ELECTRONIC SENSORS
Quality control in electronics In quality control of PCB production, the sensors are placed in such a way that they measure the PCB from above. A traversing system guides them over the PCBs and its highly-integrated components. With a measuring rate up to 8 kHz, the sensors can detect dynamic processes directly in the production line. The compactness of the sensor (46 mm x 30 mm) and its integrated controller enable the sensor to be integrated in small installation spaces. The smallest possible diameter of the light spot is just 45 μm x 40 μm, which enables high precision can be sharply focussed onto them. Another critical factor for reliable measurements on PCBs is to use a measuring procedure that can measure different materials, from plastics to metals, which is why the laser triangulation principle is the correct choice. Laser triangulation sensors from Micro-Epsilon provide the innovative Auto Target Compensation (ATC) feature that enables the sensors to measure on permanently changing surfaces, from matt as from bright to dark. ATC ensures that the exposure time adapts to the conditions presented by the respective target object. To determine the measurement values, the laser sensor projects a red laser point at a wavelength of 670 nm onto the target. The laser light is
to hit the optical system of a CMOS line. With quickly changing objects from bright to dark, only a little light would reach the receiving matrix without using the ATC feature. In contrast, the intensity would be too high when quickly changing from dark surfaces to shiny objects. In both cases, the result would be inaccurate or even useless. Therefore, the Micro-Epsilon sensor regulates the exposure time via ATC, as well as the intensity of the light emitted during the measurement task in such is in the ‘perfect’ range. The sensor then
Fig 3: In order to determine the measured values, the laser sensor projects a red laser point with a wavelength of 670 nm onto the an optical system on the CMOS line in the sensor. The sensor then calculates the distance values with micron-precision via the three-point relationship between the laser diode, the measuring point on the object and the projection on the CMOS line.
calculates the distance values to micron-accuracy via the three-point relationship between the laser diode, the measuring position on the object and the depiction on the CCD line. The values determined can be fed in as an analogue or digital output signal to the plant or machine control system.
Measuring scribe lines Another application is the scribing of pre-determined breaking points into the
panels for de-panelling. A PCB consists of several panels or smaller PCBs that go through production as one large PCB. This kind of bundling is necessary for production reasons as it makes boards easier to assemble. The scribe lines are normally produced by two opposing saw blades that cut a V-groove into the board, which allows small PCBs to be easily and cleanly de-panelled, i.e. separated from one another, by the end of the production processes. The scribe lines are around 400 μm wide.
Fig 4: Using modern sensors such as the optoNCDT 1420 laser triangulation sensors from Micro-Epsilon improves quality, reduces waste and costs. The smart laser sensor reliably measures displacement, distance and position with repeatability from 0.5 μm.
The scribe lines of PCB panels must be measured precisely. Here, the optoNCDT 1420 laser sensor is also used due to its unique combination of speed and precision combined with an extremely compact design. During production, the sensor detects whether the keyway is accurately milled into the panels. If the scribe line is too thin, the panels will break during the production process, which consumes resources and may cause damage to the machines. If the grooves are not milled deeply enough, the panels would fray during de-panelling and break irregularly, which requirements resulting in waste.
www.micro-epsilon.co.uk
FEBRUARY 2025 | ELECTRONICS FOR ENGINEERS 21
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