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Technology Paper 2007
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Thermshield Z-Axis Cooler Heat Sink Technology |
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Introduction |
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The power output capacity of current semiconductor power modules is rapidly out stripping the ability of air-cooled heat sinks to maintain acceptable semiconductor die junction temperatures. Thermshield Z-axis cooler technology pushes air-cooling another step allowing significantly increased heat levels, power outputs and heat flux densities. In many applications this new technology rivals the ability of liquid cooled systems without the complexity, cost and maintenance requirements of liquid cooling support equipment. |
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Background |
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Conventional air-cooled extrusions and bonded fin heat sinks rely on thin fins to provide heat removal. These extended surfaces remove heat that spreads laterally in the X and Y directions inside the heat sink base. These fins being very thin to increase surface area density do not offer high efficiency in moving heat away from this mounting surface in the Z-axis. In high speed air flow extended surface fins that are 1.0 to 2.0 mm thick can have efficiencies as low as 50% or less. This means that the tip of the fin will have only half of the temperature rise and half the heat dissipation as the fin does at the base. This is one of the largest restrictions in air-cooling power modules with conventional heat sinks. |
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Increasing Efficiency |
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Heat pipes with their ability to move heat with near zero temperature rise are employed as conduits to eliminate this fin efficiency problem. Z-axis cooler design uses large diameter heat pipes mounted through a base plate heat spreader perpendicular to the heat sink mounting surface. Heat spreaders integral to the heat pipes are positioned in the base plate to make maximum contact to the high heat density sites (die positions) under the power module. The heat pipes move heat away from the base plate and use a series of thin, copper fins to dissipate this heat into a forced air stream. Due to the effects of the heat pipe the copper fin furthest from the base plate will have virtually the same fin efficiency as the closest fin. In many cases Z-Axis coolers can increase cooling of a power module (IGBT or similar device) by greater than 100%. |
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Smaller Size and Better Cooling Make Smaller Systems |
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Z-axis cooler designs can be used in new applications to provide the power markets with smaller, more powerful, feature-rich systems. Decreasing heat sink size can have a significant effect on overall enclosure volume. Old designs can be upgraded to increase power output levels and hold temperature rise down, increasing system life and reliability. Typical applications range from UPS and power supplies to RF transmitters and motor drives. |
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Stacked Fin Coolers |
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- Very thin fins – down to 0.006"
- Competes with folded fin w/ lower cost
- Aluminum, copper or both
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Small Diameter Heat Pipes |
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- Very economical
- Versatile in design
- Can cool next generation microprocessors
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Ultrahigh Ratio Extrusion |
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- Up to 23:1 in 5.0 dia tool
- Up to 20:1 in 8.0 dia tool
- Replaces bonded fin at lower cost
- Fin thicknesses down to 0.040"
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High Power Heat Pipe Assemblies |
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- New designs for up to 2KW power modules
- >100% increased cooling over bonded fin
- Cost competitive with liquid cooling but without the support equipment
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Copper Inserts in Aluminum Heat Sinks |
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- Enhanced heat spreading
- Lower weight than all copper
- Lower cost than solid copper
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