LTD PKG. (Liquid Thermal Dissipation Package) Technology

Abstract

In this paper, the new LTD PKG. (liquid thermal dissipation package) technology is presented to provide the best solution for high and large-area thermal dissipation, and is applied in FCBGA (flip chip ball grid array).For LTD PKG., the enclosed space between chip and HS (heat sink) with EL (enhanced layer) is filled with liquid TIM (thermal interface material). In compare with solid TIM, liquid TIM (LM (liquid metal) or thermal grease) doesn’t cause any defect issues such as delamination, coverage, crack, and void in the thermal cycle process. In addition, the function of HS with EL can increase the efficiency of heat transfer because of the area ratio of thermal transfer (surface area of HS with EL/surface area of chip) >1 and the effect of high heat flux.In this study, the thermal simulation uses two HSs: HS1 (with NM (normal)) and HS2 (with EL) to produce three main outcomes under the following conditions: 1/12 chip size, input power 15 W, BLT (bond line thickness) 80 μm, same TIM for HS1 and HS2. First of all, in the chip temp., HS2 is lower than HS1 around 16.21 °C (−16.2 %). Secondly, for ΔT (chip-HS), HS2 of 3.45 °C is better than HS1 of 10.78 °C. Lastly, for index theta JC (°C/W), HS2 of 0.23 °C/W is better than HS1 of 0.72 °C/W. Moreover, the advanced simulation uses two TIMs: A TIM (k, 86 W/mK) and B TIM (k, 79 W/mK) to get several results under the following conditions: 1/12 chip size, input power 15 W, BLT 80 μm, HS1 with A TIM and HS2 with B TIM. Firstly, in the chip temp., HS2 is lower than HS1 around 5.62 °C (−5.85 %). In the second place, for ΔT (chip-HS), HS2 of 3.12 °C is better than HS1 of 8.88 °C. Finally, for the index theta JC (°C/W), HS2 of 0.21 °C/W is better than HS1 of 0.59 °C/W. The results of thermal simulation indeed prove the valuable function of HS with EL.The process flow of LTD PKG. technology has been built and verified through the production of the samples of FCBGA. After the thermal cycle tests (25.0 °C – 242.9 °C, 12 times), these samples show there is no leaking of liquid TIM. Besides, the results of X-Ray inspection show that LM between HS and chip is without any delamination and void.LTD PKG. technology not only has high efficiency in thermal dissipation but also simplifies the process flow. Moreover, the HS with EL can be easily designed according to the heat source of chip. As a result, the LTD PKG. technology is the best solution for high and large-area thermal dissipation.