JPH0548959B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a double-sided printed wiring board having a flexible portion. [Prior art and problems] Conventional technology has been to reduce the thickness of the film in order to make the bent parts as flexible as possible in wiring boards that have bent and non-bent parts, and to apply electrolytic treatment to withstand repeated bending. A wiring board with a structure using rolled copper foil instead of copper foil has been put into practical use. In addition, in double-sided printed wiring boards, a method is adopted in which a through-hole plating layer for conducting conduction on both sides is not attached only to the bent portions. (Jikko 56-
(Refer to No. 54607) Copper foil made by electrolytic copper plating has a hard copper structure and will break in a short period of time if it is repeatedly bent, but rolled copper foil has a ductile structure and has significantly improved resistance to repeated fatigue. However, in recent years, the wiring materials used for floppy disk drives and hard disk drives are required to have a bendability of 10 ⁸ to 10 ⁹ times, and on the other hand, many ICs, resistors, capacitors, etc. have been mounted to greatly increase functionality. Demand for multilayer wiring boards is also high. Conventionally, a double-sided wiring section is formed by laminating two layers of insulating film and copper foil using an adhesive to form a circuit, but at this time, sufficient flexibility could not be obtained only by making the bent section a single layer. The reason for this is that the thickness of the adhesive layer in a single layer has a large effect on the bending properties, and if there is a sharp step at the interface between the non-bent part and the bent part, the stress in the bend part will be transferred to the edge part. This is because the wires become concentrated and break at the edges. [Structure of the Invention] The present invention solves the above-mentioned flexibility problem and relates to a manufacturing method capable of providing a double-sided printed wiring board having a flexible portion with extremely excellent flexibility despite being a double-sided wiring board. It is something. Briefly, the present invention provides a double-sided printed wiring board that is flexible and has high flexibility, by attaching an adhesive film to the base film except for the corresponding part on one side of the base film, which will be the bent part, and applying copper foil to the entire surface of the base film on both sides. After bonding and performing through-hole plating on the non-bent part, when forming the circuit, remove by etching the copper foil on the corresponding part on one side of the base film part that will be the bent part at the same time as the circuit is formed. There are characteristics. The present invention will be explained below with reference to FIGS. 1 to 4 showing the manufacturing process of the present invention. First, as shown in FIG. 1, an adhesive film 2 in a B-stage state is applied to an insulating base film 1 that is flexible and has high flexibility, and a rolled copper foil 3 is laminated thereon. Furthermore, a B-stage adhesive film 4 excluding the bent portion is pasted on the back surface, and then a rolled copper foil 5 is pasted thereon. After that, a plating hardening jig is set on the bent part to prevent the electroplating layer from adhering. The non-bent part has a through hole 6 for connecting a double-sided circuit.
is drilled in a predetermined position, and then through-hole plating is applied to areas other than the bent portions to form the through-hole plating layer 7.
form. In FIG. 2, A and A' respectively show both sides of the bent part, and B and B' each show one side of the non-bent part. It is desirable that the through-hole plating layer 7 be formed with a gentle step difference from the non-bent portion to the bent portion. After completing the through-hole plating, a circuit of a predetermined shape is formed on the front and back sides. At this time, the step between the bent part and the non-bent part is carefully exposed to light, developed, and etched so that the circuit can be formed uniformly. As shown in Fig. 3, a circuit is formed on the bent part A side.
The copper foil 4 on the surface of the bent part A' is etched completely,
The base film 1 is exposed to improve flexibility. After the circuit is formed, a film coverlay 9 coated with an adhesive 8 is attached to the front side in a predetermined shape, as shown in FIG. At this time, it is particularly desirable that the film coverlay of the bent part A be thin and flexible. Note that a solder resist coverlay 10 may be applied instead of the film coverlay 9. Although the circuit on the back side of the base film 1 is located in the non-bent part, it is desirable that the circuit be covered at least longer in the direction of the bent part than the through-hole plating part. If the non-bent part is a double-sided plate, it is desirable to make the bent part thinner than the normal thickness, and to have a smooth gradient in the through-hole plating layer at the boundary between the non-bent part and the bent part. Its slope is 10 times the thickness of the through-hole plating layer.
It is desirable that the distance be at least twice as long. If it is less than 10 times, not only will circuit defects occur at step portions when forming fine circuits, but also stress concentration will occur at the edge portions when the bent portion slides at high speed, resulting in wire breakage immediately. These things were discovered through numerous experiments. Furthermore, in order to not only obtain conductivity on both sides, but also to withstand reliability tests such as heat cycles, high temperatures, and high humidity, the thickness of the through-hole plating must be 3 μm in general, excluding at least the portions with the above-mentioned slope.
The above is necessary. [Example] 25μ and 75μ of polyimide as base film
using epoxy adhesive on one side.
25μ coated, B stage film and no film,
Laminated with 35μ rolled copper foil. On the other hand, after applying acrylic adhesive to release paper to a thickness of 30μ,
After drying to the stage, the adhesive film in the B stage state was punched out with a blade die in the portion corresponding to the bent portion. The punched adhesive film was pasted on one side of the base film, and a 35μ rolled copper foil was placed on top of it, and pressed at 180℃, 40 minutes, and 50Kg/ ^cm2 .
Heat bonded. The resulting double-sided board has no adhesive layer.
A through hole of 1.0 mmφ was drilled in the non-bent part, and then a 0.6 mm thick stainless steel plate was attached to the surface located in the bent part as an electrical insulation plate at a distance of 3 mm from the substrate. Thereafter, through-hole plating was applied to the entire surface of the through-hole area to a thickness of about 18μ.
As a result of measuring the plating thickness, the non-bent part was average
It was 19.3μ, but it was less than 0.2μ at the center of the bend.
In addition, the inner and outer boundaries of the electrical shield are approximately 4 to 6
It formed a plating layer with a gentle gradient at a distance of mm. The through-hole plated double-sided substrate was laminated with a photosensitive dry film, and as a result, it adhered uniformly at the stepped portions, and no problems occurred during exposure, development, and etching. I used one with a circuit width and circuit spacing of 150μ, but 35μ
It was possible to form a circuit with the same etching on the 50μ portion due to the step. After etching, apply 30μ of acrylic adhesive to a polyimide film with the same thickness as the base film.
The applied film coverlay was used to cover the circuit surface. A similar film coverlay was applied so as to cover the bent end of the back side of the base film. The flexible double-sided wiring boards thus obtained were each used as a sample for the sliding bending test. The sliding bending was repeated in a U-shape with a radius of 3 mm at a stroke of 30 mm, and the number of times it took for the 150μ circuit to break was determined. For comparison with the above example, a glass epoxy plate was attached to the bent part during through-hole plating to a conventional double-sided board in which adhesive was applied to both sides of the base film and copper foil was attached to the entire surface. A mechanical shielding mask was used, through-hole plating was performed, and then circuit formation was performed in the same manner as in the previous example, and a film coverlay was applied, and a sliding bending test was performed. The test results are shown in Table 1.

