Roll-to-roll process supports over-molded LEDs on flexible foil

March 31, 2017 // By Julien Happich
The LED lit flexible wristband demonstrator showcased by the VTT Technical Research Centre of Finland at LOPEC was entirely manufactured through a roll-to-roll process.

This roll-to-roll hybrid-integrated approach removes the need for a rigid board. Instead, separate components (such as the hard LEDs) are mounted on a printed electronic foil, after which the foil can be over-molded with a thermoplastic polymer or an elastomer, using the injection molding process.

The foil itself can be made of plastic or an elastomer, designed to be thin, light, elastic and even transparent.
”For the wristband demo, we performed all of the key manufacturing stages for printed hybrid systems – the printing of conductors, the assembly of semiconductor LEDs and the over-molding – using the roll-to-roll technique. This enables the mass manufacture of small-sized, easy-to-use, flexible electronics in a cost-effective manner,” explained Sami Ihme, Senior Scientist at VTT, adding that out of the 186 LEDs over-molded in the first test run, all remained functional on the final device.

In practice, the roll-to-roll over-molding of a printed electronic foil involves feeding a LED foil with a foil-feeder into a mold, in which the over-molding is done. This technique is normally used to decorate plastic for various consumer products. However, the manufacture of flexible electronics – in place of graphics – involves feeding electronics with a range of electrical and optical features into the mold. VTT is now seeking product companies interested in trying this new technology for new product concepts.

VTT Technical Research Centre of Finland –


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