Photosynthesis-inspired manufacturing of metal patterns (photobioform)

We have invented a new patterning process, which allows the formation of metal tracks onto non-conductive, plastic, flexible substrates, coating or powder such as polyimide or PEI (polyetherimide).

The process takes place in air environment at atmosphere pressure using low cost equipment.

The process involves the simple dipping of a substrate into a solution of potassium hydroxide, following by another dipping into a metal ions solution. The first dipping allows the opening of the imide ring chemical structure and insertion of the potassium ions into the broken chemical ring. The second dipping allows the swapping of the potassium ions with the ions of the electrolyte solution.

A laser or a flood exposure equipment using a photomask can be used to reduce the surface metal ions resulting in a gradient of metal ions, then the ions diffuse into the depleted zone and reach the surface where they reduce. A mild electron-donating agent has been used to accelerate the reduction of the ions. A thin layer of metal nanoparticles is then formed using this simple process, which can be used for subsequent electroless plating or for sensing purposes. Our preliminary feasibility studies published in IEEE transactions in Nanotechnology have demonstrated the concept using a synthetic agent at the cost of long exposure time and damage to the substrate.

We started using a bio-inspired material, chlorophyll extracted from spinach leaves, to speed up the photochemical process from 3 hours to 1 minute exposure using a blue light LED. We wish demonstrate that the use of chlorophyll can enable a truly manufacturing process that can be scaled up, and fully characterised for plastic electronics, PVs, moulded interconnects in electronics, sensing applications, in conjunction with additive manufacturing for multi-material manufacturing.

This research is expected to have significant commercial, technological and scientific impact as it enables a new type of low cost, sustainable and environmental friendly manufacturing process for the fabrication of metal tracks and patterns onto substrate films, solid parts, or coating materials containing an imide ring in their chemical structure. The resultant long-term impact of this research will benefit electronic and additive manufacturing industries as a whole to develop innovative products and process manufacturing equipment. The manufacturing process proposed has numerous advantages, which facilitate its translation and increase its impact to industry. These include:
1. the absence of resist material (photo-patternable or not).
2. the absence of evaporation, pre- & post-bake resist development, etching, striping process steps. This reduces the manufacturing time and cost of materials and processing.
3. The environmental impact is greatly reduced as the overall process energy required is much less due to the reduction in process steps. The bio-inspired material (chlorophyll) is clearly sustainable and environmentally friendly. The chemical waste can also be recycled.
4. The process can be used on contoured surfaces or on parts, a definite advantage for additive manufacturing.
5. The process is suitable for laser direct-writing as well as mask-based flood exposure manufacturing.
6. It is a photochemical process only. No photothermal driving force is necessary for the metalisation, allowing therefore the optimisation of the heat-affected zone during laser processing.
7. The light sources used are in the visible spectrum (blue / blue+red combined). These light sources are less expensive than UV lights and allows at low costs the scale up of the process.
8. Several transition metals can be deposited in principle (silver, copper, nickel), enabling therefore a vast range of applications.

The novel technology is most likely to impact in the industrial sectors of plastic electronics, printed circuit boards (PCB), embedded magnetic components and additive manufacturing. The involvement of Merlin Circuit Technology Ltd, a leading advanced PCB manufacturer, even at such an early feasibility stage, is a testimonial of the importance that such technology could bestow to their long-term strategic vision. The process enables to secure UK manufacturing against the increasing scarcity and increased costs of raw materials, energy and other resources through the reduction of process steps and material wastage, utilisation of natural products, benefiting the overall economy and environment. This new process will allow companies to reduce their manufacturing costs, increase their market share for these customers who are environmentally responsible in their product purchase.