Research On The Indentation Strain Rate Sensitivity Of Lead-free Solders And Thermal Fatigue Reliability Of PBGA Solder Joint

Since the lead-free development and multi-functionalization ofelectronic products, the size of lead-free solder (used as interconnectedmaterials in electronic packaging) is becoming smaller (micron scale). Tocharacterize the mechanical properties of lead-free solder from the mesoscopicview has an important operation significance. In this paper, the mechanicalproperties and strain rate sensitivity of lead-free solders (Sn-3.0Ag-0.5Cu,Sn-0.7Cu and Sn-3.5Ag) were investigated by nanoindentation. The thermalexpansion properties of lead-free solders were measured by thermal mechanicalanalyzer, based on numerical simulation the effect of solder joint pitch on thethermal fatigue reliability of PBGA packaging were analyzed. Therelated research contents and conclusions are as follows:(1) The mechanical properties of lead-free solders under different strain rateswere measured by nanoindentation, Results show that the contact stiffness oflead-free solder increases linearly with indentation depth. The hardness andcreep deformation of lead-free solder show great strain rate sensitivity but the elastic modulus and strain rate sensitivity exponent under different strain ratesremain almost unchanged. Contrastive analysis of mechanical properties oflead-free solders can provide reference data for the selection of lead-free solderused in electronic packaging.(2) Measured by thermal mechanical analyzer, the effect of temperature onthe thermal expansion coefficient of lead-free solders was not obvious and thethermal expansion coefficient of lead-free solder with higher melting point isrelatively lower. Based on the finite element analysis software ANSYS andAnand viscoplastic constitutive relation of Sn-3.0Ag-0.5Cu lead-free solder, thethermal fatigue reliability of PBGA packaging with different solder joint pitcheswere analyzed. Results indicate that the thermal fatigue life of PBGA packagingwith solder joint pitch of1.27mm was relatively higher, but the effect of solderjoint pitch was not obvious regularly on the whole. Results of numericalsimulation have important guidance for the electronic packaging design.