Research on Deformation Control Constitutive Model for Lead Free Electronic Devices

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In this research, for lead free electronic devices, construction of a constitutive model to control deformation of lead free solder alloys was conducted referring to basic tests such as pure tension, creep and stress relaxation. Moreover, a structural analysis using the constitutive model was proposed for the read free electronic devices, and reliability evaluation and structural optimization were carried out. The outlines of the research are as follows :1. Clarification of mechanical and fatigue life characteristic of lead free solder alloys : Basic characteristic of macroscopic mechanical behavior and fatigue failure were observed using the small specimens, which have the diameter of 8mm and are made of 60Sn/40Pb and Sn-3.5Ag-0.75Cu. The tests results showed the characteristic macroscopic inelastic deformation and fatigue life of lead free and lead solder alloys.2. Construction of constitutive model for solder alloys : Considering the results (1) constitutive models adapted to explain the inelastic deformation of lead solder alloys such as 60Sn/40Pb can not used to explain the inelastic deformation of lead free solder alloys, because the viscoplastic deformation of lead solder alloys is much different from that of lead free solder alloys. Then, construction of a new constitutive model to exactly explain the inelastic deformation of the lead free solder alloys was discussed. Since the solder alloys for connecting electronic devices is a few hundreds micro millimeter the internal structural change in solder alloys should be taken into account in the constitutive model. Therefore, the constitutive model based on dislocation density is employed in this research.3. Construction of structural analysis method using the constitutive model: Structural analysis was conducted by incorporate the model into a general purposed program of FEM. The advantage of the constitutive model based on dislocation density was verified.