The Research On Surface Modification And Wettability Of Sn-Zn-Bi Lead-free Solder

In the traditional manufacturing process of electronic products,the Sn-Pb alloy solder was wildly used in the PCB(printed circuit board).The Pb contained in the products would finally separated out and infiltration into the earth,so that our environment would be polluted and the human life would be under the threaten.For preventing this,many countries have developed a series lead-free alloy solder.And Sn-Zn lead-free alloy solder was wildly research for it's low melting point(198°C)witch is close to the melting point with Sn-Pb alloy solder(183℃),and it's high strength and low cost.But it's a pity that the Sn-Zn lead-free alloy solder is easy to be oxidized, the maintain period of the solder paste is short,and the worst thing is the wettability not very good. All these factors result in the limiting use of Sn-Zn lead-free alloy solder. At the present time,the research of the Sn-Zn lead-free alloy solder is focus on putting some elements such as In,Bi,Ag,Ga,Re into the alloy solder which can improving the anti-oxidized and the wettability abilities.This research is focus on using the ball mill and liquid phase method to coating the Sn-Zn-Bi lead-free alloy solder particles by suitable organic materials such as stearic acid,organic matter A,Band C,organic acid D,malic acid and so on.We measure the acidresistivity of the solder to reflect its anti-oxidized,and measure the wettability at the same time to analyse the effect of the technological conditions;analysing the coating conditions by SEM,IR and energy spectrum;comparing the difference between the modification solder through observation of the metallic phase of spot welds by SEM and metalloscope.The results of the research indicates that the ball mill and liquid phase methods both can improve the abilities of the alloy solder,and the liquid phase method seems to be better .The best technology situation of the ball mill method is 100rpm,1.0h,coating matters are organic material B and organic acid D and the adding content is 0.9～1.2%.The best technology situation of the liquid phase method is the modified time control between 2.0～3.0h,the coating matters are organic C and stearic acid and the dissolvent is absolute ethyl alcohol and cyclohexane on each.