Session: 10-01 Interactive Presentations

Paper Number: 99223

99223 - Characterization of Viscoelastic Properties of Underfills and Effect on Reliability of Fcbga Package Exposed to High Operating Temperature 

The transition to ball grid array flip-chip packaging technology has been facilitated by the requirement for sophisticated computer capabilities in automotive underhood applications to enable safety-critical activities. The electronics found under the hood of automobiles are frequently exposed to temperatures between 150 and 200°C. Solder joints fail when operating at high temperatures due to the large CTE (coefficient of thermal expansion) mismatch between the chip and the substrate. Underfills are utilized to provide the flip chip bumps more support, which improves fatigue life and lessens pressure on solder joints. For the underfills exposed to high temperatures, models and data on material degradation are required. There hasn't been much research on the impact of the evolution of the non-linear constitutive behavior of underfills on solder balls or the evolution of the viscoelastic behavior of underfills. In this work, the development of underfill characteristics for two underfills operating at sustained high temperatures over a year has been observed. At 100°C, 125°C, and 150°C, the aging data have been recorded at 30, 60, 120, 240, and 360 days. The reliability of the FCBGA (Flip Chip Ball Grid Array) package has been assessed in relation to the impact of non-linear property (Prony series) evolution of underfills. For TTS (Time-Temperature Superposition) studies, the frequency sweep method in the Dynamic Mechanical Analyzer was utilized to obtain the viscoelastic behavior of underfills. Seven distinct frequencies have been used for the TTS experiments: 0.1, 0.21, 0.46, 1, 2.15, 4.64, and 10 Hz. The shift factors are determined using the WLF (Williams-Landel-Ferry) equations. Shift factors and TTS experiments are used to produce master curves for the storage modulus, loss modulus, and tangent delta as functions of frequency at specified reference temperatures. Schwarzl and Struiks equation is used to compute the relaxation modulus in the time domain. Prony coefficients have been integrated as underfill characteristics in the FCBGA model since the shear and bulk moduli generated from the relaxation modulus are fitted using Prony series in ANSYS. To get a constant hysteresis loop, a quarter FCBGA package was modeled and subjected to two full heat cycles from -40°C to 125°C.

Presenting Author: Madhu Kasturi Auburn University