Authored By:
Michael Konrad
Aqueous Technologies
CA, USA
Summary
Today, in modern times, society values cleanliness. The recent pandemic has exaggerated the degree to which we desire, expect, and even demand cleanliness. Even in “normal times”, cleanliness is revered. We wash our bodies, dishes, cars, and pets. We expect cleanliness in our hotels and restaurants. We require cleanliness, to the point of sterility, in our operating rooms. In many public restrooms, we even hire people to inspect for cleanliness and publish inspection reports.
Cleanliness has become a normal part of life, except in one aspect of our life. Part of our life that ensures our safety, prepares our food, transports us to work and play, monitors our health, and so much more. I’m referring to electronics. Once regarded as vital, the level of importance of a clean circuit assembly has been demoted. How did the cleanliness of circuit assemblies, once required, get shoved aside? There’s one simple answer; the environment.
During the 1980’s, scientists discovered a “hole” in the Earth’s ozone layer and attributed it to, among other things, chlorofluorocarbons (CFC’s). In order to protect the ozone layer, or at least slow down the shrink-rate, a treaty was signed, referred to as the Montreal Protocol [figure 1], originally by eleven countries, that would phase out production, and consequently availability, of most CFC-based solvents within a ten-year time frame. That was 1989. By law, these CFC-based solvents would be no longer produced by 1999.
The wildly popular cleaning/defluxing chemicals of the day were largely CFC-based and therefore subject to the ban. Necessity being the mother of invention, a new flux was introduced promising to leave behind an invisible and benign residue, not harmful to circuit assemblies. This new “no-clean” flux would eliminate the cleaning requirement. Almost instantly, the electronic assembly industry switched to no-clean fluxes and abandoned their cleaning processes. While some high-reliability manufacturers such as military and medical maintained their cleaning processes, the majority of the industry exchanged their cleaning systems and processes for the promise of a “clean without cleaning” circuit assembly.
Conclusions
Time and technology have worked in tandem to reduce the volume of residues a typical circuit assembly can tolerate. Given the three primary ECM prerequisites (electrical bias, ionic residue, and moisture), residue removal is the only practical and reliable method of ECM prevention and other residue-related reliability issues.
Initially Published in the SMTA Proceedings
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