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IEC 62490-1:2010 — ESL Measuring Method for Capacitors with Lead Terminals
ESL measuring method — Part 1: Capacitors with lead terminal for use in electronic equipment
Why ESL Matters
In high-frequency decoupling applications, a capacitor ESL determines its self-resonant frequency (SRF). Above the SRF, the capacitor behaves inductively and loses its decoupling effectiveness. Lower ESL means higher SRF and better high-frequency performance.
In high-frequency decoupling applications, a capacitor ESL determines its self-resonant frequency (SRF). Above the SRF, the capacitor behaves inductively and loses its decoupling effectiveness. Lower ESL means higher SRF and better high-frequency performance.
Critical Parameter
The lead wire straight section (shank) length must be maintained at 5 mm to 10 mm, and must be kept from bending. Any deformation of the lead wire alters the parasitic inductance and invalidates the measurement.
The lead wire straight section (shank) length must be maintained at 5 mm to 10 mm, and must be kept from bending. Any deformation of the lead wire alters the parasitic inductance and invalidates the measurement.
Engineering Insight
For reliable ESL measurements, ensure that the measurement jig contacts are clean and tight, the short compensation jig matches the DUT lead dimensions exactly, and multiple measurements are taken to establish repeatability. Even a 0.1 mm variation in lead positioning can introduce noticeable errors at the nanohenry level.
For reliable ESL measurements, ensure that the measurement jig contacts are clean and tight, the short compensation jig matches the DUT lead dimensions exactly, and multiple measurements are taken to establish repeatability. Even a 0.1 mm variation in lead positioning can introduce noticeable errors at the nanohenry level.
Introduction to ESL Measurement for Lead-Terminal Capacitors
Equivalent Series Inductance (ESL) is a critical parasitic parameter that significantly affects the high-frequency performance of capacitors. As switching frequencies in power electronics and signal processing circuits continue to rise, accurately knowing and controlling ESL has become essential for circuit designers. IEC 62490-1, published in 2010, provides a standardized method for measuring the ESL of capacitors with lead terminals in the range of 1 nH to 10 nH.
The challenge in measuring such low inductance values lies in separating the capacitor intrinsic ESL from the parasitic inductance of the measurement setup itself. A poorly designed test fixture can introduce measurement errors that exceed the value being measured. This standard addresses this challenge through a precisely defined measurement jig, short compensation jig, and spacer system.
Measurement Jig and Compensation Techniques
The standard specifies a measurement jig with screw-fixation electrodes — one fixed and one adjustable — designed to hold the capacitor lead terminals without introducing rotational movement that could alter the measurement geometry. The short compensation jig is a critical component: it must be made of the same material as the capacitor lead wires and have identical spacing (pitch) to the capacitor under test, within a tolerance of 0.25 mm.
A spacer system ensures consistent positioning and is constructed from non-magnetic materials. The measurement procedure requires an impedance analyzer or network analyzer capable of resolving nanohenry-level inductances. The standard specifies measurement at frequencies where the capacitor impedance is predominantly inductive, typically well above the self-resonant frequency of the capacitor.
Measurement Procedure and Data Interpretation
The measurement procedure involves three main steps: (1) open calibration, (2) short compensation using the short compensation jig, and (3) device-under-test (DUT) measurement. The short compensation step is particularly important as it effectively subtracts the parasitic inductance of the measurement jig and the lead wire portion from the total measured inductance.
Results are presented as the ESL value in nanohenries (nH) at the specified measurement frequency. The standard recommends reporting multiple measurements at different frequencies to characterize the frequency dependence of ESL, which can arise from skin effect and proximity effect in the capacitor internal structure.
| Component | Material | Dimension Tolerance | Purpose |
|---|---|---|---|
| Measurement jig | Non-magnetic metal | ±0.1 mm | Hold DUT with screw fixation |
| Short compensation jig | Same as lead wire | ±0.25 mm pitch | Subtract fixture parasitics |
| Spacer | Non-magnetic | Per DUT lead spacing | Ensure consistent positioning |
| Impedance analyzer | — | Resolution <0.1 nH | Measure complex impedance |
Frequently Asked Questions
Q: What ESL range does IEC 62490-1 cover?
The standard covers ESL values in the range of 1 nH to 10 nH, which is typical for lead-terminal capacitors used in high-frequency electronic equipment.
Q: Why is the short compensation jig so important?
The short compensation jig allows the measurement system to subtract the parasitic inductance contributed by the measurement fixture and the lead wires themselves. Without this compensation, the measured inductance would include these unwanted parasitics, potentially doubling or tripling the apparent ESL value.
Q: Can this method be used for surface-mount (SMD) capacitors?
No. IEC 62490-1 is specifically for capacitors with lead terminals. SMD capacitors have different ESL characteristics and require different measurement techniques, typically using microwave-compatible test fixtures.
Q: How does lead wire length affect ESL measurement?
Lead wire length directly contributes to ESL. The standard specifies a shank length of 5 mm to 10 mm to ensure consistency. Longer leads increase ESL approximately linearly, at about 1 nH per millimeter of wire length.
