Recent progress in direct exposure of interconnects on PCBs

This paper aims to use a survey of techniques to present the patterning of electric circuitry on printed circuit boards (PCBs). Second, a proposal of a new technology for direct exposure of interconnects on PCBs, using a digital micromirror device (DMD) is presented.

In this proposal, the DMD chip was incorporated into a prototype system for exposure of soldermask pattern for a mass scale production. As a light source, 52 semiconductor UV lasers were combined together to deliver UV powerful beam onto the DMD chip area.

A laser beam power of around 9 W was achieved from a single exposure head. With five exposure heads installed into a single machine, it is possible to expose 1,400 PCB panels per day. Such a production rate from a single exposure machine satisfies the demands of biggest PCB factories.

The Gaussian energy distribution of the laser beam from the 52-lasers head on the PCB surface was experimentally found. Because the exposure image needs to be highly uniform, this made a problem when the printed circuitry quality is considered. This problem was solved by using a software algorithm.

The use of UV lasers exposure heads brings economical advantages over conventional bulb UV lamps. The power consumption drops down ten times for lasers source.

Because the exposure processing can be made with lower electric costs and higher yield, it will make the PCBs cheaper.

At present, the idea of collecting a great number of lasers as a UV source for exposure head is attractive solution.