Abstract

Several device failures were experienced after they went through the board assembly process. The failure caused severe transmit pulse attenuation from circuit block called AUI (Attachment Unit Interface). The AUI serves as a medium independent communication port in Local Area Networks. After careful observation and a series of Failure Analysis processes, the malfunction, which caused severe transmit pulse attenuation was attributed to a defective metal 1 to metal 2 via. The via in question is a tie between a pair of cascoded PMOS transistors in the analog section of the chip. These transistors serve as the main biasing leg for the AUI current sink. Since the via in question was bake recoverable at temperatures as low as 175°C for 20 minutes but would show the same failure signature when operated under temperature, the exact failure location was difficult to pinpoint. After a lengthy analysis procedure, the malfunction was attributed to contamination due to Spin On Glass (SOG) outgassing.

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