The Performance of Plastic-Encapsulated CMOS Microcircuits in a Humid Environment

The major portion of this investigation is devoted to accelerated testing of plastic CMOS microcircuits under conditions of high humidity. The test results revealed a high failure rate in sharp contrast to the results of a similar investigation performed on plastic TFL IC´s. The program also investigates the effects of coating devices with a common PC card conformal coating and the effects of operation at various bias levels. A comparison is made between the results of short term pressure cooker testing and long term moisture bias fife testing. The results of testing over 1300 devices, representing the product of five (5) manufacturers are discussed. Findings of the Investigation reveal a higher failure rate for plastic CMOS than plastic TTL. Conformal coating proved to be an insignificant moisture deterrent. The results of 15PSIG, 127°, 48-h testing were observed to correlate with 85°C, 85-percent relative humidity (RH), 1000-h results. Also observed was the improved performance of CMOS B series devices in moisture compared to the A series. Removal of moisture from the ambient significantly improved the failure rate indicating that moisture was the prime failure cause.