Eagle help - specifiy size of ground plane to pad connection

Community PCB Design
1

Hi,

I need to move 2-5 Amps between a MOSFET and a pad on my board. When it’s going to ground, through the ground plane all is good. What concerns me is the size of the connection between the pad and the ground plane. See the 4 skinny connectors in the picture:

http://images5b.snapfish.com/232323232% … 3348nu0mrj

I’d feel a lot better if those were much bigger or the whole thing solid. I’ve searched and can’t find a way to tell Eagle to make these connections bigger. I can add a “wire” to that layer after it’s layed and and basically force copper to be placed there but that causes other problems and is more of a workaround. Any ideas?

Thanks!

2

You can use the “Info” tool on the ground plane polygon to turn off thermals. This will affect all ground connections to that plane.

If you don’t want to do that, you can open the MOSFET in the Library editor and use the “Info” to turn of the thermals to a particular pad.

3

Thanks, that did the trick. What exactly is the purpose of the thermals? I did some hunting but couldn’t find out what there for, just advice on how to calculate them. Could I be making a mistake by removing them?

4

Thermals are so when you solder something you are not heating the surrounding area so much. And in the process taking longer to solder your part with a higher chance of cold joints and whatnot.

They’re a good idea 95% of the time.

5

When using a wave solder process (not usual in our hobby, unless you get your projects assembled even then, you’re likely to get reflowed boards),

a cold, unreliable joint can be made due to the copper ground plane drawing the heat away from the joint.

I find that having no thermals on joints doesn’t make much difference, although i do have a fairly high wattage iron.

I don’t use thermals on high current traces.

It’s said that not having thermals on planes can lead to board de-lamination… Haven’t experienced that so far…