CIT Rework, Modification, and Repair of Electronic Assemblies 3

Question 1

What is the primary reason for pre-baking PCB assemblies before BGA rework?

Accepted Answer

To remove absorbed moisture and prevent popcorning

Answer

Pre-baking drives out absorbed moisture from the PCB and component packages, preventing steam-induced delamination (popcorning) during reflow.

Question 2

When repairing a lifted SMT pad, the technician must ensure the epoxy adhesive cure extends under the replacement pad. Why is this critical?

Accepted Answer

To provide mechanical anchoring so the pad does not lift again under thermal cycling

Answer

Epoxy under the replacement pad anchors it mechanically so thermal expansion and contraction during cycling do not cause re-lifting.

Question 3

According to IPC-A-610, a solder joint on a Class 2 through-hole assembly is acceptable if solder fill in the barrel is a minimum of:

Accepted Answer

50%

Answer

IPC-A-610 requires a minimum of 50% barrel fill for Class 2 through-hole solder joints to be considered acceptable.

Question 4

A technician must repair a cracked solder joint on a BGA ball that is not accessible for direct inspection. What technique is used to verify joint quality after repair?

Accepted Answer

X-ray inspection (2D or 3D)

Answer

X-ray inspection (2D or 3D CT) is used to verify BGA solder joint quality, including voids and opens, because the joints are hidden beneath the package.

Question 5

During chip removal on an SMT assembly, which tool setup is preferred to avoid pad damage on a 0201 component?

Accepted Answer

Tweezers with hot-air rework station at controlled temperature

Answer

Tweezers combined with a controlled hot-air station allows simultaneous reflow of both terminations, preventing pad damage from mechanical force.

(CIT) Certified IPC Trainer Practice Test

(CIT) Certified IPC Trainer Practice Test

CIT Rework, Modification, and Repair of Electronic Assemblies 3