JPS61230398A - Manufacture of high heat conductivity multilayer ceramic wiring substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a multilayer ceramic substrate, particularly a highly thermally conductive multilayer ceramic substrate.

(Prior art and its problems) With the rapid progress of the semiconductor industry, ICs and LSIs have come to be widely used for industrial and consumer purposes, and electronic devices are becoming smaller, more dense, and more sophisticated. It is being

In particular, multilayer ceramic substrates are attracting attention as high-density mounting boards for high-speed operation LSIs with high integration density. This multilayer ceramic board can be used directly with L8I
It is also possible to implement fine wiring in multiple layers.

Generally, alumina is mainly used as a material for ceramic substrates, but in recent years electronic devices have become smaller and smaller.
High density circuits are required, and the degree of integration of elements and circuit elements per unit area of a substrate is becoming higher and higher. On the other hand, L
SI chips tend to generate more heat as they operate at higher speeds. As a result, the heat generated by the board increases significantly, and the alumina board is unable to dissipate heat sufficiently, causing the board temperature to rise.
A problem has arisen in that the 8I chip and mounted elements are adversely affected. Therefore, there is a need for an insulating substrate that has higher thermal conductivity and better heat dissipation than an alumina substrate.

Therefore, a ceramic substrate containing silicon carbide as its main component was developed, and it has excellent heat dissipation properties. Silicon carbide itself electrically belongs to a semiconductor, has a specific resistance of about 1 to 10 Ω·α, and has poor electrical insulation properties, so there is a problem in using it as an insulating substrate. Furthermore, since silicon carbide has a high melting point and is very difficult to sinter, it is usually produced by the so-called hot press method in which a small amount of sintering additive is added and pressed under high pressure. The use of Be-131J oxide or boron nitride as the sintering additive is effective not only for the sintering effect but also for the electrical insulation, and the specific resistance of the sintered substrate mainly composed of silicon carbide becomes 191,094 or more. However, the dielectric constant, which is one of the important factors in mounting boards such as LSI, is quite high at 40 at the I Mllz frequency, and even with the addition of additives, the insulation at the particle interface rapidly decreases as the voltage increases. There is also a problem with the withstand voltage.

Moreover, from a process standpoint, 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.

-Multilayer ceramic substrates are a promising mounting substrate for increasing the density of harmful birds. This uses ceramic green sheets, and has various conductor patterns formed in layers within the substrate, and the layers are electrically connected via through holes. Alumina, glass ceramic, and the like are currently being developed as materials for the multilayer ceramic substrate, but silicon carbide materials using a hot pressing method are extremely difficult to process.

In general, the main properties that a high-density mounting board should have are (1) low dielectric constant, low dielectric loss, and excellent electrical insulation in terms of electrical properties, and (2) sufficient mechanical strength. (3) have high thermal conductivity;
(4) The coefficient of thermal expansion is close to that of silicon chips;
(5) It needs to have excellent surface smoothness, and (6) it needs to be easy to increase the density.

The various ceramic substrates described above are by no means sufficient in terms of these substrate properties in general.

The present inventors paid particular attention to high thermal conductivity and multilayer densification, while keeping in mind these substrate properties that should be provided.
The present invention has led to the invention of a method for manufacturing a highly thermally conductive multilayer ceramic wiring board using aluminum nitride-based powder that can be sintered by a normal pressure method and titanium metal as a conductor that can be sintered at high temperatures.

(Object of the Invention) An object of the present invention is to provide a manufacturing method for obtaining a high-density, high-density, high-thermal conductive multilayer ceramic wiring board with excellent thermal conductivity by eliminating the drawbacks of the conventional mounting board described above.

(Structure of the Invention) According to the present invention, a conductor is formed by using a paste containing titanium metal as a main component on a green sheet made of a mixed powder made of aluminum nitride powder and a sintering additive, and a mixture of an organic binder and an organic solvent. A highly thermally conductive multilayer ceramic substrate characterized by comprising a step of embedding layers and conductors, a step of laminating and thermocompression bonding green sheets on which conductors are formed, and a step of removing the binder and firing in a non-oxidizing atmosphere. A manufacturing method 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, and a sintering additive was added to improve sinterability. After firing, this material forms a dense structure of polycrystalline aluminum aluminum.

In the step of mixing with an organic binder etc. to form a slurry, an organic substance that is easily decomposed in a non-oxidizing atmosphere was used so that binder removal would occur appropriately in a non-oxidizing atmosphere.

In the film forming process, a thin, uniformly thick green sheet is formed.

Next, in the process of forming through holes that provide interlayer conduction,
Basically, extremely fine through holes are formed using mechanical methods, and conductor formation involves forming numerous conductor layers such as *# layer, ground layer, and fine signal lines, as well as embedding conductors in the through holes. Let's do it.

