Feature: Thermal protection
soldering or wire bonding. Bleed-out can also interfere with other manufacturing operations and contact-adjacent PCB components. Aſter PCB assembly is complete, bleed-out is generally only a cosmetic issue. Dry-out, separate but related, refers to
the thermally-conductive material that is leſt behind on the bond line aſter the liquid polymer’s migration. Te enhanced dry-out resistance that silicone greases provide is important because leſtover filler materials cannot wet surfaces properly. Because thermal greases are no-cure pastes, grease chemistry rather than curing must address dry-out. Termally- conductive silicones in advanced formulations do this reliably and are available with reduced volatile ingredients for sustainability and environmental health and safety. Along with bleed-out and dry-out,
traditional thermal greases may suffer from pump-out, the non-recoverable loss of thermally-conductive materials from between substrates. Pump-out happens when there are repeated bond line compressions from shape changes where different layers have different rates of expansion and contraction. Applications for thermally-conductive
silicone greases include lighting assemblies, telecommunications equipment, consumer electronics, power supplies and power components for transportation.
Encapsulants and gels Encapsulants and gels are thermally- conductive silicones that combine thermal protection with physical protection. Encapsulants can protect against mechanical and thermal shock, chemical attack, dust and humidity. Gels have a remarkably low modulus and can protect the most sensitive and delicate components against mechanical stresses, including those from thermal cycling. Encapsulants and gels have high
flowability for improved processing. Tey support fast curing with moderate heat. Tese materials come in a range of viscosities and have high thermal conductivity relative to viscosity.
Silicones offer high performance and strong cost-effective thermal management
Historically, low viscosity silicones achieved very fast dispensing at the expense of filler level and, in turn, thermal conductivity. To achieve an ultra-low modulus with maximum stress relief, older compounds also used less conductive filler. Te advanced silicones used in today’s
encapsulants and gels eliminate these unwanted tradeoffs. Tese materials can also achieve good adhesion without the use of a primer, which helps reduce cycle times. Tey require addition curing with moderate heat, offer fast cure times and harden into rubber-like elastomers for reliable protection. Tey also have excellent dielectric properties,
adhere to many substrates and are a good choice for automotive and power module applications.
Advanced silicone solutions Engineers need the reliable, long-lasting protection provided by advanced formulations of thermally-conductive silicones. It is important to choose materials that meet demanding requirements and to work with an experienced supplier that can provide technical support whenever and wherever it is needed. Termal protection is critical not just for
today’s electronics devices but for technology trends that promise faster data speeds with more heat-generating electronic content.
Thermally-conductive compounds help with surface irregularities
www.electronicsworld.co.uk December/January 2021 29
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