Journal of SMT Article

SOLDER AS THERMAL INTERFACE MATERIAL FOR HIGH POWER DEVICES

Authors: Fay Hua and Carl Deppisch
Company: Intel Corporation
Date Published: 1/1/2006   Volume: 19-1

Abstract: Polymer materials have been used as thermal interface materials (TIM) to dissipate heat from silicon devices to a heat spreader or heat sink for decades. As technology progresses, polymer TIMs are no longer meeting the technology requirements, and thus high thermal conductive solder materials become an attractive option.

While solders have a higher thermal conductivity than polymer TIMs, other technical criteria also need to be met: 1) Solder TIMs have to fit the package and assembly process temperature hierarchy. 2) TIM joints, in general, need to be very thin over large areas. Therefore, limiting void formation in the solder joints during reflow is a significant challenge. 3) Solders are stiffer than polymer TIMs in general.

In order to minimize the stress level in the package and also meet solder joint reliability requirements, specific mechanical properties are required. 4) There is no back side of die metallization needed for polymer TIM, thus a challenge remains to directly solder onto non-metallized silicon die, or an additional back side metallization will be needed.

This paper summarizes the key technical benefits and challenges of using solder as a thermal interface material for high power devices through solder selection and reliability evaluation.

Key words: solder thermal interface material, thermal materials, flux.



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