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52 DESIGN007 MAGAZINE I AUGUST 2021 can help especially on low volume or proto- type orders. What to Ask? I oen encounter designers who are reluc- tant to ask about fabrication and materials as they only feel comfortable asking "when they know what to ask." I also see some new design- ers who try to infer everything off a material datasheet, and whilst this gets part of the way to the answer, the datasheet is just that—infor- mation about a raw material that the fabricator "processes" into a finished product. Just like baking a loaf of bread, the raw ingredients for a PCB are not the same as the finished prod- uct. Pretreatment for adhesion and pressing impact the raw material in a way which will be fabricator dependant and will differ from the raw material specs. Not quite as extreme as trying to make a sandwich out of a bag of raw flour, but you get the picture. If you don't know what to ask, there are plenty of You- Tube resources that cover PCB topics, along with the networks related to industry bodies like IPC and EIPC. ese organizations aim to bring together networks of specialists with dis- ciplines from chemistry through metallurgy, drilling, high-speed signalling, reliability, and thermal capability. More and More As technology pushes higher speed, more density and more durability, and legislation restricts the use of some materials, there seems to be ever more to contend with from a design- er's perspective. As I mentioned, the only way to deal with this is to discuss requirements for each design with the appropriate source of knowledge from each discipline. e key for a new designer is to be aware that, depend- ing on the design, non-electronic parameters interplay with the design outcome. It is quite fascinating to me that so many disparate dis- ciplines need to work in harmony to produce the most fit-for-purpose design at the most economical cost. Sometimes the Laws of Physics Work in Your Favour Fortunately, sometimes technology drives in a direction to make life easier; the drive to ever- shrinking designs means that oen high-speed traces can be kept quite short—so short that some parameters which need careful treatment on a larger scale can be of low enough impact to be ignored. Insertion loss is one case where loss is directly proportional to trace length, so keeping traces short can mean you can per- haps build on a lower grade base material. If the traces are very short compared with the high- est frequency content, maybe characteristic impedance is not an issue there either. A Sticky Problem On the highest-speed interconnects, it is well known that copper roughness impacts the signal losses, and complex modelling is needed to calculate the impact, but the rough- ness is a "necessary evil" to keep the board from delaminating in the assembly process. Here, the chemists are working their magic to provide treatments and processes that chemi- cally bond the copper to the dielectric, and emerging processes for bonding smooth cop- per could ease one task from the list of design considerations over the coming years. Conclusion A new PCB designer, apart from knowledge of layout—which is aer all the job descrip- tion—needs to be aware and ready to discuss a range of peripheral influencers on the PCB's characteristics, many of which would seem to the casual observer to have no connection whatsoever to electronic interconnect. How- ever, from an industry which measures time in inches, and thickness in ounces, that surely should come as no surprise. DESIGN007 Martyn Gaudion is managing director of Polar Instruments Ltd. To read past columns or contact Gaudion, click here.