Pressure Leakage Through Material Interfaces in Pressure Sensor Packages

Pressure leak rate measurements that isolate leakage through the polymer/metallic lead interface have been performed with two different grades of poly (phenylene sulfide) (PPS), polyester, liquid crystal polymer (LCP), and epoxy housing materials in insert molded pressure sensor packages before wirebonding, after wirebonding, and after temperature cycling. Temperature cycling caused an increase in lead leak rate for all parts. Lead leakage increases with increasing polymer/metal CTE mismatch. Lead leakage measurements on packages molded in epoxy or the PPS grade with lower CTE were observed to be insignificant as-assembled and following wirebonding (maximum 0.004 ± 0.006 cm3/min). The parts molded with the PPS that had a higher CTE exhibited a moderate lead leak rate (0.065 ± 0.017 cm3/min) initially. An asymptotic pressure leakage limit is approached by these packages through temperature cycling. Both the polyester and LCP packages exhibited high lead leak rates initially (≈ 0.5 cm3/min) and gross leaks following 100 temperature cycles from −40 to 125 °C (>> 2 cm3/min). Coefficient of thermal expansion data was obtained from the manufacturer and through TMA measurements. Polymer “burn out” testing has been used to expose the filler orientation on all of the packages. Additional leak paths have been observed through “weld-lines” in the LCP material, through the silicone die-attach/LCP housing material interface, and through the epoxy backfill/epoxy housing material interface.