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By Harald Wack, Ph.D., ZESTRON
For decades, despite research and trials, chemicals have continued interacting with the cleaned surfaces in question. Cleaning materials are researched and changed based on the root cause of the observed problem. Are there issues with all cleaned parts or only with selected ones? The answer will give you an idea whether the problem is related to chemistry or not.
There is a large quality variety that exists with most wetted materials. For example, with a metal alloy, the composition of the alloy itself can vary, as can the actual quality standard from manufacturer to manufacturer. This introduces a significant variation for the situation on the line, which materials suppliers try to anticipate as closely as possible. Full predictions of the alloy composition, line factors, etc., is not possible. When unpredictability creates issues in manufacturing, the problem's origins must be determined.
With plastic materials and their respective raw materials, the story is similar. Even with high-quality materials such as Kalrez and Teflon, the final product can deviate from manufacturer to manufacturer. To address this, chemicals undergo extensive material compatibility tests for cleaning equipment, stencils, labels, components, and many other "wetted" materials. Considerations include exposure under worst-case conditions, generally for a time period that is 10× longer than the actual exposure time in the cleaning equipment. Production-site conditions also are replicated, including assembly materials and the cleaning machine in use. Chemistry can be a "black hole" on the assembly line, partially due to the fact that many product formulations are proprietary and confidential.
Chemistry also is explainable and predictable. Before premature process changes are made, cleaning equipment and materials providers can resolve any incompatibility issues within the cleaning system.
Recent globalization provides a new source of variation. While we might have previously dealt with domestic vendors in the electronics materials supply chain, we are now facing global sourcing and its effects. For example, components and stencils are manufactured in Asia and shipped to the E.U. and the U.S. for use. Despite Asia's continuous improvements in quality, materials of inferior quality are still being shipped to end-customers. A global vendor is therefore compelled to test for full material compatibility locally. In urgent cases, mutual cleaning trials at a fully equipped technical center are recommended. A technical report is unfortunately not always a proof of actual results. Before changing processes, investigate all options of materials incompatibilities, including variations from batch to batch in materials like solder alloys, PCB finishes, and plastics.
Harald Wack, Ph.D., an SMT Editorial Advisory Board member, is executive VP and CEO of ZESTRON America. Wack has authored and published several scientific articles, and has provided technical information for various publications. He received his doctoral degree in organic chemistry from Johns Hopkins University. He may be contacted at (703) 393-9880 or via e-mail at email@example.com. Dr. Wack recently wrote The Importance of Global Technical Support.