PCB Materials & Manufacturing Processes Flashcards

What is the typical glass transition temperature (Tg) range for standard FR-4 laminate?

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.

Which PCB surface finish offers the longest shelf life and is preferred for fine-pitch BGA assembly?

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.

What manufacturing defect occurs when plated through-hole copper separates from the barrel wall due to thermal stress?

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.

Which resin system is commonly used in PCB laminates requiring CAF (conductive anodic filament) resistance?

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.

In the PCB etching process, what is the primary purpose of the etch resist?

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.

What is 'undercutting' in the context of PCB chemical etching?

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.

Which IPC specification defines the qualification and performance requirements for rigid printed boards?

Answer: IPC-6012

IPC-6012 'Qualification and Performance Specification for Rigid Printed Boards' defines acceptance criteria for rigid PCB fabrication.