Closed Loop Focal Tracking Protocols for Deforming Circuit Substrates
Closed loop focal tracking continuously adjusts z-height positioning during placement and inspection to prevent solder defects on deforming board substrates.
Optical Displacement Sensor
Distance Measurement
Measurement instruments use light reflection to determine the distance between a sensing head and the surface of a target object without physical contact. An optical displacement sensor provides the feedback loop necessary for maintaining the correct height of a dispensing nozzle or a placement head above a pcb. It detects minute variations in board flatness caused by warping or bowing.
The device prevents collisions between sensitive components and the assembly hardware.
Sensing Mechanism
Triangulation methods allow the optical displacement sensor to calculate position based on the angle of reflected light. A laser diode emits a beam onto the substrate, and a position sensitive detector or a cmos array captures the return signal. As the board moves or the profile changes, the spot shifts on the detector, which the controller translates into a micron level height value.
This data allows for dynamic adjustment of the z axis during the assembly process. High speed scanning ensures that every region of the board is mapped before component placement.
Surface Limitation
Errors occur when the substrate surface is excessively transparent or specular. If the light absorbs into the solder mask or scatters off a polished copper pad, the sensor may report an invalid distance.