The rising popularity of conformal coatings extends beyond traditional applications, particularly in densely packaged portable electronic devices vulnerable to environmental-induced failures. However, navigating the selection of appropriate coating materials and application processes can pose challenges and consume significant time, especially for those unfamiliar with the subject. Lack of comprehensive understanding and adherence to relevant standards and specifications can result in costly and irreversible errors.

We created this page to answer all your conformal coating questions providing a foundational overview and hopes to remain an invaluable resource on conformal coatings.

Content Index:

1. ¿Qué es un revestimiento de conformidad?
2. What are the Different Types of Conformal Coatings?
3. ¿Cuáles son las ventajas de utilizar un revestimiento conformado?
4. How to Apply Conformal Coatings?
5. Is Conformal Coating the Same As Waterproofing?
6. ¿Es el revestimiento conformado conductor cuando está mojado?
7. Methods of Application
8. ¿Métodos de secado y/o curado de los revestimientos conformados?
9. Glossary (Terms & Definitions)
   

1.What is a Conformal Coating?

El revestimiento conformado es una capa protectora o película de polímero de 25 a 75 µm de grosor (50 µm normalmente) que se "ajusta" a la topología de la placa de circuito. Su objetivo es proteger los circuitos electrónicos de los entornos difíciles que pueden contener alta humedad, una serie de contaminantes en el aire y temperaturas variables. Al ser eléctricamente aislante, mantiene los niveles de resistencia de aislamiento superficial (SIR) a largo plazo y, por tanto, garantiza la integridad operativa del conjunto. También proporciona una barrera contra los contaminantes transportados por el aire del entorno operativo, como la salpicadura de sal, evitando así la corrosión.

Conformal coatings are a breathable protective layer that will protect against the environment the PCA is exposed to by filtering out the airborne contaminants and maintaining long-term surface insulation resistance but will also allow any moisture trapped in the circuit board to escape.

El concepto de recubrimiento conformado de la electrónica se propuso originalmente y se desarrolló a través de la investigación para satisfacer los exigentes requisitos de los militares décadas antes. HumiSeal formó parte de esas primeras investigaciones y ha seguido siendo pionero y líder durante más de 60 años, ya que la tecnología se ha expandido a una serie de industrias, entre ellas:

• Aeroespacial
• Automoción, incluidos los híbridos y los vehículos eléctricos
• Controles industriales
• Productos blancos
• Telecomunicaciones
• Energía tradicional y renovable

2.What are the Different Types of Conformal Coatings?

Conformal coatings come in a wide range of forms. From a physical standpoint, conformal coatings are commonly dispersed in organic solvents (solvent-based) or supplied in high or 100% solids (silicones and most UV curables).

From a chemical standpoint, conformal coatings’ standard chemistries include:

Acrílicos

Los revestimientos acrílicos son quizás los más populares de todos los materiales de revestimiento, ya que son fáciles de aplicar y eliminar, con un amplio margen de utilización. Los revestimientos acrílicos se secan rápidamente, son resistentes a los hongos y ofrecen una larga vida útil. Además, los materiales acrílicos producen poco o ningún calor durante el proceso de curado, lo que elimina los posibles daños a los componentes sensibles al calor. Los revestimientos tienen una baja contracción, ofrecen una importante resistencia a la humedad y presentan bajas temperaturas de transición vítrea.

Uretanos

Los revestimientos de poliuretano están disponibles en formulaciones de uno o dos componentes. Ambas opciones proporcionan una excelente resistencia a la humedad y una resistencia química mucho mayor que los recubrimientos acrílicos. Los poliuretanos monocomponentes, aunque son fáciles de aplicar y gozan de una larga vida útil, a veces requieren largos regímenes de curado para lograr un curado completo u óptimo. En algunos casos, el ciclo de curado puede acelerarse con la aplicación de calor. Las formulaciones de dos componentes pueden alcanzar las propiedades óptimas de curado en tan sólo una o tres horas con la ayuda del calor.

Siliconas

Los revestimientos conformados de silicona son los más utilizados en entornos de alta temperatura debido a su capacidad innata de soportar una exposición prolongada a temperaturas más altas que la mayoría de los demás productos químicos de revestimiento conformado. Este atributo los ha convertido en la principal elección para aplicaciones de automoción bajo el capó. También pueden aplicarse en películas más gruesas, lo que las hace útiles como herramienta de amortiguación/aislamiento de vibraciones si el conjunto revestido va a colocarse en un entorno de altas vibraciones.

