JPH0117258B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an integrated circuit package, and more particularly to an integrated circuit package characterized by matching of the coefficient of thermal expansion and heat dissipation of ceramic package members. In a small chamber airtightly surrounded by a package consisting of a ceramic insulating substrate, a cap, and a sealing material, the semiconductor element, the end of the lead piece introduced from the outside, and the wire electrically connecting the two are placed. Integrated circuit packages (referring to packaged integrated circuit products), which are enclosed structures, are widely used today. One of the drawbacks of using such a ceramic package is that the heat dissipation properties generated in the semiconductor element are extremely poor. This is a major hindrance in achieving larger capacity, higher integration, and smaller size of semiconductor devices. Therefore, in integrated circuit packages, ceramics used for insulating substrates on which semiconductor elements are mounted are required to have excellent thermal conductivity as well as electrical insulation properties. In addition, as substrate materials,
It is also desired that the material satisfies conditions such as having a thermal expansion coefficient similar to that of a silicon semiconductor and having high mechanical strength. Currently, alumina sintered bodies are used as an insulating substrate material that meets these conditions to some extent.
However, its thermal conductivity is low, 0.05 cal/cm・s・
It is about ℃. Therefore, the alumina sintered body is not a preferable material from the viewpoint of heat dissipation characteristics of semiconductor elements. On the other hand, as a proposal to improve the heat dissipation characteristics of a semiconductor element from a structural aspect while using a ceramic package, as shown in FIG. Methods of attaching the semiconductor element 1 are known. A semiconductor element 1 is placed inside a package consisting of a substrate 4, a cap 5, and a sealing material 6.
A molybdenum support plate 3 is attached to the copper stud 31 to relieve stress caused by the difference in thermal expansion between the two.
The element 1 is electrically connected to the end of a lead piece 3 bonded on a substrate 4 by a bonding wire 2 . The heat generated in the semiconductor element 1 is transmitted to the outside of the package via the support plate 32 and the copper studs 31, and is further dissipated by the cooling fins 9. In such a structure, all the heat transfer paths from the semiconductor element 1 to the cooling fins 9 are made of metal with excellent thermal conductivity, so that an integrated circuit package with high heat dissipation characteristics can be obtained. However, this method has the disadvantages of (1) an increase in the number of parts and a complicated structure, which increases the number of assembly steps, and (2) the use of parts with high specific gravity such as copper and molybdenum, which increases the weight of the product. However, there are disadvantages such as the difficulty of attaching it to a printed wiring board or the like. In order to overcome this situation, the present inventors conducted various research and developed silicon carbide ceramics that meet the above-mentioned conditions and have higher thermal conductivity than conventional materials and a coefficient of thermal expansion similar to that of silicon. By applying it to an insulating substrate, it became possible to fabricate an integrated circuit package with good heat dissipation characteristics (Application No. 56-
195986). However, as studies on the application of the silicon carbide substrate progressed, a problem arose that when a conventional alumina ceramic cap was combined with the substrate, cracks appeared in the glass layer that bonded and sealed them together. This is due to the difference in thermal expansion between silicon carbide ceramics and alumina ceramics. Based on these findings, the present invention complements the above proposal by limiting the thermal expansion coefficient of the cap material, thereby providing an integrated circuit package with excellent heat dissipation characteristics and even higher stability and reliability. is aimed at. That is, the feature is that the semiconductor element mounted on the substrate and the end of the lead piece introduced from the outside are placed in a small chamber airtightly surrounded by a silicon carbide insulating substrate, a cap, and a sealing glass. In an integrated circuit package that houses wires and wires that electrically connect them, the cap has a coefficient of thermal expansion (20 to 55) x
10 ^-7 /℃. Furthermore, in the present invention, glass having a coefficient of thermal expansion (30 to 55) x 10 ^-7 /°C, in particular, is used as the sealing material.
