Actual thickness of copper is as follows:

1oz                 35um or 0.035mm
2oz                 70um or 0.070mm
3oz               105um or 0.105mm

There will be some variation in finished thickness if the board is PTH
as they will be 'plated up' to a finished weight of copper. You should
check with your board house for their typical variation. I believe that
3oz is fairly readily available (certainly here in the UK) some board
companies may even be prepared to go thicker, but you will have to be
careful with your design rules even with 2 & 3oz.

If you can tolerate the expense of a multilayer board then use lots of
vias to pin the power pad to planes as these will also help dissipate
some heat. I also recall that one manufacturer of power devices had
figures for heat disipation into unconnected planes (ie by radiation &
conduction through the board substrate). This is obviously not as much
as direct connection, but is enough not to be ignored.

If you do plan to use 2oz or 3oz copper do discuss it with your SMD
assembly house as it will affect their temperature profiles
significantly. They will hate you lots if you mix very fine pitch stuff
with great thick slabs of copper.

At the risk of stating the obvious, have you discussed the matter with
the manufactures of the device. It is possible they have considered how
to deal with some of these issues when they planned the packaging. They
may not have of course. I was recently laying down some high-voltatge
mosfets for which it was impossible to create a footprint which obeyed
anyones idea for a 800V clearance and they also made a 1200V rated
device in the same package.

Hope this helps,

Rob Malos,
Cyborg Design.

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