JP2770692B2 - Thick film multilayer circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick-film multilayer circuit board, and more particularly to a thick-film conductor layer formed on a thick-film conductor layer by using a material having a low conductor resistance, for example, high-purity silver. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick-film multilayer circuit board capable of performing copper plating, greatly reducing wiring resistance and improving reliability.

[0002]

2. Description of the Related Art A thick-film multilayer circuit board is formed by forming a lower conductor layer on an insulating substrate such as ceramics and forming an upper conductor layer on the lower conductor layer via a dielectric layer. It is possible to increase the mounting density and improve the circuit performance. Such a thick film multilayer circuit board,
For example, in a ceramic thick film multilayer circuit board, conventionally, each conductor layer is made of a conductor obtained by adding palladium or platinum to silver instead of pure silver, that is, silver palladium or silver platinum, in order to prevent migration due to moisture intrusion from the outside. I'm using Further, by performing copper plating on such a thick film conductor, the migration resistance is improved and the conductor resistance value is reduced.

[0003]

However, in such a conventional thick-film multilayer circuit board, when copper plating is performed on a thick-film conductor, if there is a partial multilayer, that is, a crossover, there is a problem. Since the plating solution penetrates into the dielectric layer used for insulating the conductor layers in the crossover portion and the reliability is deteriorated, there is a disadvantage that the copper plating cannot be performed in the case of the multilayer structure.

Further, since silver palladium or silver platinum is used as the material of the conductor layer, there are disadvantages that the resistance value of the conductor increases and the circuit board becomes expensive. The sheet resistance of silver palladium or silver platinum is, for example, 15 to
This is 20 mΩ / square millimeter, which results in an increase in circuit loss, a reduction in current capacity, and an inability to miniaturize wiring, which has been an obstacle to improving the mounting density and miniaturization of circuit boards.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to reduce the wiring resistance by enabling copper plating while maintaining high reliability even in a multilayer structure. It is possible to achieve the miniaturization of the device.

[0006]

According to the present invention, there is provided a lower conductor layer formed on an insulating substrate and an upper conductor formed on the lower conductor layer via a dielectric layer. A thick film multilayer circuit board having a plating-resistant overcoat layer formed so as to cover the dielectric layer at least at the intersection of the lower conductor layer and the upper conductor layer. Using the layer as a mask, a copper plating layer is formed on the conductor layer other than the intersection.

The lower conductor layer and the upper conductor layer are made of a material containing silver as a main component, that is, 70% by weight to 10% by weight.
It is convenient to form it from a material containing about 0% by weight of silver.

Further, in the above-described thick-film multilayer circuit board, it is advantageous to form an organic resin resist layer on the uppermost layer except for a soldering region.

[0009]

In the thick-film multilayer circuit board according to the above structure, a plating-resistant overcoat layer is formed on the intersection of the lower conductor layer and the upper conductor layer so as to cover the dielectric layer. Copper plating is performed on the conductive layer other than the crossing portion from the plating overcoat layer.
Therefore, when performing this copper plating, since the plating-resistant overcoat layer is present, the plating solution is prevented from entering the dielectric layer, and the dielectric layer is not damaged and the reliability is improved. Therefore, copper plating can be appropriately performed on each conductor layer, and a high-performance circuit board with low wiring resistance can be realized.

Further, the lower conductor layer and the upper conductor layer are formed of a material containing high-purity silver, for example, silver of 70% by weight to 100% by weight, so that the wiring resistance of each conductor layer is greatly reduced. be able to. In this case, copper plating is applied to each conductor layer, and a resist layer of an organic resin is formed on the uppermost layer of the thick-film multilayer circuit board except for a soldering area, so that moisture from the outside can be prevented. It becomes possible to improve the migration resistance of silver.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 mainly shows a crossing portion, that is, a crossover portion, of a thick film multilayer circuit board according to one embodiment of the present invention. FIG. 2 is a sectional view taken along line XX of FIG. 1, and FIG. 3 is a sectional view taken along line YY of FIG.

As shown in these figures, the thick-film multilayer circuit board according to the present embodiment has an insulating substrate 1 formed of, for example, alumina ceramics, and a lower portion having a desired circuit pattern on the insulating substrate 1. The conductor layer 3 is formed. A dielectric layer 5 is formed on the lower conductor 3, and an upper conductor layer 7 is formed on the dielectric layer 5 to form a crossover portion.

The dielectric layer 5 is made of, for example, crystallized glass such as borosilicate glass. Further, for the lower conductor layer 3 and the upper conductor layer 7, for example, both high-purity silver is used. For example, by using a material containing 70% by weight to 100% by weight of silver, a low sheet resistance of 3 to 4 mΩ / mm 2 can be obtained. On the other hand, silver palladium or silver platinum used for a conventional thick film multilayer circuit board has a relatively high sheet resistance of 15 to 20 mΩ / mm 2.

