Effect of different temperature cycle profiles on the crack propagation and microstructural evolution of lead free solder joints of different electronic components

Temperature cycling of real electronic components was carried out in a systematic manner at two different temperature profiles in a single-chamber Heraeus climate cabinet. The first temperature profile ranged between -55/spl deg/C and 100/spl deg/C and the second between 0/spl deg/C and 100/spl deg/C. Top-side SMD components were soldered with Sn-3.8Ag-0.7Cu lead free solder paste and hole mounted components and bottom side SMD components were wave soldered with Sn-3.5Ag alloy. Both through-hole (dual in line (DIL) packages) and surface mounted components (chip resistors and ball grid arrays (BGA)) were investigated in this work. Crack initiation and propagation was analyzed after every 500 cycles while microstructural evolution as a function of the number of temperature cycles was analyzed after every 500 cycles for each temperature cycling profile. In total, 3000 cycles were run at both temperature profiles. The observation results from each profile were compared. Finite element modeling (FEM) calculations were performed, where strain and stress analysis of chip resistor joint performance corroborates the experimental work results, especially regarding the crack initiation sites. For temperature cycling ranging between -55/spl deg/C and 100/spl deg/C, cracks were visible already after 500 cycles for the DIP-packages. For the other temperature profile and DIP-packages, cracks initiated sometime between 1000 and 1500 cycles. The cracks observed after 1500 cycles were visibly smaller for the temperature profile ranging between 0/spl deg/C and 100/spl deg/C, concluding that crack initiation and propagation was slightly slower for this temperature profile. After 2000 cycles, cracks were also observed in chip resistor solder joints mounted on the secondary side of the test boards. Cracks continued to propagate as a function of temperature cycles. With regard to microstructural observation, differences could also be observed between the two temperature profiles. Microstructural changes happened faster in the first temperature profile than in the second one.