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Industry Terms and Definitions


Adhesion Promotion   The chemical process of preparing a surface to enhance its ability to be bonded to another surface, i.e. a layer of conformal coating.

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

Autoclave   Normally a medical device test that is used by utilizing high or low pressure and temperature used for sterilization.

Biocompatibility   Medical devices that contact tissue or are to be implanted, biocompatibility and biostability are the first and final requirements.

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

Capillary   The action of a surface of a liquid where it comes in contact with sold.

Chemical Vapor Deposition (CVD)   A common heat activated process that relies on gaseous chemicals processed through a series of stages in order to induce their chemical reaction over a substrate placed in a chamber.

Coefficient of Friction   The ratio between the force necessary to move one surface horizontally over another and the pressure between the two surfaces. A number expressing the amount of frictional effect: static or dynamic.

Cold Trap   The section in a Parylene deposition system, between the deposition chamber and vacuum pump used to collect the excess Parylene monomer flowing from the deposition chamber.

Connector   To join wires or circuits together and make a power connection.

Crazing    A crack in the surface or coating.


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

Crevice Penetration   Throwing power into areas that are recessed.

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.

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-Masking   The process of removing or disengaging a maskant film, tape, boot or plug.

Deposition   A phase transition in which gas transforms into solid.

De-Wetting   The rupture of a thin liquid film on a substrate (either a liquid itself, or a solid) and the formation of droplets.

Dielectric   An electrical insulator that can be polarized by electricity.

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.


Dimer   A compound consisting of two identical molecules linked together.

Dissipation   A release of energy from a previously greater state.

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.

Elastomers   Also known as "Rubber".

Elongation   A Chain of Parylene molecules that that are lengthened during the Deposition phase of the coating process.

EMI (Electromagnetic Interference)   Unwanted radiated electromagnetic energy that couples into electrical conductors.

Emulsion   A stable mixture of two or more immiscible liquids held in suspension by small percentages of emulsifiers.

EOS (Electrical Overstress)   Internal result of an unwanted application of electrical energy that results in damaged components.

ESD (Electrostatic Discharge)   Rapid discharge of electrical energy that was created from electrostatic sources.

Fish Eyes   A surface defect to the conformal coating that resembles the eyes of a fish.

Flex   A type of circuit that used on electronic assemblies that are flexible.

Flex materials   Pliable polymer films which enable two circuit card assemblies to be joined by end connectors.

FOD (Foreign Object Debris)   Object Contamination.


Gas Permeability   The ability of a gas or other volatile substance to penetrate a material.

Glass Transition Temperature Tg   The temperature at which an amorphous polymer, or the amorphous regions in a partially-crystalline polymer, changes from being in a hard and relatively-brittle condition to being in a viscous or rubbery condition.

Hardness   A property that indicates the ability of a material to resist penetration of a specific type of indent or 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.

Hydrolytic Stability   The degree of resistance of a polymer to permanent property changes from hydrolytic effects.

Hydrophobic   Lacking the affinity for water.

Hydrophilic   Having a strong affinity for water.

Impedance   The resistance to the flow of current, represented by an electrical network of combined resistance, capacitance and inductance reaction, in a conductor as seen by an AC source or varying time voltage.

Inhibition   The inability for the coating materials to obtain the desired properties at the manufacturers' specified time and temperature.

Insulation Resistance   A measure of the capability of a material to electrically insulate adjacent conductors from each other.

Linear Coefficient of Expansion   It is the fractional change in length of a material per degree of temperature change induced.

Lubricity   The measure of the reduction in friction (benefit of Parylene). Eliminates surface tack and stickiness as a dry film lubricant.


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

Mealing (Annealing)   A baking process where Parylene can be heated to increase hardness.

Mealing   A condition in form of discrete spots or patches that reveals a separation at the interface between a conformal coating and the surface to be coated.

Meniscus   The curve in the upper surface of a liquid close to the surface of the container.

Micron   A unit of measure for thin films. One (1) micron, micro meter, is equal to 3.93e-5 inches.

Mitigation   Lessening the force or intensity of the substrate.

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.

NBC Contamination   Abbreviation for Nuclear, Biological, and Chemical agents of contamination.

Nomenclature   A set of rules to generate systematic names for chemical compounds.

Nominal   Thickness that is not specific but being in a range.


Oligomer   A polymer or polymer intermediate containing relatively few structural units.

Orange Peeling   A surface defect to the conformal coating that resembles the surface or skin of an orange.

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

Paraxylylene (Parylene)   The chlorinated version of the basic Parylene N polymer with the aromatic atom replaced by one chlorine atom.

