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From [log in to unmask] Fri Apr 26 13: |
49:01 1996 |
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A little more feedback would be:
At 1.5.1.2 I would add....chemical properties of some clad
innerlayer laminar bonds degrade with excessive baking of
laminates.
1.5.2....Generally, full cure of the initial core laminate
is done.... (And) .....shipment to printed board
fabricators. Full cure of composite multilayer PCB is done
by the fabricator based on the laminate vendor's
recommendation for correct....
(Under Tg testing)
....If the second test differs significantly (Typically any
findings >4'C indicate under cure),......
1.5.3....various constituents of the laminate coupled with
the material manufacturing process.
(Under resin type)
I don't see some of these Tg values correspond to the
material (all) available. Maybe a range would be a more
representable approach. ie, Multifunctional Epoxy 140 -
150'C, High Temp Multifunctional Epoxy 160 - 180'C, etc.
Also the 220'C Polyimide probably should be pulled out
separate as a Polyimide Blend at 220'C.
The listed bake times are becoming more static because the
laminate vendors are formulating higher Tg's with quicker
cure times.
As far as baking fully assembled PWAs, I always recommend
15 minutes per layer at 220 - 230'F. This assures that high
layer count product receives ample time to drive off any
absorbed moisture. Higher layer count also has contains more
resin than fiberglass which traps, retains, and is harder to
remove than a double sided product. Also, the temperature is
high enough to remove moisture yet low enough to not destroy
most components.
Dave Hoover
Senior Process Engineer/Hadco Corp. TCII
[log in to unmask]
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