PCB Design Mistake to Avoid: Via too close to Pad

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I want to share one of the most common and possibly worst PCB design mistakes you can make. That is: Vias too close to Pads. After you spend hours designing your PCB and is ready to order your boards to the fab house, you want to all to go perfect. Bad boards will ruin your day, cost you time and money, so make sure you read this post to know what/why to avoid this:

PCB Design Mistake to Avoid: Via too close to Pad

What is that? Below is a screenshot of the issue. Vias are in green and the component pad in red.

pcb design mistake: via too close to pad

 

Why is it bad?

If you get the board above and try to solder the IC into it’s place you’ll soon fin that the solder will try to go from those two bottom pins into the via (green), and as you see, that is trouble, since those are two separate nets. If solders bridges that connection you have a short circuit, which could potentially damage your IC or the entire board.

Why it happens?

The Cadsoft Eagle autorouter default settings is not smart enough back off.

How to avoid?

The good news, is there’s a nice trick you can do to avoid this. If you’re a Cadsoft Eagle PCB user, you need to use vRestrict, which stands for “via restrict”. When ever you draw a vRestrict shape, the autorouter will stay out of it!

 

See my example below of how I placed vRestrict in the IC leads. With this trick I tell autorouter not to have any via in a spot that I’ll be hand soldering fine pitch compoments

Conclusion: Stop making useless PCBs and apply this tip in your next PCB design. I recommend once you call yourself DONE with the design & autoroute, that you do a FINAL inspection prior to sending your board to the fab house. In this final inspection do a “solderability”study: that is, imagine yourself soldering each component and verify each and every pad would be a now/no chance of short circuit.

Good luck!!

Leave your feedback if you found this tip useful!

 

  • Mike Lease

    Good tip Igor, I know from experience how expensive and frustrating it is to re-spin a board because of layout issues like this. A number of board houses that cater to people doing small runs of boards have on-line DFM tools that will catch most of the problems that make a board hard to fab or assemble.

    Mike
    http://www.cmicrotek.com

  • Glenn

    You should place via’s as close to smd pad as possible when connecting to ground. By tenting the via, this will eliminate any possible shorts with solder bridging. Tenting just covers the via with solder mask.