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Topic: Unconnected ground pins on MCU (Read 217 times) previous topic - next topic


This could be my stupidity: I was trying to use autorouter in EAGLE to help me route my board. The autorouter always leaves MCU ground pins unconnected. Here is one go with the autorouter.

I wonder why the autorouter won't first make sure the power net is all connected first. I think it's a real problem for me when I started using SMD MCU parts.

Later I reduced default net class width and clearance both to 6mil and tossed in a bunch of vias to connect ground planes and got a complete board (second image).

Any advice? Is throwing in vias by the dozen (I did about that many) how you solve your SMD MCU problem? How does "drill" property affect a net class? Thank you!


That's a problem I see often as well. Especially if Power class is defined as say 20 mil or 32 mil, it's to wide to connect to SMD pins.
You can route those first by hand, hand-touched signals are not changed by the autorouter.
Or, just do the thinner trace from decoupling cap to the pin, let the autorouter do the wider trace to the caps.  That also ensures you have your caps oriented correctly.

I don't use 6 mil if I can help it - 10 mil with 10 mil clearance.  If things are really tight, I'll go down to 8 mil with 8 mil clearance.  I believe iteadstudio needs 8 mil clearance between pads on a part to be able to apply solder mask as well.

Grounds  - autorouter does pretty well except at getting all the grounds connected in the end. Lately I've been doing more SMT designs and have been putting a 12mil GND via next to pins, that seems to help the routing a lot. 

What I haven't been able to figure out is how to consistently get 12 mil vias on 10 mil traces. It keeps sticking in 24, and I go thru and change them to 12 where space is tight and the routing couldn't finish.

I see you have many traces running under your crystal, that's not good.
See the crystal section in the attached.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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