POWER: THERMAL
to the naked eye, their characterisation typically involves some level of microscopic surface roughness and non-planarity. In practice, this means surfaces feature some degree of concave, convex, or twisted shape. Contact between these surfaces would only occur at the surface high points, with the low points forming air-filled voids or interstitial air gaps that resist heat dissipation due to the insulative properties of air. The way to eradicate these air gaps from the interface is to adopt gap-filling thermally conductive TIMs that conform to the irregularities of the surfaces, such as dispensable gels and pads. As a TIM of this type offers greater thermal conductivity than the air it replaces, resistance across the joint reduces, as does the component junction temperature. As well as providing essential thermal properties such as thermal impedance, thermal conductivity, co-efficient of thermal expansion and heat capacity (ability of the material to store heat), TIMs also offer electrical properties like voltage breakdown and volume resistivity. This is in addition to physical or elastomeric properties, such as vibration dampening. A variety of material types are available, mostly developed in response to the changing needs of electronics industry applications. Among the most common materials for electronic components such as latest-generation high-speed ICs are dispensable gels and pads. Thermally conductive gels, like the THERM-A-GAP GEL range from Parker Chomerics, are single-component dispensable thermal gap fillers that require no curing and prove highly suitable for dispensing over an electronic component such as an IC for effective cooling. Conforming perfectly to the surfaces of the heat-generating and heat-dissipating surface, thermal gels have the potential to eliminate multiple thermal gap filler pad part sizes, while their cross-linked
gel structure provides superior long-term thermal stability and performance. Gels are often preferable for filling complex shapes or providing additional adhesion. Thermally conductive pads, like the THERM-GAP PAD series from Parker Chomerics, come into their own for certain applications. These soft, silicone and non-silicone elastomers are ideal where heat must be conducted over a large and variant gap between an IC and a heat dissipating surface such as a heatsink. Pads are popular for applications requiring frequent maintenance or replacement, or in mass production scenarios prioritising consistency and convenience. These products also help in mechanical stability
by absorbing shock and vibration. Board-level shielding
Of course, chip cooling is only half the battle when looking to provide ICs with the protection they need for optimal performance and safety. The other major threat is electromagnetic interference (EMI), essentially any type of interference caused by electromagnetic fields that can disrupt the signal and operation of an electronic device. EMI, either incidental or malicious, can lead to the malfunction or even failure of electronic components such as ICs. Effective shielding is therefore of
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