Challenges to Parylene

Ultra-thin and pinhole-free, Parylene conformal coatings 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. At the same time, certain challenging variables can influence the Parylene coating process and should be accounted for in coating design and implementation. Given the substrate that needs protection and its operating environment, SCS Sales Engineers can guide customers through the coating selection and engineering process to ensure these pitfalls do not impact your product.

Improving moisture barrier performance
Coatings with a thickness lower than 5 microns face challenges while situated in operating environments characterized by persistent heat within a high-electric field. Under such conditions, resistance to corrosion can decline from contaminants or particles trapped inside the coating film. This failure has been attributed to inadequate sustained moisture diffusion when tested under accelerated soak conditions.

Minimizing leakage of current during operation
Although known for complete substrate encapsulation and superior transference of electrical impulses, leakage of current during operation can present an issue for Parylene. Where it exists, current leakage tends to increase during a product’s life, culminating at times with component dysfunction after as few as 120 days. The problems can become more severe if surface topography is complex or forces of micro motion during operation remain consistent through the component’s operation.

Bubbles and delamination within coatings
Lack of homogeneity, resulting from heterogeneous composition and structure among Parylene coating layers, can sometimes cause uncommon imperfections. Inspection by scanning electron microscopy (SEM) or energy-dispersive X-ray spectroscopy (EDS) can help discern breakdown regions in the conformal film to focus repair efforts.

Loss of coating resiliency under constant thermal treatment
Parylene coatings exhibit dependable consistency for many applications where exposure to ongoing thermal pressure is the rule; however, cases have emerged where Parylene films covering component substrates have become brittle and stiff from persistent thermal exposure.

Difficulty reworking/repairing problem areas
Parylene’s ability to permeate even the smallest crevice on the coated item generate strong adhesion. Reliably strong and hard, Parylene coatings are exceptionally difficult to chip away or otherwise mechanically compromise; all covered surfaces are typically resistant when reworking is necessary. Thermal processes often require temperatures as high 350°C (higher in a vacuum), which can also melt the underlying substrate.

Parylene’s conformal, protective qualities vary significantly among substrate materials: Although Parylene is exceptionally adaptable as a coating surface for an extensive range of materials, it is critical to select the best coating variant (e.g., Parylene N, C, D, Parylene HT®, etc.) to ensure proper coating function and long-term reliability. For assistance, contact SCS today.