CIS CIS Rework, Repair & Modification 2 — Questions and Answers
Question 1: According to IPC-7711, what must be done before performing any rework on a Class 3 assembly?
- The assembly must be tested to verify the defect location
- Written procedures and engineering authorization must be in place (Correct answer)
- The entire board must be cleaned with IPA
- The rework technician must hold an IPC-A-610 CIS certification
Correct answer: Written procedures and engineering authorization must be in place
For Class 3 assemblies, IPC-7711 requires that rework be performed only with documented procedures and engineering authorization to maintain traceability and reliability.
Question 2: What is a 'jumper wire' modification in PCB repair, and what IPC standard governs it?
- A temporary wire used to test circuits before permanent repair, governed by IPC-A-610
- A conductor added to a PCB to correct a wiring error or replace a damaged trace, governed by IPC-7711/7721 (Correct answer)
- A current-limiting resistor added in series with a component, governed by IPC-2221
- An internal layer trace bypass using surface-mounted wire, governed by IPC-6012
Correct answer: A conductor added to a PCB to correct a wiring error or replace a damaged trace, governed by IPC-7711/7721
A jumper wire is an added conductor used to replace a damaged trace or correct a wiring error; IPC-7711/7721 provides specific requirements for acceptable jumper wire installation.
Question 3: What is the minimum recommended tip temperature for soldering standard Sn63/Pb37 solder in rework operations?
- 150°C
- 183°C (melting point only)
- 315–370°C (600–700°F) at the tip with appropriate dwell time (Correct answer)
- 450°C for rapid heat transfer
Correct answer: 315–370°C (600–700°F) at the tip with appropriate dwell time
Soldering iron tip temperatures of approximately 315–370°C (600–700°F) are standard for Sn63/Pb37 rework, providing adequate heat transfer while minimizing thermal damage risk.
Question 4: When reworking lead-free assemblies, why must technicians be careful about introducing tin-lead solder?
- Lead-free assemblies reject tin-lead solder due to different surface energy
- Mixing tin-lead into lead-free solder creates a low-melting-point bismuth-tin eutectic that severely weakens joints (Correct answer)
- Lead contamination voids the IPC-7711 rework qualification of the operator
- Mixing creates a tin-lead-silver alloy that increases solder joint brittleness
Correct answer: Mixing tin-lead into lead-free solder creates a low-melting-point bismuth-tin eutectic that severely weakens joints
Mixing tin-lead solder into lead-free joints can create low-melting bismuth-tin phases (if Bi is present) or create non-uniform alloy compositions that significantly reduce joint reliability and melting temperature.
Question 5: What is 'pad conditioning' during SMT rework?
- Applying fresh solder mask to exposed copper pads after component removal
- Cleaning, re-tinning, or reshaping the solder pad to its proper form before installing a replacement component (Correct answer)
- Testing pad adhesion strength before and after rework
- Applying adhesive to hold the replacement component during reflow
Correct answer: Cleaning, re-tinning, or reshaping the solder pad to its proper form before installing a replacement component
Pad conditioning involves cleaning residual solder from the pad, re-tinning with fresh solder if needed, and verifying the pad shape and condition before installing a replacement component.
Question 6: According to IPC-7711, rework documentation should include which of the following?
- The operator's personal preferences for soldering iron temperature
- Component reference designator, defect description, procedure used, materials used, and operator identification (Correct answer)
- Only the final pass/fail test result after rework
- The equipment serial number only
Correct answer: Component reference designator, defect description, procedure used, materials used, and operator identification
IPC-7711 rework documentation must include the reference designator, defect description, rework procedure number, materials used, and operator identification to maintain full traceability.
CIS CIS Rework, Repair & Modification 2
According to IPC-7711, what must be done before performing any rework on a Class 3 assembly?