| Because of the toxicity of lead, the industry of electronics gradually prohibits itsuse, replaced by lead-free solder. Among the different kinds of lead-free solder,SAC305solder has attracted great attention for its good mechanical properties andperformance, being considered as one of the most potential substitutes for Sn-Pb solder.In this dissertation, using the self-designed equipment, shear and compressive creepbehavior of SAC305lead-free solder in Ball Grid Array have been investigated. Themain research topics of this dissertation are as followed.Creep equipment is designed as low cost and high precision of1um. It can be usedto do experiments of shear, compressive and tensile creep. Specimens are3×3array,with a shape of cross to eliminate the intrinsic stress in the structure. It could representthe actual condition of solder in electronics.Under the experimental environments, the shear stress exponent n was6.57, andthe shear creep activation energy Q was48KJ/mol, and the creep constitutive equationhas been determined. Based on the shear stress exponent and creep activation energy,we may safely draw the conclusion that climb of dislocation would be the dominantshear creep mechanism of SAC305in Ball Grid Array. When discussing the creepmechanism, it is very important to consider other factors, such as geometry models,shapes and sizes of solder. The creep properties of solder itself fail to fully represent thesituation after encapsulation.The result of compressive creep shows that as the experiments progresses, theactual compressive stress on solder becomes diminished, and after being compressed,solder grain becomes more resistive. Negative creep is possibly responsible for thisphenomenon. High temperatures make IMC spread more quickly into tin matrix andlead to thinning of IMC thickness. In case of that high temperatures influence results,doing research about compressive creep should decide the experiments time carefully. |
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