JPH0415639B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a highly thermally conductive multilayer ceramic wiring board. (Conventional technology and its problems) With the rapid progress of semiconductor technology, IC, LSI
has come to be widely used for industrial and civilian purposes. In particular, multilayer ceramic substrates are attracting attention as mounting substrates for high-speed operation LSIs with high integration density. This multilayer ceramic substrate allows direct mounting of LSI and enables fine multilayer wiring. Generally, alumina is mainly used as the material for ceramic substrates, but in recent years electrical devices have become smaller and there is a strong demand for higher circuit densities.
The degree of integration of elements and circuit elements per unit area of a substrate is increasing. On the other hand, as LSIs operate at high speeds, the chips tend to generate more heat. As a result, the heat generated by the substrate increases significantly, and the problem arises that the alumina substrate does not have sufficient heat dissipation properties. Therefore,
There is a growing need for insulating substrates that have higher thermal conductivity and better heat dissipation than alumina substrates. Therefore, a ceramic substrate mainly composed of silicon carbide was developed as a material with excellent heat dissipation properties (Japanese Patent Application Laid-open No. 180006/1983). Silicon carbide itself is an electrical semiconductor and has a specific resistance of 1 to 10.
It cannot be used as an insulating substrate because it has no electrical insulation properties of about Ωcm. Furthermore, since silicon carbide has a high melting point and is very difficult to sinter, sintering is usually done by adding a small amount of sintering aid and applying pressure at high temperature, the so-called hot press method. When beryllium oxide or boron nitride is used as this sintering aid, it is effective not only for the sintering aid but also for electrical insulation, and the specific resistance of the sintered substrate mainly composed of silicon carbide is 10 ¹⁰ Ω・cm. That's all. However, the dielectric constant, which is one of the important factors in mounting boards such as LSI, is quite high at 40 at 1MHz, and even with the addition of additives, the insulation between particles decreases rapidly when the voltage reaches about 5V. There is also a problem with withstand voltage. Furthermore, although it is possible to create a multilayer ceramic substrate using BeO powder, it is difficult to use in practice due to its toxicity. On the other hand, from a process point of view, a hot press method must be applied, which not only increases the size of the apparatus, but also makes it difficult to increase the shape of the substrate, and there are many problems with surface smoothness. Furthermore, in ceramic substrates using silicon carbide,
Utilizing alumina multilayer ceramic substrate technology using the conventional green sheet method is extremely difficult in terms of process. The green sheet multilayer ceramic substrate technology referred to herein is the following technology. 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 an organic film using this slurry by a casting film forming method. After cutting the sheet into a predetermined size and forming through holes for establishing electrical conduction between each layer, a predetermined conductor pattern is formed by thick film printing. Ceramic green sheets on which each of these conductor patterns have been formed are laminated and pressed, subjected to a binder removal process, and then fired. The main properties that a high-density mounting board should have are (1) low dielectric constant, low dielectric loss, and excellent electrical insulation properties;
(2) Sufficient mechanical strength, (3) High thermal conductivity, (4) Thermal expansion coefficient is close to that of silicon chips, (5) Excellent surface smoothness, and (6) It is necessary that the density can be increased easily. The ceramic substrate described above cannot be said to be sufficient in terms of all of these substrate properties.
On the other hand, aluminum nitride has been developed as a material for highly thermally conductive substrates (Japanese Unexamined Patent Publication No. 59-50077, etc.). However, this material must also be sintered at high temperatures, and the mainstream manufacturing method is hot pressing, and a multilayer wiring board using aluminum nitride has not yet been realized. (Object of the Invention) An object of the present invention is to eliminate the drawbacks of the conventional ceramic wiring boards mentioned above and provide a high-density, highly heat-conductive multilayer ceramic wiring board with excellent thermal conductivity and having conductors inside. (Structure of the Invention) According to the present invention, the ceramic layer is composed of a polycrystalline material containing aluminum nitride as a main component, and the conductor layer is composed of a mixture of titanium nitride and metal boride as a main component. A conductive multilayer ceramic wiring board is obtained. (Detailed Description of Configuration) The present invention solves the problems of the prior art by adopting the above-described configuration. First, aluminum nitride, which has high thermal conductivity, was used as the insulating ceramic material constituting 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 amount of oxygen contained in the sintered body is small, and therefore it is preferable to add a reducing agent having a reducing effect as an additive. Next, regarding the conductor layer, there are multiple power supply layers on the ceramic layer made of aluminum nitride.
Conductor layers such as a ground layer and fine signal lines are formed, and these multiple conductor layers are electrically connected via via holes provided in the ceramic layer. Therefore, the wiring density of the mounting board can be greatly increased, and the heat generated from elements such as LSI can be efficiently dissipated to the outside. (Example) Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram showing an embodiment of a highly thermally conductive multilayer ceramic substrate according to the present invention. Reference numeral 1 denotes an insulating ceramic layer, which is mainly composed of polycrystalline aluminum nitride. 2 is a conductor layer for signal lines, power supply, etc., which is mainly made of a mixture of titanium nitride and metal boride, and electrically connects each layer through via holes 3 formed in the insulating ceramic layer. ing. A die pad 4 and a bonding pad 5 are formed on the multilayer ceramic substrate constructed in this manner so that an LSI chip can be mounted, and for extracting signals from the mounting substrate or inputting signals into the substrate. An input/output pad 6 is formed on the back surface of the substrate, and heat generated from an LSI chip mounted on the substrate is diffused into the ceramic substrate via the die pad 4. The high thermal conductivity of the ceramic substrate allows for efficient heat diffusion, making it possible to prevent the LSI chip from increasing in temperature due to heat generation. The method for manufacturing the wiring board of this example is as follows. The ceramic material constituting the substrate of the present invention contains CaC ₂ as an additive to improve the sinterability of aluminum nitride. First, weigh aluminum nitride powder and CaC ₂ powder,
Wet mixing in an organic solvent was carried out using a ball mill for 48 hours. This mixed powder is dispersed in a solvent together with an organic binder that is easily decomposed in a neutral atmosphere, such as polycaprolactone resin or polyacrylate resin, to create a slurry having a viscosity in the range of 3,000 to 7,000 cp.
The slurry is coated with a thickness of 10 μm or more using a casting film forming method.
A green sheet is created on an organic film so that it has a uniform thickness of about 200 μm. Next, after this green sheet is peeled off from the organic film, via holes are formed for electrically connecting each layer. The via holes formed here were punched out mechanically using a connection punch and die, but they can also be punched out by other methods such as laser machining. onto the green sheet with via holes formed.
When fired in a nitrogen atmosphere, other neutral atmosphere, or reducing atmosphere, a conductive paste whose main component is a compound that becomes a mixture of titanium nitride and metal boride is printed in a predetermined pattern at a predetermined location using a screen printing method. do. A desired number of green sheets with conductors printed in this manner are stacked and hot pressed. Thereafter, it is cut into the required shape using a cutter and fired in a non-oxidizing atmosphere at a temperature of 1400°C to 2000°C. During firing, during the temperature raising process
The binder was sufficiently removed at a temperature of 400°C to 600°C. Table 1 shows the composition of the conductive paste used in the prepared samples, and Table 2 shows the characteristics of the samples.

