Water soluble paste survey for fine pitch SMT attach

Off-the-shelf water-soluble solder pastes for fine pitch (0.025-in), surface mount technology (SMT) attach applications were assessed. Twenty solder paste material vendors were surveyed. Seventeen claimed to have a water soluble paste (WSP), either on the market or in development. These pastes were evaluated with two experimental methods: manufacturing line usability testing, followed by surface insulation resistance (SIR) reliability testing. The usability matrix was designed to assess each paste´s performance in each of the key process steps: screen printing, component placement, paste reflow, and board cleaning. Rosin mildly activated (RMA) paste performance in these areas was used as a benchmark for the water soluble materials. Only three pastes met all of the desired criteria. These were, subsequently, reliability tested. An additional, very fine pitch (0.020-in), screen printing experiment was performed to determine the extensibility of the selected pastes