3-7
Conformal coating application techniques vary widely. These techniques depend on material type,
required thickness of application, and the effect of environmental conditions on curing. These procedures
cannot be effectively discussed here.
Q1. What material is applied to electronic assemblies to prevent damage from corrosion, moisture,
and stress?
Q2. What three methods are used to remove protective material?
Q3. What chemicals are used to remove protective material?
Q4. Abrasion, cutting, and peeling are examples of what type of protective material removal?
Q5. Why should the coating material be replaced once the required repair has been completed?
REMOVAL AND REPLACEMENT OF DISCRETE COMPONENTS
To properly perform the required repair, the 2M technician must be knowledgeable of the techniques
used by manufacturers in the production of electronic assemblies. The techniques, materials, and types of
components determine the repair procedures used.
Interconnections and Assemblies
Assemblies may range from simple, single-sided boards with standard-sized components to double-
sided or multilayered boards with miniature and microminiature components. The variations in
component lead termination and mounting techniques used by manufacturers present the technician with a
complex task. For example, the 2M technician is concerned about the type of solder joints on the module.
To determine the solder joint type, the technician must consider the board circuitry, hole reinforcement,
and lead termination style.
Recall the discussion from topic 1 on printed circuit board construction and the types of
interconnections used. Single-sided and some double-sided boards have UNSUPPORTED HOLES where
component leads are soldered to the pad. The clearance-hole method is also an interconnection with no
hole support. SUPPORTED HOLES are those that have metallic reinforcement along the hole walls.
In addition to the plated-through hole you studied earlier, EYELETS, shown in figure 3-4, view (A),
view (B), and view (C), are also used in both manufacturing and repair. These hole-reinforcing devices
are usually made of pure copper, but are often plated with gold, tin, or a tin-lead alloy. The copper-based
eyelet is pliable; when set, it reduces the possibility of circuit board damage. Eyelets may be inserted into
single-sided or double-sided boards and are of three different types - ROLL SET, FUNNEL SET, and
FLAT SET. All three are types referred to as INTERFACIAL CONNECTIONS. Interfacial connections
identify the procedure of connecting circuitry on one side of a board with the circuitry on the other side.
