JP2006165269A - Printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed circuit board capable of obtaining sufficient bending reliability even when a bending operation is fast and reducing the breakage of a conductor pattern.
SOLUTION: At a bent portion of a flexible printed circuit board 1, a total Te of the thicknesses of a base insulating layer 2 and a cover insulating layer 4 at both end portions in the width direction is defined as the sum of the thicknesses of the base insulating layer 2 and the cover insulating layer 4 at the center portion in the width direction. It is formed thicker than the total thickness Tc. As a result, even if the bent portion is bent by a fast bending operation, good bending reliability is achieved at the central portion in the width direction while preventing the occurrence of slack at both ends in the width direction where the thickness is thicker. Can be secured. As a result, even if the bending operation is fast, sufficient bending reliability can be obtained, and breakage of the conductor pattern 3 can be prevented.
[Selection] Figure 2

Description

  The present invention relates to a printed circuit board, and more particularly to a printed circuit board such as a flexible printed circuit board that requires bending reliability.

A flexible printed circuit board is a flexible printed circuit board that can be bent corresponding to a repetitively driven movable member and can be arranged in a bent state in a narrow space, such as a hard disk drive or an optical disk drive. Widely used in electronic equipment.
In such a flexible printed circuit board, in order to improve the bending reliability, for example, it has been proposed to make the thickness of the insulating layer of the bent portion of the flexible printed circuit board thinner than the thickness of the insulating layer of the non-bent portion. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2001-7452

However, when the insulating layer at the bent portion of the flexible printed circuit board is thin, as the bending operation becomes faster, the thin insulating layer at the bent portion is loosened and the shape becomes unstable. If it does so, it will become easy to generate | occur | produce the part with a small curvature radius, and the malfunction that a conductor pattern will fracture | rupture will arise in the part with such a small curvature radius.
An object of the present invention is to provide a printed circuit board that can obtain sufficient bending reliability even when the bending operation is fast, and can reduce breakage of a conductor pattern.

  In order to achieve the above object, a wired circuit board according to the present invention includes a base insulating layer, a conductor pattern laminated on the base insulating layer, and the base insulating layer so as to cover the conductor pattern. In the printed circuit board including the insulating cover layer laminated on the substrate, the longitudinal direction of the wired circuit board intersects with the lamination direction in which the insulating base layer, the conductor pattern, and the insulating cover layer are laminated. A bending portion that bends in a direction, wherein the sum of the thicknesses of the insulating base layer and the insulating cover layer at both ends in the width direction orthogonal to the longitudinal direction and the stacking direction is the width direction. The central insulating layer is formed thicker than the total thickness of the insulating base layer and the insulating cover layer.

In the wired circuit board according to the present invention, the base insulation at the central portion in the width direction of the bent portion and the total thickness of the base insulating layer and the cover insulating layer at both ends in the width direction of the bent portion. It is preferable that the difference between the total thickness of the layer and the insulating cover layer is 2 to 20 μm.
In the wired circuit board of the present invention, the thickness of the base insulating layer at both end portions in the width direction of the bent portion is larger than the thickness of the base insulating layer in the center portion in the width direction of the bent portion. May be.

In the wired circuit board of the present invention, the thickness of the insulating cover layer at both end portions in the width direction of the bent portion is larger than the thickness of the insulating cover layer in the center portion in the width direction of the bent portion. May be.
In the wired circuit board of the present invention, it is preferable that both end portions in the width direction of the bent portion are portions of 1 to 200 μm from the edge in the width direction to the inside in the width direction.

  In the printed circuit board according to the present invention, in the bent portion, the total thickness of the base insulating layer and the cover insulating layer at both ends in the width direction is the total thickness of the base insulating layer and the cover insulating layer in the center portion in the width direction. On the other hand, it is formed thick. For this reason, even if the bent portion is bent by a fast bending operation, it is possible to prevent the occurrence of slack at both end portions in the width direction where the thickness is thicker, and the good bending reliability in the center portion in the width direction where the thickness is thinner. Sex can be secured. As a result, even if the bending operation is fast, sufficient bending reliability can be obtained, and breakage of the conductor pattern can be reduced.

