Effect Of The Indentation Creep Property Of Sn-0.7Cu Lead-free Solder Containing Alloy Elements

In this paper, the development and research on Sn-0.7Cu as well as Sn-0.7Cu based on lead-free which were added some In, Bi, Ag. Through comparison and analysis of changes of the microstructure before creep and after creep. The main contents and results are as follows:(1) Under the test temperature of 60℃, 80℃, 100℃, 120℃, stress of 30MPa,35MPa,40MPa,50MPa,the indentation creep deformation and creep rate of Sn-0.7Cu,Sn-0.7Cu-2In,Sn-0.7Cu-2Bi,Sn-0.7Cu-1Ag were changed increased with the increasing of temperature and compressive stress, the steady creep rate obeys an empirical equation(2) For Sn-0.7Cu,Sn-0.7Cu-2In, Sn-0.7Cu-2Bi and Sn-0.7Cu-1Ag lead-free solder, the stress average exponents(n) are 5.20, 4.03, 4.20, 3.78 at different temperatures, and the apparent creep activation energies are similar with 60KJ/mol under different stresses. The creep mechanism of Sn-0.7Cu are controlled by dislocation climb; the creep mechanism of Sn-0.7Cu-2In,Sn-0.7Cu-1Bi,Sn-0.7Cu-1Ag are controlled by dislocation glide under the temperature of 60℃-80℃, by dislocation climb under the temperature of 80℃-120℃.(3) After the 2wt.% In added in Sn-0.7Cu lead-free solder, one portion of In solutes inβ-Sn matix, the InSn₄ which distribute on theβ-Sn matrix evenly comes to being with the In surplus and Sn. So the In added strengthes theβ-Sn matrix ; the creep resistance is improved.(4) After the 2wt.% Bi added in Sn-0.7Cu lead-free solder, Bi solutes inβ-Sn matrix to cause lattice distortion ,which impede the dislocation glide and the resistance to deformation increased, playing a key role in solution strength. The Bi grains are pinned on the boundery for dislocation; the creep resistance is improved.(5) Adding 1wt.% Ag to Sn-0.7Cu, the Ag can promote nucleation before the formation of intermetallic compounds and restrain the growth of the crystal grains latterly. So it refines the grains, adds to phase interfaces and increases the resistance to glide deformation in the creep. The harder and brittle phases Ag₃Sn,Gu₆Sn₅ which prevent the matrix deforming distribute in theβ-Sn matrix; the creep resistance is improved.(6) The phases Cu₆Sn₅,InSn₄ get smaller or even extinguished after creep on account of absorbing a mass of heat energy and interfacial energy in the indentation creep process. The Sn-0.7Cu-2Bi lead-free solder alloy produces plastic deformation under high temperature and pressure leading to distorted lattice and grains broken. The instable structures restore and recrystallize, grains growth in the end as the temperature increases. The longer under the high temperature, the bigger the grains. A part of acicular Ag₃Sn IMC of the Sn-0.7Cu-1Ag Lead-free solder get smaller precipitates in the process continuous extrusion.