JPS5939096A - Method of producing multilayer printed circuit board - 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 applications It is related to

Conventional configurations and problems The demand for multilayer printed wiring boards has been increasing significantly with the development of computer equipment, and further growth in demand is expected in the future as the functionality of electronic equipment improves. be. However, since the manufacturing method is complicated and expensive materials are used, the cost inevitably increases, and it has not been possible to meet the demands of users. Therefore, the conventional manufacturing method will be explained below.

Without cutting, the inner layer laminate of the copper-clad glass cloth base epoxy resin was etched to form the desired circuit and serve as the inner layer board.
Through prepreg, which is an uncured adhesive layer made of glass cloth base epoxy resin laminate, on the front and back of this inner layer substrate,
After heating and pressurizing the double-sided copper-clad glass cloth base epoxy resin laminate to integrate it, through holes are made by drilling or the like. Next, an activation treatment is performed to deposit electroless copper plating in the through hole, followed by electroless copper plating and further electrolytic copper plating, so that the copper plating is sufficient to ensure through-hole connection to the through hole wall.・Thickness (for example, 358 was applied. After that,
Apply a dry film resist to the surface of the substrate, such as Liston (
Using a method called tenting, an etching resist layer is formed using a method called tenting (trademark of Teyupon Co., Ltd., USA), and the desired outer layer conductor circuit 1, through-hole plating 2, and inner layer circuit 3 are etched as shown in FIG. A multilayer printed wiring board was obtained.

However, this manufacturing method has the disadvantage that electroless copper plating and electrolytic copper plating are used together, and the plating thickness on the front and back of the board is uneven because electrolytic copper plating cannot be used to thicken the conductor to the desired thickness. , conductor medium CL20 m
When the thickness is less than m, there is a problem that even if uniform etching is performed, a uniform conductor cannot be obtained due to variations in thickness.

Unfortunately, there is no adhesive between the surface copper foil and the base material, so the so-called copper foil and glass cloth base epoxy resin layer uses the epoxy resin on the surface layer for the adhesive layer, so it is difficult to solder after completion. There was a problem in that cracks called through-hole cracks were likely to occur between the through-hole plating and the surface conductor, and between the through-hole plating and the inner layer conductor during severe thermal shock tests assuming the application and usage environment.

This disadvantage has the disadvantage that only glass cloth-based epoxy resin laminates with a small coefficient of thermal expansion can be put to practical use.For the reasons mentioned above, capital investment is enormous, material costs are high, and the price of the finished product is high. There was a problem.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, the present invention provides a method for manufacturing a multilayer printed wiring board that has excellent through-hole connection reliability and can be manufactured easily and at low cost.

Structure of the Invention In order to achieve the above-mentioned object, the present invention heats and press-forms an outer layer laminate with an uncured adhesive layer interposed on the front and back surfaces of an inner layer substrate on which a circuit is formed. An adhesive layer such as nitrile butadiene rubber is formed on the surface of the laminate,
Further, a plating resist layer is formed on the surface, through-holes are bored at desired positions, and the copper conductor circuit is then immersed in an electroless copper plating solution.

By using only electroless copper plating, a large amount of multilayer printed wiring boards can be plated at a low cost, and the copper plating is done through an adhesive layer such as nitrile butadiene rubber. The adhesive layer acts to absorb impact on the copper plating, making through-hole cracks less likely to occur, and the reliability of through-hole connections is extremely high.

DESCRIPTION OF EMBODIMENTS A method of manufacturing a multilayer printed wiring board according to an embodiment of the present invention will be described below with reference to the drawings.

As shown in Fig. 2, 1; an inner layer laminate 5 made of double-sided steel-clad paper base epoxy resin with a thickness of 0.2 mm and covered with a copper foil circuit 4 with a thickness of 35 μm is etched into a desired circuit pattern, and an inner layer board is formed. 5a.

Next, as shown in Fig. 3, 12 inner layer substrates 5, front and back 1; prepreg 6, which is a type of paper-based epoxy resin laminate, each having a thickness of 0.2 πm and a paper-based epoxy resin having a thickness of 0.6 πm. Using a heat press, heat the outer layer of the laminated plate at a temperature of 180°.
Heat and pressure mold at a C2 pressure of 80 kg/c for 1 hour. At this time, the prepreg 6 used is one in which the epoxy resin is not completely cured, that is, the curing reaction is at one stage, and is used as the adhesive layer between the inner layer substrate 52L and the outer layer laminate 6.

As shown in FIG. 4, nitrile butadiene rubber 8 is coated to a thickness of 3Q μm with a curtain coater on the surface of the outer layer laminated board having the inner layer 1′ and the copper foil circuit 4 integrally molded in this way and cured. let Thereafter, an Evokin-based plating resist 9 is screen printed in a reverse pattern and cured, and further, through-holes 10 that require plating are punched out by press punching. In the above case, the outer layer laminate 7 and the inner layer substrate 5
If the nuclei for electroless copper plating are formed in advance by dispersing palladium chloride in a, the prepreg 6, and the nitrile rubber 8, it is possible to omit the activation treatment in the pretreatment for electroless copper plating below. possible, and the process can be shortened.

