CIS Cleaning & Contamination Control Flashcards
6 cards from real CIS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CIS Cleaning & Contamination Control flashcards as text
What is 'white corrosion' observed on tin or tin-lead solder joints in humid environments?
Answer: Tin oxide or stannic acid formation from electrochemical corrosion of the solder surface
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.
According to IPC-A-610, which type of flux residue is always classified as a defect?
Answer: Flux residue that bridges between conductors at the minimum electrical clearance distance
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.
What is the correct method for cleaning a PCB with isopropyl alcohol (IPA)?
Answer: Use 99% (anhydrous) IPA with a lint-free swab or brush, then allow to fully dry before powering the assembly
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.
What hazard does halide contamination (chlorides, bromides) pose to PCB assemblies?
Answer: Halides are aggressive activators that accelerate corrosion and electrochemical migration if not fully removed
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.
What is the purpose of a 'rinse purity monitor' in an aqueous cleaning system?
Answer: To continuously measure the ionic content of the final rinse water to ensure it is not recontaminating boards
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.
Which environmental condition most accelerates ionic contamination-driven corrosion on PCB assemblies?
Answer: High relative humidity combined with elevated temperature
High relative humidity combined with elevated temperature is the most aggressive environment for ionic contamination-driven corrosion, as moisture activates ionic residues and elevated temperature accelerates the electrochemical reactions.