ICT Symposium Reports and Presentations

The TechnoCentre at Coventry University was an appropriate venue for the 37th Annual Symposium of the Institute of Circuit Technology. “Complex PCB Solutions” was the theme and the symposium was introduced by ICT Chairman Professor Martin Goosey.

Before commencing the proceedings, Professor Goosey said a few words in tribute to the memory of Frank Coultard, formerly Technical Director of the Printed Circuit Interconnection Federation and a tireless supporter of ICT, who had recently passed away.

The keynote presentation, entitled Polymer Interconnects for Datacom and Sensing on FR4 Substrates, was given by Richard Penty, Professor of Photonics at the University of Cambridge. Professor Penty discussed the benefits of optical interconnects and techniques for the successful integration of photonics into printed circuit boards. A proprietary siloxane polymer had been engineered to exhibit a good balance of mechanical, thermal and optical properties. It could be spin-coated on to the PCB substrate and imaged photolithographically to produce optical waveguides, typically with 50 x 50 micron or 50 x 20 micron cross-section on 250 micron pitch, in a whole range of geometries and configurations. These waveguides exhibited low loss and very low crosstalk, even on crossovers, and Professor Penty demonstrated that a 10-card optical backplane combining 100 waveguides each with a 90º bend and up to 90 crossovers had the capacity to carry data at Terabit level with worst-case crosstalk less that -35dB. There had been widespread industry interest, particularly from manufacturers of supercomputers. He went on to explain how optical coupling could be achieved using electro-optic L-connectors, which had sufficient positional tolerance to enable pick-and-place assembly, and how these could be employed in designs where the electrical components and power plane were positioned on one side of an FR4 substrate and optical waveguides and ground plane on the other. Whereas multimode siloxane waveguides presented a promising technology for use in high-speed short-reach interconnection applications, alternative applications were being explored in the integration of photonic, electronic and microfluidic components on to PCBs to produce low-cost gas sensors.

Stuart Hayton, Sales and Marketing Director at Mutracx, gave a frank and factual account of the realities of bringing the ink-jet primary imaging process from concept to commercial product status. He described the background of the Lunaris project, which had set out to utilise technology developed by Océ for the graphic arts market to address the opportunity presented in printed circuit fabrication to rationalise the process of producing etch resist images on inner layers. Hayton explained how the original technology demonstrator had been critically evaluated, in close co-operation with Mutracx’s lead customers, and how each component and operation had been either refined, or where necessary re-engineered from first principles, as one of a series of functional models. These individual elements had subsequently been integrated into a product demonstrator which fulfilled the specification objectives: 100 micron lines and 60 micron spaces as printed, with line edge sharpness better than7.5 micron wave and front-to-back registration better than 25 microns over the total image area. The result was a fully-automatic self-contained machine capable of being placed in-line with etch-and-strip, producing a minimum of 60 defect-free cores per hour. Ink-jet imaging of inner layers was seen not as a rival to laser direct imaging, which addressed a particular market niche, but as a production-efficient and cost-effective alternative to mainstream contact-printing. Beta-site evaluation was about to commence, with commercial installations planned for 4th quarter 2011.

“Don’t die of ignorance....” Wendy Heyes, Sales and Marketing Director at CC Electronics Europe and Chair of the Intellect PCB Fabricators and Suppliers Group, urged her counterparts in the industry in her presentation entitled The Future of PCB Manufacturing and the Internet. “You may be the best manufacturer or supplier, but you might be missing out if you don’t connect, interact and communicate effectively with your customers.” Her opinion was that the current generation of printed circuit buyers were very much orientated towards the internet and keen to take the opportunity to play a more active role in the process of quoting and capacity planning, provided that PCB fabricators were prepared to offer an open and honest route into their internal costing and production control systems. CCEE specialised in small-batch quick-turn manufacture and were typically shipping about 30 jobs a day, of which 20 were new designs. Historically, they had been quoting up to 1200 jobs per month – an enormous task if it included checking-out the data for every job and pricing several delivery-time options. CCEE had developed a web-based system to which the customer could log-in at any time of day or night and check the status of his jobs in manufacture, look at available capacity, enter design and specification attributes of new jobs, see panelisation options and material utilisation, and generate quotes for different quantity and delivery alternatives. “How much of your company intelligence is still locked into people?” Ms Heyes asked. The two most difficult problems had been overcome: getting peoples’ knowledge and intelligence into the system, and integrating the internal system with the customer portal, and CCEE were now successfully encouraging and educating their customers to participate in a procedure which offered clear benefits to both sides.

