Dwayne,

We're using a type of lead free solder......I could get specifics, if 
necessary.

Nope, no sudden acceleration or vibration; it's for desktop use.

Several others have suggested cu floods as heatsinks and I have added as 
much as I can.

There will be vents in the enclosure and a fan so this will help, but 
until I get it all packaged up I will not know for sure what the final 
results will be.

Good thoughts.

Thanks,
Mark Skeels
Engineer
Competition Electronics, Inc.
TEL: 815-874-8001
FAX: 815-874-8181
www.competitionelectronics.com


Dwayne Reid wrote:
> At 08:47 AM 3/18/2010, Mark E. Skeels wrote:
>
>   
>> But my question is, will 105 deg C max be good long term for the FR4 pcb?
>>     
>
> What solder are you using?  Is the PCB subject to high vibration or 
> sudden high-G drops?
>
> My experience is that temperatures up to about 90C are fine.
>
> Question: do you have enough room on the PCB that you can do copper 
> floods on each of the resistor leads?  More copper area that each of 
> the leads is attached to equals lower resistor temperature.
>
> Holes under the resistors may actually increase the temperature - a 
> closed box has little air circulation and air is a better thermal 
> insulator than the FR4 substrate.
>
> dwayne
>
>   
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