Further, a plating-resistant overcoat glass 9 is provided at a portion where the lower conductor 3 and the upper conductor 7 intersect, that is, at a crossover portion. further,
A copper plating layer 11 is formed on the conductor layer 3 other than the overcoat glass portion 9. When the copper plating layer 11 is formed, the overcoat glass 9 is used as a mask to prevent a plating solution from entering the dielectric layer 5 and improve reliability. In addition, metals other than copper can be used for the plating layer 11.

Further, an organic resin resist layer 13 is formed as a solder resist on the uppermost layer. Therefore, this organic resin resist layer 13 is not shown in the drawing, but is not formed on the conductive layer portion to be soldered.

In FIG. 1, the copper plating layer 11 formed on the lower conductor layer 3 is formed on the lower conductor layer 3 outside the region except the region of the overcoat glass layer 9 in the crossover portion. Will be done.

Next, a method of manufacturing the above-described thick film multilayer circuit board will be described with reference to FIG. First, as shown in FIG. 1A, a ceramic substrate 1 made of, for example, 96% alumina is prepared, and a lower conductor layer 3 is formed thereon in a desired pattern. This lower conductor layer 3 is formed by
The paste is formed by printing a paste containing silver as a main component on the alumina ceramic substrate 1 by screen printing and firing the paste.

Next, as shown in FIG. 4B, a dielectric layer 5 is formed by printing and firing crystallized glass, ie, cross glass, on the crossover portion of the wiring.
Further, the upper conductor 7 is formed by printing and baking a silver paste in the same manner as the lower conductor layer 3 over the dielectric layer 5.

Next, as shown in FIG. 4C, plating-resistant overcoat glass is printed and fired on the region excluding the portion of the conductor layer to be plated with copper and on the crossover portion. The layer 9 is formed. Further, the reliability can be further improved by overcoating the crossover portion again with overcoat glass.

Next, as shown in FIG. 4D, a copper plating layer 11 is formed on the exposed portions of the conductor other than the overcoat glass layer 9 by electroless copper plating.

Finally, as shown in FIG. 4E, a solder resist layer 13 is formed on the wiring region except the soldered portion and on the crossover portion. This solder resist layer is formed by, for example, coating an organic resin resist.

[0022]

As described above, according to the present invention, in a thick-film multilayer circuit board, a dielectric layer provided at a crossover portion between a lower conductor and an upper conductor is protected by a plating-resistant overcoat glass. Therefore, even if copper plating is performed on the conductor layer, the dielectric layer is not deteriorated by the plating solution, and the conductor portion can be copper-plated even on the multilayer circuit board to reduce the wiring resistance. Therefore, the wiring can be made finer, the mounting density of the circuit can be improved, and a circuit board with higher performance can be realized due to a reduction in circuit loss and the like.

Further, by performing copper plating on the conductor layer, the migration resistance is improved, so that high-purity silver or the like can be used as the thick-film conductor layer, and the wiring resistance value can be further reduced. A circuit board can be provided at a lower price than when using conventional silver palladium or silver platinum. By forming a solder resist on the uppermost layer of the multilayer circuit board, the migration resistance can be further improved.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a crossover portion of a thick film multilayer circuit board according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of the thick-film multilayer circuit board of FIG. 1 taken along line XX.

FIG. 3 is a cross-sectional view of the thick-film multilayer circuit board of FIG. 1 taken along line YY.

FIG. 4 is a process chart for explaining a method of manufacturing the thick film multilayer circuit board shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic substrate 3 Lower conductor 5 Dielectric layer 7 Upper conductor layer 9 Overcoat layer 11 Copper plating layer 13 Solder resist

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05K 3/46 H05K 1/11 H05K 3/40

Claims (3)

(57) [Claims] 1. A thick-film multilayer circuit board having a lower conductor layer formed on an insulating substrate and an upper conductor layer formed on the lower conductor layer via a dielectric layer, wherein at least the lower conductor A plating-resistant overcoat layer formed so as to cover the dielectric layer on the intersection of a layer and the upper conductor layer, and formed on a conductor layer other than the intersection using the plating-resistant overcoat layer as a mask. A thick film multilayer circuit board, comprising: a plated copper layer. 2. The thick film multilayer circuit board according to claim 1, wherein the lower conductor layer and the upper conductor layer are formed of a material containing 70% by weight to 100% by weight of silver. 3. The thick-film multilayer circuit board according to claim 1, wherein an organic resin resist layer is formed on the uppermost layer except for a soldering area.