Eh. Wong et al., Underfill swelling and temperature-humidity performance of flip chip PBGA package, PROCEEDINGS OF 3RD ELECTRONICS PACKAGING TECHNOLOGY CONFERENCE, 2000, pp. 258-262
Two mechanisms for autoclave failure of flip chip PBGA package have been id
entified : Transverse hygroscopic swelling of underfill has been found to b
e responsible for the first failure mechanism typified by randomised solder
joint failure associated with localised underfill-chip delamination around
the solder joints. The localised delamination may coalesce into a larger d
elamination near the centre of the chip. In-plane hygroscopic swelling of u
nderfill and substrate is responsible for the second failure mechanism. It
results in extensive underfill-chip delamination initiating from chip edge
before solder joint failure.
Vast difference in performance has been found for flip chip package subject
ed to 85 degreesC/85%RH and 121 degreesC/100%RH conditioning respectively.
The compressive hygrothermal strain around the solder is believed to have c
ontributed to the excellent performance during 85 degreesC/85%RH test.