3-31
Because most replacement flat packs come with leads that are longer than required, they must be
trimmed before they are soldered. The removed part is used as a guide in determining lead length.
Surgical scissors or scalpels are recommended for use in cutting flat-pack leads. Surgical scissors permit
all leads to be cut to the required lead length in a smooth operation with no physical shock transmitted to
the IC.
LAP-SOLDERING CONNECTIONS.—Before a connection is lap-soldered, the solder pads are
cleaned and pretinned and the component leads are tinned. This is particularly important if they are gold
plated. The IC is properly positioned on the pad areas, and the soldering process is a matter of "sweating"
the two conductors together. When multilead components, such as ICs, are soldered, a skipping pattern is
used to prevent excessive heat buildup in a single area of the board or component. When soldering is
completed, all solder connections are thoroughly cleaned. All joints should be inspected and tested. The
standards of workmanship are more specific for flat-pack installation.
Q24. When removing the component, under what circumstances may component leads be clipped?
Q25. How are imbedded TOs removed once the leads are free?
Q26. How is a flat pack removed from a pcb?
Q27. How do you prevent excessive heat buildup on an area of a board when soldering multilead
components?
Q28. What are the two final steps of any repair?
REPAIR OF PRINTED CIRCUIT BOARDS AND CARDS
Removal and replacement of components on boards and circuit cards are, by far, the most common
types of repair. Equally important is the repair of damaged or broken cards. Proper repair of damaged
boards not only maintains reliability of the board but also maintains reliability of the system.
Cards and boards may be damaged in any of several ways and by a number of causes. Untrained
personnel making improper repairs and technicians using improper tools are two major causes of
damage. Improper shipping, packaging, storage, and use are also common sources of damage. The source
of damage most familiar to technicians is operational failure. Operational failures include cracking caused
by heat, warping, component overheating, and faulty wiring.
Before attempting board repairs, the technician should thoroughly inspect the damage. The decision
to repair or discard the piece depends on the extent of damage, the level of maintenance authorized,
operational requirements, and the availability of repair parts and materials. The following procedures will
help you become familiar with the steps necessary to repair particular types of damage. Remember, only
qualified personnel are authorized to attempt these repairs.
Repair of Conductor and Termination Pads
Conductor (run) and pad damage is very common. The technician must examine the board for nicks,
tears, or scratches that have not broken the circuit, as well as for complete breaks, as shown in figure 3-
23. Crack damage may exist as nicks or scratches in the conductor. These nicks or scratches must be
repaired if over one-tenth of the cross-sectional area of the conductor is affected as current-carrying
capability is reduced. Cracks may also penetrate the conductor.
