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, either on the market or in development. These pastes were evaluated with two experimental methods: manufacturing line useability testing, followed by surface insulation resistance (SIR) reliability testing. The useability 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. RMA (rosin mildly activated) 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 extendability of the selected pastes.
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