THE EFFECTS OF CURE PROFILE UPON THE PROPERTIES AND THERMO-MECHANICAL RELIABILITY OF FLIP CHIP UNDERFILL
Authors: Guoyun Tian, Chang Lin, Jeffrey C. Suhling, Pradee Company: Auburn University (CAVE), Auburn University (LEAP) Date Published: 9/24/2006
Abstract: In this work, the effects of underfill cure temperature and JEDEC MSL preconditioning on underfill mechanical and strength properties, as well as flip chip assembly reliability have been explored. Baseline stress-strain curves, mechanical properties, and interfacial shear strengths of a capillary underfill were recorded for curing at 150 °C and 165 °C (30 minutes). In addition, the changes in the mechanical and strength properties resulting from MSL3 and MSL2 preconditioning were evaluated. The MSL preconditioning of the underfill samples included the JEDEC specified humidity and temperature exposures, plus three simulated reflows at 245 °C or 260 °C. Thermal cycling life tests from -55 to 125 °C were also conducted on daisy chain flip chip assemblies incorporating the same underfill. The test matrix for the reliability testing included both 150 °C and 165 °C curing profiles, and two levels of precondition (none and MSL3). Finally, the failure mechanisms in the flip chip assemblies were studied using CSAM, x-ray and SEM analyses. The results clearly indicate the advantages of the higher curing temperature including improved mechanical properties, superior thermal cycling fatigue life, and enhanced resistance to detrimental effects from moisture exposure and solder reflow.