The present disclosure is related to heat sinks for cooling high power density electronic devices such as laser diodes, central processing units, etc., and more particularly to a heat sink design, elements thereof, and methods of making same.
A heat sink is a structural body with an extended surface area to facilitate heat dissipation into the environment for cooling. Heat sinks are commonly applied to a wide variety of heat-generating electronic devices to assist in maintaining a reduced operating temperature, often in conjunction with a fluid circulation system such as an air fan.
A typical heat sink has a planar surface which attaches to a device to be cooled, and a plurality of fins, pins, pipes or the like extending outward from said planar surface which form the extended surface area. Flat plate fin heat sinks are typically stamped, cast, extruded or machined monolithic structures. While relatively simple to produce, such devices are of only passable heat transfer efficiency, especially in use with high heat generating devices such as modern computer central processing units (CPUs), solid state light emitting devices (such as LEDs, solid-state lasers), etc.
Pin-fin heat sinks offer improved thermal performance as compared to flat plate fins, especially in forced convection cooling. In such designs, solid cylindrical pins are affixed to a substrate, such as by threading or soldering. Existing pin-fin heat sinks have thermal resistances on the order of 2-10 C/W (degrees C. per watt) in a fluid flow at a rate on the order of 400 LFPM (linear feet per minute) around the pin-fins. While an improvement on flat-fin heat sinks, this thermal resistance means that pin-fin heat sinks still do not reach the desired level of cooling preferred for many modern device applications.
While flat fins and pin-fins are commonly solid structures, heat pipes are typically hollow core structures, filled with air or other heat transfer medium. Heat pipes offer superior thermal resistance, as the effective conductivity is many multiples better than solid core structures such as copper. Manufacturing of heat pipes is generally an involved process, and hence more expensive than simple fins or pin-fins.
In one example of a heat pipe structure shown and described in U.S. Pat. No. 4,018,269, which is incorporated by reference herein, a heat pipe comprises concentric tubes with an inner tube covered with a metal fiber and spiral wound wire wick. In manufacture, a spool of tubing is passed through a straightener. Metal fibers are pressed onto the tube. The tube is then wound spirally with wire to produce a wicking structure. This wicking structure is then fired and wrapped with a metal sheet that is welded along a seam to create the outer tube. This blank can be cut to length, filled, and capped in separate processes. The completed filled heat pipes can be secured to a base, or otherwise attached to a device to be cooled, to produce a completed heat sink.
A current state-of-the-art heat pipe based CPU heat sink may have a thermal resistance of approximately 0.1-0.2 C/W at a flow rate of 400 LFPM, much improved over both flat-fin and pin-fin heat sinks. However, the above-described heat pipes, and the processes for making them, are relatively much more complex than simply producing either a flat-finned or pin-fin heat sink, and consequently comparatively much more expensive. The heat sink market typically must contend with low margins and high price sensitivity. Therefore, existing heat sink devices and methods of producing same either provide inadequate performance, are too large, are of overly complex design and manufacturing process, are of high unit cost, or several or all of the above.