ST-P Series Laser Displacement Sensor in PCB Thickness and Substrate Height Measurement

Measurement Solution

Industry Background In the 3C electronics manufacturing industry, PCBs (Printed Circuit Boards), as the carriers of electronic components, have dimensional parameters such as board thickness, substrate height, component height, and solder joint height that directly affect the quality of subsequent mounting, soldering, and assembly. With the trend towards thinner, lighter, and more integrated electronic products, the dimensional accuracy requirements for PCBs and PCBAs are becoming increasingly stringent. Traditional contact-based measurements are inefficient, prone to damaging workpieces, and difficult to meet the needs of online full inspection. Therefore, non-contact laser displacement sensors have been widely used in PCB inspection. Inspection Requirements PCB Thickness Inspection: Measures the thickness of bare boards or copper-clad laminates to ensure compliance with design specifications. Substrate Height Inspection: Detects the height of the PCB substrate relative to a reference plane for positioning or flatness assessment. Component Height Inspection: Measures the height of components (such as chips, resistors, and capacitors) after mounting to determine if they exceed allowable limits. PCBA Warpage Inspection: Detects the amount of warpage deformation of the PCB board after soldering to prevent assembly interference. Solder Joint Height Inspection: Measures the height of solder joints to assess soldering quality. Measurement Challenges Highly Reflective Surfaces: Copper foil, pads, and metal leads on PCBs easily generate specular reflections, affecting the stability of laser measurements. Black or Dark-Colored Substrates: High absorption rates result in weak signals, requiring the selection of appropriate wavelengths or high-sensitivity sensors. Miniature Sizes and High Precision: Component height tolerances are often within ±10μm, demanding sub-micron repeatability from the sensor. High-Speed ​​Online Inspection: Fast production line cycles require sensors with high sampling frequencies (e.g., above 10kHz) to match the movement speed. Recommended Sensor Solution: The ST-P series laser displacement sensor uses laser triangulation for non-contact measurement, suitable for detecting PCB thickness, substrate height, component height, and warpage. Based on installation distance and accuracy requirements, the following models can be selected: Model | Reference Distance | Measurement Range | Repeatability | Linearity Error | Applicable Scenarios ST-P25: Reference distance 25mm, measurement range ±1mm, repeatability 0.05μm, linearity error < ±0.6μm ST-P30: Reference distance 30mm, measurement range ±5mm, repeatability 0.15μm, linearity error < ±3μm ST-P50: Reference distance 50mm, measurement range ±10mm, repeatability 0.25μm, linearity error < ±4μm ST-P80: Reference distance 80mm, measurement range ±15mm, repeatability 0.5μm, linearity error < ±6μm ST-P150: Reference distance 150mm, measurement range ±40mm, repeatability 1.2μm, linearity error < ±16μm ST-P150: 150 mm ±40 mm 1.2 μm < ±16 For detecting large-size substrates (μm) and assembly gaps, the sensor boasts a maximum sampling frequency of 160 kHz and supports Ethernet, RS485, analog, and I/O signal outputs. It can be connected to PLCs, host computers, and vision inspection equipment for online dimensional feedback and quality control. Implementation Method: Installation: The sensor is vertically mounted above the PCB being measured. The reference distance is determined based on the model. For thickness detection, a through-beam or reflective layout can be used; for height detection, the sensor is fixed to a gantry or robotic arm. Measurement Process: The PCB moves to the area below the sensor via a conveyor belt or carrier, triggering a signal to start the measurement. The sensor outputs the distance value in real time, and the host computer or PLC determines whether it is合格 (qualified/acceptable) based on a preset threshold. Signal Output: Measurement data is uploaded to the MES system via Ethernet or RS485; analog output can be connected to a PLC analog module for closed-loop control. Selection Considerations: Measurement Range and Accuracy: Select an appropriate range based on the height variation range of the measured object, while ensuring repeatability meets tolerance requirements. Surface Characteristics: For highly reflective copper foil or black substrates, sample testing is recommended. If necessary, use a blue laser or a specially treated model. Sampling Frequency: High-speed production lines require high sampling frequency models (e.g., ST-P series up to 160 kHz) to avoid missed detections. Environmental Factors: On-site vibration, temperature changes, and dust may affect measurement stability; protection levels and installation environment must be considered. Application Value: Improved Inspection Efficiency: Non-contact measurement, thousands of samples per second, enabling online full inspection. Ensuring Product Quality: High-precision measurement, timely detection of issues such as thickness deviations, warping, and abnormal component height. Reduced Labor Costs: Automated inspection replaces manual sampling, reducing misjudgments. Data Traceability: Measurement data can be uploaded to the system for easy quality analysis. Precautions: For highly reflective glass, metal surfaces, black plastic, FPC flexible boards, adhesives, and transparent materials, sample testing and verification are required based on surface reflectivity, color, transparency, installation angle, spot size, measurement speed, and on-site cycle time. Sensor installation should avoid direct sunlight and vibration sources. Clean the lens regularly to prevent dust from affecting measurement accuracy. Specific model parameters need to be confirmed based on the actual application; it is recommended to contact the manufacturer for detailed technical solutions.