Parylene Conformal CoatingsRead More
Parylene Coating Blog by Diamond-MT
Basic Thermal Properties of Parylene Conformal Coatings
CVD-generated parylene combines high thermal stability with a low dielectric constant, minimal moisture absorption, and other advantageous properties which sustain its adhesion to substrate surfaces. Among the most beneficial of the parylenes’ thermal properties is their ability to function at an exceptional range of temperatures. Depending on the parylene type, they are operative at temperatures as low as -271º C, and as high as 450º C, representing an ability to perform within a span of 721º C.Read More
The Need for Adhesion Testing
Applied mechanical processes stimulate the binding force between surface molecules required for parylene adhesion to substrates, which is essential to both good parylene performance and assembly/component functionality. The emergence of conditions characterized by non-adherence and delamination squander parylene’s typically exceptional substrate protection against chemical attack, corrosion and moisture, as well as its superior dielectric insulation (er = 3.1).Read More
Characteristics of Noble Metals
Selecting the appropriate pre-treatment procedures is a key factor to this success of parylene adhesion to any substance. Procedures vary quite considerably, according to the materials designated for conformal coating and substrate. Chemically inert surfaces like gold, silver and other noble metals, and nonpolar thermoplastics such as parylene, are extremely difficult to bond; they require additional surface treatments besides cleaning.Read More
Parylene only adheres to substrates mechanically, and this can require assistance from additive substances; parylene’s chemically-based adherence is nonexistent. Adhesion is a consequence of molecular attraction stimulating the surface unification of two dissimilar substances; their joining creates a significant physical bond between them. Of the two primary types of adhesion, chemical adhesion results when a compound joins with another, because they share sufficient mutual chemical interaction to form a bond with each other. Because parylene is chemically inert, chemical adhesion is impossible; it adheres using the other method -- mechanical adhesion. Applied mechanical processes can stimulate this binding force between surface molecules.Read More
Poor parylene adhesion negates many of the coating’s most-valued functional properties, including dielectric strength, and resistance to the effects of chemicals, corrosive agents, and moisture. Surface treatments that amplify the interface adhesion between the deposited parylene and the coated substrate are therefore highly desirable. These treatments entail depositing parylene on a clean hydrophobic surface before its chemical vapor deposition (CVD) process is enacted.Read More
Delamination Problems of Parylene Conformal Coatings
Providing a uniform and pinhole-free substrate coating that is ultra-thin, lightweight and durable, parylene coatings completely conform to targeted components and assemblies. Parylene CVD generates a structurally continuous film that, with appropriate pre-treatment, penetrates deep within substrate surfaces, rather than simply attaching themselves to substrates as liquid-application coatings do. These provide effective, dielectrically efficient safeguards with coatings as thin as a fraction of a micrometer. Parylene is chemically and biologically inert and stable, an excellent barrier material to abrasive chemicals, bodily fluids, solvents, liquid water and water vapor.Read More
You've done your research, chosen a conformal coating provider, and coated your device. Now you want to know if the coating properly adhered.Read More
Improving Parylene Adhesion
Parylene provides an entirely conformal, durable, pinhole-free substrate coating of extreme utility for an exceptional range of materials, products and purposes. Despite its many advantages, parylene's chemical structure can actually interfere with the reliable interface adhesion required for optimal performance. The chemical vapor deposition (CVD) process that generates so many of parylene's benefits also nullifies chemically-based substrate adhesion; only mechanical adhesion is possible.
Implementing optimal adhesion can require surface modification via application of adhesion promoting agents or methods. The materials and processes used for these purposes are largely dependent on the substrate surface and component's specific operational environments and functions. Although most adhesion promotion methods are used prior to CVD, several can be integrated into the coating-process itself, Among the methods of adhesion promotion used with parylene are:
- Thorough surface-cleaning, which stimulates enhanced adhesion by eliminating accumulated substrate contaminants whose presence can diminish overall coating quality.
- Heat-treating. for three hours at temperatures of 140°C, beneficially activates longer-term adhesion and insulation.
- Active, wired devices profit from bilayer component-encapsulation processes.
While these techniques have their uses for parylene adhesion promotion, the chemical monolayer Silane A-174 (3-Methacryloxypropyltrimethoxysilane - C10H20O5Si) is used most frequently to modify substrate surfaces and improve parylene adhesion.
The Uses of Silane A-174
Silane A-174's value as an adhesion promoting agent stems largely from its versatility. It can be successfully applied to substrate materials like elastomer, glass, metal, paper, plastic or quartz, among a wide range of surface substances. The A-174 silane molecule develops a robust chemical bond with the substrate, facilitating the improved surface adhesion capacity of parylene’s mechanical property. Optimal parylene adhesion is commonly achieved by a treatment with A-174 silane prior to initiating the CVD process. However, regarding appropriate procedural scheduling:
- it is recommended that A-174's application be completed after any necessary masking operations have been finished;
- depending on substrate materials, manual spray, soaking, or vapor phase silane processing techniques may be used to apply A-174.
While the silane promotes adhesion, the parylene assures protection. Thus, appropriately proportional intermixtures of silane A-174 and parylene need to be used, in all cases. Corrosion-resistance can be diminished where the relationship between parylene and silane is inexact, causing part and function deterioration from both beneath- and external to the conformal covering. This is especially the case with medical implants, where reliable component function is mandatory, despite being subjected to persistent exposure to often harsh bodily fluids.Read More
While parylene is an extremely effective conformal coating, its benefits only come into play when it is properly applied. When parylene is either applied incorrectly or is deposited on a surface that is not prepared for adhesion, the coating can become compromised. Luckily, common parylene defects can be identified, planned for and mitigated through proper procedures.Read More