Feature: Thermal management
Thermally-conductive silicones can withstand a wide range of temperatures whilst retaining their properties over time. They also resist dust, moisture and humidity and are flexible
TIMs Silicone thermal interface materials, or TIMs, are a broad category of products designed to fill small air gaps that are poor conductors of heat. In PV inverters, silicone TIMs are applied or installed between the IGBTs and their printed circuit board (PCB). In a solar string, silicone TIMs can support the use of 1500V DC/AC inverters that handle up to 300kW of power. Compared with silicone thermal encapsulants, silicone TIMs provide broader and higher levels of thermal conductivity (0.9-5.2W/mK). TIMs include dispensable thermally-
conductive pads that are screen- or stencil-printed for higher production throughputs and lower total cost of ownership. For thinner bond lines, however, silicone thermal greases may be required. Because these greases are non- curable, they remain in a paste-like state. Tis supports optimal surface wetting, a leading factor in lower thermal interface resistance. Silicone thermal greases are easy
to rework and, depending on the formulation, have viscosities that range from non-flowable to semi-flowable. Application methods include squeegees,
needle dispensing and screen printing. Compared with curable materials, they provide less stability under harsh conditions. Silicone thermal gels are also used to
protect the IGBTs in PV inverters. Teir thermal conductivity ranges from 1.5- 6W/mK. Although thermal gels have limited adhesion, they are flowable and can be applied as printable pads or dispensed like a liquid gap filler. Compared with fabricated thermal pads, thermal gels are significantly cheaper and can support thinner bond lines. Bond line thickness ranges from 150µm to 5mm, and beaded versions are available for greater bond line control. PV inverters also use conformal coatings,
adhesives and sealants. Typically, silicone conformal coatings are used with high- current PCBs, gate driver boards, user interface boards and both, the main boards and the control boards in communications devices. Silicone sealants are applied along enclosures to protect against the ingress of dust and water. Staking adhesives
Renewable energy technologies like BESS will play a key role in domestic use 38 November 2023
www.electronicsworld.co.uk
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