In a message dated 2004-07-20 11:46:57 AM Eastern Daylight Time, 
[EMAIL PROTECTED] writes:


> A partner in a manufacturing effort is sending us full populated
> boards (ICs and passive components) that are badly warped.  We sent
> them back and rather than get the boards remade and repopulate them,
> they want to heat the boards up (fully populated) for three days at
> 150 degrees Fahrenheit in order to straighten them out.  These boards
> perform an extremely important job and I'm worried about the stress
> on both the electrical components and the boards themselves.  Should
> I allow them to do this or should I demand the boards be remade?
> 

My answer would be, "It depends". 150F is 65C, and most commercial spec 
electronics components are rated to operate up to 70C, and often rated to survive 
even hotter when unpowered. If all they want to do is let them sit on a flat 
surface at 150F for three days, and you've got a reliable test procedure for the 
boards before they go into a higher-level assembly, and you can spare the 
extra three days, I'd say quietly thank them for the extra burn-in. If they plan 
to apply some force to encourage the boards toward flatness, I'd be a lot more 
concerned, particularly given that trying to bend the boards with the solder 
already solidified will place some fairly large stresses on component leads, 
and at that temperature the plastic cases will be somewhat more yielding - 
possibly transferring the stresses to the internal bond wires. You might get some 
internal opens that way, but what would really worry me would be the possibily 
of getting an "almost open", that would later fail under normal usage 
vibration.

There would be a lot of other factors involved, like the potential cost of 
later field failures, product liability, your future relationship with this 
manufacturing partner, etc., that only you could evaluate.

Steve Hendrix


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