Thermal diffusion tomography for quantitative non-destructive characterization of electronic packages

Increasing number of transistors and reduction in product size leads to thermal management problems in electronic packages. Thermal interface materials (TIMs) are used as a passive means of thermal management and for high density interconnect packages, TIM helps heat dissipation by reducing thermal contact resistance between chip and integrated heat spreader (IHS). Therefore, TIM quality is critical for effective removal of heat generated by the chip from the package. Identification of defects within TIM is required during package assembly process development so that acceptable TIM quality can be achieved for a reliable thermal performance. While this is possible by qualitative techniques such as X-ray tomography or CSAM, quantitative non-destructive detection based on thermal tomography is proposed as an alternative. High density interconnect flip chip package that includes spreading effect due to different sized IHS and die that is used for CPU of desktop computers and servers is considered in this study. Defect size and location are detected analyzing the measured thermal response of electronic package by solving the resulting inverse problem. Levenberg-Marquardt algorithm is used as an image reconstruction technique as inverse problems are ill-posed in nature and regularization of the system is necessary. The study investigates the feasibility of the method through numerical experiments. Therefore, the experimental data is replaced with synthetic measurement data based on applying random measurement error to simulated measurement data. Results show that thermal tomography has a potential for identification of TIM defects, which cause a measurable effect regarding package specifications.