CID PCB Materials & Manufacturing Processes 2 — Questions and Answers
Question 1: What is the typical glass transition temperature (Tg) range for standard FR-4 laminate?
- 80–100°C
- 130–140°C (Correct answer)
- 170–180°C
- 210–230°C
Correct answer: 130–140°C
Standard FR-4 laminate has a Tg of approximately 130–140°C, above which the resin softens and dimensional stability degrades.
Question 2: Which PCB surface finish offers the longest shelf life and is preferred for fine-pitch BGA assembly?
- Hot Air Solder Leveling (HASL)
- Organic Solderability Preservative (OSP)
- Electroless Nickel Immersion Gold (ENIG) (Correct answer)
- Immersion Tin
Correct answer: Electroless Nickel Immersion Gold (ENIG)
ENIG provides a flat, gold-capped surface with excellent shelf life and is well-suited for fine-pitch BGA components.
Question 3: What manufacturing defect occurs when plated through-hole copper separates from the barrel wall due to thermal stress?
- Measling
- Crazing
- Barrel cracking (Correct answer)
- Delamination
Correct answer: Barrel cracking
Barrel cracking is the fracture of the copper plating inside a PTH barrel, typically caused by excessive Z-axis expansion during thermal cycling.
Question 4: Which resin system is commonly used in PCB laminates requiring CAF (conductive anodic filament) resistance?
- Cyanate ester
- Polyphenylene oxide (PPO/PPE)
- High-Tg epoxy with silica filler (Correct answer)
- Standard dicy-cured epoxy
Correct answer: High-Tg epoxy with silica filler
High-Tg epoxy with inorganic silica filler reduces resin moisture absorption and slows ion migration paths, improving CAF resistance.
Question 5: In the PCB etching process, what is the primary purpose of the etch resist?
- To promote copper adhesion to the laminate
- To protect copper traces from chemical removal during etching (Correct answer)
- To define drill locations for PTH
- To planarize the surface before solder mask application
Correct answer: To protect copper traces from chemical removal during etching
Etch resist (dry film or liquid photoresist) shields the desired copper pattern from the etchant during subtractive processing.
Question 6: What is 'undercutting' in the context of PCB chemical etching?
- Incomplete etching leaving residual copper between traces
- Lateral erosion beneath the etch resist reducing trace width (Correct answer)
- Delamination of inner layers during etch
- Copper migration into the dielectric layer
Correct answer: Lateral erosion beneath the etch resist reducing trace width
Undercutting occurs when the etchant attacks copper laterally under the resist, narrowing the final trace width below the designed value.
Question 7: Which IPC specification defines the qualification and performance requirements for rigid printed boards?
- IPC-2221
- IPC-6012 (Correct answer)
- IPC-4101
- IPC-7711
Correct answer: IPC-6012
IPC-6012 'Qualification and Performance Specification for Rigid Printed Boards' defines acceptance criteria for rigid PCB fabrication.
CID PCB Materials & Manufacturing Processes 2
What is the typical glass transition temperature (Tg) range for standard FR-4 laminate?