Counterfeit and re-marked capacitors enter the supply chain through broker lots, surplus resale, and factory overstock transfers. For an OEM buyer, the cost of installing a mislabeled part is not the component price; it is the field failure, the recall, and the qualification rework. A receiving inspection that combines physical, electrical, and document checks can catch most re-marked parts before they reach the line. This article defines the application boundary for such screening, gives concrete acceptance thresholds, and walks through a step-by-step procedure.
Application Boundary: What This Screening Covers
The procedure below targets incoming lots of aluminum electrolytic capacitors, MLCCs, and tantalum capacitors purchased from non-franchised distributors, brokers, or surplus channels where original factory traceability is not fully verifiable. It is a go/no-go authenticity screen, not a substitute for full qualification testing. Life testing, surge testing, humidity testing, and ripple-current temperature-rise testing require a properly qualified sample and several weeks of lead time; the receiving screen is meant to run in minutes to hours.
Common counterfeit targets include large-can aluminum electrolytics, where date codes and voltage ratings are commonly re-stamped; high-value X7R/X5R MLCCs, where a lower-grade dielectric may be re-marked to a higher rating; and molded tantalum capacitors. Film capacitors are less frequently counterfeited, but the same marking and dimension checks still apply. The screen also verifies that the declared RoHS/REACH status matches the part marking and the certificate of conformance (CoC).
Key Parameters and Acceptance Thresholds
Table 1 lists the checks that provide clear separation between genuine and re-marked parts. The limits are generic screening values; compare them with the manufacturer datasheet for the specific series, because a genuine part may have tighter limits. A measurement near the datasheet edge should be treated as suspect, not automatically acceptable.
| Check | Method | Acceptance limit |
|---|---|---|
| Marking clarity | 10× loupe, oblique light | No double-strike, ghost print, sanded surface, or logo mismatch |
| Body dimensions | Caliper / micrometer | Within ±0.5 mm (radial) or ±0.3 mm (SMD) of the datasheet drawing |
| Capacitance | LCR meter at 120 Hz (electrolytic) or 1 kHz (MLCC) | Within rated tolerance: ±20% (electrolytic), ±10% (X7R) |
| Dissipation factor | Same LCR reading | ≤ 0.2 at 120 Hz (electrolytic); ≤ 5% at 1 kHz (X7R) |
| ESR | LCR meter at 100 kHz | ≤ 1.2 × datasheet maximum (electrolytic) |
| Leakage current | DC supply, 2 min at rated voltage | ≤ 0.01 CV or 3 µA, whichever is greater (electrolytic) |
| Insulation resistance | Megohmmeter, 60 s at rated voltage | ≥ 10 GΩ or R × C ≥ 500 s, whichever is lower (MLCC) |
| Date / lot code | Visual + reel label cross-check | Within 24 months of the receiving date; consistent across reel, tube, and box |
Two findings should trigger immediate quarantine. First, any marking inconsistency: a logo that differs from the manufacturer’s current design, a date code that is impossible for the series, or a sanded or overcoated surface. Second, any electrical parameter outside the datasheet range by a meaningful margin. For overstamped voltage ratings, the leakage current test is a reliable indicator: a part rated 25 V but re-marked 50 V will draw excessive leakage when tested at 50 V.
Step-by-Step Receiving Inspection Procedure
- Verify documents. Compare the CoC, packing list, lot number, and country of origin against the purchase order. Confirm the RoHS/REACH declaration matches the part marking and the requested compliance level.
- Inspect packaging. Check reel labels, anti-static bags, tube orientation, and box seals. A genuine reel label has a consistent font, a complete date code, and a manufacturer part number matching the part marking.
- Check markings visually. Use a 10× loupe with oblique lighting. Look for double-strike printing, ghost logos, sanded or re-coated surfaces, and ink that smears when wiped with isopropyl alcohol.
- Measure dimensions. Measure body length, width, height, lead spacing, and lead diameter with a caliper. Compare against the datasheet drawing.
- Test electrical samples. For lots up to 1000 pieces, test 5 samples; for larger lots, test 10. Measure capacitance and DF at the specified frequency, ESR at 100 kHz for electrolytics, and leakage current or insulation resistance at rated voltage.
- Perform a solderability spot check. Reflow one sample at 245 °C peak or solder one lead at 260 °C for 3 s. Genuine parts wet evenly; re-marked parts often show poor wetting or marking that lifts off.
- Record and decide. Accept, quarantine, or reject. If any sample fails, hold the entire lot and request an independent analysis such as X-ray, decapsulation, or solvent testing before return or disposal.
Record every measurement in a format that can be shared with the supplier. A documented reject with photos and measured values is more effective than a verbal complaint, and it shortens the replacement cycle when the lot crosses a border. For global supply chains, the same screen applies whether goods arrive by air or sea freight; for sea shipments, check moisture-barrier bags and transit damage first, because mechanical handling can create failures that look like counterfeits.
