CIS Conformal Coating & Encapsulation 2 — Questions and Answers
Question 1: What conformal coating defect is described as small circular depressions or craters that expose the underlying substrate?
- Delamination
- Fisheye (cratering) (Correct answer)
- Orange peel
- Blooming
Correct answer: Fisheye (cratering)
Fisheyes or cratering are circular depressions caused by surface tension differences, often from contamination or silicone, that pull the wet coating away from a point and expose the substrate.
Question 2: An 'orange peel' texture on a cured conformal coating surface is generally considered:
- A defect requiring immediate rework
- Acceptable in most cases per IPC-A-610 (Correct answer)
- A target condition for all classes
- Only acceptable for Class 1 assemblies
Correct answer: Acceptable in most cases per IPC-A-610
Orange peel texture is a cosmetic irregularity that does not impair the protective function of the coating and is generally listed as an acceptable condition in IPC-A-610.
Question 3: Which condition would constitute a defect in conformal coating per IPC-A-610 for Class 2 and Class 3 assemblies?
- Slight color variation across the coating
- Thin coating over the tops of component bodies
- Exposed conductors or solder connections that are required to be coated (Correct answer)
- A matte finish instead of a glossy surface
Correct answer: Exposed conductors or solder connections that are required to be coated
Exposed conductors, lands, or solder connections that should be coated leave the circuit unprotected, directly violating the protective requirement and constituting a defect per IPC-A-610.
Question 4: When inspecting conformal coating under ultraviolet (UV) light, what does a dark or non-fluorescing area indicate?
- Proper coating thickness has been achieved
- The coating has cured correctly in that area
- Missing or insufficient coating coverage (Correct answer)
- The coating contains no UV tracer, which is normal
Correct answer: Missing or insufficient coating coverage
Areas that do not fluoresce under UV light lack the fluorescent tracer present in the conformal coating, indicating that no coating or insufficient coating was applied in that location.
Question 5: During conformal coating application, which types of features MUST typically be masked to prevent coating?
- SMT chip resistors and capacitors
- Through-hole component leads
- Edge connectors, test points, and adjustable components (Correct answer)
- Component reference designators
Correct answer: Edge connectors, test points, and adjustable components
Edge connectors must remain uncoated for electrical contact, test points must remain accessible for in-circuit testing, and adjustable components such as potentiometers must remain operable after assembly.
Question 6: Applying conformal coating over an assembly with ionic contamination will most likely result in:
- Improved adhesion due to increased surface energy
- Reduced coating thickness from chemical reaction
- Delamination, loss of adhesion, or accelerated corrosion under the coating (Correct answer)
- Enhanced long-term environmental protection
Correct answer: Delamination, loss of adhesion, or accelerated corrosion under the coating
Ionic contamination trapped beneath the coating retains moisture and promotes electrochemical corrosion, and the contamination can also prevent proper adhesion, leading to delamination.
Question 7: Which conformal coating application method provides the most precise deposition and reduces masking requirements by applying coating only to specified areas?
- Dip coating
- Brush coating
- Aerosol spray coating
- Selective robotic coating system (Correct answer)
Correct answer: Selective robotic coating system
Selective coating systems use programmable robotic dispensers to apply coating to defined areas only, dramatically reducing or eliminating the need for masking while improving repeatability.
CIS Conformal Coating & Encapsulation 2
What conformal coating defect is described as small circular depressions or craters that expose the underlying substrate?