Intermetallic Compounds Formed during the Reflow and Aging of Sn-3.8Ag-0.7Cu and Sn-20ln-2Ag-0.5Cu Solder Ball Grid Array Packages

摘要

After reflow of Sn-3.8Ag-0.7Cu and Sn-20In-2Ag-0.5Cu solder balls on Au/Ni surface finishes in ball grid array (EGA) packages,scallop-shaped intermetal-lic compounds(Cu_0.07Ni_0.28Au_0.02)_6Sn_5(IM1a)and(Cu_0.76Ni_0.24)_6(Sn_0.86In_0.14)_5 (IMlb),respectively,appear at the interfaces.Aging at 100 deg C and 150 deg C for Sn-3.8Ag-0.7Cu results in the formation of a new intermetallic phase(Cu_0.70Ni_0.14Au_0.16)_6Sn_5(IM2a)ahead of the former IMla intermetallics.The growth of the newly appeared intermetallic compound,IM2a,is governed by a parabolic relation with an increase in aging time,with a slight diminution of the former IMla intermetallics.After prolonged aging at 150 deg C,the IM2a intermetallics partially spall off and float into the solder matrix.Throughout the aging of Sn-20In-2Ag-.5Cu solder joints at 75 deg C and 115 deg C,partial spalling of the IMlb interfacial intermetallics induces a very slow increase in thick-ness.During aging at 115 deg C for 700 h through 1,000 h,the spalled IMlb intermetallics in the solder matrix migrate back to the interfaces and join with the IMlb interfacial intermetallics to react with the Ni layers of the Au/Ni surface finishes,resulting in the formation and rapid growth of a new(Ni_0.85Cu_0.15)(Sn_0.29)_2 intermetallic layer(IM2b).From ball shear tests,the strengths of the Sn-3.8Ag-0.7Cu and Sn-20In-2Ag-0.5Cu solder joints after reflow are ascertained to be 10.4 N and 5.4 N,respectively,which drop to lower values after aging.