Energy density estimation of crack initiation in Sn-Ag-Cu(Ni) solder bump by nano-impact

To secure the reliability of lead free solder is a critical problem for microelectronics packaging. The drop test is used to characterize the reliability of the soldered assemblies. Numerical simulation techniques are popularly used for such tests to reduce the cost. A proper working combination of the damage criterion and the numerical simulation to predict fatigue life is still an unsolved problem for the researchers. IMC layer generated during the solder bumping process between solder and under solder mask is known as a key aspect determining the failure of solder joint and cracks always initiate in this layer. In this work, the most fragile part in an electronic assembly is evaluated by FEM; nano impact tests are realized on IMC layer and on solder body. Tests prove that the IMC layer is the most fragile part and the crack initiation energy density in IMC layer as a damage criterion is proposed. Then this criterion is combined with the board level drop test simulation result to predict the number of drop necessary for the crack initiation in IMC layer and this number cannot be obtained directly during the drop test.