[Table] [Effects of the Invention] As can be seen from the above results, in the present invention, there is no adhesive layer on the back surface of the bent portion of the base film, and by eliminating the through-hole plating layer at the bent portion, the flexibility is greatly improved. Therefore, it is possible to produce a flexible double-sided wiring board with excellent flexibility and dust-free properties for use in floppy disk drives and hard disk drives without generating adhesive dust.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 sequentially show the manufacturing process of the flexible double-sided wiring board of the present invention. 1...Base film, 2...Base adhesive,
3...Copper foil, 4...B stage adhesive film, 5
...Copper foil, 6...Through hole, 7...Through hole plating layer, 8...Coverlay adhesive, 9...Film coverlay, 10...Solder resist coverlay.

Claims (1)

[Claims] 1. In manufacturing a flexible double-sided wiring board that is flexible and has high flexibility, an adhesive film in a B-stage state is attached to the entire surface of one side of the base film,
On the other side, a B-stage adhesive film is attached by punching out the parts corresponding to the bent parts of the wiring board, and then a board is made by laminating copper foil on the entire surface, and then through-holes are made in the non-bent parts. The holes are opened, through-hole plating is applied to prevent the plating layer from adhering to the bent portions, and a photosensitive film is pasted on both sides of the substrate, exposed, developed, and etched to form a circuit. A method for manufacturing a flexible double-sided wiring board, which comprises removing copper foil from a bent portion on one side. 2. The method for manufacturing a flexible double-sided wiring board according to claim 1, wherein after the circuit is formed, at least the boundary between the bent portion and the non-bent portion is covered with a coverlay. 3. The method for manufacturing a flexible double-sided wiring board according to claim 1, wherein the thickness of the through-hole plating is at least 3 μm, except for the end portions of the plating.