Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
  • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
  • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
  • H01L23/3733—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon having a heterogeneous or anisotropic structure, e.g. powder or fibres in a matrix, wire mesh, porous structures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
  • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
  • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
  • B22F3/11—Making porous workpieces or articles
  • B22F3/1103—Making porous workpieces or articles with particular physical characteristics
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/10—Details of semiconductor or other solid state devices to be connected
  • H01L2924/11—Device type
  • H01L2924/12—Passive devices, e.g. 2 terminal devices
  • H01L2924/1204—Optical Diode
  • H01L2924/12044—OLED

Definitions

• the present invention relates to the manufacture of circuit boards and integrated circuit packages. More particularly, the invention relates to low storage modulus, electrically conductive thermal interfaces for integrated circuit packages.
• Integrated circuits are well known industrial products, and are used for a wide variety of commercial and consumer electronic applications. They are particularly useful in large scale applications such as in industrial control equipment, as well as in small scale devices such as telephones, radios, and personal computers.
• Cooling fans are often provided as an integral part of an electronic device or are separately attached thereto for increasing the surface area of the integrated circuit package which is exposed to air currents. Such fans are employed to increase the volume of air which is circulated within a device's housing.
• U.S. patent 5,522,700 teaches the use of a typical fan device for dissipating heat from an electronic component.
• U.S. patent 5,166,775 describes an air manifold mounted adjacent to an integrated circuit for directing air jets onto electronic devices mounted to the circuit .
• the air manifold has an air inlet and a plurality of outlet nozzles positioned along the channel for directing air onto the electronic devices.
• U.S. patent 4,620,216 describes a unitary heat sink for a semiconductor package having a plurality of cooling fin elements, which heat sink is used to cool high density integrated circuit modules.
• U.S. patent 5,535,094 teaches the combined use of an air blower and a heat sink. It teaches a module which has an integral blower that cools an integrated circuit package. The blower is attached to a heat sink that is mounted to the integrated circuit package. Heat generated by the integrated circuit conducts to the heat sink. The blower generates a stream of air that flows across the heat sink and removes heat from the package.
• Interfaces used in the semiconductor industry typically comprise metal interfaces or polymer adhesives filled with conductive fillers.
• Metal interfaces such as solder, silver, and gold provide low resistivity, but have a high storage modulus and are not suitable for large IC dice.
• polymer adhesives can be very low modulus, but their resistivity is too high.
• thermal interfaces for use with an integrated circuit package or semiconductor die, which thermal interface has a low modulus as well as high thermal and electrical conductivity.
• thermal interfaces to be capable of being assembled and processed at low temperatures, such as about 200°C or less.
• a porous, flexible, resilient heat transfer material is formed, which material comprises network of metal flakes.
• Such heat transfer materials are preferably produced by first forming a conductive paste comprising a volatile organic solvent and conductive metal flakes.
• the conductive paste is heated to a temperature below the melting point of the metal flakes, thereby evaporating the solvent and sintering the flakes only at their edges.
• the edges of the flakes are fused to the edges of adjacent flakes such that open pores are defined between at least some of the adjacent flakes, thereby forming a network of metal flakes.
• This network structure allows the heat transfer material to have a low storage modulus of less than about 10 GPa, while having good electrical resistance properties.
• the invention provides a porous, flexible, resilient heat transfer material which comprises a network of metal flakes, said flakes having edges, which flakes are sintered only at their edges and are fused to the edges of adjacent flakes such that open pores are defined between at least some of the adjacent flakes.
• the invention further provides a method for forming a porous, flexible, resilient heat transfer material which comprises: a) forming a conductive paste comprising a solvent and conductive metal flakes having edges; and b) heating the conductive paste to a temperature below the melting point of the metal flakes, thereby evaporating the solvent and sintering the flakes only at their edges, thus fusing the edges of adjacent flakes such that open pores are defined between at least some of the adjacent flakes, thereby forming a network of metal flakes.
