Investigations of ultraviolet laser patterning QR codes on printed circuit boards for inventory management

This study aims to investigate ultraviolet (UV) laser patterning QR codes on printed circuit boards (PCBs) for the inventory management of image recognition. The developed technology is a green manufacture and can replace the harmful environmental substances of brominated epoxy resin ink for the PCB process. In this study, the recognizability of the laser-patterned QR codes and the relationship between the ablated depth and the color change were investigated. The gray relational analysis (GRA) method was adopted to obtain the optimal laser patterning parameters. Furthermore, a spectrophotometer, scanning electron microscope, laser confocal microscope, and spectrometer were used to examine the light absorbance, the ablated depth, the pattern morphology, and the change in light reflectance of the laser-patterned QR codes on PCBs, respectively. The laser-patterned results revealed that QR codes produced white images with an ablation depth ranging from 5 to 10 μm as the scan speed was 300 mm/s at a laser power of 2 W and the scan speed was 900 mm/s at a laser power of 3—6 W. Moreover, the light reflectance of the white sample was close to 0.3819—0.3139, which was a parameter for successful whitening and was easy to recognize by a smartphone app. According to GRA results, the recognized QR code image could be patterned by the parameters of 2 W laser power, 300 mm/s scan speed, and 60 μm scan space. Furthermore, the scan speed was a severe impact factor for laser-patterned QR codes.