High speed maskless lithography of printed circuit boards using digital micromirrors

The printed circuit board (PCB) industry has long used a lithography process based on a polymer mask in contact with a large, resist-coated substrate. There is a limit to this technique since both the masks and PCB substrates themselves may undergo distortion during fabrication, making high resolution or tight registration difficult. The industry has increasingly turned to digital lithography techniques which, in addition to eliminating the masks, can actively compensate for distortions. Many of these techniques rely on a "dot-matrix" style exposure technique that uses "binary" pixels and small pixel or dot spacing to achieve the required resolution. This results in limitations in write speed and throughput, since many small pixels or dots must be written over a relatively large area PCB substrate. A patented gray level technique(1) based on a commercially available digital micro-mirror device (DMD) achieves required resolutions with a relatively large projected pixel size, and thus offers a higher speed alternative to conventional digital techniques. The technique described is not limited to PCB, but may be applied to any lithography or printing-based application where high speed and accurate registration are concerns.