Mechanism elucidation of Sn-Bi alloy lapping plate surface instability

Sn-Bi alloys are currently employed as lapping plate material in the magnetic slider manufacturing process of Hard Disk Drives . However, it was observed that the Sn alloy lapping plate has surface roughness instability issues leading to poor productivity. Such plate surface instability is considered due to the metallic structure changing of Sn alloy. To elucidate the underlying mechanism, samples made from Sn-1.0 wt%Bi alloys were mounted and then subjected to polishing process at room temperature employing different polishing pressures ranging from 5 kPa to 122 kPa. The applied pressure is regarded as one factor imparting variable levels of energy onto the Sn alloy sample. The recrystallization and grain growth processes were confirmed by grain size distribution and misorientation study using Electron Backscattered Diffraction (EBSD). Furthermore, the developments of residual stress were investigated by using X-ray Diffraction (XRD). Finally, the surface roughness instabilities were confirmed in the involved Sn alloys samples via a Laser Scanning Microscope (LSM). It is recommended that a small level of pressure should be applied to the Sn-1.0 wt%Bi lapping plate to maintain the surface stable.