Evolution of a High-Reliability Molded DIP

An investigation of the effects of package. structures upon IC failure rates led to the development of a new molded DIP (dual in-line package) with exceptional reliability. The design, which is being put into production, rivals hermetic packages in mechanical and environmental reliability. The study began as an effort to reduce the initial thermal intermittent and temperature cycle reject rates encountered during production testing of industrial IC\´s packaged in silicone DIPs. The DIP used has a rigid body, but before molding of the body the die is coated with an elastomer to provide added moisture resistance and mechanical buffering. While generally more reliable than earlier DIP designs, this structure still allowed stressing of the wire bonds during temperature cycling and was not as resistant to salt atmosphere as epoxy packages. Also, the need for a die coat had become questionable since current practice is to "glass" the chips during wafer processing. Study of the problem, with optimized bonds, led to the theory that a solid, highly compressive body could be more reliable. Silicone and epoxy models with and without die coats where tested. Data were gathered on the effects of mold shrinkage upon thermal intermittent failure rates and upon ball bond and stitch bond failures during temperature cycling. Also, the effect of glass transition temperature upon failure rate was studied (at Tg, rate of change in thermal expansion coefficient of a plastic icreases markedly).