CIS CIS Cleaning & Contamination Control 3

Question 1

What is 'white corrosion' observed on tin or tin-lead solder joints in humid environments?

Accepted Answer

Tin oxide or stannic acid formation from electrochemical corrosion of the solder surface

Answer

White corrosion on tin-bearing solder is typically tin oxide or stannic acid (SnO₂/Sn(OH)₄) resulting from electrochemical corrosion in humid or contaminated environments.

Question 2

According to IPC-A-610, which type of flux residue is always classified as a defect?

Accepted Answer

Flux residue that bridges between conductors at the minimum electrical clearance distance

Answer

Flux residue that bridges across the minimum electrical clearance between conductors is a defect for all classes because it can cause leakage current or shorts.

Question 3

What is the correct method for cleaning a PCB with isopropyl alcohol (IPA)?

Accepted Answer

Use 99% (anhydrous) IPA with a lint-free swab or brush, then allow to fully dry before powering the assembly

Answer

Electronic cleaning requires 99% anhydrous IPA (water in lower concentrations can leave ionic residues), applied with lint-free materials, with complete drying before power-up to prevent shorts.

Question 4

What hazard does halide contamination (chlorides, bromides) pose to PCB assemblies?

Accepted Answer

Halides are aggressive activators that accelerate corrosion and electrochemical migration if not fully removed

Answer

Halide ions (Cl⁻, Br⁻) from flux activators are aggressive corrosion catalysts; if left on the assembly, they absorb moisture and create highly corrosive ionic solutions that accelerate metal corrosion and electrochemical migration.

Question 5

What is the purpose of a 'rinse purity monitor' in an aqueous cleaning system?

Accepted Answer

To continuously measure the ionic content of the final rinse water to ensure it is not recontaminating boards

Answer

A rinse purity monitor measures the conductivity or resistivity of final rinse water to ensure it hasn't accumulated enough ionic contamination to recontaminate boards exiting the cleaning system.

(CIS) Certified IPC Specialist Practice Test

(CIS) Certified IPC Specialist Practice Test

CIS CIS Cleaning & Contamination Control 3