In practice, glass having a coefficient of thermal expansion of (40 to 55) 10 ^-7 /°C is suitable. In the present invention, the insulating substrate to which the semiconductor element is attached is substantially silicon carbide containing silicon carbide as a main component and containing 0.05 to 5% by weight of at least one selected from beryllium and beryllium compounds. It is composed of a sintered body that is made of elementary ceramics and has a relative density of 90% or more of the theoretical density. Its thermal expansion coefficient is (35~40)×10 ^-7 /℃, which is close to that of silicon, and its thermal conductivity is 0.2 cal/℃.
cm・s・℃ or higher. This thermal conductivity is 0.2cal/
The value cm・s・℃ is the value that is suitable for silicon carbide ceramics made by sintering without adversely affecting electrical insulation (resistivity of 10 ⁷ Ω・cm or more) and thermal expansion coefficient. This means the lower limit of thermal conductivity that can be obtained with good reproducibility, and moreover, it is about four times the thermal conductivity of conventional alumina ceramic substrates. In addition, since the coefficient of thermal expansion of the silicon carbide ceramic is close to that of silicon, when a semiconductor element is attached to an insulating substrate via an adhesive layer, the thermal stress caused by the difference in thermal expansion between the two is small. . Therefore, it is not necessary to insert a stress buffer material between the substrate and the element as shown in FIG. Using ceramics having such characteristics as the constituent material of the insulating substrate is a basic condition for improving the heat dissipation properties of the semiconductor element in the present invention. Based on this condition, in the present invention, a cap for covering and enclosing semiconductor elements, wiring, etc. on an insulating substrate has a coefficient of thermal expansion (20 to 55) x 10 ^-7 /
It is characterized by being made of material that has a temperature of ℃. As such materials, silicon carbide ceramics, mullite ceramics, zircon ceramics, silicon nitride ceramics, etc., which are the same as the materials of the insulating substrate, can be used. If a cap material with the above thermal expansion coefficient value is used, conventional alumina ceramics (thermal expansion coefficient of approximately 65×10 ^-7 /°C) will be used.
Compared to use, the expansion differential with the silicon carbide insulating substrate is reduced by 20 to 60%, and therefore the possible thermal stresses between the substrate and the cap are reduced accordingly. Ideally, the sealing glass material should have a thermal expansion coefficient close to that of the silicon carbide ceramic used for the insulating substrate, and the value is (30 to 55) x 10 ^-7 / °C is appropriate.
Note that since glass sealing is performed after bonding the semiconductor element onto the insulating substrate, glass with a high melting point is not suitable for use. Glass that can be sealed at temperatures below 500°C must be selected. By using ceramics and glass with the above-mentioned characteristics for the insulating substrate, cap, and encapsulant, it is possible to cool down from the sealing temperature to room temperature, and also to withstand thermal cycles between -55 and +150°C. Even when the process is repeated, it is possible to obtain an integrated circuit package that is stable without causing cracks in the sealing portion or abnormalities in electrical characteristics, has high reliability, and has excellent heat dissipation characteristics. Next, the present invention will be explained with reference to examples. Embodiment 1 FIG. 2 illustrates a cross section of an integrated circuit package of the present invention. In the figure, a semiconductor element 1 is bonded to the center of one surface 4a of an insulating substrate 4 made of silicon carbide ceramics with a metal solder layer 7, and a sealing glass layer 6 is bonded on the same surface. One ends 3 a of the plurality of lead pieces 3 and the element 1 are electrically connected by bonding wires 2 . The other end 3b of the lead piece 3 extends outward from the periphery of the substrate 4. The end portions 3a of the element 1, bonding wire 2, and lead piece 3 are surrounded by an insulating substrate 4 and a cap 5, and the gaps between the cap 5, the substrate 4, and the lead piece 3 are separated by a solder glass layer 6. Hermetically sealed. Now, in such a structure, when glass with a coefficient of thermal expansion (50 to 55) × 10 ^-7 /℃ is used for sealing, the maximum applied to the glass in the temperature range from the sealing temperature to room temperature is We calculated how thermal stress changes depending on the thermal expansion coefficient of the cap material. This calculation was performed by modeling the package as a hollow disk, dividing it into elements, and using a finite element method analysis program for three-dimensional axisymmetric problems. The results are shown in FIG. Since the strength of glass is ^about 4Kg/mm2, the coefficient of thermal expansion is 55×10 ^-7 /
Ceramics at temperatures above ℃ will cause cracks in the glass,
Unsuitable as cap material. Materials with a coefficient of thermal expansion (α) of (20 to 55) × 10 ^-7 /°C include the silicon carbide ceramics (α = (35 to 40) × 10 ^-7 / °C), mullite ceramics (α = (43 to 55) × 10 ^-7 /℃), zircon ceramics (α = (30 to 40) × 10 ^-7 /℃), certain silicon nitride ceramics (α = (20 to 35) ×
10 ^-7 /℃) etc. are used. The silicon carbide ceramic used here for the insulating substrate consists essentially of silicon carbide except for beryllium oxide in an amount of 0.05 to 5% by weight, and is sintered with a density of 90% or more of the theoretical density. It is the body. It has electrical insulation with a resistivity (room temperature) of 10 ⁸ Ω・cm or more and a thermal conductivity of 0.2 to 0.7 cal/cm・s.
