Re: gEDA-user: Exposed copper -- still need to make a pad?

[Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>]

On Thu, Sep 27, 2007 at 09:44:36AM -0600, John Doty wrote:
> 
> On Sep 27, 2007, at 9:28 AM, Randall Nortman wrote:
> 
> > I need to make an exposed area of copper (no soldermask), to act as a
> > heat radiator.
> 
> Why no soldermask? I'll bet its infrared emissivity is better than  
> copper's, making a better radiator. In space, the radiator tape we  
> use has a thin layer of teflon over the metal for this reason.

As sayeth the datasheet, so do-eth the designer!  In fact, any exposed
copper is going to be covered in shiny silver stuff (tin/lead/silver,
depending on process) during board fab.  Would that not have pretty
darned good emissivity?  It would certainly have better conductivity,
which is important when you're not designing for vacuum.  I suspect
that most of my cooling is going to be from conduction to air and
subsequent convection (natural convection; no fan), though a big chunk
of it will be radiation.  (I did say "heat radiator" in my post --
probably "heat sink" would have been more appropriate.)

-- 
Randall


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