JPH0812954B2 - Printed wiring board - Google Patents

Description

The present invention relates to a printed wiring board.

<Prior Art> Conventionally, a flexible printed wiring board (FPC) material of a composite multilayer printed wiring board is a FPC alone which is formed by thermocompression bonding a film obtained by applying an adhesive to a polyimide film called a film cover lay. Some conductors are protected. The film coverlay also insulates the conductors of the rigid printed wiring board (PWB) material and the conductors of the FPC material.

FIG. 4 is a cross-sectional view of a conventional four-layer wiring board, and FIG. 5 is a cross-sectional view showing its manufacturing process over time.

As shown in FIG. 4, the film cover lay 20 is thermocompression bonded onto the copper foil 80 pattern-etched in the copper-clad PFC material 10. Further, the adhesive sheet 30 and the copper-clad PWB material 40 are laminated on the part excluding the range corresponding to the FPC single part. The through hole 100 is formed in the substrate in such a state, and the copper plating layer 50 is formed on the through hole 100 and the copper foil 90. Further, a solder resist 60 is applied on the pattern-etched copper plating layer 50.

The printed wiring board having such a structure is formed by the manufacturing process shown in FIG.

(A) As shown in the figure, a copper foil 80 is formed by pattern-etching a circuit in the copper-clad FPC material 10.

Next, as shown in FIG. 2B, the film cover 20 is thermocompression-bonded onto the copper foil 80 except for the lower portion of the copper-clad FPC material 10 in the range corresponding to the FPC unit.

Next, as shown in FIG. 3C, the adhesive sheet 30 and the copper-clad PWB material 40 are overlaid and thermocompression-bonded on the portion excluding the area corresponding to the FPC simple portion.

Next, as shown in FIG. 3D, a through hole 100 is formed by making a hole in the reference of the inner layer circuit by drilling or the like. Further, copper plating is performed on the substrate surface to form a copper plating layer 50.

Furthermore, as shown in FIG. 4, copper foil of copper-clad PWB material 40 9
0 and the copper plating layer 50 are pattern-etched, and a solder resist 60 is applied on the remaining copper plating layer 50.

<Problems to be Solved by the Invention> By the way, in the above-mentioned conventional technique, the polymide and the adhesive used in the film cover lay are very easy to absorb moisture, and in the printed wiring board using these, If baking is not performed before soldering the components and moisture is not sufficiently removed, the moisture vaporizes and expands during soldering, and the film cover lay peels off. This is because the adhesive of the film cover lay softens due to the heat during soldering,
It is also because the adhesive strength is almost lost.

In the conventional 4-layer structure, the film coverlay is also laminated on the part where the PWB material is laminated, but since the conductor of the FPC is protected by the PWB material in this part, it functions without the film coverlay. There is no problem. But FP
When the film cover lay is thermocompression-bonded only to the C single part, the FPC material shrinks more in the part where the film cover lay is present than in the other part, which hinders the alignment in the subsequent hole forming process. In addition, in order to prevent warpage caused by differences in shrinkage during heat treatment such as soldering, the printed wiring board with a structure in which various materials are stacked has different types of materials and thicknesses in the stacking direction. It needs to be more symmetrical than the center. Therefore, an expensive film cover lay has to be attached on both sides, and attaching the film cover lay in such a range that is not functionally required causes a high cost.

In addition, the two thermocompression bonding processes, that is, the film coverlay application process and the PWB material lamination process, cause variations in the finished dimensions of the FPC.
It is necessary to secure a conductor with a large area when forming a through hole for conducting a material. This is FP
It is an obstacle to increasing the pattern density of the C conductor.

Furthermore, when such a film cover lay is pasted, the FPC unit portion becomes thick, and the flexibility of the FPC substrate is deteriorated, and the bending diameter is limited.

The printed wiring board of the present invention solves these problems.

<Means for Solving the Problems> The printed wiring board of the present invention is a composite in which a flexible printed wiring board material and a hard printed wiring board material are laminated with an adhesive, and each conductor is made conductive by through-hole copper plating. The multilayer printed wiring board is characterized in that, among the above-mentioned flexible printed wiring board materials, at least a portion where a hard printed wiring board material is not laminated is covered with a polyimide-based ink.

<Function> The polyimide-based ink is applied to at least a portion of the flexible printed wiring board material where the hard printed wiring board material is not laminated, thereby protecting a single portion of the flexible printed wiring board material and not losing flexibility. .

<Embodiment> FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view showing its manufacturing process over time, and FIG. 3 is a sectional view of another embodiment of the present invention. Embodiments of the present invention will be described in detail below with reference to the drawings.

