Soldering D-PAK Mosfet? (TO-252)

Apr 23, 2008 5 Replies
H

I'm using Fairchilds FCD5N60 in a D-PAK (TO-252).



Data sheet



formatting link



The D-PAK I'm using has a small drain tab that extends above the plastic case; the bottom portion of the drain tab is recessed into the plastic case Like a T0-220 .



I am unsure on how to solder the drain.


  1. Are you supposed to just solder the metal tab that extends above the plastic case?


  1. Are you supposed to lay solder down on the whole drain footprint? This includes the metal Drain that is recessed into the plastic case. If so wouldn't this potentially damage the case?



I just soldered the tab part that extends above the case to a small piece of PCB for testing the FET in my circuit. There is a no contact between the drain, (the part of the drain that's recessed into the plastic case) and the copper PCB. I pushed down to try and get contact while soldering but either I wasn't pushing hard enough or it's not supposed to touch the PCB. Is there supposed to be a gap for air flow and the copper that the tab is soldered to acting as the heatsink.



Thanks


Vote
Twitter Facebook LinkedIn
E

You would normally apply solder paste underneath the tab and reflow solder it.

Graham

Vote
Twitter Facebook LinkedIn
J

huh? The drain needs as much cooling as it needs. If you only solder a very small bridge between the tab and the copper then heat must flow through that bridge... do you think thats a good idea? If you were not suppose to solder the whole thing then why would they have it exposed?

You really need to think of why the did what the did and what is the purpose and then it should be quite clear what to do.

Vote
Twitter Facebook LinkedIn
J

If heat transfer isn't critical, solder it any way that's convenient.

If you need a low thermal resistance, make sure the pcb pad and solder extend under all the metal on the part, and then make sure the heat has somewhere to go.

Soldering the entire underside of the fet won't damage it. Fets will cheerfully melt their own solder joints and fall off boards, undamaged.

John

Vote
Twitter Facebook LinkedIn
H

I see I printed out a footprint and all became clear.I'm going to have to put some solder on the drain pad lay the D-PAK on it and heat the tab and push when the solder starts to flow.

Thanks

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required