Conforming to a higher standard of reliability By Phil Kinner – HumiSeal Europe Ltd An electronic product's reliability has the potential to make or break its manufacturer and can be life-threatening in many safety critical applications. Conformal coatings have long been used to protect electronic assemblies from their operating environment but can vary hugely in their protective performance. It is the objective of this article to explain in detail why it is important to qualify coating products to the relevant standards and how different coating types affect performance. What is conformal coating? A conformal coating is a 25-75μm thick (50μm typical), protective plastic membrane (polymer film) that adheres to an assembled PCB by literally ‘conforming’ to its varied profile. Its primary function is to protect PCBs used in hostile or harsh operating environments. By being electrically insulating, it maintains long-term surface insulation resistance (SIR) levels and thus ensures the operational integrity of the assembly. It also provides a barrier to air-borne contaminants from the operating environment, such as salt-spray, thus preventing corrosion. Classic application examples include high reliability defence, automotive and aerospace, where coatings are used to protect against various combinations of moisture, aggressive chemicals and vapours, salt sprays, large temperature variations, mechanical vibration, and even organic attack (e.g. fungus). The protective nature of conformal coatings, however, means that they not only protect, but also serve to enhance product reliability and thereby reduce the potential cost and damaging effects of early field failures. As such their use is becoming increasingly common in consumer and domestic applications that can be susceptible to environmentally-induced field failure; including portable devices comprising fine pitch, densely populated assemblies, such as mobile phones, through to washing machines and televisions.