Professor Martin Goosey returned to the platform to review the progress of the ASPIS project, funded under the European Union FP7 programme, which sought to develop more reliable materials and processes for electroless nickel immersion gold finishing of printed circuit boards. The initial objective had been to understand the fundamental modes and mechanisms of failure associated with the finish, and particularly to characterise the “black pad” phenomenon and to predict the probability of its occurrence. Research at the Lithuanian Institute of Science and Technology had begun by studying electroless nickel deposition parameters and their effects on phosphorus content, thickness, porosity and internal strength of the deposit, then examined corrosion behaviour in citrate media: the interaction between immersion gold and the nickel-phosphorus surface, grain boundary effects and the influence of residual phosphorus at the interface. Indications were that corrosion of the nickel surface was due to activity in the immersion gold process and that black pad formation was promoted by a high pH in the immersion gold bath together with a high citrate content. Inadequate copper substrate preparation was another contributory factor.

 

The afternoon session was moderated by ICT Technical Director Bill Wilkie. He introduced Ian Mayoh, Technical Support Manager with Ventec Europe who observed that exponential increases in the need for thermal dissipation at the circuit level, driven in largely by growth in LED systems which were forecast to represent 40% of the global lighting market by 2020, had prompted increasing interest in cost-effective thermal management. His presentation reviewed the current status of thermally conductive printed circuit substrate options in terms of performance, construction and processing, and discussed future developments. With particular reference to insulated metal substrates, he explained the electrical, mechanical and cost considerations to be taken into account when selecting an appropriate IMS material for a particular application. There appeared to be some confusion as to the practical significance of Watts-per-metre-Kelvin values. Mayoh commented that W/mK was simply a coefficient, and the actual thermal impedance of a material was a more meaningful measure of its suitability. Moreover, in the absence of international standards for IMS materials, data sheet values could be based on arbitrary in-house tests and might be misleading if taken literally. He stressed the importance of carrying out proper qualification tests before specifying a particular material.

 

“Mostly good news but with a possible sting in the tail” was the subtitle of the presentation on the re-cast of the RoHS Directive by Len Pillinger, Product Compliance Manager with HMGCC, who has a particular talent for making a potentially unexciting topic interesting and informative. The “re-cast” was effectively a scheduled review of the RoHS directive, in anticipation of tougher WEEE recycling targets. Of forty originally-proposed new substance restrictions, only four remained in the re-cast, due to be published in June 2011 and to come into UK law by the end of 2012. These were hexabromocyclododecane HBCDD, bis-ethyl hexyl phthalate BEHP, butyl benzyl phthalate BBP and dibutyl phthalate DBP, none of which would have any particular direct impact on the printed circuit industry. There were some changes to excluded equipment, and a new catch-all, Category 11, but military and transportation equipment and active implantable devices were not included. The “sting in the tail” related to a significant change in CE marking, applied at equipment level, which would require a legally binding declaration of conformity, and any defence on the basis of Due Diligence would need to be backed by comprehensive supply chain data. Furthermore, liability could extend to persons other than the principal offender. Phrases like “not intentionally added”, “to the best of our knowledge” and “we accept no responsibility” were to be avoided.

The final presentation came from Jeremy Rygate, Engineering Director of Stevenage Circuits, describing the development of processes and materials for manufacturing stretchable PCBs, which had potential applications in medical electronics for diagnostic and monitoring purposes. Early trials using copper patterns deposited on fibrous materials had given unsatisfactory results because of non-reversible increases in resistance upon stretching, and recent work had been carried out with a base material made by bonding copper foil to a 50 micron polyurethane film, which could be processed through a conventional PCB manufacturing route. Although the material had limitations in dimensional stability and heat resistance, Stevenage Circuits had successfully fabricated “stretch-rigid” constructions, with copper tracks etched in a meander-pattern through stretchable areas. Rygate showed actual examples, and demonstrated with video how conductors maintained a consistent low resistance and full elastic recovery whilst being stretched to elongations of 69%. At 113% elongation conductors began to go open circuit there was evidence of a permanent set in the elastomeric substrate. Stretch-rigid circuits had been successfully assembled using low-melting-point solder.

In his closing remarks, Bill Wilkie thanked Ventec Europe for supporting the symposium, and Dr Andy Cobley for arranging the venue.

Now in its 38th year, the Institute of Circuit Technology continues to attract new members, to organise outstanding technical training courses, seminars and symposia, and to provide a focal point for circuit technologists to share knowledge and to network with their peers in the printed circuit industry.

Pete Starkey
ICT Council