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40 DESIGN007 MAGAZINE I FEBRUARY 2019 Eliminate Confusion This column will address eliminating confu- sion that creates remakes both from the end- user/designer and the fabrication house. First, let's talk about being clear about your inten- tions. What are some of the things that create miscommunication, lost time, and sometimes even remakes at the fabrication house of your choice? The first thing is querying the fabrica- tion house for impedance numbers. Let's say you've asked for a material type on your drawing that is neither readily available or used by your fabricator. Here, you should expect the fabrication house to respond quick- ly and have all the deviations at once for you to review. This includes any impedance width changes, material types, or copper weights to produce the part. Any deviations regarding drawing notes such as wrap plate requirements that cannot be incorporated due to insufficient space or the extra etch compensation to meet the wrap plate requirement should also be ad- dressed. If your chosen fabricator comes back and says the material you have called out is not a standard stocked material for them, you are asking for a three-day turn. Giving you an al- ternative is great, but if by changing to the ma- terial they suggest your trace widths or spaces change to the point the part has to be laid out again, this can be very frustrating for the board designer. To mitigate this from happening, give your- self an additional mil or two of space. This will allow the fabricator to resize the traces to meet your impedance and adjust dielectrics. For ex- ample, if you have designed the part as a 0.1- mm trace and space, this does not allow the fabricator to resize the traces without affecting The Bare (Board) Truth by Mark Thompson, CID+, PROTOTRON CIRCUITS

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