PREFERRED

Conformal coating covers all areas as specified on the engineering documentation. Coating exhibits uniform color, thickness, proper adhesion and is smooth, transparent and tack free. No bubbles, entrapped contaminants or particles, excessive fillets, runs, drips, etc. Identification markings are visible.

ACCEPTABLE

BRUSH APPLICATIONS

The conformal coating is evenly applied, without forming excessive fillets or thick areas. Minor brush marks are acceptable, provided minimum thickness is maintained.

NASA-STD-8739.1 [10.2.2.b]

ACCEPTABLE

BRIDGING

Conformal coating may bridge adjacent part leads, provided stress relief is not negated.

NASA-STD-8739.1 [10.2.5.e], [11.8.2.j]

UNACCEPTABLE

BRIDGING

Coating shall not bridge between the bottom of ceramic-bodied DIPs or surface mount parts and the PWB, or between the part lead an dthe PWB, thereby negating stress relief.

NASA-STD-8739.1 [10.2.4.b], [11.8.3.b]

ACCEPTABLE

BUBBLES

Small bubbles, which do not bridge uncommon conductors, expose conductor surfaces, or exceed 0.76 mm (0.030 in.) in any dimension, are acceptable.

NASA-STD-8739.1 [10.2.5]

UNACCEPTABLE

BUBBLES

Bubbles, which bridge uncommon conductors, expose conductor surfaces, or exceed 0.76 mm (0.030 in.) in any dimension, are not acceptable.

NASA-STD-8739.1 [11.8.3.h], [11.8.3.i]

ACCEPTABLE

FISHEYES

Fisheyes shall not exceed 5% of the surface area.

NASA-STD-8739.1 [10.2.5]

UNACCEPTABLE

FISHEYES

Fisheyes shall not exceed 5% of the surface area.

NASA-STD-8739.1 [11.8.3.k]

ACCEPTABLE

DIP APPLICATION

The conformal coating exhibits complete coverage. Skightly uneven thickness, uneven filleting around parts, run contours, and edge loading are acceptable, provided minimum thickness is maintained.

NASA-STD-8739.1 [10.2.2.c]

ACCEPTABLE

PULL BACK

Minor pull back from sharp points and edges is permissible, unless otherwise specified on engineering documentation.

NASA-STD-8739.1 [10.2.5.b], [11.8.2.g]

ACCEPTABLE

RUNS

Runs shall not exceed 5% of the surface area.

NASA-STD-8739.1 [10.2.5]

UNACCEPTABLE

RUNS

Runs shall not exceed 5% of the surface area.

NASA-STD-8739.1 [11.8.3.k]

ACCEPTABLE

SCRATCHES

Scratches, which so not expose conductive surfaces, or reduce the coating thickness below minimum thickness requirements, are acceptable.

NASA-STD-8739.1 [10.2.5]

UNACCEPTABLE

SCRATCHES/SCRAPES

Scratches, which expose conductive surfaces, are not acceptable.

NASA-STD-8739.1 [11.8.3.e]

ACCEPTABLE

SPRAY APPLICATION

The conformal coating is evenly applied, exhibits uniform color, thickness, proper adhesion, and is smooth and tack free. No evidence of shadowing, orange peel or dusting.

NASA-STD-8739.1 [10.2.2.a]

ACCEPTABLE

TERMINALS

Terminals shall be conformally coated, including the wire insulation gap, unless it is a solder ball termination (i.e. a high-voltage termination). Minor pullback from shrp points and edges is acceptable.

NASA-STD-8739.1 [10.2.5.d]

ACCEPTABLE

ULTRAVIOLET (UV) FLUORESCENCE

Conformal coating containing a fluorescent dye shall be examined under an ultraviolet (UV) source. The coating shall exhibit uniform fluorescence when exposed to an ultrviolet (UV) light source.

