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I've been working on a small project as an extra activity for a basic digital electronics course I was taking, in which I had to design a TTL-logic based PCB, and etch it. I've been using Ultiboard 11 as a tool in developing it.

Due to limitations of our class supplies I am required to fabricate this with only one copper side. The other side would contain This had caused one of the connections to not route as there had not been a path that Ultiboard had been able to autoroute.

However, using the "follow me" tool, I had noticed that Ultiboard would allow a trace between two IC pins as shown below to complete my currently un-routed net. This trace, which autorouting had apparently not yielded, had to pass between two THT pins on a 74LSXX IC, with the traces on the copper bottom layer (which will be soldered by hand).

enter image description here

The PCB would pass a design rules check with this trace, and would report in the connectivity check as successfully connected. However, due to Ultiboard not routing this automatically I fear that there is some sort of consideration that I must take here (other than careful solder practice).

I have roughly 16 mil clearance around the trace due to the pin spacing of the IC, with the trace itself also being 16 mil thick as it passes here. It is used for a TTL logic high/low signal. Switching speeds are not a consideration for this circuit.

The traces are 24 mil thick elsewhere.

Is this trace going to be something I need to take special considerations with?

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When I was doing through-hole boards, I think I used 12 mil tracks for most signals, and 60 mil pads on most components, leaving 14 mil spacing between track and pad.

I you had set your default track width for autorouting to 24 mils the autorouter would have been unable to route that track, but a narrower track is fine.

There appears to be a thin red track running vertically there - if that's on the copper layer, you have a problem!!

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  • \$\begingroup\$ Thanks for the response. I had autorouted at 16 mil at first, and it had not added the trace then. I thickened the traces later, and then put the trace in question in. I'll try it and see how reliably it works. \$\endgroup\$ – ζ-- Apr 9 '14 at 23:17
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1) The autorouter is only as good as whatever rules it is programmed to follow. It probably didn't know it could snake down the trace width to get it to route.

2) This width reduction of the trace is OK unless you are doing some high speed stuff where trace impedance matters. I'm assuming you're not, since this is basic digital electronics and no ground planes, etc.

3) Solder mask on the trace should prevent you from bridging solder between the holes and the trace. If you don't use solder mask, watch out for this.

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