Unable to connect two ends of the same signal

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1

Hi,

I’ve a signal connecting two components, a central pad of a small QFN IC, and a resistor.
I’m not able to connect these two ends of the signal. When I tie the trace towards the resistor pad, it’s not possible to connect it.
When I start from the resistor pad, I’m able to start the trace, bit I cannot connect it to the trace coming from the IC.
What could be the problem?

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Thanks,
Leo

2

Hi,

I’m trying to connect signals to a small IC.
I don’t succeed to connect traces to any pad.
I reduced minimum clearance to 0mm in Board Setup.
I also tried reducing the trace width, with no succeed.

image

What could be the problem?
Thanks,
Leo

3

Where did you get that QFN footprint from? It looks like there’s a border that’s not allowing tracks to reach the pads.

4

Hi,

The IC is from Texas Instruments, and from their site I was redirected to Ultra Librarian.

In which part of the footprint pad’s do you suggest checking for such border?

Thanks,
Leo

5

Does the footprint have a shape on the edge cuts layer? If so, that is the problem, that shape should instead be on a fab layer.

Always be suspicious and double-check content from services like Ultra Librarian.

You can route the trace in “ignore collisions” mode and then run DRC if you want to have KiCad tell you exactly what the problem is.

1 Like
6

This looks like pad clearance to me, but I admit, it’s narrow.

The center pad has a SMT pad with pad number 3 and a THT pad with pad number 6. That does not work well in KiCad. Give these pads both the same pad number, 3 is probably the logical choice, but I have not seen the datasheet.

7

The rats nest lines make little sense unless there are some track fragments belonging to other nets

8

Could it be the large via doesn’t have a net name associated to it?

9

I think you are onto something,
This image is a bit closer and it shows the issue.

The net “AlertPU” wants to go to pad3 HOWEVER… it is going via a … via to the BLUE layer.
The problem is Pad3 is on the RED layer and there is technically a new pad… Pad6 inside Pad3 but Pad6 doesn’t have a net associated with it.
This would appear to be a footprint issue since this “via in pad” should have the same pad number

10

Hi,

Thanks for your help, I think I found the problem.
For pads 1 to 4, the pad itself is a circle, and surrounding the circle there is a polygon in the same layer (front).
When I try to connect the trace, the polygon does not allow reaching the circle (which is actually the pad). It seems that the polygon was not associated to the pad.

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To solve this, I did the following:

  • Select the circle pad, and then right click “Finish Part Edit”. (or “control E”.)
  • Then select the polygon and “Finish Part Edit”. (or “control E”.)

For the central pad, I created a new PTH and assigned to it the same number than the pad (#3), and now it works fine, I can connect it to the trace.
Thanks @paulvdh for your help.