Gas flow simulation of a fluxless Si solder bonding oven

In this paper the technology of the “Linn” type Si fluxless solder bonding oven and gas flow simulations of the oven are discussed. This oven is used for fixing silicon chips on metal substrates with high temperature solder bonding process. The solder is applied in a foil form which is placed between the Si chip and the metal substrate and does not contain any flux. Therefore a reducing agent (Forming gas which is a mixture of 10 vol% H₂ and 90 vol% N₂) has to be applied to avoid the oxidation of the joints. The key factors of this soldering process has been studied which are the suitable temperature and the adequate H₂ concentration. A 3D gas flow model of the oven has been prepared which is based on the FVM (Finite Volume Model) method. The thermal and gas flow circumstances - used the basic and new theoretical oven settings - have been compared by simulations applied the ANSYS - FLUENT system. The model was verified by the measurements of the H₂ concentration, the temperature and the pressure inside the oven. The aim was to find new oven settings in order to improve the mechanical stability and decrease the void percent of the joints.