PCB Materials & Manufacturing Processes Flashcards

Which material property defines how much a PCB laminate absorbs moisture, directly impacting Dk and insulation resistance?

Answer: Water absorption percentage

Water absorption (expressed as a weight-gain percentage) measures moisture uptake; absorbed moisture raises Dk and lowers surface/bulk insulation resistance.

What is the purpose of 'controlled impedance' in PCB manufacturing, and which parameter does the fab house primarily adjust to hit the target value?

Answer: Controlling transmission-line impedance by adjusting trace width and/or dielectric thickness

Controlled impedance ensures consistent signal propagation; fabricators tune trace width and/or dielectric thickness to achieve target characteristic impedance (e.g., 50 Ω).

Which advanced laminate material is commonly chosen for mmWave PCB designs above 30 GHz due to its very low loss tangent?

Answer: PTFE-based (e.g., Rogers 4003C or RO3003)

PTFE-based laminates offer very low Df (≈0.001–0.004) and stable Dk across frequency, making them the preferred choice for mmWave and microwave applications.

What is 'copper pour' or 'flood fill' used for in PCB design, and what manufacturing concern does an incomplete or isolated pour introduce?

Answer: Used for thermal relief; isolated islands can cause plating thickness variations during panel electroplating

Isolated copper islands not connected to a net can cause uneven current distribution during panel electroplating, resulting in non-uniform copper thickness across the panel.

In a sequential build-up (SBU) HDI process, what does '1+N+1' stack-up notation describe?

Answer: One laser-drilled micro-via layer on each side of an N-layer mechanical-drill core

1+N+1 means one sequential build-up layer (with laser micro-vias) is added to each side of a conventionally drilled N-layer core.

What is the primary reason ceramic-filled PTFE laminates are more difficult to drill than standard FR-4?

Answer: Ceramic fillers rapidly abrade drill bits, increasing tool wear and cost

Hard ceramic particles (e.g., alumina, silica) in the PTFE matrix are highly abrasive, causing accelerated drill bit wear and requiring frequent bit changes or specialized tooling.

Which IPC-4101 slash sheet designation specifies a woven-glass, epoxy laminate with enhanced CAF resistance for high-reliability applications?

Answer: IPC-4101/126

IPC-4101/126 defines woven-glass reinforced epoxy laminate with CAF resistance requirements, targeting telecom and high-reliability interconnect designs.