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Conformal Coating: Types, Application Methods, and Defect Analysis, Exams of Advanced Education

Cheyney University of PennsylvaniaAdvanced Education

A comprehensive overview of conformal coatings used in electronic assemblies. It covers various aspects, including types of conformal coatings (acrylic resin, silicone resin, urethane resin), application methods (manual spraying, automated spraying, selective coating, dipping, brushing), common coating defects (capillary flow, cracking and ripples, dewetting, delamination, orange peel, air bubbles, pinholes, and foam) and their causes, measuring wet coating, and definitions of terms like measling, crazing, blistering, delamination, weave texture, weave exposure, haloing, fod, solder mask coating, electrostatic discharge (esd), and classifications (class 1, 2, 3). Useful for understanding the importance of conformal coatings in protecting printed circuit boards from environmental factors and ensuring their reliability.

Typology: Exams

2024/2025

Available from 05/16/2025

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IPC-A-610 Test questions updated version
comprehensive graded A+
1. 3 types of Conformal Coating: Acrylic Resin (AR): This type of coating
pro- vides FAIR elasticity and general protection. It has high dielectric
strength, and
fair moisture and abrasion resistance. This coating is different from others
because its facility for removal. This type are EASILY and quickly removed by a
variety of solvents, often without requiring agitation. This makes rework and
field repair very practical and economical. This type doesn't protect against
solvents and solvent vapors.
2. 3 types of Conformal Coating: Silicone Resin (SR): This type of coating
provides EXCELLENT protection in a very wide temperature range. This
coating provides good chemical resistance, moisture, and salt spray
resistance, and is very flexible. This type is NOT abrasion resistant because of
its rubbery nature, but
this property does make it resilient against vibrational stresses. Commonly
used in high-humidity environments. Removal can be CHALLENGING.
requiring specialized solvents, long soak time, and agitation from a brush.
3. 3 types of Conformal Coating: Urethane (Polyurethane) Resin (UR): This
type of coating is known for its EXCELLENT moisture and chemical resistance.
It is also very abrasion resistant. Combining those factors with its SOLVENT
RESISTANCE results in a conformal coating that is very difficult to remove.
Like SR, full removal generally requires special solvents, long soak time, and
agitation with a brush. This is common in aerospace application. ex:
Conathane
pf3
pf4
pf5

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IPC-A-610 Test questions updated version

comprehensive graded A+

  1. 3 types of Conformal Coating: Acrylic Resin (AR): This type of coating pro- vides FAIR elasticity and general protection. It has high dielectric strength, and fair moisture and abrasion resistance. This coating is different from others because its facility for removal. This type are EASILY and quickly removed by a variety of solvents, often without requiring agitation. This makes rework and field repair very practical and economical. This type doesn't protect against solvents and solvent vapors.
  2. 3 types of Conformal Coating: Silicone Resin (SR): This type of coating provides EXCELLENT protection in a very wide temperature range. This coating provides good chemical resistance, moisture, and salt spray resistance, and is very flexible. This type is NOT abrasion resistant because of its rubbery nature, but this property does make it resilient against vibrational stresses. Commonly used in high-humidity environments. Removal can be CHALLENGING. requiring specialized solvents, long soak time, and agitation from a brush.
  3. 3 types of Conformal Coating: Urethane (Polyurethane) Resin (UR): This type of coating is known for its EXCELLENT moisture and chemical resistance. It is also very abrasion resistant. Combining those factors with its SOLVENT RESISTANCE results in a conformal coating that is very difficult to remove. Like SR, full removal generally requires special solvents, long soak time, and agitation with a brush. This is common in aerospace application. ex: Conathane
  1. 5 Coating application methods: Manual Spraying: Aerosol can or handheld spray gun. Time consuming method of coating for a small quantity of boards. Lots of masking beforehand. Quality and consistency of outcome are operator- dependent.
  2. 5 Coating application methods: Automated spraying: Programmed spray sys- tem that moves the board on a CONVEYOR under an alternative spray head that applies a conformal coating.
  3. 5 Coating application methods: Selective coating: An automated conformal coating process that uses PROGRAMMABLE ROBOTIC SPRAY NOZZLES to apply the coating to very specific areas on the circuit board. May eliminate the need for masking using the program. The UV lamp in machine helps cure the coating right after it is sprayed.
  4. 5 Coating application methods: Dipping: The circuit board is first immersed, Then withdrawn from the conformal coating solution. Immersion speed, withdrawn speed, Immersion time, and Viscosity determine the resulting film formation. Com- mon for high volume processing. Masking may increase. This method is good to coat both Front and Back of the board.
  5. 5 Coating application methods: Brushing: Simple application method used mainly in repair and rework. Conformal Coating is applied with a BRUSH to specific areas on the board. Low-cost method but requires lots of manual labor and is highly variable depending on operator proficiency and consistency. This is the best for a small batch or a single board.
  6. **1. Solvent Removal
  7. Peeling
  8. Microblasting: using a concentrated mix of soft abrasive and compressed air to abrade the coating.
  9. Grinding/Scaping:** What are the Conformal Coating Removal Methods by
  1. (6) Most Common Coating Defects and causes: Orange Peel: Coating appears dull, resembling the skin of a fruit or basketball. Causes: -substrate is too hot. -improper mixture of solvent and coating ratio.
  • environment is too dry during application. -Second coat has been applied before the first coat is dry.
  1. (6) Most Common Coating Defects and causes: Air Bubbles, Pinholes, and Foam: Bubbles occur when pockets of air get trapped under a conformal coating layer. Foam is an extreme form of bubbling, and some- times bubbles burst through the coating, forming a pinhole. Causes: -coating is too viscous. -The coating is too thick. -application equipment not setup properly.
  2. What is the purpose of Conformal Coating?: Conformal coatings can be used in a wide range of environments to protect printed circuit boards from moisture, salt spray, chemicals and temperature extremes in order to prevent such things as corrosion, mold growth, and electrical failures.
  3. Measuring wet coating (2) Wet Film Comb: Most common method to measure wet coating. The gauge consists of a series of combs with different distance between the marked points and the baseline. After placing the comb into the wet coating film, the thickness can be measured in Microns or Mils. Measurement determined by the number between the last tooth coated and the following tooth which is free of coating.
  4. Measuring wet coating (2)

