Information About Dow Corning® Brand Conformal Coatings
Silicones and Electronics
Long-term, reliable protection of sensitive circuits and components has become increasingly more important in many delicate and demanding electronic applications. Silicones function over a wide temperature and humidity range as durable dielectric insulation, as barriers against environmental contaminants, and as stress-relieving shock and vibration absorbers. In addition to sustaining their physical and electrical properties over a broad range of operating conditions, silicones are resistant to ozone and ultraviolet degradation and have good chemical stability. Most Dow Corning silicones contain significantly less solvent than organic coatings and are available in a wide variety of cure systems.
Conformal coatings are materials applied in thin layers (typically a few mils or microns) onto printed circuits or other electronic substrates. They provide environmental and mechanical protection to significantly extend the life of the components and circuitry. Conformal coatings are traditionally applied by dipping, spraying, or simple flow coating, and increasingly by select coating, or robotic dispensing.
Conformal coatings protect electronic printed circuit boards from moisture and contaminants, preventing short circuits and corrosion of conductors and solder joints. They also minimize dendritic growth and the electromigration of metal between conductors. In addition, the use of conformal coatings protects circuits and components from abrasion and solvents. Stress relief is also provided, as is protection of the insulation resistance of the circuit board.
Dow Corning coatings are particularly useful for protecting circuitry in severe-service environments, while maintaining a low-stress environment for components and connections. These severe environments range from everyday temperature and humidity extremes seen in consumer electronics to the harsher automotive under-hood environment, up to the extreme conditions demanded in military or industrial applications. Recently Dow Corning coatings have also been used in a variety of consumer appliances and devices to protect against unpredicted conditions imposed by the end user. The coatings are supplied in a variety of forms that can be cured at room temperature or accelerated by heat, adaptable to your processing needs. Most conformal coatings contain a UV indicator enabling blacklight visualization of the coating.
Dow Corning® Conformal Coatings are supplied in three product families:
- Solventless RTV elastomeric conformal coatings require atmospheric moisture to cure. This family of coatings is rapidly gaining popularity because it is more environmentally friendly than solvent-based materials. Further, its rapid cure rates can be dramatically accelerated by mild heat, plus it is reworkable and cost-effective. These elastomers, when cured, offer the optimum stress relief for components and interconnections in a variety of service environments. Coatings manufactured for controlled volatility are offered for applications where low outgassing at package level or in confined environments is necessary.
- Solventless heat cure conformal coatings are designed for rapid processing at moderate temps (above 100°C). They require some heating to cure, offering long bath life at room temperature. Like the room-temperature-curing elastomers, these products offer optimum stress relief for components and interconnections in a variety of service environments.
- RTV elastoplastic conformal coatings have firm, dry surfaces for better handling and abrasion resistance after cure. They require atmospheric moisture to cure and their cure rates can be accelerated by mild heat. They are supplied in solvent, with low-VOC versions available.
Dow Corning manufactures a wide variety of coatings to meet the needs of most application and process situations, and we are continuously expanding the product offerings in each of these families to ensure that there are specific products to meet your needs. However, if you can’t find an exact match for your needs, Dow Corning can modify any of our existing products to help meet your exact needs through our Fast Formulation process. Examples of Fast Formulation options include modification of a product’s cure schedule, 2 modulus, viscosity, or color, or adding an inert intermediate such as UV indicator – all in a timely manner.
Product Finder – Dow Corning features a unique interactive product finder on our website that can help you select the right materials for your applications. You can access the product finder at www.dowcorning.com/electronics by selecting “Technical Data” on any of our product family pages.
Production of Prototype Coated Boards or Process Design – We can produce coated boards or test patterns for early evaluation of a coating’s protective abilities. Coatings will be applied simulating your own process of spraying, dipping, or flow coating. Based on our extensive industry experience, we can advise you on the best methods and conditions for your process.
Analytical, Environmental, and Physical Testing – We have expertise to share on a wide range of testing to monitor quality, on specialized testing for troubleshooting, or to simulate accelerated service conditions.
