Using TO247 as a SMD component in offline 30W Flyback?

[Faringdon]

Hi,
Can we lie a TO247 flat on a big SMD pad, and kind of manually "flood" solder beneath it, and then put a screw through to heatsink on PCB bottom, with thermal vias going through, or will the edge plastic of the TO247 get melted up?....and so we need to use (smaller) D2PAK instead?

[David Hess]

A D2PAK has edge plastic also and does not get melted up.  What you are suggesting has been done with TO-220 packages.  The problem with the TO-247 package is that the tab is not exposed on top, but I think it could still work. 

Solder will be extruded through the vias making the surface uneven so something will need to be done about this before attaching the heat sink.

[TimNJ]

If your goal is to heatsink, then I'd suggest to skip soldering and just use use a thermal pad + M3 screw and nut/washer on the back-side of the PCB.

If your goal is to make an electrical connection, sure you can do it by reflowing the solder under it, but I'd generally just try to find the right part in D2PAK or some of the more modern flat/lead-less packages.

[Gyro]

You say "Using TO247 as a SMD component". How are you going to reliably and repeatably (crop and) form the leads so that they meet the solder pads accurately and give a flat seating plane? This is essential if you are going to successfully use solder paste.

[T3sl4co1l]

They make a "D3PAK" for that.  Though I don't think they're widely available outside of.... IXYS?

If you need that much power dissipation, a vertical heatsink is needed.  No point trying to force it through a PCB.

Tim