European projects use stretchable substrate for soft circuits
Panasonic has demonstrated a stretchable film that is used as a substrate for printed electronics with three partners in Germany, France and Portugal.
Beyolex is a fully cross-linked, non-silicone, thermosetting stretchable film specifically designed as a soft, stretchable, and durable substrate for reliable printed electronics.
InnovationLab in Heidelberg, Germany, worked with Panasonic on a pliable PCB demonstrator using Beyolex and sintered copper ink. Generally, the copper inks require a high sintering temperature (>160 °C), which is extremely challenging for substrates. The substrate had no difficulty tolerating the sintering temperature and exhibited no damage from the process.
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“Beyolex exhibits superior performance when compared to existing stretchable films like Thermoplastic Polyurethane (TPU) and Polydimethylsiloxane (PDMS) and is under evaluation and qualification for a wide variety of demanding applications, says Tsuyoshi Takeda, Product Marketing Manager in the Electronic Materials Business Division of Panasonic Industry.
The combination of the high temperature tolerance of Beyolex and the solderability of the sintered copper ink enabled component mounting with standard solders such as Sn-Bi or SAC305 resulting in reliable and high density assemblies and delivering a functional PCB with more pliability and softness than typical flexible printed circuits (FPCs.)
Using proprietary Direct Material Deposition (DMD) technology, Kelenn Technology in Igny, France, printed land pads with copper ink and circuit traces with stretchable silver-based paste onto Beyolex film. This hybrid circuit produced a solderable, stretchable PCB configuration that would be difficult to achieve with copper circuitry alone.
Panasonic engineers reflowed solder paste onto test vehicles prepared by Kelenn Technology.
“We printed an industry standard SAC305 solder paste and reflowed the part in a Vapor Solder Oven with a temperature of 230°C. We confirmed both the solderability of the copper ink pads provided by Kelenn Technology as well as the mechanical integrity of Beyolex after soldering,” said Takeda.
“As a result of this test, we believe Beyolex with sintered copper ink is a promising solution for solderable, pliable or even stretchable PCB constructions.”
Stretchable silver pastes are also an attractive conductor solution for new form factor devices. However, these polymer composite pastes have inherent limitations for forming truly stretchable electronics; typically, the resistance increases significantly with each elongation cycle and these increases are cumulative, climbing with each stretch cycle.
A printable Liquid Metal Based Composite developed by University of Coimbra (UoC) in Portugal is a promising solution to this issue. UoC’s ink exhibits metallic conductivity and much lower resistance change during stretch cycles compared to silver-polymer pastes. The lack of plastic deformation of Beyolex means the ink printed on the substrate looks to be a promising combination for truly stretchable electronics requiring repeated stretching.
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