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The fabrication of thick-film hybrid circuits using the solder system consists of screen printing conductor and resistor networks on alumina substrates and attaching other circuit elements (capacitors, discrete semiconductors etc.) to the conductor using tin-lead solder. The difficulty encountered with this technique has been that, although components are rigidly attached at the time of assembly, deterioration of the solder bonds occurs.
The objective of the investigation was to develop a suitable test method for testing incoming materials, optimizing process variables, and in-process quality control of the product.
After review of methods of conductor adherence testing, a method, pull-peel at 90 deg, was chosen which represented the worst case in actual module application. In order to hold the variables to a minimum, one standard test module was chosen for all experimental work. Part of this test module was incorporated into the design of production modules so that quality control of the product could be directly correlated with the initial testing results and with any process variables. Tests were conducted under controlled conditions which optimized all the assembly steps. Four areas have been found to have marked influence on conductor adhesion: the initial thickness of screened material, the preparation of substrate before soldering, the amount of solder used to make a joint, and the rate of cooling of the soldered joint. Implementing these controls results in a product with improved conductor adhesion.
thick films, adhesion, soldering, manufacturing, variability, temperature cycling, cooling rate, conductivity
Senior chemist, Microwave and Power Tube Division, Industrial Components Operation, Raytheon Company, Quincy, Mass.