FIG. 1 is a plan view of an essential part of a bent portion of a flexible printed circuit board according to a first embodiment of the wired circuit board of the present invention, and FIG. 2 is a sectional view of an essential part of the bent portion of the flexible printed circuit board shown in FIG. is there.
As shown in FIG. 1, the flexible printed circuit board 1 has a substantially rectangular flat strip shape extending in a specific direction in plan view. As shown in FIG. 2, the base insulating layer 2 and the base insulating layer 2 A conductive pattern 3 laminated on top and a cover insulating layer 4 laminated on the base insulating layer 2 so as to cover the conductive pattern 3 are provided.

In the flexible printed circuit board 1, the bent portion is referred to as a longitudinal direction (hereinafter referred to as “longitudinal direction”) of the flexible printed circuit board 1 along the stacking direction of each layer (hereinafter referred to as “thickness direction”). Bend in the direction that intersects.
The base insulating layer 2 is thicker in the width direction both ends 5 than in the width direction central portion 6 in a direction perpendicular to the longitudinal direction and the thickness direction (hereinafter referred to as “width direction”). The cross section is formed in a substantially concave shape.

Both end portions 5 of the insulating base layer 2 are formed so as to protrude in a substantially rectangular cross section toward the side where the insulating cover layer 4 is laminated, and the inner side surface in the width direction has a width from the upper outer side in the width direction. It is formed so as to incline downward in the direction.
Each end portion 5 of the insulating base layer 2 is formed so as to extend inward in the width direction from the edge in the width direction of the flexible printed circuit board 1, and its width (maximum width) W1 is, for example, 1 to 200 μm, preferably 5 to 100 μm. Moreover, thickness T1 of each edge part 5 is 4-90 micrometers, for example, Preferably, it is 6-50 micrometers.

The central portion 6 of the base insulating layer 2 is between the end portions 5 in the width direction of the base insulating layer 2 and has a thickness T2 of, for example, 3 to 40 μm, or preferably 5 to 20 μm.
In the insulating base layer 2, the difference [Delta] T _1-2 and the thickness T2 of the thickness T1 and the central portion 6 of each end portion 5, for example, 1～60Myuemu, preferably from 3 to 30 .mu.m.
As shown in FIG. 1, the conductor pattern 3 is composed of a plurality of wirings 7 extending along the longitudinal direction, and the wirings 7 are spaced apart from each other in the width direction. The width of each wiring 7 is, for example, 10 to 200 μm, preferably 15 to 50 μm, and the interval between the wirings 7 is, for example, 10 to 200 μm, preferably 15 to 50 μm. The thickness of the conductor pattern 3 is 3-50 micrometers, for example, Preferably, it is 5-15 micrometers.

As shown in FIG. 2, the conductor pattern 3 is formed in the central portion 6 between the end portions 5 in the width direction of the base insulating layer 2.
The insulating cover layer 4 is laminated over the end portions 5 and the central portion 6 of the insulating base layer 2 while covering the conductor pattern 3. The insulating cover layer 4 is formed in a substantially concave shape in cross section where a step 8 is formed corresponding to the boundary between each end portion 5 and the central portion 6 of the insulating base layer 2.

The insulating cover layer 4 has a thickness of, for example, 3 to 20 μm, preferably 5 to 10 μm.
Although not shown, the cover insulating layer 4 has an opening at a specific portion, and each wiring 7 exposed from the opening serves as a terminal portion for connecting to an external terminal.
In this flexible printed circuit board 1, the width of both end portions 5 in the width direction is formed thicker than the thickness of the central portion 6 in the width direction in the insulating base layer 2. The total Te of the thicknesses of the base insulating layer 2 and the cover insulating layer 4 at both ends is thicker than the total thickness Tc of the base insulating layer 2 and the cover insulating layer 4 at the center in the width direction.

More specifically, the difference ΔT between the total Te of the thickness of the base insulating layer 2 and the cover insulating layer 4 at both ends in the width direction and the total Tc of the thickness of the base insulating layer 2 and the cover insulating layer 4 at the center in the width direction. _ec is, for example, 2 to 20 μm, preferably 5 to 10 μm. If the difference ΔT _ec is smaller than this, loosening may occur easily. On the other hand, if the difference ΔT _ec is larger than this, the repulsive force may increase and the flexibility may decrease.

