BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a principal part of a wiring board according to the present invention;
FIG. 2 is an illustration showing a first step of a method for manufacturing a wiring board according to the present invention;
FIG. 3 is an illustration showing a second step of the method;
FIG. 4 is an illustration showing a third step of the method;
FIG. 5 is an illustration showing a fourth step of the method;
FIG. 6 is an illustration showing a fifth step of the method;
FIG. 7 is a sectional view of a principal part of a conventional wiring board;
FIG. 8 is an illustration showing a first step of a conventional method for manufacturing the conventional wiring board;
FIG. 9 is an illustration showing a second step of the conventional method;
FIG. 10 is an illustration showing a third step of the conventional method; and
FIG. 11 is an illustration showing a fourth step of the conventional method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 shows a principal part of a wiring board according to the present invention in cross section. FIG. 2 illustrates a first step of a method for manufacturing the wiring board according to the present invention. FIG. 3 illustrates a second step of the method. FIG. 4 illustrates a third step of the method. FIG. 5 illustrates a fourth step of the method. FIG. 6 illustrates a fifth step of the method.
The wiring board has a configuration as described below. With reference to FIG. 1, the wiring board includes a ceramic substrate 1 having a via-hole 1a, a via-conductor 2 disposed in the via-hole 1a, and a metal thin-film pattern 6. The ceramic substrate 1 is made of low-temperature co-fired ceramic (LTCC). The via-conductor 2 contains sliver or a material principally containing silver. A silver deposit 2a that is a piece of the via-conductor 2 is disposed on a surface portion of the ceramic substrate 1 that is located near the via-hole 1a.
Cavities 3 are present between the via-conductor 2 and the wall of the via-hole 1a, the cavities 3 being formed together with the silver deposit 2a when the ceramic substrate 1 and the via-conductor 2 are fired. A catalyst layer 4 that contains palladium or a metal material principally containing palladium extends over an exposed face of the via-conductor 2, the surface portion of the ceramic substrate 1, and the silver deposit 2a. The catalyst layer 4 has portions that occupy the cavities 3.
A metal layer 5 containing nickel phosphide overlies the catalyst layer 4. The metal thin-film pattern 6 contains copper or a metal material principally containing copper and extends over the metal layer 5 to the ceramic substrate 1.
A thick conductive pattern 7 is disposed on a face of the ceramic substrate 1 that is opposed to the metal thin-film pattern 6. The conductive pattern 7 is connected to the via-conductor 2. The configuration of the wiring board is as described above.
In this embodiment, the conductive pattern 7 has a large thickness. A thin metal pattern may be used instead of the conductive pattern 7.
The method will now be described with reference to FIGS. 2 to 6. In the first step shown in FIG. 2, the via-hole 1a is formed in a green sheet 8 for forming the ceramic substrate 1 and a conductive paste 9 that contains silver or a metal material principally containing silver is then provided in the via-hole 1a.
In the second step shown in FIG. 3, the green sheet 8 and the conductive paste 9 are fired at a temperature of at 800° C. to 900° C. such that the green sheet 8 is converted into the ceramic substrate 1, the conductive paste 9 is converted into the via-conductor 2, silver in the conductive paste 9 is diffused in the ceramic substrate 1, and the silver deposit 2a is formed on the surface portion of the ceramic substrate 1. In this step, the cavities 3 are formed between the via-conductor 2 and the wall of the via-hole 1a.
In the third step shown in FIG. 4, the catalyst layer 4 is formed over the exposed face of the via-conductor 2 and the surface portion of the ceramic substrate 1 by immersing the ceramic substrate 1 in a catalyst solution containing palladium such that the portions of the catalyst layer 4 occupy the cavities 3.
In the fourth step shown in FIG. 5, the metal layer 5 is provided on the catalyst layer 4 by electroless plating. The catalyst layer 4 and the metal layer 5 extend over the exposed face of the via-conductor 2 to the ceramic substrate 1 and have gentle slopes.
In the fifth step shown in FIG. 6, the metal thin-film pattern 6 is formed over the metal layer 5 and the ceramic substrate 1 such that the metal thin-film pattern 6 is connected to the metal layer 5 with the catalyst layer 4 disposed therebetween, whereby the wiring board is obtained.
Patent Application
20070236896
