>> I would like to hear you all confirm that a temp not exceeding 105C is
>> fine all day long on FR4 pcb.
>
> My opinion is that should be fine.
>
> Have you looked at using copper and plated through holes to make PCB
> heat sinks for the resistors?  It can make a huge difference.

That was my though too. Have a copper flood on the outside surface under the 
resistor, to absorb the heat from the resistor, and have big wings on it to 
radiate the heat after it is conducted away. A bunch of PTH to a similar 
area on the other side will help radiate some more. 

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