JPH0544840B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a multilayer ceramic substrate, particularly a multilayer ceramic substrate having high thermal conductivity. (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. is in progress. In particular, multilayer ceramic substrates are attracting attention as high-density mounting substrates for high-speed operation LSIs with high integration density are essential. This multilayer ceramic substrate can be used to directly mount LSIs, and it is also possible to perform fine wiring in multiple layers. Generally, alumina is mainly used as the material for ceramic substrates, but in recent years electronic devices have become smaller and higher circuit densities are required, and the degree of integration of elements and circuit elements per unit area of the substrate has increased. It's getting higher and higher. On the other hand, LSI 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 a problem in that the board temperature rises and adversely affects the LSI chip and mounted elements. 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·cm, and has poor electrical insulation properties, so it is problematic to use as an insulating substrate. Furthermore, since silicon carbide has a high melting point and is very difficult to sinter, it is usually produced by a so-called hot press method in which a small amount of sintering additive is added and pressed under high pressure. When beryllium oxide or boron nitride is used as a sintering additive, it is effective not only for the sintering effect but also for electrical insulation, and the specific resistance of the sintered substrate, which is mainly composed of silicon carbide, is ¹⁰ Ω.
cm or more. However, the inductivity, which is one of the important factors in mounting boards such as LSI, is 1MHz.
The frequency is quite high at 40, and even with the addition of additives, the insulation at the particle interface rapidly decreases as the voltage increases, so there is also a problem with the withstand voltage. Further, 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. On the other hand, a multilayer ceramic board is a mounting board that is expected to be used for higher density. 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 in terms of electrical properties;
Low dielectric loss and excellent electrical insulation, (2) sufficient mechanical strength, (3) high thermal conductivity, and (4) coefficient of thermal expansion close to that of silicon chips. (5) It must have excellent surface smoothness; and (6) It must 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 have developed a highly thermally conductive multilayer ceramic using aluminum nitride powder that can be sintered by normal pressure, paying particular attention to high thermal conductivity and multilayer densification, while keeping in mind these substrate properties. This led to the invention of a method for manufacturing a substrate. (Object of the Invention) An object of the present invention is to provide a manufacturing method for obtaining a high-density, high-thermal-conducting multilayer ceramic substrate with excellent thermal conductivity by eliminating the drawbacks of the conventional mounting substrate described above. (Structure of the Invention) According to the present invention, aluminum nitride powder, Ca,
Sr, Ba, Na, K, Rb, Cs, Cu, Ag, Mg,
A process of mixing a mixed powder consisting of at least one sintering additive among acetylide compounds of Cd, Hg, Zn, Al, and Ce with an organic binder and an organic solvent to sludge it, and applying it onto an organic film. A process of forming the film, a process of forming through holes in the formed green sheet to provide interlayer conduction, a process of embedding a conductor layer and a conductor in the green sheet with the through holes formed, and forming a conductor. A method for producing a highly thermally conductive multilayer ceramic substrate is obtained, which is characterized by comprising a step of laminating and thermocompressing the green sheets, and a step of removing the binder and firing in a non-oxidizing atmosphere. (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 nitride. In the process of mixing with an organic binder and the like to form a slurry, an organic substance that decomposes sufficiently in a non-oxidizing atmosphere was used so that binder removal could occur completely in a non-oxidizing atmosphere. In the film forming process, a thin green sheet with a uniform thickness is formed. Next, in the process of forming through-holes that provide interlayer conduction, extremely fine through-holes are basically formed using a mechanical method, and conductor formation is performed using a large number of conductors such as power supply layers, ground layers, and fine signal lines. At the same time as forming the layers, conductors are also filled into the through holes. In the lamination thermocompression bonding process, it is possible to obtain a raw laminated substrate in which fine patterns are stacked and integrated with high precision. After completely removing organic matter from the green 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 formed on the ceramic layer. It has a structure in which it is electrically connected via a through hole provided in the layer. Therefore, the wiring density of the mounting board is greatly increased, and the heat generated from elements such as LSI 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. Sintering additives used here include Ca, Sr, Ba, Na, K, Rb, Cs, Cu,
It consists of at least one type of acetylide compound of Ag, Mg, Cd, Hg, Zn, Al, and Ce, and the amount of sintering additive is 0.1wt%, 0.3wt%, 0.5wt
%, 0.6wt%, 1.0wt%, 2.0wt%, 6.0wt%,
They were weighed to be 8.0wt%, 12.0wt%, and 16.0wt%. In addition, as a comparative example, a sample containing no additives was prepared. The weighed powder was wet mixed in a ball mill for 48 hours. This thoroughly mixed powder was mixed with an organic binder such as polymethacrylate, polyacrylate, polycaprolactone, etc., which is easily decomposed and evaporated in a non-oxidizing atmosphere, 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 less than 1000 cp, repellency will occur due to surface tension on the organic film during the film formation process.
If it is over 10,000 cp, it will be difficult for the slurry to pass through the mesh net when filtering out foreign substances contained in the slurry, and gas will not be released sufficiently during the defoaming process to remove gas from the slurry. It becomes difficult to cut, resulting in poor film-forming properties. Next, the slurry adjusted to an appropriate viscosity is coated on a polyester organic film using a casting method.
A sheet is formed to have a uniform thickness of about 10 μm to 200 μm. This thin green sheet is peeled off from the organic film, and as shown in Figure 1a and b, through holes 1 are made to electrically connect each layer.
form. Here, Figure 1 a is a plan view, Figure 1 b
is a sectional view. The through holes are formed mechanically using a punch and die, but they can also be formed by other methods such as laser machining. Through-holes formed by mechanical methods could have a minimum diameter of about 70 μm. As shown in FIGS. 2a and 2b, a predetermined pattern 2 is thick-film printed onto the green sheet in which through-holes are formed at predetermined positions using a screen printing method using conductor paste. 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, such as molybdenum, tungsten, manganese, and platinum, or a combination of these metals. The above alloys were used. 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 green 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. Thermocompression bonding conditions are temperature 70℃~110℃
°C pressure was 200-300Kg/ ^cm2 . 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. Fourth
The figure shows an example of the temperature profile for debinding and firing. Until the binder removal process is completed, the temperature increase speed is slowed down and kept in the range of 400 to 500℃.
Organic residues were sufficiently removed by holding for 10 hours. Subsequently, the temperature was raised to 1500°C and 2000°C at a heating rate of 100°C/H, 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 450°C and the sintering temperature is 1700°C. During this series of steps, the atmosphere was controlled using nitrogen gas, helium gas, argon gas, or a mixed gas of nitrogen gas, hydrogen gas, nitrogen gas and carbon monoxide gas, or the like. Further, sintering was performed under normal pressure. If the temperature increase speed during binder removal is too high, rapid decomposition and evaporation of organic matter will occur, causing 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, prepared 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 supplies, etc., which is made of a single metal such as molybdenum, tungsten, manganese, and platinum, or an alloy containing two or more of these metals, and is formed on an insulating ceramic layer. The layers are electrically connected through through holes 13. A die pad 14 and a bonding pad 15 are provided on the multilayer ceramic substrate constructed in this manner so that an LSI chip can be mounted.
An I/O pad 16 is formed on the back surface of the board for taking out signals from the mounting board and inputting signals into the board. Heat generated from the LSI chip mounted on the substrate is diffused into the ceramic substrate via the die pad 14. As a result of measuring the electrical properties of this sintered substrate, the specific resistance was 10 ¹¹ Ωcm or more, the dielectric constant was 8.7 (1MHz),
The dielectric loss was small, less than 10 ^-3 (1MHz). It was found that the electrical properties were comparable to those of conventional boards, and were sufficient to be used as a mounting board. Table 1 shows substrate properties and various characteristics of an example of a multilayer ceramic substrate produced by the manufacturing method of the present invention. This example is used as a sintering additive.
The table shows the amount added when CaC ₂ is used and the weight of aluminum nitride is 100. As can be seen from the table, a substrate was obtained in which fine wiring patterns and through holes were formed, extremely high bending strength, and extremely high thermal conductivity. Furthermore, its coefficient of thermal expansion is close to that of silicon, making it extremely convenient for mounting LSIs and the like.

