CROSS-REFERENCE TO RELATED APPLICATIONS
FIELD OF THE INVENTION
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/499,483, filed Sep. 2, 2003 and U.S. Provisional Patent Application Ser. No. 60/502,125, filed Sep. 11, 2003.
- BACKGROUND OF THE INVENTION
The present invention generally relates to thermal management systems for semiconductor devices and, more particularly, to systems for cooling such semiconductor devices during burn-in testing.
In the conventional manufacture of semiconductor devices, semiconductor wafers are first produced in batches. Each semiconductor wafer can contain many individual electronic devices or electronic circuits, which are known as dies. Each die is electrically tested by connecting it to special purpose test equipment. Probes, which are connected to the test equipment, are brought into contact with the die to be tested. This generally occurs at a prober station, which conventionally includes a platform arranged for supporting the wafer. It is important to test each individual circuit chip die while it is still attached in a wafer, and to also test the individual integrated circuit devices once they have been packaged for their intended use. In many testing applications, the tests must be performed at elevated temperatures which, if not regulated, could cause damage to the chip during testing. Accordingly, automated test systems are commonly outfitted with temperature control systems which can control the temperature of a semiconductor wafer or packaged integrated circuit under test.
For example, and referring to FIGS. 1 and 2, a semiconductor device test system A often includes a temperature-controlled semiconductor package support platform B that is mounted on a prober stage C of prober station D. A top surface E of the device support platform B supports a semiconductor device F and incorporates conventional vacuum line openings and grooves G facilitating secure holding of semiconductor device F in position on top surface E of device support platform B. A system controller and heater power source H are provided to control the temperature of device support platform B. A cooling system I is provided to help regulate the temperature of device support platform B. A user interface is provided in the form of a touch-screen display J where, for example, a desired temperature for the top of support platform B can be input. Temperature controlled systems for testing semiconductor devices during burn-in are well known, as disclosed in the following patents which are hereby incorporated herein by reference: U.S. Pat. Nos. 4,037,830, 4,213,698, RE31,053, 4,551,192, 4,609,037, 4,784,213, 5,001,423, 5,084,671, 5,382,311, 5,383,971, 5,435,379, 5,458,687, 5,460,684, 5,474,877, 5,478,609, 5,534,073, 5,588,827, 5,610,529, 5,663,653, 5,721,090, 5,730,803, 5,738,165, 5,762,714, 5,820,723, 5,830,808, 5,885,353, 5,904,776, 5,904,779, 5,958,140, 6,032,724, 6,037,793, 6,073,681, 6,245,202, 6,313,649, 6,394,797, 6,471,913, 6,583,638, and 6,771,086.
In many cases such support platforms are required to be able to both heat and cool the device. Many types of temperature-controlled support platforms are known and are widely available. Cooling is very often provided by a heat sink that is cooled by a recirculating fluid, or in other designs by passing a fluid through the support platform without recirculating it. The fluid can be a liquid or a gas, usually air in the latter case. The liquid or air can be chilled for greater cooling effect in passing through the support platform, and can be recirculated for greater efficiency. A support platform cooled by means of a fluid chilled to a temperature below ambient temperature enables device probing at temperatures below ambient. In general, conventional heat-sink designs often incorporate simple cooling channels cross-drilled and capped in the support platform.
- SUMMARY OF THE INVENTION
None of the foregoing systems and methods have been found to be completely satisfactory.
The present invention provides a cooling system for a semiconductor device burn-in test station. In one embodiment of the invention, one or more evaporators are provided in close thermal proximity to a semiconductor device being tested. Each evaporator includes a chambered enclosure having a capillary wick disposed on the walls of the enclosure that define the chamber. A condenser is arranged in fluid communication with each chamber, and a pump is arranged in flow communication between each evaporator and the condenser so as to circulate a coolant liquid between a pool of the coolant liquid that is maintained within the chambered enclosure and the condenser.
