Influence of die and lid shapes on void formation in solder thermal interface materials

Thermal interface material (TIM) is used to improve heat transfer between surfaces such as die to the lid. Solder-TIM is the popular choice for lidded electronic packages to effectively remove the heat from the compute die during operation due to its high thermal conductivity. However, solder-TIM is susceptible to form voids between the lid and the die which reduces the heat transfer effectiveness. In this study, computational fluid dynamics (CFD) was used to understand the mechanisms and behaviors of solder-TIM voiding for different die and lid shapes. Results from the simulations were validated with error less than 1 % to the experiments. It was found that the die shape is a crucial factor that influences the solder-TIM voiding. At same flatness of 60 μm, concave die resulted more voids at 30 % located near the die centre as compared to 3.66 % voids for convex die located near the die edges. For the lid shapes, it was found that conforming the lid to the die shape reduces the air gaps and which translated to minimum voids. For concave lid matching to convex die of same flatness, significant solder-TIM voids reduction of 0.55 % from 3.66 % was observed. This study signifies the importance of die and lid shapes to understand the solder-TIM voiding behavior and accurate method to mitigate it.