The world of thermal interface materials continues to evolve as the cooling requirements for applications in the automotive, consumer, medical and aerospace markets continue to demand lower prices and higher performance. As each new product generation requires higher power in smaller packages the challenges associated with thermal management become more intense.
The criteria which engineers use to select these thermal interface materials will by necessity include the thermal conductivity. However other properties of the material such as its hardness, dielectric strength, dielectric constant, compression set, cut-through resistance, toughness, tensile strength and resistance to chemical and environmental attack is equally important, as well as their suitability for rework or repair.
So which is the best product for your application? Here are the top four thermal interface materials.
Highly conformable, dispensable, one and two component, pre-cured, or cure-in-place silicone, such as Chomerics THERM-A-GAP® gels are ideal for filling large and uneven gaps in electronics assemblies. The viscoelastic paste is a form stable, cured silicone material that takes considerably less force to deform during assembly than traditional form stable gap fillers. This characteristic helps avoid placing excessive stress on component solder joints and leads that can result in either premature failure of the device or damage to the circuit board on which it is placed.
Parker Chomerics has also developed pre-cured and cure-in-place non-silicone gels to resolve the issues of silicone contamination in some applications. This unique material has similar thermal and physical properties to the silicone gel without the problems silicone can sometimes cause.
Gap filling pads
Chomerics THERM-A-GAP® silicone based gap filler pads have supported the utilization of equipment enclosures or chassis as heat dissipaters in place of costly and heavy dedicated heat sinks. By fitting a piece of soft gap filling material between a device requiring thermal management and an enclosure, heat can be channeled away effectively. Because of the typically large surface area of the equipment enclosure coupled to the fact that it provides a direct thermal path to the lower temperature of the ‘outside world’, adopting this approach can also negate the need for fans where they were previously required for a specific design.
Gap filling pad materials are available in a wide range of thicknesses that now extends beyond 5mm, allowing even very large gaps to be bridged. Their extremely soft nature means that large mechanical tolerances can be taken up with relatively low assembly forces being used. Accurate blending of silicon-based gap fillers, using a range of materials with different thermal conductivities, results in a choice that allows designers to select a material that accurately meets the thermal requirements of their specific design.
These are generally very thin materials (around 0.25mm) that comprise a silicone elastomer blended with a thermally conductive filler. Fiber glass cloth is commonly used to reinforce the material and provide some resistance to cut through that would reduce the electrical isolating properties of the material. There is a wide choice of CHO-THERM® insulator pad materials available.
These use a variety of different fillers that provide a wide range of thermal and electrical performance levels. Options such as low-tack adhesive coatings, pressure sensitive adhesives, and tabbed release liners, which aid assembly, may also be specified.
Thermally conductive tapes, such as Chomerics THERMATTACH® provide effective alternatives to mechanical fasteners such as screws, clips and rivets for bonding heat sinks to either ceramic or metal device packages.
The benefits include, lower assembly times, smaller footprints, and reduced material costs.