【table】

[Table] TiN, TiB, TaB ₂ as conductor paste materials,
ZrB, ZrB ₂ , VB ₂ , MoB, HfB, NbB and
_NbB2 was used. The amount of additive (CaC ₂ ) shown here is the value when aluminum nitride is taken as 100. Further, the amount of frit is a value relative to the combined weight of the conductor material and the frit material. As a result of measuring the electrical characteristics of the created substrate, the specific resistance was 10 ¹¹ Ω・cm or more, and the dielectric constant was 8.7 (1M
Hz), and the dielectric loss was less than 1×10 ^-3 (1MHz). It can be seen that the electrical characteristics are also at least the same as those of conventional boards, and are sufficient as a mounting board. On the other hand, additives include CaO, BeO, Y ₂ O ₃ , CuO,
AgO, BaC ₂ , SrC ₂ , Na ₂ C ₂ , K ₂ C ₂ , CuC ₂ ,
Even when MgC ₂ , Ag ₂ C ₂ , ZrC _{2 ,} etc. were used, the effect of improving the sinterability of aluminum nitride was obtained. (Effects 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 having conductors including signal lines and power supply layers, and to improve heat dissipation. A highly thermally conductive multilayer ceramic wiring board which is also very effective in terms of performance can be obtained. The thermal conductivity of the conventionally used alumina substrate is
17 W/mK, which indicates that the thermal conductivity of the substrate of the present invention is at a very high level. Furthermore, the thermal expansion coefficient of the alumina substrate is 65×10 ^-7 /°C, whereas the substrate of the present invention has a small value, which is advantageous because it is closer to the thermal expansion coefficient of a silicon chip.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a highly thermally conductive multilayer ceramic wiring board showing one embodiment of the present invention. 1... Insulating ceramic layer, 2... Conductor layer, 3... Via hole, 4... Die pad, 5... Bonding pad, 6... Input/output pad.

Claims (1)

[Scope of Claims] 1. A multilayer ceramic wiring board in which a conductor is three-dimensionally formed through ceramic layers, including a ceramic layer containing aluminum nitride as the main component and a mixture of titanium nitride and metal boride as the main component. A multilayer ceramic wiring board characterized by comprising a conductor. 2 The metal boride is one or more substances selected from titanium boride, tantalum boride, zirconium boride, niobium boride, vanadium boride, molybdenum boride, and hafnium boride. The multilayer ceramic wiring board according to item 1.