Next, the substrate formed by the above process was mixed with a chromic acid aqueous solution (
After roughening the nitrile butadiene rubber 8 on the outer layer laminate 7 and cleaning the end face of the copper foil circuit 4 in the through hole 10, the electroless copper plating solution (not shown) is applied. ) to form a through-hole plated conductor 11 with a thickness of 36 μm and an outer layer conductor 12 as shown in FIG.

Thereafter, post-processing required for ordinary printed wiring boards, such as solder resist printing and component layout printing finishing processing, is performed to obtain a multilayer wiring board.

A method of manufacturing a multilayer wiring board according to another embodiment of the present invention will be described below with reference to the drawings of FIGS. 6 to 9.

Instead of the paper-based epoxy resin laminate described in the above example,
Glass cloth-based epoxy resin laminates were used for the inner layer laminate 13, the prepreg 14, and the outer layer laminate 15, respectively.

As shown in FIG. 6 in the same process as in the previous example, a curtain coater was used to apply a 30 μm thick 2L lilbudadiene rubber 8 on the outer layer laminate 15 of the glass cloth base epoxy resin which was integrally molded and had an inner layer circuit. After coating and curing, through-holes 16 requiring through-hole plating are drilled.

Next, as shown in FIG. 7, the laminate is immersed in a chromic acid aqueous solution (not shown), and the surface of the nitrile butadiene rubber 8 on the laminate and the end face of the copper foil circuit 4 in the through hole 16 are removed. After dissolving and removing the epoxy smear adhering to the surface by drilling, it is further immersed in a palladium chloride-tin chloride aqueous solution to precipitate plating nuclei for depositing electroless copper plating. (b) A conductor 17 with a thickness of 35 μm is formed on the wall surface of the Surbol and the outer layer surface of the laminate.

Next, as shown in FIG. 8, an etching resist 18 is formed on the surface of the laminate having the inner layer circuit which has been plated on the entire surface. This method involves filling the through-hole plating holes with an etching resist called the hole-filling method, and printing the etching resist into a circuit shape using screen printing for the outer layer, which requires less man-hours and costs less materials. However, if a conductor of 0.1 to 0.271 is desired, an etching resist may be formed by a photo printing method.

Next, the board is etched with a cupric chloride solution, and as shown in FIG.
1 and an outer layer conductor 12 is obtained. Of course, it is beyond the scope of the invention to perform processes required for ordinary printed wiring boards, such as solder resist printing as shown in the above embodiments.

Effects of the Invention As described above, in the present invention, since the elastic nitrile butadiene rubber is present as an adhesive layer between the outer layer laminate and the surface conductor, it acts as a damper during thermal shock, and the through-hole plated conductor and outer layer The connection with the conductor is highly reliable, and electroless copper plating provides a surface conductor with a uniform thickness, making it possible to form high-density circuits, and the material of the base material can be selected according to the application. It is possible to choose between a fully additive method, which is highly cost-effective, and highly suitable for mass production, depending on the need for cutting, or a combined method of etching, which forms a conductor circuit by etching electroless full-surface plating with a uniform thickness. Because it can be selected, its industrial value is significant.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a conventional multilayer printed wiring board, FIGS. 2 to 6 are process diagrams showing the manufacturing process in an embodiment of the present invention, and FIGS. 6 to 9 are It is a process diagram which shows the manufacturing process in another Example. 4... Copper foil circuit, 5, 13... Inner layer laminate, 5a゛゛... Inner layer board, 6, 14...
Prepreg, 7115... Outer layer laminate, 8...
...Nitrile butadiene rubber, 9...Plating resist, 10.16 Old...Through hole, 11...
...Through-hole plated conductor, 12...Group/outer layer conductor,
18...Etching resist. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 4 Figure 5 Figure 6 Figure 6 Figure 7 Figure l. N\ Umami δ Figure

Claims (4)

[Claims] (1) The copper-clad inner laminate is etched to form the desired circuit, and the outer laminate, which is not coated with copper foil, is heated and pressure-molded with an uncured adhesive layer interposed between the front and back sides of the inner layer board. After the integration, an adhesive layer such as nitrile butadiene laher is formed on the surface of the outer laminate, a plating resist is formed on the surface other than the desired circuit pattern, and through holes are drilled at desired positions. 1. A method for manufacturing a multilayer printed wiring board, comprising: forming a copper conductor circuit by immersing it in an electroless copper plating solution. (2) The multilayer according to claim 1, characterized in that the inner layer laminate and the outer layer laminate are made of glass cloth-based epoxy resin, paper-based epoxy resin, paper-based phenolic resin, or paper-based phenol resin. A method for manufacturing printed wiring boards. (3) Claim 1, characterized in that plating nuclei made of palladium chloride are dispersed in an adhesive layer such as nitrile butadiene rubber, an inner layer substrate, and an outer layer laminate.
A method for producing a multilayer printed wiring board as described in Section 1. (4) A method for producing a wiring board, in which a conductor is formed on an adhesive layer such as nitrile butadiene rubber and the entire surface of the through hole by electroless copper plating, and then an etching resist is printed in a desired circuit shape.