IeMRC plastic and printed electronics

Citation

Ling, J. (2012), "IeMRC plastic and printed electronics", Microelectronics International, Vol. 29 No. 3. https://doi.org/10.1108/mi.2012.21829cab.007

IeMRC plastic and printed electronics

Article Type: Exhibitions and conferences From: Microelectronics International, Volume 29, Issue 3

Monday 19 March 2012

Held at the Henry Ford College of Loughborough University, and organised by IeMRC, this one-day (and completely sold-out) seminar looked at the interconnects and manufacturing challenges for the printed electronics market, now at a value of $9.4 billion.

Jerome Joimel came over from Germany to tell us about Plastic Logic, a company which began life in the UK in 2001 as a spin-off from Cambridge Technology Centre, located at the Science Park in Cambridge. Whilst Cambridge remains their innovation R&D and advanced engineering, centre, they are now located in Dresden, Germany, thanks to some generous funding, and also in Zelenograd, Russia, with their HQ in Mountain View, CA.

They use plastic instead of traditional silicon semiconductors and glass, with the advantage of weight, durability, flexibility and thickness. It is used in a combination of backplanes and e-ink media, the e-ink being a white pigmented ink, and Dresden was the first plastic electronics factory in the world, with production commencing in 2010, after three years of establishment.

The key areas of expertise are the printing, spraying and deposit of inorganic and organic materials to form layers, and by fine tuning their equipment they have improved performance by a factor of 5 over the years since they started in production. On site analysis includes testing of transistor and display parameters in production, using AOI. Mr Joimel described the reliability testing procedures that were specific to their production, and the reliability of displays is vital. The first application was an A4 size display that was easy to read, had clear definition, and is now used in schools, rather like a Kindle. That pupils will have iPads and the like instead of text books is already a reality.

Professor Martin Taylor from Bangor University spoke about a project which he and his team were working on in conjunction with colleagues at Oxford and Manchester, which was much to do with security packaging. They are developing a new process, producing roll-to-roll vacuum processed carbon based electronics. 50 μm lines and spaces are well defined, with resolution down to 30 μm. In effect this is high speed transistor production, at 120 m/m. The basis was the vacuum deposition evaporating pentacene in a diacrylate monomer, using e-beam curing, for the bottom gate of a TFT, with spin-coating being used for the top gate. They have tested inverters, 35 μm, and have noted good performance with high gain on PEN, with a DNTT TFT. There is good progress being made with regard to vacuum preparation, and early attempts at circuit simulation are encouraging; device fabrication needs to be optimised, as does parameter extraction.

Martin Wickham from the National Physical Laboratory (NPL) spoke about the work being done there, a very wide diversity of work hinged around reliability, and a project, entitled ReUSE, set against a background of end-of-life disposal strategies. Some statistics – 85 percent of all PCB scrap went to land-fill, of which 70 percent is non-metallic content, which amounts to 1 million tonnes annually in the UK, the equivalent to 81 HMS Belfasts! There is some 880,000 tonnes of scrap that we are not collecting or re-cycling.

At present PCBs are separated from cases, some high Pb count components are removed, but the rest is ground to a powder and goes then into a furnace for metal reclamation. Here printed electronics has a part to play, Martin described the formation of printed electronics on a flex substrate, which they have developed, for switch panels, reliability test panels, and an inverter for an EL lamp. They produce this printed electronic substrate using standard SM assembly equipment, have a comprehensive ReUSE testing programme, and he illustrated how they take it all apart. The product appears to be very stable, chip resistor joints are good, as are SOIC daisy-chain joints, but the clever bit is that the system allows recovery levels of over 90 percent of the original structure, v 2% on a PCB. This is done in hot water; it is a simple as that. Unzippable layers have been developed, which allows the easy separation of components, substrate and interconnect. It can be applied to both rigid and flex 3D structures.

Dr David Hutt of Loughborough University had copper filled conductive adhesives for PCB fabrication as his subject, a project being undertaken at the Wolfson School on the campus. Here copper is used as a substitute for silver, with the aim to achieve low cost, high volume, on a variety of substrates and with reliability. Many conductors are based on silver, but nanoparticle based inks can also be used, sintered to meld into a conductive format, and conductive inks and adhesives based on micron sized particles are available for screen and stencil printing. With copper it is surface oxidation that causes poor conductivity, so the copper has to be treated and protected with a self-assembled monolayer (SAM) and then the powder can be kept in a freezer for several weeks. The powder can then be mixed with either a single pack or a two pack epoxy adhesive, and applied to the substrate, and cured in a glove box with argon, so that no oxidation takes place; the results show a strong similarity to silver. They have also tried microwave curing, with good results; the curing time is much shorter and resistivity is not impaired. But after 24 h the copper paste increases in conductivity but not if it conformally coated. They have also tried placing components on wet film copper, then thermally curing, which works just fine, and due to the low temperatures used they can use polymer film. Work still needed, but it all looks very promising.

