Underfill characterization for low-k dielectric/Cu interconnect IC flip-chip package reliability

Due to low dielectric constant inter-metal-dielectric (Low-k IMD) materials possess weaker mechanical property and high coefficient of thermal expansion (CTE) comparing with IC silicon substrate, integrity of Low-k IMD layer/silicon substrate structure of advanced IC in a package form becomes great of concern. Flip-chip underfill characterization was conducted to investigate the key factors of underfill material property that can yield good Low-k IC package integrity after reliability test. A simplified stress-coupling-index concept was proposed and used to select five underfills for evaluation based on their different property characteristics. 27x27 mm(2) FCBGA packages with heatspreader were built Using 8x10 mm(2) Low-k test die, and tested by temperature cycle test. The test result showed FC package with Low Tg underfills yield good performance for Low-k package integrity.