JPS62242393A - Flexible printed wiring board and manufacture of the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a flexible wiring board having terminal portions and land portions, particularly a high-quality flexible wiring board with excellent heat resistance, and a method for manufacturing the same.

[Prior Art] Flexible wiring boards are widely used in the field of electronic equipment because they are highly flexible and thin. However, the manufacturing process of the conventional method for manufacturing a flexible wiring board is complicated, and the flexible wiring board manufactured by the conventional method has drawbacks that inevitably arise from its structure.

That is, a conventional flexible wiring board uses a material in which a copper foil 3 as a conductor is bonded to an insulating base film 1 using an adhesive 2, as shown in an example in FIG. An insulating coverlay film 5 is further provided on top using an adhesive 4.

For this reason, even when polyimide film is used as an insulating film, rubber-modified epoxy resin or rubber-modified phenol resin is used as the adhesive layer, which results in poor heat resistance, especially soldering heat resistance. Resin blistering or peeling may occur during dip coating.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to solve the above-mentioned conventional drawbacks and to provide a flexible wiring board with high quality, particularly excellent heat resistance, and a method for manufacturing the same.

[Means for Solving the Problems] In order to achieve such an object, the flexible wiring board of the wooden invention has a structure in which predetermined portions of both the front and back surfaces of the metal conductor plate, excluding the terminal portions and land portions, are Both the front and back sides of a metal conductor plate are directly coated with polyimide resin, which has excellent heat resistance and flexibility, without using adhesives.

That is, the first embodiment of the flexible wiring board of the present invention is characterized in that only predetermined portions of both the front and back surfaces of the metal conductor plate are directly coated with polyimide resin.

A second embodiment of the flexible wiring board of the present invention has a terminal portion of a metal conductor on at least one end of the metal conductor plate, and at least one surface of the terminal portion is not covered with an insulating layer, and other than the terminal portion of the metal conductor plate. It is characterized in that only a predetermined number of both the front and back surfaces of the sheet are directly coated with polyimide resin.

The method for manufacturing a flexible wiring board of the present invention includes a step of forming a photoresist pattern on a thin metal plate, a step of forming a conductor pattern on the thin metal plate using the photoresist pattern, and a step of forming the conductor pattern on the thin metal plate. a step of forming a first insulating layer by coating a solvent-soluble polyimide resin only on a predetermined portion of the side surface, a step of removing the thin metal plate, and a step of forming a first insulating layer only on a predetermined portion of the side surface from which the thin metal plate has been removed. The method is characterized in that it includes a step of forming a second insulating layer by coating with a solvent-soluble polyimide resin.

[Function] Since the flexible wiring board of the present invention has a structure without adhesive, the advantages of polyimide resin can be fully utilized and excellent heat resistance can be exhibited. Moreover, the flexible wiring board can be manufactured through a simple manufacturing process.

[Example] Below, the tree invention will be described in detail based on the drawings.

FIGS. 1(a) to 1(e) show an example of a wiring board having terminals and lands as an embodiment of the flexible wiring board of the present invention.

FIG. 1(a) is a plan view of a portion of the flexible wiring board including the terminal portion, FIG. 1(b) is a plan view of the flexible wiring board including the land portion, and FIG. ), FIG. 1(d) is a cross-sectional view taken along line X-X at FIG.
), and FIG. 1(e) is a sectional view taken along line Z--Z in FIG. 1(b).

In FIGS. 1(a) to (e), 11 is a conductive plate made of copper or the like, IIA is its terminal portion, IIB is an exposed land portion of the conductive plate 11, and 12.12' are both main surfaces of the conductive plate 11. An insulating layer 13 made of polyimide resin disposed above is a photoresist layer filling the gaps between the patterns of the conductive plate 11.

As shown in the figure, the flexible wiring board according to the present invention is
The conductor plate 11 except for the terminal portion 11A and the land portion 11B
The front and back surfaces of the substrate are directly coated with polyimide resin layers 12 and 12' having excellent heat resistance and flexibility.

A flexible wiring board with such a structure is shown in Fig. 3(a).
~(e), Figures 4(a)~(e), and Figure 5(a)~
(e) It can be easily made by the process shown in (e).

3(a) to 3(e) are cross sections along the line XX in FIG. 1(a), FIG. 4(a) to (e) are cross sections along the line YY, and FIG. 5 (a) to (e) show cross sections along line 2-2.

Next, each process will be briefly explained.

(1) Forming a photoresist pattern 22 on a thin metal plate 21 (Fig. 3(a), Fig. 4(a), Fig. 5(a))
).

(2) Forming the conductor pattern 23 on the thin metal plate 21 along the resist pattern 22 by pattern plating (
Fig. 3(b), Fig. 4(b), Fig. 5(b)).

(3) By pattern coating, the first insulating layer 24 is formed only on the necessary portions of the resist pattern 22 and the conductor pattern 23 (Fig. 3(C), Fig. 4(C), Fig. 5). (C)). Lands 25 are exposed in the uncovered portions of the insulating layer 24, that is, in the open portions.

