Application of parylene’s xylylene monomer employs a chemical vapor deposition (CVD) process implemented under a vacuum. Unlike wet coating application methods – brushing, dipping, spraying, etc. – parylene CVD is not line-of-sight. Because the vaporous monomer envelopes all sides of the assembly being coated, appropriate process control allows vacuum deposition of an entirely conformal coating, one that penetrates deep into any crevices, rivulets, or sharp edges and points that exist on the assembly’s surface. The resultant parylene film is insulating, ultra-thin, and pinhole-free, exhibiting superior protective barrier qualities and very low moisture permeability.
Among many others, these properties distinguish parylene as a conformal coating, when compared to liquid coatings such as acrylic, epoxy, silicone and urethane. Exceptionally stable biologically, chemically and electrically, parylene’s versatility recommends its usage for a wide range of products and purposes, including aeronautic, automotive, consumer, electronic, medical and military, encompassing MEMs- and nanotechnologies. Nevertheless, it is always necessary to establish parylene’s capacity for prolonged, safe-use for whatever coating application it is directed to.
Safe-use of Parylene in Storage and Manufacture
A white, granular (powdered) solid with a distinctive, organic odor, parylene’s health hazards are limited, but need to be monitored. While its reactivity hazards are negligible, parylene can be dangerous to workers due to over-exposure, which causes potential irritation to the handler’s eyes, skin or mucous membranes.
A minor fire hazard also exists. At higher temperatures, parylene may ignite and burn, generating potentially irritating vapors and toxic gases, like carbon dioxide, carbon monoxide and hydrogen chloride, due to thermal decomposition from excessive temperature. Furthermore, detectable quantities of dioxins, furans and a variety of other substances may result under certain conditions.
While these problems are undoubtedly serious, they can be easily controlled with careful worksite monitoring. Parylene infection targets the respiratory system, skin, and eyes at the ACUTE level of toxicity; skin problems can also reach CHRONIC levels if prolonged exposure is unchecked.
Inhalation of dusts and contact with skin and eyes represent the most likely conduits of occupational overexposure. Workers’ respiratory systems, particularly the nose and throat, are most significantly infected by inhalation of parylene-derived dust or particulates. Severe coughing, sneezing, or sore throat are the most evident symptoms of such parylene over-exposure in the workplace. The symptoms are typically alleviated when the afflicted individual is separated from exposure and given access to fresh air. If this is insufficient to generate recovery, artificial respiration should be instituted to support improvement of the victim’s vital functions.
Parylene that comes into contact with skin may instigate mild-to-moderate irritation, particularly after prolonged exposure. Dermatitis (reddened, dried skin) may develop if the worker’s exposure to parylene is especially intensive and protracted. While no parylene components are known to be absorbed through the skin, contact with eyes can result in irritation, reddening, and pain. After skin contamination, running water should be used to sanitize the affected area. Flushing should continue no fewer than 15 minutes; additional cleansing is suggested if any sign of skin irritation develops. Immediate medical attention needs to be provided workers victimized by the development of any antagonistic exposure symptoms. Eye exposure also requires liquid decontamination with gently running water, again uninterrupted for a minimum of 15 minutes. Medical attention must be provided as necessary.
Neither ingestion nor injection of parylene are major conduits of worker overexposure, with incidents of swallowing (etc.) far outnumbering those of accidental injection (being jabbed by a parylene-contaminated object). Inflammation of the mouth, throat, esophagus, and other digestive tissues can occur upon contact if parylene is swallowed. Excessive ingestion can incite nausea, stomach-ache, vomiting, and related gastric disorders. Contacting a physician or poison control center is recommended if parylene is swallowed. The victim’s mouth should be rinsed thoroughly with water. Vomiting should NOT be induced, although it should be assisted by leaning the victim forward if it occurs naturally. However, those unable to swallow, having convulsions or rendered unconscious should receive NO dilutents, and be treated by a physician immediately. Injection causes a wound at the site of the puncture, with attendant irritation, swelling and pain.
