Application of multi-wavelength light source to micro welding inspection

Abstract

We have developed a multi-wavelength light source and apply it to micro welding inspection. We project light rays from multiple white light super bright LEDs on a reflection grating. These LEDS are mounted on the specific position to give the diffracted ray with the wavelength range from 480 to 680 nm. The diffracted ray is pass to an optical fibre. The orientation of fibre tube is fixed so diffracted light from each LED will give a specific wavelength. The bandwidths of lights from all LEDS are quite narrow (< 50 nm), which is possible to be used as a light source for multi-wavelength imaging. The diffracted light is transported via optical fibre to a microscope used to inspect the micro welding points on a microelectronics circuit. Due to its very small size, the welding defects are hard to detected, even with high intensity white light. We find that, for typical welding points, the light with wavelength 500 to 600 nm can significantly enhance the contrast of welding image. This agree well with our preliminary result that, with our RGB light source, the maximum contrast can be obtained with the green - yellow to orange - red light. We expect our results to be useful to the inspection of micro welding, especially when integrated to some automation, e.g. machine vision system.