How to mount heatsink on GBPC-package rectifier

[seb1982]

Hi all!

I'm about to make a homebrew prototype PCB for something which starts by rectifying AC from a mains transformer.  The bridge rectifiers I've got are these GBPC-W packaged ones from RS:

http://docs-europe.electrocomponents.com/webdocs/0dad/0900766b80dadbc1.pdf (<-- link to .pdf datasheet)

There'll be a max current of 3 Amps through it, and I'm probably going to have to have a fan inside the enclosure anyway, so I was hoping to get away with keeping it mounted on the PCB, with its own heatsink on top.  My question is: how do I mount it best on the PCB with the heatsink?

I note from the datasheet that it has a hole for a #10 imperial screw, which seems to be as near as dammit 5mm.  Should this screw "bite" into the sides of the hole in the rectifier, or fit through it easily? 

Also, should the screw be a self-tapper and actually screw through the heatsink & rectifier into a pilot hole in the FR4 PCB, or would this stress and shatter the PCB?  Should it pass easily through the PCB and then be tightened with a nut on the bottom?

As you can see, I've no idea, so any help would be greatly appreciated!  I was just planning to use a finned heatsink with some compound.  Also, if anyone happens to be able to recommend a heatsink from RS for this purpose, that'd be great too, but I'm sure I can find something anyway.

Thanks ever so much for your help. 

[mariush]

Technically, for 3A those don't require heatsink... look at the graph on second page. Especially with a fan moving air through the case, the rectifier shouldn't heat that much.

But anyway, the diameter is 5.08mm
Depending on heatsink i'd just use a 3-5mm screw (with maybe washers on both sides and locking washer on the heatsink side) and I'd use some regular thermal paste/grease between the heatsink.

These look nice if you'd use some adhesive tape to glue them to the rectifier: http://uk.rs-online.com/web/p/heatsinks/5040700/

I'd probably use something like this (if i were to be forced to get from rs) : http://uk.rs-online.com/web/p/heatsinks/0402951/   - it's 19x22 mm , so fits within the footprint of the rectifier, hole pretty much in the center (4mm diameter)

[seb1982]

Apologies for not replying sooner - I suddenly came down with a rather nasty stomach bug! 

Thank you so much for that comprehensive answer - lots of very useful thoughts there, and I really appreciate it.

Thanks.

[madires]

For vertical mounting there are heatsinks with two studs (to be soldered on the bottom layer) or two mounting holes (or the profile provides some places to force a self-tapper in).  In any case use the PCB more like a washer, i.e. if you're using self-tappers you need something solid on the other side of the PCB.