No-clean soldering processes

AT&T is committed to a scheduled phase-out of emissions of chlorofluoro-carbons and other solvents from its manufacturing operations. The proper use of low-residue solder pastes and low-solids fluxes obviates the need for post-reflow and post-wave solder cleaning in circuit-pack assembly and, therefore, contributes significantly toward achieving these corporate goals. For proper solder joints to be formed with low-residue solder pastes, we found that the reflow atmosphere must be controlled. The appropriate thermal and atmospheric control capabilities have been identified. Factory implementation is underway and, by the end of 1991, a minimum of 13 lines capable of using low-residue solder pastes will have been installed. For the low-solids fluxes used for wave soldering, test results showed we need to control the quantity of flux applied. This control was realized with the development of a spray fluxer. The unit has been successfully deployed at many AT&T manufacturing locations.