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Disclosed is a method of building internal plane printed circuit boards that eliminates up to 85% of the dimensional instability that happens in the composite lamination process.
English (United States)
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Substituting FULLY CURED DIELECTRIC for PREPREG at the COMPOSITE
Disclosed is a method of building internal plane printed circuit boards that
eliminates up to 85% of the dimensional instability that happens in the composite
Manufacture of internal plane circuit boards (composites) begins with core
blanks. They consist of dielectric encased between copper layers. Core blanks
are circuitized in commonly known lithographic and copper etching or additive
copper processes. Both provide desired circuitry.
Multi-layer composites are made using one or more of the circuitized cores.
The cores are stacked with prepreg between them and also between them and
external copper layers (Fig. 1). Prepreg is a partially cured (B-staged) glass-
resin sheet that will become liquid and flow during the composite lamination
process. A large part of the instability at this process is caused by the prepreg.
Substitution of fully cured dielectric layers in place of the composite prepreg
(Fig. 2) eliminates up to 85% of the movement. The dielectric layers have an
adhesive applied to bond them to adjacent cores and copper. Adhesive need not
be restricted to the resin used in prepreg. Adhesive is normally in the range of 0.002 inch thick. This is governed by the need for fill in power and signal planes.
The end result is greatly improved laminate stability that provides better
registration yields. It also gives more product design latitude.