JPH01283996A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To reduce thermal expansion coefficients of directions X, Y, Z by forming an insulating layer between patterns of unidirectional fiber reinforced plastic. CONSTITUTION:Insulating layers 10 formed between patterns 1a and 2a, 2a and 2b, and 1b and 2b are formed of unidirectional fiber reinforced plastic 8, and vertically laminated unidirectional fiber reinforced plastic 9. Reinforcing fiber generally has small thermal expansion coefficient itself. Accordingly, if the fiber volume content ratio is raised, the coefficient can be reduced. That is, the unidirectional fiber reinforced plastic is used as the insulating layer, the fiber volume content ratio is raised, thereby reducing the thermal expansion coefficients in directions X, Y, Z.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multilayer printed wiring board that has a low coefficient of thermal expansion as a substrate, is therefore suitable for surface mounting of ceramic chips, and has highly reliable through holes. It is.

(Prior art) Conventional multilayer printed wiring boards have a structure in which the insulating layer between metal patterns is made of fiber-reinforced plastic made by impregnating glass fabric with epoxy resin or polyimide resin and curing it. It has become.

FIG. 2 shows an example of the structure of such a conventional multilayer printed wiring board (four-layer board).

In the figure, la and lb are metal outer layer patterns, 2a
, 2b indicates a metal inner layer pattern.

3 is a fully bent plating layer with through holes, and the outer layer pattern la
, lb and are connected to the inner layer pattern 2b. 7 is an insulating layer made of epoxy resin or polyimide resin on glass fabric.
It is made of fiber-reinforced plastic impregnated with T and cured. In the insulating layer 7, 4 indicates horizontal glass fibers, 5 indicates vertical glass fibers, and 6 indicates a resin layer.

[Problem to be solved by the invention]

However, in the conventional multilayer printed wiring board, the insulating layer 7
However, as mentioned above, it is made of fiber-reinforced plastic made by impregnating glass fabric with epoxy resin or polyimide resin and curing it. Therefore, the fiber volume content Vf is 50%
Therefore, it has the disadvantage of having a large coefficient of thermal expansion in the XY direction and Z direction (5-axis direction).

For this reason, there have been problems with surface mounting of ceramic chips and with the reliability of through holes when the number of layers increases.

That is, a ceramic chip, for example, an alumina chip carrier, has a thermal expansion coefficient of 5.5 to 6.5xlO-'
Therefore, if surface mounting is carried out on a conventional glass epoxy board with a temperature of about 16 x 10-'°C-1 or a glass polyimide board with a temperature of about 14 x 10-6°C-1, thermal stress can be fatal to the solder joint. There was a risk that it might get in.

Furthermore, in recent years, there has been a tendency for printed wiring boards to become more and more multilayered, and as a result, board thickness has also tended to increase. However, since the fiber-reinforced plastic has a still large coefficient of thermal expansion in the Z direction, there is a risk of cracks occurring in the metal plating layer of the through hole, resulting in a lack of reliability.

Of course, such a problem can be solved by reducing the thermal expansion coefficient.

In other words, reinforced fibers have a very small coefficient of thermal expansion; for example, glass fibers have a coefficient of thermal expansion of approximately 5.0 x 10-6°C.
It is 1. In addition, it is large for resins, for example, about 50 to 125xlO-'C-1 for epoxy resins. Therefore, from this fact, the thermal expansion coefficient can be reduced by increasing the fiber volume content vf. That's right,
The above problem can be solved.

However, in the case of conventional fiber-reinforced plastics, since textiles are used as reinforcement materials, the vertical and horizontal fibers overlap each other, creating many spaces without ya groups, which are filled with resin to increase the fiber volume content. It is difficult to increase the ratio v1 to 50% or more. Therefore, as long as conventional MM reinforced plastics are used, it is difficult to solve the above problems.

This invention was made to solve these conventional problems, and has a small coefficient of thermal expansion in the X, Y, and Z directions, making it possible to surface-mount ceramic chips, and improving the reliability of through-holes. The objective is to obtain a multilayer printed wiring board with high resistance.

(Means for Solving the Problems) In the multilayer printed wiring board according to the present invention, metal patterns and insulating layers between the patterns are formed of unidirectional fiber-reinforced plastic.

[Effect]

In this invention, since unidirectional fiber-reinforced plastic is used for the insulating layer, the fiber volume content V' can be increased and the coefficient of thermal expansion in the XYZ directions can be reduced.

(Example) An embodiment of the present invention will be described below with reference to FIG.

Figure 1 shows the configuration of a four-layer board.
a and lb indicate metal outer layer patterns, and 2a and 2b indicate metal inner layer patterns. Reference numeral 3 denotes a metal plating layer of through holes, which is connected to the outer layer patterns la and lb and the inner layer pattern 2b. 10 is pattern 1a and 28, pattern 2
A unidirectional fiber-reinforced plastic 8 laminated in the horizontal direction with an insulating layer provided between a and 2b and patterns 1b and 2b.
and unidirectional fiber-reinforced plastic 9 laminated in the vertical direction.
It is formed by

The fiber-reinforced plastic that forms the insulating layer 7 of the conventional multilayer printed wiring board has a structure in which the vertical and horizontal fibers of the fabric, which is the reinforcing material, intersect vertically and overlap each other, so there are many layers between each fiber. A space is created, which is filled with resin to form a clear resin layer 6 as shown in FIG. Therefore, the fiber volume content V is usually 50% or less, and the coefficient of thermal expansion in the x, y, and z directions is large. On the other hand, the unidirectional fiber-reinforced plastics 4 and 5 have a structure in which the resin is mixed between the fibers, so the fiber volume content V, becomes large, and X.

The coefficient of thermal expansion in the Y and Z directions is small.

Table 1 shows three types of multilayer printed wiring boards (
Examples 1 to 3) were prepared, and the results of measuring their thermal expansion coefficients at room temperature are shown together with comparative examples.

Table 1 In Table 1, the glass fabrics are No. manufactured by Asahi Schniebel Co., Ltd.
7628, the epoxy resin is FR-4 grade product, the polyimide resin is Kerimide 601 manufactured by Mitsui Petrochemical Industries, Ltd., and the unidirectional glass m fiber is ERI 15 manufactured by Asahi Fiberglass Co., Ltd.
0. One-way aramid mtm is DuPont Kevlar 49
Type 968 was used in each case.

As is clear from Table 1, the multilayer printed wiring boards of Examples 1 to 3 all had a large fiber volume content vr, but had small coefficients of thermal expansion in the x, y, and z directions. .

(Effects of the Invention) As described above, according to the present invention, since the insulating layer between the patterns is formed of unidirectional fiber-reinforced plastic, the coefficient of thermal expansion in the xYZ directions can be reduced, making it suitable for surface mounting. It is possible to obtain a multilayer printed wiring board that is suitable and has high through-hole reliability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a multilayer printed wiring board according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional multilayer printed wiring board. la and lb are outer layer patterns, 2a and 2b are inner layer patterns, 3 is a through-hole metal plating layer, 8.9 is a unidirectional fiber reinforced plastic, and 10 is an insulating layer. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A multilayer printed wiring board characterized in that an insulating layer between patterns is made of unidirectional fiber-reinforced plastic.