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Parylene is considered by many to be the ultimate conformal coating for the protection of devices, components and surfaces in the electronics, instrumentation, aerospace, medical and engineering industries.
Some materials are difficult for the parylene to adhere to using traditional cleaning methods but with plasma treatment it can enhance the adherence.
You get the whole service: Cleaning; Masking; Coating; De-masking; Inspection plus a Certificate of Conformity if required. We will apply the coating you specify using spray, dip, hand, or gel processes as required. We will give advice on what is best for your application.
Parylene is unique in being created directly on the surface at room temperature.
There is no liquid phase involved. Coatings are truly conformal, of uniform controllable thickness, and are completely pinhole-free at thicknesses greater than 0.5μ.
No initiators or catalysts are involved in the polymerisation so the coating is very pure and free from trace ionic impurities.
Room temperature formation means the coatings are effectively
stress free.
Any substrate that is vacuum-stable can be coated and the coating adheres strongly to all materials, even stainless steel, provided the appropriate adhesion-promotion techniques are used.
Parylenes are chemically and biologically inert and stable and make excellent barrier materials.
Parylenes are almost completely unaffected by solvents, have low bulk permeability and are hydrophobic. Coatings easily pass a 100hr salt-spray test.
Parylenes have excellent electrical properties: low dielectric constant and loss with good high-frequency properties; good dielectric strength; and high bulk and surface resistivities.
Parylenes have good thermal endurance: Parylene C performs in air without significant loss of physical properties for 10 years at 80°C and in the absence of oxygen to temperatures in excess of 200°C.
Parylenes are transparent and can be used to coat optical elements.
Coatings perform well as dry lubricants: static and dynamic friction coefficients are equal and comparable to fluoropolymers with the advantage that they also have good wear and abrasion resistance.
FDA approval of parylene-coated devices is well-documented. The coatings comply with USP Class VI Plastics requirements and are MIL-I-46058C / IPC-cc-830B listed (as class XY).
Parylene is the generic name for the poly-para-xylylenes. These materials form linear, highly-crystalline polymers but can be usefully produced only as coatings and films. The most commonly used is Parylene C, the mono-chloro substituted compound. Parylene N, the un-substituted compound, has better high-frequency dielectric properties, better penetrating power for coating the bore of very small diameter tubes, and is often preferred in medical applications. Parylene D, the di-chloro-substituted compound, has better high temperature endurance.
The Parylene process is unique in coating technology and is best described as a vapour deposition polymerisation. It is carried out under vacuum and requires specialised equipment.
Substrates such as circuit boards are jig-mounted in a manner to ensure an even distribution of the monomer within the coating chamber and thus a consistent coating thickness. Small items such as ferrite cores are gently tumbled in the chamber, giving a very cost-effective process since many thousands may be coated at one time.
Parylene coating has been commercially available for over 30 years
and its properties are exploited in a wide range of applications.
Coatings are thin, truly conformal, stress-free and resistant to solvent and fungal attack. Good adhesion minimises ionic conduction at the coating-substrate interface and strengthens solder joints. Low dielectric constant minimises loading in high frequency applications.
Good adhesion to ceramic substrates. Good throwing power enables coating within spaces as narrow as 10μ. Interior of packages may be coated via a 1mm hole - coating strengthens wire-bonds and immobilises particles of debris such as solder balls.
Ferrite cores and bobbins are coated to reduce friction and abrasion in coil forming and to prevent chipping and dust formation. Coating cast metal magnets gives corrosion protection and electrical insulation. Accelerometers, strain gauges, pressure sensors etc may be coated for electrical insulation and environmental protection.
In the coating process the monomer is able to penetrate the surface of rubbers and plastics giving very good adhesion. A 2μ coating imparts dry lubricant and wear resistance characteristics to the surface. For example silicone rubber keypads are coated to improve the 'feel' of the surface and to protect the printing and 'O'-rings are coated to reduce friction in, for example, syringes. A thicker coating improves chemical and solvent resistance.
Because Parylene has excellent barrier properties, it cannot be hydrolytically degraded in the corrosive biological environment and is capable of penetrating and coating the bore of narrow tubes it has many uses in this field:
The excellent optical and barrier properties of Parylene and the stress-free nature of the coatings find many uses in this field, particularly in protecting moisture-sensitive elements such as potassium bromide windows. Freestanding films of Parylene may be produced by stripping the coating from suitably prepared glass plates and are used to produce windows and other components in instrumentation.
The unique application process and the predictable barrier properties and mechanical strength of Parylene coatings have also found other interesting applications:
| Property | units | Parylene C | Parylene N | Parylene D | ASTM method |
|---|---|---|---|---|---|
| General | |||||
| Density | g/cm3 | 1·29 | 1·11 | 1·42 | D1505 |
| Refractive Index | ηd23 | 1·64 | 1·66 | 1·67 | |
| Mechanical | |||||
| Tensile Modulus | GPa | 3·2 | 2·4 | 2·8 | D882 |
| Tensile Strength | MPa | 70 | 45 | 75 | D882 |
| Yield Strength | MPa | 55 | 42 | 60 | D882 |
| Elongation to Break (un-aged) | % | 200 | 30 | 10 | D882 |
| Yield Elongation | % | 2·9 | 2·5 | 3 | D882 |
| Rockwell Hardness | °R | 80 | 85 | D785 | |
| Coefficient of Friction - static | 0·29 | 0·25 | 0·35 | D1894 | |
| - dynamic | 0·29 | 0·25 | 0·31 | D1894 | |
| Thermal | |||||
| Melting Point | °C | 290 | 420 | 380 | |
| Thermal Conductivity | W/m.K | 0·08 | 0·12 | ||
| Property | units | Parylene C | Parylene N | Parylene D | ASTM method |
|---|---|---|---|---|---|
| Electrical | |||||
| Dielectric Constant - 50 Hz | 3·15 | 2·65 | 2·84 | D150 | |
| - 1 kHz | 3·10 | 2·65 | 2·82 | D150 | |
| - 1 MHz | 2·95 | 2·65 | 2·80 | D150 | |
| Dissipation Factor - 50 Hz | 20.10-3 | 0·2.10-3 | 4.10-3 | D150 | |
| - 1 kHz | 19.10-3 | 0·2.10-3 | 3.10-3 | D150 | |
| - 1 MHz | 13.10-3 | 0·6.10-3 | 2.10-3 | D150 | |
| Dielectric Strength @ 25μ - short time | MV/m | 220 | 275 | 215 | D149 |
| - step-by-step | 185 | 235 | D149 | ||
| Resistivity @ 23°C, 50%RH - Volume | Ω | 8·8.1016 | 1·4.1017 | 2.1016 | D257 |
| - Surface | Ω | 1.1014 | 1.1013 | 5.1016 | D257 |
| Barrier | |||||
| Water Absorption | % | <0·1 | <0·1 | <0·1 | D570 |
| Water Vapour Transmission @ 37°C | ng/(Pa.s.m) | 0·4.10-3 | 1·2.10-3 | 0·2.10-3 | E96 |
| Gas Permeability @ 25°C - N2 | amol/(Pa.s.m) | 2·0 | 15·4 | 9·0 | D1434 |
| - O2 | 14·4 | 78·4 | 64·0 | D1434 | |
| - CO2 | 15·4 | 429 | 26·0 | D1434 | |
| - H2S | 26·0 | 1590 | 2·9 | D1434 | |
| - SO2 | 22·0 | 3790 | 9·5 | D1434 | |
| - Cl2 | 0·7 | 148 | 1·1 | D1434 | |