  Therefore, in this flexible printed circuit board 1, even if the bent portion is bent by a fast bending operation, it is possible to prevent the occurrence of slack at the thicker width direction both ends, while at the thinner widthwise central portion. Good bending reliability can be ensured. As a result, even if the bending operation is fast, sufficient bending reliability can be obtained, and breakage of the conductor pattern 3 can be prevented.

Next, a method for manufacturing the flexible printed circuit board 1 will be described with reference to FIG.
In this method, first, as shown in FIG. 3C, the base insulating layer is formed on the support substrate 9 so as to have a substantially concave cross section in which the widthwise end portions 5 are thicker than the widthwise central portion 6. 2 is formed.
As the support substrate 9, for example, a metal foil or a metal thin plate made of stainless steel, 42 alloy, aluminum, copper-beryllium, phosphor bronze, or the like is used. From the viewpoint of rigidity, corrosion resistance and workability, a stainless steel foil is preferably used. The thickness of the support substrate 9 is, for example, 10 to 100 μm, preferably 15 to 30 μm.

The insulating base layer 2 is made of, for example, a film of synthetic resin such as polyimide resin, polyamideimide resin, acrylic resin, polyether nitrile resin, polyether sulfone resin, polyethylene terephthalate resin, polyethylene naphthalate resin, or polyvinyl chloride resin. Used. Preferably, a polyimide resin film is used.
Further, in order to form the insulating base layer 2 on the support substrate 9 as described above, for example, a varnish 10 of a photosensitive resin is applied on the support substrate 9 as shown in FIG. To do. As the photosensitive resin, the above-described synthetic resin that is photosensitive is used. Preferably, a photosensitive polyimide resin is used. As the photosensitive resin varnish, a polyamic acid resin (polyimide precursor resin) varnish is preferably used.

  Then, as shown in FIG. 3B, the varnish 10 is exposed through the gradation exposure photomask 11, and then developed as shown in FIG. Then, patterning is performed. For the exposure, a gradation exposure method using a gradation exposure photomask 11 is used. For development, a developing method such as a dipping method using a developer or a spray method is used.

In addition, in FIG.3 (c), the patterning by a negative image is illustrated, but it is selected by the kind of varnish 10 whether it is a negative image or a positive image.
Further, in this exposure and development, in order to pattern the both ends 5 in the width direction into a substantially concave shape with a thicker thickness than the central portion 6 in the width direction, for example, in the gradation exposure photomask 11, The light transmittance of the portion facing the portion 6 is adjusted to semi-transmission between the total transmission and the total light shielding, and the light transmittance of the portion facing the width direction both end portions 5 is adjusted to the total transmission (negative image). In the case of the above-mentioned case) or full shading (positive image), gradation exposure is performed, and then, at the time of development, the varnish 10 in the central portion 6 in the width direction is left in the middle of the thickness direction.

Then, as shown in FIG. 3D, when the varnish 10 is cured by heating, the base insulating layer has a substantially concave shape in cross section in which the widthwise end portions 5 are thicker than the widthwise central portion 6. 2 is formed.
In addition to the above-described method, the insulating base layer 2 is formed, for example, by forming the insulating base layer 2 with the same thickness as the both end portions 5 in the width direction and the uniform thickness, It can also be formed by half-etching halfway in the thickness direction.

  Further, for example, a first base insulating layer that is difficult to be etched is formed with the same thickness as the widthwise central portion 6, and a second base insulating layer that is easily etched is formed on both ends of the width direction on the first base insulating layer. After the base insulating layer 2 is formed so as to have the same thickness as 5, the center portion 6 in the width direction of the second base insulating layer that is easily etched can be etched.

Further, for example, after the first base insulating layer made of a non-photosensitive resin is formed with the same thickness as the widthwise central portion 6, the second base insulating layer made of a photosensitive resin is made the same thickness as the widthwise both ends 5. It can also be formed by exposing, developing and curing with a pattern formed only at both ends 5 in the width direction.
In this method, the conductor pattern 3 is then formed on the central portion 6 in the width direction of the base insulating layer 2 as shown in FIG.

As the conductive pattern 3, for example, a metal foil such as copper, nickel, gold, solder, or an alloy thereof is used, and a copper foil is preferably used from the viewpoint of conductivity, inexpensiveness, and workability.
Moreover, in order to form the conductor pattern 3, well-known patterning methods, such as a subtractive method and an additive method, are used, for example.