[Table] *Sample 1 shows a comparative example.On the other hand, as sintering additives other than ^CaC2 , Sr, Ba,
Na, K, Rb, Cs, Cu, Ag, Mg, Cd, Hg,
A multilayer ceramic substrate made of aluminum nitride doped with acetylide compounds of Zn, Al, and Ce and their oxides including Ca was fabricated. The same manufacturing method was used with the firing temperature ranging from 1500°C to 2000°C. As a result, the thermal conductivity of the created substrate was able to achieve a value of 100W/mk or more when the additive amount was from 0.5wt% to 4.0wt%, and a value of 80W/mk or more from 0.3wt% to 8.0wt%. was obtained, and had superior heat dissipation properties compared to alumina substrates. (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 substrate which is also very effective in terms of properties can be obtained. The thermal conductivity of conventionally used alumina substrates is about 17 W/mk, and it can be seen that the thermal conductivity of the substrate according to the method of the present invention is at a very high level.
In addition, in terms of thermal expansion coefficient, Lumina substrate has a coefficient of 65×
10 ^-7 /°C, whereas the substrate prepared by the method of the present invention has a smaller coefficient of thermal expansion, which is closer to that of a silicon chip, and is advantageous in this respect as well.

[Brief explanation of the drawing]

1 to 3 are diagrams showing each manufacturing process of a highly thermally conductive multilayer ceramic substrate according to an embodiment of the present invention,
FIG. 4 is a diagram showing a firing profile in the firing process of the example, and FIG. 5 is a schematic perspective view of a completed substrate. 1... Through hole, 2... Conductor layer, 3... Insulator green sheet, 11... Insulating ceramic layer, 12... Conductor layer, 13... Through hole, 1
4... Die pad, 15... Bonding pad, 16... I/O pad.

Claims (1)

[Claims] 1. A method for manufacturing a multilayer ceramic substrate in which the ceramic layer is composed of a polycrystalline material mainly composed of aluminum nitride, in which aluminum nitride powder and Ca, Sr, Ba, Na, K, Rb, Cs, Cu, Ag,
A process of mixing a mixed powder consisting of at least one sintering additive among acetylide compounds of Mg, Cd, Hg, Zn, Al, and Ce with an organic binder and an organic solvent to form a slurry; a step of forming a film of the slurry, a step of forming a through hole in the formed green sheet to provide interlayer conduction, and a step of forming a conductor layer and embedding the conductor in the green sheet in which the through hole is formed. 1. A method for manufacturing a multilayer ceramic substrate, comprising the steps of laminating and thermocompression bonding green sheets each having a conductor formed thereon, and removing the binder and firing in a non-oxidizing atmosphere.