More Sustainable PCBs Biodegradable FR-4 Alternative is Suitable for RF Applications

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FAULHABER Drive Systems

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Soluboard PCBs from Jiva Materials present a biodegradable alternative to FR-4, which also impresses in terms of its carbon footprint. Infineon, for instance, uses the material for demo boards. The University of Glasgow has now demonstrated its suitability for high-frequency applications.

Worldwide, a combination of fiberglass fabric and epoxy resin is primarily used to serve as a rigid, dimensionally stable, and cost-effective substrate, acting as the standard material for rigid PCBs. The substrate is called FR-4, a name that refers to the flame resistance class of the material, which is typically achieved through brominated flame retardants in the resin.

FR-4 consists of two main components: a substrate made of woven fiberglass fabric and a flame-retardant epoxy resin that fully saturates and cures this fabric. The fiberglass provides the material with mechanical stability, tensile strength, and dimensional stability, while the epoxy resin ensures electrical insulation, thermal stability, and chemical resistance. The issue: FR-4 circuit boards have a relatively high CO₂ footprint, estimated at around . Depending on the res3.5 lb/ft²in system, glass content, and production process, this can actually range between 2.5 and 5.1 lb/ft². One fact that applies to all FR-4 boards: the material is difficult to recycle and almost economically unfeasible.

The team at Jiva Materials from the UK designed a circuit board substrate based on natural fibers (jute or flax) and a halogen-free, water-soluble polymer some time ago. According to the company, with support from the University of Portsmouth, the material produces around 12.1 lb of CO₂ per square meter during production. In this regard, the material is already more environmentally friendly. However, the main feature of the material is that it dissolves in water during recycling, allowing assemblies to be easily separated and then reprocessed.

Water Solubility ... Under Specific Conditions

Before you immediately assume that the solubility excludes the Soluboard from industrial applications, there is an insightful clarification: the material only dissolves after prolonged exposure to hot water. "Hot" means that the water reaches 194 °F, and the circuit board, depending on its complexity, remains in the water for 30 to 120 minutes. "Both SMT and THT components can, in certain applications, be removed and reused after processing. For materials that cannot be reused, water-based recycling reduces the loss of precious metals that typically occurs during incineration processes," the company explains.

If you regularly follow our reporting, you may already have heard of Soluboard and that Infineon uses the material for demo and evaluation boards. In collaboration with researchers, the suitability of Soluboard for RF applications has now also been confirmed.

Soluboard in RF Applications

As part of a study conducted by the James Watt School of Engineering at the University of Glasgow, Soluboard was tested for its RF and high-speed properties, according to the company. The paper is titled "Biodegradable RF PCBs Towards Sustainable Wireless and IoT" and is available on the university's website. Researchers demonstrated that the material supports wireless signals above 4 GHz and enables data rates of more than 3 Gb/s without significant distortion. This means Soluboard meets the requirements of typical applications such as Wi-Fi, Bluetooth, RFID, and digital high-speed interfaces.

This demonstrates that biodegradable substrates can also be used without compromise in areas previously considered the domain of conventional FR-4 materials. Challenges remain in processing natural fiber composites and optimizing them for RF applications, such as through suitable circuit and antenna designs.

The project is part of a larger research program by the "Responsible Electronics and Circular Technology Centre" (REACT) at the University of Glasgow, funded by UKRI. The collaboration between research and industry aims to promote sustainable material alternatives and strengthen the circular economy in electronics. (sb)

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