In the embodiment of the present invention, as shown in FIG. 1, a polymide-based ink 7 is formed in a region corresponding to a single FPC portion on a copper foil 8 pattern-etched on a copper-clad FPC material 1.
On the copper foil 8, the adhesive sheet 3 and the copper-clad PWB material 4 are formed in the portion excluding the area corresponding to the single FPC portion.
Through-holes 10 are formed in the substrate in such a state, and copper-plated layer 5 is formed on the through-holes 10 and copper foil 9. Further, a solder resist 6 is formed on the pattern-etched copper plating layer 5.

The printed wiring board having such a structure is formed by the manufacturing process shown in FIG.

(A) As shown in the figure, a copper foil 8 is formed by pattern-etching a circuit in the copper-clad FPC material 1.

Next, as shown in FIG. 3B, the polymide-based ink 7 is applied by screen printing to the area that will be the FPC simple substance portion, and then cured at a predetermined temperature and time. Since the copper foil 8 exposed in this step is easily oxidized and discolors, the discolored portion is removed by polishing with a brush, immersion in dilute sulfuric acid, or the like. In addition, the polymide-based ink 7 used in this process
There are various curing temperatures and times, but FP
It can be selected depending on how to combine with C material. That is, when the polymide-based ink 7 has a curing temperature of 260 ° C. and a time of about 10 seconds, it is suitable to use a conveyor furnace, and as the FPC material 1, a copper foil is attached to the polymide film with an epoxy-based adhesive. A structure can be used. Further, when the polymide-based ink 7 requires a curing temperature of 260 ° C. and a time of about 10 seconds or more, the FPC material 1 has a structure in which the polymide film and the copper foil are directly bonded without an epoxy-based adhesive. Is suitable.

Next, as shown in FIG. 3C, the copper-clad PWB material 4 and the adhesive sheet 3 are overlapped and thermocompression-bonded to the portion excluding the area corresponding to the single FPC portion.

Next, as shown in (d), a predetermined position of the wiring board in the state of (c) is punched, copper plating is performed on the through hole 10 and the surface of the wiring board, and the copper plating layer 5 is formed. Form.

Finally, the copper foil 9 and the copper plating layer 5 are pattern-etched, and a solder resist 6 is applied to form a first pattern.
A printed wiring board as shown can be formed.

Next, FIG. 3 shows another embodiment of the present invention, showing a case of a 6-layer wiring board, in which the polymide-based ink 7 is used for the PPC other than the FPC unit.
It is characterized in that it is also applied to the portion where the WB material 4 is bonded. In the manufacturing process, the PWB material 4 obtained by coating the copper foil 8 by applying the polymide-based ink 7 to a predetermined portion as described above and then pattern-etching the inner layer side circuit on the material copper-clad on both sides is used as the FPC simple substance. The PFC material 1 is superposed on the PFC material 1 through the adhesive sheet 3 except for the area corresponding to the portion and thermocompression bonded. After that, holes are formed in the same manner as in the four-layer wiring board, pattern etching is performed on the outer layer side of the PWB material 4, and the solder resist 6 is applied. The curing temperature of the polymide-based ink is as high as 260 ° C, and the heat resistance is superior to that of the conventional adhesive for the film coverlay, and the ink does not peel off at the soldering temperature of 240 to 250 ° C. Further, such heat treatment can be performed in a short time, and it is not necessary to apply pressure.

<Effects of the Invention> The material cost of the polymide ink is lower than that of the film cover lay, and the processing ratio is higher than that of the thermocompression bonding of the film cover lay because it is applied by screen printing and cured by a conveyor furnace or BOX furnace. Very few and very short processing time. Therefore, the manufacturing cost is significantly reduced.

Even when the polymide-based ink is partially applied to the FPC material and cured, the curing time is shorter than the thermocompression bonding of the film coverlay, and there is no need to apply pressure. Small quantity and small variation.

Therefore, even after the PWB material is laminated, the variation in the finished dimensions of the FPC material is smaller than when using the conventional film cover lay, and the inner layer conductor can be drilled more accurately than before, so it is connected to the through hole. The area of the inner layer conductor can be reduced, and high-density wiring can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view showing manufacturing steps of the embodiment of the present invention over time, FIG. 3 is a sectional view of another embodiment of the present invention, and FIG. FIG. 5 is a cross-sectional view of the conventional example, and FIG. 5 is a cross-sectional view showing the manufacturing process of the conventional example over time. 1 …… Copper-clad FPC material 3 …… Adhesive sheet 4 …… Copper-clad PWB material 5 …… Copper plating layer 6 …… Solder resist 7 …… Polymide ink 8,9 …… Copper foil 10 …… Through hole

Claims (1)

[Claims] 1. A composite multilayer printed wiring board in which a flexible printed wiring board material and a hard printed wiring board material are laminated via an adhesive, and each conductor is electrically connected by through-hole conductive plating. Among them, a printed wiring board is characterized in that at least a portion where a hard printed wiring board material is not laminated is covered with a polyimide-based ink.