• the invention still further provides a method for conducting heat away from a microchip which comprises: a) forming a conductive paste comprising a solvent and conductive metal flakes having edges; b) attaching a layer of the conductive paste between a microchip and a heat spreader, thus forming a composite; d) heating the composite to a temperature below the melting point of the metal flakes, thereby evaporating the solvent and sintering the flakes only at their edges, thus fusing the edges of adjacent flakes such that open pores are defined between at least some of the adjacent flakes, and forming a heat transfer material layer between the microchip and the heat spreader, which heat transfer material comprises a network of metal flakes.
• FIG. 1 shows a top view of a layer of heat transfer material of the invention.
• FIG. 2 shows a close-up top view of a layer of heat transfer material of the invention.
• FIG. 3 shows a side view of a layer of heat transfer material of the invention.
• FIG. 4 shows a side view of a layer of heat transfer material of the invention attached to a microchip.
• FIG. 5 shows a side view of a layer of heat transfer material of the invention attached to a microchip and a heat spreader.
• the invention relates to a porous, flexible, resilient heat transfer material which comprises network of metal flakes.
• a conductive paste is first formed which comprises a mixture of metal flakes and a solvent.
• the paste may be formed using any conventional method known in the art such as mixing and the like.
• the metal flakes preferably comprise a metal such as aluminum, copper, zinc, tin, gold, palladium, lead and alloys and combinations thereof. Most preferably, the flakes comprise silver.
• the flakes preferably have a thickness of from about 0.1 ⁇ m to about 2 ⁇ m, more preferably from about 0.1 ⁇ m to about 1 ⁇ m, and most preferably from about 0.1 ⁇ m to about .3 ⁇ m.
• the flakes preferably have a diameter of from about 3 ⁇ m to about 100 ⁇ m, more preferably from about 20 ⁇ m to about 100 ⁇ m, and most preferably from about 50 ⁇ m to about 100 ⁇ m.
• the each flake has edges which are thinner than the center of the flake.
• the solvent preferably serves to lower the melting point of the metal flakes.
• the solvent preferably comprises a volatile organic solvent having a boiling point of about 200 °C or less.
• Suitable volatile organic solvents nonexclusively include alcohols, such as ethanol, propanol and butanol.
• a preferred volatile organic solvent comprises butanol.
• the conductive paste is heated such that the solvent evaporates away and the metal flakes are sintered only at their edges.
• the flakes are thus fused to the edges of adjacent flakes such that open pores are defined between at least some of the adjacent flakes, thereby forming a porous, flexible, resilient heat transfer material which is substantially absent of solvents and binders.
• Heating of the conductive paste is preferably conducted at a temperature below the melting point of the metal flakes. In a preferred embodiment, the heating is conducted at a temperature ranging from about 100°C to about 200°C, more preferably from about 150°C to about 200°C, and most preferably from about 175°C to about 200°C.
• the heat transfer material is produced in the form of a heat transfer material layer. This is preferably done by applying a layer of conductive paste to a surface of a substantially flat substrate, and heating the conductive paste layer as described above to form a heat transfer material layer. The heat transfer material layer may then optionally be removed from the substrate.
• suitable substrates nonexclusively include heat spreaders, silicon die, and heat sinks.
• a preferred substrate comprises silicon die.
• the paste may be applied using any known conventional techniques such as by dispensing from a syringe..
• the heat transfer material layer has a thickness of from about lO ⁇ m to about 50 ⁇ m, more preferably from about lO ⁇ m to about 35 ⁇ m, and most preferably from about 20 ⁇ m to about 30 ⁇ m.
• the heat transfer material layer preferably comprises a storage modulus of less than about 10 GPa, more preferably from about IGPa to about 5GPa, and most preferably from about 1 GPa to about 3 GPa.
• the heat transfer material layer also preferably comprises an electrical resistance of from about 1 x 10 "6 ohm/ cm to about lx 10 "4 ohm/cm, more preferably from about 1 x 10 "6 ohm/ cm to about 5 x 10 "5 ohm/cm, and most preferably from about 1 x 10 "6 ohm/ cm to about 2 x 10 "5 ohm/cm.
• the heat transfer materials of this invention may be used for various purposes such as a thermal interface between a metal surface and a silicon die, or between heat emitting articles and heat absorbing articles, and the like.
• a first surface of the heat transfer material layer is attached to a heat emitting article.
