Thermal deformation analysis of electronic packaging by viscoplastic constitutive model (comparison of lead solder alloys with lead free solder alloys)

In this paper, experimental and theoretical researches on the viscoplasticity of lead and lead-free solder alloys are conducted. First, experiments such as tension-compression loading with several stress amplitudes and strain rates, creep tests at several stress levels, and stress relaxation tests are conducted using specimens made of Sn-37 Pb as the lead solder alloys and Sn-3Ag-0.5Cu as the lead free solder alloys at several temperatures. The test results show that the lead-free solder alloy has smaller strain rate effects, creep strain and stress relaxation than those of the lead solder alloy. The viscoplastic deformations of both lead and lead-free solder alloys are simulated by a viscoplastic constitutive model. The simulations show that the constitutive model can successfully apply to the pure sension, the cyclic loading, the creep deformation and the stress relaxation of both the lead and the lead-free solder alloys. FEM analysis of the bend of the substrate is also conducted by MSC. Marc, in which the constitutive model for viscoplasticity is incorporated. As a result, it is found that the bend of substrate using the lead-free solder joints has much larger bend than that using the lead solder joints.