In another embodiment of the invention, a cooling system is provided that includes one or more evaporators, each having walls that define a chamber with a capillary wick disposed on the surfaces of the walls that bound the chamber. Advantageously, a pool of liquid coolant is disposed within the chamber. A condenser is arranged in fluid communication with each chamber, and a pump is arranged in flow communication between each evaporator and the condenser so as to circulate coolant liquid between the chamber and the condenser thereby maintaining the pool of coolant liquid within each chamber.
In yet another embodiment of the invention, a semiconductor device burn-in test station is provided including one or more evaporators, each having a wall arranged so as to support at least one semiconductor device and including a chambered enclosure having a capillary wick disposed on the walls of the enclosure that define the chamber. A condenser is arranged in fluid communication with each chamber, a pump is arranged in flow communication between each evaporator and the condenser so as to circulate a coolant liquid between a pool of the coolant liquid maintained within the chambered enclosure and the condenser.
BRIEF DESCRIPTION OF THE DRAWINGS
A method for cooling a heat source is also provided that includes pumping a coolant liquid into a chamber of an evaporator so as to form a pool. A portion of the coolant liquid is continuously drawn from the pool through a capillary wick to a position located adjacent to the heat source so that the coolant fluid is vaporized, The vaporized coolant fluid is condensed, and arranged in flow communication with the pump.
These and other features and advantages of the present invention will be more fully disclosed in, or rendered obvious by, the following detailed description of the preferred embodiment of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein:
FIG. 1 is a front elevational view of a temperature-controlled semiconductor device testing system of the type contemplated for use with the present invention;
FIG. 2 is an exploded, perspective view of a support platform or chuck used in the semiconductor device testing system shown in FIG. 1, and showing a typical semiconductor device; and
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 3 is a schematic illustration, partially in cross-section, of a two phase cooling system for burn-in testing of semiconductors devices formed in accordance with one embodiment of the invention.
This description of preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawing figures are not necessarily to scale and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. In the claims, means-plus-function clauses are intended to cover the structures described, suggested, or rendered obvious by the written description or drawings for performing the recited function, including not only structural equivalents but also equivalent structures.
Referring to FIG. 3, a two phase cooling systems 3, for burn-in testing of semiconductors devices F, formed in accordance with one embodiment of the invention includes one or more evaporator assemblies 5,8, a condenser assembly 12, a network of conduits 15, and a pump 19. More particularly, each evaporator assembly 5,8 often comprises at least one chambered enclosure 21 having walls 17 that define an interior chamber 18, an inlet opening 22 and an outlet opening 24 both located in a bottom portion 25 of chambered enclosure 21, in spaced confronting relation to one another. Inlet opening 22 is arranged in flow communication with pump 19, via liquid conduit 27, and outlet opening 24 is arranged in flow communication with condenser assembly 12, via vapor conduit 28. In one embodiment, chambered enclosure 21 has a top wall 29 that forms a portion of a device support platform arranged in a probe-station (such as the one shown in FIGS. 1 and 2) for supporting and thermally engaging semiconductor devices F to be burn-in tested. Each evaporator assembly 5,8 may include external and/or internal features and structures to aid in the rapid vaporization of a coolant fluid 30. For example, an externally applied thermally conductive coating may used to enhance heat transfer and spreading from the heat source throughout each evaporator assembly 5,8.
Advantageously, a porous internal surface coating , e.g., a capillary wick 32, is deposited on the interior surfaces of walls 17 that define chambered enclosure 21. Capillary wick 32 may comprise any of the typical heat pipe wick structures, such as grooves, screen, cables, adjacent layers of screening, felt, or sintered powders. Capillary wick 32 draws coolant fluid 30 up into the portion of capillary wick 32 that is adjacent to top wall 29 of chambered enclosure 21 from a pool 33 of coolant fluid 30 continuously saturating capillary wick 32 in bottom portion 25 of chambered enclosure 21, by capillary action. Advantageously, this arrangement separates the thermal performance of the evaporator wall (i.e., top wall 29) from the unstable two phase flow dynamics associated with pump 19. It thereby ensures that the heat source (i.e., top wall 29) is always exposed to a saturated wick, but never to a boiling pool of liquid which often allows all heat generator components (i.e., semiconductors F) to share the same vapor space and thereby the same isothermal conditions are present for all heat sources. A liquid level control valve 38, e.g., a float valve, is located within inlet opening 22, and arranged in flow control communication with pump 19, via liquid conduit 27. Liquid level control valve 38 helps to maintain the level of pool 33 within bottom portion 25 of chambered enclosure 21 so that pool 33 never completely fills the chamber.
