition temperature (Tg) of 30 ° C. or less from the viewpoint that it exhibits rubber elasticity (entropy elasticity) at room temperature, like the first insulating layer 30 described above. preferable.

<Second conductive layer 50>
The second conductive layer 50 is a conductive layer formed in a predetermined pattern on the second insulating layer 40. Similar to the first conductive layer 20 described above, the second conductive layer 50 is formed by screen-printing a conductive paste containing conductive particles and a binder resin, and then curing the conductive paste. As the conductor particles and binder resin to be included in the conductor paste, the same materials as those of the first conductive layer 20 described above can be used.

In the present embodiment, the second conductive layer 50 preferably has a Young's modulus Ec2 [MPa] satisfying the following formula (8), and the breaking elongation Bc2 [%] satisfies the following formula (9). It is preferable to satisfy.
100 MPa <Ec2 <1000 MPa (8)
Bc2 ≧ 10% (9)

  The Young's modulus Ec2 and the breaking elongation Bc2 of the second conductive layer 50 can be measured, for example, in the same manner as the Young's modulus Ec1 and the breaking elongation Bc1 of the first conductive layer 20 described above. The Young's modulus Ec2 and the breaking elongation Bc2 of the conductive layer 50 are the same as the Young's modulus Ec1 and the breaking elongation Bc1 of the first conductive layer 20 described above. It can be controlled by adjusting the type of the binder resin contained in the two conductive layers 50.

<Third insulating layer 60>
The third insulating layer 60 is an insulating layer formed on the second insulating layer 40 so as to cover the second conductive layer 50 formed in a pattern. The third insulating layer 60 is formed by a method of laminating an insulating resin film or a method of screen-printing an insulating paste containing an insulating resin and then curing the same as the first insulating layer 30 described above. Is done. As insulating resin, the thing similar to the 1st insulating layer 30 mentioned above can be used. Moreover, it is preferable that the 3rd insulating layer 60 contains the inorganic filler, As such an inorganic filler, the thing similar to the 1st insulating layer 30 mentioned above can be used.

In the present embodiment, the third insulating layer 60 preferably has a Young's modulus Ei3 [MPa] satisfying the following formula (10) and the following formula (11), and has a breaking elongation Bi3 [%]. It is preferable that the following formula (12) is satisfied.
Ei1 <Ei3 (10)
10 MPa <Ei3 <500 MPa (11)
Bi3> 100% (12)

  The Young's modulus Ei3 and the breaking elongation Bi3 of the third insulating layer 60 can be measured, for example, in the same manner as the Young's modulus Ei1 and the breaking elongation Ei1 of the first insulating layer 30 described above. The Young's modulus Ei3 and the breaking elongation Bi3 of the insulating layer 60 are the same as the Young's modulus Ei1 and the breaking elongation Ei1 of the first insulating layer 30, and the content ratio of the insulating resin contained in the third insulating layer 60, It can be controlled by adjusting the type of the insulating resin contained in the third insulating layer 60.

  The third insulating layer 60 also preferably has a glass transition temperature (Tg) of 30 ° C. or lower from the viewpoint that it exhibits rubber elasticity at room temperature, as with the first insulating layer 30 described above.

  Furthermore, the third insulating layer 60 includes an inorganic filler in the third insulating layer 60, so that the surface roughness Ra of the surface (the surface opposite to the second conductive layer 50) has a surface roughness Ra of 0.1 μm <Ra. It is preferably controlled within a range of <10 μm. In particular, when the glass transition temperature of the third insulating layer 60 is 30 ° C. or lower in order to make the third insulating layer 60 exhibit rubber elasticity at room temperature, the desired flexibility is obtained at room temperature. Although it is obtained, stickiness or transfer may occur on the surface. Therefore, in the present embodiment, in order to prevent such a problem, by adding an inorganic filler, the surface roughness Ra of the third insulating layer 60 is set in the above range, thereby the surface of the third insulating layer 60. By roughening the surface, stickiness and blocking of the third insulating layer 60 can be prevented.