In the lamination thermocompression bonding process, it is possible to obtain a kE laminated substrate in which fine patterns are laminated and integrated with high precision. After appropriately removing organic matter from the raw laminated substrate in a non-oxidizing atmosphere, it is baked at a high temperature.

In the highly thermally conductive multilayer ceramic substrate manufactured in this way, multiple power layers, ground layers, fine signal lines, etc. are formed on the ceramic layer made of aluminum nitride, and these conductor layers are connected to the ceramic layer. It has a structure in which electrical connections are made through through-holes provided inside.Therefore, the wiring density of the mounting board is greatly increased, and the heat generated from elements such as LSIs is reduced.

It becomes possible to efficiently dissipate to the outside.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

First, high-purity aluminum nitride fine powder and sintering additive powder are weighed. The sintering additive used here is Ca
, 8r, Ba, Na, Rb, Ca, Cu
, person 11 *Mg tcd eHg, Za, kl, C
It consists of at least one kind of acetylide compound and oxide such as e, and the amount of the sintering additive is 0.1 wt% to
The weighed powder was wet-mixed using an organic solvent using a ball mill. This thoroughly mixed powder was mixed with an organic binder such as polymethacrylate, polyacrylate, polycaprolactone, or polyvinyl butyral and an organic solvent using a stirrer such as a homomixer to form a slurry. The appropriate viscosity of the slurry at this time is in the range of 3000 to 7000 cp. If the viscosity is 1000 cp or less #
! In the membrane process, repellency occurs on the organic film due to surface tension, and if it exceeds 10,000 cp, it will be extremely difficult for the slurry to pass through the mesh when filtering out foreign substances contained in the slurry. During the defoaming process to remove the gas inside, gas cannot be removed sufficiently and film forming properties deteriorate.

Next, the slurry adjusted to an appropriate viscosity is coated on a polyester organic film with a film casting method of 10 μm to 20 μm.
A sheet is formed to have a uniform thickness of about 0 μm. Peel this thin green sheet from the organic film,
As shown in FIGS. 1(a) and 1(b), through holes 1 for electrically connecting each layer are formed. Here, FIG. 1(,) is a plan view, and FIG. 1(b) is a sectional view. The through holes were formed mechanically using a punch and die, but they can also be formed by other methods such as laser processing. Through-holes formed by mechanical methods could have a minimum diameter of about 70 μm.

A predetermined conductor pattern 2 is thick-film printed onto the green sheet in which through-holes have been formed at predetermined positions using a conductor paste using a screen printing method, as shown in FIGS. 2(a) and 2(b). As the conductor used here, since the ceramic substrate must be sintered at a high temperature of 1500'C or higher, it is necessary to use a high melting point metal.

In the present invention, a conductive paste using titanium metal powder was used as the conductive material. After sintering, this conductor paste can become TiN or metallic titanium or a mixture thereof. Titanium nitride has a cubic crystal structure and exhibits a low electrical resistance of 22XIQ-'Ω·flaw. Titanium metal also exhibits an electrical resistance value of 47.8 x 10-60. Therefore, even when a thick film is formed as a conductor paste, it can exhibit a sufficiently low resistance value as a wiring conductor, even if it does not exhibit the original electrical resistance value of titanium nitride or titanium metal. This printing process includes a step of embedding a similar conductive paste into through holes for making electrical connections between layers.

As shown in FIG. 3, a desired number of green sheets having each pattern printed and embedded with conductors were laminated and thermocompression bonded. FIG. 3 shows a sectional view of a raw laminate having a structure in which a large number of insulating green sheets 3 on which conductive patterns 2 are formed are stacked. The number of stacked green sheets is 10 to 50. The thermocompression bonding conditions were a temperature of 70° C. to 110° C. and a pressure of 200 to 300 m/d.

In this process, green sheets each having finely formed wiring patterns and through holes must be laminated with high precision without misalignment.

Next, the laminated and integrated raw substrates are debindered in a non-oxidizing atmosphere and sintered at a high temperature. FIG. 4 shows an example of a temperature profile for binder removal and firing. Until the binder removal step is completed, the temperature increase speed is kept at a slow rate (maintained in the range of 400 to 600° C. for a certain period of time). In this binder removal step, the removal of organic matter is appropriately controlled.

This is because the residue greatly affects the sinterability and properties of the aluminum nitride sintered body. Subsequently, the temperature was raised to 1500 DEG C. to 2000 DEG C., and sintering was carried out by holding at the maximum temperature for 2 hours.

FIG. 4 shows an example in which the holding temperature for binder removal is 500°C and the degree of sintering is 1900°C. The atmosphere during this series of steps is nitrogen gas and helium gas.

