Moisture sensitivity characterization of plastic surface mount devices using scanning acoustic microscopy

An attempt was made to characterize the moisture ingress kinetics of six known vendor-supplied moisture-sensitive IC surface mount devices. Induced damage response by exposure to IR reflow was then characterized using C-mode scanning acoustic microscopy. Damage analysis indicated that moisture ingress sensitivity can vary significantly from device to device with little correlation to total pin count. Accelerated performance testing using temperature cycling revealed that this test is only second order effective in accelerating the failure of moisture-damaged devices. Correlation between ambient aging and accelerated testing was possible using both an established failure criteria assessment and moisture diffusion calculations. Safe ambient exposure times from out-of-the-dry-bag to board assembly for these devices were determined using this methodology.<>