US20050067146A1 - Two phase cooling system method for burn-in testing - Google Patents

Abstract

A cooling system for a semiconductor device burn-in test station includes one or more evaporators arranged in close thermal proximity to a semiconductor device. 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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• 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.
FIELD 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.
BACKGROUND OF THE INVENTION
• 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 toFIGS. 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.
• None of the foregoing systems and methods have been found to be completely satisfactory.
SUMMARY OF THE INVENTION
• 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.
• 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.
BRIEF DESCRIPTION OF THE DRAWINGS
• 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 inFIG. 1, and showing a typical semiconductor device; and
• 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.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• 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 toFIG. 3, a twophase cooling systems3, for burn-in testing of semiconductors devices F, formed in accordance with one embodiment of the invention includes one ormore evaporator assemblies5,8, acondenser assembly12, a network ofconduits15, and apump19. More particularly, eachevaporator assembly5,8 often comprises at least onechambered enclosure21 havingwalls17 that define aninterior chamber18, an inlet opening22 and an outlet opening24 both located in abottom portion25 ofchambered enclosure21, in spaced confronting relation to one another.Inlet opening22 is arranged in flow communication withpump19, vialiquid conduit27, andoutlet opening24 is arranged in flow communication withcondenser assembly12, viavapor conduit28. In one embodiment,chambered enclosure21 has atop wall29 that forms a portion of a device support platform arranged in a probe-station (such as the one shown inFIGS. 1 and 2) for supporting and thermally engaging semiconductor devices F to be burn-in tested. Eachevaporator assembly5,8 may include external and/or internal features and structures to aid in the rapid vaporization of acoolant fluid30. For example, an externally applied thermally conductive coating may used to enhance heat transfer and spreading from the heat source throughout eachevaporator assembly5,8.
• Advantageously, a porous internal surface coating , e.g., acapillary wick32, is deposited on the interior surfaces ofwalls17 that definechambered enclosure21.Capillary wick32 may comprise any of the typical heat pipe wick structures, such as grooves, screen, cables, adjacent layers of screening, felt, or sintered powders.Capillary wick32 drawscoolant fluid30 up into the portion ofcapillary wick32 that is adjacent totop wall29 ofchambered enclosure21 from apool33 ofcoolant fluid30 continuously saturatingcapillary wick32 inbottom portion25 ofchambered enclosure21, by capillary action. Advantageously, this arrangement separates the thermal performance of the evaporator wall (i.e., top wall29) from the unstable two phase flow dynamics associated withpump19. It thereby ensures that the heat source (i.e., top wall29) 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 liquidlevel control valve38, e.g., a float valve, is located withininlet opening22, and arranged in flow control communication withpump19, vialiquid conduit27. Liquidlevel control valve38 helps to maintain the level ofpool33 withinbottom portion25 of chamberedenclosure21 so thatpool33 never completely fills the chamber.
• Eachevaporator assembly5,8 acts as a heat exchanger transferring the heat given off by semiconductor devices F that are being burn-in tested adjacent totop wall29. Ascoolant fluid30 is heated, the pressure within each chamberedenclosure21 increases, vaporizing the saturated fluid contained in that portion ofcapillary wick32 that is adjacent totop wall29. The vapor flows throughvapor conduit28, towardcondenser assembly12.Pump19 is arranged in fluid communication between eachevaporator assembly5,8 andcondenser assembly12.Pump19 provides a continuous flow ofcoolant30 to eachpool33 within eachevaporator assembly5,8 fromcondenser assembly12. When liquidlevel control valves38 are closed, i.e., whenpool33 withinbottom portion25 has reached an optimum level, abypass valve39 located withinconduit41 of network ofconduits15 allowsexcess coolant fluid30 provided bypump19 to be redirected back tocondenser assembly12.
• Condenser assembly12 comprises a chamberedenclosure40 having aninlet opening42 arranged in flow communication with each ofevaporator assemblies5,8, viavapor conduit28, and anoutlet opening44 arranged in flow communication with eachevaporator assembly5,8, throughpump19 andbypass valve39, vialiquid conduits27,41 of network ofconduits15.Condenser assembly12 acts as a heat exchanger transferring heat contained invaporous coolant fluid50 to the ambient surroundings or with a liquid cooled,secondary condenser46 that is located within chamberedenclosure40, and chilled by a flowing liquid or gas, e.g., chilled water or air, from a pumped source (not shown).
• In operation, twophase cooling system3 provides cooling to support platform B for burn-in testing of semiconductors devices F bypump19 supplying a measured amount ofcoolant liquid30 to pool33 at thebottom portion25 of each chamberedenclosure21. Eachevaporator assembly5,8 is supplied withcoolant liquid30 such that liquid is allowed to formpool33 inbottom portion25 of each chamberedenclosure21. Significantly,coolant liquid30 never completely fills chamberedenclosure21 as a result of liquidlevel control valves38.Capillary wick32 draws upcoolant liquid30 frompool33, keeping that portion ofcapillary wick3220 that is disposed on the interior surface oftop wall29 saturated, but adjacent areas of chamberedenclosure21 filled withcoolant vapor50. As the incoming heat throughtop wall29 generatescoolant vapor50 fromcoolant liquid30 in the adjacent wick, the vapor flows into thevapor space18 of the chamber. The vapor then flows tocondenser assembly12 where it is cooled and condensed, to once again be pumped, viapump19, toevaporator assemblies5,8. As this occurs,capillary wick32 replenishes itself by drawing up moreliquid coolant30 frompool33.
• This construction advantageously separates the thermal performance of eachevaporator assembly5,8 from the sometimes unstable two phase flow dynamics ofpump19. Furthermore, the present invention ensures that the heat source, i.e., semiconductor device F, is always in thermal communication with a saturatedcapillary wick32 disposed on the under side oftop wall29, but never subject to the unstable thermal effects caused by boiling ofcoolant liquid30, thereby obtaining stable, well determined thermal evaporation characteristics. As evaporation occurs,capillary wick32 retains anycoolant liquid30, ensuring that the onward flow throughvapor conduit28 is nearly purelycoolant vapor50. This allows eachevaporator assembly5,8 to share the same vapor space, thereby maintaining an isothermal condition at all heat sources. In another embodiment of the invention, onepool33 is used to feedseveral evaporator assemblies5,8.
• 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.

