======== Original Message ========
     Technetters:

     Let me make the scenario simpler:

     The ficticous multilayer board (10" x 10", 0.062" FR4, HASL) has
     already been fabricated and delivered to an assembly subcontractor for
     stuffing.

     For the sake of this scenario, the assumption is that the wrong
     prepreg was selected in the layup process, leading to a partially
     cured board.  The board is flat at the time it begins the first reflow
     process at the assembler. After first reflow, the board has twisted
     (not just board sag on the conveyor rails).

     Questions:

     What effect does undercured prepreg have on warpage during the
     assembly process?

     Is subsequent warpage (if any) predictable as a percentage of the
     original warpage?

     Has a reliable process been developed to correct for the warpage after
     assembly?

     Thanks for your thoughts!

     Bill Fabry

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======== Fwd by: Richard MacCu ========
I'm not sure warpage is your biggest problem here.  Undercured resin which
sees thermal cycles above the current Tg can lead to resin recession and
barrel cracking.
The actual crosslinking which takes place during cure will affect the PTH
bond.  Also, etchback may be severe at any layer which has not cured.  Its
resistance to chemical attack will be different.
Subsequent warpage may occur.  Once the panel has reached a temperature
above the current minimum Tg of the board any stresses which have been put
into the laminate and not already released to equilibrium will want to
equalize.  This makes prediction very difficult.

Not a scenario I would like to face.
Good Luck

Richard 8{).

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