Effect of liquid bridge on the thickness deviation between wafers sawn by diamond wire

Diamond wire web will be rearranged due to the reduction of structural stiffness and the enhancement of capillary force in the system for sawing ultra-thin wafers with fine-diameter diamond wire, which can cause uneven thickness between the as-cut wafers and affect the subsequent processing. A model for analyzing the transverse sawing behavior of the diamond wire caused by the liquid bridge after sawing into a workpiece was developed in this study by extending the dynamical model for a double-wire system with liquid bridge action to a multi-wire system. The stable transverse sawing state of the wire was obtained by analyzing the variation of the transverse sawing force with the as-cut wafer thickness thinning. Accordingly, the wafers thickness deviation rate affected by the wire groove wear and the liquid bridge action was calculated. The effects of the wire groove wear, the initial wire web gap, and the wire length between the guide wheel and the workpiece on the thickness deviation between the wafers sawn by the diamond wire were explored. The results show that the wafers thickness deviation increases with the increased wear of the wire grooves when the initial wire web gap is smaller than the minimum gap at which spontaneous wires adhesion can occur. The increase of wire groove wear makes the double-wire sawing more likely to occur. In addition, the wafers thickness deviation increases with decreases in the initial wire web gap and increases in the wire length between the guide wheel and the workpiece. Reducing the ratio of the initial wire span to the workpiece width helps to suppress the liquid bridge action during slicing and avoid the double-wire sawing. Since the minimum gap at which spontaneous wires adhesion can occur is large for the thick-diameter diamond wire, the fine-diameter diamond wire can be a better option for sawing the ultra-thin wafer to avoid the effect of liquid bridge on the wafers thickness deviation to the greatest extent.