MICROSTRUCTURE OF SN-AG ALLOYS ELECTRODEPOSITED FROM PYROPHOSPHATE-IODIDE SOLUTIONS

Tin-silver (Sn-Ag) alloys, which are considered to be suitable for use as Pb-free solder, were made by an electrodeposition method. A newly developed Sn-Ag alloy electroplating bath containing pyrophosphate and iodide as the complexing agents of Sn and Ag was used. The compositio n, morphology, phases and microstructure of electrodeposited Sn-Ag all ays were studied. The results are summarized as follows: (1) A good re lationship was observed between the morphologies of the electrodeposit ed Sn-Ag alloys and their compositions. (2) The electrodeposited Sn-Ag alloys ranging in Ag content from 5 to 75 at% exhibited two phases (b eta-Sn and an intermetallic compound), and were composed of grains of submicron-order diameter. (3) The phase diagram of the electrodeposite d Sn-Ag alloys resemble the equilibrium phase diagram of the Sn-Ag all oys.