JPH0636473B2 - Multilayer ceramic board - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic substrate, particularly a multilayer ceramic substrate having high thermal conductivity.

(Prior art and its problems) Due to the dramatic development of the semiconductor industry, ICs and LSIs have come to be widely used for industrial and commercial purposes.

In particular, a multi-layer ceramic substrate has attracted attention as a substrate for mounting an LSI having a high integration density and operating at high speed. This multilayer ceramic substrate can be directly mounted with an LSI, and fine multilayer wiring is possible.

Generally, alumina is mainly used as the material of the ceramic substrate, but in recent years, electric devices have been further downsized,
There is a strong demand for higher density circuits, and the degree of integration of elements and circuit elements per unit area of the substrate is increasing. On the other hand, LSI
In the above, the amount of heat generated from the chip tends to increase as high speed operation is performed. As a result, the heat generation of the substrate is significantly increased, and the alumina substrate has a problem that the heat dissipation is not sufficient. Therefore, an insulating substrate having a higher thermal conductivity than the alumina substrate and excellent heat dissipation has been required.

Therefore, a ceramic substrate containing silicon carbide as a main component has been developed as a material excellent in heat dissipation. Silicon carbide itself belongs to the semiconductor electrically, and the specific resistance is 1 to 10Ω.
・ Cannot be used as an insulating substrate because it does not have electrical insulation at about cm. Further, since silicon carbide has a high melting point and is extremely difficult to sinter, it is usually produced by a so-called hot pressing method in which a small amount of a sintering aid is added and pressure is applied at a high temperature. When beryllium oxide or boron nitride is used as this sintering aid, it is effective not only for the effect of the sintering aid, but also for electrical insulation, and the specific resistance of the sintered substrate containing silicon carbide as the main component is 10 ¹⁰ Ωcm or more. Become. However, the dielectric constant, which is one of the important factors in mounting boards such as LSI, is 1MHz.
It is considerably high at 40, and the insulating property with additives also has a problem with respect to the withstand voltage because the insulation between particles drops sharply when the voltage reaches about 5V.

Although it is possible to prepare a multilayer ceramic substrate using BeO powder, it is practically difficult because it is toxic.

On the other hand, the hot pressing method has to be applied from a process point of view, and not only the apparatus becomes large in size, but also the shape of the substrate is difficult to have a large area, and there are many problems in surface smoothness. Furthermore, in the case of a silicon carbide-based ceramic substrate, it is extremely difficult in terms of process to utilize the conventional alumina multilayer ceramic substrate technology using the green sheet method.

The green sheet method multilayer ceramic substrate technology mentioned here is the technology described below. First, ceramic powder is mixed with an organic vehicle to form a slurry. A sheet having a thickness of about 10 μm to 400 μm is formed on the organic film by the casting film forming method using this slurry. The sheet is cut into a predetermined size to form through holes for obtaining conduction between the layers, and then a predetermined conductor pattern is formed by a thick film printing method. The ceramic green sheets on which each of these conductor patterns is formed are laminated and pressed, and then subjected to a binder removal step and fired.

The main properties that a high-density mounting board should have are:
(1) Low dielectric constant with respect to electrical characteristics, low dielectric loss, and excellent electrical insulation, (2) sufficient mechanical strength, (3) high thermal conductivity, (4) The coefficient of thermal expansion is close to that of silicon chips, and (5)
It must have excellent surface smoothness, and (6) easy densification.

The ceramic substrate described above is by no means sufficient for all of these substrate properties.

The present inventors have arrived at the invention of an aluminum nitride multilayer ceramic substrate, paying attention to high thermal conductivity and multilayer densification while paying attention to these substrate properties to be provided.

(Object of the Invention) It is an object of the present invention to provide a high-density, high-thermal-conductivity multilayer ceramic substrate having excellent thermal conductivity by eliminating the above-mentioned drawbacks of the conventional mounting substrate.

