3C Electronics
ST-P Series Laser Displacement Sensor in PCB Thickness and Substrate Height Measurement
A non-contact ST-P laser displacement setup measures PCB thickness, substrate height, component height and board warpage in-line. The solution combines model selection by working distance with high-speed acquisition and PLC or host-computer integration.
Background
PCB and PCBA production requires consistent board thickness and height control before printing, placement, soldering and final assembly. Copper, solder mask, dark substrate materials and dense component layouts create changing optical conditions, while short production cycles make contact sampling unsuitable for full inspection.
Pain Points
- • Copper pads, solder mask and dark substrates return very different signal levels.
- • Board vibration and fixture tilt can be mistaken for real thickness or height change.
- • Small component and solder-joint tolerances require stable sub-micron repeatability.
- • The measurement must remain synchronized with conveyor position and line speed.
- • Inspection results must be transferred to PLC, host software or the quality database.
Measurement Solution
Mount one ST-P sensor above a stable reference surface for height and warpage measurement. For thickness, use two opposed sensors and calculate the difference between the synchronized upper and lower readings. Select the model from the verified working-distance and range table below, then set the optical angle and exposure for the actual copper, solder-mask or substrate finish.
Trigger acquisition from the conveyor encoder or fixture-ready signal. The controller samples at the required line speed, applies the qualified reference offset and sends distance or calculated thickness to the PLC or host computer. The ST-P family supports sampling rates up to 160 kHz and provides Ethernet, RS485, analog and discrete I/O options for line integration.
During commissioning, establish the fixture datum, verify the measurement against traceable reference pieces and record acceptance thresholds for each board type. For multi-point warpage inspection, move the board under one sensor or use multiple synchronized sensors at defined positions. Keep the optical path clean and isolate the mounting bracket from machine vibration.
| Model | Reference Distance | Measuring Range | Repeatability | Linearity Error |
|---|---|---|---|---|
| ST-P25 | 25 mm | ±1 mm | 0.05 μm | <±0.6 μm |
| ST-P30 | 30 mm | ±5 mm | 0.15 μm | <±3 μm |
| ST-P50 | 50 mm | ±10 mm | 0.25 μm | <±4 μm |
| ST-P80 | 80 mm | ±15 mm | 0.5 μm | <±6 μm |
| ST-P150 | 150 mm | ±40 mm | 1.2 μm | <±16 μm |
Technical Advantages
- • Non-contact measurement avoids marking or mechanically loading thin boards.
- • Five working-distance options cover compact component inspection and wider-range substrate measurement.
- • High-speed acquisition supports continuous in-line inspection instead of manual sampling.
- • Ethernet, RS485, analog and I/O outputs simplify PLC and host-system integration.
- • Synchronized measurements support thickness, height, flatness and warpage calculations.