257 W/cm2 power-density laser-driven white-light source for high-speed inspection in semiconductor packaging

Abstract

The demand for high-power-density white-light sources has been increased for high-speed inspection conductor and display products. However, focusing the conventional halogen lamps or light-emitting (LEDs) remains challenging due to the large emission area at the light sources, which is governed by limit. Here, we report a high-power-density light illumination of the laser-driven white-light with a spot size of 25 mu m. By using a laser diode (LD) instead of an LED, the strong optical power can be concentrated to the phosphor in a small spot size near the diffraction limit, enabling the emission of low-e<acute accent>tendue cence. The blue LD pump (2=445 nm) and broad yellow luminescence (2=480-750 nm) were focused on to the sample with a small spot diameter of 25 mu m (full width at half maximum, FWHM), producing high power-density of 257 W/cm2. The speckle constants of the blue LD, yellow luminescent light, and white-light after passing through the diffuser plate were carefully evaluated to 0.28, 0.02, and 0.14, respectively. Furthermore, the power scalability was demonstrated by spatially combining the independently generated light sources, which did not show any noticeable coherent speckle increase. This tightly-focusable white-light will find its strong potential in next-generation high-speed inspection of advanced semiconductor packaging.