Inspection for thick film circuits must verify both appearance and function. A beautiful printed pattern is not enough if the resistor value, insulation, conductor continuity, or sensor output curve is wrong.
Visual inspection
- Check conductor continuity, missing paste, pinholes, cracks, blistering, and contamination.
- Confirm resistor-to-silver overlap at terminal electrodes.
- Check dielectric coverage, overcoat position, and clearance between separate nets.
- Inspect substrate chips, cracks, warpage, edge defects, and hole quality.
Electrical checks
- Continuity and open/short testing for all intended nets.
- Resistance measurement for fixed resistors, resistor networks, and heater patterns.
- Insulation resistance between isolated nets and substrate-related structures.
- Dielectric withstand where the design has voltage or safety requirements.
- Functional output curve for fuel level, throttle, linear, and rotary sensor circuits.
Reliability screening
Depending on the application, additional checks may include thermal cycling, humidity bias, power load, adhesion, solderability, vibration, fuel/oil exposure, or aging. The inspection plan should match the real operating risk instead of using a generic checklist.
Data to include in shipment
For engineering lots, useful data includes resistance values, curve report, photos, inspection standard, test conditions, lot number, and any deviations approved during prototype review.