PCB Quality Control & Assurance 3

Question 1

In PCB quality control, what is a 'lifted land' defect?

Accepted Answer

A copper pad that has partially or fully detached from the board surface

Answer

A lifted land occurs when a copper pad separates from the substrate, often caused by excessive heat during soldering or mechanical stress.

Question 2

What is the primary purpose of ionic contamination testing (such as ROSE testing) on a PCB?

Accepted Answer

To detect residual flux and ionic contaminants that could cause corrosion or leakage

Answer

ROSE (Resistivity of Solvent Extract) testing measures ionic contamination levels on PCBs, which if excessive can cause electrochemical migration, corrosion, and field failures.

Question 3

What does the term 'tombstoning' refer to in SMT assembly quality?

Accepted Answer

A component that stands up on one end due to uneven solder wetting forces

Answer

Tombstoning (also called drawbridging) occurs when one end of a small SMD component lifts off its pad, typically caused by unequal wetting forces or thermal imbalance.

Question 4

Which test method applies electrical current between opposing copper features to detect short circuits or leakage paths?

Accepted Answer

Insulation resistance test

Answer

Insulation resistance testing applies voltage between conductors to measure the resistance of dielectric material and detect leakage paths or shorts.

Question 5

A PCB manufacturer reports a 'bow and twist' measurement of 0.75% on a standard FR4 board. According to IPC-6012, is this acceptable?

Accepted Answer

No, the maximum allowed is 0.5% for SMT boards

Answer

IPC-6012 limits bow and twist to 0.75% maximum for boards with SMT components and 1.5% for through-hole only boards; 0.75% on an SMT board is at the boundary and typically rejected.

PCB - Design Practice Test

PCB - Design Practice Test

PCB Quality Control & Assurance 3