Conformal parylene coating

The parylcne process has certain similarities with vacuum metallizing. The principal distinction is that truly conformal parylene coatings are deposited even on complex, three-dimensional substrates, such as on sharp points and in hidden or recessed areas. Vacuum metallizing, on the other hand, is a line-of-sight coating technology. 

Parylene s use in the medical field is linked to electronics. Certain pacemaker manufacturers use it as a protective conformal coating on pacemaker circuitry (69). The coated circuitry is sealed in a metal can, so that the parylene coating serves only as a backup should the primary barrier leak. There is also interest in its use as an electrode insulation in the fabrication of miniature electrodes for long-term implantation to record or to stimulate neurons in the central or peripheral nervous system, as the "front end" of experimental neural prostheses (70). One report describes the 3-yr survival of functioning parylene-coated electrodes in the brain of a monkey (71). 

Parylene s use in the medical field is linked to electronics. Certain pacemaker manufacturers use it as a protective conformal coating on pacemaker circuitry (75). The coated circuitry is sealed in a metal can, so that the parylene coating serves only as a backup should the primary barrier leak. There is also interest in... 

The Parylene conformal coatings are ultrathin, pinhole-free polymer coatings that provide a number of high-value surface treatment properties, such as, excellent moisture, chemical and dielectric barrier properties, thermal and UV stability, and dry-film lubricity. These properties make Parylene coatings the ideal choice for a number of industrial applications throughout the medical device, electronics, automotive, military, and aerospace industries. Some examples are listed [155]. 

Union Carbide Corp. Parylene conformal coatings, photoresists, developers, etchants, solder masks, potting compounds... 

Polymer Properties. The single most important feature of the parylenes, that feature which dominates the decision for their use in any specific situation, is the vapor deposition polymerization (VDP) process by which they are applied. VDP provides the room temperature coating process and produces the films of uniform thickness, having excellent thickness control, conformality, and purity. The engineering properties of commercial parylenes once they have been formed are given in Table 2. 

The most important application of parylenes is as a conformal coating for printed wiring assemblies. These coatings provide excellent chemical resistance, and resistance to fungal attack, hi addition, they exhibit stable dielectric properties over a wide range of temperatures. 

Parylene s use in the medical field is linked to electronics. For example, as a protective conformal coating on pacemaker circuitry. 

Direct deposition of the contacts and gate insulator on to the crystal [95, 96], In this technique the gate dielectric is the polymer parylene, which forms conformal coatings with good dielectric and mechanical properties. The polymer is deposited in a three-zone reactor, in which the deposition zone can be kept at room temperature. 

The most common conformal coatings are derived from polyurethanes, acrylics, and epoxies the more special formulations for high-temperature performance are based on silicones, diallyl-phthalate esters, and polyimides. An example of a vapor deposited conformal coating is Parylene. It is obtained by vapor deposition of p-xylylene, which is formed as a transient by dehydrogenation of p-xylene at high temperature, and polymerization on the surface of the object to be coated. Because p-xylylene monomer is not stable, it is advantageous to work with the cyclic dimer, di-p-xylylene (paracyclophane), which, upon heating under reduced pressure, will produce the transient monomer which converts to the polymer at low temperatures. 

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