  That is, in the subtractive method, first, a metal foil is laminated on the entire surface of the base insulating layer 2 through an adhesive layer as necessary. Next, an etching resist is formed on the surface of the metal foil with a pattern corresponding to the conductor pattern 3. The etching resist is formed from a dry film resist or the like by a known method of exposing and developing. Then, after etching the metal foil exposed from the etching resist, the etching resist is removed by etching or peeling.

  In the additive method, first, a metal thin film serving as a seed film is formed on the entire surface of the base insulating layer 2. The metal thin film is formed from chromium, nickel, copper, and alloys thereof by a thin film forming method such as a sputtering method. Next, a plating resist is formed on the surface of the metal thin film with a reverse pattern of the conductor pattern 3. The plating resist is formed from a dry film resist or the like by a known method of exposure and development. Thereafter, the conductor pattern 3 is formed on the surface of the base insulating layer exposed from the plating resist by electrolytic plating, preferably electrolytic copper plating. Thereafter, the plating resist is removed by etching or peeling, and the metal thin film exposed from the conductor pattern 3 is removed by etching.

As a result, the conductor pattern 3 composed of the wiring 7 is formed.
Thereafter, in this method, as shown in FIG. 3 (f), the insulating cover layer 4 is formed on the insulating base layer 2 so as to cover the conductive pattern 3.
The insulating cover layer 4 is made of the same synthetic resin as the insulating base layer 2. The insulating cover layer 4 can be formed, for example, by applying a photosensitive resin varnish, drying, developing after exposure, and curing to form the opening not shown above. it can.

Alternatively, it may be formed by pasting a synthetic resin film having an opening formed in advance and having an outer shape processed, if necessary, on the base insulating layer 2 including the conductor pattern 3 via an adhesive layer. it can.
Thereafter, in this method, as shown in FIG. 3G, the flexible printed circuit board 1 is obtained by removing the support substrate 9 by etching or peeling.

Note that, depending on the purpose and application of the support substrate 9, the base insulating layer 2 can be supported as it is without being removed.
Further, in the flexible printed circuit board 1 of the first embodiment described above, the base insulating layer 2 is formed in a substantially concave shape in cross section in which both end portions 5 protrude toward the side where the cover insulating layer 4 is laminated. However, for example, as in the flexible printed circuit board 1 of the second embodiment shown in FIG. 4, the base insulating layer 2 has its both end portions 5 facing away from the side on which the cover insulating layer 4 is laminated. You may form in the cross-sectional substantially concave shape which protrudes.

In FIG. 4, the same members as those described above are denoted by the same reference numerals, and the description thereof is omitted.
In FIG. 4, in this flexible printed circuit board 1, the insulating base 2 is formed in a flat shape in which both sides 5 are laminated with the insulating cover 4 on the side where the cover insulating layer 4 is laminated. The opposite side is formed so as to protrude into a substantially rectangular cross section.
In the flexible printed circuit board 1, since the insulating base layer 2 is formed as described above, the insulating cover layer 4 has steps corresponding to the boundaries between the end portions 5 and the central portion 6 of the insulating base layer 2. 8 is formed without being formed.

  And also in the flexible printed circuit board 1 of this 2nd Embodiment, since the thickness of the width direction both ends 5 is formed thicker than the thickness of the width direction center part 6 in the base insulating layer 2, a flexible printed circuit The total thickness of the base insulating layer 2 and the cover insulating layer 4 at both ends in the width direction of the substrate 1 is formed thicker than the total thickness of the base insulating layer 2 and the cover insulating layer 4 at the center in the width direction. .

  Therefore, even in the flexible printed circuit board 1 according to the second embodiment, even if the bent portion is bent by a fast bending operation, the thickness is thinner while preventing the occurrence of slack at both ends in the width direction where the thickness is thicker. Good bending reliability can be secured at the center in the width direction. As a result, even if the bending operation is fast, sufficient bending reliability can be obtained, and breakage of the conductor pattern 3 can be prevented.

Next, a method for manufacturing the flexible printed circuit board 1 of the second embodiment will be described with reference to FIG.
In this method, first, the base insulating layer 2 is prepared as shown in FIG. The base insulating layer 2 is prepared as a synthetic resin film. The insulating base layer 2 is prepared with the same thickness as that of the widthwise both ends 5 of the obtained flexible printed circuit board 1.

