Parylene Conformal Coating - Conformal Coating Services

About Parylene Conformal Coating - Conformal Coating Services

Diamond MT is proud to offer Global Subcontract Parylene Conformal Coating and Liquid Conformal Coating Services: Offering ALL types of conformal coating including acrylic coating, epoxy coating, silicone coating, urethane coating, and parylene coating. Facilities Available in the United States, Europe, and Asia Conformal Coating systems available including selective spray robots and dip machines Low, Medium, or High Volume Capacity Cleaning and Ionic Contamination Testing also available 100% Inspection of completed product Dedicated Services within customer facilities, as required Qualified with automotive, aerospace, medical, electronics, and defense companies globally.

Parylene Conformal Coating

Parylene is considered by many to be the ultimate conformal coating for protection of devices, components and surfaces in electronics, instrumentation, aerospace, medical and engineering industries. Parylene is unique in being created directly on the surface at room temperature. It is chemically stable and makes an excellent barrier material, has excellent thermal endurance, as well as excellent mechanical properties and high tensile strength.

• 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.
• Parylene coating completely penetrates spaces as narrow 0.01mm.
• No initiators or catalysts are involved in the polymerization, so the coating is very pure and free from trace ionic impurities.
• Room temperature formation means the coatings are effectively stress-free.
• Parylene is chemically and biologically inert and stable and make excellent barrier material.
• Parylene is unaffected by solvents, have low bulk permeability and are hydrophobic. Coatings easily pass a 100hr salt-spray test.
• Parylene has excellent electrical properties: low dielectric constant and loss with good high-frequency properties; good dielectric strength; and high bulk and surface resistance.
• Parylene has 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.
• Parylene is transparent and can be used to coat optical elements.
• 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.
• Parylene coatings are completely conformal, have a uniform thickness and are pinhole free. This is achieved by a unique vapor deposition polymerization process in which the coating is formed from a gaseous monomer without and intermediate liquid stage. As a result, component configurations with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids.
• Parylene coating provides an excellent barrier that exhibits a very low permeability to moisture and gases.
• Parylene coating has excellent mechanical properties, including high tensile strength.
• Parylene is stable over a very wide temperature range (-200 ‘C to +200 ‘C), allowing the chamber items coated in Parylene to be put in an autoclave.

Parylene Coating Applications

Here is a brief list of some of the items that can be parylene coated:

Printed Circuit Boards	MEMs	LEDs
Catheters	Stents	Magnets
Paper	Needles	Sensors
Ferrite Cores	Metallic Blocks	Optical lenses
Implantable devices	Valves	O-rings
Tubing	Silicon Wafers	Keypads
Stoppers	Seals	Mandrels
Molds	Motor Assemblies	Power Supplies
Backplanes	Photoelectric Cells	Forceps
Test Tubes	Probes	Fiber Optic Components
Pace-makers	Bobbins	Plus Many More...

The Parylene Deposition Process

Relatively easy to understand, the parylene deposition process can be difficult to implement, particularly with respect to controlling coating-thickness and otherwise ensuring a successful coating cycle.

Because coating type and required surface thickness vary according to substrate material and coating-project, deposition rates fluctuate. Processing can require less than an hour or more than 24 hours, at a deposition rate of about .2/mils-per-hour. While this slower rate of substrate covering generates parylene\'s superior conformal coating, compared to other coating options, it also adds to its cost. Mastering the parylene coating process helps assure these production expenditures are diminished.

Parylene\'s complex and specialized vapor-phase deposition technique ensures the polymer can be successfully applied as a structurally continuous film, entirely conformal to the characteristics of the selected substrate. To correctly master the process, assure each incoming order possesses all pertinent information affecting parylene application. This will include drawings, specifications, and special instructions that distinguish the order from others, allowing creation of customized solutions for the particular item.

Parylene deposition process completely eliminates the wet deposition method used by such other coating materials as epoxy, silicone, or urethane. It begins in a chemical-vacuum chamber, with raw, powdered parylene dimer placed in a loading boat, and inserted into the vaporizer. The dimer is initially heated to between 100º - 150º C, converting the solid-state parylene into a gas at the molecular level. The process requires consistent levels of heat; the temperature must increase steadily, ultimately reaching 680º C, sublimating the vaporous molecules and splitting it into a monomer.

Drawn by vacuum onto the selected substrate one molecule-at-a-time in the coating chamber, the monomer gas reaches the final deposition phase, the cold trap. Here, temperatures are cooled drastically to levels sufficient to remove any residual parylene materials pulled through the coating chamber from the substrate, between -90º and -120º C.

Pre-Deposition

Mastering the parylene coating process requires detailed attention to these procedures, prior to commencement of deposition and coating:

Thorough inspection of incoming items to-be-coated, verifying their quantity and condition. Preparation procedures enacted as necessary. For instance, cleaning/cleanliness-testing, or similar unique processes, are commenced, followed by masking of connectors and electrical components. Accumulated substrate contaminants diminish adhesion, so assuring appropriate levels of surface cleanliness is integral to parylene coating. Depending on the substrate surface, cleaning may be enacted manually, or through application of batch, inline, or ultrasonic methods. Most materials--glass, metal, plastic, etc.--require treatment with A-174 silane to effect appropriate surface modification before parylene application. Typically, doing so employs either manual-spray, soaking, or vapor-phase technology, applied after the masking operation, A-174 silane\'s molecule forms a unique chemical bond with the substrate\'s surface, sufficient to improve parylene adhesion.

