PCB Risk Assessment & Management 5 — Questions and Answers
Question 1: What is the purpose of a DFMEA (Design Failure Mode and Effects Analysis) in the PCB design process?
- To systematically identify potential failure modes, their causes, and their impact before design is released (Correct answer)
- To select the lowest-cost components
- To automate PCB routing
- To generate bill of materials automatically
Correct answer: To systematically identify potential failure modes, their causes, and their impact before design is released
DFMEA proactively identifies design weaknesses and their effects on system functionality, enabling risk prioritization and mitigation before fabrication.
Question 2: A PCB is designed for outdoor use but the designer does not specify a conformal coating. What is the primary risk?
- Moisture, condensation, and contaminants can cause corrosion and leakage currents leading to electrical failure (Correct answer)
- Increased board weight
- Higher assembly cost
- Longer lead time
Correct answer: Moisture, condensation, and contaminants can cause corrosion and leakage currents leading to electrical failure
Without conformal coating, outdoor PCBs are exposed to humidity and pollutants that can corrode conductors and create parasitic leakage paths.
Question 3: Which risk is specifically addressed by performing an electromagnetic compatibility (EMC) pre-compliance test during PCB development?
- Identifying EMI emissions or susceptibility issues before formal regulatory certification testing (Correct answer)
- Measuring board flatness
- Validating solder joint strength
- Checking BOM accuracy
Correct answer: Identifying EMI emissions or susceptibility issues before formal regulatory certification testing
Pre-compliance EMC testing catches radiation and immunity problems early when design changes are still inexpensive, reducing re-certification risk.
Question 4: What risk does a design with no test points for critical nets introduce during production?
- In-circuit testing (ICT) cannot probe key nodes, reducing fault coverage and increasing escape rate of defective boards (Correct answer)
- Higher BOM cost
- Slower PCB routing
- Lower component count
Correct answer: In-circuit testing (ICT) cannot probe key nodes, reducing fault coverage and increasing escape rate of defective boards
Without accessible test points, ICT fixtures cannot verify correct operation of critical nets, allowing defective boards to ship to customers.
Question 5: What risk does using a non-halogen-free laminate present when the PCB is used in a consumer product sold in Europe?
- Non-compliance with RoHS and REACH regulations restricting halogenated flame retardants (Correct answer)
- Improved thermal stability
- Better dielectric performance
- Lower moisture absorption
Correct answer: Non-compliance with RoHS and REACH regulations restricting halogenated flame retardants
Halogenated flame retardants are restricted under EU regulations, and using them in consumer products can result in legal non-compliance and product recalls.
Question 6: A PCB has dense component population with no keepout zones around connectors. What assembly risk does this create?
- Mechanical interference during connector mating/unmating can stress solder joints of adjacent components (Correct answer)
- Lower component cost
- Improved thermal dissipation
- Better high-frequency performance
Correct answer: Mechanical interference during connector mating/unmating can stress solder joints of adjacent components
Forces applied during connector use can flex the board and crack solder joints on nearby components if adequate clearance is not maintained.
Question 7: What is the risk of specifying too tight a tolerance on controlled impedance without confirming fabricator capability?
- Fabricator may reject the design or yield losses increase significantly if their process cannot meet the specification (Correct answer)
- Faster fabrication turnaround
- Lower cost per board
- Better EMC performance guaranteed
Correct answer: Fabricator may reject the design or yield losses increase significantly if their process cannot meet the specification
If the impedance tolerance is tighter than what the fabricator can reliably produce, yield drops and costs rise, or the order may be declined.
PCB Risk Assessment & Management 5
What is the purpose of a DFMEA (Design Failure Mode and Effects Analysis) in the PCB design process?