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What material is applied to electronic assemblies to prevent damage from corrosion, moisture, and stress?
Conformal coating.
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What three methods are used to remove protective material?
- Chemical
- Mechanical
- Thermal.
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What chemicals are used to remove protective material?
Solvents or xylene and trichloroethane.
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Abrasion, cutting, and peeling are examples of what type of protective material removal?
Mechanical.
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Why should the coating material be replaced once the required repair has been completed?
To ensure protective characteristics are maintained.
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What term is used to identify the procedure of connecting one side of a circuit board with the other?
Interfacial connections.
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Name two types of through-hole termination.
Clinched lead, straight-through, and offset pad.
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Turret, bifurcated, and hook terminals are used for what type of termination?
Above-the-board termination.
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When a lead is soldered to a pad without passing through the board, it is known as what type of termination?
On-the-board termination.
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When does most printed circuit board damage occur?
During disassembly or repair.
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What procedure involves the use of finely braided copper wire to remove solder?
Wicking.
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What is the most effective method of solder removal?
Continuous vacuum.
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When, if at all, should the heat-and-shake or the heat-and-pull methods of solder removal be used?
These methods should not be used.
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To what standards should a technician restore electronic assemblies?
Manufacturer's standards.
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How is oxide removed from pads and component leads?
A fine abrasive.
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Leads are formed approximately how many degrees from their major axis?
90 degrees.
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When you replace components, identification marks must meet what requirements?
They should be readable from a single point.
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In what direction are component leads clinched on single- and double-sided boards?
In the direction of the run.
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What is solderability?
The ease with which molten solder wets the surfaces of the metals to be joined.
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What is the most common source of heat in electronic soldering?
Conductive-type soldering iron.
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What determines the shape and size of a soldering iron tip?
The type of work to be done.
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What term describes a device used to conduct heat away from a component?
A thermal shunt.
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What is the appearance of a properly soldered joint?
Bright and shiny with no cracks or pits.
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When removing the component, under what circumstances may component leads be clipped?
If the component is known to be defective or if the board may be damaged by normal desoldering.
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How are imbedded TOs removed once the leads are free?
By pushing it gently out of the board.
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How is a flat pack removed from a pcb?
Heat each lead and lift with tweezers.
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How do you prevent excessive heat buildup on an area of a board when soldering multilead components?
Use a skipping pattern.
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What are the two final steps of any repair?
Inspect and test.
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List three causes of damage to printed circuit boards.
- Operational failures
- Repairs by untrained personnel
- Repair using improper tools
- Mishandling
- Improper shipping
- Packaging
- Storage.
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What is the preferred method of repairing cracked runs on boards?
Clinched staple.
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Damaged or missing termination pads are replaced using what procedure?
Epoxy a replacement pad to the board, set an eyelet, and solder it.
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How is board damage caused by technicians?
Repairs by untrained personnel and technicians using improper tools.
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What combination of materials is used to patch or build up damaged areas of boards?
Epoxy and fiberglass powder.
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List two causes of damage to ESD-sensitive electronic components.
Esd, improper stowage, and improper handling.
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What is the purpose of the wrist ground strap?
To discharge any static charge built up in the body.
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What is the cause of most accidents?
Deviation from prescribed safe operating procedures.
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