Hey techies,

I have three questions for all you PCB technology guru's out there.

1)  First of all, I was provided (in a PCB technology training seminar) the
following information:
Because of the way the laminate material is made (it follows the textile
industry equipment), there is always more yarn (glass fibers) in the warp
direction, then in the fill direction.  Because of this you will have a more
stable board in one direction then the other.  When running the smaller size
panels (12" X 36") a lay-up called a "cross-ply layup" of the pre-preg
material would make the board more stable, and less likely to have warping
issues.
Can anyone tell me if this is correct or not?

2) I was also informed of the following information:
        The warping of the boards will never go away, especially by running
the boards through more thermal cycles.  This will only make it worse.  The
Epoxy in the laminate material continues to cross link and with each thermal
cycle the epoxy cross links more and more.  This means everytime you run the
board through an oven you lose some of its ductility.
        The board is in its relaxed state while in the warped state, and
trying to flatten the board out during a heating process will cause even
more problems, because as soon as the board is heated up again it will go
back to its relaxed (or warped) state again.
        Usually the warping of the board is caused by the following
problems:
        1) Bad design -- uneven stack up of the layers
        2) The PCB house did not use the same Pre-Preg (stage B) laminate
material as the Cored (stage C) material.
Can anyone tell me if this is correct or not?

3)  Can anyone tell me what the other causes for warping of a PCB are?

As always, thanks in advance for your feedback!

Kind Regards,
Kathy Palumbo
Manufacturing Engineer
IPC Certified Instructor
Viking Components, Inc.
30200 Ave. De Las Banderas
Rancho Santa Margarita, Ca. 92688
BUS: (949) 643-7255 ext. 352
Fax:  (949) 459-5360
CELL:  (949) 422-4145
E-Mail: [log in to unmask]
Web: http//www.vikingcomponents.com/

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