Service manual

STP 11-25R13-SM-TG
A - 6
(10) Soldering aids are used for desoldering components. The slotted ends are for moving and
lifting component leads and the pointed ends are used to remove solder from the terminal holes and
slots. Figure A-11 shows the most common types of soldering aids.
Figure A-11. Common Soldering Aids
A-6. Solder.
Solder is a metal alloy composed primarily of tin and lead that has a relatively low melting point.
Other metals such as copper, bismuth, antimony, and silver may be added to change the melting point of
the solder. The two most common types of solder used for electronic equipment are 60/40 (60 percent
tin/40 percent lead) and 63/37 (63 percent tin/37 percent lead). Of these two, the 63/37 is preferred due
to its low melting point and eutectic characteristics. Eutectic means that the solder will change from a
solid to a liquid without going through a plastic (semi-solid) state. The 60/40 solder forms a stronger
solder joint and is used for general purpose soldering work.
A-7. Flux.
Flux is a highly corrosive cleaning agent that removes oxidation film from the surfaces to be
soldered, ensuring a clean metal-to-metal bond. There are three general types of flux: chloride (acid),
organic, and rosin. Rosin flux is most suited for electronic soldering applications. At room temperature,
rosin flux is inert and nonconductive; therefore, it is safe for use on electronic circuitry. When heated to
soldering temperatures, the flux becomes molten and highly corrosive.
A-8. Soldering Terms.
There are terms used in soldering which may be new to you. Some of these are listed below:
a. Eutectic solder
is a solder alloy that changes back and forth from solid state to liquid state
without ever going through a plastic or semisolid condition.
b. Dewetting
is a condition in which solder did not completely join a metal surface, as evidenced
by the partial or total separation of the solder from the connection and the absence of a solder fillet. This
is commonly known as a cold solder joint.