Cu-Sn intermetallic compounds (IMC), formed at the interfacebetween the solder and the copper substrate are found to play animportant role in determining the thermal fatigue life of a surfacemount solder joint. In order to predict the growth of this IMC layerduring the operating life of the solder joint and its effect on thethermal fatigue life, the formation characteristics of Cu-Sn IMCs in0805 and 1206 LCCC solder joints fabricated from an IR-reflow processare investigated in this work. Only the stable Cu6Sn5 η-phase intermetallic compound was observed in allas-solidified solder joints. The mean layer thickness was found toincrease almost linearly with reflow time. The thickness of theinterfacial IMC layer increased with increasing reflow temperature in0805-type solder joints up to around 250° C and reached anequilibrium thickness above this temperature. Further intermetallicformation due to higher reflow temperature or longer reflow timeappeared as Cu-Sn whiskers in the bulk solder of the solder joints. Thecopper land pad size and qualify of component lead metallization werealso found to greatly affect the formation of Cu-Sn IMC in surface mountsolder joints
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