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PCB design mistake — Parallax Forums

PCB design mistake

Jay KickliterJay Kickliter Posts: 446
edited 2011-03-14 14:06 in General Discussion
I made a mistake on some boards that I were hoping to actually get right the first time, which has never happened to me. I'd like to avoid another quickturn order, and fix them if possible. What I did was wire the EEPROM's SDA and SCL lines backwards to the Prop (see the picture).

My idea to fix it is this: cut the Prop's pin 28 and pin 29 with a razor blade, leaving just nubs one the Prop, and use the thinnest magnet wire I can find to jumper those pins to their neighbor's original trace. The board doesn't have a solder mask, so at least I have that going for me.

Any suggestions?
EEPROM Mistake-Board.png
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EEPROM Mistake-Schematic.png
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Comments

  • kwinnkwinn Posts: 8,697
    edited 2011-03-11 21:50
    What you are proposing to do is a time honored technique usually done with wire wrap wire.The folks responsible for the board layout used a wire color as close to the board color as possible to avoid it being noticed, everyone else used the brightest most visible color possible (usually yellow).
  • doggiedocdoggiedoc Posts: 2,246
    edited 2011-03-12 04:59
    Jay, wouldn't it be easier to cut the traces and solder jumpers that way?
    Paul
  • Jay KickliterJay Kickliter Posts: 446
    edited 2011-03-12 05:33
    doggiedoc wrote: »
    Jay, wouldn't it be easier to cut the traces and solder jumpers that way?
    Paul

    I think it would, if I wasn't impulsive and already cut the pins.

    The worst part is when I was laying out the board, I thought to myself that it was easier to route the EEPROM this time around. Of course, because I didn't have to make those two traces jump each other.
  • Erik FriesenErik Friesen Posts: 1,071
    edited 2011-03-12 06:04
    Get some 0403?, or 0603? size 0 ohm resistors, cut trace from 36, and solder bridge, or wire bridge to the low pin, then span from 35 to 6 using the resistor, the bottom will insulate from the track on 5.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-03-12 07:26
    Instead of a razor blade (x-acto, et al.) I prefer a Dremel with
    the narrow-thickness cutting disk ("cut-off wheel", the red ones); whirrr,
    zing-zing, zing-zing, done.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2011-03-12 07:35
    same here PJ .. with a knife I seem to over cut and kill more then just one trace..
  • Jay KickliterJay Kickliter Posts: 446
    edited 2011-03-12 14:40
    After four hours, and a few broken chips, I finally fixed it. I tried jumping off the board/pads, but it was just too tight. Instead, I bent one pin from the Prop and the EEPROM to the top of the chips, cut traces, and jumped one on the board and one above. I did't have any wire on hand that was small enough, so I used leads from the smallest resistor I had. Even that's too big, but everything works.
    EEPROM Fix 2.jpg
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    EEPROM Fix 1.jpg
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  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-03-12 14:43
    Jay, I never thought it would come to this, but, um...
    You're fired!
    :)
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-03-12 16:08
    Jay,

    'Glad it works, but ... um ... here's an idea: build a small dam around that part of the PCB and fill it with epoxy. Opaque epoxy. :)

    -Phil
  • doggiedocdoggiedoc Posts: 2,246
    edited 2011-03-12 16:20
    Jay,

    What kind of time frame are you working with? If this is a product you have to deliver to a customer you migh want to consider a second run on the pcb. <grin>

    Jus' saying. I do like Phil's idea though.

    Paul
  • Jay KickliterJay Kickliter Posts: 446
    edited 2011-03-12 16:36
    It's just a prototype. Normally I'd correct the design and order a new one, but this is a for a student project my buddy and I are showing at a trade show next week, and I've already spent more on FedEx for this project than parts. Luckily, an XBee sits over the Prop, so my art wont be visible.
  • SteveLSteveL Posts: 6
    edited 2011-03-14 14:06
    My preferred method for cutting traces is to use a small drill bit. You can use a pin vise if you have one, or just simply spinning the bit between your fingers works as well. Less likely to slip and cut something accidentally than with using a blade or Dremel tool.

    Buy a spool of wire-wrap wire for the next time this happens. Trust me, there will be a next time. At 30 ga., it is the perfect size.
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