Why the Capacitor Can Is Not a Reliable ICT Test Point
Learn why using an aluminum electrolytic capacitor can as an ICT electrode can cause unstable readings, false failures and possible component damage.
The Capacitor Passes Inspection, but the PCB Fails ICT
An aluminum electrolytic capacitor is checked before assembly. Its capacitance and leakage current are acceptable, and there is no visible damage. After the component is mounted, however, the PCB fails the in-circuit test.
Before rejecting the capacitor batch, look at where the test fixture is making contact. In some fixtures, a probe touches the aluminum can and treats it as the negative terminal. That shortcut can produce unstable or misleading results.
Why the Aluminum Can Is Not a Normal Terminal
Inside a non-solid aluminum electrolytic capacitor, the aluminum can may have an electrical relationship with the negative side through the electrolyte. But this is not a stable, guaranteed terminal connection.
The measured result can change with the capacitor design, surface condition, probe pressure, test current and the exact point where the probe touches the can. A reading that appears acceptable on one fixture may be different on another.
The sleeve also should not be treated as proof of electrical insulation. Its main job is identification and exterior protection. Testing and equipment design should follow the insulation conditions stated for the exact capacitor series.
What Can Go Wrong in Production
Using the can as an ICT electrode may create several practical problems:
- Good capacitors may be rejected as defective.
- The same PCB may pass and fail on repeated tests.
- Two fixtures may produce different readings.
- Probe pressure or surface contamination may affect continuity.
- Excessive or unsuitable test current may stress the capacitor.
This is why an ICT failure should not automatically be recorded as a component failure. First confirm that the measurement path is valid.
Where the Test Probes Should Connect
For a repeatable measurement, connect the fixture to the actual positive and negative terminals. If direct terminal access is difficult, provide clearly defined PCB test points that are electrically connected to those terminals.
Do not assume that a metal surface is a reliable electrical node simply because a meter shows occasional continuity.
A Practical Fixture-Review Checklist
- Confirm that both probes connect to the real positive and negative terminals.
- Check whether any fixture uses the aluminum can as the negative electrode.
- Verify the polarity, test voltage, test current and test duration.
- Compare the result with a direct terminal-to-terminal measurement.
- Repeat the test on a second fixture and review any difference.
- Inspect probe wear, contamination, pressure and alignment.
- Record the exact failure mode instead of reporting only “ICT failed.”
How to Separate a Test-Method Problem from a Capacitor Problem
Remove a failed board sample from the fixture and measure the capacitor through its actual terminals using the approved test conditions. If the direct measurement is stable but the ICT result changes, the fixture or test path deserves closer attention.
If both measurements are abnormal, continue with normal component analysis, including polarity, soldering, electrical stress and handling history.
Information to Provide for Technical Review
When requesting support, provide the capacitor model, PCB drawing, ICT connection points, test voltage, current, duration, fixture photo and the difference between direct measurement and in-circuit results.
That information is far more useful than sending only a message saying that the capacitor failed.
COREVIA Application Support
COREVIA supports aluminum electrolytic capacitor selection and application review for UPS systems, inverters, industrial drives, charging equipment and other power-electronics applications.
A reliable diagnosis begins with the component, the circuit and the test method—not with the component name alone.
