The Measurement of Flux Residues from Chip Carrier Attachment and Their Effect On Other Thick Film Hybrid Components

There is some concern that flux residues resultant from the solder attachment of thick film hybrid substrates can have a deleterious effect on other components on the substrate. Three aspects of this have been considered. First the measurement of flux residues has been evaluated by two different techniques: Auger electron spectroscopy and dynamic conductivity monitor (DCM). Quite low levels of flux residue were measured following two separate cleaning techniques on a variety of substrates containing chip carriers. The two measurement techniques gave comparable results but the DCM was considered more applicable to routine use in a hybrid production area. Second, the effect of long term environmental testing on thick film resistors located under chip carriers was assessed. It was concluded that what flux residues remained had no significant effect on the resistors. Third, a similar long term environmental test program was carried out on other thick film hybrid components deliberately contaminated with I percent of a rosin mildly activated (RMA) flux. The flux was found to have no significant effect on thick film conductors, chip resistors, or chip capacitors.