The Design and Evaluation of Reliable Plastic-Encapsulated Semiconductor Devices

A summary of the proposed conditions for control or evaluation of each feature of a design for a plastic-encapsulated device is as follows: 1. Screening and life testing for siliconchip surface problems, with high confidence of achieving the required reliability and with reasonable times, requires junction temperatures of the order of 175-300C, with reverse bias. This dictates the use of a silicone molding material, or other material which wi stand the test temperature. 2. For assurance against alkali ion contamination, the chip should be protected with a barrier, such as silicon nitride, over the usual thermally-grown oxide. Testing with deliberate sodium contamination can serve to determine the resistance of a product to sodium ion effects. The plastic should not, however, contain fillers which can provide sodium ions to the chip surface since that would place an additional burden on assuring the perfection of the barrier material. 3. Gold metallizing should, be used in order to avoid intermetallic compound growth at internal lead bonds (with gold wires) and to avoid the electromigration and chemical and electrolytic corrosion problems of aluminum. The lack of an hermetic seal increases the necessity of this protection against corrosion 4. The shape of the plastic mold and the choice of lead-frame material and dimensions should assure lead seal integrity at all conditions of test and field use. This assures freedom from introduction of gross amounts of water vapor to the areas of closely-spaced metals at the chip surface. 5.