Compared to straight sawing wires the geometry of structured wires causes a significant positive effect on the wafering process. In order to optimize the cutting performance it is crucial to characterize their specific geometry and its mechanical behaviour under tensile load. The structured wire is formed by two periodical bending shapes (see Figure 1), which have to be characterized separately. For this purpose, Fraunhofer Center for Silicon Photovoltaics CSP provides measuring equipment and evaluation software, which enables the investigation of wire samples at different forces representing the tensile loading during the sawing process.
The wire surface geometry is detected optically with a sensitivity of 1µm and a lateral resolution of 1 µm. The surface scan includes all geometrical information of the wire based on the manufacturing process. In particular, a mathematical algorithm was developed to extract sawing process related wire parameters from the surface scan data.
Important wire parameters are:
- wire core diameter
- amplitudes and periods of the two wire bending shapes
- torsion of the wire
- angle between bending planes
- position probability of the wire center point
Thus, using results of various tensile loads allow an accurate assessment of the wire structure. Furthermore, a Finite-Element model of the wire was created in order to predict the non-linear mechanical behaviour of the wire and the change of its geometrical structure (see Figure 2). The model considers the plastic deformation (hardening) of the wire material due to bending during manufacturing as well as in tensile loading during the experiment. Thus, the experiment and the simulation model enable a systematic investigation of different wire structures and diameters in order to improve the structure design and wire parameters for optimal sawing performance.