Flexible Termination - Reliability in Stringent Environments

Failure due to board flex cracks persists as the dominant failure mode in multi-layer ceramic capacitors (MLCC). Board flex-crack failures are sometimes detected at in-circuit test or at functional test; but in a more critical point, they may be found in the field by the end customer. For high capacitance (HiCV) MLCC, the introduction of the flexible termination option (also referred to as soft termination or polymer termination) gives board designers an option to reduce the risk of board flex failure when board flex stress cannot be systematically removed from the board assembly process. In automotive and other market segments, board flex failures cannot be tolerated and long-term reliability is paramount. Some under-thehood (UTH) environments now have ambient temperatures up to 175°C. Other applications exhibit longterm, low-frequency vibration, and other applications may allow multiple bend events to occur. All of these specialized application environments lead to questions about the fatigue capabilities of the flexible termination solution when exposed to high stress environmental conditions. This paper is intended to show the impact of temperature cycling, high-temperature life tests, and multiple bend exposures to the MLCC with this flexible termination. Purpose The additional layer of conductive-epoxy in the termination is to allow a break to occur in the termination and not in the ceramic. Conductive-epoxy is a conductive flake laden epoxy, which does not have as much mechanical strength as the metals in the termination. In KEMET’s device in Figure 1, this epoxy is applied after the fritted metal termination (copper) is fired on, but before the nickel and tin platings occur. [1]