Improvement of flux-less, lead-free solder wettability on CF4-plasma-fluorinated Sn and Ag substrates using ‘atmospheric pressure non-equilibrium plasma’

Atmospheric pressure non-equilibrium plasma inducted CF4 gas was irradiated to Sn and Ag substrates to obtain fluorinated Sn and Ag surfaces with a high affinity of a lead-free solder without fluxes. The plasma was produced by applying microwave power inducted with Ar–CF4–O2 mixed gases. The plasma irradiation successfully fluorinates the metal surfaces completed within 15 min. The fluorinated metal surfaces were observed using a scanning electron microscopy (SEM) and analyzed using an X-ray photoelectron spectroscopy (XPS). The Sn and Ag surfaces were covered mainly with SnF2 and AgF2 through the plasma irradiation respectively.The contact angle of the solder mounted on the metal substrates was measured to evaluate the wettability. The contact angle was minimized at the flow ratio of CF4/O2 which was 1/9. Surface fluorination by non-equilibrium plasma irradiation would be applicable to improve the wettability of flux-less solder.