CIS Quality Control & Inspection Procedures 2 — Questions and Answers
Question 1: During a first-article inspection, a CIS inspector finds solder joints on a fine-pitch QFP that appear dull but have adequate fillet geometry. What is the most likely cause?
- Insufficient flux activation
- Cold solder joint from inadequate heat
- Grainy appearance from lead-free alloy solidification (Correct answer)
- Excess solder causing bridging risk
Correct answer: Grainy appearance from lead-free alloy solidification
Lead-free solder alloys (e.g., SAC305) naturally produce a duller, grainier surface finish compared to tin-lead solders due to their solidification characteristics.
Question 2: Which IPC-A-610 acceptance condition describes a solder connection that does not meet minimum requirements but is not cause for rejection under certain conditions?
- Target condition
- Acceptable condition
- Process indicator (Correct answer)
- Defect condition
Correct answer: Process indicator
A 'process indicator' in IPC-A-610 flags a condition that could indicate process control problems but does not by itself constitute a defect.
Question 3: When inspecting through-hole components, what is the minimum acceptable solder fill percentage in the barrel for a Class 3 assembly?
- 50%
- 75%
- 100% (Correct answer)
- No minimum is specified
Correct answer: 100%
IPC-A-610 Class 3 (high-reliability) requires 100% vertical fill in the through-hole barrel to ensure maximum joint integrity.
Question 4: An inspector using automated optical inspection (AOI) flags a component as misaligned, but manual re-inspection finds it acceptable. What is the best corrective action?
- Override the AOI result and accept the board
- Recalibrate the AOI thresholds using golden-board references (Correct answer)
- Remove and replace the component anyway
- File a non-conformance report for the AOI machine
Correct answer: Recalibrate the AOI thresholds using golden-board references
AOI false-call rates should be managed by recalibrating the system against approved golden-board samples to reduce pseudo-defects without compromising defect detection.
Question 5: Per IPC-7711/7721, what is the maximum number of times a surface-mount pad may be reworked before it must be scrapped for a Class 2 product?
- 1 time
- 2 times
- 3 times
- The standard does not set a limit; engineering disposition is required (Correct answer)
Correct answer: The standard does not set a limit; engineering disposition is required
IPC-7711/7721 does not specify a universal rework cycle limit; instead, engineering disposition is required based on pad condition, substrate type, and product class.
Question 6: What does a 'lifted pad' defect indicate during PCB inspection?
- The copper pad has delaminated from the substrate surface (Correct answer)
- The solder mask has lifted away from the copper trace
- The component lead is bent upward above the pad
- Excessive flux residue has lifted the solder fillet
Correct answer: The copper pad has delaminated from the substrate surface
A lifted pad occurs when the copper foil pad separates from the laminate substrate, typically caused by excessive heat, mechanical stress, or repeated rework.
Question 7: Which sampling plan standard is most commonly referenced in IPC documentation for incoming inspection of electronic components?
- MIL-STD-105 / ANSI/ASQ Z1.4 (Correct answer)
- ISO 9001
- IPC-A-600
- JESD22
Correct answer: MIL-STD-105 / ANSI/ASQ Z1.4
ANSI/ASQ Z1.4 (formerly MIL-STD-105) provides attribute sampling procedures widely referenced for incoming component inspection in IPC environments.
CIS Quality Control & Inspection Procedures 2
During a first-article inspection, a CIS inspector finds solder joints on a fine-pitch QFP that appear dull but have adequate fillet geometry.
What is the most likely cause?