The present invention relates to dissipating heat generated by integrated circuit (IC) modules, and a method of constructing such devices. In particular, the present disclosure relates to a method and apparatus for eliminating a dry out condition of a heat transfer or cooling fluid in a vertical heat sink assembly configured to dissipate heat generated by integrated circuit modules.
As is known, operating electronic devices produce heat. This heat should be removed from the devices in order to maintain device junction temperatures within desirable limits: failure to remove the heat thus produced results in increased device temperatures, potentially leading to thermal runaway conditions. Several trends in the electronics industry have combined to increase the importance of thermal management, including heat removal for electronic devices, including technologies where thermal management has traditionally been less of a concern, such as CMOS. In particular, the need for faster and more densely packed circuits has had a direct impact on the importance of thermal management. First, power dissipation, and therefore heat production, increases as the device operating frequencies increase. Second, increased operating frequencies may be possible at lower device junction temperatures. Finally, as more and more devices are packed onto a single chip, power density (Watts/cm2) increases, resulting in the need to remove more power from a given size chip or module. These trends have combined to create applications where it is no longer desirable to remove the heat from modern devices solely by traditional air cooling methods, such as by using traditional air cooled heat sinks.
For example, with the advent of multichip modules (MCMs), containing multiple integrated circuit (IC) chips each having many thousands of circuit elements, it has become possible to pack great numbers of electronic components together within a very small volume. As is well known, ICs generate significant amounts of heat during the course of their normal operation. Since most semiconductor or other solid state devices are sensitive to excessive temperatures, a solution to the problem of the generation of heat by IC chips in close proximity to one another in MCMs is of continuing concern to the industry.
A conventional approach to cooling components in electronic systems in which devices contained in MCMs are placed on printed circuit/wire boards or cards is to direct a stream of cooling air across the modules with the addition of heat sinks attached to the module to enhance the effectiveness of the airflow.
Limitation in the cooling capacity of the simple airflow/heat sink approach to cooling has led to the use of another technique, which is a more advanced approach to cooling of card-mounted MCMs. This technique utilizes heat pipe technology. Heat pipes per se are of course, well known and heat pipes in the form of vapor chambers are becoming common. In the related art, there are also teachings of heat pipes/vapor chambers for dissipating the heat generated by electronic components mounted on cards.
One approach includes using a cooling fluid or heat transfer fluid in a vapor chamber heat sink. A vapor chamber base enables heat sinks to perform better as the thermal resistance to spreading the heat in the base is reduced. The heat is removed from one side of the base in thermal communication with a heat source by evaporation of the heat transfer fluid and travels rapidly in a gaseous state until it condenses on a fin side of the base. In this manner, the heat is transferred from the base to the fins for subsequent conduction to convectively cooled fins extending from the base.
However, vapor chamber technology has several limitations when applied to MCMs. One limitation is that the above described heat transfer mechanism can fail if inadequate heat transfer fluid or cooling fluid is present on the evaporator surface of the base near the heat source. This is often the case when the vapor chamber is positioned vertically such that gravity causes the returning or condensed cooling fluid to accumulate at a lower area of the vertically oriented vapor chamber. For applications where the heat source is centrally located with respect to the vertically oriented heat sink, dry out conditions are often created near the heat source.
For the foregoing reasons, therefore, for an efficiently cooled electronic module or MCM that employs vapor chamber cooling. In particular, there is a need in the art for a method and apparatus of providing a vertically oriented vapor chamber and corresponding heat source to be cooled with a fluid coolant, while simultaneously eliminating dry out conditions near the heat source.
One embodiment is an electronic package includes a substrate; a heat source component operably coupled to the substrate, and in direct contact with and electrically connected to a top surface of the substrate; a heat sink assembly in thermal communication with the substrate. The heat sink assembly includes a plurality of distinct vapor chambers, each containing a heat transfer fluid configured to evaporate on a wall in thermal contact with a back surface of the heat source component and condense on an opposing wall defining an exterior wall defining the vapor chambers. Each of the plurality of distinct vapor chambers are serially aligned having facing sidewalls defining each relative to contiguous vapor chambers and at least one of the plurality of distinct vapor chambers includes a lower sidewall defining one distinct vapor chamber substantially aligned with a bottom defining the heat source component such that a bottom portion defining the one distinct vapor chamber is substantially aligned with a bottom portion of the heat source component.
Another embodiment is a method for lowering a thermal resistance of a vertically oriented heat sink assembly to dissipate heat from a heat source component. The method includes configuring a heat sink assembly with a plurality of distinct vapor chambers, each of the distinct vapor chambers containing a heat transfer fluid configured to evaporate on a wall in thermal contact with a back surface of the heat source component and condense on an opposing wall defining an exterior wall of the heat sink assembly; and configuring each of the plurality of distinct vapor chambers to be serially aligned having facing sidewalls defining each relative to contiguous vapor chambers and at least one of the plurality of distinct vapor chambers includes a lower sidewall defining one distinct vapor chamber substantially aligned with a bottom defining the heat source component such that a bottom portion defining the one distinct vapor chamber is substantially aligned with a bottom portion of the heat source component.
