CIS CIS Rework, Repair & Modification 1 — Questions and Answers
Question 1: Which IPC standard is the primary reference for rework, repair, and modification of electronic assemblies?
- IPC-A-610
- IPC-7711/7721 (Correct answer)
- IPC-2221
- IPC-6012
Correct answer: IPC-7711/7721
IPC-7711/7721 (Rework, Modification and Repair of Electronic Assemblies) is the primary IPC standard covering procedures for reworking and repairing PCB assemblies.
Question 2: What is the key difference between 'rework' and 'repair' in IPC terminology?
- Rework restores the assembly to original design; repair allows deviation from original design to restore function (Correct answer)
- Rework is performed by operators; repair requires engineer approval
- Rework applies only to through-hole components; repair applies to SMT only
- Rework involves replacing components; repair involves re-soldering existing joints only
Correct answer: Rework restores the assembly to original design; repair allows deviation from original design to restore function
Rework restores the assembly to its original design intent within acceptable workmanship standards; repair involves processes that deviate from original design to restore functional capability.
Question 3: What is the maximum number of times a through-hole plated barrel may be thermally stressed during rework per IPC-7711?
- One time only
- Two times (original solder plus one rework)
- Four times (Correct answer)
- There is no IPC limit on thermal cycles
Correct answer: Four times
IPC-7711 generally limits plated through-holes to a maximum of four thermal excursions (original solder plus up to three rework operations) to prevent barrel fatigue and cracking.
Question 4: When removing a BGA component for rework, which technique is most commonly used?
- Hot air pencil direct on each solder ball individually
- Localized infrared or hot-air rework station that heats the entire BGA body uniformly (Correct answer)
- Immersion in solder pot to melt all balls simultaneously
- Wicking with desoldering braid across the component body
Correct answer: Localized infrared or hot-air rework station that heats the entire BGA body uniformly
BGA rework requires a controlled rework station (infrared or hot-air convection) that heats the entire component uniformly to reflow all solder balls simultaneously without damaging adjacent components.
Question 5: Which tool is used for the controlled removal of desoldering braid (wick) excess from a PCB pad without lifting the land?
- Vacuum desoldering tool
- Side-cutting pliers trimmed close to the pad
- Low-temperature soldering iron with a chisel tip held at a shallow angle to slide braid off (Correct answer)
- Hot air pencil to loosen the braid before lifting
Correct answer: Low-temperature soldering iron with a chisel tip held at a shallow angle to slide braid off
A soldering iron at a low angle is used to gently reheat and release desoldering braid from the pad, preventing the mechanical force of pulling that could lift or damage the pad.
Question 6: What is 'skipping' in the context of wave soldering rework evaluation?
- A component that moved from its pad during rework
- A through-hole lead that did not receive solder during wave soldering, leaving an open joint (Correct answer)
- A flux skip causing areas of unwetted pads
- A wave soldering defect where alternating joints are bridged
Correct answer: A through-hole lead that did not receive solder during wave soldering, leaving an open joint
A 'skip' or 'solder skip' is a through-hole lead that passed over the wave without receiving solder, resulting in an open (no solder) joint.
CIS CIS Rework, Repair & Modification 1
Which IPC standard is the primary reference for rework, repair, and modification of electronic assemblies?