PCB Materials & Manufacturing Processes Flashcards

What is the typical dielectric constant (Dk) of standard FR-4 laminate measured at 1 GHz?

Answer: 3.5–4.5

Standard FR-4 has a Dk of approximately 3.8–4.5 at 1 GHz, though the value decreases slightly at higher frequencies.

In PCB fabrication, what is the purpose of an 'oxide treatment' (black oxide or brown oxide) applied to inner-layer copper?

Answer: To increase surface area and adhesion between copper and prepreg during lamination

Oxide treatment creates a microrough copper surface that mechanically interlocks with the flowing prepreg resin, dramatically increasing peel strength after lamination.

Which type of PCB via is formed entirely within the inner layers and is NOT visible from the board surface?

Answer: Buried via

A buried via connects two or more inner layers and does not extend to either outer surface of the finished PCB.

What manufacturing process is used to apply liquid photoimageable (LPI) solder mask to a PCB?

Answer: Screen printing or curtain/spray coating followed by UV exposure and development

LPI solder mask is applied by screen printing or spray/curtain coating, then selectively exposed to UV through a film tool and developed to open pads.

What is 'measling' in PCB laminate and what typically causes it?

Answer: White spots in the laminate from moisture vaporization during thermal stress

Measling appears as discrete white spots or crosses within the laminate caused by moisture rapidly vaporizing and separating the glass weave from the resin under thermal shock.

Which plating chemistry is most commonly used to deposit copper in PTH barrels after electroless (catalytic) copper seeding?

Answer: Electrolytic (electro) copper sulfate bath plating

After electroless copper seeds the hole walls, an electrolytic acid copper sulfate bath deposits the bulk copper required to meet IPC barrel plating thickness requirements.

What is the minimum annular ring requirement for Class 3 (high reliability) PTH lands per IPC-6012?

Answer: 0.05 mm (2 mil)

IPC-6012 Class 3 requires a minimum annular ring of 0.05 mm (2 mil) for PTH lands after allowable breakout conditions on external layers.