JPH0810735B2 - Ceramic package - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ceramic package excellent in heat dissipation, which uses a silicon nitride sintered body having a high thermal conductivity as a substrate on which a semiconductor chip is mounted. is there.

(Prior Art) Along with the high integration and high speed of semiconductor chips, the amount of heat generated is increasing. This tendency is particularly remarkable for chips having a bipolar circuit, and in recent years, as a package for mounting these chips, a ceramic package using a material having excellent heat dissipation, that is, having good thermal conductivity is required. became.

Conventionally, a ceramic package made of alumina ceramic has been widely used for such a chip because of its high reliability and good heat dissipation compared with a substrate using a resin. For example, as shown in FIG. 4, the alumina ceramic 21 has metal conductor wiring inside, and a large number of metal pins 23 are used for connecting terminals of the mounted semiconductor chip 22 and external circuits.
There is known a pin grid array type ceramic package in which are arranged, and a chip carrier type ceramic package using metal leads instead of metal pins.

However, with respect to the heat generation amount of semiconductor chips, which is increasing more and more recently, the heat dissipation of the alumina package is insufficient, and a package having excellent heat dissipation has been demanded. Also, the alumina package does not match the thermal expansion coefficient of silicon, which is the material of the semiconductor chip,
There has been a problem that the chip is thermally stressed or, in some cases, is broken by the thermal stress.

Recently, aluminum nitride ceramics, which has better thermal conductivity and a coefficient of thermal expansion that matches that of silicon, are the fourth
It is beginning to be used as the ceramic material in the package shown. However, the aluminum nitride ceramic has a problem of poor environmental resistance such as water resistance and alkali resistance. In addition, mullite ceramics have begun to be used as the ceramic material of the package shown in FIG. 4 because the thermal expansion coefficient of silicon is matched with that of silicon. However, since mullite has a poor thermal conductivity, it has a drawback that the heat dissipation of the package is poor.

Therefore, recently, in order to solve these problems,
Packages such as those shown in Figures and 2 are beginning to be used. In these, a ceramic substrate having a high thermal conductivity is used as a heat dissipation substrate only in a substrate portion on which a semiconductor chip is mounted, and alumina or mullite ceramic is used in a substrate portion having circuit wiring inside.

These alumina and mullite ceramics are industrially used in large quantities and are inexpensive, and the manufacturing process has a low firing temperature, and the manufacturing process of packages using these ceramics, which have been used in large quantities in the past, is used as is. It also has the advantage that it can be done. In addition, if a high-speed signal propagates in the wiring circuit or if you want to reduce the resistance of the power supply circuit, it is necessary to use a conductor with a low conduction resistance such as Ag, Cu, or Au, so these low resistance metal A low temperature fired ceramic that is fired below 1100 ° C., which is below the melting point, is used. Further, a wiring circuit may be formed by using a polyimide resin as an insulating material, forming a thin film as a conductor by sputtering, vapor deposition, plating or the like, and obtaining a conductor pattern by photolithography. Then, a silicon carbide substrate, which is made into an insulator by adding aluminum nitride or Be0, is used for the heat dissipation substrate portion on which the semiconductor chip is mounted.

For joining the heat dissipation board and the board that has circuit wiring inside, join with glass, join with activated metal containing Ti or Zr metal in Ag, Cu or their alloys, or join with each board There is a case where the conductors formed in the above are joined by a metal braze, or a case where the conductors are joined by firing a metal paste. However, when an alumina substrate is used as a substrate having circuit wiring inside, the coefficient of thermal expansion does not match that of the silicon carbide substrate that has been made into an insulator by adding aluminum nitride or Ba0, which is a heat dissipation substrate. Since cracks may be generated due to thermal stress, a ceramic or metal frame having an intermediate coefficient of thermal expansion may be sandwiched between them.

When the low temperature fired ceramic is used as a substrate having a circuit arrangement inside, the low temperature fired ceramics can be joined at the same time when firing. When a polyimide resin is used, a wiring circuit is directly formed on the heat dissipation substrate by the polyimide resin and a thin film circuit. However, the aluminum nitride used for the heat dissipation substrate has poor environment resistance such as water resistance and alkali resistance, and although the environment resistance of other wiring board parts is good, the reliability of the entire package is impaired. Further, since the silicon carbide substrate has an insulating property only in the grain boundary portion of the crystal grains of the ceramic, there is a problem that the withstand voltage is low, and there is a problem as an insulating substrate.

(Problems to be Solved by the Invention) In the present invention, a silicon nitride sintered body is used as a substrate material for heat dissipation. As is well known, silicon nitride has very good insulating properties and excellent environmental resistance. Further, the coefficient of thermal expansion is closer to that of silicon, which is 3 to 4 ppm / ° C., as compared with that of alumina, which is 6 to 7 ppm / ° C., and is more closely matched, so that reliability when a semiconductor chip is mounted is also high. However, most of ordinary silicon nitrides have a composition that pursues mechanical strength at room temperature and high temperature, and their thermal conductivity is small, which is equivalent to that of alumina ceramics. Therefore, it was not possible to obtain a package having good heat dissipation even with the structure shown in FIGS.

