Simulating Analysis ofDynamicResponses forCSPunderBoardLevelDropTest

Alongwiththemoreandmoreuseofportable electronic products, suchasmobile phones andPDA,thedropimpact performance ofsolder joints forCSPisacritical concern to semiconductor andelectronic product manufacturers. This problem ismoreserious withtheapplication ofleadfree soldering, because compared withthetraditional SnPbsolder alloy, leadfreesolder alloy havehigher rigidity andlower ductibility, andthetraditional droptest ishighcostandtime consuming, anditisquite difficult toobserve thefull dynamic responses during thedropimpact. Aim atthisproblem, ANSYS/LS-DYNAisemployed anda three-dimensional quarter modelwith15representatives leadfreeTFBGA mounted atPCBisdeveloped tosimulate theboard level drop test. Inthis model, die, adhesive, solder mask,andpadare taken into account. Thepaddefinition isNSMD (non-solder maskdefined) onPCBside according totheJEDECstandard (JESD22-B 111)andeffects oftwodifferent padsdesign on package side areconsidered bymodeling. Thefull dynamic dropprocess ofthemodelaresimulated, andfurther dynamic response curves ofPCBandsolder joints aregenerated and analyzed, including thevelocity, stress-strain curve, bending andsoon.Fromthedynamic responses, thenormal stress of solder joint showscyclic withtheamplitude decreased gradually asPCBbendsdownandupduring theprocess of dropimpact. Theresults generated fromthecurrent modelare ingoodagreement withotherresearchers' experimental results, namely, thenormalstress isthedominant failure indicator ofsolder joint whenitisusedtocompare withthe sameorsimilar boards, whichisproven byprofessor Tee.So thenormal stress criterion isapplied topredict thepotential failure locations ofsolder joints during thedropimpact.