Claims (26)

1. A cooling system for a semiconductor device burn-in test station comprising:

at least one evaporator including a chambered enclosure having a capillary wick disposed on the walls of said enclosure that define said chamber;

a condenser arranged in fluid communication with each said chamber; and

a pump arranged in flow communication between said at least one evaporator and said condenser so as to circulate a coolant liquid between a pool of said coolant liquid maintained within said chambered enclosure and said condenser.

2. A cooling system according toclaim 1 wherein said chambered enclosure includes an inlet opening arranged in flow communication with said pump and an outlet opening arranged in flow communication with said condenser.

3. A cooling system according toclaim 1 wherein said chambered enclosure includes a top wall that forms a portion of a device support platform arranged in a probe-station for supporting and thermally engaging a semiconductor device to be burn-in tested.

4. A cooling system according toclaim 1 wherein said at least one evaporator includes an externally applied thermally conductive coating.

5. A cooling system according toclaim 1 wherein said capillary wick comprises a porous internal surface coating deposited on the interior surfaces of said chambered enclosure.

6. A cooling system according toclaim 1 wherein said capillary wick comprises a structure selected from the group consisting of grooves, screen, cables, adjacent layers of screening, felt, and sintered powders.

7. A cooling system according toclaim 1 wherein said capillary wick draws coolant fluid to a top wall of said chambered enclosure from said pool thereby continuously saturating a portion of said capillary wick adjacent said top wall.

8. A cooling system according toclaim 2 comprising a liquid level control valve located within said inlet opening, and arranged in flow control communication with said pump so as to maintain a predetermined level of said coolant pool within said chambered enclosure.

9. A cooling system according toclaim 8 wherein said pump is arranged in fluid communication between said at least one evaporator and said condenser so as to provide a continuous flow of said coolant liquid to said at least one evaporator from said condenser.