(Structure of the Invention) According to the present invention, a plurality of conductor layers are formed on a ceramic layer composed of a polycrystalline body containing aluminum nitride as a main component, and the plurality of conductor layers are electrically connected in the ceramic layer. A multilayer ceramic substrate is obtained in which via holes for forming are laminated and laminated.

(Detailed Description of Configuration) The present invention has solved the problems of the prior art by adopting the above configuration.

First, aluminum nitride, which has a high thermal conductivity, was used as the insulating ceramic material that constitutes the multilayer ceramic substrate.
After firing, this material forms a dense structure of polycrystalline aluminum nitride. In order to obtain high thermal conductivity, it is preferable that the sintered body contains a small amount of oxygen, and therefore, it is preferable to add a reducing agent having a reducing effect as an additive.

Next, regarding the conductor layer, a plurality of conductor layers such as a power source layer, a ground layer and fine signal lines are formed on a ceramic layer made of aluminum nitride, and these conductor layers are provided in the ceramic layer. It is electrically connected via a via hole.

Therefore, the wiring density of the mounting board is greatly increased, and the heat generated from elements such as LSI can be efficiently dissipated to the outside.

Example 1 An example of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory view showing an embodiment of a high thermal conductive multilayer ceramic substrate according to the present invention. Reference numeral 1 is an insulating ceramic layer, which is composed of a polycrystal of aluminum nitride as a main component. Reference numeral 2 is a conductor layer for signal lines, power supplies, etc., which is formed of a simple substance of a metal such as molybdenum, dangsten, platinum and manganese, or an alloy containing two or more of these metals, and is formed in an insulating ceramic layer. The respective layers are electrically connected via the via hole 3 formed.
L is formed on the multilayer ceramic substrate constructed in this way.
The die pad 4 and the bonding pad 5 are formed so that the SI chip can be mounted, and the I / I for extracting a signal to the outside of the mounting board or inputting a signal into the board is provided.
The O pad 6 is formed on the back surface of the substrate. The heat generated from the LSI chip mounted on the substrate is diffused into the ceramic substrate through the die pad 4. Due to the high thermal conductivity of the ceramic substrate, thermal diffusion is efficiently performed, and it is possible to prevent the temperature of the LSI chip from rising due to heat generation.

The table shows various characteristics of the aluminum nitride multilayer ceramic substrate when CaC ₂ was used as an additive and the addition amount was changed. The CaC ₂ amount shown here is a value when aluminum nitride is 100. As shown in the table, aluminum nitride powder and CaC ₂ powder were weighed,
Warm mixing was performed for 48 hours with a ball mill.

This mixed powder is dispersed in a solvent together with an organic binder capable of decomposing in a neutral atmosphere such as a polycaprolactone-based or polymethylmethacrylate-based resin, and a viscosity of 3000-
Create sludge in the range of 7,000 cp. A green sheet is formed on the organic film by a casting film forming method so that the slurry has a uniform thickness of about 10 μm to 200 μm.

Next, peel off this green sheet from the organic film, and
After punching into a shape of 0 mm x 120 mm, a via hole for electrically connecting each layer is formed. The via hole formed here is mechanically punched using a punch and a die, but it can also be opened by a method such as laser processing.

On the green sheet in which the via holes are formed, a conductive paste containing molybdenum, tungsten, platinum or the like as a main component is printed at a predetermined position by a screen printing method. A desired number of green sheets on which the conductors are printed in this manner are stacked and heated and pressed. After that, cut with a cutter to obtain the required shape, 1400 ℃ ~ 20
Bake at a temperature of 00 ° C in a neutral or reducing atmosphere. During firing, the binder was sufficiently removed by holding it in a non-oxidizing atmosphere at 400 ° C. to 500 ° C. for 8 hours during the heating process.

