JPH0748591B2 - Multilayer printed wiring board - Google Patents

Description

The present invention relates to a multilayer printed wiring board which has a low coefficient of thermal expansion as a substrate and is therefore suitable for surface mounting of a ceramic chip or the like and has high through-hole reliability. Is.

[Prior Art] Conventionally, in a multilayer printed wiring board having wiring patterns made of metal in the inner layer and the outer layer, and insulating between them with fiber reinforced plastic, one-way glass fibers are impregnated with epoxy resin and semi-cured. There is one in which a directional prepreg is laminated in an orthogonal direction to form an insulating layer. In this kind of multilayer printed wiring board, the unidirectional fibers are not regulated in the lateral direction, so the fibers are disturbed by the softening flow of the resin during curing, which causes twisting, bending, and strength reduction of the product.

An improved multilayer printed wiring board for solving such a drawback has a structure in which a metal fiber pattern of an inner layer and an outer layer is insulated by a fiber reinforced plastic obtained by impregnating a glass fiber woven fabric with an epoxy resin or a polyimide resin and curing the same. have.

FIG. 3 is a vertical sectional view of a four-layer printed wiring board as an example of a conventional multilayer printed wiring board. In FIG.
(1a) and (1b) are metal outer layer patterns, and (2a) and (2
b) shows the inner layer pattern. (3) is the outer layer pattern (1
a), (1b), an inner layer pattern (2a), an insulating layer provided between (2b), a reinforcing fiber made of a woven fabric of warp yarn (4) and weft yarn (5) such as glass fiber is a resin. Layer (6)
Made of fiber reinforced plastic embedded in. (7) shows the through-hole metal plating, and the outer layer pattern (1
It is connected to a), (1b) and the inner layer pattern (2b).

In such a conventional multilayer printed wiring board, since the fibers are woven fabric, the fibers are not disturbed during curing, but they have the following drawbacks. That is, in the fiber-reinforced plastic layer that is the insulating layer (3), when the conventional glass fiber woven fabric is impregnated with epoxy resin or polyimide resin and cured, the coefficient of thermal expansion in the X, Y and Z directions (thickness direction) There is a limit to how small it can be made, and there are problems with surface mounting of ceramic chips and through-hole reliability when the number of layers increases. This is because ceramic chips are, for example, 5.5 to 6.5 × 10 ^-6 in alumina chip carriers.
It has a coefficient of thermal expansion of ℃ ^-1 , which is about 16 × 10 ^{-6 -1 for} conventional glass epoxy board and about 14 × 10 ^{-6 for} glass polyimide board.
If surface mounting is performed with a material having a coefficient of thermal expansion in the X and Y directions such as ° C ^-1 , fatal cracks may occur in the solder joint due to thermal stress.

Further, since the printed wiring board tends to be multi-layered in the future and therefore the board thickness also tends to be thick, if the coefficient of thermal expansion in the Z direction is large, cracks may occur in the metal plating layer of the through hole. Therefore, the appearance of a printed wiring board having a small coefficient of thermal expansion in the Z direction, that is, a highly reliable through-hole, is desired as a base material.

[Problems to be Solved by the Invention]

The present invention has been made to solve the above-described problems, and since twisting, bending, strength reduction, etc. of the product due to the disorder of the fiber at the time of curing do not occur and the fiber volume content increases, X , A thermal expansion coefficient in the Z direction as well as in the Y direction is small, a surface mounting of a ceramic chip or the like is possible, and a multilayer printed wiring board having a highly reliable through hole is obtained.

[Means for Solving the Problems]

The multilayer printed wiring board according to the present invention has a wiring pattern made of metal in the inner layer and the outer layer, and in the multilayer printed wiring board in which insulation is performed between them with fiber-reinforced plastic, the multilayer printed wiring boards are arranged in different directions and are respectively placed on the upper and lower sides without bending. A fiber-reinforced plastic using a non-crimp cloth in which movement of fibers is regulated by weaving or knitting fibers arranged so as to intersect with each other with an adhesive or a thin auxiliary thread is used as an insulating layer.

The non-crimp cloth is a general term for a woven fabric, a knitted fabric, or an adhesive cloth in which fibers in the vertical direction and the horizontal direction are arranged straight without bending. Due to their structure, non-crimp fabrics include those formed by adhering fibers in the vertical and horizontal directions, and those woven or knitted with a thin auxiliary thread. These are described in, for example, Japanese Patent Publication No. 57-52221, Japanese Patent Publication No. 58-104255, and Taft et al. (38th, SPI, 2-C).
(1983)) and the like.

[Action]

In the multilayer printed wiring board of the present invention, by using the non-crimp cloth as the insulating layer, the fibers are not disturbed at the time of curing, so that the product is not twisted or bent, and the strength is increased. Fiber volume content (Vf)
Rises and the coefficient of thermal expansion in the X, Y and Z directions decreases.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a vertical sectional view of a four-layer printed wiring board as a multilayer printed wiring board of an embodiment, and FIG. 2 is a plan view of a non-crimp cloth. In the drawing, the same reference numerals as those in FIG. 3 denote the same or corresponding parts. Show. The non-crimp fabric (11) has the warp yarns (4) and the weft yarns (5) made of glass fiber or the like arranged in a straight line so that they do not ride on each other like a normal plain weave cloth, and they are respectively placed above and below. They are arranged so that they are orthogonal to each other. In order to prevent the warp yarn (4) and the weft yarn (5) from being disturbed, the warp auxiliary yarn (12) and the weft auxiliary yarn (13) are woven with each other as the warp yarn (4) and the weft yarn (5). . Here, the vertical auxiliary thread (12) and the horizontal auxiliary thread (13) are bent up and down,
By using very thin and flexible yarns, the fabric (11) can be formed without reducing the density of the warp yarns (4) and the weft yarns (5).

