JPH04125950A - Ceramic package - Google Patents

Abstract

PURPOSE:To manufacture the title ceramic package in excellent heat dissipation characteristics compared with alumina by a method wherein a semiconductor chip is mounted in the silicon nitride body containing specific amount of aluminum and crystal grains. CONSTITUTION:The slurry produced by adding rare earth oxide as a sintering assistant to the silicon nitride powder in different Al2O3 contents is molded in specific shape. Next, the mold is baked in specific nitrogen atmosphere to manufacture a ceramic base 3 and a ceramic cap 4. Next, the thermal conductivity of a silicon nitride diffused substrate and the package thermal resistance are adjusted meeting the requirements for the silicon nitride crystal grains existing in the space per linear distance of 10mum not exceeding 20 each and the containing Al2O3 amount not exceeding 0.3weight%. Through these procedures, the silicon nitride base ceramic package in excellent heat dissipation characteristics compared with alumina can be manufactured.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a ceramic package of circa dip type, circuquat type, and flat type that uses a silicon nitride sintered body with high thermal conductivity and has excellent heat dissipation properties. It is.

(Prior Art) As semiconductor chips become more highly integrated and faster, the amount of heat generated is increasing. This trend is particularly noticeable for chips with bipolar circuits, and in recent years, ceramic packages using materials with excellent heat dissipation, that is, good thermal conductivity, have been required as packages for mounting these chips. became.

Conventionally, ceramic packages made of alumina ceramic have been widely used for such chips because they are more reliable and have better heat dissipation than substrates made of resin. For example, a ceramic base 3 on which a semiconductor chip 1 is mounted via an Au conductor layer 2 as shown in FIG.
and a ceramic cap 4 are sealed with a sealing agent 5 made of glass or resin adhesive, and a metal lead frame 7 is electrically connected to the semiconductor chip 1 via a bonding wire 6. and flat-type packages are known.

However, the heat dissipation properties of alumina packages are insufficient for the recent increase in the amount of heat generated by semiconductor chips, and a package with excellent heat dissipation properties has been desired. In addition, alumina packages have problems with alumina ceramics, such as the brittleness of alumina ceramics, that is, low fracture toughness, which makes it easy to chip the etch of the package. There was a problem in that stress was generated and in some cases, thermal stress caused destruction.

Recently, aluminum nitride ceramics, which have better thermal conductivity and a coefficient of thermal expansion matching that of silicon, and BeO
Silicon carbide ceramics with small amounts of added are beginning to be used as package ceramic materials. However, aluminum nitride ceramics have problems with poor environmental resistance such as water resistance and alkali resistance. In addition, silicon carbide ceramics to which a small amount of BeO is added have poor voltage resistance because only the grain boundaries of the ceramic are insulating, and they cannot be densified unless hot press firing, resulting in high process costs.

On the other hand, when silicon nitride sintered bodies are used as the ceramic material for packages, they have better environmental resistance and mechanical strength than conventional ceramics, but their thermal conductivity is as low as that of alumina, resulting in packages with excellent heat dissipation. I couldn't get it.

For this reason, there has been a demand for ceramic packages with excellent environmental resistance, mechanical strength, and heat dissipation.

(Problems to be Solved by the Invention) In the present invention, a silicon nitride sintered body is used as the substrate material, but as is well known, silicon nitride has extremely high strength and excellent environmental resistance. There is.

In addition, the coefficient of thermal expansion is closer to that of silicon, 3 to 4 ppm/'C, compared to that of alumina, 6 to 7 ppm/'C, and is more consistent, so it is highly reliable when a semiconductor chip is mounted. However, most silicon nitrides have compositions that pursue mechanical strength at room and high temperatures.
The thermal conductivity of these materials was low and comparable to that of alumina ceramics. Therefore, it was not possible to obtain a substrate with good heat dissipation properties.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a ceramic package such as a ceramic package having good heat dissipation properties.

(Means for Solving the Problems) A ceramic package of the present invention includes: a ceramic base on which a semiconductor element is mounted; a ceramic cap bonded to the base substrate with a glass or resin adhesive;
The present invention relates to a ceramic package having a metal lead frame and having excellent heat dissipation properties, the ceramic base being made of a sintered silicon nitride body.

