Thermal Fatigue Life Determination of CCGA Interconnect Using a Simple Method

Abstract

A simplified method was developed to determine the fatigue life of a ceramic column grid array (CCGA) solder joint when exposed to thermal environments. The CCGA package with 90Pb/10Sn solder columns is soldered onto the printed circuit board with a tin-lead solder paste. Failure of the solder joint occurs at the CCGA solder column. A closed-form solution with the equilibrium of displacements of electronic package assembly was first derived to calculate the solder joint strains during the temperature cycling. In the calculation, an iteration technique was used to obtain a convergent solution in the solder strains, and the elastic material properties were used for all the electronic package assembly components except for the solder materials, which used elastic-plastic properties. A fatigue life prediction model, evolved from an empirically derived formula based upon a modified Coffin-Manson fatigue theory, was then established. CCGA test results, obtained from various sources, combined with the derived solder strains were used to calibrate the proposed life prediction model. In the model calibration process, the 625- and 1657-pin CCGA test results, which were cycled between 20°C/90°C, 0°C/100°C, −55°C/110°C, or −55°C/125°C, were reasonably well correlated to the calculated values of solder strains. In addition, this calibrated model is remarkably simple compared to the model used in an evaluation by a finite element analysis. Therefore, this model could be used and is recommended to serve as an effective tool to make a preliminarily estimate at the CCGA solder joint thermal fatigue life. It is also recommended to 1) select more study cases with various solder joint configurations, package sizes, environmental profiles, etc. to further calibrate this life prediction model, 2) use this model to conduct parametric studies to identify critical factors impacting solder joint fatigue life and then seeking an optimum design, and 3) develop a similar life prediction model for lead-free solder materials.