The following is a study Guide Snapshot on the topic COPPER CLAD
LAMINATES. The  topic relates to QODs #128; #129; #130.


COPPER CLAD LAMINATES

Copper clad laminates used to produce printed boards consist of
three constituents;  the resin which is a natural or synthetic
resinous material, the reinforcement such as different forms of
paper, matte glass or woven glass, and the copper foil.  The
resin and reinforcement make up the base material which is the
insulating material upon which a conductive pattern may be
formed.  Base material may be rigid or flexible or both.  It may
be a dielectric or insulated metal sheet.
   
The copper is available in rolled, annealed, or electrodeposited
(ED).  The copper forms the cladding.  Unclad base material can
also be used when producing printed boards using additive
technology, where copper is deposited only where required.  

The most popular laminate resin system is epoxy.  The most common
thicknesses for laminate for rigid base material is .75 mm (.030 
inches), 1.5 mm (.060 inches), 2.40 mm (.090 inches), however,
the minimum thicknesses for rigid base material is 0.05 mm (.002
inches).  There are various improvements that have been made to
epoxy resins over time.  These include difunctional epoxy,
multifunctional epoxy, BT epoxy and others.  All of the
improvements are intended to provide better and more consistent
dimensional stability and minimal thermal expansion
characteristics.

The most popular reinforcement is woven glass.  It provides the 
structural strength to the resin, and comes in various
thicknesses to accommodate the various thicknesses of the sheets
used to produce the laminate.  A sheet of woven glass that has
been coated with resin is referred to as "prepreg" or
"preimpregnated" resin.  This material also is known as "B" stage
since it is at a partial stage of cure of the resin.  "B" stage
material can be handled, combined with other sheets and then
laminated under heat and pressure to form the base material.

Copper foil thickness is defined in ounces.  The origin of the
practice comes from the days when a copper foil was used to cover
roofs.  Therefore,  half ounce copper is defined as the weight of
a square foot of copper foil that is 35 micrometers thick (0.0007
inches).  Subtractive boards can be made by the process that
starts with copper foil which is then plated, and etched where
the unwanted copper is removed.  Printed boards can also be
additively produced, where the copper is patterned on a bare
laminate in an electroless process (no electricity involved in
moving the molecules of copper to the surface of the board).

New resins are appearing on the scene.  These include such
products as cyanade ester, polyimide, or PTFE (teflon), however
epoxy resin is still the most popular resin used in the United
States.

Another polymer material used with the printed board is an epoxy 
permanent polymer coating known as soldermask.  The fact that the
polymers are very similar to the laminate permits good adhesion
of the two systems to one another.  

Resources:  IPC-T-50, Specific terms, and IPC-D-275 para 3.7.3.1,
3.8.1, 3.8.1.12, 3.8.2.1, 3.8.3.1, 3.8.5.1, 5.5.1

3A.1