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Thermal Performance of an Adhesive Bonded Superconducting Multichip Module on a Gifford-McMahon Cryocooler
Keywords: Cryogenics (4K), MCM Packaging, thermal management
Low temperature cryogenic (4 K) environment provides electronic devices an environment conducive for faster switching speeds, and higher heat dissipation. Particularly, niobium based low temperature superconducting electronic devices (LSCE) which operate at liquid helium (4K) temperature offers performance attributes not realizable with semiconductor electronics. LSCE devices offer ultra fast switching speeds, low noise, high sensitivity and very low power dissipation. The performance of LSCE devices has been demonstrated in a liquid helium environment. In the current paper, we report the experimental study of the thermal resistance of a flip chip bonded superconducting multichip module in a liquid cryogen free environment. A 5mm X 5mm indium-tin bumped superconducting chip was flip chip bonded on a 1cm X 1cm superconducting carrier chip. A non-conductive adhesive was used as an underfill to enhance the robustness of the package. We designed a test bed where the LSCE module was mounted onto the cold head of a Gifford McMahon (GM) cryocooler. The module was conductively cooled down to 4 K and the thermal resistance between the chip and the carrier chip were analyzed. The experimental results showed that for the power dissipation (2-5 mW), which is typical for LSCE devices, the thermal resistance was 22.75 +/- 1.08 K/W. Thermal model of the current LSCE package was investigated using Comsol multi-physics. Theoretical estimates showed that for the current package setup the expected thermal resistance was 5 K/W. The discrepancy between the model and experimental analysis has been explained due to the presence of voids and improper bump contact area. To our knowledge, this is the first such experimental investigation of the thermal performance of adhesive bonded LSCE package on a cryocooler. This experimental analysis is of paramount importance for future trends in single chip and multichip module packaging of LSCE devices.
Ranjith S. E. John, Senior Graduate Assistant
University of Arkansas
Fayetteville, AR

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