Cleaning RMA Flux Residues in a High Lead Wafer Bumping Process

摘要

During a wafer bump process using high lead (5/95 Sn/Pb) solder, a RMA flux is used for the solder reflow process following solder evaporation. Because the reflow temperatures reach 340-360℃, flux residues can be polymerized and are difficult to remove. A cleaning solvent with high solvency for flux residue is required, yet must not cause pitting or corrosion of the solder bumps. Additionally, the solvent must rinse clean and leave no detrimental residue that would affect the subsequent die-attach process for flip-chip packaging. Finally, it is attractive for the cleaning solvent to be recycled multiple times to prevent excessive amounts of waste. Environmental concerns were also considered during the selection of the cleaning solvent. To reach these goals, a semi-aqueous cleaning solvent combined with a centrifugal batch cleaner has been effective. The solvent is currently recycled through 800 cleaning cycles before being discharged to the wastewater stream.