Synthetic rubbers

Los productos de caucho sintético de HumiSeal son fórmulas únicas que pueden permitir al usuario alcanzar objetivos específicos de protección/medio ambiente que no ofrecen los revestimientos "tradicionales". Los materiales de caucho sintético se caracterizan por sus temperaturas de transición vítrea extremadamente bajas, lo que da lugar a un módulo estable en un amplio rango de temperaturas y a una flexibilidad extrema. Los cauchos sintéticos tienen la menor permeabilidad a la humedad de todas las resinas disponibles actualmente. Estos productos no representan necesariamente nuestra gama completa de caucho sintético.

UV curable acrylated urethanes.

Los revestimientos conformados curables por UV de HumiSeal representan una emocionante innovación que proporciona un rendimiento superior. Cuando se combinan con un curado extremadamente rápido, permiten tiempos de ciclo cortos y velocidades de producción máximas. Estos productos se pueden pulverizar utilizando equipos de pulverización automatizados tradicionales con la adición relativamente sencilla de una unidad de curado por luz UV de tamaño reducido.

Each chemistry is associated with certain physical properties that are suited for certain conditions and end-uses. For example, silicones tend to have the highest temperature resistance while synthetic rubbers and UV curables often provide the highest level of humidity resistance.

3- What Are the Advantages of Using a Conformal Coatings?

The advantages of conformal coatings can be summarized as follows:

1. Insulating property allow a reduction in PCB conductor spacing of over 80%
2. Puede ayudar a eliminar la necesidad de recintos complejos y sofisticados
3. Light weight
4. Completely protect the assembly against chemical and corrosive attack
5. Eliminate potential performance degradation due to environmental hazards
6. Minimize environmental stress on a PCB assembly
7. Inherent flexibility conforms to varied component profiles

Ideally, conformal coatings should exhibit the following characteristics:

8. Simple application
9. Easy removal, repair and replacement
10. High flexibility
11. Protection against thermal and mechanical shock
12. Protection against environmental hazards

4-How to Apply Conformal Coatings?

La forma de aplicar un revestimiento de conformidad depende principalmente de:

1. Método de aplicación preferido
2. Existing Available Equipment (Dip/Spray equipment, curing equipment etc.)
3. Diseño de la placa/complejidad/necesidades de enmascaramiento
4. Volúmenes deseados/tiempos de ciclo.

5-Is Conformal Coating the Same as Waterproofing?

Un revestimiento de conformación proporciona resistencia a la humedad, pero no es la barrera impermeable que uno espera con el término impermeable. De hecho, se requiere que los revestimientos conformados sean algo permeables para permitir que los contaminantes atrapados o la desgasificación de los componentes electrónicos escapen de forma segura y sin daños.

6-Is Conformal Coating Conductive When Wet?

Un revestimiento conformado está diseñado con una resistencia relativamente alta a la conducción de electricidad. Este rendimiento dieléctrico no se ve afectado por la presencia de líquidos (como el agua) en la superficie del revestimiento. Sin embargo, el propio líquido seguirá siendo conductor en la superficie, y la exposición prolongada a líquidos estancados acabará por degradar las propiedades dieléctricas de un revestimiento conformado hasta cierto punto debido a la absorción en el tiempo dentro del revestimiento, así como a la degradación química.

7-Methods of Conformal Coating Application: (In order of sophistication)

	Ventajas	Disadvantages
Brush on	Low capital cost	Labor intensive Inconsistent/poor quality Slow / low volume
Dip coat	Moderate/high volume Fairly consistent coating	Limited coating choices due to pot life issues Large masking requirements
Hand Spray	Low capital cost Moderate volume Light masking required	Operator dependent
Selective automated spray	Highest productivity/volume Most consistent results Minimizes masking Efficient, only coat where needed	Capital cost

 

8- Methods of Drying and/or Curing Conformal Coatings?

Con los cuatro métodos de aplicación mencionados anteriormente, también será necesario secar y, en algunos casos, curar o reticular el revestimiento aplicado. No todos los métodos serán aplicables o posibles para todos los productos químicos, por ejemplo, los revestimientos de curado UV sólo pueden curarse con equipos de curado UV.

	Ventajas	Disadvantages
Air Dry	Low investment	Slow Inconsistent/environment Dependent
Oven dry (batch or contiuous)	Moderate investment Higher volume possible	Investment
UV light cure	Very fast Very consistent	Capital cost Shadow areas

9- Conformal Coatings Glossary (terms & definitions)

Adhesion promotion
Either a chemical process of preparing a surface to enhance its ability for a coating to adhere to it (eg. Plasma) or an
internal modification to the conformal coating material to help ensure it adheres to the intended, or difficult to adhere to
substrate.

Adhesion failure
The rupture of an adhesive bond such that the separation appears to be at the adhesive-adherent interface.

AR/UR
Abbreviation standing for acrylic resin and urethane resin combination chemistries.

Bridging
Fillet or meniscus formation of coating around the leads of a component caused by capillary action.

Creep
Strain, deformation, or movement of coatings caused by time and/or temperature.