℃, and has a bending strength of 30Kg/mm2 or ^more . The integrated circuit package obtained with the above-mentioned material composition has an insulation resistance of 10 ⁸ Ω or more between the lead pieces, and when cooled from the sealing temperature (460°C) to room temperature, and - 55-150℃ cooling cycle
Even after 1,000 tests, there were no accidents such as damage or abnormalities in electrical characteristics. Example 2 An integrated circuit package was produced basically in the same manner as in Example 1. The insulating substrate is silicon carbide ceramic made of a sintered body with a density of 98% of the theoretical density, except for the beryllium content (by weight of beryllium oxide) and other impurities that inevitably include silicon carbide. Made with. Its characteristic is that the specific gravity is approximately
3.2, resistivity ^10-13 Ω・cm (room temperature), thermal expansion coefficient (25
~300℃) around 35×10 ^-7 /℃, thermal conductivity 0.6cal/
cm・s・℃ and bending strength values of around 45 kg/mm ² were obtained. The cap was made from mullitic ceramics with a coefficient of thermal expansion of 45 x 10 ^-7 /°C. When glass having various coefficients of thermal expansion is used for sealing the insulating substrate and cap, the relationship between the maximum thermal stress applied to the glass and its coefficient of thermal expansion is shown in FIG. 3 of Example 2. I asked for it in the same way as in the case. The results are shown in FIG. When the coefficient of thermal expansion of glass exceeds 55×10 ^-7 /°C, the glass is subjected to excessive stress and cracks. On the other hand, glasses with thermal expansion coefficients of less than 55×10 ⁻⁷ /° C. experience only small thermal stresses. But 30×
Since it is impossible to obtain a glass having a coefficient of thermal expansion of 10 ^-7 /°C or less and a low melting point desired for sealing, it is not practically practiced. Therefore,
Glass having a thermal expansion of (30 to 55)×10 ^-7 /°C is desirable. An integrated circuit package was prepared using the above-mentioned insulating substrate, cap, and sealing glass having a thermal expansion coefficient of (45 to 48) x 10 ^-7 /°C and a sealing temperature of 450 to 460°C. The integrated circuit package provided characteristic values of insulation resistance between lead pieces of 10 ⁸ Ω or more and thermal resistance between the semiconductor element and the surface of the insulating substrate of 12.5° C./W. Also,
The package can withstand heating and cooling cycles between -55 and 150℃.
Even after being tested 100 times, there were no accidents such as damage or abnormalities in electrical characteristics. Example 3 In the integrated circuit package described in Example 1, cooling fins 9 made of metal such as aluminum were attached to the insulating substrate 4 and the adhesive layer 10, as shown in FIG. The fins 9 are preferably bonded with an epoxy resin or silicone resin adhesive filled with a thermally conductive filler. Furthermore, the fins can be bonded to the metalized portion of the silicon carbide insulating substrate by solder, as desired. In such a configuration, the thermal resistance between the semiconductor element and the outside atmosphere is
9.3℃/W, 12.5℃/W in Example 2
was further reduced. This value corresponds to the thermal resistance of a conventional integrated circuit package (see Figure 1), which is approximately 11.5
Approximately 20% lower than ℃/W. Furthermore, as a modification, the substrate and the fins can be integrally made of silicon carbide ceramics, and by applying this, the thermal resistance of the integrated circuit package can be reduced to 5.1° C./W. In addition, the integrated circuit package did not cause any accidents such as breakage or abnormality in electrical characteristics even after being subjected to 100 cycles of cooling and heating cycles at -55 to 150°C. Embodiment 4 The structure of the integrated circuit package of the present invention is not limited to the above embodiments. Various variants are possible. Examples (cross sections) are shown in FIGS. 6 and 7. A semiconductor element 1 is placed in the center of the inner bottom surface of the box-shaped insulating substrate 4 through a metallized layer 8.
is glued. One end of the lead piece 3 is electrically connected to the semiconductor element 1 by the bonding wire 2, and the end that rises along the inner surface of the other insulating substrate and is drawn out to the periphery of the substrate is bonded to the lead frame 11 by a solder layer 7. Ru. Then, the substrate 4
A lid-shaped cap 5 is fitted into the opening of the board, and a glass 6 is provided to fill the gap between the board, cap, or lead piece.
