the best solution when rework is important. A thin layer of paste is applied between the device and heat-sink to fill the air-gaps and improve contact. Paste applicationmethods include stencil printing, screen printing, automatic dispensing equipment or even an aerosol spray.
products tend to exhibit lower oil bleed and evaporationweight loss, plus a higher upper temperature limit exceeding 200o
there are applicationswhere siliconesmay be unsuitable, for examplewhen devices are sensitive to silicone contamination.
Two non-silicone thermal pastes, called HTCX and HTCPX, are
also offered by Electrolube. The products are designed to provide increased thermal conductivity, lower oil-bleed and lower evaporation weight loss. In fact the company states these versions possess oil-bleed and evaporation weight loss performance as good as, and in some cases better than, Electrolube’s silicone-based pastes.
RTV and adhesives
Certain applications benefit froma solid cure product,whichmay or may not bond the surfaces together. Electrolube offers three products in this category: TBS, TCOR and TCER.
Thermal Bonding System(TBS) is a two-part, epoxy adhesive
designed to bond a heat sink to the component. The adhesive containsmineral fillers and small glass beads of controlled diameter which control the adhesive thickness.
TCOR and TCER are Electrolube’s neutral cure, silicone RTV
products. TCOR is an oxime cure RTV,while TCER is an ethanol cure version. TCER has the advantage that it is very lowviscosity and higher in thermal conductivity compared to TCOR. However, TCOR exhibits improved bond-strength properties.
Epoxy/polyurethane potting compounds
For certain types of heat generating circuitry such as power supplies, itmay be beneficial to encapsulate the device in a heat-sink enclosure using a thermally conductive potting compound.
Electrolube produces a variety of two-part encapsulation
solutions utilising epoxy and polyurethane technologies. ER2074 is a thermally conductive encapsulation product. This
highly-filled epoxy resin offers high thermal conductivity of 1.26 W/mK but also has high viscosity of 16700 cPs.
The reduced filler content of ER2183 offers lower viscosity of
5000 cPs, yet has little effect on the thermal conductivity: ER2183 is 70 per cent lower in viscosity but only exhibits a 13 per cent decrease in thermal conductivity at 1.1W/mK.
UR5097 is a polyurethane potting compound that offers similar
viscosity to ER2183 at 6000 cPs. This product offers thermal conductivity of 0.65W/mK, but also has the added benefit of UL94V0 certification. This is useful for applications requiring a thermally conductive, flame retardant resin.
December 2010 | 31
Modern aluminium enclosures in an extensive range of sizes and styles:
• Compact instrument cases • Desktop enclosures • Portable enclosures • 19” rack cases
• Sloping front enclosures • 19” instrument cases •Wall enclosures
• Customised enclosures For more information visit our website: www.metcase.co.uk
METCASE ENCLOSURES A division of OKWEnclosures Ltd Tel: 01489 583858
Electrolube offers silicone and non-silicone thermal pastes. Silicone C. However,
Heatsinks are usually finned tomaximise surface area per unit volume
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