Cc. Young et al., Microstructural evolution in the Sn-Cu-Ni and Pb-Sn solder joints with Cu and Pt-Ag metallized Al2O3 substrate, J ELEC MAT, 30(9), 2001, pp. 1241-1248
The growth mechanism of intermetallics between solders and metallized subst
rates, after thermal aging, are investigated. The solders used in this stud
y are unleaded Sn-Cu-Ni solder and eutectic Pb-Sn solder. The Pt-Ag/Al2O3,
Cu block and the electroless Cu/Pt-Ag/Al2O3 are employed as the metallized
substrates. Microstructure evolution of the interfacial morphology, element
al, and phase distribution are probed with the aid of electron-probe microa
nalyzer (EPMA) and x-ray diffractometry. Two kinds of intermetallics, Cu3Sn
and Cu6Sn5, are formed at the solder/Cu interface. However, for the solder
/Pt-Ag system, only Ag3Sn is observed at the interface. The thickness of Cu
3Sn, Cu6Sn5, and Ag3Sn compound layers for all solder/metallized substrate
systems shows a t(0.5) dependence at 100, 125, 150 and 170 degreesC. Accord
ing to the calculated activation energy and diffusion constant, the growth
rate of Cu3Sn and Cu6Sn5 intermetallics in the electroless Cu metallized su
bstrate is relatively higher than that for Cu block one at the range of 100
degreesC to 170 degreesC. However, the growth rate of Cu,Sn, and Ag3Sn is
reduced in the Sn-Cu-Ni solder with respect to the eutectic Pb-Sn solder. O
n the other hand, the Sn-Cu-Ni solder system exhibits a thicker Cu3Sn inter
metallic layer than the eutectic Pb-Sn solder after various aging times at
100 degreesC. The thickness of Cu3Sn in the eutectic Pb-Sn solder is, howev
er, thicker than that for Sn-Cu-Ni solder at 170 degreesC.