[PLUG-TALK] Busted motherboards

[Keith Lofstrom]

Paul Mullen writes:

> ... What are the chances that one of
> the procs was busted by whatever impact UPS provided the package with?
> I'm wondering if I should bother trying to test out a new proc (or two)
> before continuing with the hassle of a UPS damage claim. Is it possible
> the motherboard itself is toast? How fragile are modern PCBs?

If the case was not packed with a couple of inches of corner foam or
cardboard equivalent, it could very easily be bent beyond usefulness,
and the motherboard also.  The traces of a motherboard are extremely
fragile - if there is a single trace with a small crack in it, that 
trace might pass factory inspection (hah!) just fine, and not manifest
itself until the motherboard has been subjected to some mechanical
strain that finishes pulling apart the crack.  Or tiny little bits
of metal may have come loose and shorted something.  Or one of the
solder balls under a chip package separated from the board.  Chances
are that 99.9% of that motherboard is just fine, and there is one
single short or open caused by strain on the weakest link.

The possibilities are endless, but the bottom line is that whatever
torqued that case enough to leave the metal warped was obviously 
a much bigger twist than what is manifested now.  Bend a piece of
metal - it mostly springs back.  Since the motherboard is under strain
now, it must have been under a hell of a strain when the case got bent.
Metal is more elastic than FR4 circuit board material, so if the
motherboard was mounted on a load-bearing portion of the case,  most
of the case stress was actually taken up by the motherboard.  And
the heavier the case, the more strain on the motherboard. (!!!)  

I betcha that the case fell, perhaps just a foot or two, and landed
on one corner.  There should be room inside the box for the metal
to keep going for an inch or two, and the force to have time to
translate into torque and bring down the other corners of the box. 
When you calculate the forces involved in an impact of a hard object
on another hard object, is is surprising even solid metal doesn't
shatter when it lands.  Take a look at the video simulation at:

http://www.engenuity.net/private/case_zoom.php?case_id=00000013&pic_id=00000118&item=movie&fromsec=2 

Good luck on getting your insurance money.  If there weren't suitable
corner cushions inside the box, UPS may well claim improper packaging
and disallow your claim.  

Keith

-- 
Keith Lofstrom           keithl at ieee.org         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs