Joining contact elements to gold layers on a carrier - by means of solder preforms and heating of assembly

The contact element, gold wire or strip is cleaned using a dilute organic acid and the gold layer on the carrier is cleaned using a mixt. of organic acids. A fluxing agent composed of a mixt. of organic acids and amines in an alcohol soln. is applied to the surface of the elements and gold layer to be joined. The soft solder alloy contg. >30% In in the shape of preforms is placed on the surface of the gold layer which is then heated for 3-6 sec. to 20-60 degree above the m p. of the solder alloy. After removal of the flux the contact element is positioned and the assembly heated for 3-6 sec. to 20-60 degrees above the m.p. of the solder alloy. The gold layer is cooled at a rate of about 50 degrees C/sec. After applying a flux for the second time to the joint the assembly is heated to 20-60 degrees C below the m.p. of the solder alloy. The contact element is fixed and the joint is once again solder for 3-6 sec. with a soldering iron of max. temp. 20-60 degrees C above the m.p. of the solder and the joint cleaned to remove the flux.