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56 DESIGN007 MAGAZINE I MAY 2024 economical or possible. If anyone has tried this, I would be delighted to hear from you. Smooth (as necessary): Smooth copper is great for high speed signals, but for reliability not so much, so keeping the traces as short as possible allows you to use rougher copper whilst keeping losses under control. Of course, materials are improving as are bonding meth- ods, and one day, the use of chemical adhesion promoters on copper may obv iate the need for rough copper to make a reliable b o n d . C h e m i c a l adhesion promoters are what help to bond epoxy to glass fiber, but for copper, these treatments still have a cost and equip- ment burden. However, I can see a day when perhaps this paragraph will obsolete itself. (Mis)communication-driven constraint: In these times, engineering has become so spe- cialised it can be challenging to communi- cate requirements across disciplines where the terminology is so unique to each skill. is is oen where the role of the PCB technolo- gist comes into play, bridging the knowledge gap between designer, procurement, fabri- cator, and material supplier, ensuring that materials are not overspecified. In a previous life, I had an experience where a lack of sup- ply chain communication caused significant wastage and could have been easily fixed with clear and open communication. Components were sourced with a 2% specification, and on inspection, all components received were pre- cisely centered on +2%. e buyer insisted this was just new technology and because the parts were laser-trimmed they were precisely on specification. In practice, this meant 50% met the specification, and 50% were outside of tolerance. Aer much pressure, I travelled to meet the supplier, who proudly showed the process of making the parts "on spec." No one had clarified to the laser trim operator that 2% should be the limit and the spec was ±2%. To be fair to the laser operator, they were nontechni- cal, but they could drive the trimming process very well indeed, and once they understood they were shooting for 0% rather than +2, all the parts came in exactly centered. Such an easy miscommunication, but the enemy was in the procurement chain, which tried to clamp down on awkward questions and be defensive. Modeling: Back to the main focus of over- constraining, knowing which levers to pull in terms of constraint is now so much easier, given the wide variety of simulation tools avail- able to designers. By simulating up front, it is much easier to explore design space and see where advanced materials are mandatory, and where there may be flexibility to use a lower specification of materials. PCB designers have access to a range of brokers who, at the top end, are very familiar with available materials, or to an in-house PCB technologist. Alterna- tively, most base material and chemistry sup- pliers have applications people who can guide you to the correct material choice, and because there is so much competition in material sup- ply, it is in their interest to steer you in the most economical direction for your project. Conclusion PCB designers need to balance the end-use application of the product with time-to-mar- ket and material lead times with high speed and reliability considerations. Modeling and simulation of PCB characteristics and clear communication with supply chain partners are vital to delivering a product that is "correctly constrained" for the application. More than ever, it is important to understand that the differing skill sets and terminology across the supply chain mean that open and clear com- munication is vital. DESIGN007 Martyn Gaudion is managing director of Polar Instruments Ltd. To read past columns, click here. Martyn is the author of The Printed Circuit Designer's Guide to… Secrets of High-Speed PCBs, Parts 1 and 2.