I've looked at the conductive pens.  They have a resistivity of 0.2Ohm 
mils, which is 5.08x10^-6 ohm meters.  For comparison, nichrome wire, a 
common heating element, has a resistivity of 1.10x10^-6 ohm meters.  
Nickel, Tungsten, Calcium, Aluminium, Gold, and Copper are all on the 
order of 10^-8 ohm meters.

Those pens are only used for touchups because they introduce a lot of 
resistance into a trace.  If I were to use pens, it would require very 
careful power delivery.

3M may have the requisite product, but I haven't found it yet. 

Thanks for the suggestions.

Brendan
Dr. Skip wrote:
> A few come to mind:
>
> http://www.mgchemicals.com/products/8420p.html
>
> http://parts.digikey.com/1/parts/956980-conductive-pen-std-tip-3oz-cw2200stp.html
>
> http://www.circuitspecialists.com/prod.itml/icOid/825
>
> Frys and RadioShack also have ones similar.
>
> 3M makes a copper foil tape with conductive adhesive too. They 
> probably have
> other conductive items as well along the line you're looking at.
>
> -Skip

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