Classification:
Prologue:
Epilogue:

Re; the attached note:

"Bending" is bad and should be avoided.  How much bending is a problem will
depend upon the laminate material used and the line widths involved among other
things.    Bending during assembly (assembling the compliant pins into a board
if compliant pin backpanel)  should be zero, with the use of proper backing
plates during compliant pin insertion.  In application, try to limit any
flexing of a compliant pin backpanel (no soldered or smt components) to less
than 0.010 to 0.020 inches total deflection. Bending of a backpanel that has
soldered components should be even less due to stresses induced into solder
joints.  You may be able to estimate the strain in solder joints elsewhere on
the board.  It's better, though, to provide a stiffener.  Backpanels in PC's
are notorious for flexing when installing option cards.  Beyond the stress
problems with bending, you also must consider the problems of proper contact
seating when the mating card is plugged.  many connectors have over 0.100" of
wipe length, but not all do, especially when multiple pin lengths are used for
hot plugging.  Subtract the bending from the contact wipe length, then subtract
additional losses due to movement during thermal cycling, shipping and
vibration, add a bit of a safety factor, and you'll quickly see that you really
want  zero bending if you can get it.   I don't know of any "specs", as this is
a package level concern, and is very application dependent..  Warpage of
assembled compliant pin boards, before they are attached to a stiffener,  is
generally held to 0.010 to 0.015 inches per inch length in the assembled
condition.  Warpage of solder assembled boards is usually desired to be 0.007
to 0.010 inches per inch max.  These numbers based upon experience.

Jim Herard
[log in to unmask]
---------------------- Forwarded by Jim Herard/Endicott/IBM on 03-11-97 05:26 PM
 ---------------------------

        TechNet-request @ ipc.ipc.org
        03-11-97 04:58 PM


To: technet @ ipc.org@internet
cc:
Subject: backplane bending

Is there a spec that tells how much a backplane can bend when inserting
cards?  How much is allowable (permanent) if the cards are put under pressure
in order to keep them from vibrating out, thus flexing the backplane?

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