Research On Properties Of Sn-18Bi-xCu Lead-free Solderand Interface Behavior Of Joints

In the world-wide,conventional Sn-Pb solder has been gradually replaced by new lead-free solder because of its adverse effects on health and environment.Industrial production in the demand for lead-free solder was low cost and high quality.Sn-Bi solder has a broad application prospects and market valuein the field of low-temperature packagingfor the low melting point.However,the nature of Bi was fragile,so that Sn-Bi solder shows brittle and poor plasticity,which affects the performance of welded joint.At the same time,the over-growth of interfacial intermetallic compound(IMC)will seriously shorten the life of microelectronics products.Using the alloying method,preparation of new Sn-18Bi-xCu low temperature lead-free solder(Sn-18 Bi,Sn-18Bi-0.3Cu,Sn-18Bi-0.5Cu,Sn-18Bi-1.0Cu)by adding Cu to Sn-18 Bi solder.The microstructures of solder/Cu interface,the growth of interfacial intermetallic compound,the shear strength of solder joints,and the microstructure of fracture surface were studied,and the influence of the addition of Cu on the long-term stability of solder joints was investigated.The result shows that the addition of Cu can reducethe melting point of the solder forrefining the Bi-rich phase.The Bi-rich phase presents in the form of fine dispersionin the solder.The spreading area is gradually decreasedwith the increase of Cu content.The addition of Cu can improve the tensile strength of the solder alloy,mainly due to the rod-like Cu6Sn5 interfacial intermetallic compounds play an enhanced role in the alloy.The shear strength of the solder joint is increased with Cu addition,and the shear strength of the solder joint is decreased gradually during the isothermal aging process.For the agedSn-18Bi-xCu/Cujoint,it is found that the growth activation energy of Sn-18Bi-1.0Cu/Cu interfacialintermetallic compoundis the highest,so the thickness of IMC layer is the thinest under the same conditions.Then the interfacial reactions of Sn-18Bi-0.5Cu/Ni-Pjoint and Sn-18Bi-0.5Cu/Co-P joint were studied.Sn-18Bi-0.5Cu/Ni-P joint was aged at 240?for different times.(Cu,Ni)6Sn5interfacialintermetallic compound is immediately appearedafter reflow.During the aging process progresses,(Cu,Ni)6Sn5is continuously reacted to form the(Ni,Cu)3Sn4.Sn-18Bi-0.5Cu/Co-P joint was aged at 240?for different times.With the increase of the aging time,the thickness of the IMC layer is increasing.The shape of the IMC is gradually changed from the fine needle to the prismatic and the size is gradually increased.Due to the continuous diffusion of Cu during the aging process,(Cu,Co)Sn3is formed between(Cu,Co)6Sn5 and CoSn3.Compared with Sn-18Bi-0.5Cu/Cu andSn-18Bi-0.5Cu/Ni-P,the IMC growth rate of Sn-18Bi-0.5Cu/Co-P is the fastest.