This study is to investigate the wetting behavior between the
copper substrate which was deposited with electroless nickel as
a diffusion barrier for the ternary eutectic Sn-Zn-Al solder.
The copper plating was deposited on the electroless nickel to
improve the wetting behavior. The wetting experiment was
conducted with the wetting balance for the two systems of Cu/Ni-
P and Cu/Ni-P/Cu Plating at various temperature and fluxes. The
interfacial reactions between the solder and these two systems
after heat treatment were examined with Scanning Electron
Microscope and with X-ray diffraction. The contact angle
investigation was applied for estimating the temperature needed
for the occurrence of solder wetting without flux. The
experimental results for the Ni-P/solder system showed that good
wetting was achieved only at high temperature (above 350℃) and
with high concentration of active fluxes (above 5g/l DMAHCl).
The solder layer contains pores. The crystallization of
electroless nickel layer and less active fluxes could not
improve wetting. The experiment results of the Ni-P/Cu system
showed that the surface coverage of solder on Ni-P/Cu was more
than that on Ni-P at low concentration of fluxes (above 2.5g/l
DMAHCl), although it also showed partial wetting. The results of
the interfacial elemental line - scanning showed that the Zn
atom diffused to the interface between the solder and copper.
The X-ray showed that the interaction between solder and Ni-P/Cu
resulted in the formation of g-Cu5Zn8 compound which further
avoids the tin diffusing into the layer of copper plating.