IBM Technical Disclosure Bulletin (Research Disclosure n293 09-88)
English (United States)
1 pages / 11.5 KB
Circuit Board Soldering Through Conformal Coating
A metallic electrical conductor, such as on a printed circuit card, is covered with a protective conformal coating, and then soldered to, without removing the coating. As shown in the drawing, conformal coating, such as FLUORAD FC- 725*, can be used to cover a circuit card which subsequently can be screened with solder paste on the surface of the coating over the metallic conductors on the card. Application of heat reflows the solder paste, which penetrates the protective coating, and wets the metallic surface below.
One application of this is to cover tightly spaced conductor lines on printed circuit cards. Current solder masks either do not have the necessary characteristics to allow them to be screened onto such a card and adequately cover circuit lines without going onto solderable surfaces (screenable wet solder masks) or are expensive (photo-imageable dry film solder masks). This new procedure allows coating the entire card without having to keep the coating from the solderable surfaces. Also, this new procedure can be used as a localized coating for certain areas of a printed circuit board, being applied only where necessary.
Another application is solely to achieve a protective coating. Currently, panels have a shelf life due to the aging of solderable surfaces when they are exposed to the atmosphere. By coating the panel, access to the solderable surface could be denied to air and, potentially, to moistur...