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What's your biggest PCB mistake?

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slburris:
Since I'm just a hobbyist and don't make PCB's for a living, I have
yet to make a board that's perfect the first time.  Luckily most boards
I have been able to modify if they don't work.

So where have I gone wrong?  Let's start with the worst.  I've had two
board runs that have been little more than green coasters.

The first involved my first FPGA design where I didn't pay enough attention
to pins that were input only and needed to be outputs or I/O.  Too many mistakes
to fix that one.  Some pins didn't lead to vias that I could solder to, and
I just couldn't tack wires to pins on a VQFP100 packages well enough.

The other disaster was a 16 digit LED display for a clock where I incorrectly
made the symbol for the constant current driver chip.  Somehow I
had the pin mappings off by one pin.  On first power up, all the magic
smoke came out of those chips.  The second spin of the board worked...

Biggest fixable oops I've made was forgetting to put a clock oscillator
on a board.  "No problem, I'll just use the internal oscillator.....oh this chip
doesn't have one".  Had to mount that dead bug style with double sided foam
tape and wire the leads into the board.

Most mistakes involve mixing up TX and RX for RS232 connections, and wiring
up TDI and TDO backwards for JTAG connections.  I've learned to double check
those :-)

Scott

Hypernova:
Neglecting thermal reliefs on polygon fills. The GND pins were a real bitch with solder.

JohnS_AZ:
The board is 13" X 3", a 6-digit "universal LED display".
There are no traces from the common cathodes of the left most 2 LED displays to the driver.
There's no ground trace to the regulator.

The mistake? Not using a gerber viewer to double check the art before sending it off.

Luckily, this was a proto run of 8 boards (thus no silk screen or mask). Everything was fixed before the production run.

Time:
I usually sit on a board for atleast 3-4 days before I send it off.  It always helps to go over your design again and again with fresh eyes.  Hell, even have a few beers and see if a slightly altered state brings out an error you might not of seen otherwise (though I would double check it the next day just to make sure it was real :P).

I have made home revisions on boards plenty.  The first version of anything I make will have atleast one or 2 errors on it.  I think the worst mistake is probably just goofing a footprint.  I am a control freak so I never use footprint libraries other than my own which I have built up over time to have all the standard footprints with different clearances.  I like to customize the clearances when I know if I am going to be using an iron, hot air, or reflow oven.  If you take a razor blade you can cut/scrape small spots of the solder mask off points on traces and use those spots as soldering points.  If I need to cut a trace I do it with a metal engraver.  This tends to make a nice controlled trench that isn't too terribly ugly.

TheDirty:
Most of my boards are home made, so it's never much of a problem for me, cuz I can just fix and re-etch a new board, but I've made a lot of boards and errors are pretty uncommon for me now.  I also make a lot of breakouts, so I can breadboard everything before hand and footprint errors would come out then.

The ones I have sent away for, the biggest error I've done was forgotten a diode to separate the backup battery for the RTC, so I had to scrape off some solder mask and cut a trace to solder I diode in.

Bottom right, the SOT-23 that's at a 45 degree angle.

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