Ground net tracks moving unexpectedly

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Ground net tracks moving unexpectedly

Postby guyt » Mon Dec 29, 2014 3:53 pm

I am creating a 4 layer board with an inner ground plane. As I start to make traces which attach to the ground plane, they are not actually locked in place with the part which they are attached to. PCB123 makes apparently random connections between various pins on different parts which are connected to the global ground net.

Example: it shows a 'connection' between the cathode of an LED and a microcontroller ground pin, both of which are attached to the ground net. I create a trace for each of them, with a very short trace and a via to the ground plane. So far, so good. But...

Now I need to relocate the LED on the board. When I drag the LED, BOTH of the vias and their associated short tracks move!

How do I get around this? I happens with every last connection to the net has not been made. For smaller nets I've learned to just be careful. But with ground, a huge number of connections are to the ground net. If I don't connect them, then the ratsnet is a lot of noise from the ground net alone and I can't see anything else very well.

Though I am still not quite sure I understand the example above, and why the LED net to the processor ground pin was so sticky. Sometimes this happens with completely unrelated sections of the circuit, with the only thing in common that they have Vcc connections for instance.

Do I really have to wait to connect any large nets until I am certain every part has been placed exactly? That doesn't seem practical, as editing and moving things around during layout it normal. Just a small change can move existing traces...
guyt
 
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