In order to improve electronics packaging design, it is important to evaluate cooling performance and reliability of the electronics packaging structure. To that end, it is necessary to predict the temperature, deformation, and stress distribution of the package under field conditions. In the case of a packaging structure comprising a flip-chip ball grid array (FC-BGA) package, a heat spreader, thermal grease, a cooling structure, solder joints, and a motherboard, an increase in the contact thermal resistance may occur, depending on the interface contact condition between the cooling structure and the heat-spreader due to the thermal deformation of the package. Contact thermal resistance problems involve the interactive relationship of the thermal and stress distribution. A coupled thermal-stress analysis, with consideration of the time-space variation of contact thermal resistance, was conducted to duplicate the behavior of temperature, deformation, and stress distributions of a FC-BGA package under field conditions. It was found (1) that the average contact thermal resistance across the interface between the heat-spreader and the plate fin, which was predicted by the coupled thermal-stress analysis, increased compared to that in the case of uniform contact pressure, and (2) that the contact thermal resistance will vary depending on the deformation mode, such as convex upward and downward, due to heat dissipation during field conditions. In addition, a reliability prediction method for thermal fatigue failure of solder bumps based on coupled thermal-stress analysis and statistical and probabilistic methods was proposed in order to select a suitable packaging solution at an early stage of design.
Reliability Design Method for Solder Joints Based on Coupled Thermal-Stress Analysis of Electronics Packaging Structure