An object of the present invention is to solve the above-mentioned problems and to provide a ceramic package having good heat dissipation.

(Means for Solving the Problems) A ceramic package of the present invention is a heat dissipation board made of silicon nitride on which a semiconductor chip is mounted, and a wiring circuit for signal propagation and a power supply wiring circuit, which are connected to the heat dissipation board. And a heat dissipation substrate made of silicon nitride containing 20 or less crystal particles in a linear distance of 10 μm, and containing 0.3 wt% or less of aluminum in terms of alumina.

(Operation) In the present invention, a substrate on which a semiconductor chip is mounted 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 is characterized by containing 20 or less silicon nitride crystal grains at a linear distance of 10 μm. A component forming a liquid phase during firing is usually added to a silicon nitride sintered body as a sintering aid. Typically, rare earth oxides, alkaline earth metal oxides, and other metal oxides are considered.

In addition, molybdenum, tungsten metal, or oxides or compounds thereof may be added for coloring as an additive peculiar to the ceramics for the package.

The present invention can be applied to a silicon nitride sintered body of basically any composition as long as the amount of aluminum is not more than the above-mentioned limited amount. This is because the thermal conductivity of the silicon nitride sintered body is most affected by the amount of aluminum.

The silicon nitride sintered body used in the present invention has a thermal conductivity of 40 W /
Since it is more than mk, typically 100 W / mk, which is much larger than about 20 W / mk of alumina, a package with good heat dissipation can be obtained. If a silicon nitride sintered body containing more than 0.3% by weight of aluminum in terms of alumina is used, the heat conductivity of the ceramic deteriorates, resulting in a package with poor heat dissipation.

Further, the silicon nitride substrate material of the present invention is also extremely excellent in environmental resistance, and does not have the problem that aluminum nitride causes. Since the withstand voltage characteristic is also very good, there is no problem like silicon carbide.

(Embodiment) FIGS. 1 to 3 are sectional views showing the structure of an example of the ceramic package of the present invention. In the example shown in FIG. 1, the semiconductor chip 3 is mounted on the heat dissipation substrate 1 made of a predetermined silicon nitride via the gold plating layer 2, and the wiring conductor 5 and the semiconductor chip 3 of the wiring substrate 4 made of mullite are arranged. Connecting with the bonding wire 6, and arranging a large number of metal pins 7 for connecting terminals to the external circuit, and finally, the heat dissipation board 1
2 shows a pingrit array type ceramic package in which the wiring board 5 and the wiring board 5 are connected to each other through a connection active metal 8 and a cap 9 is provided. FIG. 2 shows a chip carrier type ceramic package using metal leads 10 instead of metal pins 7. FIG. 3 shows a ceramic package in which a multilayer wiring board made of Au thin film in a polyimide resin is used as the wiring board 4 and a conductor pad 11 for an external terminal is used for connection with the outside.

 Hereinafter, an actual example will be described.

Example 1 Rare earth oxides shown in Table 1 were added as a sintering aid to silicon nitride powders having different Al ₂ O ₃ contents, water was added, and the mixture was wet mixed with silicon nitride boulders using a resin pot. The obtained slurry was dried and granulated with a spray dryer. The granulated powder was molded into a predetermined shape by usual dry press molding using a mold. The molded body was fired in a nitriding atmosphere of 9.5 atm at 1750 to 1950 ° C. for 1 to 10 hours as shown in Table 1.
The thermal conductivity of the obtained sintered body was measured by the laser flash method. Further, the number of silicon nitride particles in the fired body was calculated from the number of silicon nitride particles present per linear distance of 10 μm. The number of particles was measured as follows. First, a microstructure of an arbitrary cross section of a silicon nitride body was photographed with a scanning electron microscope at a magnification at which Si ₃ N ₄ particles could be individually identified. Next, a straight line was drawn on the photograph, and the number of particles crossing the straight line was counted. By changing the field of view until the number of particles exceeds 1000, draw a straight line, and from the total distance L (μm) of the straight line required to measure 1000 particles, (1000 / L) × 10
It was converted to the number per 10 μm. For example, if a straight line of 500 μm is required to measure 1000 particles, the number of particles per 10 μm will be 20. The amount of Al ₂ O ₃ in the sintered body was measured by a fluorescent X-ray analysis method. Table 1 shows these measured values.
In addition, the coefficient of thermal expansion is 2 to 4 ppm / ° C for any sintered body.
Met.

