What does EPC recommend for solder flux being used in assembling lead free (PbF) eGaN FETs?
EPC recommends the use of no clean flux solders. However, to prevent the formation of thermal and electrical dendrites, it is recommended to clean the flux from the board even if no-clean flux is used. EPC uses Kyzen Aquanox® A4625 chemical in a Nu/Clean AquaBatch XL standard system manufactured by Technical Devices Company to remove the no clean flux.
If a no-clean flux is used and it is not rinsed off, a post-reflow bake for a minimum of 60 minutes at 150°C is recommended. This ensures that the no clean flux is properly cured and helps prevents dendrite formation.
If a water rinseable flux is used, the eGaN device needs to be rinsed on all four sides to ensure proper flux removal. A tilted device can obstruct the flow of the rinse and cause flux to remain trapped under the die. For this reason, using a no rinse solder flux with low ionic content and then rinsing the no rinse flux is recommended. For more information, please see our assembly application note: Assembling eGaN FETs and Integrated Circuits.