A thermally stable water soluble solder paste

Electronic card assembly manufacturers are only too aware of the challenge that must be faced in eliminating chlorofluorocarbons (CFC's) from their assembly process. The issuance of the Montreal Protocol and its subsequent follow-on restrictions have forced these manufacturers to seek alternative approaches. [1] Replacement of the typical rosin based materials (paste and flux) with their water soluble or no-clean counterparts seem to be the most viable approach. However, the replacement of the materials is not transparent to the process. Each unique material set forces the printed circuit assembly shop to adopt both a process methodology and test strategy in order to implement the new materials successfully into their assembly line process. Initially, the water soluble approach was chosen at IBM. An initial survey of off-the-shelf water soluble paste products noted that no one paste met the IBM ECAT requirements. Those pastes that came close had a marked sensitivity to thermal changes. Therefore a work effort was initiated by Austin to develop a thermally stable, water soluble paste that would remain stable at various conditions, encountered prior to use. Any paste developed would have to be suitable for 0.025 in., SMT attach.<>