CID PCB Materials & Manufacturing Processes 3

Question 1

What is the primary function of a prepreg (pre-impregnated) layer in multilayer PCB construction?

Accepted Answer

To act as an adhesive dielectric bonding inner cores together

Answer

Prepreg is B-stage (partially cured) resin-impregnated glass fabric that bonds inner core layers under heat and pressure during lamination.

Question 2

Which copper foil type offers superior high-frequency electrical performance due to its smoother surface profile?

Accepted Answer

Ultra-low profile (VLP) copper

Answer

VLP (very low profile) copper has minimal surface roughness, reducing skin-effect losses at high frequencies compared to standard ED or RA foils.

Question 3

In sequential lamination for HDI boards, what process step immediately follows inner-layer imaging before the next lamination cycle?

Accepted Answer

Via drilling and plating

Answer

After inner-layer imaging and etching, micro-vias are drilled (laser or mechanical) and plated before adding the next dielectric and copper layer.

Question 4

What is the primary advantage of using a back-drill (controlled-depth drilling) on high-speed PCBs?

Accepted Answer

Removes the unused stub portion of a PTH to reduce via resonance

Answer

Back-drilling removes the non-functional stub below the last connected layer, eliminating the transmission-line stub resonance that degrades signal integrity.

Question 5

Which laminate property is most critical when selecting a material for lead-free solder assembly processes?

Accepted Answer

High decomposition temperature (Td)

Answer

Lead-free soldering peaks at 260°C+, so a high Td ensures the resin does not decompose and delaminate during the assembly thermal cycle.

(CID) Certified Interconnect Designer Practice Test

(CID) Certified Interconnect Designer Practice Test

CID PCB Materials & Manufacturing Processes 3