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|Nano-Mechanical Analysis of Pb-Free Solders for Reliability Optimisation in High Performance Microelectronics Systems|
|Keywords: Lead free solders for aerospace, nanoindentation, reliability|
|The development of thermomechanical models of Pb-free solders are complex because the microstructure after reflow and in service continues to change with time and temperature. Similarly, the interpretation of reliability tests can be complicated and challenging since failure mechanisms may change through the test. In this work nanoindentation as function of temperature has been explored for its potential to characterize Pb-free solders used in real microelectronic joints/interconnects, rather than studying the constituent materials in bulk form. Hardness, elastic modulus, yield strength and creep behaviour of micro-phases formed in a Sn-Ag-Cu/Cu solder joint were characterized at temperatures from 25 to 175°C. The interpretation of nanoindentation creep data is proposed to be not as straightforward as often assumed: the indenter subjects progressively larger volumes of solder to primary creep and then steady state creep as the test proceeds. Finite element analysis has been used to better understand the creep data found in this work and its relationship with creep data obtained from other methods. Finally, nanoindentation creep and other data has been implemented in a FE model of a ball grid array package and results compared with those obtained by alternative approaches.|
|V.M.F. Marques, PhD Student
University of Oxford
Oxford, Oxfordshire OX1 3PH,