High-Temp Vibration Reliability of Thermally Aged Lead-Free Assemblies
In this paper, the reliability of lead-free SAC solder alloys at high temperature and vibration for pristine and thermally aged assemblies is analyzed.
Materials Tech
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Summary
Applications in downhole drilling, automotive industry and avionics industry require exposure of electronics to sustained high temperatures electronics combined with vibration loads. In these conditions, maximum temperature can exceed 200 ℃ and vibration G-level up to 10g. Combined effect of elevated temperature and vibration can cause faster failure in electronics components. In this study, reliability for SAC105 and SAC305 electronics operation at elevated test temperature and vibration has been studied. Pristine and aged test board with lead-free SAC daisy chain CABGA packages have been subjected to harmonic vibration at their 1st natural frequency at three test temperatures (25°C, 55°C and 155°C) and vibration with amplitude of 5g, 10g and 14g. Test boards were exposed to isothermal aging conditions at 150°C for 60 days.
Hysteresis loop and plastic work density of critical solder joint extracted using FEA based global and local method. S-N curves were obtained for test vehicle. Failure mode analysis has been done for test board. Anand Viscoplasticity material data from the prior studies by the authors have been used to capture the high-strain rate temperature dependent aging behavior of the solder joints. A new model has been proposed to predict the high frequency fatigue life under simultaneous temperature-vibration.
Conclusions
The reliability of test boards with SAC solder interconnects (SAC105 and SAC305) have been studied at different vibration G-Level and at elevated temperatures. The FEA based modal analysis and Experimental modal analysis have been conducted to determine the PCB characteristics such as natural frequencies, mode shapes. A good correlation was achieved between the experimental and FE based natural frequencies. Effect of operating temperatures have been studied and it was found that natural frequencies decreased with increase in the temperatures.
Resistance data have been monitored using high speed data acquisition system till failure. Effect of Location of packages also has been studied and we found that packages at center location failed quicker compare to other locations due to higher strain at center of board. Anand Model has been used to describe the deformation behavior of critical solder joint. It was observed the maximum stress happened between the solder joint and copper pad. FEA based global and local method has been used to extract hysteresis loop and plastic work density of critical solder joint at different G-level and elevated temperatures. Effect of temperatures, locations of package and G-level have been studied on hysteresis loop.
The area of hysteresis loop increased with larger input G-level and higher operating temperatures and package located at center of PCB has maximum area compare to other location due to larger displacement at center. Plastic work per cycle shows an increase with increase in G-level and operating temperatures leading to faster failure rate. Energy based Fatigue life prediction model has been developed for SAC solder materials during combined high operating temperature and vibration loads.
Initially Published in the SMTA Proceedings
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