Excessive board bending of PCB during manufacturing or assembly is common, and after being soldered to the board, ceramic components are especially prone to damage. The cracking of the ceramic material has been a leading cause of MLCC failure for years. The crack can bend the electrode margins to where they may touch each other and create shorts, rendering the component useless.
Companies responded to this problem with open mode capacitors. Open mode capacitors offset the electrode margins, so even if there is a crack in the capacitor, the margins would not contact one another.
The Open Mode capacitor may experience a drop in capacitance; however, a short is unlikely because a crack will not typically propagate across counter electrodes within the device’s “active area.” Since there will not be any current leakage associated with a typical Open Mode flex crack, there is no localized heating and therefore little chance for a catastrophic and potentially costly failure event.
Driven by the demand for a more robust and reliable component, the Open Mode capacitor was designed for critical applications where higher operating temperatures, temperature cycling, and mechanical stress are a concern. These capacitors are widely used in automotive circuits as well as power supplies (input and output filters) and general electronic applications.
Flexible termination, soft termination, or board flex technology inhibits the transfer of board stress to the rigid ceramic body, therefore mitigating flex cracks which can result in low IR or short circuit failures in regular non-open mode MLCC’s. Although flexible termination technology does not eliminate the potential for mechanical damage that may propagate during extreme environmental and handling conditions, it does provide superior flex performance over standard termination systems. When flexible termination technology is combined with open-mode, these devices offer the ultimate level of protection against a low IR or short circuit condition.
You can find open mode capacitors by clicking here. You can ID them under our features section and it will have the nice clear “open mode” or “floating electrode” under it.
Content and images provided courtesy of TDK’s FAQ and Kemet Datasheet.
Types of Mechanical Cracks in Components