Novel Electronic Packaging Low-silver Lead-free Solder Research

Micro-interconnect technology occupies an important position in microelectronic packaging. The teny solder joints have the function of mechanical bonding, electric conduction, thermal conduction et al, so it has much requirements on their qualities. Now, a series of lead-free solders has been developed, and Sn-3.0Ag-0.5Cu solder is one of the most remarkable and widely used solders, but its too much high silver content results in too much cost. In recent years, for the soaring of silver price, the research for low-silver electronic solders becomes important.This reseach attempted to improve the wettability and solder point appearance of the available low-silver solders Sn-0.3Ag-0.7Cu and Sn-1.0Ag-0.5Cu, and raise the mechanical strength and reliability of the solder joints, and lastly invent a novel solder alloy. Through literature review and patents analysis, and with the help of phase diagrams and thermodynamic datas, the composition of the new solder alloy is designed. With the Simultaneous Thermal Analyzer, metallographic microscope, metallographic analysis software, Field Emission Scanning Electronic Microscope, X-ray diffractometer and universal material testing machine, this research researched the influence of Zn, Mn on the wettability, melting character, oxidation resistance, alloy microstructure, soldering joint microstructure, joint mechanical strength, joint fracture and thermal stability et al of Sn-0.3Ag-0.7Cu solder alloy.The research finds that Mn, Zn doping reduces the spreadability and wettability of the low-silver solders, but the addition of less than0.02wt%Mn could keep the spreadability at a rather high level and improve the gap filling performance compared with Sn-0.3Ag-0.7Cu. DSC test shows that the addition of small amount of Mn and Zn doesn’t have much influence on the melting point of Sn-0.3Ag-0.7Cu solder, the variation range is±4℃, and no chang low is observed. And from the view point of melting range, the addition of small amount of Mn and Zn doesn’t have much influence on it, the variation range is±2℃, and no change low is observed. High temperature oxidation resistence test shows that Mn can degrades the oxidation resistance of the solder alloy and Zn doping make it even worse. Mn doping can make the microstructure of the as-cast alloys become more uniform and finer, and Mn, Zn multi-doping can produce the same effect. Mn doping or Mn, Zn multi-doping can inhibit the growth of the Cu6Sn5layer of the joint interface, and with the same Zn adding amount, the directional growth phenomenon of the Sn matrix microstructure of the solder joint is changed gradually as Mn content increases. Tensile strength and shear strength tests show that as Mn content increases from0to0.1wt%, the joint strength rises first and falls later. With the same Mn content, the joint strength rises first and fall later as Zn content increases, proper multi-adding amount of Mn, Zn is0.05wt%and0.1wt%respectively. Through tensile fracture and shear fracture surface analysis, it’s found that most fracture path develops through the solder matrix, but not the intermetallic compound layer.Mn doping or Mn, Zn multi-doping can both restrain the coarsening of Cu6Sn5and Cu3Sn layers while annealing and this can improve the reliability of solder joint, and Mn, Zn multi-doping has a better effect.