Microstructure and Mechanical Properties of Sn–0.7Cu Flip Chip Solder Bumps Using Stencil Printing Method

Abstract

The interfacial microstructure of Sn-0.7Cu solder with ENIG (electroless Ni/immersion Au) was studied using scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and transmission electron microscopy (TEM). (Cu,Ni) 6 Sn 5 intermetallic compound (IMC) layer was formed at the interface between the solder and Ni-P under bump metallurgy (UBM) upon reflow. The thickness of the (Cu,Ni) 6 Sn 5 IMC layer increased with isothermal aging time. Two distinctive layers, P-rich and Ni-Sn-P, were additionally found from TEM observation. Analytical studies using energy dispersive spectrometer (EDS) equipped in TEM revealed that the composition of the P-rich layer is close to that of a mixture of Ni 3 P and Ni, while that of the Ni-Sn-P layer is analogous to the P-rich layer but containing a small amount of Sn in it. The shear force of the joints decreased during isothermal aging. The decrease of the shear force should be mainly due to the microstructural degradation within the solder.

Effect of temperature and alloying elements (Fe and Bi) on the electrical resistivity of Sn–0.7Cu solder alloy

“…Addition of In of up to 5% indicated an increase in tensile strength, along with a decrease in melting temperature of up to 10 degrees. [17][18][19][20] Electrical resistivity of the solder is equally important, and it should not be negotiated at the expense of superior mechanical and microstructural properties. For adequate functioning of the device, a lower electrical resistivity of the connection is extremely decisive.…”