Make Electronics

Experiment 12: Joining Two Wires Together

106 Chapter 3

BAckground

Soldering myths

Myth #1: Soldering is very difficult.

Millions of people have learned how to do it, and statis-

tically, you are unlikely to be less coordinated than all

of them. I have a lifelong problem with a tremor in my

hands that makes it difficult for me to hold small things

steadily. I also get impatient with repetitive detail work.

If I can solder components, almost anyone should be

able to.

Myth #2: Soldering involves poisonous chemicals.

Modern solder contains no lead. You should avoid

inhaling the fumes for prolonged periods, but that also

applies to everyday products such as bleach and paint.

If soldering was a significant health hazard, we should

have seen a high death rate among electronics hobby-

ists decades ago.

Myth #3: Soldering is hazardous.

A soldering iron is less hazardous than the kind of iron

that you might use to iron a shirt, because it delivers

less heat. In fact, in my experience, soldering is safer

than most activities in a typical home or basement

workshop. That doesn’t mean you can be careless!

Soldering alternatives

As recently as the 1950s, connections inside electronic ap-

pliances such as radio sets were still being hand-soldered by

workers on production lines. But the growth of telephone

exchanges created a need for a faster way to make large

numbers of rapid, reliable point-to-point wiring connec-

tions, and “wire wrap” became a viable alternative.

In a wire-wrapped electronics project, components are

mounted on a circuit board that has long, gold-plated,

sharp-cornered square pins sticking out of the rear. Special

silver-plated wire is used, with an inch of insulation stripped

from its ends. A manual or power-driven wire-wrap tool

twirls the end of a wire around one of the pins, applying

sufficient tension to “cold-weld” the soft silver plating of

the wire to the pin. The wrapping process exerts sufficient

pressure to make a very reliable joint, especially as 7 to 9

turns of wire are applied, each turn touching all four corners

of the pin.

During the 1970s and 1980s, this system was adopted by

hobbyists who built their own home computers. A wire-

wrapped circuit board from a hand-built computer is shown

in Figure 3-37. The technique was used by NASA to wire the

computer in the Apollo spacecraft that went to the moon,

but today, wire-wrapping has few commercial applications.

The widespread industrial use of “through-hole” compo-

nents, such as the chips on early desktop computers, en-

couraged development of wave soldering, in which a wave

or waterfall of molten solder is applied to the underside of a

preheated circuit board where chips have been inserted. A

masking technique prevents the solder from sticking where

it isn’t wanted.

Today, surface-mount components (which are significantly

smaller than their through-hole counterparts) are glued to

a circuit board with a solder paste, and the entire assembly

is then heated, melting the paste to create a permanent

connection.

Figure 3-37. This picture shows some of the wire-wrapping in

Steve Chamberlin’s custom-built, retro 8-bit CPU and com-

puter. “Back in the day,” connecting such a network of wires

with solder joints would have been unduly time-consuming and

prone to faults. Photo credit: Steve Chamberlin.