Why do capacitance and inductance values often appear inaccurate during incoming QC inspection of component-kitting deliveries?

Was the component kitting done with the wrong specifications, or were some of the components already past their expiration date?

Since BK’s component kits are usually from lots within the past two years, what other reasons could there be?

After the customer services of  component kitting from the supplier, incoming inspection is usually required. For ICs, this typically involves a visual check or non-electrical methods such as X-ray. However, for passives, some customers use a multimeter or LCR meter and occasionally find that the measured capacitance or inductance appears to differ from the values stated in the datasheet. Does this indicate a problem with the incoming goods?

Core Causes & Quick Solutions for Inaccurate Capacitance / Inductance Measurements
Ⅰ. Common Causes

    Instrument Issues
        Low-end LCR meters or DMMs: 5 %–10 % error; high-end bridges: ≈0.1 %.
        Calibrate regularly with 0.1 % reference standards.
    Environmental Disturbances
        Temperature: Aluminum electrolytics shift ±2 % per 10 °C rise; MLCCs need thermal pre-conditioning before testing.
        Humidity / Wiring: Long leads introduce stray C/R, especially in HF tests.
    Device-Specific Behavior
        Inductors: 30 %–50 % drop in inductance under DC bias (e.g., Murata curves).
        Capacitors: Voltage coefficient changes capacitance; test under actual operating conditions.

Ⅱ. Critical Mistakes in Bridge-Based Inductance Measurements

    Wrong Parameters
        Frequency: A 10 µH power inductor reads 10 µH @ 100 kHz but only 8 µH @ 1 MHz due to parasitic C.
        Signal Level: AC >1 Vrms can saturate the core, collapsing inductance.
    Operational Errors
        No Cal: Skipping open/short calibration adds 0.5–2 Ω residue, ruining sub-µH readings.
        Poor Contact: Omitting four-terminal Kelvin hurts low-Q (Q<10) parts.

Ⅲ. HF / Special-Device Testing Tips

    HF parts: Use coaxial fixtures, leads <5 cm, and a 1 MHz–3 GHz bridge.
    Transformers / CTs: Employ dedicated bridges (e.g., PTB330) with isolated architecture for turns ratio & leakage (1–100 µH).

Ⅳ. Quick-Fix Checklist

    Instruments: Periodic calibration; prefer 0.1 % bridges.
    Environment: Stable T & RH, pre-heat MLCCs, keep HF leads short.
    Parameter Matching: Follow datasheet—e.g., power inductors tested with DC bias.

The images below give a clear visual of how an MLCC’s capacitance and an inductor’s inductance vary under different external conditions.

So next time you run into inaccurate passive-component readings during incoming QC, reach out to your component-kitting supplier. They’ve almost certainly seen this before and can guide you on the correct way to test.