CID Research Methods & Evidence-Based Practice 2 — Questions and Answers
Question 1: When researching minimum conductor spacing for a 150V PCB application, which IPC document is the primary design reference?
- IPC-A-610 (Acceptability of Electronic Assemblies)
- IPC-2221 (Generic Standard on Printed Board Design) (Correct answer)
- IPC-6012 (Qualification and Performance for Rigid Boards)
- IPC-7711 (Rework, Modification and Repair)
Correct answer: IPC-2221 (Generic Standard on Printed Board Design)
IPC-2221 Table 6-1 provides voltage-dependent minimum conductor spacing requirements for various environmental conditions.
Question 2: A CID finds two applicable IPC standards with conflicting requirements for the same parameter. What is the correct evidence-based approach?
- Default to the older standard as it has more established history
- Apply the more conservative requirement from either document
- Consult the scope sections of both documents to determine which takes precedence for the specific application (Correct answer)
- Apply whichever standard reduces manufacturing cost
Correct answer: Consult the scope sections of both documents to determine which takes precedence for the specific application
Each IPC standard defines its own scope; reviewing the scope sections identifies which document has authority for the specific application or product class.
Question 3: Which IPC document series provides standardized test methods for evaluating PCB materials, laminate properties, and process verification?
- IPC-TM-650 (Correct answer)
- IPC-A-610
- IPC-2220 design series
- IPC-7000 series
Correct answer: IPC-TM-650
IPC-TM-650 is the Test Methods Manual containing standardized procedures for measuring PCB and material properties.
Question 4: IPC Class 3 requirements differ from Class 2 primarily because Class 3 specifies:
- Applies exclusively to military applications with no commercial use cases
- Allows wider dimensional tolerances to reduce manufacturing cost
- Is reserved for prototype and engineering sample boards only
- Tighter tolerances and higher reliability for electronics where continued performance is critical (Correct answer)
Correct answer: Tighter tolerances and higher reliability for electronics where continued performance is critical
IPC Class 3 targets high-reliability products—such as medical and aerospace electronics—where performance failure cannot be tolerated.
Question 5: When evaluating published research on a new PCB surface finish, which source provides the highest quality evidence?
- The manufacturer's product data sheet
- A peer-reviewed reliability study with controlled experiments and statistical analysis (Correct answer)
- An industry blog post from an experienced engineer
- A conference presentation without published test data
Correct answer: A peer-reviewed reliability study with controlled experiments and statistical analysis
Peer-reviewed controlled studies with statistical analysis represent the strongest evidence tier because they are independently validated and reproducible.
Question 6: IPC-2221 Table 6-1 (conductor spacing vs. voltage) primarily governs which design variable?
- Maximum number of layers in a multilayer stackup
- Minimum copper weight for current-carrying capacity
- Minimum conductor spacing as a function of voltage and environmental condition (Correct answer)
- Maximum PCB thickness for rigid board designs
Correct answer: Minimum conductor spacing as a function of voltage and environmental condition
Table 6-1 maps peak voltage levels to minimum electrical clearance requirements under different coating and altitude conditions.
Question 7: What is the most appropriate first step when a PCB design requirement is not covered by any known IPC standard?
- Contact IPC and search peer-reviewed literature for relevant data before proceeding (Correct answer)
- Proceed entirely on personal engineering judgment without documentation
- Apply the most restrictive requirement from any adjacent standard regardless of applicability
- Halt design activity until a new standard is formally published
Correct answer: Contact IPC and search peer-reviewed literature for relevant data before proceeding
Engaging standards bodies and searching technical literature provides documented, defensible evidence when no specific standard yet exists.
CID Research Methods & Evidence-Based Practice 2
When researching minimum conductor spacing for a 150V PCB application, which IPC document is the primary design reference?