Precision Etching Technology Permits Production of High Resolution Printed Circuit Boards

Through precise control of the etching process, a researcher in Oxford University’s Photofabrication Unit has made the reliable production of high resolution printed circuit board (PCBs), with conducting tracks down to 10µm wide, a more cost-effective reality.

The increasing demand for greater miniaturisation and the use of flexible circuitry means the need for improved fabrication methods for high-resolution printed circuit boards is becoming more important. Printed circuit boards currently include conductors with a width of 150µm, but industry now requires tracks to be as narrow as 25µm, and even 10µm in some cases. With current manufacturing techniques it is not possible to attain the required precision, especially where the spacing between the conductors varies. The etching rate is highest where the conductors are furthest apart, leading to over-etching and subsequent under-cutting of very fine conductors in these areas. The resultant PCB has copper conductors of variable width, and therefore its performance is not optimum.

By controlling the etch conditions and the area to be etched, the Oxford group has reduced the amount of over-etching to an acceptable level, and under-cutting has been virtually eliminated. The spaces between the conductors are now all of uniform width, but with more redundant copper remaining on the PCB resulting in the etching being confined to narrow tracks. In the magnified view of a PCB the white areas represent the exposed copper tracks, while the black areas show the intervening non-conducting substrate.

This new technology will benefit many of the applications that now demand PCBs with fine conductors, or alternatively require flexible circuitry to facilitate yet further miniaturisation, including mobile phones, personal flip-top organisers and inkjet printers.

A patent for this technology has been filed by Isis Innovation, Oxford University’s technology transfer company.

Posted April 2003