Effect Of Alloying Elements And Aging On Microstructure And Solder Interface Of Sn-Zn Lead-free Solders

Sn-Zn Lead-Free Solders were quite being concerned due to low metting point, low price and non-toxicity.However,the aplication of Sn-Zn lead-free solders was restricted in engineering because of oxidized easily and poor wettability.In this paper,the effect alloying elements and aging on microstructure and Solders/Cu interface of Sn-9Zn lead-free solder and Sn-9Zn which added respectively 3wt.%Bi,0.5wt.%RE,0.45wt.%Al were studied by optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrdmeter(EDS),X-ray diffractometry(XRD).The conclusion was obtained as follows:(1)Amount of Bi dissolved and few of Bi precipitated in P-Sn base after added 3wt.%Bi in Sn-9Zn lead-free solder matrix.The microstructure of lead-free solder was refined,the distribution of needle-like Rich-Zn was much disordered.(2) The discountinuous riticular Rich-Al phase was precipitated in grain boundary,the number of needle-like Rich-Zn was reduced,the microstructure of lead-free solder was refined after added 0.45wt.%Al.(3)The bulk-like Sn-La-Ce compound was formed in lead-free solder matrix, and the microstructure of lead-free solder was refined after added 0.5wt.%RE.(4)The needle-like Rich-Zn phase reduced gradually,the microstructure of Sn-9Zn,Sn-9Zn-3Bi,Sn-9Zn-0.45Al,Sn-9Zn-0.5RE solder was refined after aging 600 hours at 100℃.(5)The solder interfaces of Sn-9Zn,Sn-9Zn-3Bi,Sn-9Zn-0.45Al, Sn-9Zn-0.5RE with Cu aging for different at 100℃were investigated.The result indicate,it was found that the formation of a thick Cu-Zn intemetallic compound (IMC) layer on interface between solder and Cu substrate.It was also found that the planar morphology which being close to the Cu substrate wasγ-Cu₅Zn₈ compound, being close to the solder wasβ-CuZn compound.The thickness of the solders/Cu solder interface intemetallic compound increased with aging time increaseing,the IMC thickness of solder interface which added 3wt.%Bi was thick,which added 0.5wt.%RE,0.45wt.%Al was thin.(6)The growth law of solder interface intemetallic compound of Sn-9Zn lead-free solder and Sn-9Zn which added respectively 3wt.%Bi,0.5wt.%RE, 0.45wt.%Al was investigated after aged for different time at 100℃.The solder interface intemetallic compound growth rate is different with added different alloying elements.The growth rate constants of Sn-9Zn/Cu,Sn-9Zn-3Bi/Cu, Sn-9Zn-0.45Al/Cu,Sn-9Zn-0.5RE/Cu solder interface intemetallic compound were 0.1467,0.1139,0.0332,0.0677,respectively.The total thickness of solder interface intemetallic compound and aging time basically according with T= Kt^1/3 growth law.