Modern vehicles are using more and more electronic components. The reliability of these parts has a powerful effect on the overall vehicle ownership experience – and the reputation of the car manufacturer. The automotive environment is known to be particularly harsh, and vibration is a challenge for all designers and manufacturers of electronic equipment. The ability to withstand vibration is one factor that has a significant influence on the selection of capacitors for automotive applications, including under-the-hood, for purposes such as filtering, to be used as a decoupling capacitor, transient-voltage-suppression and energy storage.
A combination of material selection and capacitor construction enhances a capacitor’s resistance to vibration in automotive applications. KEMET’s unique C0G materials have high-break-strength properties, making them capable of withstanding high G-force shocks. The modulus of rupture can be more than twice that of the industry’s standard X7R material.
Preventing Ceramic Capacitor Flex Cracking
Flex Cracking results from excessive tensile and shear stress generated when the PCB is flexed, or during thermal cycling. These cracks are the primary failure mode of multi-layer ceramic capacitors (MLCCs). Our (FT-CAP) Flexible Termination MLCCs incorporate a conductive silver epoxy between the base metal and nickel barrier layers of the standard termination system. This additional layer introduces pliability while maintaining terminal strength, solderability, and electrical performance.
A whitepaper is available to discuss the Reliability of Flexible Termination in Harsh Environments, in our Knowledge Library.
Fail-Open Ceramic Capacitor Technology
A ceramic capacitor with Fail-Open technology is designed to minimize the probability of low insulation resistance or a short-circuit condition in the event of device failure due to flexing of the PCB. KEMET offers a series called FO-CAP, with and without flexible terminations, with an X7R dielectric.
Floating electrode, or FE-CAP, is also available. The internal design of these capacitors prevents cracks propagating across counter electrodes within the device’s active area, which is the location where a crack is most likely to result in a short circuit leading to device failure. With this technology, the potential for catastrophic failure may be avoided. The cracks inside the capacitor may result in a drop in capacitance, however.
Stacked Ceramic Capacitor Options
Alternatively, a stacked capacitor such as the KEMET KPS combines two or more vertically stacked capacitors joined by a lead-frame that effectively minimizes mechanical and thermal stress on the MLCCs. This type of device also provides higher capacitance within the same board footprint as a single MLCC.
Previously we wrote about the exaggerated death of the through-hole ceramic capacitor. One construction type to consider in mechanically stressful environments is a through-hole or leaded capacitor.
Leaded devices such as radial molded MLCCs also benefit from high tolerance to stresses that can cause failures in conventional ceramic chip capacitors. The flexibility of the leads provides strain relief, but the lead attachment must be capable of withstanding high operating temperatures. KEMET’s C052H and C062H molded radial high-temperature C0G MLCCs are assembled using High Melting-Point (HMP) solder to ensure the integrity of all lead attachments.
Ceramic Capacitor Reliability Conclusion
Whether you need to operate in a high vibration drilling application or at the rising temperatures under-the-hood of an automobile, KEMET has a high-temperature ceramic capacitor solution that will work in your design.