Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2000-02-25
2003-11-11
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S762000
Reexamination Certificate
active
06646344
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a new composite material and, more particularly, to a copper composite material of low thermal expansion and high thermal conductivity, and various kinds of uses such as a semiconductor equipment in which this composite material is used.
2. Description of the Prior Art
Techniques related to the conversion and control of electric power and energy by means of electronic devices and, in particular, power electronic devices used in an on-off mode and power conversion systems as applied techniques of these power electronic devices are called power electronics.
Power semiconductor devices with various kinds of on-off functions are used for power conversion. As such semiconductor devices, there are put to practical use not only rectifier diodes which contain pn junctions and which have conductivity only in one direction, but also thyristors, bipolar transistors, MOS FETs (metal oxide semiconductor field effect transistors) and etc. which differ from each other in various combinations of pn junctions. Moreover, there are also developed insulated gate type bipolar transistors (IGBTS) and gate turn-off thyristors (GTOs) which have a turn-off function by gate signals.
These power semiconductor devices causes the generation of heat by energization and the amount of generated heat tends to increase because of the high capacity design and high speed design of power semiconductor devices. In order to prevent the deterioration of the properties of a semiconductor device and the shortening of its service life from being caused by the heat generation, it is necessary to provide a heat-radiating portion to thereby suppress a temperature rise in and near the semiconductor device. Because copper has a high thermal conductivity of 393 W/m·k and is inexpensive, this metal is generally used as heat-radiating members. However, because a heat-radiating member of a semiconductor equipment provided with a power semiconductor device is bonded to Si having a thermal expansion coefficient of 4.2×10
−6
/° C., a heat-radiating member having a thermal expansion coefficient close to this value is desired. Because the thermal expansion coefficient of copper is as large as 17×10
−6
° C., the solderability of copper to the semiconductor device is not good. Therefore, materials with a coefficient of thermal expansion close to that of Si, such as Mo and W, are used as a heat-radiating member or installed between the semiconductor device and the heat-radiating member.
On the other hand, integrated circuits (ICs) formed by integrating electronic circuits on one semiconductor chip are sorted according to their functions into a memory, logic, microprocessor, etc. They are called electronic semiconductor devices in contrast with power semiconductor devices. The integration degree and operating speed of these semiconductor devices have been increasing year by year, and the amount of generated heat has also been increasing accordingly. On the other hand, an electronic semiconductor device is generally housed in a package in order to prevent troubles and deterioration by shutting it off from the surrounding atmosphere. Most of such packages are either a ceramic package or a plastic package, in which ceramic package a semiconductor device is die-bonded to a ceramic substrate and sealed, and in which plastic package a semiconductor device is encapsulated with resins. In order to meet requirements for higher reliability and higher speeds, a multi-chip module (MCM) in which multiple semiconductor devices are mounted on one substrate is also manufactured.
In a plastic package, a lead frame and terminals of a semiconductor device are connected by means of a bonding wire and encapsulated with plastics. In recent years, with an increase in the amount of generated heat of semiconductor devices, a package in which the lead frame has a heat-dissipating property and another package in which a heat-radiating board for heat dissipation is mounted have also come to be thought of. Although copper-base lead frames and heat-radiating boards of large thermal conductivity are frequently used for heat dissipation, there is such a fear as problems may occur due to a difference in thermal expansion from Si.
On the other hand, in a ceramic package, a semiconductor device is mounted on a ceramic substrate on which wiring portions are printed, and the semiconductor device is sealed with a metal or ceramic cap. Moreover, a composite material of Cu—Mo or Cu—W or a kovar alloy is bonded to the ceramic substrate and used as a heat-radiating board, and in each of these materials there is required an improvement in workability and a low cost as well as lower thermal expansion design and higher thermal conductivity design.
In an MCM (multi-chip module), multiple semiconductor devices are mounted as bare chips on the thin-film wiring formed on an Si or a metal or a ceramic substrate, are housed in a ceramic package, and are encapsulated with a lid. When the heat-radiating property is required, a heat-radiating board and a heat-radiating fin are installed in the package. Copper and aluminum are used as the material for metal substrates. Although copper and aluminum have the advantage of a high thermal conductivity, these metals have a large coefficient of thermal expansion and have inferior compatibility with semiconductor devices. For this reason, Si and aluminum nitride (AlN) are used as the substrate of a high-reliability MCM. Further, because the heat-radiating board is bonded to the ceramic package, a material having good compatibility with the package material in terms of coefficient of thermal expansion and having a large thermal conductivity is desired.
As mentioned above, all semiconductor equipments each provided with a semiconductor device generate heat during operation, and the function of the semiconductor device may be impaired if the heat is accumulated. For this reason, a heat-radiating board with excellent thermal conductivity for dissipating the heat to the outside is necessary. Because a heat-radiating board is bonded directly or via an insulating layer to the semiconductor device, its compatibility with the semiconductor device is required not only in thermal conductivity, but also in thermal expansion.
The materials for semiconductor devices presently in use are mainly Si (silicon) and GaAs (gallium arsenide). The coefficients of thermal expansion of these two materials are 2.6×10
−6
/° C. to 3.6×10
−6
/° C. and 5.7×10
−6
/° C. to 6.9×10
−6
/° C., respectively. As the materials for heat-radiating boards having a coefficient of thermal expansion close to these values, AlN, SiC, Mo, W, Cu—W, etc., have been known. However, because each of them is a single material, it is difficult to control to an arbitrary level the coefficients of heat transfer and thermal conductivity and, at the same time, there is a problem that they are poor in workability and require a high cost.
Recently, Al—SiC has been proposed as a material for heat-radiating boards. This is a composite material of Al and SiC and the coefficients of heat transfer and thermal conductivity can be controlled in a wide range by changing the proportions of the two components. However, this material has the disadvantage of very inferior workability and a high cost. A Cu-Mo sintered alloy is proposed in JP-A-8-78578, a Cu—W—Ni sintered alloy being proposed in JP-A-9-181220, a Cu—SiC sintered alloy being proposed in JP-A-9-209058, and-an Al—SiC is proposed in JP-A-9-15773. In these publicly known composite materials obtained by powder-metallurgical processes, the coefficient of thermal expansion and thermal conductivity can be controlled in wide ranges by changing the ratio of the two components. However, their strength and plastic workability are low and the manufacture of sheets is difficult. In addition, there are problems of a high cost related to the production of powder, an increase in the steps of manufacturing process and etc.
SU
Abe Teruyoshi
Aono Yasuhisa
Kaneda Jun'ya
Koike Yoshihiko
Kondo Yasuo
Antonelli Terry Stout & Kraus LLP
Clark Sheila V.
Hitachi , Ltd.
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