Equipment Recommendations – Through many years of providing materials for electronics protection, Dow Corning has developed strong alliances with key equipment suppliers worldwide. We have just launched the External Equipment Provider Alliance with nine leading companies, including PVA and Asymtek for conformal coatings. Save time and expense by taking advantage of these alliances to ensure the optimum integration of material and processing.
Consultation with Technical Experts – Have our experts visit your facility or join us at one of our global application centers to work together on your material and processing needs. We can provide seminars and training for your personnel to allow them to work more knowledgeably. With material, process, and equipment integration solutions from Dow Corning, you can manufacture more modules and assemblies in less time, at less cost, with fewer shutdowns and fewer customer rejects.
Tutorials – Conformal coating tutorials, including an overview and a processing tutorial, can be found on our website. The tutorials are accessible from the product family pages or the left-hand navigation bar under Technical Library.
Solventless RTV Elastomeric Conformal Coatings
Type Solventless, one-part, non-corrosive, RTV moisture-curing, silicone elastomers; most are fast cure
Physical Form Translucent liquids; available in different viscosities
Special Properties Can be accelerated with mild heat to provide very fast cure times; transparent to translucent; resist humidity and other harsh environments; good dielectric properties; available in controlled volatility for very sensitive applications such as relays, certain electric motors, potentiometers, and optical devices
Primary Uses Low-stress protective coatings for rigid and flexible PCBs; frequently used as a more environmentally friendly alternative to organic coatings
Solventless Heat Cure Conformal Coatings
Type One-part solventless silicone elastomers
Physical Form Translucent liquids; available in different viscosities; heat cure to low-stress elastomeric films
Special Properties Fast thermal cure; transparent; resist humidity and other harsh environments; good dielectric properties; self-priming adhesion
Primary Uses Protective coatings for rigid and flexible printed circuit boards; resist humidity and other harsh environments; frequently used as a more environmentally friendly alternative to organic coatings
RTV Elastoplastic Conformal Coatings
Type One-part RTV silicone resins
Physical Form Translucent liquids; available in traditional or OS solvent dilutions; cure to clear elastoplastic resin films
Special Properties Can be accelerated with mild heat to provide faster cure times; abrasion resistant; resist humidity and other harsh environments; good dielectric properties
Primary Uses Abrasion-resistant protective coatings for rigid and flexible PWBs, plus a variety of ceramic and hybrid circuits, components, connectors, and connections
POT LIFE AND CURE RATE
The pot life of Dow Corning RTV Conformal Coatings is dependent on the application method chosen. To extend pot life, minimize exposure to moisture by using dry air or dry nitrogen blanketing whenever possible.
The pot life of Dow Corning Heat Cure Conformal Coatings is also dependent on the conditions in which they are processed, but is typically greater than 2 months. Dip tanks or containers should be closed and sealed when not in use. To maximize pot life, tank temperatures should be maintained at less than 29°C (85°F).
In the manufacture of electronic devices, it is often desirable to salvage or reclaim damaged or defective units. Dow Corning Conformal Coatings offer excellent repairability because they can be removed from substrates and circuitry by scraping or cutting, or by using solvents or stripping agents. If only one circuit component is to be replaced, a soldering iron may be applied directly through the coating to remove the component.
After the circuit board has been repaired, the area should be cleaned by brushing or by using solvent, then dried and recoated with the original coating, as the coatings have very good adhesion to themselves. Heat cure coatings can be repaired with RTV coatings, but heat cure coatings may not work well when used to repair RTV coatings.
Certain materials, chemicals, curing agents, and plasticizers can inhibit the cure of Dow Corning® Q1-4010 Conformal Coating and Dow Corning® 1-4105 Conformal Coating. Most notable of these include:
- Organotin and other organometallic compounds
- Silicone rubber containing organotin catalyst
- Sulfur, polysulfides, polysulfones, or other sulfur-containing material
- Amines, urethanes, or amine-containing materials
- Phosphorus or phosphorus-containing materials
- Unsaturated hydrocarbon plasticizers
- Some solder flux residues
If a substrate or material is questionable with respect to potentially causing inhibition of cure, it is recommended that a small scale compatibility test be run to ascertain suitability in a given application. The presence of liquid or uncured product at the interface between the questionable substrate and the cured conformal coating indicates incompatibility and inhibition of cure.
