The application of UV-LEDs to printed circuit board process

This study investigated using high power UV light emitting diode (LED) to replace the traditional UV lamp in printed circuit board process. It was expected to take the advantages of energy conservation, long life and quick response of UV-LEDs. The feasibility of this replacement was evaluated. There were two kinds of light modules in this work; Type 1 composed of six 1-Watt UV-LEDs arranging as a circle of diameter in 50 mm. Type 2 was equipped with twelve 3-Watt LEDs soldered on a MCPCB of 100 mm in diameter. Both modules emitted a spectrum distribution peaking at a wavelength of 400 nm. The angle of view measuring apparatus was completed for measuring light module angle of view and UV intensity. In order to obtain collimated light source, the parabolic reflectors were used for Type 1. The reflectors showed the six to ten times enhancement of intensity and the improvement of the angle of view from 140° to 30°. In order to approach the practical process, only the original light source was replaced by UV-LED light modules. Other parameters on the automation system remained unchanged. After etching, the patterns were observed and measured by image measurement software. Following the PCB standards, only results with relative errors under 15% were accepted. At present, the minimum reproducible feature size is 75 ¿m by Type 2 light source with 50 mm or 100 mm distance between light source and mask. The results show the feasibility and potential usage of UV-LED in PCB lithography.