NASA-STD-8739.1 [11.9.2]

ACCEPTABLE

VACUUM DEPOSITION

Conformal coating covers all areas as specified on the engineering documentation. The coating is thin, of uniform thickness and fillet free.

NASA-STD-8739.1 [10.2.2.d]

UNACCEPTABLE

BLISTERING

Blistering is typically caused by improper preparation/priming or entrapped moisure or contaminants, and is cause for rejection.

NASA-STD-8739.1 [11.8.3.e]

UNACCEPTABLE

CONTAMINATION

Contamination (i.e. flux, loose particles, foreign material, etc.) shall be cause for rejection.

NASA-STD-8739.1 [10.2.5.c], [11.8.3.f]

UNACCEPTABLE

CRACKING

Cracking is typically caused by improper cure, excessive heat during cure, or excessive flexure of the substrate, and negate the environmental sealing properties of the coating.

NASA-STD-8739.1 [11.8.3.e]

UNACCEPTABLE

DISCOLORATION

Conformal coating shall not exhibit discoloration (due to such things as excessive curing oven temperature, contamination, etc.).

NASA-STD-8739.1 [10.2.5.f], [11.8.3.g]

UNACCEPTABLE

DUSTY/POWDERY FINISH

A dusty or powdery finish is typically caused by over-spray from adjacent boards and/or improper spray distance.

NASA-STD-8739.1 [10.2.5.a]

UNACCEPTABLE

EXCESSIVE THICKNESS

Conformal coatings shall completely encapsulate the components with a uniform thickness of material, and follow the contours of the PWA.

NASA-STD-8739.1 [10.2.5.b]

UNACCEPTABLE

FINGERPRINTS/INDENTATIONS

Permanent fingerprints or indentations in the coating are an indicator of improper cure or handling.

Best Workmanship Practice

UNACCEPTABLE

HAZY/MILKY FINISH

A hazy or milky appearance is an indicator of entrapped moisture, improperly mixed material, or material with an outdated shelf-life.

NASA-STD-8739.1 [10.2.5.b], [11.8.3.a]

UNACCEPTABLE

IMPROPER/MISSING COATING

PWAs exhibiting coating that has not been applied to required areas, or coating on areas required to be free of coating, shall be rejectable.

NASA-STD-8739.1 [10.2.5.b], [11.8.2.g]

UNACCEPTABLE

LIFTING/MEASLING/PEELING

Coating exhibiting excessive lifting, mealing or peeling may be an indicator of improper cleaning, priming, curing or excessive thickness. Any lifting on conductive areas is nonconforming.

NASA-STD-8739.1 [11.8.3.j]

UNACCEPTABLE

ORANGE PEEL

Uneven surface textures, such as orange peel, are an indicator of improper application, thickness and/or cure.

NASA-STD-8739.1 [10.2.5.b]

UNACCEPTABLE

PINHOLES

Pinholes in the coating allow moisture and contaminants to potentially reduce the reliability of the PWA.

NASA-STD-8739.1 [10.2.5.b], [11.8.3.e]

UNACCEPTABLE

SHADOWING

Shadowing is caused by the incomplete/improper application of coating material during the spray process, and results in improper thickness or missing coverage.

NASA-STD-8739.1 [10.2.2.a], [10.2.5.b]

UNACCEPTABLE

SOFT SPOTS/TACKINESS

Soft spots/tackiness (stickiness) indicate that the coating may not have been properly cured. Silicone coatings have a slightly rubbery feel, but are not sticky.

NASA-STD-8739.1 [10.3.1], [11.8.3.d], [11.9.4]

UNACCEPTABLE

WHITISH SPOTS (MEASLING)

Whitish spots are an indication of moisture/solvent contamination, and shall be rejectable.

NASA-STD-8739.1 [11.8.3.e]

UNACCEPTABLE

WRINKLING

Wrinkling is an indicator of an improper/uneven cure or a reaction to unevaporated solvents on the laminate surface.

NASA-STD-8739.1 [11.8.3.e]