Conductive Resin Layer Ensures High Resistance against Thermal Shock and Board Flexing
JIS specifies various test methods for multilayer ceramic chip capacitors soldered to a printed circuit board, to determine characteristics such as resistance to thermal and mechanical influences. In an ECU located in the engine compartment of a car, vibrations and shocks reaching the PCB will cause it to flex. In addition, thermal shocks (temperature cycling) causing expansion and contraction also increase the risk of cracks. The top graph illustrates the data for thermal shock testing (3,000 cycles), with a temperature cycle of -55°C to +125°C. While the adherence strength of the conventional product has been reduced by 90 percent, the drop in the product with conductive resin terminals is only 50 percent. The conventional product shows cracks in the solder. By ontrast, the product with conductive resin terminals only shows a partial separation of the nickel plating layer and the conductive resin layer.
The bottom graph illustrates the data for a board bending test (flexure limit). The conventional product already shows a crack in the ceramic element at a 4 mm deflection, while the product with conductive resin terminals can easily withstand more than twice the deflection amount. When excessive pressure is applied, the ceramic element of the conventional product develops a crack, while the product with conductive resin terminals only shows a separation of the nickel plating layer and the conductive resin layer, but no cracking. This demonstrates the superior cracking control achieved thanks to the conductive resin layer.