Next, in this method, as shown in FIG. 5B, the conductor pattern 3 is formed by a known patterning method such as a subtractive method or an additive method, as described above.
In order to form the conductor pattern 3 on the base insulating layer 2, for example, a two-layer base material in which a metal foil is laminated on the base insulating layer 2 in advance is prepared, It can also be formed by forming a metal foil on the conductor pattern 3 by a subtractive method.

Thereafter, as shown in FIG. 5C, the insulating cover layer 4 is formed on the insulating base layer 2 so as to cover the conductive pattern 3 by the same method as described above.
And in this method, as shown in FIG.5 (d), after covering the flexible printed circuit board 1 other than the part with the etching resist 12, the width direction center part 6 of the base insulating layer 2 is exposed. Then, half etching (wet etching) is performed so that the central portion 6 in the width direction remains, and then the etching resist 12 is removed as shown in FIG. The base insulating layer 2 is formed in a substantially concave shape with a thickness that is thicker than that of the substrate 6, whereby the flexible printed circuit board 1 is obtained.

  Further, in the flexible printed circuit board 1 of the first and second embodiments described above, the base insulating layer 2 has a substantially concave cross section in which the widthwise end portions 5 are thicker than the widthwise center portion 6. However, as in the third embodiment shown in FIG. 6, the insulating base layer 2 is formed to have a uniform thickness, and the insulating cover layer 4 has both end portions 13 in the width direction with respect to the center portion 14 in the width direction. Alternatively, the cross section may be formed in a substantially concave shape in which the thickness increases.

In FIG. 6, the same members as those described above are denoted by the same reference numerals, and the description thereof is omitted.
In FIG. 6, in the flexible printed circuit board 1, the base insulating layer 2 is formed with a uniform thickness, and the thickness is, for example, 3 to 30 μm, preferably 5 to 15 μm.
Both end portions 13 of the insulating cover layer 4 are formed so as to protrude in a substantially rectangular shape in cross section toward the side opposite to the side in contact with the insulating base layer 2, and the inner side surface in the width direction is the outer side in the width direction. It is formed so as to incline from the upper side toward the lower side in the width direction.

Each end 13 of the insulating cover layer 4 is formed so as to extend inward in the width direction from the edge in the width direction of the flexible printed circuit board 1, and its width (maximum width) W2 is, for example, 1 to 200 μm, preferably 5 to 100 μm. Moreover, thickness T3 of each edge part 13 is 6-120 micrometers, for example, Preferably, it is 10-60 micrometers.
The central portion 14 of the insulating cover layer 4 is between the end portions 13 in the width direction of the insulating base layer 2 and has a thickness T4 of, for example, 5 to 100 μm, or preferably 8 to 50 μm.

In the insulating cover layer 4, the difference ΔT _3-4 between the thickness T3 of each end 13 and the thickness T4 of the central portion 14 is, for example, 1 to 70 μm, preferably 2 to 30 μm.
The conductor pattern 3 is formed in the central portion 14 between the end portions 13 in the width direction of the cover insulating layer 4.
Although not shown, the cover insulating layer 4 has an opening at a specific portion, and each wiring 7 exposed from the opening serves as a terminal portion for connecting to an external terminal.

  And in the flexible printed circuit board 1 of this 3rd Embodiment, since the thickness of the width direction both ends 13 is formed thicker than the thickness of the width direction center part 14 in the cover insulating layer 4, this 3rd The total Te of the thickness of the base insulating layer 2 and the cover insulating layer 4 at both ends in the width direction of the flexible printed circuit board 1 of the embodiment is the total Tc of the thickness of the base insulating layer 2 and the cover insulating layer 4 at the center in the width direction. On the other hand, it is formed thick.

More specifically, the flexible printed circuit board 1 according to the third embodiment also has a total Te of the thicknesses of the base insulating layer 2 and the cover insulating layer 4 at both ends in the width direction, and a central portion in the width direction, as described above. The difference ΔT _{ec from} the total thickness Tc of the base insulating layer 2 and the cover insulating layer 4 is set to 2 to 20 μm, preferably 5 to 10 μm, for example.
Therefore, even in the flexible printed circuit board 1 according to the third embodiment, even if the bent portion is bent by a fast bending operation, the thickness is thinner while preventing the occurrence of slack at both thicker end portions in the width direction. Good bending reliability can be secured at the center in the width direction. As a result, even if the bending operation is fast, sufficient bending reliability can be obtained, and breakage of the conductor pattern 3 can be prevented.