Outer layer pattern (1a), (1b), Outer layer pattern (2a),
The insulating layer (3) provided between (2b) has a structure in which the reinforcing fiber made of the non-crimp cloth (11) is embedded in the resin layer (6). Other configurations are the same as those in FIG.

In the multilayer printed wiring board configured as described above, since the non-crimp fabric (11) has no bending (crimp) due to the crossing of the warp yarn (4) and the weft yarn (5), it is arranged straight. When a fiber reinforced plastic (FRP) is used, a molded product having a smooth surface is obtained, and the fiber volume content (Vf) can be increased by uniformly dispersing the fibers. And in terms of strength, 0 ° of unidirectional prepreg.
The characteristics are almost the same as when there is no fiber turbulence in the / 90 ° cross-laminated product, and since the fiber turbulence that is likely to occur in normal cross-laminated products does not occur, product twisting, bending, strength reduction, etc. Does not happen.

The effect of reducing the coefficient of thermal expansion by the fiber-reinforced plastic using the non-crimp cloth of the multilayer printed wiring board of the present invention is mainly due to the effect of increasing Vf. Means
Reinforcing fibers generally have a small coefficient of thermal expansion, for example, glass fibers have a thermal expansion coefficient of about 5.0 × 10 ^-6 ° C. ^-1 , while resins such as epoxy resins have a thermal expansion coefficient of about 50-125 × 10 ^-6 ° C. ^-1 . This is a large value, and it can be seen from this that the thermal expansion coefficient can be reduced by increasing Vf.

Further, the multilayer printed wiring board of the present invention has an advantage that dimensional shrinkage during press hardening is small. This is also warp thread (4)
Also, this is because the fibers of the weft yarn (5) are arranged in a straight line, which does not cause expansion and contraction at the bent portion of the yarn unlike a cloth. As a result, misalignment between the multilayer patterns is unlikely to occur and reliability is improved.

On the other hand, in the conventional insulating layer using the woven fabric, there is a limit in improving Vf, and it is usually difficult to set Vf = 50% or more. This is because in conventional fabrics, the warp yarn (4) and the weft yarn (5) ride on top of each other,
This is because there are many spaces without fibers as shown in the figure, and the space is filled with resin.

Comparing FIG. 1 and FIG. 3, although there is a clear resin layer (6) in FIG. 3 showing the conventional multilayer printed wiring board,
An embodiment of the present invention, FIG. 1, shows a clear resin layer (6).
Is almost absent, and the resin is mixed between the fibers of the warp yarn (4) and the weft yarn (5) of glass fiber to form a fiber-reinforced plastic layer. As described above, the fibers are densely filled in as much as the resin layer (6) is not formed.

Next, as examples and comparative examples, a multilayer printed circuit board having the structure shown in FIG. 1 was prepared, and the respective thermal expansion coefficients at room temperature were measured.

In Table 1, the glass fiber woven fabric is manufactured by Asahi Schwebel,
No.7628, Epoxy resin is FR-4 grade product, Polyimide resin is Kelimide 601 (trademark) manufactured by Mitsui Petrochemical Industry, Non-crimp glass fiber cloth is Composite Reinfo
Cofab (trademark) biaxial type manufactured by rcements Business was used.

From Table 1, it can be seen that Examples 1 and 2 clearly have lower thermal expansion coefficients in the X, Y, and Z directions than Comparative Examples 1 and 2 using the conventional glass fiber woven fabric.

〔The invention's effect〕

As described above, according to the present invention, since the fiber reinforced plastic using the non-crimp cloth is used as the insulating layer,
It is possible to obtain a multilayer printed wiring board having a small coefficient of thermal expansion in the X, Y and Z directions, suitable for surface mounting of a ceramic chip or the like, and having high through hole reliability.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a multilayer printed wiring board according to an embodiment of the present invention, FIG. 2 is a plan view showing an example of a non-crimp fabric used in the present invention, and FIG. 3 is a vertical view of a conventional multilayer printed wiring board. FIG. In each figure, the same reference numerals indicate the same or corresponding parts, and (1
a) and (1b) are outer layer patterns, (2a) and (2b) are inner layer patterns, (3) is an insulating layer, (4) is a warp yarn, (5) is a weft yarn, (6) is a resin layer, ( 7) is a through-hole metal plated portion, (11) is a non-crimp cloth, (12) is a vertical auxiliary thread, and (13) is a horizontal auxiliary thread.

Claims (1)

[Claims] 1. In a multilayer printed wiring board having metal wiring patterns in the inner layer and the outer layer, and insulating between them with fiber reinforced plastic, the wiring patterns are arranged in different directions and cross each other at upper and lower surfaces without bending. A multi-layer printed wiring board characterized by using, as an insulating layer, a fiber-reinforced plastic using a non-crimp cloth in which the movement of the fibers is regulated by weaving or knitting the fibers arranged in (1) with an adhesive or a thin auxiliary thread.