SMD Pad thermal relief for high current.

[jonboysteg]

Hi, I have put together a design based around a LM2742.. given it to my PCB designer who has put thermal relief in for the inductor pads. Not having much experience with PSU design I would like to know if these pads should have thermal relief and to what thickness as they have to carry a lot of current (20A+) or should they be a direct connection to the power plane.

Many thanks

 

[felixc]

At such currents you may think about removing the thermals. Make sure that all of the thermals in the high current path are removed.

Without thermals, some SMT solders might need rework, as the temperature may not rise enough for a good solder joint. But it is better than problems caused by poor current paths.

Thermals appear automatically on ground connections in many CAD packages. Sometimes you need a manual operation to remove the thermal. Ask your PCB designer, to make sure that you won't be fooled by a thermal that reappears without warning at your next PCB revision.

 

[jonboysteg]

Thanks, I had asked him to enlarge the connection to the current path but I think you have confirmed what I was thinking and it is much better to have a reliable product than a better looking solder joint! I will ask him to remove the thermal relief.

Cheers.

John

 

[sreid]

Personally, I never trust one PTH to carry high current to a ground plane with or without thermal restrictors. I always pump in multiple vias even if I have to add them to the "Part Puppet."