Electronic equipment in automotive, agricultural and avionics can expose during storage, operation and handling to different temperatures (-55 to 200°C) as well as to high strain levels, during which the electronics equipment fails. An electronic component can experience 1-100 per sec of strain during lifetime. Temperature in electronic assemblies depends typically on location, energy dissipation and thermal architecture. Some investigators have indicated that the required operating temperature is between -40 to 200 ° C (Eddy 1998, Hattori 1999, Johnson 2004 & Watson 2012) for automotive electronics which are located underhood, on engine driver interior, and the ECU box.  Evolution in microstructure due to change in temperatures for lead free solder alloys can cause degradation in mechanical properties of solder alloys. So, we need more reliable lead-free solder alloys which can survive in these extreme harsh environments. Recently, SAC-Q are formulated with Sn-Ag-Cu with addition of Bi (SAC+Bi). Cai et.al. (2010) found that adding dopant (Bi, Ni, In, Mg, Mn, La, Ti) to SAC solder alloys can improve wettability, melting temperature, shock and drop reliability and microstructure. \[Cai 2010, Matahir 2011 and Pandher 2007\]. A microstructure study has found that adding Bismuth (Bi) to SAC alloy can play an important role to make the alloy relatively insensitive to aging-induced degradations \[Ahmed 2017\].

The previous study was performed with a different high strain rate (1-100 per sec) and high temperature (25-200 °C) for aged and unaged samples up to 1-year and studied the evolution of mechanical properties and anand model parameters for SAC solder (SAC105, SAC305 and SAC-Q) \[Lall 2014-2019\]. The addition of dopants in SAC alloys have been observed that may help improve mechanical properties and minimize deterioration due to aging. However, data on SAC solder alloys at high strain rate levels at low operating temperatures are not available in published literature. Also, there is lack of data in published literature on microstructural evolution for SAC solder alloys. 

In this paper, effect of low operating temperatures (-65°C-0°C) on high strain rates (10-75 per sec) mechanical behavior for unaged and aged SAC (SAC105 and SAC-Q) solder alloys has been studied. Stress-Strain curves have been obtained at low operating temperatures using tensile tests. The SAC leadfree solder samples were subjected to isothermal aged up to 6 months at 50°C before testing. Evolution of microstructure for SAC lead free solder alloys has been investigated induced due to thermal aging and studied using scanning electron microscopy (SEM). Anand Viscoplastic model has been used to describe the material constitutive behavior. Evolution of Anand Model parameters for SAC solder has been investigated. The computed parameters of the experimental data were used to simulate the tensile test and verified the accuracy of the model. A good correlation was found between experimental data and Anand predicted data.


Evolution of Sac Leadfree Alloys at High Strain Rate at Low Operating Temperatures

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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