Chris Williams of Logystyx spoke about plastic electronics in the UK. This guide, produced by HMG, is all about plastic electronics, and this is the book you need to be in. It is an industrial tool for use by industry for industry, which meets the knowledge transfer raison d’etre. He needs your name and address, about 175 words on what you do, and this is then circulated right around the world, to anyone involved with plastic electronics. If he could have such information from anyone interested, he would be very pleased.

Henry Ford College have a new chef, judging by the excellence of the lunch, and after that was demolished the delegates returned to listen to Dr Steve Jones of Printed Electronics Limited, located just down the road in Tamworth. His company has been down the path of conception to birth, from infancy to maturity, and was ready to look after the needs of all-comers in a changing world. The R of R&D, he thought belongs to the universities, and the D is for the development which tends to lie more with industry. Innovation takes place through all generations, and in this area it is the radical technologies that are the most exciting, as they can create markets that did not previously exist. Thanks to government thinking, manufacturing is back on the agenda, and the Technology Strategy Board (TSB) and research councils have been the vehicles to encourage technology.

The appetite for new technology is evidenced by the fact that 14.5 million iPads were being shipped in Q42011 against 12.9 million in 2010. Steve explained what OEMs are, and how they are different from EMS companies, and ODMs. In the field of printed electronics, the UK and Germany lead the field. At PEL they have but six years experience, so collaboration and cooperation is vital, and the TSB have been invaluable. Specialising in wearable electronics, plastic and paper assemblies, displays, a nascent supply chain has been recognised, and PEL are on the brink of being one the major “names” in this industry.

Dr Paul Reip of Intrinsiq Materials Ltd has been working on the development of nano-scale metal inks for printed electronics. A former QinetiQ company, Intrinsiq has its HQ in Rochester, NY, plus Farnborough and Malvern in the UK. Making nano-materials is their speciality, and they have perfected production systems for this. Back in 2004, their early work was with copper, and whilst at the time the work was unsatisfactory, they have returned to the subject, as it is cheaper, highly conductive, and readily available, BUT it oxidises. They looked at what was required to have copper suitable for ink jet printing, here it was nanoparticle coated copper, which remained stable and oxide free. Using the photonic route, they can use laser or UV for curing, and is thus suitable for paper, polyimide and ceramic and combines printing and photonic curing in one process. It has use in many areas, and can be applied also by screen printing, with very high resolution., and can be cured by UV, IR, laser, and Xenon. Future developments will include nickel, and silicon inks.

They are also looking at gravure inks, a laser sintering technology (3.8 μm line) and biosensors. Three programmes involving IML are PROPRESS; Light Touch (one touch for illuminating e-readers) and LAPTRANS; it is good to see evidence of technologies in application. They have done the work (e-mail: paulreip@intrinsiqmaterials.com).

David Watson of Heriot-Watt University is working with Professor Marc Desmiuillez on laser-direct writing of metals on plastic substrates. Behind this is the need for low cost electronics, rapid prototyping of designs, additive bottom up manufacturing, and a faster turnaround from prototype to manufacturing. Polyimide, such as Kapton, is treated to break the bonds in the polyimide chain, then is coated with MPEG which allows the silver ions to bond with the polymer chain, in a silver electroless bath madefor them in Sweden. Tracks are defined by laser, at slow speeds with higher energies but ablations are but one of the problems with laser imaging, so they have tried UV exposure through a photo mask instead, with much better results.

In the end a compromise was reached between degradation of the substrate and the UV energy of the imaging, but this led to work with chlorophyll, and replace MPEG, and use a blue light at 460 nm, and silver ion reduction occurred without substrate degradation (e-mail: Degw1@hw.ac.uk).

Dr Steve Wakeham of Plasma Quest Ltd, in Hook, Hampshire, informed the seminar about HiTUS, an enabling technology. Plasma Quest specialise in sputter deposition, which has near ideal physical properties, and is good for large area compatibility with ITO and gold as the metals. At a multitude of high deposition rates, dielectrics can be deposited onto plastic substrates, and a very thin film onto ceramics or plastics or glass, just a few nanometres thick.

High ion densities are achieved over the whole target. The key advantages include low temp process, excellent adhesion, large areas can be treated, and it is compatible with roll-to-roll processing. Dr Wakeham was able to provide very broad thin film coatings onto temperature sensitive plastics. Stress can be controlled and fully defined films onto substrates can be produced at a high rate.

Professor Martin Goosey, the IeMRC Technical Director, summed up a most interesting and varied programme, which had provided some fascinating insight into the work being done in both academic and industrial worlds, which undoubtedly further commercial application to great effect.

John LingAssociate Editor