Factors Impacting the Reliability of Ultralow Silver Lead Free Alloys
Authors: Neil Poole, Ph.D., Brian J. Toleno, Ph.D., and Mark Curie, Ph.D. Company: Henkel Electronic Materials, LLC Date Published: 9/27/2015
Abstract: Although the price of silver has stabilised, it remains the most expensive element of the lead free Tin silver Copper (SAC) alloys. Lowering the level of silver has a number of effects beyond simply the cost of the alloy. It has been shown that decreasing the silver can improve the drop/mechanical shock resistance, a desirable parameter for many hand held applications, but at the cost of an increase in liquidus and a drop in thermal fatigue resistance. Although this impact has been studied for low silver alloys 1-3% little work has been don on ultralow silver alloys (less than 1%). In this paper the key parameters impacting the thermal fatigue of SAC0307 are studied, as well as the delta of the thermal cycle being important the peak temperature and dwell at each end of the thermal cycle are determined to be significant contributors to the ultimate performance of the solder joint. The contribution was determined to vary with the component tested. Thus care should be taken in extrapolating the thermal cycle data from one test vehicle to an actual circuit assembly.