Thermal Performance of an Adhesive Bonded Superconducting Multichip Module (MCM) on a Gifford-McMahon Cryocooler

We report the experimental study of the thermal resistance of a flip chip bonded superconducting multichip module (MCM) in a liquid cryogen free environment. A 5×5 mm2 indium-tin bumped superconducting chip was flip chip bonded on a 1×1 cm2 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 was analyzed. The experimental results showed that for the power dissipation (2 – 5 mW), which is typical for low temperature superconducting electronic LSCE devices, the thermal resistance was 20.1 +/− 1.9 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 of the bump path to be 6.2 K/W. The discrepancy between the model and experimental analysis has been explained due to the presence of voids and inadequate 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.