Projection welding of TO style packages is a resistance welding process used to join cover and package. The materials are Kovar™ 29=Ni/17-Co/Bal Fe alloy, CTE of 6 PPM, with 1.27µ Au/Ni plate on top. The weld is an alloy of Kovar™ Au/Ni which is corrosive-resistance and compliant with MIL-STD-883 Test Method 1009 Salt Atmosphere. The Au/Ni plate Kovar™ material may be hydrogen fired by the materials supplier. No forming gas is required. There is no stringent cleanliness requirement.
A local extension (projection) is provided to concentrate the power and heat. The collapse of the projection and increase in bulk resistance leads to a weld along the entire perimeter of the package. There is low temperature and pressure exposure to multiple glass or ceramic feedthroughs. The projection weld is Kovar™ Au/Ni alloy which is corrosive-resistance and compliant with MIL-STD-883 Test Method 1009 Salt Atmosphere.