JPH0286188A - Ceramic wiring board baked at a low temperature - Google Patents

Abstract

PURPOSE:To make a ceramic wiring board of a low dielectric constant and high bending strength by forming said ceramic wiring board from a first ceramic layer of high bending-resisting strength and a second ceramic layer of a low dielectric constant and baking the first and second ceramic layers at the same time. CONSTITUTION:A ceramic wiring board, including an insulating base material baked at a low temperature and an external terminal for input and output connected thereto, is made of a green sheet comprising a first ceramic layer 1 of bending-resisting strength of 25kg/mm<2> or larger and a second ceramic layer 2 of a dielectric constant of 7 or lower. Through holes are made in the ceramic layers 1 and 2 by punching and filled up with conductive paste 3 and conductive paste 4 is formed on the surfaces of the layers by screen printing. A desired number of the printed layers are piled up. These green sheets are applied to each other in the specific conditions and baked at the specific temperature at the same time. Thereby the wiring board having sufficiently high bonding strength to an external terminal, excellent signal propagation characteristic, and a reliable external terminal can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low temperature fired ceramic wiring board.

(Prior Art) By appropriately selecting a suitable glass composition such as a glass-ceramic composite or a crystallized glass body, a low-temperature fired insulating substrate can have a low dielectric constant, and this can be used as a wiring board. It is useful for increasing the speed and density of signal propagation in

(Problem to be solved by the invention) However, since the low-temperature fired insulating substrate itself has low bending strength, external terminals for input/output are connected to the substrate through a metallized layer provided on the substrate. Melting point brazing filler metal (
When brazing with eutectic silver solder (for example, eutectic silver solder, etc.), the thermal stress generated during brazing will generate residual stress in the parts where external terminals are attached, resulting in minute cracks, cracks, and even porcelain breakage. There was a problem that the terminal adhesion strength was not sufficient.

On the other hand, in order to solve the problem, it is possible to increase the bending strength of the substrate. The following two methods are known as methods for increasing the flexural strength. The first method is to increase the flexural strength of the substrate by increasing the content of, for example, alumina as a ceramic in the composition of the low-temperature fired insulating substrate. A second method is to use lead borosilicate glass as the glass in the composition of the low temperature fired insulating substrate and crystallize the glass to increase the bending strength of the substrate. However, increasing the bending strength of the substrate by the above two methods causes a problem in that the dielectric constant of the substrate increases at the same time as the substrate strength increases, and the characteristics of the low-temperature fired substrate deteriorate.

The purpose of this invention is to solve the above problems and inconveniences,
The object of the present invention is to provide a low-temperature fired ceramic wiring board that is formed by simultaneous firing and has both a low dielectric constant and high bending strength.

(Means for Solving the Problems) The present invention is a ceramic wiring board to which input/output external terminals are bonded to a low-temperature fired 8M substrate, the ceramic wiring board having a bending strength of 25 kg/mm2 or more. the first of
and a second ceramic layer having a dielectric constant of 7 or less, and is characterized in that the first ceramic layer and the second ceramic layer are co-fired.

(Function) In the present invention, a low-temperature-fired ceramic wiring board is formed from two types of ceramic layers that are fired simultaneously, and a second layer is formed on which the wiring conductors of the wiring board are formed (that is, through which signals mainly propagate).
By lowering the dielectric constant of the ceramic layer, high-speed signal propagation is achieved by taking advantage of the characteristics of the low-temperature fired substrate.

In addition, the first ceramic layer on which the external terminal is formed includes:
A material with high bending strength (bending strength) is selected to form a wiring board with sufficiently high adhesion strength for external terminals.

(Example) The present invention will be explained below based on some examples.

First, N shown in Table 1 is used as a glass component of the substrate.

Three types of low melting point glasses, No. 1 to No. 3, were prepared.

Table 1 Glass composition (wt%) Here, the bending strength of the substrate was measured with a width of 8 mm and a length of 40 mm.
A three-point bending test with a span of 30 mm was performed on a test piece with a thickness of 0.8 mm. Also, the measurement of dielectric constant is JIS K
6911.

Table 2 Composition and physical properties of low-temperature fired ceramics Next, the three types of low-melting glasses mentioned above were mixed with alumina powder and quartz glass in various proportions as shown in Table 2 below, and various mixtures were prepared using the doctor blade method. A green sheet of ceramic layer is formed having a dielectric constant and a bending strength of .

