Failure analysis of plastic packaged optocoupler light emitting diodes

Failure mechanisms in plastic packaged optocouplers have been investigated. The high failure rate of the optocouplers, specifically the reverse bias leakage current of the light emitting diodes (LEDs), was found to be moisture-related. Using scanning electron microscopy coupled with energy dispersive X-ray microanalysis, a significant concentration of copper was detected on the surface of failed LEDs, possibly migrated from the copper leadframe. By applying infra-red photoemission microscopy it was found that bandgap emission was associated with the reverse leakage path in the area of the pn junction of the LEDs.