Next, a method for manufacturing the flexible printed circuit board 1 of the third embodiment will be described with reference to FIG.
In this method, first, an insulating base layer 2 is prepared as shown in FIG. The base insulating layer 2 is prepared as a synthetic resin film.
Next, in this method, as shown in FIG. 7B, the conductor pattern 3 is formed by a known patterning method such as a subtractive method or an additive method, as described above.

In order to form the conductor pattern 3 on the base insulating layer 2, for example, a two-layer base material in which a metal foil is laminated on the base insulating layer 2 in advance is prepared, It can also be formed by forming a metal foil on the conductor pattern 3 by a subtractive method.
In this method, as shown in FIG. 7 (f), both end portions 13 in the width direction are thicker than the central portion 14 in the width direction on the insulating base layer 2 so as to cover the conductor pattern 3. The insulating cover layer 4 is formed in a substantially concave shape.

In order to form the insulating cover layer 4 in this way, for example, as shown in FIG. 7C, a varnish 15 of a photosensitive resin is applied on the insulating base layer 2 including the conductor pattern 3. As the photosensitive resin, the same photosensitive resin as described above is used.
Then, as shown in FIG. 7D, the varnish 15 is subjected to gradation exposure through the gradation exposure photomask 16 as described above, and thereafter, as shown in FIG. In addition, by performing development so that the central portion 14 in the width direction remains, patterning is performed so that the cross section is substantially concave.

Then, as shown in FIG. 7 (f), when the varnish 15 is cured by heating, the cover insulating layer has a substantially concave cross section in which the width direction end portions 13 are thicker than the width direction center portion 14. 4 is formed, whereby the flexible printed circuit board 1 is obtained.
The insulating cover layer 4 is formed by the same method as described above, for example, after forming the insulating cover layer 4 with the same thickness as the widthwise end portions 13 and a uniform thickness, It can also be formed by half-etching halfway in the thickness direction.

  In addition, for example, a first cover insulating layer that is difficult to be etched is formed with the same thickness as the widthwise central portion 14, and a second cover insulating layer that is easily etched is formed on both ends of the width direction on the first cover insulating layer. After forming the cover insulating layer 4 to have the same thickness as 13, the width direction central portion 14 in the second cover insulating layer which is easily etched can be etched.

Further, for example, after the first cover insulating layer made of a non-photosensitive resin is formed with the same thickness as the width direction center portion 14, the second cover insulating layer made of a photosensitive resin is made the same thickness as the width direction both end portions 13. It can also be formed by exposing, developing, and curing with a pattern formed only at both ends 13 in the width direction.
In the above description, the bent portion of the flexible printed circuit board 1 has been described in the first embodiment, the second embodiment, and the third embodiment. However, the flexible printed circuit board 1 is all bent portions. Moreover, a part may be a bending part. In the case where a part is a bent portion, a known configuration is appropriately adopted for the portion other than the bent portion depending on the purpose and application.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
Example 1
A support substrate made of a stainless steel foil having a thickness of 20 μm was prepared, and a photosensitive polyamic acid resin varnish was applied to the entire surface of the support substrate (see FIG. 3A), followed by gradation exposure having a light semi-transmissive portion. By gradation exposure through a photomask (see FIG. 3B) and development (see FIG. 3C), the varnish becomes thicker at both widthwise ends than the widthwise center. Patterned into a substantially concave cross section. Thereafter, the varnish is cured at 380 ° C. for 2 hours, so that the thickness at both end portions in the width direction (50 μm portion from the edge in the width direction to the inner side in the width direction) is 20 μm, and the central portion in the width direction (300 μm between both end portions in the width direction The base insulating layer having a thickness of 10 μm was formed (see FIG. 3D).

  Subsequently, a chromium thin film having a thickness of 30 nm and a copper thin film having a thickness of 150 nm are sequentially formed on the entire surface of the base insulating layer by sputtering, thereby forming a metal thin film. A plating resist having a thickness of 20 μm made of a dry film resist was formed. And after forming a 10-micrometer-thick conductor pattern by electrolytic copper plating, the plating resist was peeled and the metal thin film exposed from the conductor pattern was etched (refer FIG.3 (e)).