  In the present embodiment, the second insulating layer 40 and the third insulating layer 60 are formed by using the insulating paste for forming the second insulating layer 40 and the third insulating layer 60. This is the case where the yield point is not shown or the yield point is shown when a tensile test is performed using a film-like molded body produced under the same conditions as those for forming the third insulating layer 60. However, the yield elongation is preferably 100% or more. Even if the second insulating layer 40 and the third insulating layer 60 do not show a yield point or show a yield point, the yield elongation is 100% or more, so that the electronic device can be obtained. When incorporating, even if it is bent a plurality of times, the occurrence of plastic deformation of the second insulating layer 40 and the third insulating layer 60 can be made difficult to occur. As a result, the second insulating layer 40 and the third insulating layer 60 are plastically deformed, whereby the resistance value of the second conductive layer 50 located between the second insulating layer 40 and the third insulating layer 60 increases. It is possible to effectively suppress the inconvenience.

  According to the present embodiment, as described above, the Young's modulus Ei1 of the first insulating layer 30 and the Young's modulus Ei2 of the second insulating layer 40 satisfy the above expressions (5) and (6). Thus, as shown in FIG. 2, the printed wiring board 1 of the present embodiment has a curvature radius of 0.5 mm or less, preferably a curvature radius of 0.3 mm or less, and more preferably under a condition that the curvature radius is substantially zero. Even when bent, it is possible to effectively prevent disconnection of the conductive layers 20 and 50 and generation of cracks of the insulating layers 30, 40, and 60.

  In addition, in the present embodiment, the Young's modulus Ei1 of the first insulating layer 30 and the Young's modulus Ei2 of the second insulating layer 40 satisfy the above expressions (5) and (6) as described above. The Young's modulus and elongation at break of the first conductive layer 20, the first insulating layer 30, the second insulating image 40, the second conductive layer 50, and the third insulating layer 60 are the above formulas (1) to (4), (7 ) To (12) are preferably satisfied, so that the printed wiring board 1 of the present embodiment has a radius of curvature of 0.5 mm or less, preferably a curvature radius of 0.3 mm or less, more preferably a curvature radius substantially. The effect of suppressing the breakage of the conductive layers 20 and 50 and the occurrence of cracks in the insulating layers 30, 40, and 60 when bent under zero conditions can be further enhanced. In addition, in this embodiment, the said formula (1)-(4), (7)-() from the point that the suppression effect of a disconnection of each conductive layer and generation | occurrence | production of the crack of each insulating layer can be heightened more. It is sufficient to satisfy at least one of 12), but from the viewpoint that the effect of suppressing the breakage of each conductive layer and the occurrence of cracks in each insulating layer is higher, the above formula (3) or the above formula (8) It is preferable to satisfy at least.

  The embodiment described above is described for facilitating the understanding of the present invention, and is 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.

  For example, as shown in FIG. 3, a configuration in which an additional layer 70 is formed on the surface opposite to the surface on which the first conductive layer 20 of the base material 10 is formed may be employed. Even when the la is bent under the condition that the radius of curvature is 0.5 mm or less, in particular, the radius of curvature is 0.3 mm or less, and the curvature radius is substantially zero, the substantial curvature radius is obtained by the effect of the additional layer 70. Can be increased by the thickness of the additional layer 70, thereby further enhancing the effect of suppressing the disconnection of the conductive layers 20, 50 and the occurrence of cracks in the insulating layers 30, 40, 60. The additional layer 70 may be either a conductive layer or an insulating layer, and can be formed in the same manner as the conductive layers 20 and 50 or the insulating layers 30, 40 and 60 described above, for example.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

<Preparation of printed wiring board sample>
A conductive paste is screen-printed on a 25 μm-thick PET film as the base material 10, and after removing the solvent, it is thermally cured to obtain a pattern-shaped first film having a thickness of 10 μm, a width of 0.4 mm, and a length of 20 mm. One conductive layer 20 was formed. Next, on the base material 10 on which the first conductive layer 20 was formed, an insulator paste was screen-printed, and after removing the solvent, the first insulating layer 30 having a thickness of 20 μm was formed by irradiating with ultraviolet rays.

