Effect Of Copper Content In The Impression Creep Behavior Of Sn-Cu Lead-free Solder

Sn-Cu lead-free solder is one of the common lead-free solder in microelectronics welding technology,its creep resistance relating to the life of the product.In this paper,Sn-0.7Cu?Sn-1.5Cu?Sn-2.3Cu?Sn-3.1Cu four kinds of Sn-Cu lead-free solder was used to have a creep test by homemade device under the condition of 60-80? and 21-27MPa,their impression creep mechanism in the creep test was analyzed.And the effect of copper content in the impression creep behavior of Sn-Cu lead-free solder was discussed.Moreover,the creep behavior of Sn-0.7Cu lead-free solder made in different cooling rates was studied,and its influence law was determined.The main results are as follows:1.Under the experimental conditions of 60-80? and 21-27MPa,the stress exponent n of Sn-0.7Cu,Sn-1.5Cu,Sn-2.3Cu,Sn-3.1Cu four kinds of Sn-Cu lead-free solder are 3.45,4.69,5.07,5.43 respectively,the creep activation energy are 33.4 KJ/mol?41.2 KJ/mol?54.7 KJ/mol?64.3 KJ/mol respectively,and the constitutive equations of the steady-state creep rate are as follows respectively:? = 2.5×10-9 ?3.45 exp(-33400/RT)?= 1.69×10-13 ?4.69 exp(-41200/RT)?= 2.86×10-15 ?5.07 exp(-54700/RT)?= 2.9×1-10-12 ?5.43exp(-64300/RT)2.Under the experimental conditions of 60-80? and 21-27MPa,the impression creep deformation mechanism of Sn-0.7Cu lead-free solder is mainly controled by dislocation slip,the impression creep deformation mechanism of Sn-1.5Cu,Sn-2.3Cu,Sn-3.1Cu three kinds of lead-free solder is mainly controled by dislocation climb.3.Under the experimental conditions of 60-80? and 21-27MPa,the creep resistance of Sn-0.7Cu,Sn-1.5Cu,Sn-2.3Cu,Sn-3.1Cu four kinds Sn-Cu lead-free solder are in turn improved with the increasing of copper content,in which the creep resistance of Sn-0.7Cu solder is worst,the creep resistance of Sn-3.1Cu is best.4.The phases of Sn-0.7Cu,Sn-1.5Cu,Sn-2.3Cu,Sn-3.1Cu four kinds Sn-Cu lead-free solder are all made up by Sn and Cu6Sn5,and there is no new phase to be found after creep.Under this experimental conditions,in the organization of Sn-0.7Cu lead-free solder Cu6Sn5 phase mainly in eutectic,in the organization of Sn-1.5Cu,Zn-2.3Cu,Sn-3.1Cu three kinds of lead-free solder Cu6Sn5 phase not only in the eutectic but also become the primary phase.With the increase of Cu content,the Cu6Sn5 phase are more and more.Moreover primary Cu6Sn5 phase can become the heterogeneous nucleation base of ?-Sn,promote ?-Sn dendrites to form and grow up.5.During the creep experiment,in the region far from indenter and the region under the indenter which has an approximately hemispherical shape,no microstructural changes are detectable.The remaining region is deformation region.In the deformation region,the grain is gradually elongated along the deformation direction.6.For the Sn-0.7Cu lead-free solder,under this experimental conditions,the higher cooling rate is,the higher creep activation energy will be,the better creep resistance is.Increasing the cooling rate can refine the ?-Sn and eutectic structure,the Cu6Sn5 particles in eutectic structure will be more disperse and more subtle,which can more effectively block the movement of dislocation,and improve the creep resistance.If the cooling rate is too low,the organization will become thick,and the Cu6Sn5 particles will grow at a high temperature for a long time.