Wet Film Wheel: Method to measure wet coating using two outer wheels fixed to a central spindle wheel. Thickness is measured by rolling the wheel on the maximum scale towards accurately ground zero. When rolling the wheel on the coated board, the central wheel will touch the coating. The first point of contact on the central wheel determines the wet film thickness.

  1. Measling: Internal condition occurring in laminated base material in which the glass fibers are separated from the resin at the weave intersection. This condition manifests itself in the form of discrete white spots or crosses below the surface of the base material, and is usually related to THERMALLY INDUCED STRESS.
  2. Crazing: Internal condition occurring in the laminated base material in which the glass fibers are separated from the resin at the weave intersections. This condition manifests itself in the form of CONNECTED white spots or crosses below the surface of the base material and usually related to MECHANICALLY INDUCED STRESS.
  3. Blistering: Delamination in the form of a localized swelling and separation between any of the layers of a lamination base material, or between base material and conductive foil or protective coating.
  4. Delamination: Separation between plies within base material, between a base material and a conductive foil or any other planar separation within a printed board.
  5. Weave Texture: Surface condition of a base material in which a weave pattern of glass cloth is apparent although the unbroken fibers are completely covered with resin.
  6. Weave Exposure: Surface condition of a base material in which the unbroken fibers of woven glass cloth are NOT completely covered by resin.
  7. Haloing: condition existing in the base material in the form of a light area

Class 1 (General Electronic Products): Type of classification that includes prod- ucts suitable for applications where the major requirement is FUNCTION of the assembly.

  1. Classification: Class 1,2, Class 2 (Dedicated Service Electronic Products): Type of classification that includes products where continued performance and extended life is required, and for which uninterrupted service is desired but not critical.
  2. Classification: Class 1,2, Class 3 (High performance Electronic Products): Type of classification that includes products where CONTINUED HIGH PERFORMANCE or perfor- mance-on-demand is critical. Equipment downtime cannot be tolerated, end- use environment may be uncommonly harsh. EX: military circuit boards
  3. Thermally induced stress: Heat might build up in the PCB because of inade- quate ventilation OR during PCB assembly, the heat produced during drilling and soldering might cause undue thermal stress on the components and lead defective boards.
  4. Solder Wetting: Metal in the solder bonds with metal on the printed circuit board or component. During this process, the Solder becomes fluid molten and can adhere properly to the component for a optimal solder joint. -the solder connection angle shall not exceed 90 Degrees.
  • CANNOT always be judged by surface appearance. The acceptable solder connection shall indicate evidence of and adherence where the solder blends to the soldered surface.
  1. Non-Wetting: The inability of molten solder to form a metallic bond with the basis metal.