EIPC Summer Conference 2022: Day 2 Review

Estimated reading time: 11 minutes

The bonding of PTFE multilayers has traditionally presented many challenges. Helmut Kroener, senior marketing director for PWB materials at Showa Denko Materials, introduced a new low-loss thermoset bonding film for PTFE HDI and any-layer multilayer.

With the rapidly increasing growth and diversity of applications operating at radio frequencies, there is an ongoing need for high-performance substrates with good dielectric and loss properties. Of all the low-loss materials PTFE, although expensive, offers the lowest transmission-loss, and multilayer substrates based on PTFE has excellent low-dielectric properties. But its high melting point makes multilayer lamination difficult, especially in hybrid constructions where the other component materials can’t withstand the bonding temperature.

The low-loss bonding film described by Kroener offered the opportunity to build multilayer constructions at a processing temperature of 200°C, offering a lower-cost higher-speed solution. Functional groups in the thermosetting material interacted strongly with the PTFE material, and it was also capable of excellent adhesion to low-profile copper foil, offering further improvements in transmission loss.

The film was unreinforced by glass cloth but contained an inorganic filler, so its properties were isotropic, with Dk of 3.0 and Df of 0.0023. It was supplied in widths up to 520 mm, in thicknesses of 25, 50, or 65 microns, on a 50 micron polyester carrier film. Alternatively, it was available as a resin-coated copper foil in the same dielectric thicknesses, on 12 or 18 micron copper. The resin had low melt viscosity and good gap-filling ability. Once cured, it could be laser-drilled for microvia formation or drilled mechanically, and plated using normal PTFE processes. 

And now for something completely different. The final presentation of the EIPC Summer Conference was a non-chemical process for making roll-to-roll flexible circuits. Dry phase patterning was described by Tommy Höglund, sales and marketing manager with DP Patterning in Sweden.

The process he described could take flexible circuit manufacturing out of the PCB shop and into the EMS shop, feeding direct to the pick-and-place line. 

The tooling was a laser-engraved metal cylinder, set-up time five minutes, processing time about one hour, to produce a roller with the required circuit pattern effectively engraved as a sharply-defined negative image and the insulating areas remaining as part of the original surface. 

The production line, 18 feet long, had a roll-to-roll transport system for single-sided flexible laminate and the imaging mechanism rotated the prepared tool, known as a cliché, at web speed. This was running at very close clearance against a high-speed rotating cylindrical cutter, with the clearance corresponding to the thickness of the base film of flexible laminate, typically polyester in the range 35 to 75 microns.

The material was fed under tension around the cliché and where it passed through the nip between cliché and cutter. The cladding-metal layer, typically copper or aluminium, was milled away in areas corresponding to the original surface of the cliché, to leave the required circuit. The system appeared to work remarkably well in the production of antennas, heaters, RFID circuits, and conventional flexible circuits with 300 micron lines and 200 micron spaces on 18 micron copper.

Sustainability benefits of dry phase patterning were listed as low carbon footprint, low energy consumption, no chemicals, no water usage and recyclable residuals. Target market segments were communication, automotive, LED lightning, and heaters in general.

Kirsten and Carol

As this conference came to a close, there was unanimous consensus on the success of the event, and universal praise for the efforts of Kirsten Smit-Westenberg, Tarja Rapala-Virtanen, and Carol Pelzers in bringing it all together. 

With grateful thanks to Alun Morgan for the excellent photographs.

Pete Starkey is a technical editor for I-Connect007.

Did you miss Day 1 Review? Click here!

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