Next, a varnish of a photosensitive polyamic acid resin is applied to the entire surface of the base insulating layer so as to cover the conductor pattern, and then exposed through a photomask and developed to form an opening, and then By curing, a base insulating layer made of a polyimide resin having a thickness of 5 μm was formed (see FIG. 3F).
Subsequently, the flexible printed circuit board was obtained by removing the support substrate (see FIG. 3G). In the obtained flexible printed circuit board, the total thickness of the base insulating layer and the cover insulating layer at both ends in the width direction is 25 μm, and the total thickness of the base insulating layer and the cover insulating layer at the center in the width direction is 15 μm. Met.

Example 2
A two-layer base material in which a copper foil having a thickness of 8 μm was laminated on a base insulating layer made of a polyimide resin film having a thickness of 25 μm was prepared. On the copper foil of the two-layer substrate, after forming an etching resist having a thickness of 10 μm in a pattern corresponding to the conductor pattern, etching the metal foil exposed from the etching resist, and then peeling the etching resist, A conductor pattern was formed on the base insulating layer (see FIG. 5B).

Next, a varnish of a photosensitive polyamic acid resin is applied to the entire surface of the base insulating layer so as to cover the conductor pattern, and then exposed through a photomask and developed to form an opening, and then By curing, a cover insulating layer made of polyimide resin having a thickness of 5 μm was formed (see FIG. 5C).
Then, after covering the flexible printed circuit board other than that portion with an etching resist so that the central portion in the width direction of the base insulating layer is exposed (see FIG. 5D), the central portion in the width direction remains. Half-etching (wet etching) and then removal of the etching resist results in a thickness of 25 μm at both ends in the width direction (50 μm from the edge in the width direction to the inner side in the width direction) A base insulating layer was formed in a substantially concave cross section with a thickness of 15 μm between the portions), thereby obtaining a flexible printed circuit board (see FIG. 5E). In the obtained flexible printed circuit board, the total thickness of the base insulating layer and the cover insulating layer at both ends in the width direction is 30 μm, and the total thickness of the base insulating layer and the cover insulating layer at the center in the width direction is 20 μm. Met.

Example 3
A two-layer base material was prepared in which a copper foil having a thickness of 8 μm was laminated on a base insulating layer made of a polyimide resin film having a thickness of 12.5 μm. On the copper foil of the two-layer substrate, after forming an etching resist having a thickness of 10 μm in a pattern corresponding to the conductor pattern, after etching the metal foil exposed from the etching resist, by peeling the etching resist, A conductor pattern was formed on the base insulating layer (see FIG. 7B).

  Next, a varnish of a photosensitive polyamic acid resin is applied to the entire surface of the base insulating layer so as to cover the conductor pattern (see FIG. 7C), and then passed through a gradation exposure photomask having a light semi-transmissive portion. When the tone is exposed (see FIG. 7 (d)) and developed (see FIG. 7 (e)), the varnish has a substantially concave shape in which both end portions in the width direction are thicker than the central portion in the width direction. Patterned. Thereafter, the varnish is cured at 380 ° C. for 2 hours, so that the thickness of both end portions in the width direction (portion of 50 μm from the end in the width direction to the inner side in the width direction) is 15 μm, and the center portion in the width direction (300 μm between both end portions in the width direction A cover insulating layer having a thickness of 5 μm was formed (see FIG. 7F), thereby obtaining a flexible printed circuit board.

In the obtained flexible printed circuit board, the total thickness of the base insulating layer and the cover insulating layer at both ends in the width direction is 27.5 μm, and the total thickness of the base insulating layer and the cover insulating layer at the center in the width direction is 17.5 μm.
Comparative Example 1
A flexible wiring is formed by the same method as in Example 1 except that a base insulating layer made of a polyimide resin having a thickness of 10 μm and having a uniform thickness in the width direction is formed on a support substrate made of a stainless steel foil having a thickness of 20 μm. A circuit board was obtained.

