The　selection　of　soldering　flux　plays　a　critical　role　in　promoting　wetting　and　product　reliability　of　printed　circuit　board　assemblies.　In　this　study,　the　effects　of　fluxes　on　the　wetting　characteristics　of　the　Sn-3.0Ag-0.5Cu　solder　alloy　on　Cu　substrates　was　researched　by　using　various　flux　systems　at　different　soldering　temperatures.　Because　of　the　distinct　characteristic　of　the　lead-free　solder-poor　wettability-three　kinds　of　fluxes　[no-clean　flux　with　high　solid　content　(NCF),　rosin　mildly　activated　flux　(RMA)　and　water-soluble　flux　(WSF)]　were　chosen　for　the　wetting　experiments.　The　wetting　time　and　force　were　the　evaluating　indicators.　The　experimental　observations　indicated　that　the　wettability　clearly　depended　on　the　soldering　temperature　and　flux　system　when　using　the　same　solder.　Furthermore,　the　corrosion　potential　of　flux　residues　was　measured　by　surface　insulation　resistance　(SIR)　testing.　Scanning　electron　microscope　(SEM)　and　energy-dispersive　X-ray　spectroscopy　(EDS)　were　used　to　determine　the　contents　of　the　flux　residues　and　corrosion　products.