Control was performed using argon gas, hydrogen gas, etc.

Further, sintering was performed under normal pressure. If the temperature rise speed during binder removal is too fast.

Rapid decomposition and evaporation of organic matter causes defects such as cracks and delamination.

FIG. 5 shows a schematic perspective cross-sectional view of a highly thermally conductive multilayer ceramic substrate made of aluminum nitride as a main component, produced in this way. Reference numeral 11 denotes an insulating ceramic layer, which is mainly composed of polycrystalline aluminum nitride.

Reference numeral 12 denotes a conductor layer for signal lines, power supply, etc., using titanium metal conductor paste, forming chambered titanium polycrystal or titanium metal after firing, and through hole 13 formed in the insulating ceramic layer. Each layer is electrically connected through the . A die pad 14 and a bonding pad 15 are formed on the multilayer ceramic substrate configured in this manner so that an LSI chip can be mounted, and for extracting signals from the mounting board or inputting signals into the board. An I10 pad 16 is formed on the substrate surface.

Heat generated from the L8I chip mounted on the substrate is diffused into the ceramic substrate via the die pad 14.

As a result of measuring the electrical characteristics of this sintered substrate, the specific resistance was 1
The dielectric constant was 8.7 (IMHz), and the dielectric loss was 10 −3 or less (IMHz), which were small values.

It was found that the electrical characteristics were comparable to those of conventional boards, and were sufficient to be used as a mounting board.

Table 1 shows the substrate properties of an example of a multilayer ceramic substrate produced by the manufacturing method of the present invention, and this example uses CaC2 as a sintering additive and the weight of aluminum nitride is reduced to 1.
The table shows the amount added when 00. A substrate was obtained that had a fine wiring pattern and through-holes visible from the surface, had extremely high bending strength, and had extremely high thermal conductivity. Furthermore, the coefficient of thermal expansion is close to that of silicon, making it extremely convenient for mounting L8I and the like.

On the other hand, Ca (8r other than 4, Ba, Na) is used as a sintering additive.
.

K, Rh, Cs, Cu, Ag, Mg, Cd, Hg, Zn
, person 1. A multilayer ceramic substrate mounted with aluminum nitride to which an acetylide compound of Ce and oxides thereof including Ca were added was prepared. The firing temperature is 15
The same manufacturing method was used in the range of 00°C to 2000°C.

As a result, the thermal conductivity of the created substrate 1 was 0.5wt.
%~4. It is possible to achieve 100 W/mk or more up to 0.3vt% and 8. Owt%
A value of 80 W/mk or more was obtained, and the heat dissipation property was superior to that of an alumina substrate.

(Effects of the Invention) As is clear from the examples, by employing the manufacturing method of the present invention, it is possible to easily form a high-density circuit, and the high thermal conductivity of the ceramic substrate improves heat dissipation. A highly thermally conductive multilayer ceramic wiring board is obtained which is also very effective.

The thermal conductivity of conventionally used alumina substrates is approximately 17.
It can be seen that the thermal conductivity of the substrate obtained by the method of the present invention is at a very high level.

Also, in terms of thermal expansion coefficient, the alumina substrate has a coefficient of 65X 1
0-'/'C, whereas the substrate produced by the method of the present invention has a smaller coefficient of thermal expansion, which is closer to the coefficient of thermal expansion of a silicon chip, and is advantageous in this respect as well.

On the other hand, the conductor paste using titanium metal according to the present invention exhibited sufficient electrical resistance as a mounting board after sintering.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing each manufacturing process of a highly thermally conductive multilayer ceramic substrate according to an example of the present invention, Figure 4 is a diagram showing a firing profile in the firing process of the example, and Figure 5 is a completed substrate. FIG. DESCRIPTION OF SYMBOLS 1... Through hole, 2... Conductor layer, 3... Insulator green sheet, 11... Insulating ceramic layer, 12
...Conductor layer, 13...Through hole, 14...Gui pad. 15...ponding pad, 16...I10 pad. Figure 1 1 Through Hole Figure 2 Figure 3 Temperature ('C) Figure 5

Claims (1)

[Claims] A green sheet made of a mixed powder of aluminum nitride powder and a sintering additive, an organic binder, and an organic solvent, in a method for manufacturing a multilayer ceramic substrate in which the ceramic layer is a polycrystalline body mainly composed of aluminum nitride. There are two steps: forming a conductor layer and embedding the conductor in the through holes using a conductor paste containing metallic titanium as the main component, laminating and thermocompressing each green sheet on which the conductor has been formed, and bonding these in a non-oxidizing atmosphere. A method for manufacturing a highly thermally conductive multilayer ceramic wiring board, comprising the steps of removing binder and firing.