Epoxy flux - an answer for reliable no-clean flip chip assembly

A novel epoxy flux PK-001 is developed and tested for no-clean flip chip attachment processes with tin-lead eutectic solder bumps. Results indicate that soldering and flux residue curing can be accomplished with a single reflow process. PK-001 provides adequate solder wetting and excellent non-voiding behavior for flip chip applications. The latter is attributable to its low volatility at above solder melting temperature. The uniformity of joint coverage area enables a tight soldering quality control. This is particularly crucial for high I/O count flip chip applications. The thermoset flux residue nature allows good compatibility with underfills, particularly under high temperature and high humidity conditions. Low ionics content, low corrosivity, and high SIR performance provide the essential remaining properties required for no-clean applications.