Elongation Properties of Parylene

For conformal coatings, elongation is a measure of material ductility — a specific coating’s ability to undergo significant plastic deformation before rupture. A coating’s yield elongation is the maximum stress the material will sustain before fracture. Thus, computed Parylene elongation measurements represent the total quantity of strain the conformal film can withstand before failure. While elongation is equal to a material’s operating failure strain, it has no exclusive units of measurements. Typically, it is represented as % strain, or percent area reduction from a tensile test, equaling the ratio between the affected material’s physical change (deformation) and the original length, generally defined as the change in length divided by the initial length.

The result is a figure for material elongation expressed as a percentage (%), showing how much bigger the object is after deformation has completed. Signified by the Greek letter ε, strain measures a material’s deformation/extension when subjected to a force or set of forces. Five percent (5%) elongation is considered significant; conformal coating needs to withstand that level and more for reliable, ongoing performance.

Tensile testing is often used to determine elongation at break. Synthetic polymer materials generally show enhanced ductility; this is true for Parylene, widely used for conformal coatings, protecting performance of printed circuit boards (PCBs) and related electronics within a wide range of uses. Parylene typically records high levels of elongation to failure, imperative for dependable conformal film protection.

Using a chemical vapor deposition (CVD) application process, one of Parylene’s major advantages is room-temperature deposit and cure; unlike liquid coatings — resins of acrylic, epoxy, silicone and urethane — it requires no separate curing procedure. This factor also bypasses the substantial temperature excursion associated with liquid conformal films. Implemented in a vacuum chamber, CVD generates inherently cleaner film application. Tests of Parylene’s elongation capabilities have provided a variety of generally positive results, especially in comparison to liquid coatings.

Considering fundamental components of elongation performance, a recent study of Parylene C’s barrier properties measured its elongation to break at 200%, with a yield elongation of % = 2·9 3. Thus, Parylene can elongate thrice its original size before breaking (the original length [100%] + twice more [200%] = three times longer). In addition, this study registered Parylene’s yield strength — the quantity of stress corresponding to a coating’s specified permanent plastic deformation — at 5·52 x 107n1m². Parylene C’s tensile strength was 6·90 x 107n1m² in this report, evidence corroborated by an additional study.

Parylene has been used for over 50 years to protect applications in a wide variety of industries. To learn more about elongation and see data tables regarding the many properties of the Parylenes, contact SCS.