CIS CIS PCB Design & Fabrication Standards 2 — Questions and Answers
Question 1: What IPC class designation applies to high-reliability electronic products such as life-support equipment?
- Class 1
- Class 2
- Class 3 (Correct answer)
- Class 4
Correct answer: Class 3
IPC Class 3 applies to high-reliability products where continued performance is critical, such as medical life-support and military hardware.
Question 2: What is the purpose of a 'via-in-pad' design in PCBs?
- To reduce board layer count
- To place a via directly within a surface mount pad to save space (Correct answer)
- To improve mechanical strength of through-hole components
- To increase annular ring size
Correct answer: To place a via directly within a surface mount pad to save space
Via-in-pad places the via directly inside the SMT land pad, saving board real estate and improving electrical performance for dense designs.
Question 3: The glass transition temperature (Tg) of a PCB laminate is important because:
- It defines the maximum copper plating thickness
- It indicates the temperature at which the laminate transitions from rigid to soft (Correct answer)
- It determines the minimum drill bit diameter required
- It sets the maximum current-carrying capacity of traces
Correct answer: It indicates the temperature at which the laminate transitions from rigid to soft
Tg is the temperature at which the PCB laminate transitions from a rigid, glassy state to a softer, rubbery state, affecting reliability during thermal excursions.
Question 4: What is the function of a 'thermal relief' in PCB design?
- It dissipates heat from high-power components
- It reduces stress on solder joints near copper pours
- It connects a through-hole pad to a copper plane with spoke connections to ease soldering (Correct answer)
- It prevents warpage during reflow soldering
Correct answer: It connects a through-hole pad to a copper plane with spoke connections to ease soldering
A thermal relief connects a pad to a copper plane through spoke-shaped connections, reducing heat dissipation during soldering to allow proper solder wetting.
Question 5: According to IPC-6012 Class 3, what is the minimum acceptable annular ring for supported holes in internal layers?
- 0.025 mm
- 0.050 mm (Correct answer)
- 0.075 mm
- 0.100 mm
Correct answer: 0.050 mm
IPC-6012 Class 3 requires a minimum 0.050 mm (50 µm) annular ring for supported holes in internal layers.
Question 6: What does 'DFM' stand for in PCB fabrication?
- Design for Manufacturing (Correct answer)
- Dielectric Film Measurement
- Drill Feed and Motion
- Defect-Free Manufacturing
Correct answer: Design for Manufacturing
DFM stands for Design for Manufacturing, the process of designing PCBs to be easily and reliably fabricated with minimal defects.
CIS CIS PCB Design & Fabrication Standards 2
What IPC class designation applies to high-reliability electronic products such as life-support equipment?