Nowadays, electronics are everywhere: Not only in mobile phones, computers & Co do electronic assemblies on circuit boards ensure smooth functioning. In our everyday lives, literally nothing works if electronics fail, beginning in the early morning with the ringing of the alarm clock, the hairdryer, the electric toothbrush via the toaster, cooker, refrigerator and TV sets or microwaves and ending with the car, motorbike, bus or train.
Therefore, it is all the more important to ensure a smooth functioning and a safe insulation of the devices. Installed in ever-smaller spaces, electronics are becoming more and more vulnerable. Many material properties of coating materials must be taken into account: Electrical properties such as dielectric strength or resistance to moisture and insulation, thermal ones including thermal conductivity, flammability or temperature resistance , constructive ones such as workability, tensile or compressive strength and chemical-physical ones related to climate resistance, water absorption or UV light protection.
A variety of external influences can cause malfunctions in electronic assemblies. Besides vibrations (particularly relevant for the ever smaller devices we carry with us, e.g. smartphones, wearables such as fitness trackers or watches) these include humidity, temperature changes, air pressure, harmful gases or contamination by salts, dust or operating materials that are also potential sources of interference.
Electronic assemblies are built on insulators that can degrade as to their insulation capacity due to moisture or contamination, with the result that the devices no longer function properly. Unlike the carrier and solder resist, the exposed solder joints and components legs do not generally fulfil the insulation requirements under severe conditions. To avoid functional failures, coating materials are applied, such as conformal coatings, thick-film coatings or casting compounds. Among the coating materials for assembled PCBs, insulating systems based on plastics or synthetic resins are chosen almost exclusively. Plastics act as electrical insulators.
The coated electronic assemblies are tested for reliability. Basically, functional faults must be avoided for all electronic products. For this reason, elaborate tests are performed to guarantee the expected average service life of several years or decades, depending on the electronic device or component. The service periods are quite different: While an average of 1-3 years is customary for consumer electronics, it can be 10 years for aerospace and 15 years in the automotive industry, for example.
