3-18. The repair of circuit cards
3. Cracks, chips, and gouges are not
requires proper tools and careful work
acceptable on the contact strip edge of
or undue force applied to components or
to the circuit card, can seriously dam-
4. Cracks or chips should not extend
from one conductor to another conductor.
age the assembly. In general, the fol-
lowing precautions should be observed:
5. Delamination of the base material
is not acceptable.
1. Never try to save a component part
3-15. CIRCUIT CARD ETCH STANDARDS.
at the possible expense of damaging a
Circuit card etch standards are as
circuit card. Most component parts can
be clipped from the circuit card. When
clipping, the defective part, be careful
1. Cracks, pits, or voids in the
to protect the printed circuit conductor
contact strip area are not acceptable.
(etch) and other component parts.
2. Scratches which expose the copper
are not acceptable.
3. Cracks, pits , or voids in any etch
2. A vacuum resoldering unit should
which reduce the conductor by more than
be used, if available, to remove the
20 percent are not acceptable. No
leads of a clipped part. The technical
defect should reduce the conductor to
manual for the vacuum resoldering unit
less than 0.010 inch.
contains operating procedures for the
unit. Basically, the vacuum resoldering
4. Lifting of a conductor above the
unit operates as follows: a high flow
surface of the board is not acceptable.
hole, across the pads and around the
leads to remove the solder and cool down
5. Reduction in the area of any pad
in excess of 25 percent is not accept-
these areas to prevent reseating of the
able. Cracks, pits, or voids should not
lead. At the same time, the temperature-
extend to a plated-through hole.
controlled desoldering tip, which ini-
tially provided the heat to melt the
3-16. STORAGE AND HANDLING
solder, is cooled rapidly by the air
flow to prevent further heat from being
CARDS. When stored, circuit cards
applied to the workpiece. Once the air
should be wrapped individually in poly-
flow is stopped, the tip heats up rap-
ethylene bags , or equivalent, and
stacked in storage pans. Other objects
idly for continued vacuum desoldering.
The coaxial, in-line design of the hand-
should not be placed in the storage pans
piece allows molten solder and clipped
with circuit cards. Avoid touching the
leads to be drawn into the heat-resistant
circuit card surface with bare hands or
chamber where solder is solidified.
fingers. Handle the circuit card by its
3. Exercise care when using a sol-
3-17. CIRCUIT CARD REPAIR PROCEDURES.
dering iron to remove the leads of a
clipped part, to connect a new part, or
to service the circuit card itself.
Circuit cards are easily damaged by
Vapors emitted during certain
heat. Prolonged application of heat
circuit card repair procedures
will destroy the adhesive quality of the
may be irritating to personnel.
bonding agent that holds the printed
Always perform circuit card
etch to the circuit card. Use the recom-
repair procedures in a well