Dow Corning Conformal Coatings have shown good compatibility with no- or low-lead solder residue.
Dow Corning Conformal Coatings are formulated to provide adhesion to most common electronic substrates and materials including adhesion to most low-solids (no clean) and no-lead solder flux residues. With heat-cure coatings, the adhesion is complete with the full cure time and temperature. With RTV cure coatings, adhesion typically lags behind cure and may take 72 hours to build in some coatings. On certain difficult, low-surface-energy surfaces, adhesion may be improved by priming or by special surface treatment such as chemical or plasma etching.
USEFUL TEMPERATURE RANGES
For most uses, silicone elastomers (including Dow Corning® 3-1753 Conformal Coating, Dow Corning® 3-1765 Conformal Coating, Dow Corning® 3-1744 Conformal Coating, Dow Corning® 3-1953 Conformal Coating, Dow Corning® 3-1965 Conformal Coating, Dow Corning® 3-1944 Conformal Coating, Dow Corning® 3140 RTV Coating, Dow Corning® Q1-4010 Conformal Coating, Dow Corning® 1-4105 Conformal Coating) should be operational over a temperature range of -45 to 200°C (-49 to 392°F) for long periods. However, at both the low- and high-temperature ends of the spectrum, behavior of the materials and performance in particular applications can become more complex and require additional considerations.
For low-temperature performance, thermal cycling to conditions such as -55°C (-67°F) may be possible, but performance should be verified for your parts or assemblies. Factors that may influence performance are configuration and stress sensitivity of components, cooling rates and hold times, and prior temperature history. RTV elastoplastic coatings maintain performance at -65°C (-85°F) and below.
At the high-temperature end, the durability of the cured silicone elastomer is time and temperature dependent. As expected, the higher the temperature, the shorter the time the material will remain useable.
STORAGE AND SHELF LIFE
Storage conditions and shelf life (“Use by” date) are indicated on the product label.
Special precautions must be taken to prevent moisture from contacting Dow Corning RTV Conformal Coatings. Containers should be kept tightly closed and head or air space minimized. Partially filled containers should be purged with dry air or other gases, such as nitrogen.
These products are neither tested nor represented as suitable for medical or pharmaceutical uses.
In general, Dow Corning Conformal Coatings are supplied in nominal 0.45-, 3.6-, 18-, and 200-kg (1-, 8-, 40-, and 440-lb) containers, net weight. Not all coatings may be available in all packages and some additional packages, such as bladder packs or tubes, may be available for certain coatings and package sizes.
SAFE HANDLING INFORMATION
PRODUCT SAFETY INFORMATION REQUIRED FOR SAFE USE IS NOT INCLUDED. BEFORE HANDLING, READ PRODUCT AND MATERIAL SAFETY DATA SHEETS AND CONTAINER LABELS FOR SAFE USE, PHYSICAL AND HEALTH HAZARD INFORMATION. THE MATERIAL SAFETY DATA SHEET IS AVAILABLE FROM YOUR DOW CORNING REPRESENTATIVE, OR DISTRIBUTOR, OR BY WRITING TO DOW CORNING CUSTOMER SERVICE, OR BY CALLING (989) 496-6000.
LIMITED WARRANTY INFORMATION – PLEASE READ CAREFULLY
The information contained herein is offered in good faith and is believed to be accurate. However, because conditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer’s tests to ensure that Dow Corning’s products are safe, effective, and fully satisfactory for the intended end use. Suggestions of use shall not be taken as inducements to infringe any patent.
Dow Corning’s sole warranty is that the product will meet the Dow Corning sales specifications in effect at the time of shipment.
Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted.
DOW CORNING SPECIFICALLY DISCLAIMS ANY OTHER EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY.
DOW CORNING DISCLAIMS LIABILITY FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES.