Integrated circuit package with low-thermal expansion lead pieces

DETAILED DESCRIPTION The object of the present invention is to provide an integrated circuit package which is capable of preventing the glass layer from being cracked thereby maintaining increased reliability.
Along with the study to utilize the silicon carbide substrate, the inventors have prepared an integrated circuit package in which semiconductor elements were mounted on the silicon carbide substrate, ends of electric leads were connected to the semiconductor elements, portions where the leads were connected to the semiconductor elements were packaged with a sealing glass, and the electric leads were taken out to the external side through the glass accompanied, however, by a problem that the sealing glass was cracked and, particularly, the glass around the lead terminals was cracked.
Should that happen, a cell containing the semiconductor element is communicated with the open air, and moisture contained in the open air enters into the cell so that the device may malfunction.
It is considered that the sealing glass is cracked by the thermal stress produced by the lead material that has a large coefficient of thermal expansion.
In order to prevent the sealing glass from being cracked, it can generally be considered to use a lead material having a coefficient of thermal expansion that is in agreement with the coefficient of thermal expansion of the sealing glass.
Through the study, however, the inventors of the present invention have confirmed that in the case of the package of the present invention that employs a silicon carbide ceramics as the substrate, the sealing glass was not at all prevented from being cracked even when the coefficient of thermal expansion of the lead material was brought into agreement with the coefficient of thermal expansion of the glass.
The inventors therefore have furthered the study and have found the fact that the sealing glass can be very effectively prevented from being cracked if the coefficient of thermal expansion of the lead material is set to be nearly equal to, or smaller than, the coefficient of thermal expansion of the substrate, instead of selecting the coefficient of thermal expansion of the lead material relying upon the coefficient of thermal expansion of the glass as a reference