Dark Packages, Metal Shields and Shadowing in PCB IR Heating
Dark packages, shield cans and tall components can distort an IR temperature map, but their appearance alone does not identify the cause. Determine whether the pattern moves with the PCB or remains fixed relative to the preheater.
Use the rotation test
Create a height and material map. Mark tall packages, shield cans, reflective connectors, dark molded bodies, board edges and fixture walls. Instrument the solder interface plus likely hot and cold surfaces. Run the same instrumented engineering board first in its normal orientation and then in a controlled rotated or shifted position, provided that the equipment and safety procedure permit the change.
| Observation | First place to investigate |
|---|---|
| Hot/cold pattern moves with the PCB | Package height, surface absorption, shields or fixture contact |
| Pattern stays in machine coordinates | Lamp output, reflector, guard/window, zoning or airflow |
| Display changes but process evidence does not | Sensor attachment, emissivity setting or reflected background |
Correct the field carefully
Possible responses include increasing the working distance, changing the lamp pitch, heating from multiple angles, adding zones, using a different reflector or adopting a hybrid heating method. Change one variable at a time. Increasing power to heat a shadowed joint can overheat an exposed package before the hidden location responds. Thermal cameras require a validated emissivity and reflected-background setup. Confirm critical locations with an appropriate reference method. If the machine field is causal, Henruite quartz and reflector configurations provide candidate geometry options through Henruite; none eliminates line-of-sight physics. Use the distance and spacing study to validate the correction.