Referring to the exemplary drawings wherein like elements are numbered alike in the accompanying Figures:
The present disclosure will now be described in more detail by way of example with reference to the embodiments shown in the accompanying figures. It should be kept in mind that the following described embodiments are only presented by way of example and should not be construed as limiting the inventive concept to any particular physical configuration.
Further, if used and unless otherwise stated, the terms “upper”, “lower”, “front”, “back”, “over”, “under”, and similar such terms are not to be construed as limiting the invention to a particular orientation. Instead, these terms are used only on a relative basis.
For the purposes of the present disclosure, the terms printed circuit board (PCB) and printed wire board (PWB) are equivalent terms. The terms “in contact” and “contacting” indicate mechanical and thermal contact
Lid 130 includes a lower wall 135 having an outer surface 140, an upper wall 145 having an outer surface 150 and sidewalls 155 defining a vapor chamber 160. It will be noted that opposing sidewalls 155 defining vapor chamber 160 are shown closer together than with respect to
Vapor chamber 160 contains a heat transfer fluid such as, inter alia, water, freon or glycol. Front sides 110 of components 105 are electrically connected to a top surface 165 of substrate 102. Components 105 may be flip chip, wire-bonded or soldered to substrate 102. A thermal transfer medium 170 is in contact with back surfaces 115 of components 105 and outer surface 140 of lower wall 135 of lid 130 to enable thermal contact, mechanical restraint and pressure support over the contacting region. Thermal transfer medium 170 enables heat generated by the operation of components 105 to be efficiently transferred to lid 130.
Because of the excellent heat transfer capability afforded to lid 130 by vapor chamber 160, the lid may be fabricated from many different materials including but not limited to metals such as aluminum, copper, nickel, gold or Invar and other materials such as plastics, ceramics and composites. Because of the wide range of materials available, lid 130 may fabricated from a material having a CTE matched to (between about 25% to 700% of the coefficient of thermal expansion) substrate 102 or from the same material as the substrate. For example, if MCM 100 is a HyperBGA® International Business Machine Corp., Armonk, N.Y., in which substrate 102 is a polytetraflouroethylene (PTFE) based material having a CTE of about 10-12 ppm/° C., then lid 130 may be fabricated from an aluminum-silicon carbide composite having a CTE of about 10 ppm/° C.
Thermal transfer medium 170 may include a thermal adhesive, thermal grease, thermal-conductive pads, phase change or other materials known in the art.
A heat sink 180 having a plurality of horizontal fins 182 (see also
In an exemplary embodiment referring to
While MCM 100 has been illustrated in
Referring now to
Referring now to
In an exemplary embodiment as illustrated, barrier 370 is a horizontal solid section separating vapor chamber 360 into two distinct chambers, 361, 362. The larger upper vapor chamber 361 will have an ample supply of heat transfer fluid available near heat source 210 in spite of gravity acting thereon in vertical mount applications. Even though the lower vapor chamber 362 still works against gravity, lower vapor chamber 362 still provides some added cooling. Vapor chambers 361 and 362 together outperform a single vapor chamber in most vertical applications because adequate liquid is available and local to heat source 210 to evaporate heat load proximate heat source 210. Heat from heat source 210 is less prone to dry out vapor chamber 361 since a bottom of vapor chamber 361 is substantially aligned with heat source 210. In particular, a bottom of heat source 210 substantially coincides with a bottom of vapor chamber 361 where heat transfer fluid 220 would tend to accumulate due to gravity. Thus, the heat transfer path is less likely to increase because vapor chamber 361 insures that the local evaporator area is wet, thus lowering thermal resistance of heat transfer to heat sink 180.
The thermal performance is increased by lowering thermal resistance due to a decreased path length for the heat to travel to heat sink 180 because of eliminating a dried out section local to the centrally located heat source 210.
In an exemplary embodiment, upper vapor chamber 361 is configured having a bottom portion thereof substantially aligned or alternatively, not extending much past heat source 210 insuring that the evaporator area local to the heat source 210 is wet with condensed heat transfer fluid 220. The lower vapor chamber 362 works against gravity over a region similar to that described with respect to the single vapor chamber 260 in
For example,
Thus, an efficiently cooled IC, such as a MCM, that employs vapor chamber cooling with a plurality of separate vapor chambers in thermal communication with a vertically oriented heat sink assembly while minimizing dry out conditions and reducing thermal resistance has been described.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention is not to be limited to the particular embodiment disclosed as the best or only mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.