Crystal structure and microstructure of electrodeposited Sn-Ag alloys

Sn-Ag alloys, which are considered to be suitable for use as Pb-free solders, were formed by an electrodeposition method. In the alloys formed by an electrodeposition method, un-equilibrium phases, which do not exist in the phase diagram occasionally appear. Therefore the composition, morphology, produced phases and microstructure of the elecrtodeposited Sn-Ag alloys were studied. The results are summarized as follows. (1) A good relationship was observed between the morphologies of the electrodeposited Sn-Ag alloys and their compositions. (2) The electrodeposited Sn-Ag alloys had two phases (P-Sn and an intermetallic compound) in the range of 5 to 75 atomic percent Ag content, and were composed of grains of submicron-order diameter. (3) The phases which exist in the electrodeposited Sn-Ag alloys were those reported in the Sn-Ag alloy phase diagram.