Parylene C   It is the chlorinated version of the Parylene N polymer. It has the basic Parylene N structure with the aromatic atom replaced by one chlorine atom.

Parylene D   It is the doubled-chlorinated version of the Parylene N polymer. It has the basic Parylene N structure with the aromatic atom replaced by two chlorines atoms.

Parylene F   It is the doubled-chlorinated version of the Parylene N polymer. It has the basic Parylene N structure with the aromatic atom replaced with fluorine.

Parylene N   It can be considered the base Parylene polymer out of most commercialized Parylene films. It is composed of an aromatic group with methylene groups attached at the para positions.

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

Physical Vapor Deposition (PVD)    A common heat-activated process that relies on a solid processed through a series of stages to yield atoms and induce their deposition over a substrate placed in a chamber.

Plasma Etch   The method by which to remove material from a surface using ions, generated through plasma excitation, bombarding the surface to release its atoms.


Polymer   A compound of high molecular weight that is derived from either the joining together or many small similar or dissimilar molecules or by the condensation of many small molecules by the elimination of water, alcohol, or some other solvent.

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

Priming   A surface treatment utilizing a surfactant to promote adhesion of conformal coating.

Propagation   The process of spreading to a larger area (i.e. cracks in coating, PCB boards, acrylic, etc.)

Pyrolysis Furnace   The heating element in a Parylene deposition system, between the vaporizer and deposition chamber, which is used to split the sublimated dimer molecule.

Rainbow Effect   Description of Parylene coating deposited over a substrate as a very thin film, below a micro meter. The light refraction by the Parylene film generates this optical phenomenon.

Repair   The act of restoring the functional capability of a defective article in a manner that precludes compliance of the article with applicable drawings or specifications.

Rework   The act of reprocessing noncomplying 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.


Shadowing, Coating   1. A situation that can occur during spray coating of a PCA when components may hide or "shadow" the area underneath them, relative to the spray direction, preventing the surfaces beneath the component from being coated.   2. Also used in reference to curing of coatings by UV rays when components may hide or "shadow" the area underneath, not allowing it to be exposed and cured by the UV rays.

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

Solder Balls   A small sphere of solder adhering to a laminate, resist, or conductor surface. The connecting pins on the underside of a BGA (Ball Grid Array).

Solder flux residue   A residual residue left from the manufacturing process of circuit assemblies.

Solder Pads   The pads on circuit assemblies that are solder.

Spectroscopy   The production and investigation of spectra, or the process of using a spectroscope or spectrometer.

Static Coating   The process by which substrates are Parylene coated on a fixture with adjustable vertical levels. The substrates remain still throughout the process while the fixture rotates at low and constant speed.

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.

Sublimated   A solid transforming directly into a gas bypassing the liquid stage.

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


Tensile Modulus   The measure of the initial resistance of a material to longitudinal stretching. Also called modulus of elasticity.

Tensile Strength   The pull stress required to break a given specimen or the the greatest longitudinal stress it can bear without tearing apart.

Tin Whiskers   Tin whiskers are tiny hairs growing at a right angle from a surface containing a high concentration of tin. They are the result of a crystalline metallurgical phenomenon involving the spontaneous growth not to be confused with dendrite growth.

Tumble Coating    The process by which substrates are Parylene coated in a horizontal cylinder with open lids. The substrates are in constant movement with minimal impact throughout the process given the low constant tumbling speed.

Vaporizer   The section in a Parylene deposition system that sublimates the Parylene dimer.

Vessication   The formation of blisters at the interface between a semi-permeable polymer film coating and another material caused by an osmotic effect from the interaction of water soluble matter with moisture.

Viscosities   A measure of resistance to gradual deformation by stress or tensile stress.

Viscosity   The property of a polymer to frictionally resist internal flow that is directly proportional to the applied force.

VOC (Volatile organic compound)   Regulated compounds containing carbon that have measurable vapor pressures.

Water Absorption   The ratio of the weight of water absorbed by a given material under specified conditions, to the weight of that material when dry. It is generally expressed as a percentage./p>

Wetting   The formation of a relatively uniform, and adherent film of materials on a surface.

Withstand Voltage   See 'dielectric strength'.

Yield Strength   The stress required to deform an (elastic) material permanently. This amount of stress will change the dimensions of the materials and when removed the material will not return to its original state.

Young's Modulus   Modulus of elasticity. A measure of the flexibility of a material. The lower the modulus, the more flexible the material.



Contact Curtiss-Wright Parylene Services with questions related to Parylene use in industrial and commercial coating applications, or for assistance with process development and full coating services for your products.


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