Abstract

Red phosphorous is one of the inorganic phosphorous compounds used as a flame retardant in microelectronic applications. One of the concerns is a red phosphorus induced pin-to-pin short in the molding compound. This paper discusses the red phosphorous-induced shorts in a 100 Lead TQFP (14x20x1.4mm) plastic package. The devices first failed on boards in the field. After de-soldering them from the boards, the devices were tested and found to have resistive pin-to-pin shorts. Common failure analysis techniques, including parallel lapping, cross sectioning, and X-ray, failed to reveal the resistive shorts and the shorting mechanism. Removing the molding compound by means of a wet chemical etching method using sulfuric acid on a hot plate worked very well and enabled to expose particles in three dimensions. It was concluded that the resistive shorts were not necessarily due to a single large phosphorous particle, but due to small and fragmented pieces of phosphorous.

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