It is sealed with. The insulating substrate was made of silicon carbide ceramic containing 0.05 to 5% by weight of beryllium, and the cap was made of mullite ceramic having a coefficient of thermal expansion of 45×10 ^-7 /°C. Furthermore, glass having a thermal expansion coefficient of 47×10 ^-7 /°C and a sealing temperature of 460°C was used for sealing. The fabricated integrated circuit package is -55 to 150℃
It withstood 100 heating and cooling cycles without any damage or abnormalities in electrical characteristics. Comparative Experimental Example As shown in Table 1, packages were created using sealing glasses with different thermal expansion coefficients for bonding the substrate and cap. Using this, we conducted a post-sealing leak test (He gas) and a comparative experiment on cooling and heating cycles. The results are shown in Table 1.

[Table] As is clear from Table 1, No.5, 6, 8~
The packages of the present invention designated by No. 11 and No. 15 both showed excellent results in the leak test and the cooling/heating cycle, indicating that there were no cracks or the like in the sealed portion.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional integrated circuit package.
2, 5, 6, and 7 are cross-sectional views of an integrated circuit package that is an example of the present invention, and FIG. 3 is a relationship between the thermal expansion coefficient of the cap material and the maximum thermal stress generated in the sealing glass layer. FIG. 4 is a graph showing the relationship between the coefficient of thermal expansion of the sealing glass and the maximum thermal stress generated in the glass layer. DESCRIPTION OF SYMBOLS 1... Semiconductor device, 2... Bonding wire, 3... Lead piece, 4... Insulating substrate, 5... Cap, 6... Sealing glass, 7... Metal solder layer, 8... Metallized layer, 9 ...cooling fin, 1
0... Adhesive layer, 11... Lead frame, 31...
...Copper stud, 32...Molybdenum support plate.

Claims (1)

[Scope of Claims] 1. A semiconductor placed on the silicon carbide insulating substrate, a cap, and an end of a lead piece introduced from the outside into a small chamber airtightly surrounded by a sealing glass. In the integrated circuit package, the silicon carbide insulating substrate is made of substantially silicon carbide containing 0.05 to 5% by weight of at least one of beryllium and beryllium compounds as beryllium. A sintered body with a relative density of 90% or more of the theoretical density and a thermal conductivity of 0.2cal/at room temperature.
cm・s・℃ or more, thermal expansion coefficient (35 to 40) x 10 ^-7 /
℃ is an electrically insulating substrate, and the cap has a thermal expansion coefficient (20~55) x
10 ^-7 /℃ made of ceramic material selected from mullite, silicon carbide, zircon, and silicon nitride, and the substrate and cap have a melting point of 500℃ or less and a thermal expansion coefficient (30 to 55). ×10 ^-7 /°C bonded and sealed with a sealing glass, and the lead piece is inserted into the small chamber through the bonded and sealed portion of the substrate and the cap. . 2. In a small chamber airtightly surrounded by a silicon carbide insulating substrate, a cap, and a sealing glass, the semiconductor placed on the substrate, the ends of the lead pieces introduced from the outside, and the ends of the leads are electrically connected. In the integrated circuit package, the silicon carbide insulating substrate is a sintered body substantially made of silicon carbide containing 0.05 to 5% by weight of at least one of beryllium and beryllium compounds as beryllium. Relative density to theoretical density is 90% or more, thermal conductivity at room temperature is 0.2cal/
cm・s・℃ or more, thermal expansion coefficient (35 to 40) x 10 ^-7 /
℃ is an electrically insulating substrate, and the cap has a thermal expansion coefficient (20~55) x
10 ^-7 /℃ made of ceramic material selected from mullite, silicon carbide, zircon, and silicon nitride, and the substrate and cap have a melting point of 500℃ or less and a thermal expansion coefficient (30 to 55). ×10 ^-7 /℃ bonded and sealed with sealing glass, the lead piece is inserted into the small chamber through the bonded sealing part of the substrate and the cap, and the semiconductor element is mounted. An integrated circuit package characterized in that cooling fins are provided on the back side of a printed circuit board.