Masking is exceptionally labor-intensive. Exceptional care is required to ensure every connector is effectively sealed, so gaseous parylene molecules do not penetrate their surfaces. All tape, or other covering materials, must thoroughly encompass the keep-out regions, without gaps, crevices or other openings, to ensure connector function is retained after coating.

Further inspection assures masking is in compliance with customers\' specifications.

The diversity of adhesion promotion methods requires a similarly diverse list of raw materials. Establishing best-adhesion practices is only part of mastering the parylene coating process; once established, strict adherence standards need to be reliably enforced to ensure quality of the conformal coatings. Using industry best practices, such as substrate cleansing and A-174 silane application, appropriately combined with standard, repeatable processes, will ensure strong adhesion for parylene coating. Adhesion promotion methods are typically used prior to the actual coating process, however some can be integrated during the process itself.

Coating Requirements

The parylene coating is applied through the deposition process described above. Once coating has been deposited, masking materials are removed; extreme caution must be exercised not to damage the thin layer of applied parylene.

An important consideration of appropriate parylene thickness is total required clearance. While an enclosure-PCB has few clearance issues, in many cases even an additional millimeter of parylene coating can be sufficient to generate dysfunctional mechanical abrasion, damaging the parylene surface and reducing its conformal qualities.

Regarding dielectric strength, items whose required levels of dielectricity are higher will need a thicker coat of parylene. Balancing dielectric strength with clearance generally requires quality testing to determine their correct ratio. The end-item customer may not always provide these specifications; learning how to determine dielectric/clearance ratios without this data is integral to mastering the parylene deposition process.

The coating process must generate a conformal covering explicitly meeting the customer\'s precise specifications. If changes are necessary, making them to order and on time are essential elements of mastering the parylene coating processes. A final inspection ensures successful completion of all process phases, and that the final product complies with the customer’s drawings and specifications.

Parylene Disadvantages

The raw material, parylene dimer, is rather expensive ranging from $200-$10,000+ per pound. Because parylene is applied through a vapor deposition process, everything, including items that do not need to be coated like inner diameter of the chamber, gets coated. This makes parylene an inherently inefficient process and wasteful with materials, which escalates the end cost to the customer.

Masking and otherwise prepping an article for parylene coating can be a labor intensive affair. Because parylene is applied as a vapor, it literally gets everywhere that air can. Our operators and quality inspectors must take this into account prior to coating to ensure that every one of the customer’s coating free areas are just that.

One major issue that often comes up for several of our high volume manufacturers is the limited throughput of parylene. Runs of the parylene machine can take anywhere from eight to over twenty-four hours. As a result of the limited chamber space, there is a fixed amount of product that can be processed during one coating cycle. This, coupled with the high capital cost of new equipment, can wreak havoc with our internal and our customer’s delivery schedules.

One final disadvantage of parylene to consider is the poor adhesion to many metals. Parylene has always had poor adhesion to gold, silver, stainless steel and other metals. Many printed circuit board manufacturers use gold in their products because of its conductivity. While there are some adhesion promotion methods that will greatly improve adhesion to these metals, they are either material or labor heavy and can increase costs significantly.

More about Parylene Conformal Coating - Conformal Coating Services

At Diamond MT, we offer parylene coatings of different polymeric varieties (N, C, and F) as listed in the following Table. The basic parylene molecule is the Parylene N (poly-para-xylylene) monomer. Modification of the Parylene N monomer by a functional group such as Chlorine and Fluorine leads to Parylene C (poly(2-chloro-para-xylylene)) and Parylene F, respectively. The derivatization of new varieties can be done by the addition of functional groups to Paryelene N main-chain phenyl ring and its alip

hatic carbon bonds. Derivatization results in a set of new material properties: crystallinity, melting temperature, resistivity, mechanical and electrical properties. New derivatives with enhanced properties can be used under different service conditions.

Table: Parylene Types and Properties *Materials data: MatWeb

Parylenes are pure organic polymers that contain trace amount of impurities or zero percent chloride, sodium,  potassium ions [2]. Parylene thin films offer complete coverage of surface even between closely spaced features that is useful in microelectronic applications. Due to their multiple advantages they have a wide application area in various industries.

Parylenes are transparent in the visible region of the solar spectrum. They exhibit a high absorption in the UV- region, λ˂ 350 nm. This high absorption results in their photodegradation process through chain scission and formation of macroradicalar species [3]. Accordingly, the photodiscoloration of Parylene C was reported to be higher compared to that of Parylene N. For all cases, parylene conformal coatings are advised to be used indoors without direct exposure to sun. Parylene F on the other hand is less susceptible to photodegradation. A problem interfering with wider scale adaptation of Parylene F is difficulty synthesizing dimer.  Low availability of F dimer inhibits it commercial viability, although researchers actively seek alternatives to dimer synthesis.

