Thermal Performance of Advanced TIMs for High-Power FCLBGAs

As next generation artificial intelligence (AI) and high-performance computing systems continue to increase their power consumption, thermally-enhanced packaging solutions become increasingly important. Advanced cooling systems, such as air cooling, liquid cooling and even immersion cooling, have been developed to reduce device operating temperatures. However, those approaches: a) require additional space in the system and b) add costs to end users, which are not acceptable for applications such as cell phones, laptops and portable devices.Another thermal management method for high power packages is to apply thermal interface material (TIM) in the package. TIMs provide an effective way to compact and manage system spaces and reduce costs if an appropriate material is selected. Even with advanced cooling systems, the effects of superior TIMs become greater as the power consumption increases.This paper explains the thermal performance of various highly conductive TIMs, including thermal test results, lid attach processes, TIM coverage and reliability test results. The junction to case thermal resistance (ӨJC) of 60-mm x 60-mm Flip Chip lidded ball grid array (FCLBGA) packages with three different TIM types: metal filler added polymers, graphite and Indium-based metal TIM, were evaluated with a customized water-based cooling system. Values were tracked correlating with scanning acoustic tomography (SAT) images, before and after high temperature storage tests (HTS). TIMs built in FCLBGA thermal test vehicles (TTV) with 25.6 x 25.6mm die were divided into 36 squares and each sector’s temperature was measured individually.Thermal test results were analyzed based on above perspectives. Gel and adhesive polymers appear to have different performances with same lid attach method, since the material behavior is different at a given force. Thermal performances were better with higher thermal conductivity, but feasibility in bond line thickness (BLT) reduction as well as coverages determined the overall values. Metal TIM showed 100% superior performances at the center of a device compared to other TIM types. Thermal simulations were conducted to validate the simulation results and understand the phenomena.After HTS, depending on TIM types, improvements and degradation in ӨJC were shown in center and corner points. SAT and other analysis were conducted to understand TIM degradation. Results will be used to guide proper TIM selection and overcome challenges in future device applications.