Alternative Techniques for Cross-Sectioning and Quality Analysis of Solder-TIM Joints with Soft Indium Alloys

The high thermal conductivity and mechanical compliance of reflowed indium-based alloys known as solder thermal interface material (sTIM)s have made them an intriguing choice for applications with high power (heat generation) density. The physical integrity and long-term reliability of sTIM joints have yet to be analyzed to ensure the theoretical performance is achieved. Studying cross-sections from the reflowed parts allows for extensive evaluation of joint quality, voiding extent, and the state of IMCs at both sTIM/lid and sTIM/die interfaces that are helpful in reliability analysis of the parts. Due to the softness of the sTIM alloys, mechanical abrasion techniques lead to particle embedment and subsequent damage to the solder region. An alternative sectioning technique based on application of microtome sectioning tool is proposed here that can be used to generate sharp damage-free sections for metallographic analysis. In addition, peel-off test explained in this work provides important information on joint quality and the state of solder wetting at both interfaces.