Each evaporator assembly 5,8 acts as a heat exchanger transferring the heat given off by semiconductor devices F that are being burn-in tested adjacent to top wall 29. As coolant fluid 30 is heated, the pressure within each chambered enclosure 21 increases, vaporizing the saturated fluid contained in that portion of capillary wick 32 that is adjacent to top wall 29. The vapor flows through vapor conduit 28, toward condenser assembly 12. Pump 19 is arranged in fluid communication between each evaporator assembly 5,8 and condenser assembly 12. Pump 19 provides a continuous flow of coolant 30 to each pool 33 within each evaporator assembly 5,8 from condenser assembly 12. When liquid level control valves 38 are closed, i.e., when pool 33 within bottom portion 25 has reached an optimum level, a bypass valve 39 located within conduit 41 of network of conduits 15 allows excess coolant fluid 30 provided by pump 19 to be redirected back to condenser assembly 12.
Condenser assembly 12 comprises a chambered enclosure 40 having an inlet opening 42 arranged in flow communication with each of evaporator assemblies 5,8, via vapor conduit 28, and an outlet opening 44 arranged in flow communication with each evaporator assembly 5,8, through pump 19 and bypass valve 39, via liquid conduits 27,41 of network of conduits 15. Condenser assembly 12 acts as a heat exchanger transferring heat contained in vaporous coolant fluid 50 to the ambient surroundings or with a liquid cooled, secondary condenser 46 that is located within chambered enclosure 40, and chilled by a flowing liquid or gas, e.g., chilled water or air, from a pumped source (not shown).
In operation, two phase cooling system 3 provides cooling to support platform B for burn-in testing of semiconductors devices F by pump 19 supplying a measured amount of coolant liquid 30 to pool 33 at the bottom portion 25 of each chambered enclosure 21. Each evaporator assembly 5,8 is supplied with coolant liquid 30 such that liquid is allowed to form pool 33 in bottom portion 25 of each chambered enclosure 21. Significantly, coolant liquid 30 never completely fills chambered enclosure 21 as a result of liquid level control valves 38. Capillary wick 32 draws up coolant liquid 30 from pool 33, keeping that portion of capillary wick 32 20 that is disposed on the interior surface of top wall 29 saturated, but adjacent areas of chambered enclosure 21 filled with coolant vapor 50. As the incoming heat through top wall 29 generates coolant vapor 50 from coolant liquid 30 in the adjacent wick, the vapor flows into the vapor space 18 of the chamber. The vapor then flows to condenser assembly 12 where it is cooled and condensed, to once again be pumped, via pump 19, to evaporator assemblies 5,8. As this occurs, capillary wick 32 replenishes itself by drawing up more liquid coolant 30 from pool 33.
This construction advantageously separates the thermal performance of each evaporator assembly 5,8 from the sometimes unstable two phase flow dynamics of pump 19. Furthermore, the present invention ensures that the heat source, i.e., semiconductor device F, is always in thermal communication with a saturated capillary wick 32 disposed on the under side of top wall 29, but never subject to the unstable thermal effects caused by boiling of coolant liquid 30, thereby obtaining stable, well determined thermal evaporation characteristics. As evaporation occurs, capillary wick 32 retains any coolant liquid 30, ensuring that the onward flow through vapor conduit 28 is nearly purely coolant vapor 50. This allows each evaporator assembly 5,8 to share the same vapor space, thereby maintaining an isothermal condition at all heat sources. In another embodiment of the invention, one pool 33 is used to feed several evaporator assemblies 5,8.
It is to be understood that the present invention is by no means limited only to the particular constructions herein disclosed and shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims.