REFLOW PROFILE OPTIMIZATION FOR MINIMIZING FATIGUE FAILURES ON LEAD-FREE ASSEMBLIES USING ALLOY 42 BASED LEAD-FREE TSOP PACKAGES

摘要

Reliability of lead-free solder joints has been a widely discussed topic in the electronics industry. Thermal fatigue reliability of solder joints formed on Alloy 42 leaded TSOP components has been a concern for several years with leaded solder paste systems. TSOP leads are short and moreover Alloy 42 by nature is stiffer as compared to other materials like copper. One of the ways to minimize thermal fatigue failures due to CTE mismatch on this component is to use a different leadframe material, the CTE of which closely matches the solder alloy and FR-4 material. However, the use of Alloy 42 is inevitable as several component suppliers still prefer using it as a leadframe material due to reasons beneficial to the packaging process .This continues to be an issue even with a lead-free soldering process requiring special process/design modifications to compensate for this issue. This paper presents a systematic lead-free reflow profile optimization approach used for enhancing the thermal cycling reliability of solder joints formed on TSOP devices using Alloy 42 leadframe on a lead-free product. A profile with longer soak time and a slower cooling rate was observed to work best in minimizing fatigue cracking thereby producing reliable solder joints for the assembly and material combination considered in this study.