Multi-layer ceramic capacitors handle board flexing

Two approaches are available to deal with board flexure, the first being better handling of boards during assembly and subsequent SMT processes as well as better circuit design where components are placed away from areas of high flexure stress. The second approach is to mitigate the effects of a board flex crack with innovative design of the MLCC itself as flexure stress often cannot be eliminated.

Kemet offers four MLCC designs to address board flexure: Floating Electrode designated FE-CAP for low capacitance values, Open Mode for mid-capacitance MLCCs, Flexible Termination or FT-CAP for high capacitance devices as well as FF-CAP, which combines the Floating Electrode and Flexible Termination technologies for low capacitance values.

FT-CAP is a surface mount MLCC that incorporates a flexible termination system that integrates a conductive epoxy between the standard conductive metallization and nickel barrier finish to achieve pliability while maintaining terminal strength, solderability and electrical performance.

This technology directs board flex stress away from the ceramic body and into the termination area, thus mitigating the risk of low IR or short-circuit failures. FT-CAP capacitors are available in case sizes of 0603 to 1210.

Open Mode capacitors use an enhanced electrode and dielectric design where the end margins are widened, causing the active area to be squeezed into the middle of the chip, thus greatly increasing the margin area where flex cracks occur and creating a safe zone. Open Mode does not prevent the flex crack, but mitigates the effect, as the crack does not cross electrodes of opposing polarity.

Further, as there is no current leakage associated with a typical Open-Mode flex crack there is no localized heating and, therefore, no chance for a catastrophic failure event. Because the active area occupies a smaller space, Open Mode is suitable for mid range capacitance values with higher values in larger case sizes. Open Mode capacitors are available in case sizes of 0805 to 1812.

FE-CAP is a cost-effective surface mount MLCC that uses a floating internal electrode design based on multiple separate capacitors in series within an individual case size. The design does not utilize a classic active area and any flex crack will be isolated to just one of the capacitive regions. Consequently, a flex crack will not lead to the creation of a short circuit path (there is no direct path between electrodes of positive and negative polarity).

However, as with the open mode design, significant active area has been sacrificed in order to provide a flex mitigation solution, making FE-CAP applicable for lower capacitance values. Case sizes range from 0402 to 1812.

FF-CAP capacitors combine both the floating electrode and flexible termination technologies. The CV offering is the same as the FE-CAP range but the addition of the flexible termination provides the design engineer with a much more flexible, robust, high reliability solution.