Electronic – What design testing can I do before fabbing a PCB

pcb-designproductiontesting

I'm an EE graduate who enjoyed the first taste of designing and fabricating hardware. My first board was a really low speed microcontroller board using mostly DIP and through-hole components, like something straight out of the 80s. It's very easy to translate to a PCB from a breadboard using these packages, but they are large and cost per square inch is very high for single-digit run project boards. To cut down on costs I designed a board using solely SMT components which was far more compact (as well as complex) than any other previous board I've made. I'd like to verify as much as possible that my designs work before spinning a board so I don't waste my limited budget (and have to delay for the new boards).

What verification practices should I use, besides making a breadboard facsimile, when making a (low speed) PCB? Up until now I've just made sure everything was routed, passed DRC and ERC and hoped the board works. I feel like there's more I should do.

Best Answer

My answer is more for obsessively checking your first (or second) personal "low speed" PCB rather than verifying your design.

  • Make sure your DRC is checking for off page connectors
  • Print out the datasheet pages for each IC/transistor etc and go through with a highlighter and verify every pin against the pin on your schematic.
  • Do the same obsessive check with your layout
  • Check all three pin devices like transistors against their diagram in the datasheet make sure that the pin numbers on your PCB are correct. It's easy to do these SOT-23 style devices wrong ( I usually draw a diagram for my layout guys).
  • Do a similar check for polarized components, did you get diodes correct and are they marked which way they go in? What about polarized caps?
  • Is this a four layer board? No? It probably should be :) signal-gnd-power-signal Even at low speeds this will help you. Sometimes you just gotta go 2, but do it because you know the consequences or that it won't hurt you.
  • Open your gerbers/drill in a gerber viewer like the free GC-Prevue, now print them to a laser printer 1:1. Order your more complex parts and see if they fit on paper. Is it perfect? No. Will you catch using the wrong footprint or wrong spacing? There's a good chance of that.
  • What did you do for power did you verify your regulators can supply enough current? How about how much heat they will burn off trying to do it? How about power dissipation for a linear regulator or switchers fets. You want to make sure you don't burn them up. We could go deep into the power section but I'll leave it at that.
  • Sounds like your design is cost conscious, consider only mounting parts on the top of the PCB. It will save a whole step during automated assembly if that's where you hope to get to, and that will lower the price.
  • Make sure your gerbers files are clearly labeled for the fab house, a drawing usually helps showing what layer goes where, some people go as far as labeling the layers in copper to make sure it's done right.
  • If possible have someone else review your schematic and pcb, peer review, peer review.
  • Have your 30 Gauge rework wire handy for when the boards come back, I like to use blue for rework :)

The list goes on but I'm tired and I hear the baby crying :) Hope some of that helps.