Abstract
ffect of indium addition on microstructure of the solders, their enthalpy changes, wetting of copper substrate, strength and structure of the copper joints were studied. Lead-free solders near to eutectic binary Sn-3.5Ag alloy containing 0, 6.5 and 9 wt.% of indium were prepared in induction furnace in Ar atmosphere followed by planar flow casting into the form of ribbon. Indium decreases the onset temperature for melting and freezing to 206 and 181°C for 9 wt.% indium, respectively. Enthalpy change of the melting as well as of the freezing also decreases with increase the amount of indium. Wetting of Cu substrate by the solders was investigated by sessile drop method at the temperatures 250, 280 and 320°C. Indium decreases the contact angle down to 36° for 9 % In, 320°C and 1800 s. Copper joints were made with solders at the temperatures 250, 280 and 320°C for 1800 s in air. Cu plates prior to joining were daubed by flux based on rosin. Shear strength moderately decreases with amount of indium and with joining temperature from 23.6 MPa for indium free solder at 250°C to 17.6 MPa for highest amount of indium at 320°C.

Key words
lead-free solder, wetting, copper joints, shear strength

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