Evaluation The flexible printed circuit board of each Example and Comparative Example was bent with a curvature radius of 3 mm, and a bending test based on IPC-240 was performed under the condition of a bending speed of 25 Hz.
As a result, in Comparative Example 1, the conductor pattern was disconnected 80 million times, but in Examples 1 to 3, the conductor pattern was not disconnected even when bent 100 million times or more.

It is a principal part top view of the bending part of the flexible wired circuit board of 1st Embodiment of the wired circuit board of this invention. It is principal part sectional drawing of the bending part of the flexible printed circuit board shown in FIG. It is process drawing which shows the manufacturing method of the flexible printed circuit board shown in FIG. 1, Comprising: (a) is the process of apply | coating the varnish of photosensitive resin on a support substrate, (b) is gradation exposure of a varnish. The step of performing gradation exposure through a photomask, (c) is a step of developing the varnish into a substantially concave shape in cross section in which both end portions in the width direction are thicker than the center portion in the width direction, and (d) is a step of developing the varnish. (E) is a step of forming a conductor pattern on the central portion in the width direction of the base insulating layer, and (f) is a cover on the base insulating layer so as to cover the conductor pattern. Step (g) of forming an insulating layer shows a step of removing the support substrate. It is principal part sectional drawing of the bending part of the flexible printed circuit board of 2nd Embodiment of the wired circuit board of this invention. FIG. 5 is a process diagram illustrating a method for manufacturing the flexible printed circuit board shown in FIG. 4, wherein (a) is a step of preparing a base insulating layer, (b) is a step of forming a conductor pattern on the base insulating layer; (C) is a step of forming a cover insulating layer on the base insulating layer so as to cover the conductor pattern, and (d) is an etching resist, so that the central portion in the width direction of the base insulating layer is exposed. The step of covering the flexible printed circuit board other than the portion, (e) shows the step of removing the etching resist after half etching so that the central portion in the width direction remains. It is principal part sectional drawing of the bending part of the flexible printed circuit board of 3rd Embodiment of the wired circuit board of this invention. FIG. 7 is a process diagram illustrating a method for manufacturing the flexible printed circuit board shown in FIG. 6, wherein (a) is a step of preparing an insulating base layer, (b) is a step of forming a conductor pattern on the insulating base layer; (C) is a step of applying a photosensitive resin varnish on the base insulating layer including the conductor pattern, (d) is a step of gradation-exposing the varnish via a gradation exposure photomask, (e). Is a step of developing the varnish into a substantially concave cross section in which both end portions in the width direction are thicker than the center portion in the width direction, and (f) is a step of curing the varnish by heating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flexible wiring circuit board 2 Base insulating layer 3 Conductor pattern 4 Cover insulating layer 5 The width direction both ends of a base insulating layer 6 The width direction center part of a base insulating layer 13 The width direction both ends of a cover insulating layer 14 The width direction of a cover insulating layer Center

Claims (5)

In a printed circuit board comprising a base insulating layer, a conductor pattern laminated on the base insulating layer, and a cover insulating layer laminated on the base insulating layer so as to cover the conductor pattern,
A bending portion that bends in a direction intersecting with a lamination direction in which the base insulating layer, the conductor pattern, and the cover insulating layer are laminated with respect to the longitudinal direction of the wired circuit board,
In the bent portion, the total thickness of the base insulating layer and the cover insulating layer at both end portions in the width direction orthogonal to the longitudinal direction and the stacking direction is the base insulating layer in the center portion in the width direction and The printed circuit board is formed thicker than a total thickness of the insulating cover layers.   The total thickness of the base insulating layer and the cover insulating layer at both end portions in the width direction of the bent portion, and the total thickness of the base insulating layer and the cover insulating layer at the center portion in the width direction of the bent portion. The printed circuit board according to claim 1, wherein a difference between the printed circuit board and the circuit board is 2 to 20 μm.   The thickness of the base insulating layer at both end portions in the width direction of the bent portion is thicker than the thickness of the base insulating layer at the center portion in the width direction of the bent portion. 3. The printed circuit board according to 2.   The thickness of the cover insulating layer at both end portions in the width direction of the bent portion is thicker than the thickness of the cover insulating layer in the center portion of the bent portion in the width direction. 3. The printed circuit board according to 2.   The both end portions in the width direction of the bent portion are portions of 1 to 200 µm from the edge in the width direction to the inside in the width direction, respectively. Printed circuit board.

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