ST-P Series Laser Displacement Sensor in PCB Solder Joint Height Inspection

Measurement Solution

Industry Background In the 3C electronics manufacturing industry, PCBs (Printed Circuit Boards) are core components, and the height of their solder joints directly affects soldering quality and product reliability. As electronic products trend towards miniaturization and high density, solder joint sizes are constantly shrinking, leading to increasingly higher requirements for height detection accuracy. Traditional contact-based measurements are inefficient and prone to damaging components, making them unsuitable for online full inspection. Laser displacement sensors, with their advantages of non-contact operation, high precision, and high-speed response, have become the ideal choice for PCB solder joint height detection. Detection Requirements The main objectives of PCB solder joint height detection include: Measuring solder joint height to determine if it meets process standards (e.g., 0.1-0.5mm). Detecting for defects such as cold solder joints, bridging, and uneven height. Achieving high-speed online detection in conjunction with automated production lines, with a cycle time typically required to be less than 1 second per point. Measurement Challenges The following challenges are faced in actual inspection: The complex reflective properties of the solder joint surface (e.g., solder paste gloss, metallic reflection) can easily lead to unstable measurement signals. Color differences on the PCB surface (e.g., green solder mask, white solder mask) affect the intensity of laser reflection. Significant height differences between adjacent components necessitate measures to avoid interference. The vibration environment of the production line places high demands on measurement repeatability. Recommended sensor solution: The ST-P series laser displacement sensor employs laser triangulation for non-contact measurement, suitable for PCB solder joint height detection. Based on installation distance and accuracy requirements, the recommended model parameters are as follows: 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 The sensor's maximum sampling frequency can reach 160 kHz, and it supports Ethernet, RS485, analog, and IO signal outputs, allowing connection to PLCs, host computers, or vision inspection equipment. Implementation Method Typical Installation: Align the sensor vertically above the solder joint and adjust the reference distance to the corresponding value for the model. The sensor is fixed to the production line gantry or the end effector of a robotic arm using a bracket, and uses an encoder to trigger point measurement. Measurement data is uploaded to the MES system in real time via Ethernet for quality traceability. Selection Considerations Choose a model with a suitable measurement range based on the solder joint height range. For example, ST-P30 is suitable for solder joint heights of 0.2-0.8 mm. Consider PCB Surface Reflectivity: For highly reflective solder joints, the ST-P series is recommended, as its optical design can adapt to different surfaces. If strong reflection is encountered, a polarizer or adjustment of the installation angle is required. Production Line Cycle Time Requirements: For high-speed scenarios (e.g., >100 points/second), a model with a high sampling frequency, such as ST-P25 or ST-P30, should be selected. Environmental Factors: Vibration and temperature changes may affect accuracy. Ensure the sensor is securely installed and perform temperature compensation if necessary. Application Value The ST-P series sensors can achieve the following in PCB solder joint height detection: * Non-contact measurement, avoiding damage to solder joints and surrounding components. * Micron-level repeatability, meeting the requirements of high-end 3C electronics manufacturing. * High-speed sampling, supporting online full inspection and improving production efficiency. * Multiple output interfaces for easy system integration. Precautions In practical applications, please note the following: * For highly reflective solder joints (such as mirror-like solder paste), it is recommended to conduct sample testing to verify measurement stability. * Differences in PCB board color may affect laser reflection; sensor gain or exposure time needs to be adjusted. * The installation angle should avoid direct laser light causing mirror reflection interference; tilted installation (e.g., 10°-15°) is recommended. * The sensor spot size must be smaller than the solder joint diameter to ensure accurate measurement.