- Author
-
Cider, L.
- Title
- Brandskadad elektronik: sanering och tillforlitlighet. BEST-projektet. [Reconditioning Surface Mount Electronics After Smoke Contamination.]
- Coporate
- IVF-Insitutet for Verkstadsteknisk Forskning, Stockholm, Sweden
- Report
-
IVF-Internrapport 92/20
1992
38 p.
- Keywords
-
electronics
|
smoke
|
contamination
|
cleaning
|
chlorine
|
chloride salts
- Abstract
- [ABSTRACT IN ENGLISH] This work deals with problems arising when modern surface mount electronics is to be reconditioned after smoke contamination. The result can to some extent be used in other cases where chloride contamination has occurred. In a fire, hydrogen chloride is formed when polyvinyl chloride is present. This aggressive acid will be deposited on various materials. Electronic equipment is especially sensitive since malfunction may occur after longer or shorter time of operation due to ionic contamination. Earlier work has shown that through-hole electronics can be reconditioned, with a good result, after deposition of up to 100 mu g chloride/cm2 in the surrounding area. The lower limit when cleaning is needed is often specified to 10 mu g chloride/cm2. In this work surface mount electronics has been exposed to smoke containing hydrogen chloride. This has given a contamination from 45 to 75 mu g chloride/cm2 on the test boards. Three different cleaning methods were investigated; manual, automatic spray and ultrasonic. All methods were able to pass the often used cleanliness level for electronic manufacturers. This standard requires a level lower than 1,5 mu g sodium chloride equivalent/cm2. One of the methods does not pass the optical inspection. All three methods do pass the electricial reliability test. Conformal coating is to a large extent able to protect the electronics against corrosive smoke. Decontamination of these boards may be complicated since smoke products have been partly absorbed into the conformal coating. This type of boards is steadily being more common and may become a problem when decontaminated. The large difference between chloride contamination at fire and at manufacturing of electronic equipment is the nature of deposition. Experiments in this work has shown that the hydrogen chloride reacts with lead in the solder forming lead chloride. At manufacturing chloride salts are being deposited all over the test board. Migration between conductors with different voltage has not occured. This is due to the fact that chloride is localized to the conductors. Galvanic corrosion, on the other hand, has occurred between metals within one conductor.