Study On High-temperature Mechanical Properties And Interconnect Reliability Of Lead-free Alloy

With the lead-free and miniaturization of solder joints in electronic packaging, temperature environment have a considerable impact on the mechanical properties and connection reliability of solder joints. In this paper, the high-temperature mechanical properties of lead-free solder reflowed were investigated using nanoindentation, the tensile and shear strength test was carried out on the samples after aging for different time. The influence of different micromorphology of IMC on the fracture behavior of solder joint was analyzed by numerical simulations of the intergranular cracking of IMC.1.The high-temperature mechanical properties of Sn96.5Ag3Cu0.5 lead-free solder reflowed were investigated using nanoindentation at 50、70、90、110℃. Results show that the temperature has a great effect on the mechanical properties of lead-free solder. With increasing temperature, the elastic modulus and hardness decreases and the solder generates softening. The creep stress exponent under high temperature is relatively smaller, indicating the lower creep resistance. Accordingly, the creep activation energy of Sn96.5Ag3Cu0.5 lead-free solder reflowed is 75.5KJ/mol.2. Sn-Ag-Cu solder mechanical property reliability at high-temperature was studied in this paper by planning an experiment. Sn-Ag-Cu solder joints samples were stored at a constant temperature which is 120℃ for 240 h and 480 h. After aging, the tensile and shear strength test was carried out on the samples by INSTRON mechanical testing machine, exploring influence of solder joints after different high-temperature aging to its interconnect reliability. We can get the result that, with the increasing aging time, the tensile and shear strength of solder joint decline and strain of solder joint samples when broken increases. Observing tensile and shear factures of samples by SEM. Fracture mode of solder joints transforms from ductile facture to ductile brittle mixed facture.3. In the process of reflow soldering that products solder joints, interface of copper and lead-free solder will generate a thin and fragile transition layer——intermetallic compound. With the formation and growth of IMC, the shape and size of grains changes, which affects its facture mode. In this paper, The 2D Voronoi algorithms were used for geometric modeling of microstructure of IMC grain, and the cohesive interface elements are embedded between the grain boundaries. By this way, crack propagation path and mode of grain boundary is analyzed by numerical simulation at the micro scale.