The obtained sintered body was used as a heat dissipation substrate on which a semiconductor chip was mounted. Further, as a substrate having wiring inside, a wiring substrate using mullite ceramic as an insulating material and tungsten as a conductor was used. Ag these substrates
Bonding was performed with an activated metal containing a small amount of brazing Ti. Thus, the semiconductor chip package having the structure shown in FIG. 1 was prepared. Actually mounted semiconductor chip to generate heat and wind speed
The thermal resistance of the package was measured after cooling with air under the condition of 4 m / s. The results are shown in Table 1. For comparison, the thermal resistance measured by the same method using alumina as a heat dissipation substrate was 22 ° C./W.

It can be seen from Table 1 that the heat dissipation substrate made of silicon nitride has excellent heat dissipation characteristics as compared with alumina. Further, in the case of silicon nitride as well, it can be seen that it is further excellent if the number of silicon nitride particles present per linear distance of 10 μm is 20 or less and the amount of Al ₂ O ₃ contained is 0.3 wt% or less. The reason for this is a linear distance of 10 μm
It is considered that if the number of silicon nitride particles present per area is 20 or more, the heat scattering at the grain boundaries becomes large and the thermal conductivity decreases, and if the amount of Al ₂ O ₃ is 0.3 wt% or more. It is considered that if there is, it forms a solid solution in the silicon nitride particles and reduces the thermal conductivity of the silicon nitride particles.

Example 2 Ceramic composition mixed powder for low temperature firing substrate consisting of 90% by weight of glass powder of cordierite composition and 10% by weight of alumina powder, acrylic organic binder, plasticizer, toluene and alcohol solvent in alumina pot and alumina. Mix well with a ball to make a slurry. further,
A green tape with a thickness of 0.3 mm was created by the doctor blade method.

Ag-based powder, acrylic organic binder, and terpineol-based organic solvent were well kneaded with a three-roller to obtain a conductive paste for printing. Using this paste
A conductor wiring pattern was printed on the green tape. The green tapes on which these conductor patterns are printed are superposed in a predetermined order, placed on a silicon nitride substrate prepared by the same method as in Example 1, and laminated under pressure of 100 ° C. and 100 kg / cm ^2. Integrated. The connection of each conductor layer was realized by filling a through hole formed by punching a green tape with a conductor paste. It was baked at 900 ° C in an air atmosphere.
As a result, as shown in FIG. 2, on the silicon nitride substrate,
A package having a structure in which low-temperature fired wiring boards are joined was obtained. The metal leads were joined by Au—Sn alloy brazing.

Example 3 On a silicon nitride substrate of the present invention obtained by the same method as in Example 1, a via hole for connecting a conductor pattern and an interlayer conductor pattern was formed by photolithography using a photosensitive polyimide resin and an Au sputtered thin film. A multilayer wiring circuit was obtained. As a result, a package as shown in FIG. 3 was obtained.

(Effects of the Invention) As is clear from the above description, according to the present invention, the heat dissipation substrate contains silicon nitride, preferably 0.3% by weight or less of aluminum in terms of alumina, and the crystal particles are contained in a linear distance of 10 μm. By including 20 or less of silicon nitride, heat dissipation characteristics can be improved, and thus a ceramic package having excellent heat dissipation can be obtained.

[Brief description of drawings]

1 to 3 are sectional views showing the structure of an example of the ceramic package of the present invention, and FIG. 4 is a sectional view showing the structure of an example of a conventional ceramic package. 1 ... Heat dissipation board, 2 ... Gold plating layer 3 ... Semiconductor chip, 4 ... Wiring board 5 ... Wiring conductor, 6 ... Bonding wire 7 ... Metal pin, 8 ... Connection activation metal 9 ... … Cap, 10 …… Metal lead 11 …… Conductor pad

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Manabu Isomura 3-150 Omoteyama, Tenpaku-ku, Nagoya, Aichi NGK Yasushi Dormitory B-204 (56) References JP-A-62-232943 (JP, A)

Claims (4)

[Claims] 1. A heat dissipation board made of silicon nitride on which a semiconductor chip is mounted, and a wiring board connected to this heat dissipation board and having a wiring circuit for signal propagation and a wiring circuit for power supply therein. However, the linear distance of the crystal particles is 10 μm
A ceramic package which is made of silicon nitride containing 20 or less and contains 0.3% by weight or less of aluminum in terms of alumina. 2. The ceramic package according to claim 1, wherein the insulating material of the printed circuit board is mullite ceramic. 3. The insulating material of the printed circuit board has a firing temperature of 11.
It is fired at a temperature below 00 ° C, and the internal wiring conductor is Ag-based, Cu
The ceramic package according to claim 1, wherein the ceramic package is made of an Au-based material. 4. The ceramic package according to claim 1, wherein the insulating material of the printed circuit board is a polyimide resin.