A Novel Lead-Free Low-Temperature Solder with Excellent Drop-Shock Re-sistance

The 2017 International Electronics Manufacturing Initiative's (iNEMI) Board and Assembly Roadmap had forecast a 20% adoption rate of low-temperature solders (LTS) for board assembly by 2027. BiSn solders are the leading candidates in these studies. How-ever, the intrinsic brittleness of Bi phases renders poor drop shock performance, which restricts it from drop-critical applications. An In-containing Sn-rich solder paste- Durafuse™ LT, developed on basis of Durafuse™, a mixed solder powder technology-allows re-flow around 200°C and above, and shows excellent drop-shock per-formance. The primary In-containing powder in Durafuse™ LT will melt first around 118°C to spread and wet. The additive Sn-rich pow-der will dissolve into the molten solder during reflow. After reflow, the solder joint exhibits a remelting temperature around 189°C. The drop shock failure of Durafuse™ LT joints reflowed at 200°C peak temperature is about two-orders-of-magnitudes higher than that of the BiSnAg eutectic solder. By optimizing the reflow profile, the drop shock performance of Durafuse™ LT is even superior to SAC305. Thermal cycling tests (-40 to 125°C, 10min dwelling) on BGA192 and chip resistors demonstrated the dependence of the char-acteristic life on the reflow profiles. A plateau-type profile is pre-ferred for excellent drop shock resistance and acceptable reliability performance. The success of Durafuse™ LT in mobile applications encourages ongoing work on second generation pastes, which will reflow at 190°C without sacrificing drop shock and TCT performances.