CID PCB Materials & Manufacturing Processes 2

Question 1

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

Accepted Answer

130–140°C

Answer

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?

Accepted Answer

Electroless Nickel Immersion Gold (ENIG)

Answer

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?

Accepted Answer

Barrel cracking

Answer

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?

Accepted Answer

High-Tg epoxy with silica filler

Answer

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?

Accepted Answer

To protect copper traces from chemical removal during etching

Answer

Etch resist (dry film or liquid photoresist) shields the desired copper pattern from the etchant during subtractive processing.

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