Influences Of Al On The Performance And Microstructure Of Sn-9Zn-2Cu Lead-free Solder

Because of the legislative concerns of environmental protection and therequirement of high-integrated microelectronics development,the research anddevelopment of new lead-free solder has become one of the critical issues inelectronics and materials industry. Eutectic Sn-9Zn alloy is widely recommended asone of the promising lead-free solder instead of Sn-Pb.But Zn has a poor wettabilityin the Cu substrate because of its larger surface tension and easily oxidized,which is abottleneck of restricting to applications and development of Sn-Zn solder.In recentyears, the alloying method to improve Sn-Zn solder wettability and other propertiesresearches has made great progress, but the problems have not been fundamentallyresolved.On the basis of summarizing the previous study of a large number of Sn-Znsolder, the paper has researched the using of Al element micro-alloying method toenhance the oxidation resistance,further improved the wettability and othercomprehensive performance etc of Sn-Zn-Cu leader-free solder.In addition,theinterfacial reactions and IMCs growth behaviors of Sn-Zn-Cu leader-free solder withCu substrate have been studied through long-term aging method,and discussed theinfluence of Al element which is added to Sn-Zn-Cu alloy on solder joint reliability.The above study shows:The wettability of Sn-9Zn-2Cu-0.035Al is the best, then the wetting force is upto2.1725mN, wetting time is0.44s, spreading area could be up to48.29mm2, theminimum of spreading and wetting angle is up to58.76degrees, so the wettability ofSn-9Zn-2Cu-0.035Al solder is the best; at the same time, the Al element added couldenhance the oxidation resistsnce of the solder, the oxidation resistsnce ofSn-9Zn-2Cu-0.035Al is the best, which can steadily improve the antioxidantproperties of the leader-free solder.The melting point of the alloy increased about1～3℃because of addition oftrace Al element,the average melting point is about203degrees; and the meltingprocess of the leader-free solder is shortened up to4.5℃, the minimum meltingprocess of Sn-9Zn-2Cu-0.035Al was up to4℃; the acicular zinc enrichment phasesize was decreased because of the amount of Al element added, refined themicrostructure and dispersd uniformity; the hardness of the alloy was improved because of trace Al element, the hardness of Sn-9Zn-2Cu-0.035Al was the largest.In addition, at the temperature of120℃,the thickness of interface intermetalliccompounds (IMC) where was in joint of Sn-Zn-Cu-xAl four element alloy solderincreased in the aging process with aging time.The thickness of intermetalliccompound layer could be reduced by joining Al elements,and inhibit excessivegrowth, which is to improve the reliability of solder joint is very favorable.