AKKN ElectronicsCounterfeit and re-marked capacitors usually enter the supply chain through grey-market brokers, excess-stock resellers, or distributors that do not maintain direct relationships with the original manufacturer. The risk concentrates on commodity parts with high turnover: aluminum electrolytics in the 10–100 µF range, X7R MLCCs from 0402 to 1210 sizes, and polymer electrolytics carrying low-ESR claims. When these parts are re-labeled with a higher voltage rating, a lower ESR, or a premium brand name, the substitution may pass a bench check but will degrade under ripple stress and elevated temperature.
Incoming inspection for authenticity is not a full qualification test. It is a screening process designed to catch parts that are significantly off-spec before they enter production. The screen must be fast, low-cost, and repeatable. Set the pass/fail thresholds from the datasheet values, not from the brand reputation.
Application Boundary and Scope of Inspection
Inspect every lot that comes from a non-authorized source. If the distributor or broker cannot provide an original manufacturer certificate of conformance, treat the lot as suspect. Inspection depth should scale with the criticality of the application: a DC-link capacitor in a 3 kW inverter justifies a fully sampled electrical test; a decoupling MLCC in a consumer board may only need a capacitance and ESR spot check.
A practical sample plan is 5 parts per reel or tray, up to a maximum of 20 parts per lot. This sample size is not statistically rigorous on its own; it is a first-pass screen. If any sample fails, escalate to a 10% sample of the lot before deciding whether to quarantine.
Decision Thresholds for Key Parameters
The following thresholds are typical for aluminum electrolytic and polymer capacitors and can be adapted to the specific datasheet:
- Capacitance: measured at 1 kHz with an LCR meter. Tolerance is usually ±20% for electrolytics and ±10% for X7R MLCCs. Reject if measured capacitance is below the lower tolerance limit by more than 5 percentage points. A counterfeit often reads 10–15% low because the dielectric is smaller than the original.
- ESR (equivalent series resistance): measured at 100 kHz. The datasheet gives a maximum ESR at 25 °C. Reject if the measured ESR exceeds the datasheet maximum by 2×. Re-marked parts typically show 2–5× the genuine ESR because the internal foil and electrolyte are of lower quality.
- Leakage current: apply rated DC voltage for 2 minutes, then measure leakage. For aluminum electrolytics, the limit is approximately 0.01·C·V or 3 µA, whichever is greater (C in µF, V in volts). Reject if leakage exceeds 2× that limit.
- Withstanding voltage: apply 1.2× rated voltage for 2 seconds. The part must not arc, smoke, or show a leakage increase after the test. Counterfeits with a boosted voltage rating often fail this gate.
- Temperature rise at ripple: apply a ripple current equal to 70% of the rated value at 25 °C ambient for 30 minutes. Measure the case temperature rise with a thermocouple. Acceptable rise is typically 5–10 °C. A counterfeit with excessive ESR will show a rise above 15 °C.
Comparison of Genuine and Counterfeit Behavior
| Parameter | Genuine part | Counterfeit / re-marked part |
|---|---|---|
| Capacitance at 1 kHz | Within ±20% of stamped value | 10–15% lower than nominal, sometimes out of tolerance |
| ESR at 100 kHz | Below datasheet maximum, stable over test | 2–5× datasheet maximum |
| Leakage current | Below 0.01·C·V or 3 µA | Exceeds limit, often erratic between samples |
| Temperature rise at 70% rated ripple | 5–10 °C above ambient | Above 15 °C, rises quickly |
| Withstanding voltage (1.2× rated, 2 s) | Passes without failure | May arc, crack, or show a leakage spike |
Step-by-Step Inspection Procedure
- Inspect markings and physical appearance. Check the legibility of the brand print, the vent design for electrolytics, and the presence of a laser-marked lot code on MLCC reels. Re-marked parts often show faint or double printing, uneven terminal finish, or a vent that is not typical for the manufacturer.
- Measure capacitance and ESR with an LCR meter at the datasheet frequency (1 kHz for capacitance, 100 kHz for ESR). Record values for all sampled parts.
- Apply rated voltage for 2 minutes and measure leakage current. This step catches re-marked parts with a raised voltage rating because the internal oxide layer breaks down at the higher field strength.
- Run the withstanding voltage test on a subset of 2 parts per lot. Apply 1.2× rated voltage for 2 seconds and look for arcing or leakage increase.
- Perform the temperature-rise test on 5 parts. Mount each part on a test PCB with airflow typical of the end application, apply 70% of rated ripple current for 30 minutes, and measure case temperature rise.
- If any part fails one gate, increase the sample to 10% of the lot. If the failure rate holds above 1 sample in the expanded set, quarantine the lot and return it to the supplier.
This screening procedure is not a substitute for a full reliability test, but it catches the most common counterfeit failure modes: low capacitance, high ESR, high leakage, and poor ripple-current handling. For distributors and design engineers, the cost of the screen — roughly 10 minutes per 5-part sample — is lower than the cost of a field failure caused by a substandard capacitor.
