Hi!
Although no real experience in making those kind of hibrid boards I could
say the following:
Time and temperature are somehow complementing one another. If you are using
the lesser material temperature, you should increase the time, to give the
other material larger percentage of cure, even doing a "post-cure" out of
the press can help.
I would not use two materials with very large differences in temperature
cure, but try to find the most similar materials.
If your finish is HASL or Sn/Pb reflow and the board did not warp there, it
will not do that during assembly.
The possibility of warp during reflow or other thermal process will depend
also on the symmetry of the panel, if your partially cured material is
symmetric around the center plane of the board there is less chance for warp.
Other things to take into account are the types of glass used and the
dimensional stability of the different materials.
I could say that if the materials are chossed properly and the symmetry
conserved (and the board is not very big), you can have a fairly flat board
using the two different materials (at 1/16" thickness at least).
Warpage is not suppose to increase as succesive thermal cycles are done.
Roberto Tulman
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Roberto Tulman
e-mail: [log in to unmask]
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