Considerations in the Use of the Laser Flash Method for Thermal Measurements of Thermal Interface Materials

With increasing thermal fluxes, the performance of thermal interface materials (TIMs) that are used to reduce the thermal resistance between contacting surfaces in electronic devices, such as at the die-to-heat sink or heat spreader-to-heat sink interfaces, is becoming critical. However, measuring the thermal resistances of TIMs in a manner representative of actual applications is difficult. The laser flash method is a technique that may be used to determine the thermal resistance of TIMs and their degradation under environmental exposure. This paper examines three issues associated with using the laser flash method that could limit its effectiveness in calculating thermal resistance: sample holder heating, clamping, and error in the Lee algorithm outputs due to coupon-TIM thermal diffusivity differences. As a case study, the thermal performance of polymer TIMs in pad form, as well as an adhesive and a gel, were examined. Finite element simulations indicated that, without proper consideration, sample holder heating can lead to significant error in the calculated TIM thermal conductivity values.