Patent ID: 7291201

Claim:
A method for making Nano-scale lead-free solder, the lead-free solder being Sn-3.5Ag (96.5Sn-3.5Ag), comprising the following steps of: (a) mixing a pre-determined amount of SnSO 4 (aq) and a pre-determined amount of AgNO 3 (aq) to 0.4 liter and then forming a mixture solution of Sn-Ag which has a weight ratio of Sn and Ag being 96.5:3.5; (b) making a reducing dispersing solution comprising NaBH 4 and 1 M NaOH as reducing agents and 0.01 M alkyl sodium sulfate (C 12 H 25 OSO 3 Na) as a dispersing agent per liter of solution; (c) adding the mixture solution Sn-Ag from step (a) to the reducing dispersing solution during fast stirring of the reducing dispersing solution, thereby producing reactant Sn and Ag by means of the oxidation reduction between both solutions; and (d) settling the reactant from step (c), then adding an ethanol concentration at 95%, and cleaning the reactant by using a supersonic vibrator for removing boron (B) and sulfur (S) atom which adhere to the reactant, thereby producing the Nano-scale lead-free solder Sn-3.5Ag.