• suitable heat emitting articles nonexclusively include microchips, multi-chip modules, laser diodes, and the like.
• a preferred heat emitting article comprises a microchip.
• a second surface of the heat transfer material layer may then optionally be attached to a heat absorbing article.
• suitable heat absorbing articles nonexclusively include heat spreaders, heat sinks, vapor chambers, heat pipes, and the like.
• a preferred heat absorbing article comprises a heat spreader.
• Such heat emitting or heat absorbing articles may be attached to the heat transfer material layer using any suitable conventional method known in the art.
• the heat transfer material layer is formed by first forming a composite which comprises a layer of conductive paste attached between a heat emitting article and a heat absorbing article. The entire composite is then heated to form a heat transfer material between the heat emitting article and the heat absorbing article.
• the heat transfer materials of the invention are particularly useful in the production of microelectronic devices.
• Silver flakes were mixed with an organic solvent to form a homogeneous paste. At least four pastes were mixed. The ratios of organic solvent to the metal flakes of the pastes are shown in Table 1 below.
• a minimum of three slides per profile were prepared as follows: a. A 1" x 3" glass slide was cleaned with isopropyl alcohol and air dried. b. A glass slide was placed securely in a glass slide holder. c. Using the lines scribed on the holder as a guide, strips of tape were placed 100 mils apart, parallel to the length of the slide. The length of the applied strips was be at least 2.5" long. d. There were no wrinkles or air bubbles under the tape.
• the silver paste was placed on one end of the slide. Using a razor blade maintained at an approximate 30 degree angle to the slide surface, the silver paste material was drawn towards the opposite end of the slide, and the material was squeezed between the tape strips.
• the cross-sectional area (in ⁇ m 2 ) of the cured material was measured at three different locations along the tape strips.
• the adhesion strength of the sintered metal flakes to three metal surfaces was tested using a die shear, to determine the bond strength of the silver paste.
• the test surfaces were formed by coating silver paste onto nickel plated surfaces, silver spot plated surfaces, and bare copper surfaces. The metal surfaces were attached onto lead frames, and cured in an oven.
• a substrate was set in the appropriate holding jig on a die shear tester. 2.
• a die shear tool tip was aligned against the widest side of the element to be tested. The die shear tool was set as perpendicular to the substrate and as close as possible to the substrate without contracting the substrate surface.
• the 'TEST' button was pressed on the tester's panel to initiate the shear test cycle.
• Steps 1 through 4 were repeated until all elements were sheared on that substrate.
• Adhesion strength were done with 100 x 100 mils die
• the material did not sinter on nickel plated surfaces, while the adhesion on bare copper surface was rather low. Copper oxidizes at elevated temperatures and thus caused a barrier to sintering onto the surface.
• the silver spot plated surface gave good adhesion at a peak temperature of 200 °C.
• the adhesion was significantly lower at 180 °C.
• the cure at 200 °C for Profile 2 however, had a higher level of sintering. The interface of failure there had been transferred to the die/paste interface where the adhesion to bare silicon was lower.
• Adhesion strength were done with 100 x 100 mils die.
• the adhesion for the silver spot plated surface was the highest, followed by the bare copper surface.
• the nickel plated surface showed a minimal amount of adhesion.
• This particular lot of material showed significantly less adhesion to the silver spot plated surface as compared to Lot #3. This may be due to the higher level of organic solvent within Lot #4.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• Materials Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Powder Metallurgy (AREA)
• Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Conductive Materials (AREA)
• Die Bonding (AREA)

Applications Claiming Priority (1)

Publications (1)

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• 2001
  • 2001-10-18 CN CNA2007100968120A patent/CN101038795A/zh active Pending
  • 2001-10-18 WO PCT/US2001/032544 patent/WO2003041165A2/en active Application Filing
  • 2001-10-18 CA CA002454155A patent/CA2454155A1/en not_active Abandoned
  • 2001-10-18 JP JP2003543099A patent/JP4202923B2/ja not_active Expired - Fee Related
  • 2001-10-18 EP EP01988123A patent/EP1436835A2/en not_active Ceased
  • 2001-10-18 CN CNB018235581A patent/CN1319162C/zh not_active Expired - Fee Related
  • 2001-10-18 KR KR1020047001319A patent/KR100782235B1/ko not_active IP Right Cessation
• 2002
  • 2002-10-18 TW TW091124081A patent/TW578180B/zh not_active IP Right Cessation

Non-Patent Citations (1)

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