01 March 2005
NAVAIR 01-1A-509-1
TM 1-1500-344-23-1
TO 1-1-689-1
3-14.2.3. Microbial Nutrients. Since fungi, bacteria,
concern after working hours because the absence of
and other microorganisms are classified as living, it was
shop personnel (body heat) and the lack of heat
previously thought that only materials derived from
generated by operating various equipment create lower
living organisms could provide food for microorganisms.
temperatures. Thermostats should be adjusted to
Thus, wool, cotton, feathers, and leather are known to
prevent excessive cooling and condensation after
be microbial nutrients. To a large extent this rule of
working hours.
thumb is still valid, but the increasing complexity of
synthetic materials makes it difficult, if not impossible, to
3-15.3. SOLDER FLUX CORROSION. The simple task
determine from the name alone whether a material will
of soldering a component in a circuit board can cause
support growth of microorganisms. Many otherwise
corrosion, often due to failure to remove flux residues.
resistant synthetic materials are rendered susceptible
Most metals exposed to the atmosphere develop a thin
to microbial attack by the addition of chemicals, which
film of oxide. This film is not visible and solder alone
change the properties of the material. In addition,
cannot dissolve it. During soldering operations, the
different species of microorganisms have different
addition of flux removes the oxide film and prevents
growth requirements. The service life, size, shape,
further metal oxidation. Although most flux is burned
surface smoothness, cleanliness, environment, and
away during the soldering process, some residues
species of microorganism involved all determine the
remain and must be removed. Residues from solder
degree of microbial attack on the affected item.
fluxes can degrade circuitry by causing solder joints to
corrode, causing corrosive flux vapors that settle on
adjacent components, reducing insulation resistance,
3-15. MAN-MADE ENVIRONMENTS.
changing the resistivity of the solder joint, and attracting
3-15.1. INDUSTRIAL POLLUTANTS. Carbon from
dirt and other contaminants that may absorb moisture.
internal combustion engine exhaust, nitrates from
Refer to ANSI/J-STD-001 for general solder information.
agricultural fertilizers and industrial processes, ozone
Refer to ANSI/J-STD-004, -005, -006 for solder flux
from electrical motors and welding operations, sulfur
requirements for securing connections in electrical or
dioxide from engine exhaust and industrial and ship
electronic equipment. Refer to NAVAIR 01-1A-505
smoke stacks, and sulfates from automobile exhaust
(Navy), TO 1-1A- 14 (Air Force), or TM 55-1500-323-24
are significant pollutants. Corrosive solutions form when
(Army) for additional information on solder fluxes and
these contaminants are absorbed by condensed
soldering techniques.
moisture. Many of the fumes and vapors emitted by
ships and from factories can greatly accelerate metal
3-15.4. EQUIPMENT HANDLING. Equipment removed
corrosion. Industrial atmospheres may exist over large
from aircraft for maintenance or inspection may be
areas, since wind may carry these corrodents many
exposed to various environments. Equipment that
miles from their source. The combination of these
requires handling or protection against the environment
pollutants contributes to the deterioration of non-metallic
should be preserved and packaged accordingly. In
materials and severe corrosion of metals.
some cases, special containers are furnished for the
purpose of protecting the equipment. Where containers
3-15.2. M A N U F A C T U R I N G , A S S E M B L Y A N D
or special packaging are not furnished, steps shall be
taken to provide the protection required. For example,
REPAIR. During the manufacture, assembly, or repair
a printed circuit board (PCB) that has been repaired but
of aircraft and subsystem components, many factors
not coated with conformal coating requires protection
that might lead to corrosion may be introduced. The use
against electrostatic discharge and contaminants. It
of unsuitable materials and improper material processing
should be placed in an antistatic bag and transported
can cause corrosion. Shearing or hole-punching
using a covered antistatic tote tray or fast pack from the
operations on some metal alloys, especially high-
repair station to the test bench. Components with
strength aluminum, may introduce stresses that
conductive coatings shall be protected from abrasion,
eventually lead to corrosion. Assembly or repair of
damage, and electrostatic discharge. Corrosion that
avionic components in areas contaminated by fumes or
develops as a result of improper handling or inadequate
vapors from adjacent operations (such as welding,
packaging, storage, and shipment is extremely
paint spraying, and solvent cleaning) may result in
destructive. Some of the same design characteristics
entrapment of fumes in the equipment and may cause
that support corrosion in equipment on board aircraft
corrosion. Air conditioned avionic shops are inherently
also lead to deterioration in inadequately packaged,
lower in temperature than surrounding spaces. In
stored, and shipped components. All uninstalled avionic
shops without humidity control, the air conditioning
equipment should be preserved and stored in shock
system can create condensation. This is of particular