(Function) In the present invention, the ceramic base is constituted by a silicon nitride sintered body containing 0.3% by weight or less of aluminum in terms of alumina. After firing, this silicon nitride sintered body has a linear distance lO
It is characterized by containing 20 or less silicon nitride crystal particles per μm.

The silicon nitride sintered body used in the present invention has a thermal conductivity of 40
W/mk or more, typically 100 W/mk, which is much larger than the 20 W/mk of alumina, so the package has good heat dissipation, is very strong, has excellent environmental resistance, and has excellent heat resistance. The coefficient of expansion matches the coefficient of thermal expansion of silicon, resulting in a ceramic package with extremely excellent characteristics.

The ceramic cap may be the same as the silicon nitride sintered body used in the present invention, or may be made of inexpensive ceramic such as alumina ceramic, mullite ceramic, or glass ceramic. Since the cap does not directly mount a semiconductor chip, it does not significantly contribute to the heat dissipation of the package, so it can also be used with ceramics with poor thermal conductivity such as alumina ceramics, mullite ceramics, and glass ceramics. However, reliability will be higher if the thermal expansion coefficients of the base and cap match, so use mullite ceramics with a thermal expansion coefficient of 2 to 5p.
pm/°C glass ceramic is preferred. When alumina-based ceramic is used for the cap, a glass with a thermal expansion coefficient intermediate to that of the silicon nitride sintered body used in the present invention may be used for sealing, or a buffer frame which also has an intermediate thermal expansion coefficient may be used. It is preferable to use the device by sandwiching the body between the base and the cap. The excellent features of the substrate of the present invention will be described in more detail below.

[High heat dissipation]

The ceramic used for the base in the present invention is a silicon nitride sintered body containing 0.3% by weight or less of aluminum in terms of alumina, and preferably further has a linear distance of 1
It is characterized by containing 20 or less silicon nitride crystal particles in 10l1. A component that forms a liquid phase during firing is usually added to the silicon nitride sintered body as a sintering aid. Typically, rare earth oxides, alkaline earth metal oxides, and other metal oxides are considered. Furthermore, molybdenum, tungsten metal, or oxides or compounds thereof may be added as additives specific to package ceramics for coloring. The present invention can basically be applied to silicon nitride sintered bodies of any composition as long as the amount of aluminum is below the above-mentioned limit. This is because the thermal conductivity of the silicon nitride sintered body is most influenced by the amount of aluminum, and if the amount is below the above limit, it will be 40W/mk
The silicon nitride ceramic described above can be obtained, and a package can be obtained which has superior heat dissipation properties compared to alumina. If a silicon nitride sintered body containing more than 0.3% by weight of aluminum in terms of alumina is used, the thermal conductivity of the ceramic will deteriorate, resulting in a package with poor heat dissipation.

[High strength]

Another important feature of the silicon nitride substrate of the present invention is that it has high strength. Conventional alumina substrates have a bending strength of 30
kg/mm'', but the etch of the package was easily chipped due to the brittleness peculiar to ceramics.However, the silicon nitride ceramic substrate of the present invention has a bending strength of more than 30 kg/mm', and has a high fracture toughness. Value 5 MP
am”, so the brittleness is also significantly improved compared to an alumina substrate.

[High reliability]

Another important feature is good environmental resistance. In other words, a major feature of ceramic substrates is that they have superior environmental resistance such as water resistance compared to resin substrates, resulting in high reliability.For example, alumina substrates have been evaluated as having sufficiently high reliability. I was getting a lot of money.

However, aluminum nitride substrates, which are ceramic substrates with excellent heat dissipation properties, have poor environmental resistance such as water resistance and alkali resistance, so there has been a problem with reliability, which is a major feature of ceramic substrates. On the other hand, the silicon nitride substrate material of the present invention has excellent environmental resistance and does not have the problems that occur with aluminum nitride.

[Electrical characteristics]

The electrical insulation properties are very good, and there is no problem of low withstand voltage as with silicon carbide substrates.

As described above, the ceramic package obtained by the present invention has superior characteristics compared to not only conventional alumina packages but also packages using aluminum nitride or silicon carbide.

(Example) FIG. 1 and FIG. 2 are sectional views each showing the structure of an example of the ceramic package of the present invention.

