The test board is designed so that the capacitance of the part can be measured while the part is being flexed (See figure 1). The capacitor is mounted at the center of the board. The testing equipment has a pressing block that is located so that it applies force at the center of the test board from below the part at a constant rate. Since the edges of the board are held in place by the support pins, this causes the board to flex. The amount of flex is measured in millimeters from the center of the board to the edge, please see "A" in Figure 2.

As the test board is flexed, the capacitance is constantly being measured by a capacitance meter which is connected to the test boards through capacitance probes. The capacitance is first measured at 0mm flex to establish the nominal value. The test board is then flexed to 1mm and held for at least on second, then the capacitance is measured, it is then flexed to 2mm, and so on up to 5mm. Any change in capacitance that exceeds 5% of the nominal value is considered a failure.