Simple Testing to Evaluate Ball Attach Fluxes.
BY JIM HISERT, Indium Corp. and SIGURD R. WATHNE PE, Sikama International, Inc.
When testing a flux on the production line is impractical due to the number of materials included in the evaluation processes, it makes sense to perform a simple comparison. This test procedure can be used to initially compare fluxes with minimal time, capital expense, and equipment.
The best way to test a flux is in the production line under actual working conditions. This can be impractical if too many materials are included in the evaluation process. There are, however, ways to understand the capabilities of range of flux materials without scrapping a large amount of production parts and time. One test procedure can be used to initially compare fluxes with minimal time, capital expense, and equipment. The key data is the quality of a flux to promote wetting of various alloys on a variety of surface finishes.1 This will be calculated as a change in solder diameter after reflow. Although solder spread is the numerical outcome of testing, cleanability of water-soluble fluxes and post reflow residue of no-clean fluxes may become apparent.
Performing this test requires only 5 pieces of equipment: a razor blade, tape, tweezers, calipers, and a hot plate. A series of multiple hot plates will speed testing because multiple temperatures can be used without waiting for temperature change and equilibrium. In this testing, a 5-zone conduction system* was used to reflow the samples. With a reflow system such as this, a precise nitrogen atmosphere can be maintained, if desired. The testing for this report was done in air to force a worst case scenario for each flux.
Solder spheres of different alloys are required for the test. The spheres were chosen to test different reflow temperature ranges, and consisted of the following alloys: 95.5Sn/3.8Ag/0.7Cu (solidus 217