Stamping ‘thin’ circuits into a single sheet

A new way of producing high-density circuits has been developed – it avoids the need for conventional PCB manufacturing techniques. Tom Shelley assesses the situation Tools have been developed to stamp circuits into very thin sheets of plastic at high production rates and potentially low cost. The process could further reduce the cost of electronics manufacture as well as allowing the development of entirely new products that are truly paper thin. Stamping fine features into plastic products is an established process generally referred to as micro replication. Typical micro replicated products include compact discs, reflective road signs and plastic fresnel lenses. As applied to producing thin PCBs, the micro replication process has been developed by George Gregoire of Dimensional Circuits in San Diego, California. According to Nick Hollinshead of Tecan, the Weymouth Company making the foil stamping tools, the laminated dielectric substrate is only 160µm thick. The foil tools are used to hot stamp in circuit conductor paths and vias from both sides. Vias require elements of the foil tools, 80µm high, to almost meet when they are pressed toward each other, leaving only a very thin skin which may subsequently be etched through. The next step is to metallise the plastic substrate on both sides, and then ‘squeegee’ on an etch resist into the recessed conductor paths and vias. The remaining metallisation on the top level, above the recesses filled with resist, may then be removed. In this way, it is possible to make very thin flexible circuit boards at lower cost, with circuit line widths down to 50µm. The foil tools themselves are remarkable pieces of engineering, being only 250µm thick, with 40µm-high features to produce circuit paths and 80µm-high features to produce vias. The tools are 300mm square and made by photo-electroforming. In service, they will be backed by steel plates to make the stamped imprints. One of the advantages of the new process is that all vias are stamped in by a single operation, and none have to be drilled. Furthermore, manufacturing time to produce conductor tracks is greatly reduced over that required in conventional photo etch processes, since the photo-based process is limited to that required to produce the tools as opposed to that required to produce each board. Tecan, in association with Dimensional Circuits, recently received a ‘Special Recognition Award’ from the US Institute of Printed Circuits. And it is not beyond the realms of possibility that the process could one day be applied to laying down circuitry on the insides of product plastic enclosures, although such circuits would have to do without vias.Tecan and George Gregoir