nowevery piece of electronic
equipment is built up on one or more printed circuit or
‘PC’ boards. Each board not only supports the smaller
components, but also supplies the wiring which links
them all together. This makes assembly and construction
much easier, and also results in a product with greater
reliability.
As you’re no doubt aware, most simple PC boards
consist of a thin sheet of insulating material with thin
copper connection pads and tracks or ‘traces’ attached
to one or both sides. (More complex multi-layer boards
are made from a number of even thinner boards
sandwiched together under heat and pressure, so they
have copper pads and tracks i in ns si id de e the insulating
material as well.)
The first PC boards had the basic insulating ‘substrate’
made from a laminate of paper and synthetic resin,
bonded under heat and pressure to form S SR RB BP P
(synthetic resin bonded paper) material. This is still used
for PC boards in some mass produced consumer
equipment, because of its low cost. However SRBP is
fairly brittle and has a tendency to absorb moisture, so
most modern boards for higher-quality equipment use a
laminate made from sheets of woven glass cloth bonded
with epoxy resin, again under heat and pressure. This is
known as e ep po ox xy y f fi ib br re eg gl la as ss s laminate material, and it’s not
only strong and flexible, but has excellent electrical
insulating properties as well.
How are the conducting pads and tracks added to one
or both sides of this laminate? Well, there are a variety
of possible ways of doing this, including printing them
directly on the surface in conducting metallic inks. It’s
also possible to get small pads and thin strips punched
out of thin copper foil, which can be cemented onto the
surface(s) of the substrate sheet. But the most common
approach is to laminate thin sheets of pure copper metal
foil to one or both sides of the substrate sheets as
they’re being made, and then remove the unwanted
metal later to leave just the wanted pattern of
conducting pads and tracks.
So the starting place for most PC boards is a sheet of
epoxy fibreglass laminate complete with thin copper foil
covering either one side (‘single sided laminate’) or both
sides (‘double sided laminate’
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