CIS Quality Control & Inspection Procedures 3 — Questions and Answers
Question 1: An inspector observes a solder bridge between two adjacent SMD pads on a Class 2 assembly. Which of the following best describes the disposition?
- Process indicator — monitor but accept
- Acceptable if the bridge is less than 0.1 mm wide
- Defect — requires rework or rejection (Correct answer)
- Target condition — ideal fillet formation
Correct answer: Defect — requires rework or rejection
Solder bridges between conductors that should not be electrically connected are unconditional defects under IPC-A-610 for all product classes.
Question 2: What is the purpose of a control chart in a PCB assembly quality system?
- To document all non-conforming units found during final inspection
- To track process variation over time and detect out-of-control conditions (Correct answer)
- To record the AQL level applied to each production lot
- To certify that solder paste meets J-STD-005 requirements
Correct answer: To track process variation over time and detect out-of-control conditions
Control charts (SPC tools) monitor process metrics over time, enabling detection of trends or special-cause variation before defects are produced.
Question 3: Per IPC-A-610, which condition is allowed for a Class 1 product but not for Class 3 regarding chip component solder joints?
- Any solder wetting on the component end cap
- Less than 25% side-overhang of the component end cap
- End-cap solder coverage extending only onto the bottom face (Correct answer)
- Solder fillet height below the top of the component termination
Correct answer: End-cap solder coverage extending only onto the bottom face
For Class 1, solder restricted to only the bottom (land) face of a chip component termination may be acceptable, whereas Class 3 requires solder on the end cap for maximum mechanical strength.
Question 4: When performing solderability testing per J-STD-003, what does the wetting balance test measure?
- The melting temperature of the solder alloy
- The force exerted on a component lead as it is immersed in molten solder (Correct answer)
- The volume of solder deposited on a test coupon
- The thickness of the intermetallic compound layer
Correct answer: The force exerted on a component lead as it is immersed in molten solder
The wetting balance (Meniscograph) test measures the time-force curve as a lead is immersed in solder, quantifying the speed and degree of solder wetting.
Question 5: A CIS inspector observes a through-hole lead that extends 0.5 mm beyond the secondary side of the board on a Class 3 assembly. Per IPC-A-610, this is:
- Acceptable if solder covers the lead tip
- A defect — lead protrusion is below the minimum (Correct answer)
- A process indicator requiring process review
- Acceptable for all classes if solder fill is 100%
Correct answer: A defect — lead protrusion is below the minimum
IPC-A-610 Class 3 requires a minimum lead protrusion of 0.5 mm (some versions specify slightly higher), so 0.5 mm is at the borderline — verify against the current revision, but insufficient protrusion is a defect.
Question 6: What does the term 'Cpk' represent in a PCB assembly quality control context?
- The number of defects per unit in a lot
- A process capability index accounting for both spread and centering relative to spec limits (Correct answer)
- The AQL applied to a given inspection lot
- The ratio of scrap cost to total production cost
Correct answer: A process capability index accounting for both spread and centering relative to spec limits
Cpk measures process capability by comparing the process spread to the specification limits while also accounting for how centered the process is between those limits.
Question 7: Which of the following is an example of a destructive inspection technique used in PCB quality assurance?
- X-ray inspection of BGA solder balls
- Cross-sectioning a solder joint for metallographic analysis (Correct answer)
- AOI scanning of populated boards
- Flying probe electrical test
Correct answer: Cross-sectioning a solder joint for metallographic analysis
Cross-sectioning (microsectioning) requires cutting and polishing a sample, permanently destroying the board, but reveals internal joint quality, barrel fill, and intermetallic layers.
CIS Quality Control & Inspection Procedures 3
An inspector observes a solder bridge between two adjacent SMD pads on a Class 2 assembly.
Which of the following best describes the disposition?