60 Fundamentals of Electricity and Electronics
3.2 SPECIAL CONDUCTOR
PATHWAYS
There are several special conductor pathways used in
electrical and electronic work. They are the breadboard,
printed circuit board, and metal chassis. These pathways
serve special needs. Yet, their main purpose is the same as
any other conductor, to provide a good conductive path
for electron flow.
Breadboards
A breadboard is a useful device for learning about cir-
cuits. A breadboard consists of a series of holes aligned in
rows across the entire surface of an insulation material,
such as plastic. Copper strips are run in parallel under the
rows of holes and are used as conductor pathways. Elec-
tronic devices, such as resistors and transistors, are inserted
into the holes. Jumper wires are then used to make addi-
tional connections between the devices. The breadboard
provides an easy system for constructing circuits quickly.
The boards are commonly used in experiments or to make
a prototype of a circuit before the circuit is soldered or con-
structed in mass assembly systems. Some boards are called
proto boards. See Figure 3-11.
circuit board layout. The heat sink area is a wide copper
surface that is used for a common connection point for
many devices, as well as to dissipate the heat generated by
the electronic devices. Edge connectors provide the elec-
trical point of attachment to other electrical equipment.
The conductor paths can be less than 0.001 inch in
thickness. These strips can be on one side or both sides,
depending on the design of the board. The currents used
on most circuit boards are very low and usually do not
require heavy wiring.
Construction of printed circuit boards
A printed circuit board starts out with a thin sheet of
copper foil covering the entire surface of an insulating
material. If the PCB is to be double sided, both sides will
be covered with a thin sheet of foil. There are a couple of
common methods used to produce the circuit design on
the foil. The layout of the circuit can be put on the copper
using a resist material. The board is then dipped in an
etchant. The etchant removes all of the copper surface not
protected by the resist material. The board is then cleaned
to remove any excess resist or etchant. Holes are then
drilled at the connection pads.
Printed circuit boards can also be made using a pho-
tographic process. Light-sensitive material covers the sur-
face of the board. A negative of the circuit board layout is
placed over the board. The board is then exposed to light
and developed in a manner similar to that used in
photography. After developing, the unexposed areas are
washed away with a solvent. The exposed area, the pat-
tern of the circuit, remains. The board is then etched as
was described in the first method.
Circuit board components can be installed by hand
or by automated systems. The choice is usually based on
Heat sink
area
Connection
pad
Conductor
path
Edge
connectors
Figure 3-12. A typical printed circuit board layout consists
of thin foil copper ribbons on the surface of an insulated
board.
Printed Circuit Boards
A printed circuit board (PCB) is made from a thin
layer of conductor material, usually copper foil, cut in
strips and attached to an insulated board. The strips act as
the circuit paths. Components are inserted through holes
in the insulated board and then soldered to the conductive
strips at circular spots called connection pads. The
connection pads provide the extra area required for mak-
ing good solder connections. Figure 3-12 shows a typical
Figure 3-11. A common breadboard.