CIS CIS Cleaning & Contamination Control 1 — Questions and Answers
Question 1: Which IPC standard governs cleaning and cleanliness of electronic assemblies?
- IPC-A-610
- IPC-CH-65 (Correct answer)
- IPC-7711
- IPC-2221
Correct answer: IPC-CH-65
IPC-CH-65 (Guidelines for Cleaning of Printed Board Assemblies) provides guidance on cleaning processes and cleanliness verification for electronic assemblies.
Question 2: What is the primary purpose of flux in the soldering process, and why must residues be managed?
- Flux improves heat transfer; residues can crack solder joints when hardened
- Flux removes oxides to promote solder wetting; ionic residues can cause corrosion and leakage currents if not cleaned (Correct answer)
- Flux acts as a bonding agent; residues increase mechanical strength of joints
- Flux prevents tombstoning; residues attract moisture and cause delamination
Correct answer: Flux removes oxides to promote solder wetting; ionic residues can cause corrosion and leakage currents if not cleaned
Flux removes oxides to enable proper solder wetting; however, ionic flux residues left on the board can absorb moisture and cause electrochemical corrosion and leakage currents.
Question 3: The ROSE (Resistivity of Solvent Extract) test measures:
- The thickness of solder mask coating on the PCB surface
- The ionic contamination level on a printed board assembly (Correct answer)
- The residual flux activity after reflow soldering
- The resistance of conformal coating to solvent attack
Correct answer: The ionic contamination level on a printed board assembly
The ROSE test measures the ionic contamination level on a PCB assembly by extracting ionic residues with a solvent-water mixture and measuring the resulting resistivity change.
Question 4: What is 'no-clean' flux, and when is cleaning still recommended?
- Flux that contains no activators; cleaning is never needed
- Low-residue flux designed to leave benign residues; cleaning is still recommended for high-reliability Class 3 assemblies or when residues are under components (Correct answer)
- Flux removed by the PCB laminate; cleaning is needed only when the flux is visible
- Aqueous flux that self-rinses; cleaning is recommended after wave soldering only
Correct answer: Low-residue flux designed to leave benign residues; cleaning is still recommended for high-reliability Class 3 assemblies or when residues are under components
No-clean flux leaves minimal, low-ionic residues considered safe for most applications, but high-reliability Class 3 assemblies or residues trapped under low-standoff components may still require cleaning.
Question 5: Which cleaning agent type is most commonly used in modern aqueous PCB cleaning systems?
- Chlorinated solvents
- Saponifiers in hot DI water (Correct answer)
- Isopropyl alcohol (IPA) spray
- Vapor-phase trichloroethylene
Correct answer: Saponifiers in hot DI water
Modern aqueous cleaning systems typically use saponifiers (alkaline cleaning agents) combined with hot deionized water to remove flux residues from PCB assemblies.
Question 6: What does a white residue on a PCB assembly after soldering most likely indicate?
- Silver migration from component leads
- Incompletely activated or thermally degraded flux residue (Correct answer)
- Copper oxidation from insufficient solder coverage
- Lead-free solder oxidation products
Correct answer: Incompletely activated or thermally degraded flux residue
White residue after soldering typically indicates incompletely activated flux or thermally degraded flux chemistry that has left hygroscopic residues on the board surface.
CIS CIS Cleaning & Contamination Control 1
Which IPC standard governs cleaning and cleanliness of electronic assemblies?