Welding, Joining and Additive Manufacturing International Conference 2015

The project was aimed at finding alternate ways to joining semiconducting ceramics to metals by eliminating brittle intemetallics formed during furnace soldering.

The proposed solution was heating by high frequency electromagnetic wave/material interaction instead of furnace-, laser- or other heating methods. The interface filler material was a combination of metal powders and an organic suspension of polymers, placed in a WR340 single mode waveguide operating at 2.45 GHz, and 3 kW power.

The waveguide was capped with a moveable reflecting end for closed-loop control and a FLIR T300 infrared camera was used to control the system following material-specific algorithms. A patent is pending on this prototype. The other novelty was in separating the three modes of microwave-material interactions in a plasma-less environment, namely: 1) dielectric heating of the polymer and ceramic, 2) eddy current resistive heating, and 3) hysteresis loss heating of the metal powder. The COMSOL multi-physics modeling software was used to predict heating at the electrical- vs magnetic wave maxima in the wave guide. The result was a well-defined heating rate at optimum powder /polymer ratio at the interface, that also indicated the extensive role of dielectric heating of different polymers. It was also found that forced cooling of the sample was an important factor in accomplishing good temperature control, together with reaching vacuum levels below 1 mtorr to avoid arcing in the chamber. Successful FEA model validations were completed and the separation between the electric- and magnetic field peaks was found to be one of the most important parameters used in closed-loop controlled microwave heating. Current studies include tungsten carbide brazing on steel, carbon nanotube alloying of copper, and aluminum brazing for cryogenic applications.