Grain structure and roughness characterization of electrolytic nickel phosphorous, electrolytic nickel and electroless nickel phosphorous on copper by Focus Ion Beam Voltage Contrast

Impact of high temperature at back end assembly with temperature up to 400°C to electroless Nickel Phosphorous (NiP) and electrolytic Nickel (Ni) and Nickel Phosphorous (NiNiP) grain structure and surface roughness is normally ignored. Focus Ion Beam Voltage Contrast, FIB, showed that the amorphous structure of electroless NiP did not change after the heating at 400°C. For electrolytic Ni, two layers of nickel were observed and for electrolytic NiNiP, the amorphous NiP layer did not change after the heating but the Ni layer changes to bigger grain structure. Electroless NiP samples showed no significant differences on its surface roughness before and after heat treatment. However, significant difference observed on electrolytic Ni samples in all parameters tested. Increased surface roughness is generally observed at electrolytic Ni. For electrolytic NiNiP samples there was a slight difference on its surface roughness before and after heat treatment due to the structure change for Ni layer influencing the overall surface roughness. It is concluded that heating at high temperature will change the grain structure of Ni but not the NiP layer and due to this, it changes the surface morphology and roughness of electrolytic Ni and electrolytic NiNiP but not to electroless NiP. Thus temperature in back end assembly process is critical to determine the grain structure, surface morphology and surface roughness.