Study On Indentation Creep Behavior Of The Sn-Ag-Bi Lead-free Solder

In this paper, indentation creep property of Sn-3.5Ag-2Bi lead-free solder and adding repectively 0.7wt % Cu, 1.5wt % In, 1wt % RE in it is studied, and through comparison and analysis of changes of the microscopic structure before creep and after creep, the conclusions is obtained as follows:(1) In the circumstances 323K,333K,353K,373K and 16.7MPa,25.0MPa,35.0 MPa,43.2 MPa , indentation creep rates of Sn-3.5Ag-2Bi,Sn-3.5Ag-2Bi-0.7Cu,Sn-3.5Ag-2Bi-1.5In,Sn-3.5Ag-2Bi-1RE enhance along with temperature rising and pressure increasing , and showed accelerated upward trend.Their constitutive equations of the steady- state creep rates is obtained respectively:(a) (?)=0.679σ^3.304exp(-61181/RT);(b) (?)=0.423σ^3.181exp(-59189/RT);(c) (?)=0.307σ^3.246exp(-59740/RT);(d) (?)=0.265σ^3.069exp(-57174/RT).(2) In the circumstances the temperature and the stress to be tested, their stress exponents n values are within 3～3.4, the activation energy differs a little bit with theβ-Sn dislocation pipeline diffusing activation energy, and it approachs 60 KJ/mol or so. When 0.7wt % Cu , 1.5wt % In , 1wt % RE are added in Sn-3.5Ag-2Bi lead-free solder respectively, the stress exponents diminish from 3.304 to 3.181,3. 246 and 3. 069 respectively, and the material structure constants diminish from0.679 to 0.423,0. 307 and 0. 265 respectively. However, the effect of anti-creep property rising is the most obvious when 1wt % RE is added in Sn-3.5Ag-2Bi.(3) Bi dissolved inβ-Sn matrix increases the resistance of dislocation slipping, and thus it plays a strengthened role to a certait extent, thereby, the creep resistance of Sn-3.5Ag-2Bi lead-free solder is improved.(4) Dimension of the metal intermetal compound Ag₃Sn is fined when 0.7wt % Cu and 1.5wt % In element is added in Sn3.5Ag2Bi lead-free solder respectively, IMC Cu₆Sn and InSn₄ is formed at the same time. The study indicate finally that IMC Cu₆Sn and InSn₄ and fined Ag₃Sn hold back effectively dislocation gliding and climbing, thereby creep resistance is improved.(5) When 1wt % RE is added in Sn3.5Ag2Bi lead-free solder , on one hand, the stability compound forms in crystal boundary place;On the other hand, the part of RE element dissolves inside ofβ-Sn , and restricts dislocation moving to a certain extent.thereby, the two hands improve the creep resistance of the lead-free solder finally.(6) Ag₃Sn,Cu₆Sn₅ and InSn₄ IMC recrystallize after indentation creep.(7) The creep deformation mechanism of Sn-Ag-Bi lead-free solder is dominated by dislocation gliding and climbing mainly, but dislocation gliding holds a leading post.