The Secret Language of the PCB Designer

To walk the walk, you gotta talk the talk.

The PCB Designer position is a hub where a lot of abstract and concrete information is funneled into a physical product. The boards start with the inspiration of an inventor. The idea is fleshed out in terms of the mechanical and the electrical requirements. Those two teams speak their own languages with just a little overlap.

The signal integrity and power integrity experts add their own flavor. The signal integrity people “speak” primarily in S-parameters shown on charts that are “off the charts”. Their counterparts in the power integrity domain bring us tables of data augmented with power trees that trace the current from the main input to the last termination resistor. These people are a direct substitute for trial and error so we must accommodate their input as best we can.

The folks who plan and schedule our work will speak to us in Gantt charts, lead times, and Bill of Materials. Long tent poles and other euphemisms for bottlenecks are part of their vernacular. The time between the original component selection and the final artwork is enough for the procurement landscape to have changed. Show stoppers arise and an expediter gets involved. Remain calm and get them unstuck if there is anything you can do.

A reliability team is a normal part of research and development. The PCB and all of the parts are subject to scrutiny. The Component Engineers are fond of a number of phrases such as Mean Time Between Failure (MTBF) and use of the bathtub curve. Failure Analysis has them doing all sorts of destructive and non-destructive tests. Their methods are described in a sprawling document that may be familiar. IPC-T M-650 has many chapters; one is for cross-sectioning. They get a lot of data by slicing the board up after interrogating it from the outside.

Image credit: Lifewire

First Article Inspection is exactly that. The new product is subject to every dimensional or notational attribute on the drawing. Have a note or detail for everything that is required. Try to avoid asking for things that are not measurable. I can tell if a solder joint is well formed. I can’t look at it and be able to say if the PCB was baked prior to assembly. Processes are documented and maintained as separate documents.

What Is or How To...

This veers into syntax but is an important part of the way we communicate. We don’t want our drawings tethered to the process. Of course, your Manufacturing Engineer would like to include this stuff so that the operators on the assembly line only need one document in front of them. They mean well but they are wrong-headed on this matter.

If you accommodate this request, expect to get a negative comment from any auditors who may come along to certify your system. We live in a world where continuous improvement is the only option. Expect that you will be editing these drawings to keep up with the dynamic nature of production lines. It may be hard to say “no”. In the long run, it is the correct answer.

When I was teaching my fellow designers about military drafting requirements, one of the juniors came up to me after one lesson on geometric dimensioning and tolerancing and said that she liked the way I made words up such as “perpendicularity” and “parallelism”. Want to know how I knew that she had not read chapter 9 of the Mil-Std 100 Drawing Requirements Manual?

The DRM is a yellow pages size book that most drafters use as a reference. The link goes to the 84-page preamble loaded with definitions and other reference docs. Mil-Specs are always referencing other documents. One document calls out another that calls out others and in this way, the entirety of the Library of Congress seems to be in play when we discuss how to draw and label a picture.

The article continues here.

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