10. A cooling system according toclaim 9 wherein when said liquid level control valve is closed, said pool is at an optimum level for continuously saturating said capillary wick.

11. A cooling system according toclaim 9 wherein said liquid level control valve allows excess coolant fluid provided by said pump to be redirected back to said condenser.

12. A cooling system for a semiconductor device burn-in test station comprising:

at least two evaporators each including a chambered enclosure having a capillary wick disposed on the walls of said enclosure that define said chamber;

a source of coolant arranged in fluid communication with each said chamber; and

a pump arranged in flow communication with said source of coolant and said at least two evaporators so as to circulate a coolant liquid between a pool of said coolant liquid maintained within said chambered enclosure and said source of coolant.

13. A cooling system comprising:

at least one evaporator having walls that define a chamber with a capillary wick disposed on the surfaces of said walls that bound said chamber;

a pool of liquid coolant disposed within said chamber;

a condenser arranged in fluid communication with each said chamber; and

a pump arranged in flow communication between said at least one evaporator and said condenser so as to circulate said coolant liquid between said chamber and said condenser so as to maintain said pool within said chamber.

14. A cooling system according toclaim 13 wherein said chamber includes an inlet opening arranged in flow communication with said pump and an outlet opening arranged in flow communication with said condenser.

15. A cooling system according toclaim 14 comprising a liquid level control valve located within said inlet opening, and arranged in flow control communication with said pump so as to maintain a predetermined level of said pool of coolant liquid within said chamber.

16. A cooling system according toclaim 15 wherein said pump is arranged in fluid communication between said at least one evaporator and said condenser so as to provide a continuous flow of said coolant liquid to said at least one evaporator from said condenser.

17. A cooling system according toclaim 16 wherein when said liquid level control valve is closed, said pool is at an optimum level for continuously saturating said capillary wick.

18. A cooling system according toclaim 13 wherein said chamber includes a top wall that forms a portion of a device support platform arranged in a probe-station for supporting and thermally engaging a semiconductor device to be burn-in tested.

19. A cooling system according toclaim 13 wherein said at least one evaporator includes an externally applied thermally conductive coating.

20. A cooling system according toclaim 13 wherein said capillary wick comprises a porous internal surface coating deposited on the interior surfaces of said chambered enclosure.

21. A cooling system according toclaim 13 wherein said capillary wick comprises a structure selected from the group consisting of grooves, screen, cables, adjacent layers of screening, felt, and sintered powders.

22. A cooling system according toclaim 13 Wherein said capillary wick draws coolant fluid to a top wall of said chamber from said pool thereby continuously saturating a portion of said capillary wick adjacent said top wall.

23. A cooling system according toclaim 15 wherein said liquid level control valve allows excess coolant fluid provided by said pump to be redirected back to said condenser.

24. A cooling system for a semiconductor device burn-in test station comprising:

at least two evaporators including a chambered enclosure having a capillary wick disposed on the walls of said enclosure that define said chamber;

a condenser arranged in fluid communication with each said chamber; and

a pump arranged in flow communication between said at least two evaporators and said condenser so as to circulate a coolant liquid between a pool of said coolant liquid maintained within said chambered enclosure and said condenser so that said coolant from said pool continuously wets said capillary wick.

25. A semiconductor device burn-in test station comprising:

at least one evaporator 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 said enclosure that define said chamber;

a condenser arranged in fluid communication with each said chamber; and

a pump arranged in flow communication between said at least one evaporator and said condenser so as to circulate a coolant liquid between a pool of said coolant liquid maintained within said chambered enclosure and said condenser.

26. A method for cooling a heat source comprising the steps of:

(A) pumping a coolant liquid into a chamber of an evaporator so as to form a pool;

(B) drawing continuously a portion of said coolant liquid from said pool through a capillary wick to a position located adjacent to said heat source so that said coolant fluid is vaporized; and

(C) condensing said vaporized coolant fluid and arranging said condensed coolant fluid in flow communication with said pump.

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