Effect of Workpiece Rotational Speed on Surface Quality in YAG Double-sided Planetary Lapping With the Trajectory Method

Abstract The double-sided planetary lapping technology with fixed grit is a good candidate to process thin Y3Al5O12(YAG) crystals wafer. However, the influence of workpiece rotational speed nw in the planetary wheel on grit trajectory distribution and surface quality has not been revealed, which is of most significance to obtain a better surface workpiece. To solve this problem, the mathematical model for calculating the grit trajectory left on the workpiece in double-side lapping considering the workpiece rotation is established, and a variation coefficient for uniformity of the track point distribution (NUTPD) is introduced to evaluate the trajectory uniformity. Then, the trajectory of multiple grits and the NUTPD value at different workpiece rotational speeds were simulated in MATLAB software. The simulation result showed that the workpiece rotational speed had an extraordinary effect on the uniformity of the motion trajectory leaving on the workpiece surface. The preferred workpiece rotational speed values for lapping are nw=1,3,5,7,9. By conducting a series of tests on the YAG wafer at two typically selected rotational speeds, the surface roughness Ra and the peak-to-valley (PV) error of flatness were used to characterize the uniformity of surfaces quality. The experimental results demonstrate that there was a more uniform lapping effect, when nw=5 rpm, and the Ra and PV were 147 nm, 2.62 μm, and 141 nm, 2 μm at the upper and lower surface after lapped, which was smaller. They were 161 nm, 3.05 μm, and 149 nm, 2.74 μm after lapping when nw=6 rpm. The experimental result is consistent with the simulation result, and the feasibility and validity of the trajectory method for controlling workpiece surface quality on the planetary double-side lapping were verified.