Experimental Study of Moisture Ingress in First and Second Levels of Electronic Housings

Moisture uptake of polymer materials used for electronic packaging and moisture ingress into automotive electronic sensor housings have been studied by exposure to constant and cyclic humidity and temperature conditions. The first-level housing is made of epoxy molding compound (EMC) and encapsulates the sensor silicon-chip. The second-level housing is made of polybutylene terephthalate and contains the EMC attached to a printed circuit board (PCB). The novel approach was to perform in situ measurements of the temperature and the relative humidity (RH) inside the EMC next to the silicon chip, and to measure the humidity transfer from outdoor to the second, and through the first-level housings up to the chip. The effect of the presence of PCB and the self-heating of components have been investigated. The results showed that the time constants for humidity to reach 63% of outdoor conditions are about 2 and 7 days at 60 °C for the second- and first-level housings, respectively. Exposure to cyclic conditions showed that the internal RH tends to reach a steady state, close to the mean value of the cyclic outdoor profile, while the presence of polymeric materials (as PCB) can act as a humidity buffer and absorb and desorb water when subjected to temperature fluctuations.