The green sheets of these ceramic layers are selected so that the first ceramic layer 1 has a higher bending strength than the second ceramic layer 2 (see Table 3), and through holes are punched in each of the ceramic layers 1 and 2. A conductive paste 3 is embedded in the through holes, and a conductive paste 4 is formed on the surfaces thereof by screen printing. In the example shown in FIG. 1(a), the first ceramic layer is
A through hole is formed in the green sheet using a mold, and a conductive paste is filled in the through hole to form the second ceramic layer.A second ceramic layer is formed by forming a through hole in the green sheet and filling the through hole with conductive paste. The desired number of layers are stacked on top of each other by screen-printing a conductive paste. These layers are laminated so that electrical connections can be made.

Further, the green sheets of the first and second ceramic layers are also overlapped so that a conductive connection can be established. 1st
The thickness of the ceramic layer 1 is preferably about 10 to 800 μm. These green sheets have a temperature of 120°
C2 pressure is maintained at 50 kg/cm2 for 5 minutes. This situation is shown in FIG. 1(a). Subsequently, each sample was simultaneously fired at the firing temperatures shown in Table 3. Next, electrolytic nickel plating 5 is applied to the terminal connection portion of the 2 mmφ pad of the wiring conductor formed in the ceramic layer using conductive paste. A Kovar lead pin 6 with a diameter of 0.3 mmφ is brazed to this pad using eutectic silver solder 7 by heat treatment at a temperature of 800°C for 5 minutes in a nitrogen atmosphere (Fig. 1(b)). reference).

For the low-temperature fired ceramic wiring board obtained as described above, in order to check the adhesion strength after brazing the external terminals,
A vertical tensile test was conducted. In this vertical tensile test, the lead bin bonded to the wiring board was pulled in a direction perpendicular to the adhesive surface of the test piece bonded via eutectic silver solder at a tensile rate of 0.5 mm/min. This is to measure the strength when the lead bin is peeled off from the substrate.

The results of this vertical tensile test are also shown in Table 3 above as "lead pin adhesion strength".

For comparison, a single low-temperature fired ceramic substrate with relatively low bending strength was selected as a comparative example, and a wiring board was formed using it in the same manner as in the above-mentioned example. Further, an example in which the first ceramic layer and the second ceramic layer were formed by post-baking instead of being co-fired was used as a comparative example. These comparative examples were also subjected to the vertical tensile test described above.

As can be seen from the adhesion strength of the glue-doped pins in Table 3, sufficient adhesion strength cannot be obtained on a single wiring board having a small bending strength, unlike the examples according to the present invention. In addition, when the second ceramic layer is post-baked on the first ceramic layer, unlike the simultaneous firing of the present invention example, since the adhesion of both layers is not sufficient, they peel off from the interface and the The adhesion strength of the lead pin could not be obtained.

The embodiments of the present invention have been described above, but the second ceramic layer may be laminated in the form of a green sheet or may be printed on the first ceramic layer by screen printing. A similar result is obtained.

(Effects of the Invention) As is clear from the above description, a low-temperature fired ceramic wiring board is formed from two different types of ceramic layers, and the dielectric constant of the second ceramic layer mainly on the signal propagation side of this wiring board is lowered. This enables high-speed signal propagation by taking advantage of the characteristics of the low-temperature fired substrate.

On the other hand, for the first ceramic layer on the side where the external terminals are formed, a material with high bending strength is selected, and by co-firing these ceramic layers, a wiring board with sufficiently high adhesion strength for the external terminals can be created. Form.

Therefore, a wiring board with excellent signal propagation characteristics and reliable external terminals can be obtained, which can be applied to high-performance IC packages and the like.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are explanatory diagrams showing an example of the present invention. 1...First ceramic layer 2...Second ceramic layer 3.4...Conductive paste 5...Nickel plating 6...Lead bin 7...Silver solder patent applicant Nippon Insulator Co., Ltd.

Claims (1)

[Claims] 1. A ceramic wiring board to which input/output external terminals are bonded to a low-temperature fired insulating base, the ceramic wiring board comprising a first ceramic layer having a bending strength of 25 kg/mm^2 or more and a dielectric constant of 7. A low-temperature fired ceramic wiring board comprising the following second ceramic layer, the first ceramic layer and the second ceramic layer being co-fired.