Investigating Sn-Ag-Cu (SAC) Solder Bump Joints Produced Using Modulated Pulse Laser Soldering
F. Yusof and S.R.R Aisha Idris
The Sn-Pb solder is a conventional solder used in electronic assembling applications which needs replacement due to environmental concerns and legislation. In this study it was found that Pb-free Sn-Ag-Cu (SAC) solder was able to replace Sn-Pb solders. The soldering process was successfully performed with SAC305 by applying modulated pulse laser technique in the duty cycle of a 1070 nm fiber laser under ambient atmospheric pressure. The laser power is set at a constant of 85 W and the pulse frequency was 250 Hz with different duty cycles of 99, 90, 80, 70, 60 and 50%. There was a surface finish of electroless nickel immersion gold (ENIG) located between solder ball and Cu substrate. The formation of (Cu,Ni)6Sn5 as an intermetallic compound (IMC) layer at the SAC305/ENIG interface were observed using a scanning electron microscope (SEM) fitted with and energy dispersive spectroscopy (EDS). As a result, the modulated pulse affected the growth behaviour of interfacial layer. Also, a Ni3P layer is formed as the interfacial layer. Finally, the results showed that the hardness values fluctuated according to the duty cycle percentage.
Keywords: Fibre laser, Sn-Ag-Cu (SAC) solder, electroless nickel immersion gold (ENIG), intermetallic compound (IMC), interfacial layer, laser soldering, modulated pulse