One of the advantages of parylene conformal coatings is that they are stress free, this aids in protecting the underlying application from generated stresses due to the coating process. They are light and mechanically strong with high tensile and yield strengths (table).

As discussed earlier Parylene N is the most basic form of parylenes, its advantages are its availability, constant dielectric coefficient at all frequencies, low friction and high dielectric strength. Parylene N is has a lifetime of 10 years at 60°C before failure, at 80°C it fails in a year, and can only withstand 24 hours at 120°C in air. Under vacuum parylenes can withstand longer at higher temperatures. [2]. The decomposition of Parylene N takes place through diffusion of oxygen into the molecule and reacting with C in the polymer at the decomposition temperature. The reported temperatures for decomposition under air, N2 and vacuum are 175, 350, and 425 °C, respectively [4]. Parylenes C and D follow similar Electrical properties of Parylene N were reported to be more favorable than that of Parylene C [2].  Parylene C’s volume resistivity drops to 10-15 compared to 10-16 of Parylene C at 160 °C’s. Dielectric constant of Parylene C increases with temperature while Parylene N has a relatively stable dielectric coefficient between 20 -200 °C’s [2].  As the thickness of Parylene C and Parylene N increases from 0.5 μm to 4-5 μm their breakdown voltage becomes closer and Parylene N shows a higher breakdown voltage at higher thicknesses. Parylene N was shown to be useful as a dielectric layer for use in microelectronic systems. In an advanced study, it was used as a conformal dielectric layer in 50 μm through silicon vias (TSV) [5].

Parylene C on the other hand is the most widely used type. It finds applications in microelectronics, microfluidic devices, medical implants (stents, needles, etc.), PCBs due to its diverse properties such as fast deposition rates, common CVD type deposition method. It complies with the FDA regulations with the biomedical use (ISO-10993 Biological Evaluations for Medical Applications).

Paryleen F is deposited using the Gorham method, with the cyclic dimer octofluoro-[2.2|paracyclophane].    Low availability and price of F dimer inhibits it commercial viability, although researchers actively seek alternatives to dimer synthesis.

Parylene N, C and F offer a low dielectric constant (k≈2-3) which makes them well suited for use as intra- and interlayer dielectrics electronic devices [6]. The dielectric constant is relatively high for Parylene C due to the polar bonds C-Cl. Among them, Parylene F exhibits a very high melting temperature (≤ 500 °C) compared to parylene N (420 °C) and C (290 °C). And, the highest thermal durability is observed for ParyleneF. The decomposition of fluorinated parylene takes place by the decoposition of -CF2- functional groups into -CF- functional groups both in air and nitrogen at the decomposition temperature and no reaction products with oxygen was observed [4]. It has the lowest dielectric constant (2.17 @ 1 MHz) among the three which makes Parylene F more attractive. It can be used as a dielectric layer in the semiconductor chips where high temperature exposure is required. Also, they were shown to be patternable in the micro-scale using Ar/O2 and N2/O2 discharges with straight sidewalls under right processing conditions [6]. The drawback of fluorinated parylene is the difficulty in obtaining the commercial dimer which makes it an expensive alternative to other parylenes. Also, it has the best conformal coating property through entering the smallest crevices.

In conclusion, each parylene type offers different advantages under various types of service conditions (optical, thermal, mechanical, electrical, biomedical). The selection criteria must be based on the aimed end use of the product.

 To discover more about parylene coatings, download our parylene whitepaper now:

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on Parylene 101

A natural process, corrosion enacts chemical/electrochemical reactions that degrade and gradually destroy materials or components within a functional environment.  The outcome can be dangerous and costly to repair.  

For printed circuit boards (PCBs) and similar assemblies, corroded electrical contacts can cause potentially life-threatening mechanical malfunction of aerospace/automotive/industrial systems during operation; corroded medical implants may disrupt pacemaker function or lead to blood poisoning.  PCBs can suffer electrolytic corrosion, when:

• electrical contacts within the assembly are subject to water or other moisture trapped between them. 
• Applied electrical voltage causes development of unintended electrolytic cells, which can decompose chemical compounds, initiating corrosive reactions.  
• However, contaminants such as chemical residue, dirt, oil and salt trapped between the substrate surface and the conformal film can also generate corrosion.
• Although corrosion generally starts from underneath a conformal coating, because of liquid/residue on the substrate surface, rapid changes in temperature can also crack or rupture the coating’s external layer, instigating  corrosion response.  
• Similarly, metal components within a PCB can produce oxides or salts within the operating environment, leading to corrosive dysfunction.  
• Other assembly materials, like ceramics or plastics, can also suffer corrosion and subsequent degradation of their useful properties, performance expectations and structural integrity.  

Considering the smaller size of PCBs, some corrosion mechanisms are less visible and therefore difficult to predict, but pits and cracks can develop, leading to wider spread physical disruption of assembly surfaces and interiors.  Conformally coating PCBswith the non-critical, non-toxic layer material parylene (XY/poly-para-xylylene), can prevent corrosion in most cases.