Next, on the first insulating layer 30, an insulating paste is screen-printed, and after removing the solvent, the second insulating layer 40 having a thickness of 20 μm is formed by irradiating with ultraviolet rays (thermal curing in Comparative Example 3). Then, a conductive paste is screen-printed thereon and the solvent is removed, followed by thermosetting, thereby forming a patterned second conductive layer 50 having a thickness of 10 μm, a width of 0.4 mm, and a length of 20 mm. Formed. Finally, on the second insulating layer 40 on which the second conductive layer 50 is formed, an insulator paste is screen-printed, and after removing the solvent, irradiation with ultraviolet rays (thermal curing in Comparative Example 3) is performed. Thus, a printed wiring board sample shown in FIG. 1 was obtained by forming a third insulating layer 60 having a thickness of 20 μm. In this example, the thermosetting conditions when forming each conductive layer were 150 ° C. and 30 minutes, and the ultraviolet irradiation amount when forming each insulating layer was 500 mJ / cm ² .

<Bending test>
The obtained printed wiring board sample was cut into a width of 5 mm, and a bending test was performed according to the following procedures (1) to (4).
(1) The printed wiring board sample is bent under the condition that the curvature radius is substantially zero as shown in FIG. 2 so that the PET film as the base material 10 is on the inside.
(2) About the bent printed wiring board sample, the stress of 20N was applied for 5 seconds, and the resistance value of the 1st conductive layer 20 and the 2nd conductive layer 50 was measured with the resistance meter.
(3) The folded printed wiring board sample is stretched, and 20N stress is applied for 5 seconds.
(4) Repeat (1) to (3) above 10 times.
And after completion | finish of a bending test, the printed wiring board sample which performed the bending test was observed with the electron microscope, and the presence or absence of the crack was confirmed.

<Insulator paste conditions>
In each Example and each Comparative Example, the following insulator pastes were used in combinations shown in Table 3 as insulator pastes for forming the insulating layers 30, 40, 60. The composition of the insulator paste used is shown below.
Insulator paste A _i : UV curable urethane acrylate resin (glass transition temperature: 0 ° C.) 70% by weight (solid content conversion) and talc (particle diameter 5 to 10 μm) 30% by weight (solid content conversion)
Insulator paste B _i : UV curable urethane acrylate resin (glass transition temperature: 15 ° C.) 70% by weight (solid content conversion), and talc (particle diameter 5 to 10 μm) 30% by weight (solid content conversion)
Insulator paste C _i : UV curable urethane acrylate resin (glass transition temperature: 35 ° C.) 70% by weight (solid content conversion) and talc (particle diameter 5 to 10 μm) 30% by weight (solid content conversion)
Insulator paste D _i : polyester thermosetting resin (glass transition temperature: 40 ° C.) 100% by weight (in terms of solid content) and butyl carbitol acetate as a solvent

Table 1 shows the Young's modulus, elongation at break, and yield elongation obtained by conducting a tensile test in accordance with JIS K7127 for the obtained insulator film using each insulator paste. 4 shows the measurement results of the tensile test. Insulator pastes A _i , B _i , and C _i were screen-printed on a substrate with a predetermined thickness, and after removing the solvent, an insulator film was prepared by irradiating with 500 mJ / cm ² ultraviolet rays. . Also, the insulating paste D _i, then screen printed on the substrate at a predetermined thickness, after removal of the solvent, 0.99 ° C., to prepare a dielectric film by thermally cured at 30 minutes. Further, in the figure 4, the insulating paste _{A i, B i, C i} , an insulator film formed by using the _{D i,} respectively, the insulator film _{A i, B i, C i} , D i It was.

<Conductor paste conditions>
In each example and each comparative example, the following conductor pastes were used in the combinations shown in Table 3 as the conductor paste for forming the respective conductive layers 20 and 50. The composition of the conductive paste used is shown below.
Conductor paste A _c : polyester-based thermosetting resin (glass transition temperature: 0 ° C., filler / resin ratio: 85/15) 10% by weight (in terms of solid content), particulate silver particles (particle diameter of 1 to 2 μm) 90% by weight (in terms of solid content) and butyl carbitol acetate / conductor paste B _c as a solvent: polyester thermosetting resin (glass transition temperature: 0 ° C., filler / resin ratio: 85/15) 10% by weight (In terms of solid content), scaly silver particles (particle size 2 to 3 μm) 90% by weight (in terms of solid content), and butyl carbitol acetate as a solvent

Table 2 shows the Young's modulus, elongation at break, and yield elongation obtained by conducting a tensile test in accordance with JIS K7127 for the obtained conductor film using each conductor paste. 5 shows the measurement results of the tensile test. The conductor film was prepared by using each conductor paste, screen-printing on a substrate with a predetermined thickness, removing the solvent, and then thermosetting at 150 ° C. for 30 minutes. Further, in the figure 5, the conductive paste A _c, the conductor film formed using B _c, and each conductor film A _c, and B _c.

