Applicability of no-flow fluxing encapsulants and flip chip technology in volume production

Applicability of no-flow fluxing encapsulants and flip chip technology in volume production was studied. Adhesion of the underfill materials to different solder resists was measured with single lap shear test and the results compared with traditional underfills. No-flow underfiller was dispensed with standard in line dispenser. SnPb-bumped flip chip test structures were pick and placed on FR4 substrates by using standard volume production line. The bump pitch of the test chips was 250 /spl mu/m. Sample boards were also precured in standard production oven and postcured in baking oven. No-flow underfillers showed exceptionally good adhesion to used solder resists. With the no-flow underfillers flip chip proved to be transparent to the current SMA process, however the process window for dispensing and reflowing is relatively narrow.