Climate-friendly Conformal Coating in Electronics
The neologism “climate hysteria“ was voted non-word of the year 2019 on the drastic grounds that "in the opinion of the jury, this word defames climate protection efforts and the climate protection movement and discredits important debates on climate protection".
Since the continued debate on climate change which has been actively fuelled by the "Fridays for Future" movement for some time now, more and more companies have started to work on the development of climate-friendly products and processes.
This emotional debate is often supported by national guidelines in the field of climate protection. As an example, the Technical Instructions for Clean Air should be mentioned here. This regulation is the "First General Administrative Directive on the Federal Immission Control Act" of the German Federal Government; it provides calculation rules for essential air pollutants. Similar regulations in the United States are those of the California Air Resources Board ("CARB") or the South Coast Air Quality Management District ("SCAQMD") which are aimed at improving air purity. As part of its Blue Sky strategy, China has presented a three-year plan to reduce VOC emissions by 10% as early as in 2020. Several key industries are affected by these regulations, such as the chemical industry, the automotive industry or the electrical industry.
As far as conformal coatings in the electrical industry are concerned, it is possible to reduce VOC emissions through different measures in the processing of such coating systems, or by selecting VOC-free systems from the outset. Here one can use aqueous coating systems such as the conformal coating ELPEGUARD SL 1305 AQ-ECO or cleaning systems such as ELPESPEC R 5888, or as another option, select systems with a 100% solids content. By using such systems, it is possible to sidestep solvents/VOC emissions and thus reduce the environmental impact.
Established solvent-based conformal coating systems sometimes have a VOC content of 40-80%, which can be reduced promptly by introducing newly developed coating systems.
Not only the conformal coatings themselves, but also the specific curing processes for such products can be viewed from the angle of "climate friendliness": Oxidative-curing coating systems widely used in the market are usually dried physically in a continuous oven. The subsequent oxidative curing can surely be carried out at room temperature, but in practice, the curing time is often shortened by several hours of storage in an oven, in view of increasing the productivity. In consequence, there is a permanent high energy consumption for operating such ovens.
For this reason, UV curing conformal coatings offer numerous benefits not only in terms of product performance, but also for the operator. Besides the fact that they are solvent-free, their curing by the UV curing method is more energy-efficient than conventional drying. Further advantages include reduced space requirements, a significant increase in cycle time and less exhaust air. Statistics have shown that the energy for curing was reduced by up to 90%.
As a disadvantage for environmental reasons, this UV curing method makes use of lamps with mercury components in the UV curing machinery (on the lines of the energy-saving lamp).
This in turn leads to the further development of UV curing conformal coating systems for the electronics, which are cured by means of UV LED machines.
Nowadays, conformal coatings are already available which are cured by special UV LED units. Here the light of the UV LEDs of a very narrow wave range is used for curing the coating systems. The advantages of the LED technology over against energy-saving lamps are transferrable to the field of UV LED curing. The energy efficiency is significantly higher because LEDs radiate (almost) no heat, the lifespan of LEDs is longer than that of conventional lamps, and in addition, UV curing machines can be supplied with a compact design.
Besides the benefits mentioned above, no harmful ozone, which is another pollutant controlled by numerous emission protection laws, is generated due to the narrow wave band of the UV LEDs. And what is more, no separate exhaust device is needed either.
Given the fact that there is no exposure to dangerous ozone and UVC radiation when UV LED curing conformal coating systems are chosen, the risk potential for the operator is limited, too.
The new ELPEGUARD thick film coating Twin-Cure DSL 1602 FLZ/400 has been especially developed for UV LED curing at a wavelength of 395 nm. The coating layer cures within seconds, based on an energy of 1500 mJ/cm2 and an output of 1500 mW/cm2. It is tack-free after UV curing and therefore inline-capable.
The curing in shadow areas such as under components is reliably ensured at room temperature, owing to a reaction with air humidity.
This thick film coating combines the excellent final properties of a polyurethane system (UR) with the fast UV LED curing of unsaturated polyacrylates (AR) in a single-component copolymer, which is characterized by a very high resistance under mechanical, chemical and climatic stress, as well as under extreme temperature changes.
Besides the basic requirement of high robustness that a conformal coating must fulfil even under demanding climatic loads, other aspects such as the processability and occupational safety play an essential role when selecting a conformal coating; nevertheless, environmental considerations and energy balance aspects are more and more coming to the fore.