<Evaluation results>
Table 3 shows the combinations of the insulator paste and the conductor paste used in each example and each comparative example, the evaluation results of the presence or absence of cracks after the bending test in each example and each comparative example, and the bending test. 2 shows the resistance increase values of the first conductive layer 20 and the second conductive layer 50 at the time of the tenth bending (resistance increase value = resistance value at the time of the tenth bending−resistance value before the bending test).

  From Table 3, the Young's modulus Ei1 of the first insulating layer 30 and the Young's modulus Ei2 of the second insulating layer 40 satisfy the above formula (5) and the above formula (6) (that is, the second insulating layer 40 is In Examples 1 and 2, the Young's modulus Ei2 is assumed to have a Young's modulus Ei2 higher than 10 MPa and less than 500 MPa and higher than the Young's modulus Ei1 of the first insulating layer 30 described above. The occurrence of cracks was not confirmed after the bending test, and the increase in resistance of each conductor layer after the bending test was suppressed, which was a good result.

  On the other hand, the Young's modulus Ei1 of the first insulating layer 30 is equal to the Young's modulus Ei2 of the second insulating layer 40, and the Young's modulus Ei2 of the comparative example 1 that does not satisfy the above formula (5) and the second insulating layer 40 is 500 MPa. In the comparative examples 2 and 3 that do not satisfy the above formula (6), the increase in the resistance of each conductor layer after the bending test, in particular, the increase in the resistance of the second conductor layer 50 is large. became. Here, in FIG. 6, the result of the resistance value of the 2nd conductor layer 50 in Examples 1, 2 and Comparative Examples 1-3 at the time of a bending test is graphed and shown. As can be confirmed from FIG. 6, in Examples 1 and 2, as compared with Comparative Examples 1 to 3, the increase in the resistance value accompanying the increase in the number of bendings was effectively suppressed.

DESCRIPTION OF SYMBOLS 1, 1a ... Printed wiring board 10 ... Base material 20 ... 1st conductive layer 30 ... 1st insulating layer 40 ... 2nd insulating layer 50 ... 2nd conductive layer 60 ... 3rd insulating layer 70 ... Additional layer

Claims (6)

A printed wiring board used by bending,
A substrate;
A first conductive layer formed on the substrate;
A first insulating layer formed on the substrate so as to cover the first conductive layer;
A second insulating layer formed on the first insulating layer;
A second conductive layer formed on the second insulating layer,
A printed wiring board satisfying the following formulas (I) and (II) when the Young's modulus of the first insulating layer is Ei1 and the Young's modulus of the second insulating layer is Ei2.
Ei1 <Ei2 (I)
10 MPa <Ei2 <500 MPa (II) The printed wiring board according to claim 1,
A printed wiring board characterized by satisfying the following formula (III).
1 MPa <Ei1 <100 MPa (III) The printed wiring board according to claim 1 or 2,
When the Young's modulus of the second conductive layer is Ec2, the printed wiring board satisfies the following formula (IV).
100 MPa <Ec2 <1000 MPa (IV) The printed wiring board according to any one of claims 1 to 3,
The printed wiring board, wherein a glass transition temperature of the first insulating layer is lower than a glass transition temperature of the second insulating layer. The printed wiring board according to any one of claims 1 to 4,
A third insulating layer formed on the second insulating layer so as to cover the second conductive layer;
The printed wiring board, wherein the third insulating layer has a surface roughness Ra of 0.1 μm <Ra <10 μm. A printed wiring board according to any one of claims 1 to 5,
The printed wiring board further comprising an additional layer on the surface of the substrate opposite to the surface on which the first conductive layer is formed.

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