As described above, in the example shown in FIGS. 1 and 2, the ceramic base 3 and the ceramic cap 4, preferably made of silicon nitride having predetermined properties, on which the semiconductor chip 1 is mounted via the Au conductor layer 2, are made of glass. The package is of a cer-deep type and has a metal lead frame 7 which is sealed with a sealing agent 5 made of a resin adhesive and is electrically connected to a semiconductor chip 1 via a bonding wire 6.

An actual example will be explained below.

Rare earth oxides shown in Table 1 were added as sintering aids to silicon nitride powders with different AAxOs contents, water was added, and wet mixing was performed using silicon nitride cobblestones and a resin pot. The obtained slurry was dried and granulated using a spray dryer.

The granulated powder was molded into a predetermined shape by ordinary dry press molding using a mold. The molded body was heated at 1750 to 1950°C under a nitrogen atmosphere of 9.5 atm as shown in Table 1.
After firing for 10 hours, a ceramic base and a ceramic cap were obtained.

Thermal conductivity of these ceramic bases and ceramic caps was measured by a laser flash method. Further, the number of silicon nitride particles in the sintered body was determined from the number of silicon nitride particles present per 10 μm of linear distance. The amount of Aj'203 in the sintered body was measured by fluorescent X-ray analysis. These measured values are shown in Table 1. Moreover, the coefficient of thermal expansion was 2 to 4 ppm/'C in all the sintered bodies.

Using the obtained ceramic base and ceramic cap, a 160-pin semiconductor chip package was prototyped with the structure shown in FIG. 1. A semiconductor chip was actually mounted to generate heat, and the package was cooled with air at a wind speed of 4 m/s to measure the thermal resistance of the package. The results are shown in Table 1. Note that when a package was prototyped using alumina, the thermal resistance was 27°C/W.

Next, a package having the structure shown in FIG. 2 and having 120 lead pins was fabricated in the same manner as in Example 1. A semiconductor chip was actually mounted to generate heat, and the package was cooled with air at a wind speed of 4 m/s to measure the thermal resistance of the package. The results are shown in Table 2. The thermal resistance when the package was prototyped using alumina was 24
°C/W.

From Tables 1 and 2, it can be seen that the silicon nitride heat dissipation substrate has better heat dissipation characteristics than alumina. Also, in the silicon nitride sintered body, the number of silicon nitride particles present per 10 μm of linear distance is 20 or less, and the amount of Al2O3 contained is 0.
．． It can be seen that if it is 3 wt% or less, it is even better. The reason for this is thought to be that when the number of silicon nitride particles existing per linear distance lOμm is 20 or more, the scattering of heat at grain boundaries becomes smaller and the thermal conductivity becomes higher.
It is thought that this is because when the amount of 3 exceeds 0.3 wt%, it forms a solid solution within the silicon nitride particles, reducing the thermal conductivity of the silicon nitride particles.

(Effects of the Invention) As is clear from the above description, according to the ceramic package of the present invention, the ceramic base of the ceramic base, such as a ceramic base, is made of silicon nitride, preferably contains 0.3% by weight or less of aluminum in terms of alumina, and the straight line distance is Since silicon nitride ceramics containing 20 or less crystal grains per 10 μm are used, a ceramic package with good heat dissipation characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are sectional views each showing the structure of an example of the ceramic package of the present invention. 1... Semiconductor chip 2... Au conductor layer 3...
・Ceramic base 4...Ceramic cap 5・
... Sealing agent 6 ... Bonding wire 7 ... Lead frame Figure 1 Figure 2 Procedural amendment March 5, 1991

Claims (1)

[Claims] 1. In a ceramic package consisting of a ceramic base on which a semiconductor element is mounted, a ceramic cap bonded to the base substrate with a glass or resin adhesive, and a metal lead frame, the ceramic base is made of silicon nitride sintered material. A ceramic package with excellent heat dissipation that is characterized by being made of a solid body. 2. The ceramic package according to claim 1, which is a silicon nitride sintered body containing 20 or less silicon nitride crystal grains at a distance of 10 μm. 3. The ceramic package according to claim 1 or 2, wherein the silicon nitride sintered body contains 0.3% by weight or less of aluminum in terms of alumina.