CIT Acceptability of Electronic Assemblies 3 — Questions and Answers
Question 1: For a chip component (0402) on a Class 2 assembly, the maximum side overhang allowable relative to the land is:
- 0% of component width
- 25% of component width
- 50% of component width (Correct answer)
- 75% of component width
Correct answer: 50% of component width
IPC-A-610 allows up to 50% side overhang for chip components on Class 2 assemblies before it becomes a defect.
Question 2: What is the IPC-A-610 term for a solder joint condition where solder has not wetted the component termination or land surface?
- Dewetting
- Nonwetting (Correct answer)
- Cold joint
- Bridging
Correct answer: Nonwetting
Nonwetting occurs when solder fails to wet and adhere to the base metal surface at all.
Question 3: A gull-wing lead's toe extends beyond the land end on a Class 2 assembly. Per IPC-A-610, this is:
- Always a defect
- Acceptable if the solder joint criteria are met (Correct answer)
- Acceptable only with engineering approval
- A process indicator only
Correct answer: Acceptable if the solder joint criteria are met
Toe overhang on gull-wing leads is acceptable for Class 2 provided the solder joint meets all other criteria.
Question 4: According to IPC-A-610, 'lifted lands' or pad liftoff is classified as:
- A process indicator requiring review
- Acceptable for Class 1 only
- A defect for all classes (Correct answer)
- Target condition if less than 50% lifted
Correct answer: A defect for all classes
Lifted lands/pad liftoff is a defect condition for all classes per IPC-A-610.
Question 5: For BGA components, IPC-A-610 inspection of solder joints typically relies primarily on:
- Visual inspection under 40× magnification
- X-ray inspection or automated optical inspection (Correct answer)
- Manual probing of each solder ball
- Cross-section analysis of every joint
Correct answer: X-ray inspection or automated optical inspection
BGA joints are hidden under the package and require X-ray or AOI for inspection per IPC-A-610 guidance.
Question 6: A solder ball found on the surface of a PCB assembly (not attached to a joint) is classified per IPC-A-610 as:
- Acceptable if smaller than 0.13 mm
- A process indicator if isolated
- A defect if it can cause a short circuit (Correct answer)
- Always a target condition
Correct answer: A defect if it can cause a short circuit
Solder balls that can cause electrical shorts or detach and create shorts are defects per IPC-A-610.
Question 7: Which SMT solder joint feature is described as solder that has pulled away from the land after initially wetting, leaving a thin film?
- Nonwetting
- Dewetting (Correct answer)
- Bridging
- Voiding
Correct answer: Dewetting
Dewetting is when molten solder initially wets but then recedes, leaving an irregular, thinly coated surface.
CIT Acceptability of Electronic Assemblies 3
For a chip component (0402) on a Class 2 assembly, the maximum side overhang allowable relative to the land is: