Study on the double-sided grinding of sapphire substrates with the trajectory method

Trajectory distributions on the workpiece surface, which are decided by the relative movement between workpiece and abrasive grit in the double-sided planetary grinding process, play an important role in workpiece surface quality, especially uniformity. To improve the uniformity of the workpiece surface during double-sided planetary grinding, the relative movement between workpiece and abrasive grit was analyzed, and a mathematical model was established on the basis of the double-sided planetary grinding machine. Then, the trajectories left on the workpiece surface by abrasive grits were simulated with the help of MATLAB software. The workpiece surface was divided into many equal areas, and trajectory dots in each area were counted; then, its variation coefficient of standard deviation (VCSD) was calculated to indicate the surface uniformity directly. Simulation results showed that the grinding wheel speed had a significant influence on the uniformity of the workpiece surface. Some experiments were performed on the double-sided planetary grinding machine with sapphire wafers. The uniformity of the sapphire wafer surface was indirectly represented by the non-uniformity coefficient of surface roughness (Ra) and total thickness variation (TTV). The experimental results have good consistency with simulation results, validating the reliability of the simulation results.