I have no direct experience but I know what I would do. I would put the
rivets in the thermal pad area first, cover the rest of the board with
adhesive plastic film, and sand the rivets with maybe 320 grit wet until the
heads were flush with the plastic, then bend the SMD leads slightly to
compensate for the extra thickness.
--
Phil M.
----- Original Message -----
From: "Kaelin Colclasure" <kaelin@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, July 10, 2013 7:55 AM
Subject: [Homebrew_PCBs] How to tackle thermal pads on SMT packages?
> I'm looking to stretch my luck by trying a design that uses all SMT
> packages. At the moment I am pondering how to tackle the thermal pads
> commonly found on SMT power converter packages (for an onboard buck
> converter).
>
> The data sheets commonly specify that a pattern of plated vias should be
> used to conduct heat from the thermal pad of the package on the top copper
> layer to the bottom layer. The idea, obviously, is to provide more copper
> surface area for radiating away waste heat. My problem with this is that I
> don't have a way to plate through holes. I am using old-fashioned copper
> rivets to connect between layers. And while the rivets are smashed pretty
> flat by the tool, you can definitely feel where they are, and the tool
> also tends to leave a slight deformation in the surrounding copper layer.
> I am concerned that this could cause problems with reflow soldering.
>
> I thought about simply making a larger copper area on the component side
> of the board, but the relevant data sheets are also adamant that circuit
> paths to supporting components must be as short as possible.
>
> I've got a couple of ideas to try:
>
> 1) Use riveted vias in a copper area that's as close as possible to the
> package without actually being embedded in the thermal pad landing. But
> will they still conduct away enough heat?
> 2) Forget the through-holes and stick some kind of heat sink on top of the
> package. But again, since the package is quite small, and not designed for
> a heat sink on top, will it work?
>
> Any other suggestions? Has anyone here tackled this sort of thing before?
>
>