# I forgot a resistor on my PCB prototype - how do I add one in?

I need to add a resistor into a data line on my project. The data line is a trace and carries low speed data. A through-hole resistor will be fine. The pins for both ends of the trace are exposed, but how do I add the resistor and remove the trace?

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Why did you create a bodge tag? –  Kevin Vermeer Jun 25 '11 at 16:36
@Kevin - I didn't notice that. Maybe rework is more appropriate. That one at least exists already. –  stevenvh Jun 25 '11 at 16:41
@Kevin My error, but I am thinking it would be a bodge. The solution, of course, is to do another design revision. I've already ordered this, but it will be some time as I selected slow turn to lower costs. –  Thomas O Jun 25 '11 at 19:04

If your PCB has a solder mask you can fix this with an SMT resistor even when traces are close together. Cut the trace and scrape the solder mask away on both sides of the cut, over a few mm. Solder an 0603 or 0402 over the cut. If I patch like that I actually make two cuts a mm apart, and remove the trace(*) between both cuts to make sure there's a decent interruption of the trace.
Alternatively you can do the same and solder a PTH resistor, whose wires you first bent so that they lay flat on the trace. Won't probably work as well on narrow traces, like 0.5mm.

This type of knife allows for very accurate work (pingswept mentioned the brand X-Acto):

Success!

(*) davidcary uses a dental pick for this,

but the tip of the X-Acto is fine and sharp enough to do it with that.

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To add to stevenvh: use an X-Acto knife to cut the trace. –  pingswept Jun 25 '11 at 16:15
@pingswept - Yes, that's the type of knife I'm using. Could be another brand, though. –  stevenvh Jun 25 '11 at 16:17
After cutting a gap in the trace with utility knife or X-Acto knife, I use a "dental pick" to scrape away the green soldermask upstream and downstream of the cut, revealing shiny scratched-up copper. –  davidcary Jun 25 '11 at 22:40
@David - I just use the same knife for that. Changing tools costs money! :-) –  stevenvh Jun 26 '11 at 10:33