ICT Evening Seminar: Design Forum.

The Institute of Circuit Technology Design Forum , in Coventry on the evening of 24 th May 2006 was structured to provoke the interchange of ideas, opinions and grievances between designers, fabricators and suppliers of materials and processes.

Pete Starkey introduced short presentations from Alan Kelly, Dennis Price and Neil Chamberlain, which set the scene for a lively interactive session.

Having begun his career as a designer, Alan Kelly of Somacis captured the attention of the meeting with a thought-provoking keynote, using as examples the Bell Rock Lighthouse and the Formula 1 Ferrari to illustrate the significance of design and the relationship between the designer and the front man, be he construction engineer or Grand Prix driver. The contributions of each to the end product, whether building the lighthouse or winning the race, and the proportions in which ownership and responsibility, credit and reward, were shared between the two, were explored and analysed before examining the equivalent situation in a printed circuit board context. Kelly believed that the printed circuit fabricator would increasingly be the dominant force controlling design rules and parameters, by ownership of the manufacturing technology, but feared that the ongoing trend towards outsourcing, and the lengthening of the supply chain, would result in a general “dumbing-down” of printed circuit technology and, consequently, of printed circuit design. The traditional strategy of “design driven by functionality” was being replaced by one of “design driven by cost” – the acceptance of poor printed circuit design “ as long as it's cheap” , with an increasing reliance upon tweaking the silicon to compensate for the functional limitations of the interconnect.

Veteran PCB fabricator Dennis Price of Merlin Circuits used the topical issue of RoHS compliance to exemplify the predictable situation whereby the designer did not truly appreciate either the significance or the detail of current legislation, but expected the fabricator to be able to anticipate his requirements, in a similar way to the way he would send the Gerber files and challenge the fabricator to guess what he really wanted in the absence of a clear manufacturing specification! The whole question of effective ownership of the PCB specification was debated – designer? layout engineer? fabricator? assembler? end user? – as well as the consequential effects of the trend to supply-chain-elongation on communication, as already noted by Alan Kelly. Returning to his RoHS theme, Price reviewed the major effects of lead-free assembly conditions on printed circuit reliability, particularly the thermal robustness of laminate and the integrity of small via holes, concluding that if the designer had a sufficient understanding of the properties of available materials and manufacturing processes he could define a specification and design rules which would yield highly reliable product.

Providing a link between designer and fabricator, Polar Instruments' Neil Chamberlain described software tools developed to enable the complex task of impedance modelling on multiple dielectric substrates, commenting that the only thing actually constant in “dielectric constant” was the name, particularly in fine-line designs where “dielectric composition”, local variation due to the effective non-homogeneity of woven-glass epoxy resin laminate, could have significant effect on conductor characteristics. But even the cleverest modelling techniques could only give meaningful prediction of impedance if the right numbers were inserted in the first place, and the ability of the engineer to know what were the right numbers depended heavily upon his understanding of materials manufacturing processes. Chamberlain's underlying message was to stress the importance of communication and co-operation between the designer and his preferred fabricator from the earliest stages of a project.

The design forum achieved its objective in provoking some energetic and constructive discussion although it probably raised more questions than answers. Ironically, it was those designers who had been invited but, for whatever reason, had not attended the forum who would probably have gained most benefit by getting involved in the argument.

The significant and perhaps predictable conclusion was that, notwithstanding the efforts of pro-active fabricators like Steve Kerr of Invotec to operate structured training courses for design engineers, there remained a general lack of communication between designer and manufacturer, and insufficient mutual appreciation of the realities and constraints of each other's position in the supply chain. A good case was made for a uniform best-practice design-rule standard within the industry, although it was admitted that many previous attempts in this direction had shown only modest success. It was agreed to explore the possibility of holding a future event in co-operation with Intellect's Electronic Design and Innovation Group

The hospitality of Rohm and Haas Electronic Materials, who hosted the event, was gratefully acknowledged.

Pete Starkey,
ICT Council.

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