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A Thermal Management System for High Heat Flux ASIC’s with High Bandwidth Memory (HBM)
Keywords: HBM, hot spot, 2.5D
In order to meet the performance demands in modern microelectronics, novel ASIC’s consist of single or multiple High Bandwidth Memory (HBM) modules on the same electronic package. Moore’s law may not hold for “post 28 nm architectures” leading to higher density and higher power (so higher heat flux), and ASIC temperatures almost always exceed pre-determined allowable limits. In addition, while the power dissipation at the HBM core is lower compared to that of the ASIC die, the resulting heat flux of the former may be higher compared to that of the latter, thanks to the HBM’s smaller footprint. In aforementioned ASIC’s, if a traditional air cooling heat sink assembly was used, heat generated both at the ASIC die and the HBM module(s) would utilize the same conduction path through the package lid to a single heat sink located on the top. Therefore, it is very likely to generate some hot spots, especially on the HBM cores due to the higher heat flux produced. Furthermore, the allowable junction temperature of the HBM module(s) and the ASIC die are significantly different, i.e. the former has a max temperature limit 20-25 oC lower than that of the latter. Hence, the HBM module needs even more aggressive cooling requirements. In order to solve the aforementioned problem, a unique thermal design is proposed for the ASIC’s with HBM and an attached air-cooled heat sink assembly, in which the ASIC lid is separated with a thin gap and each of these lid surfaces accommodating its own heat sink on its top. Consequently, the design under consideration demarcates the vertical conduction paths of the ASIC side and the HBM side leading to lower temperatures on the latter. It should also be noted that the overall footprint of the new arrangement is essentially the same compared to that of the traditional heat sink assembly. The aforementioned technique has been applied to a dual HBM ASIC and the results have exhibited that the maximum temperature on the HBM base decreases considerably while the local temperature reduction throughout the entire module can be even higher. Due to its highly effective heat dissipating path, the design shown here can be used to target any high heat flux ASIC packages with single or multiple HBM modules.
Baris Dogruoz, Technical Leader
Cisco
San Jose, CA
United States


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