Institute of Circuit Technology Annual Symposium

Citation

Goosey, M. (2007), "Institute of Circuit Technology Annual Symposium", Circuit World, Vol. 33 No. 1. https://doi.org/10.1108/cw.2007.21733aac.001

Institute of Circuit Technology Annual Symposium

Institute of Circuit Technology Annual Symposium

National Physical Laboratory (NPL), Teddington 4 July 2006

The Institute of Circuit Technology held its 2006 Annual Symposium at the National Physical Laboratory (NPL) in Teddington on 4th July. The theme for the event was Printed Electronics and, in addition to six presentations from industry and academia, there were also a significant number of table-top exhibits. The ICT's Technical Director, Bill Wilkie chaired the day's proceedings and opened the meeting by welcoming everyone to the event. There then followed a short introduction and overview of NPL's activities by Dr Chris Hunt. Chris stated that the NPL was the UK's national metrology centre and the place where much work was done to characterise materials. He highlighted three current streams of work at NPL that were pertinent to the ICT and its activities. These were high reliability lead-free electronics, coatings technology and sustainability. Examples of work in these areas included studies of tin whiskering, tin pest, surface insulation resistance and new laminates. They were also carrying out creep and fatigue studies on solders using very small volumes of material. In terms of sustainability, investigations were being made into the possibilities for using conductive adhesives in place of solder joints as well as the use of thermoplastic substrates that could be recyclable. Tin whiskering was being investigated in terms of deposit ageing and hardness and its effect on whisker growth. NPL was also described as being the Node for Electronics Assembly Technology (NEAT).

After this very interesting introduction the first main presentation of the day was given by Dr Steve Jones of Printed Electronics. Steve's presentation was entitled “Printed (plastic/organic) electronics: opportunities and threats” and in it he discussed the opportunities for digital and printed electronics within Europe as an alternative to the more conventional methods of producing interconnects. He began by highlighting the growth of electronics manufacturing in the Far East and the loss of volume manufacturing from Europe. In order to continue in electronics manufacturing, European manufacturers had to exploit their benefits such as local service, shorter lead times and local procurement. Printed electronics gave an opportunity for electronics to continue to be made in Europe. There then followed an overview of the different types of printing techniques that can be used and it was stated that gravure printing could, for example, give micron line resolution capability. However, most interest was currently focussed on ink jet printing (IJP) where there was the possibility to produce anything from one offs, through prototype batches to high volume production. IJP offered the advantages of modest capital cost, small equipment footprints and low running costs. Up to now a key limitation of IJP had been its relatively poor ability to reliably print high-resolution features. There was also the need for a cost effective supply of suitable inks. There had been many improvements in ink jet technology in recent years such as the “HSS” system from Xaar which improved reliability via the use of a recirculating ink pathway.

For those that doubted digital could replace conventional PCB fabrication processes, Steve highlighted the similar transition that had occurred in the photographic industry. Printed electronics was predicted to be valued globally at $7.9 billion in 2010 and $16.4 billion in 2011. The support provided by the DTI for digital/direct write activities was highlighted; the DTI was currently supporting 11 projects in this area and had also established the Direct Write Association. Steve was leading a multipartner project that was planning to scale up IJP printing capability for PCB production via the use of an ink jet array head structure with 40,000 nozzles. He concluded by introducing the possibilities of nano- particle based inks. They could be used for example to exploit the reduced meting point of silver when in a nanoparticulate form. Digital and printed electronics could have wide applicability in a market that was becoming even more commodicised.

The second presentation of the morning was from Mike Johnson of Conductive Ink Technology (CIT) and was entitled “An overview of conductive inkjet technology”. Mike began by reviewing the different types of ink jet print heads that were available and how they varied between the different suppliers. CIT had taken a pragmatic approach to IJP and their objective was the direct writing of conductors onto non-porous substrates. Before describing the route developed by CIT, Mike reviewed the alternative methods that could be used for depositing metallic conductors such as the traditional PCB fabrication technology as well sintering techniques that required the removal of solvents, dispersants and binders, etc. CIT had developed a low temperature process in which a catalytic ink was ink jet printed on to a substrate and cured using UV. The catalytic deposit could then be used to initiate the deposition of a range of metals including copper, silver, gold, nickel and cobalt. It was stated that copper films deposited using this technique had a particularly tarnish resistant finish, although at this stage it was not clear why. Variants of the process had been developed for a range of substrate materials including PET, PVC, ABS, polyimide, polycarbonate and FR4. The process used standard industrial print heads and had the capability to produce 50m lines and spaces.

