Improved thermal management and manufacturing flexibility in power module heatsinks through rapid large-area laser soldering and maximized convective heat transfer

This work represents a direct cooling method that overcomes the limitations of the method of directly cooling the power module and the pin-fin type heat sink face-to-face bonding. While the soldering direct cooling method of the existing pin-fin type face-to-face heat sink was very difficult to suppress the large voids and void clusters, the serpentine-shaped heatsink channels were successfully bonded to the backside of power modules within 30 s using a laser soldering process without voids or visible defects, forming an intermetallic compound (IMC) layer of less than 1 μm at the bonding interfaces. This level of manufacturing capability is visibly effective in significantly improving yield at the production process level, thereby enabling successful mass production. The temperature and deformation behavior with time history during the laser soldering process and the conventional mass reflow process using nonlinear heat transfer FEM have also been investigated. The deformation of Cu plate with laser soldering was measured less than 0.8 mm within 30 s, whereas in the case of conventional reflow soldering, deformation of more than 1.2 mm is observed for a longer period of time. Moreover, these channels have the potential to further increase the convective heat transfer coefficient; their CFD simulation results show that with an automotive coolant flow rate of 12 LPM and a power semiconductor device generating 80 W of heat loss, the operating temperature was 73.4 °C using our directly cooled channel. In comparison, even under the assumption of void-free bonding, the maximum operating temperature with a conventional pin-fin type heat sink reached 85.7 °C. This study experimentally and numerically provides a basis for a cooling method that increases yield and maximizes heat dissipation performance when implementing direct cooling of a power module and a heat sink.