Gideon Analytical Laboratories received four Vishay SS26 Surface Mount Schottky Barrier Rectifiers for possible premature conditions to failure. A Schottky barrier is a potential energy barrier for electrons formed at a metal-semiconductor junction. Schottky barriers have rectifying characteristics, suitable for use as a diode. These Vishay SS26 Surface Mount Schottky Barrier Rectifiers feature a low profile package, high surge capability, and are RoHS compliant. The diodes came from PCB P/N 170310142001 Rev A03 S/N 051208-231. Positions D8, D9, D18, and D27 were identified as possible trouble spots. The goal was to determine the cause of failure.
Gideon Analytical Laboratories performed failure analysis on the Vishay SS26 Surface Mount Schottky Barrier Rectifiers. There was no sign of external damage on any of the diodes. All four diodes were X-rayed, decapsulated, curve traced, and analyzed by SEM-EDS. D8 showed considerable voiding in the solder to lead frame attachments. The failure site on D8 appeared to be the result of an over voltage spike which expelled the tin/silver solder on to the silicon dioxide glass insulator. A curve trace of D9 revealed a dead short. After removing the lead frame on D9, the failure site and step coverage damage were identified. X-rays of D18 showed solder voiding. On D27, the solder puddle did not touch the silicon passivation and no step damage occurred. In conclusion, these Vishay SS26 Surface Mount Schottky Barrier Rectifiers were failing due to external factors.
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