For economic reasons it is desirable to detect and discard as early as possible in the production chain those pre-damaged wafers which prospectively will break during further processing. The applicability of acoustic methods such as acoustic vibration analysis and acoustic emission analysis is described already in [1].

Another test method was used to solve the following practical problem: An unknown

number of silicon cells could contain damages which were not visible, but could lead to fracture during very later manufacturing processes causing major costs. For samples of cells with and without such damages the strength was measured using a concentric ring bending test. As is illustrated in Figure 15, the scatter range of the strength values for cells without damages (black bar) lies considerably higher than that for damaged cells (grey bar). Thus it can be decided, if a cell is damaged or not: The cell is loaded up to a stress somewhat above the maximum strength of the damaged cells (dashed line in Figure 15). A damaged cell then will break, a non-damaged one will remain intact. This proof-test is relatively simple and can be automatised.