Famous golfers are not the only ones who can wear a prized green coat. How about your automotive electronics? Are they wearing green?
Many of today’s automotive circuit boards can benefit from the use of conformal coatings that allow them to reliably operate in rather harsh underhood environments. Conformal coatings have proven track records of protecting boards from dust and debris, liquids, and from contact with a wide gambit of harsh conditions thrown against them. Protective coatings work by forming a barrier to conductive contaminants that closely conforms over surfaces, components, wire bonds and solder joints. Additionally they electrically insulate and isolate conductors which may be in close proximity.
Benefits of Silicone Conformal Coatings
Several studies have shown that silicones have been one of the best conformal coatings at slowing the formation and growth of these tin-whisker species. Additionally they may also deflect the growth direction which can prolong the expected life expectancy of the electronic assembly.
Economic Benefits of Conformal Coatings
It is easy to concentrate on the price per kg when considering various types of coatings, but it is only part of the total cost of ownership. Likewise, materials which require a cure oven not only add capital costs when setting up a production line, but also incur energy costs to run. Other costs can include the cost of quality such as measured by first time reject and rework rates. Besides cost of ownership, performance criteria certainly must be met in automotive electronics.
Factors Affecting the Potential Environmental Benefits of Conformal Coatings
Besides cost and performance, a rapidly expanding concern for low environmental impact in the automotive industry is impacting the value board assemblers consider when evaluating conformal coating choices.This paper is reviewing elements that affect environmental impact of conformal coatings in automotive electronics.
Solvents in Acrylic Coatings
Most production lines capture only a fraction of the solvent vapors given off by many coatings, and in particular acrylic coatings. These solvents are typically vented to the atmosphere where they are usually counted as greenhouse gases. Additionally, most solvents have noxious odors that are quite objectionable to workers – and to neighbors as well. Solventless coatings create far fewer volatiles/vapors and therefore may contribute far less to environmental conditions such as global warming. Parylene, urethanes and silicones are commonly available in solventless versions, and silicones are in some cases available in solvents that are not considered VOC’s or greenhouse gases.
Toxicity from Coating Production
While nearly all materials can be considered as having at least some toxicological effects in certain concentrations or exposures, some coatings are recognized as needing particular care when handling, applying, curing and disposing of waste materials. Some acrylics and many urethanes in particular can present significant challenges in this regard. Parylene and silicone have some of the least issues in this regard.
Manufacturing Hazards Associated with Conformal Coating Production
Besides flammability and toxicology issues, worker exposure to unpleasant and/or noxious fumes and potential skin contact are of concern. Parylene, which must be deposited under highly controlled vacuum conditions, is commonly only applied at specialized vendors. Silicones generally are more user and operator – “friendly” than most conformal coatings.
When considering the environmental impact of a coating, evaluations of the waste associated with its application and use should be taken into consideration. While most spray, flow and dip tank applications can contain waste to a relatively low percentage, parylene application in contrast can generate 90% or greater rates of material waste.
It is easy to overlook the end fate of materials once they leave a manufacturing site. Organic carbon-based coatings will last a long time when used within their specification limits, but eventually they will chemically degrade and break down with exposure to sunlight, heat, ozone, bacteria and a host of other environmental conditions. Coating degradation causes the release of their chemical components to the environment. Silicones are widely recognized as having far superior stability to harsh and prolonged exposure conditions.
When carbon-based coatings do degrade, they release considerable carbon-content chemicals into the air and ground since they are typically made up of >90% carbon. However, since silicones are based on an inorganic mineral-like structure they have far less carbon to release when they do eventually degrade – typical silicones have only 33% carbon content.
There are many factors that go into the selection of conformal coatings used to protect electronic circuit boards in the automotive industry. Environmental “green” concerns are growing in importance, even in emerging markets. Each type of conformal coating has its own set of benefits and detractions that must be considered to make the best performance, economic and environmental choice.
Silicones have a relatively high purchase price, but their ease of use, high performance, superior stability, relatively low environmental impact and reliability improvements can often reduce their total cost of ownership to be equal to or even lower than other common coatings and the top choice when deciding what protective conformal coating to use.
This information has been sourced, reviewed and adapted from materials provided by Dow Corning.
For more information on this source, please visit Dow Corning.