JPS624878B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit board, and particularly to a so-called multilayer circuit board in which a plurality of wiring patterns are stacked and the wiring patterns in each layer are electrically connected through through holes.

First, in order to facilitate understanding of the present invention, a conventional multilayer circuit board will be explained. FIG. 1 shows an example of a conventional multilayer circuit board in the order of steps. First, as shown in A and B in the same figure, copper foils are placed on the upper and lower surfaces of an insulating substrate 1 made of phenol resin, epoxy resin, etc. A so-called copper-clad laminate 3 made of copper-clad laminates 2 and 2' is provided, and through-holes 4 that pass through the laminate 3 vertically are bored at desired positions, and then the inner surface of the through-hole 4 and the copper foil are A copper plating layer 5 is formed by sequentially applying chemical plating and electroplating to the surface so as to include 2 and 2' (FIG. C), and then an etching resist 6 is applied in the through hole 4.
At the same time, an etching resist 7 with a pattern corresponding to the wiring pattern is printed on the copper foils 2 and 2' (D and E in the same figure), and then resists 6 and 7 are etched as shown in F and G in the same figure. After selectively etching the copper foils 2 and 2' as masks to form wiring patterns 8 and 8', respectively, the resists 6 and 7 are removed.

Figure 3 shows another example of a conventional multilayer circuit board.
This is done by first selectively etching the copper foils 2 and 2' on the same copper-clad laminate 3 as above to form the wiring pattern 8.
and 8' (see A and B in the same figure), and then, after drilling a through hole 4 spanning patterns 8 and 8' at a required position, silver paint 9 is filled in the through hole 4, and both wiring patterns are formed. 8 and 8' are electrically connected.

However, the conventional multilayer circuit boards shown in FIGS. 1 and 3 have the following drawbacks. For example, in the multilayer circuit board 10 shown in FIG.
The process of plating is complicated and the yield is low, and the wastewater treatment due to pollution is not easy.The copper plating layer 5 is plated all over, and the copper deposits in unnecessary areas are wasted, as shown in Fig. 2. After forming the copper plating layer 5, the wiring pattern 8 or 8' is formed by the undercut 12 during selective etching.
There were drawbacks such as thinning and poor pattern accuracy. Furthermore, in the multilayer circuit board 11 shown in FIG. 3, the silver paint 9 filled into the through holes 4 contains a large amount of resin and solvent, so as shown in FIG. Disadvantages include that even if the resistance is increased, there is a limit to the resistance value (10 ^-4 Ωcm), breakage is likely to occur, and it is difficult to fill the small-diameter through hole 4 with silver paint 9, making it difficult to create a high-density circuit. It was hot.

The present invention solves the above-mentioned conventional drawbacks and provides a circuit board that is easy to manufacture and has high reliability.

Hereinafter, the circuit board according to the present invention and its manufacturing method will be explained using FIGS. 5 to 7.

In the present invention, as shown in FIG. 5A, a so-called copper-clad laminate 3 is prepared by coating copper foils 2 and 2' on the upper and lower surfaces of an insulating substrate 1 made of, for example, phenolic resin, epoxy resin, etc. Next, the upper and lower copper foils 2 and 2' of the laminated board 3 are selectively etched to form predetermined wiring patterns 8 and 8' on both sides of the board 1, respectively. A through hole 4 is formed so as to span the patterns 8 and 8' (FIGS. 5B and 5C). After that, the through hole 4 is filled with a paste-like metal mixture 15, which will be described in detail below, and this mixture 15 is solidified as an alloy to form a conductor that electrically connects both wiring patterns 8 and 8'. 17 is formed to constitute the intended circuit board 18 shown in FIG.