(4) Remove the metal thin plate 21 (Fig. 3(d), Fig. 4(d), Fig. 5(d)).

(5) By pattern coating, the second insulating layer 2 is applied only to the necessary portions of the exposed surfaces of the patterns 22 and 23.
4' (Fig. 3(e), Fig. 4(e), Fig. 5)
Figure (e)). The uncoated portion of this insulating layer 24',
That is, the land 25' is exposed at the opening.

In this way, a flexible wiring board having terminals and lands as shown in FIGS. 1(a) to 1(e) is produced.

Next, specific examples of the flexible wiring board of the present invention will be shown, but the present invention is not limited only to these examples.

Example 1 A negative resist "Microresist 747" manufactured by Eastman Kodak was applied on a thin aluminum plate with a thickness of 80 μm.
” was applied to a film thickness of 5 μm. The resist-coated aluminum plate was prebaked, exposed to light using a high-pressure mercury lamp through the wiring board pattern, developed using a special developer and rinse solution, and post-baked to form a resist pattern on one side of the aluminum thin plate.

Next, electrolytic copper plating was performed using a birophosphate copper plating bath using the aluminum thin plate on which the resist pattern was formed as a cathode. The conductor width of the obtained conductor pattern is 2
The conductor spacing was 250 μm and the conductor thickness was 40 μm.

Thereafter, using a stainless steel metal mask, a polyimide resin "U varnish" manufactured by Ube Industries, Ltd. was pattern-coated, for example, by screen printing, except for the terminal portions and land portions, and dried and cured to obtain an insulating layer with a thickness of 20 μm. The thin aluminum plate was then etched away using 10% by weight hydrochloric acid. At this time, the photoresist left on the terminal part has weak mechanical strength and is not supported by the insulating layer, so it is cut at the end of the insulating layer (section 128 in Figure 1 (a)). . Therefore, no photoresist remains in the terminal area. Again, using a stainless steel metal mask, pattern coat the back side with "U varnish" except for the terminals and lands, dry and harden for 20 minutes.
A flexible wiring board with terminals and lands was obtained with an insulating layer having a thickness of μm. Thereafter, the terminal portion and the land portion were subjected to flux treatment, and solder coating was performed by dipping them in a solder bath at 280° C. for about 5 seconds, but no deterioration was observed in the resin layer.

Example 2 As in Example 1, a resist pattern was formed on a thin aluminum plate, and then copper plating was performed to obtain a conductor pattern with a conductor width of 300 μm, a conductor interval of 350 μm, and a conductor thickness of 35 μm.

Thereafter, a solvent-soluble polyamideimide resin synthesized from diamino-diphenyl ether and trimellitic acid chloride was pattern-coated by screen printing using a stainless steel metal mask, except for terminals and lands, dried, and heat-treated to form an insulating layer with a thickness of 30 μm. I got it. Next, the thin aluminum plate was removed by etching with 10% hydrochloric acid, and the photoresist was removed using a resist remover rN-500J manufactured by Nagase Chemical Industries, Ltd. Again, using a stainless steel metal mask, the solvent-soluble polyamide-imide resin was pattern coated on the back surface, dried and heat treated to form an insulating layer with a thickness of 30 μm, to obtain a flexible wiring board with terminals. Thereafter, the terminal portion was subjected to flux treatment, and solder coating was performed by dipping it in a solder bath at 300° C. for about 20 seconds, but no deterioration was observed in the resin layer. Adhesive strength and dimensional accuracy were also excellent.

In these Examples, the conductor pattern was formed on the metal thin plate by electroplating, but it is also possible to form the conductor pattern by pattern etching after forming a uniform conductor layer.

It is also possible to form a conductive pattern by pattern-coating an insulating layer on one side of the metal foil at the required portions, drying and heat-treating, and then pattern-etching.

Any metal that can be electroplated may be used as the conductor metal, but copper is preferred from the viewpoint of conductivity and economy.

The thin metal plate can be removed not by etching as in this embodiment, but by peeling off. However, in order not to disturb the conductor pattern, etching is preferable, and if etching is used, it is preferable to use a material with etching characteristics different from those of the conductor metal. When copper is used as the conductive metal as in this example, aluminum is used.

It is desirable to use tin, zinc, etc.

The photoresist used for pattern plating of the conductor layer is
It is also preferable to peel off at an appropriate time after completion of plating, for example after completion of λ-plating or after removal of the thin metal plate.

The polyimide resin used in the present invention is pattern-coated and is therefore solvent-soluble. Unlike the case of bonding a film to metal foil, since a liquid coating is applied, there are no air bubbles left between the metal and the insulating layer, improving adhesion, and there is no need to apply external force. It is possible to improve the dimensional accuracy of the product.

