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

The migration of solder alloy elements due to thermal cycling

Answer

Electrostatic buildup that causes components to shift during reflow

Answer

Copper dissolution into flux during wave soldering

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

1.0 µg NaCl eq/cm²

Answer

3.1 µg NaCl eq/cm²

Answer

5.0 µg NaCl eq/cm²

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

DI water has a lower surface tension, improving penetration under components

Answer

DI water is heated to a higher temperature than tap water in industrial cleaners

Answer

DI water contains surfactants that improve flux removal

Question 4

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

Accepted Answer

Solder mask pigments

Answer

Perspiration from ungloved human hands

Answer

Flux activator residues

Answer

Atmospheric contamination in high-humidity environments

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

The mechanical peel strength of solder mask from the copper surface

Answer

The resistivity of the PCB laminate base material

Answer

The adhesion of conformal coating to the board surface

Question 6

Ultrasonic cleaning is generally NOT recommended for PCB assemblies because:

Accepted Answer

Cavitation energy can damage wire bonds, crystal oscillators, and MEMS devices

Answer

It is too slow for production volumes

Answer

It leaves more ionic residue than aqueous spray systems

Answer

It cannot remove no-clean flux residues effectively