example, tin is noted as “Sn,” silver is “Ag,” copper is “Cu,”
and lead is “Pb.”
Following this logic, the designation of a common lead-free solder is SAC305. This means that the alloy is made up
of 96.5% tin, 3% silver, and 0.5% copper. Knowing what
kind of solder alloy you will need to work with is important
because different solders will have different melting points
and will change the amount of heat you need to liquify the
solder quickly.
For example, SN63/PB37 tin-lead solder has a melting
point of 361°F (187°C), while some lead-free solders melt
at a temperature of approximately 422°F (217°C).
With this knowledge, you will be better able to limit
the maximum temperature during the soldering
operation and minimize the soldering time to make
sure you get a reliable solder joint. In addition, it is
important not to cross-contaminate lead-bearing and
lead-free soldering materials.
The next thing you’ll need for soldering is flux.
Flux is essential to assure solderability and the
formation of proper solder joints. The main purposes
of flux are to remove surface oxides from the
solderable surfaces and to aid in heat transfer. This
will allow the solder to “wet” or stick to the surface
better.
There are primarily two types used for hand
soldering operations. The first is rosin flux. Pure rosin
flux is weak at room temperature, but reacts strongly
with metal oxides at elevated temperatures. That’s
why we say that flux is heat activated. The other
main type of flux is No-Clean. No-Clean fluxes are
made of an entirely different composition compared
to rosin fluxes. They are largely composed of organic or
inorganic materials with approximately 97% being the
carrier (alcohol or water). In conjunction to an external flux
application, we also apply flux via the solder wire we use
(Figure 2). Solder wire may have either 1.1, 2. 2, or 3. 3
percent flux by volume in the core of the wire.
You’ll also want to think about which method you will
use to transfer heat when soldering. There are two
common types of heating methods used in hand soldering.
These types are convective (Figure 3) and conductive
(Figure 4).
SERVO 12.2014 59
Figure 2. Wire cored solder contains flux — make
sure you use the right alloy and flux.
Figure 3. Convective soldering is typically used for more
complex SMT components.
Figure 4. Conductive soldering.
Roboticists need a plethora of skills to create and
construct their automatons. Knowing how to solder
is a major part of moving from simple kits into the
realm of advanced circuits and chassis.
