CIS CIS Cleaning & Contamination Control 2

Question 1

What is 'electrochemical migration' and how does contamination contribute to it?

Accepted Answer

Metal ion movement through the PCB laminate caused by voltage gradients in the presence of moisture and ionic contamination

Answer

Electrochemical migration (ECM) occurs when metal ions dissolve and migrate across the surface under a voltage bias in the presence of moisture, often seeded by ionic contamination, potentially forming conductive dendrites that cause shorts.

Question 2

What is the acceptable ionic contamination level per IPC-CH-65 for a Class 2 PCB assembly (ROSE method)?

Accepted Answer

1.56 µg NaCl eq/cm²

Answer

The traditionally referenced ionic cleanliness limit is 1.56 µg NaCl equivalent per cm² (10.06 µg/in²) as established by older MIL-P-28809 criteria, still widely referenced for Class 2.

Question 3

Why is deionized (DI) water used in aqueous PCB cleaning rather than tap water?

Accepted Answer

DI water is free of ionic minerals that could leave conductive deposits on the assembly

Answer

Deionized water removes mineral ions, preventing ionic contamination deposits on the board; using tap water would deposit minerals (calcium, magnesium, etc.) that are conductive.

Question 4

Which of the following is NOT a typical source of ionic contamination on PCB assemblies?

Accepted Answer

Solder mask pigments

Answer

Solder mask pigments (the materials that give solder mask its color) are not a significant source of ionic contamination; human perspiration, flux residues, and atmospheric contamination are common ionic sources.

Question 5

What does SIR (Surface Insulation Resistance) testing evaluate on a PCB assembly?

Accepted Answer

The electrical resistance between conductors under controlled temperature and humidity, assessing contamination impact on leakage current

Answer

SIR testing measures the electrical resistance between specific conductor patterns under elevated temperature and humidity, providing a direct measure of how contamination affects leakage current and insulation integrity.

(CIS) Certified IPC Specialist Practice Test

(CIS) Certified IPC Specialist Practice Test

CIS CIS Cleaning & Contamination Control 2