In all cases, victims should be taken for medical attention if they feel unwell or if adverse effects occur. Such pre-existing conditions as:
- asthma, emphysema, and related respiratory syndromes,
- dermatitis and associated skin disorders, and
- existing eye disorders,
may be aggravated by over-exposure to parylene. To prevent these occurrences, worksites are advised to ensure reliable ventilation throughout manufacturing areas. Compliance with germane regulations -- local, state, federal and international – governing the use of parylene is mandatory. Where excessive exposure occurs, covering or outright removal of contaminated materials is recommended to avoid subjecting rescuers to the dangerous conditions. Emergency responders are strongly advised to wear protective equipment best-suited to the particular circumstances of the response situation, in those rare occurrences where parylene handling becomes unsafe.
Consumer Safety of Parylene-coated Products
One category of products where parylene coatings are an integral to the product is implantable medical instruments, such as blood pressure sensors and cardiac-assist devices like pacemakers. Other medical devices benefitting from parylene film protection include:
- brain probes,
- bone-growth stimulators,
- bone pins,
- electronic circuits,
- electrosurgical devices (ESU) instruments,
- injection needles,
- pneumatically-powered surgical instruments,
- prosthetic components,
- orthopedic devices of all kinds,
- sensors for diagnostic monitoring of patients' conditions, and
- ultrasonic transducers.
Consumer safety is generated because the devices themselves maintain operation in conditions where reliable functionality may be necessary to sustain the patient’s life. Parylene
- protects the body from electronic impulses and other functional inevitabilities – vibrations, etc. – that are required from efficient operation, while
- safeguarding the device itself from often harsh bodily fluids.
- Pinhole-free coverage prevents internal leakage or incursion from the bodily environment.
Exceptionally stable biologically, chemically and electronically, parylene provides an effective electrical insulator that will not degrade in the presence of electrical current. It resists solvents and is insoluble at temperatures to 150°C. These factors generate reliable consumer safety under most performance circumstances, for the majority of parylene’s uses. However, repeated cyclic stressing MAY generate stress cracking and pinholing of parylene coatings for implants after prolonged use (2+ years), a situation requiring accurate monitoring.
Biocompatible, parylene possesses no pigment or similar properties that might:
- Irritate or infect internal tissues or organs
- Leak into the human system during application and interfere with medical instruments' measurements or readings.
Moreover, parylene’s ultra-thin, dielectric coatings can usefully be applied to MEMS or nano medical technologies, designed for use in less accessible, more-constricted bodily regions, offering medical service otherwise unavailable to patients. Parylene’s durable biocompatibility has no negative impact on bodily functions; implants enhance organ/tissue performance, and ensure the device's acceptance in these critical, difficult-to-reach regions of the body. Superior medical product service includes better lubrication along devices’ surfaces, improving patient comfort, further supporting consumer safety. In all, parylene-protected implants assure the lowest level of negative and potentially infectious surface-to-tissue interaction of any currently available conformal coating.
In addition to its utility coating medical devices, parylene's reliable combination of adhesion, electrical conductivity, durability, and flexibility augments consumer safety for other products:
- Aerospace/military: Escalating application of commercial off-the-shelf (COTS) electronics for aerospace/military systems is made safer by use of parylene coatings, which enhance functionality for embedded on-site weaponry, manned spaceflight/satellite electronics, and radar/detection equipment.
- Automotive: Protecting automotive circuits from engine environments typified by ongoing contact with harsh automotive fluids, engine humidity, exhaust fumes, and gasoline, parylene films help maintain sensors' functionality through changes in engine conditions, improving consumer safety.
In all, parylene coatings are chosen for a wide range of both consumer and specialized products because they generate consistently reliable protection, shielding components and exteriors without diminishing their functionality. In this way they add value and consumer safety.
To learn more about parylene's safety and other problems that may arise, download our whitepaper here: