Using a Consistent Time Reference When Reviewing MLCC Aging

A ceramic capacitor measured immediately after a thermal process can have a different capacitance from the same part measured later under otherwise similar conditions. Before treating the difference as a supplier discrepancy or circuit defect, establish whether the selected dielectric has an aging characteristic.

Identify the relevant capacitor class

Murata’s aging explanation describes capacitance reduction over time in high-dielectric-constant ceramic capacitors and recovery after heating above the material’s relevant transition temperature. Apply the selected part’s documentation rather than assuming the same behavior for every ceramic dielectric.

Record the complete capacitor part number, nominal value and temperature-characteristic code. Obtain the supplier’s aging information and reference conditions where available. Keep aging separate from initial tolerance, DC-bias dependence and reversible temperature behavior.

Establish the thermal and time history

For each comparison sample, record when it last experienced the relevant thermal process and when capacitance was measured. Include reflow and later rework where applicable. Avoid comparing a freshly processed board with a long-stored loose component without acknowledging that difference.

If a supplier specifies an aging rate per logarithmic time interval, use its stated reference time and calculation method. Do not apply that rate as a linear percentage loss per day. A consistent time basis is necessary for the resulting estimate to have meaning.

Relate capacitance to the circuit requirement

Determine the minimum capacitance needed during the product’s intended service interval. Combine the relevant effects using the manufacturer’s supported data and clearly stated assumptions. A nominal value printed in the BOM does not by itself establish the available capacitance after bias, temperature and time are considered.

For an illustrative startup reservoir, an early laboratory test may occur soon after assembly, while the product must also start correctly after long storage. Identify whether the capacitance margin covers both conditions and which physical effect limits the result.

Make measurements comparable

Use the specified measurement frequency, AC level and conditioning when checking conformance. Record DC bias and temperature for application measurements. Do not heat an assembled board simply to normalize a reading without an approved procedure compatible with all its components.

Keep measurement dates and thermal history beside the capacitance values. When investigating drift, compare samples under a common reference condition before assigning a cause. The resulting record helps distinguish expected dielectric behavior from changed test conditions or damage, and it prevents a favorable measurement soon after heating from becoming the only evidence supporting a long-term circuit margin.