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

Tin whisker growth accelerated by moisture

Answer

Lead carbonate deposits from atmospheric carbon dioxide reaction

Answer

Crystalline flux activator residue remaining after reflow

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

Clear, glassy, rosin residue from fully activated rosin flux

Answer

White chalky residue from no-clean flux

Answer

Brown residue at the base of through-hole component leads

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

Soak the assembly in 70% IPA for 30 minutes

Answer

Apply 50% IPA solution and immediately power up to verify function

Answer

Use standard 70% IPA and blow-dry with compressed shop air

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

Halides reduce solder joint strength by forming brittle intermetallic compounds

Answer

Halides cause delamination of PCB laminate during thermal cycling

Answer

Halides reduce the dielectric constant of the PCB base material

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

To measure the cleanliness of components before they enter the cleaner

Answer

To test the cleaning agent concentration in the wash chamber

Answer

To monitor the temperature uniformity of the rinse water across the conveyor width

Question 6

Which environmental condition most accelerates ionic contamination-driven corrosion on PCB assemblies?

Accepted Answer

High relative humidity combined with elevated temperature

Answer

Low temperature (below 0°C)

Answer

Low humidity (below 20% RH)

Answer

Exposure to UV light