As a result of measuring the electrical characteristics of the created board, the specific resistance is 10
^{It was 11} Ωcm or more, the dielectric constant was 8.7 (1 MHz), and the dielectric loss was 1 × 10 ^-3 or less (1 MHz). The electrical characteristics are similar to or higher than those of the conventional board, which indicates that the board is sufficient as a mounting board.

(Example 2) A mixed powder containing 1.0 wt% of CaO as an additive was used as a raw material powder. After mixing an organic binder that can be decomposed in a non-oxidizing atmosphere with an organic solvent to form a slurry, 150
A green sheet having a thickness of μm to 300 μm was prepared.

A via hole of about 300 μm is formed in the green sheet, and a high melting point metal paste such as molybdenum, tungsten or platinum is printed and laminated by a screen printing method, and after hot pressing, a neutral atmosphere in nitrogen or helium or argon, and Sintering was performed at a temperature of 1800 ° C. under a reducing atmosphere containing hydrogen. The characteristics of the multilayer board at this time are that the thermal conductivity is
It was as high as 100 W / mK, and the coefficient of thermal expansion was 41 × 10 ^-7 / ° C, which was close to that of silicon. On the other hand, the bending strength as a mechanical property was 4100 kg / cm ^2, which was a sufficient value for a mounting substrate.

In this embodiment, since the pressureless sintering method is used, the sintering process is simpler than the high pressure sintering method such as the hot pressing method, and it is very advantageous in terms of mass productivity. As described above, the process is easy and the raw material cost is low, so that the production cost can be reduced.

(Example 3) An aluminum nitride multilayer ceramic substrate was prepared using a material generally known as an additive or a reducing agent.
For example, BeO, Y ₂ O ₃ , CuO, AgO, BaC ₂ , S
rC ₂ , Na ₂ C ₂ , K ₂ C ₂ , Rb ₂ C ₂ , CsC ₂ , CuC
₂ , MgC ₂ , Al ₂ C ₆ , Ce ₂ C ₆ , Ag ₂ C ₂ , ZuC ₂
Was formed into a green sheet using aluminum nitride raw material powders containing up to 10 wt.

The firing temperature was in the range of 1500 ° C to 2000 ° C in a neutral or reducing atmosphere.

The thermal conductivity of the prepared substrate is 100 W / mK or more in the range of 0.5 wt% to 4.0 wt% addition, and 0.3 wt% to 8.0 wt%.
It showed 80 w / mk in the range up to wt%, and was excellent in heat dissipation compared with the alumina substrate.

Even when a plurality of the above-mentioned additives or reducing agents were added, good thermal conductivity was obtained.

(Effect of the invention) As is clear from the examples, by having the structure of the present invention, it is possible to easily form a high-density circuit,
It is possible to obtain a highly heat conductive multilayer ceramic substrate which is also very effective for heat dissipation.

The thermal conductivity of conventionally used alumina substrates is 17 W / m.
It is k, and it can be seen that the thermal conductivity of the substrate of the present invention is at a very high level. Regarding the coefficient of thermal expansion, the alumina substrate has a value of 65 × 10 ⁻⁷ / ° C., whereas the substrate of the present invention has a small value, which is advantageous because it is closer to the coefficient of thermal expansion of a silicon chip.

[Brief description of drawings]

FIG. 1 is a schematic view of a high thermal conductive multilayer ceramic substrate showing an embodiment of the present invention. 1 ... Insulating ceramic layer, 2 ...
... Conductor layer, 3 ... Via hole, 4 ... Die pad, 5 ...
... bonding pad, 6 ... I / O pad.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Takamizawa 5-33-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (56) References JP-A-60-178688 (JP, A) JP-A-SHO 60-180954 (JP, A) JP-A-53-102310 (JP, A)

Claims (1)

[Claims] 1. A conductor layer made of a plurality of refractory metals is formed on a ceramic layer composed of a polycrystalline body containing aluminum nitride as a main component, and the plurality of conductor layers are electrically contacted in the ceramic layer. A multilayer ceramic substrate having a via hole for forming and laminating.