a quick tip for preventing PCB-induced stress

PCB stress

Most of the products we design have at least one Printed Circuit Board.

The design process usually goes something  like this:

  1. Specifiy the components (sensors, batteries, switches, etc.) required for the device to perform it’s desired function.
  2. CAD-up the components per their respective spec sheets.
  3. Drop them into the CAD assembly to see how much clearance you’ve got.
  4. Realize you’ve got buttloads of clearance.
  5. Eat up some of that clearance by shrinking the plastic housing (compact designs are great!).
  6. Do a few (dozen?) interference checks.
  7. Ship it.

That’s how I used to do it.  But I’ve been scared straight. I know a guy who knew a guy (seriously) that ignored the following advice, had parts come in, and they didn’t fit.  That is a real sucky feeling.

Enough beating around the bush (there’s got to be a better phrase than that)

Model components at their Maximum Material Condition.

In the olden days (a few weeks ago), all the components I modeled or snatched from 3D Content Central were nominal.  I just hadn’t thought of doing it any other way.  But if you look closely at the tolerances on a components spec sheet, you will see that they are huge.  Factor in the tolerance of the placement of the component, positioning of the board, and the plastic surrounding the board, and your components could go for a stroll.  Maybe even (cringe) interfere with some other geometry.

In a perfect world, you would do a tolerance analysis between every component everywhere.  And you should do that, it just takes time.

In the meantime, I’ll make my components bigger. Conservative clearances help me sleep better .

But I’m paranoid.  You?

Related posts:

  1. The dirty little secret about environmental impact
  2. a quick thought on attention
  3. video: flexible shaft couplings

Article by chris loughnane

Chris is Design Engineer + Sustainability Advocate at a Boston area design consultancy and has written 127 sweet posts for the Product Development Notebook.

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