David Woodley of Technograph then gave a presentation on the production of advanced electronics for demanding applications. The presentation began with a short overview of the evolution of the printed circuit board from its conception by Eisler in 1943 through to the current day. Various examples were shown to illustrate this evolution. David then went on to describe some of the very demanding high reliability applications for which his company manufactured products. One example was a device that was used in a smart mortar shell that had to survive more than 10,000G. There were many other examples of devices that had to operate in other types of extreme conditions such as high temperature or low temperature, where there was a need for high sensitivity and the utmost reliability. Technograph were also working on various MEMS devices and had produced other types of assemblies for the Eurofighter and the Airbus A380.

The next paper was from Brunel University and was given jointly by Professor David Harrison and Darren Southee. Brunel University had a long history of working on the development of printing conductors onto novel polymer paper substrates using offset lithography. David began the presentation by giving an overview of how offset lithography worked and he pointed out that it was widely used for printing books and magazines. The process relied on the dissimilar wetting properties of certain materials and was ideal for high speed and high volume production. It was also low cost and capable of high resolution with 10m features having been printed. The work on lithographically printable inks had initially resulted in the development of silver based inks suitable for deposition of conductors but other inks had also been developed that could be used to form capacitors, resistors and inductors. Examples of assembled boards were shown: the components were assembled and connected using conductive adhesives. For the silver based conductors the practical minimum line width achieved was 80m. This was because of the need to have three print operations in order to give a sufficiently continuous and conductive film. The overall aim of this work was to develop more sustainable electronics using low cost displays and power sources all being integrated using similar printing processes. The work had also embraced the development of a range of sensors, e.g. humidity.

The second part of the presentation was given by Darren who described work on an IeMRC funded feasibility study to extend the lithographic printing process to the deposition of printable zinc carbon cells. A process had been developed and work was currently focussed on increasing the capacity of the cells deposited. Work had also been done to improve the printed cell structure and to optimise the printing process. Data was shown for a variety of cells showing the cell voltage against time when operating with 1 and 5kV loads. Although there were still some technical issues to be overcome, it was also stated that it was theoretically possible to deposit other features such as conductors and components on top of the cells thereby offering enhanced space utilisation.

Following an excellent lunch and the opportunity to visit the sponsors' stands, the afternoon session commenced with a presentation entitled “A journey towards direct write by ink jet” given by Rob Haslett of Patterning Technologies Ltd (PTL). PTL were described as being integrators of ink jet technology for a wide range of industrial applications. After describing the benefits of ink jet, which included price, flexibility, rapid response and the fact that it was digital, the presentation focussed on PTL's work to develop processes for the direct printing of etch resist masks. The new ink jet process was contracted with the conventional processing routes and this clearly highlighted the significant reduction in process steps that could be achieved. The etch resists that had been used were based on a UV curable acrylate chemistry and by using a granite base on the equipment it was possible to achieve ,20m accuracy. A machine had also been developed with an optical system that enabled double- sided printing. By using this type of approach it was possible to run the ink jet etch resist process alongside existing processes. A lower cost machine had also been developed specifically for ident printing.

Solder masks could also be printed, but because the mask became part of the final product there was a need to acquire user approvals. A high accuracy platform would also be required. Work had also been carried out to deposit transparent conductor materials and films with conductivities in the region of 700V/square has been achieved on both plastic and glass substrates. The presentation concluded with a brief discussion of potential future applications such as the deposition of bioactive layers, solar cell structures and micro lenses.

The final presentation of the day was given by Chris Williams, Director of the UK Displays and Lighting Knowledge Transfer Network. Chris began by comparing the European and Far Eastern business model approaches to the production of displays. In the Far East there was still a good deal of vertical integration whereas in Europe, many parts of the jigsaw existed but they were often disparate. The role of this KTN was to help bring together all these different elements. Chris also emphasised where there really were applications for digital and printed electronics and also where the technology would never be able to compete. For example, high density silicon processing such as encountered on a mcirprocessor chip would not be possible using printing techniques. However, the printing of discrete transistors over a large surface area, such as would be required in a display would be one area where printing offered significant opportunities.

Chris highlighted how newspapers and magazines were printed locally and that the principle was already well established, so the printing of electronics locally should not present too many conceptual problems in the future. Some of the difficulties of printing electronics onto polymer substrates, e.g. dimensional stability were reviewed but the results of some recent developments were also given. For example, organic semiconductors had already been produced that could operate at 13MHz and it was expected that this would be pushed to 100MHz in the near future. There was said to be an urgent need for the development of pin-hole free organic and inorganic dielectrics up to 0.5mm thick as well as a requirement for reliable, fast via manufacturing processes that could be used on a variety of materials. Chris concluded by inviting attendees to join the KTN. Membership was free and more details could be found at www.ukdisplays.net

Overall this was a most interesting event and one that addressed a subject of growing importance. The ICT is to be congratulated for putting together such a useful event for its members and the choice of venue certainly added to the overall quality of the symposium.

Martin GooseyJuly 2006