As shown in FIGS. 6A and 6B, the mixture 15 is made by mixing an appropriate amount of a metal 13 that is liquid at room temperature and a metal powder 14 (single metal powder or alloy powder) that can form an alloy with the metal 13. This mixture 15
initially forms a paste, and over time it alloys and solidifies. That is, it becomes an alloy solid 16 as shown in FIG. 6C. The solidified alloy is generally called an amalgam.
Mercury Hg is suitable as the metal 13 which is liquid at room temperature. Also, a metal powder 14 alloyed with the metal 13,
Therefore, metal powders that can be alloyed with mercury include, for example, silver Ag, tin Sn, copper Cu, and palladium.
Pd, zinc Zn, indium In, gold Au, aluminum Al, etc., and alloys such as Ag-Sn-Cu, Ag-Sn, Cu-
Sn, Ag- _Sn -Pb, etc. can be used, and the alloyed form is _Ag2Hg3 , _Sn7Hg , _{Cu2Hg3 ,} etc.
The particle size of these metal powders 14 is preferably in the range of 0.5μ to 200μ. The mixing ratio of liquid metal 13 and metal powder 14 is 30: liquid metal 13:metal powder 14.
A range of 70 to 70:30 (wt%) is preferred. If the metal powder exceeds 70% by weight, the mixture 15 will not become pasty, and if it is less than 30% by weight, the liquid metal 13, in this example mercury Hg, will remain and will not solidify completely. On the other hand, after the process shown in FIG. 5C, the through holes 4 are filled with the mixture 15, as shown in FIG. 1 and fill it with the mixture 15 using a squeegee 20. Furthermore, mercury Hg
By mixing the metal powder 14 and the metal powder 14 for 1 to 2 minutes, a plastic paste-like mixture 15 is obtained, and this mixture is filled and alloyed and solidified at room temperature for one day. During filling, the mixture 15 is not attached to the surface of the substrate 1 due to surface tension and is filled only into the through holes 4, so that the surface of the substrate is not contaminated. Furthermore, small-diameter through holes 4 can be easily filled.

In addition, in FIG. 5, the application is applied to a two-layer circuit board having wiring patterns 8 and 8' on both sides, but as shown in FIG. Of course, the present invention can also be applied to

According to the present invention described above, the volume of the conductor 17 after filling is reduced by filling the through hole 4 with the mixture 15 made entirely of metals, which is paste-like at room temperature and has the property of alloying and solidifying over time. There is no shrinkage, and the resistance of the conductor 17 in the through hole 4 is determined by the specific resistance of the metal, and exhibits an excellent value. For example, thickness
Comparing the conductor resistance in the through hole 4 with a diameter of 1.6 mm and 0.5 mm, it is 0.35 with copper plating (in the case of Figure 1).
mΩ, 500m for silver paint (in the case of Figure 3)
Ω, in the present invention (Ag-Sn-Hg), was 0.9 mΩ, and it is recognized that the present invention is superior.

In addition, the manufacturing process is simplified because the same process as in the case of FIG. 3, in which electrical conduction is achieved using silver paint, is sufficient, and filling with the mixture is also easy.
Further, since it is easy to fill the mixture 15 into the small-diameter through-holes 4, high-density wiring can be easily achieved, and a highly reliable circuit board can be provided.

[Brief explanation of the drawing]

FIGS. 1A to 1G are cross-sectional views showing an example of a conventional multilayer circuit board in the order of steps; FIG. 2 is a cross-sectional view of its main parts;
FIG. 3 is a sectional view showing another example of a conventional multilayer circuit board in the order of steps, FIG. 4 is a sectional view of its main parts, and FIG. 5 is a sectional view in order of steps showing an example of the circuit board of the present invention. ,
6A to 6C are diagrams showing the form of the mixture applied in the present invention, FIG. 7 is a cross-sectional view showing an example of a method of filling the mixture, and FIG. 8 is a cross-sectional view showing another example of the circuit board of the present invention. It is a diagram. 1 is an insulating substrate, 4 is a through hole, 8 and 8' are wiring patterns, 13 is a metal that is liquid at room temperature, 14 is another metal powder, 15 is a mixture, and 17 is a conductor.

Claims (1)

[Claims] 1 first and second wiring formed through an insulated substrate, a through hole formed in the substrate across the first and second wiring, and a through hole filled with the first wiring. and a conductor that electrically connects the second wiring, the conductor being made of an alloy of a first metal and another metal that is liquid at room temperature.