Since the 1980’s, the electronics industry has undergone explosive growth, as higher transistor densities have fueled substantial performance advances while paving the way for miniaturization. In order for these systems to function properly, the electronic circuits within them must be protected from extreme temperatures, contaminants, shock and vibration, and harsh environmental conditions. Silicones have played a major role in the electronics revolution, enabling advanced functionality by sealing and coating sensitive electronics.
Silicone is a synthetic material made of polymers that has a chemical structure based on chains of alternate silicon and oxygen atoms. It can remain stable in extreme environments, whether hot or cold, and maintain its properties as temperatures fluctuate. Physical forms include gum, room-temperature vulcanization (RTV), fluid, monomer, gel, and resin.
Silicones’ wide service temperature range, flexibility, superior electrical properties, and ability to protect components from environmental contaminants make them useful as adhesives, sealants, coatings, and potting compounds. Their ability to withstand extreme environmental conditions gives them an edge over other types of adhesives and related compounds for certain applications.
Business, consumer, and military applications rely on silicones to protect electronic components from heat, moisture, contamination, and accidental damage. Silicones are used in automotive systems, including airbag, brake, ignition, fuel, air, and transmission systems, to protect electronic parts from contaminants and to insulate them against extreme temperatures. In aviation and space systems, silicone adhesives, sealants, and encapsulants protect electronics from moisture and contaminants across a range of temperature extremes, ensuring the operational integrity of these complex systems.
Silicones are commonly found in power electronics and high frequency applications, protecting semiconductors in systems such as cell phone base towers which are often exposed to harsh weather conditions. That temperature range makes RTV silicones suitable to bond lenses onto telescopes and secure optics onto satellites and other structures. The outstanding ability to withstand incredible thermal and mechanical stress makes it possible to use silicones for sealing and protecting many items in aircraft and rocket construction.
The number of applications benefiting from silicones has grown tremendously over the years, as the increased heat generated by more transistors placed in smaller packages has called for higher temperature resistance to ensure reliability.
The use of silicones to protect sensitive microelectronic components from heat has led to extraordinary growth in the number and variety of consumer electronic devices, and contributed to highly reliable, longer lasting products in many industries.
Silicones offer unique combination of properties
The molecular structure of silicones is very different from that of epoxies and other organic polymers. The nature of the siloxane bonds (-Si-O-Si-) that form the backbone of silicone compounds gives silicones properties that are not found in other organic polymers. The geometry, stability, and high binding energy of these siloxane bonds make silicones highly flexible and much more resistant to high temperatures than other polymers. It is this rare combination of flexibility and high temperature resistance that sets silicones apart.
Silicones adhere well to many surfaces and offer a number of other beneficial properties. They have a relatively low dielectric constant, high dielectric strength, low dissipation factors, and are exceptional electrical insulators — properties that are little changed over a wide range of frequencies. Silicones are durable and exhibit exceptional weatherability, standing up to wind, rain, and ultraviolet light exposure with minimal effect on physical, mechanical, and electrical properties.
Silicones can typically withstand temperatures ranging from roughly -55°C to 200°C — with specialty formulations resisting temperatures as high as 300°C — while maintaining their other useful properties. The actual service temperature range and degree of high temperature stability of a silicone can vary, depending on the specific chemistry of a formulation. Because of their stability over a wide range of temperature, humidity, and frequency, silicones are often selected for use in applications subject to especially challenging operating conditions.
Certain properties of silicone systems can be engineered to address specific application requirements. For instance, although silicones are natural thermal insulators, they can be made to be thermally conductive through the use of fillers. Fillers can also be used to improve the electrical conductivity of silicones, for use in applications that call for EMI/RFI shielding.
Although silicones are most commonly translucent, they can be formulated to be optically clear or opaque, if needed, for optical and opto-electronic applications. Certain grades are designed to meet MIL-A-46146 and MIL-A-46146A Type 1 military specifications, or USP Class VI and other biocompatibility specifications. Because silicones do not ignite easily, they can be made to meet UL94V-0 and UL94V-1 specifications for flame retardancy, which is required for certain transportation, appliance, electro-optical, and other electronic systems
Silicones obtained at low temperatures with the help of air
With rare exception, the classical methods for synthesizing silicones (first monomers, then polymers) do not allow one to obtain functional organosilicon substrates. As a rule, these methods are either applicable to a narrow range of substrates or are time-consuming, expensive and involve multiple stages.
Russian scientists have developed a new method for synthesizing para-carboxyplenylsiloxanes, a unique class of organosilicon compounds. The resulting compounds are promising for creating self-healing, electrically conductive, heat- and frost-resistant silicones.
A team of scientists from A.N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (INEOS RAS), in collaboration with colleagues from the Russian Federation, used a combination of a metallic and organic reaction accelerators (catalysts), which allowed them to solve these problems: the reaction conditions were softened and high process selectivity was achieved. The reaction occurred with involvement of molecular oxygen, in liquid phase and at temperatures slightly above the room temperature, whereas many industrial processes are performed in gas phase under drastic conditions. Even now, the method can be scaled to gram amounts in order to produce a required compound. According to the scientists, this is very important since it is far not always that chemists can offer a reaction that can be used for applied purposes already tomorrow.
“Thus, we suggested a highly efficient method based on aerobic metal- and organo-catalyzed oxidation of starting para-tolylsiloxanes to para-carboxyphenylsiloxanes. This approach is based on “green”, commercially available, simple and inexpensive reagents and employs mild reaction conditions: molecular oxygen as the oxidant, a process temperature of 40-60°?, atmospheric pressure”, – says Dr. Ashot Arzumanyan, the leader and one of the contributors of this study, Senior Scientist of the Laboratory of organosilicon compounds named after K.A. Andrianov, INEOS RAS.
Furthermore, it has been shown that the suggested method is applicable to the oxidation of organic derivatives (alkylarenes) to the corresponding acids and ketones, as well as hydridosilanes to silanols (and/or siloxanols).
The scientists also studied whether materials can be obtained on the basis of para-carboxyphenylsiloxanes, including an analogue of such an industrially important polymer as PET that is used, for example, to bottle water and other beverages, to obtain fibers for clothes and for technical applications, etc. “The compounds that we obtained open prospects for the creation of self-healing, electrically conductive, heat- and frost-resistant and mechanically strong silicones. They can also serve as a base for developing new hybrid materials that may find use in catalysis, drug delivery, fuel storage, and in other fields of science, technology and medicine”, Ashot notes.
According to the analysts at Zion Market Research, global silicone Market was capitalized at USD 15.0 Billion in 2015 and is likely to cross USD 20.0 Billion in 2021, developing at a CAGR of 5.1% from 2016 to 2021.
Some of the key companies of global silicone market are BASF SE, Bluestar Silicones, Momentive Performance Materials Inc., Emerald Performance Materials LLC, Shin-Etsu Chemical Company, Zhejiang Xinan Chemical Industry Group Co. Ltd, Nusil Technology, Specialty Silicone Products Inc, The DOW Corning Corporation, Wacker Chemie AG, Kaneka Corporation, Rogers Corporation, and Jiangsu Hongda New Material Co. Ltd. These players are set to cross new heights in the global silicone market.