Cross-linking
The formation of chemical bonds between molecules in a thermosetting resin during a polymerization reaction.

CTE
Coefficient of Thermal Expansion – linear dimensional change with respect to an original dimension due to a change in
temperature. Generally, the greater the value, the more mismatch there is between the coating and substrate during
thermal excursions, which can result in stress-cracking.

Cure
A change in the physical properties of a polymer by a chemical reaction.

Degradation
Decrease in quality or integrity. Loss of desired physical, chemical or electrical properties.

Delamination
A separation between a conformal coating layer and the surface it is adhering to.

De-wetting
The propensity of the coating material to refuse to wet the surface evenly. This phenomenon is generally a sign of
localized contamination, or that the surface energy of the substrate was too low to start with.

Dielectric constant
The ratio of the capacitance of a configuration of electrodes with a specific material as the dielectric between them to the
capacitance of the same electrode configuration with a vacuum or air as the dielectric.

Dielectric strength
The maximum voltage that a dielectric can withstand under specified conditions without resulting in a voltage breakdown,
usually expressed as volts per unit dimension.

Dilution
Reduction in viscosity. Can be achieved by mixing a non-reacting, soluble agent (solvent) into the material.

Dissipation factor
A value that represents the tendency of insulating or dielectric materials to absorb some of the energy in an alternating-current signal.

Durometer
A measure of the degree of hardness or the resistance to be deformed or fractured.

Filler
A substance that is added to a material to modify its solidity, bulk, or other properties.

Fish eyes
A surface defect to the conformal coating that resembles the eyes of a fish, usually resulting from localized surface contamination.

Gel time
Time taken for a liquid polymer to begin to exhibit pseudo-elastic properties or to be immobilized.

Glass transition temperature Tg
The temperature at which an amorphous polymer, or the amorphous regions in a partially-crystalline polymer, changes from behaving more
like a glass to more like a rubber.

Hardness
A property that indicates the ability of a material to resist penetration of a specific type of indentor when forced into the material under
specified conditions. Indentation hardness is inversely related to the penetration and is dependent on the elastic modulus and viscoelastic
behavior of the material.

Insulation resistance
A measure of the capability of a material to electrically insulate adjacent conductors from each other. Moisture Insulation Resistance (MIR) is
the same measure made under hot and humid conditions, usually 65ºC/95%RH.

Masking
The process of applying a temporary film, tape boot or plug that prevents the area covered from being coated.

Monomer
A chemical compound that can undergo polymerization.

MSDS
(Material Safety Data Sheet) Provided by the manufacturer, contains relevant properties of the material with regards to safety concerns.

Multi-layering
The process of applying more than one layer of coating to make up the desired thickness.

Orange peeling
Surface defects in the conformal coating that resembles the surface or skin of an orange. Orange peeling is generally caused by a
combination of excessive drying speed resulting in wetting issues.

Outgassing
The gaseous emission from a processed coating layer when it is exposed to heat or reduced air pressure, or both.

Permeability
The ability of molecules of one material to flow through the matrix of another material. The degree of permeability is dependant on the
molecular structure of both materials.

Polymerization
The formation of a matrix of cross-linked long chain molecular structure from short chain monomer molecules.

Pot life
The length of time a material, substance, or product can be left in an open package or dispenser, while it meets all
applicable specification requirements and remains suitable for its intended use.

Rework
The act of reprocessing non-complying articles, through the use of original or alternate equivalent processing, in a manner
that assures compliance of the article with applicable drawings or specifications.

RTV
(Room Temperature Vulcanizing) The development of desired dry film properties at room temperature..

Shelf life
The length of time a material, substance, or product can be stored, under specific environmental conditions, while it
meets all applicable specification requirements and remains suitable for its intended use.

Shrinkage
Reduction in volume as a wet, freshly applied layer dries/cures into a coating film with desired properties.

Solids content
The ratio of the resin or polymer material to the solvent carrier. The percentage of material converted to solid coating
during curing.

Stripping
The process of eroding a material by chemical reaction. Stripping agents can be used to remove certain types of
conformal coating for the purpose of rework or repair.

Surface tension
The natural, inward, molecular-attraction force that inhibits the spread of a liquid at its interface with a solid material.

Viscosity
The property of a polymer to frictionally resist internal flow in the liquid state that is directly proportional to the applied
force. High viscosity materials generally resist flowing and levelling.

VOC
(Volatile organic compound) Regulated compounds containing at least one carbon atom and having a measurable vapor
pressure.

Wetting
The formation of a relatively uniform, and adherent film of materials on a surface. Surface tension of the applied material
must be lower than the surface energy of the substrate to enable this. Inability of a coating to wet a substrate is usually
indicative of surface contamination or an inherently low surface energy substrate (eg Teflon).