Examples of polyimide resins include polyamic acids, polyimide resins, polyamideimide resins, polyester-modified imide resins, and silicone imide resins. Solvent-soluble imide group-containing polymers, particularly solvent-soluble polyamide-imide resins, are preferred, and pinholes and air bubbles can be avoided. There is no occurrence of this, and a product with excellent adhesiveness and dimensional accuracy can be obtained.

FIG. 6 shows another embodiment of the flexible wiring board of the present invention, and is a sectional view corresponding to FIG. 1(c). This embodiment is an example in which the second insulating layer 12' is provided after the photoresist is peeled off as described above.

FIGS. 7 and 8 show other embodiments with different structures of the terminal portions, respectively.

If there is no problem even if only one side of the terminal part is exposed and the other side is insulated, when pattern coating the insulating layer 12, 12', the first insulating layer 12 is Provided uniformly up to the tip of the terminal portion 11A, the second
The insulating layer 12' is not provided in the terminal portion 11^.

Alternatively, as shown in FIG. 8, it is also possible to provide the end portion of the first insulating layer 12 only on the soil of the terminal portion 11A.

In this way, the insulating layer 12 can also be used as a reinforcing material for the terminal portion 11.

FIG. 9, FIG. 1O, and FIG. 11 show three embodiments of the flexible wiring board of the present invention having different land portion structures.

In the embodiment shown in FIG. 9, an insulating layer 1 is formed on both sides of the land portion 11B.
2 and 12' are not provided.

In the embodiment shown in FIG. 1θ, the uncovered portion of the insulating layer 12, that is, the opening portion is made larger than the land portion 11B.

In the embodiment shown in FIG. 11, a through hole 20 is formed in the land portion 11B, and a bottle or the like can be inserted into this hole 20.

The explanation so far has mainly been about the flexible wiring board at the terminal portion, but the terminal portion does not necessarily need to be provided in advance. It is also possible to cut out necessary dimensions from a flexible wiring board with no exposed terminal portions, and remove the polyimide resin with a corrosive solution such as hydrazine to expose the terminal portions.

[Effects of the Invention] As described above, according to the present invention, since there is no adhesive layer between the conductive layer and the insulating layer, there is no deterioration due to heat caused by the adhesive, and the heat resistance of the polyimide resin is improved. By taking advantage of the characteristics, it is possible to obtain a high-quality flexible wiring board with excellent heat resistance, and furthermore, such a wiring board can be easily manufactured using a simple manufacturing process.

[Brief explanation of drawings]

1(a) and (b) are plan views showing an embodiment of the flexible wiring board of the present invention, and FIG. 1(C) and (d) are respectively shown in FIG. 1(a).
Figure 1(e) is Figure 1(b) +7) Z-Z line sectional view,
Figure 2 is a sectional view showing the structure of a conventional flexible wiring board, Figures 3 (a) to (e), Figures 4 (a) to (e), and Figures 5 (a) to (e) are 6 is a sectional view showing the structure of another embodiment of the flexible wiring board of the invention; FIGS. 7 and 8 are sectional views of the flexible wiring board of the invention. 9 to 11 are cross-sectional views showing two other embodiments of the terminal portion of the board, and FIGS. 9 to 11 are cross-sectional views showing three other embodiments of the land portion of the flexible wiring board of the present invention. DESCRIPTION OF SYMBOLS 1... Base film, 2.4... Adhesive, 3... Conductor, 5... Coverlay film, 11... Conductor plate, 11A... Terminal part, 11B... Land part , 12, 12'... Insulating layer made of polyimide resin, 13... Photoresist layer, 21... Metal thin plate, 22... Resist pattern, 23... Conductor pattern, 24, 24'... - Insulating layer made of polyimide resin, 25, 25'...land. ^ ^
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e) ＾ Figure 4 National Invention f') 4 A gruesome face of the late J (Sha 4 Ta 1) Figure 6 4 Lyse Ming's I, mostly excerpted from the 11th face view - ゝ2θ penetrating lotus hole

Claims (1)

[Scope of Claims] 1) A flexible wiring board characterized in that only a predetermined portion of both the front and back surfaces of a metal conductor plate is directly coated with a polyimide resin. 2) A metal conductor plate has a terminal portion of a metal conductor on at least one end portion, at least one side of the terminal portion is not covered with an insulating layer, and both the front and back surfaces of the metal conductor plate other than the terminal portion A flexible wiring board characterized in that only predetermined portions are directly covered with polyimide resin. 3) forming a photoresist pattern on a thin metal plate; forming a conductor pattern on the metal thin plate using the photoresist pattern; and a predetermined portion of the surface of the metal thin plate on the side where the conductor pattern is provided. a step of forming a first insulating layer by coating a solvent-soluble polyimide resin only on the surface; a step of removing the metal thin plate; and a step of coating a solvent-soluble polyimide resin only on a predetermined portion of the surface from which the metal thin plate has been removed. A method for manufacturing a flexible wiring board, comprising the step of forming a second insulating layer by coating with resin.