Abstract: Gas-atomizing process has been used for developing SMT-purposed raw material tin based alloy soldering powder of free-cleaning type soldering paste,the alloy composition and impurity component contents of which have reached US-QQ-SS-571E and JAP JIS-Z-3282A grade standards with oxide contents meeting the standard of US Multicore Co.'s oxygen free flux powder and with an average single powder production rate over 70%.