+

WO2003041165A2 - Electrically conductive thermal interface - Google Patents

Electrically conductive thermal interface Download PDF

Info

Publication number
WO2003041165A2
WO2003041165A2 PCT/US2001/032544 US0132544W WO03041165A2 WO 2003041165 A2 WO2003041165 A2 WO 2003041165A2 US 0132544 W US0132544 W US 0132544W WO 03041165 A2 WO03041165 A2 WO 03041165A2
Authority
WO
WIPO (PCT)
Prior art keywords
flakes
heat transfer
transfer material
edges
microchip
Prior art date
Application number
PCT/US2001/032544
Other languages
French (fr)
Other versions
WO2003041165A3 (en
Inventor
Ignatius J. Rasiah
Original Assignee
Honeywell International, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Honeywell International, Inc. filed Critical Honeywell International, Inc.
Priority to CA002454155A priority Critical patent/CA2454155A1/en
Priority to EP01988123A priority patent/EP1436835A2/en
Priority to KR1020047001319A priority patent/KR100782235B1/en
Priority to CNA2007100968120A priority patent/CN101038795A/en
Priority to PCT/US2001/032544 priority patent/WO2003041165A2/en
Priority to JP2003543099A priority patent/JP4202923B2/en
Priority to CNB018235581A priority patent/CN1319162C/en
Priority to US10/483,370 priority patent/US7083850B2/en
Priority to TW091124081A priority patent/TW578180B/en
Publication of WO2003041165A2 publication Critical patent/WO2003041165A2/en
Publication of WO2003041165A3 publication Critical patent/WO2003041165A3/en

Links

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00Details of semiconductor or other solid state devices
    • H01L23/34Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H01L23/373Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
    • H01L23/3733Cooling 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
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00Details of semiconductor or other solid state devices
    • H01L23/34Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H01L23/373Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22FWORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10Sintering only
    • B22F3/11Making porous workpieces or articles
    • B22F3/1103Making porous workpieces or articles with particular physical characteristics
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22FWORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00Supplementary information concerning processes or compositions relating to powder metallurgy
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001Technical content checked by a classifier
    • H01L2924/0002Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/10Details of semiconductor or other solid state devices to be connected
    • H01L2924/11Device type
    • H01L2924/12Passive devices, e.g. 2 terminal devices
    • H01L2924/1204Optical Diode
    • H01L2924/12044OLED

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.

Landscapes

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

Abstract

A porous, flexible, resilient heat transfer material which 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.

Description

Docket No.: H0002384
ELECTRICALLY CONDUCTIVE THERMAL INTERFACE
BACKGROUND OF THE INVENTION
Field of the Invention
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.
Description of the Related Art
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.
As the desire for more intensive electronic applications increases, so does the demand for electrical systems that operate at faster speeds, occupy less space, and provide more functionality. To meet these demands, manufacturers design electrical and electronic devices containing numerous electrical components residing in relatively close proximity. These components tend to generate large amounts of heat which must be dissipated by some means to avoid failure or malfunction of the device.
Traditionally, electronic components have been cooled using forced or convective circulation of air within the housing of the device. 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.
Unfortunately, as integrated circuits continue to decrease in size while power densities increase, simple air circulation is often insufficient to adequately cool circuit components. Heat dissipation beyond that which is attainable by air circulation can be achieved by attaching a heat sink or other thermal dissipation device to the electronic component. 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.
It is known in the art to use a thermal or electrical interface to attach such thermal dissipation devices to a heat emitting component. However, conventional interfaces have been known to suffer from several disadvantages. 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. Furthermore, polymer adhesives can be very low modulus, but their resistivity is too high. As the amount of heat emitted from chips gets higher, there is a need for a thermal interface 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. There is also a need for such interfaces to be capable of being assembled and processed at low temperatures, such as about 200°C or less.
The present invention provides a solution to this problem. According to the invention, 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.
SUMMARY OF THE INVENTION
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.
BRIEF DESCRIPTION OF THE DRAWINGS
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.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
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 μm to about 2 μm, more preferably from about 0.1 μm to about 1 μm, and most preferably from about 0.1 μm to about .3 μm. The flakes preferably have a diameter of from about 3 μm to about 100 μm, more preferably from about 20 μm to about 100 μm, and most preferably from about 50 μm to about 100 μm. In a most preferred embodiment, 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.
In a preferred embodiment, 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. Examples of 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.. Preferably, the heat transfer material layer has a thickness of from about lOμm to about 50 μm, more preferably from about lOμm to about 35μm, and most preferably from about 20 μm to about 30 μm. 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. In one preferred embodiment, a first surface of the heat transfer material layer is attached to a heat emitting article. Examples of 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. Examples of 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. In a most preferred embodiment, 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.
The following non-limiting examples serve to illustrate the invention. It will be appreciated that variations in proportions and alternatives in elements of the components of the invention will be apparent to those skilled in the art and are within the scope of the present invention.
EXAMPLE 1
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.
Table 1: Ratio of Solvent to Flakes
Figure imgf000009_0001
The pastes were then filled into syringes, and the viscosity of the pastes were tested using a Haake viscometer with a 1°C cone and plate. The measurements were done at 22s"1 and 40s"1. The viscosity of the different materials prepared is as shown in the Table 2. Table 2: Viscosity at 22s"1 and 40s"1
Figure imgf000010_0001
As shown in the table, both Lot #1 and Lot #2 had similar viscosities at around 4000 cps. This was expected, since they both have the same mixing ratio of pomponents. Lot # 3 and 4, however, had significantly different viscosities which can be correlated to their respective mixing ratio of components.
The materials were then cured with four different cure profiles, as described below in Table 3. Curing was conducted using the following procedure:
1. 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.
2. 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.
3. The tape was carefully removed. 4. The material was cured in an oven.
Table 3: Cure Profiles for Paste Formulations
Figure imgf000011_0001
The cured materials were then tested for their volume resistivity. Since Lots # 1 and 2 had the same mixing ratio of components, Lot #2 was not tested. The volume resistivity was tested using the following procedure:
1. The cross-sectional area (in μm2) of the cured material was measured at three different locations along the tape strips.
2. Resistance measurements were made using a Hewlett-Packard 4-point probe, model number 34401 A.
3. The resistance measurements were recorded, and the resistivity was determined using the following formula:
P = R (A/2.54) cm
Where:
P = resistivity, ohm. cm
R = measured resistance, ohms
A = cross-section area, cm"
2.54 = distance between inner pair of electrodes, in cm. Results are shown below in Table 4. It can be observed from the results that the material did not sinter in Profile 3. This is due to the fact that the peak temperature of 150°C was too low for silver to sinter.
Table 4: Volume Resistivity Results for Materials (in Ohm. cm)
Figure imgf000012_0001
* The sample cured using Profile 3 cannot be measured because the strips cracked when the probes were placed on it. It was observed that the silver flakes did not fuse together and there was a residue on the glass slide when the strips were removed from it. For Profiles 1 and 2, the strips remained intact when removed from glass slide and no residue was seen.
^ The values indicated resulted in curing of samples without Clean Dry Air
(CDA).
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.
The cured samples were tested according to the following procedure:
1. 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.
3. The 'TEST' button was pressed on the tester's panel to initiate the shear test cycle.
4. After the shear test cycle was completed, the force level displayed on the panel was recorded.
5. Steps 1 through 4 were repeated until all elements were sheared on that substrate.
6. The average shear strength was calculated for the elements on the substrate.
It was observed from the results that cure profile 1 was too high for the industry while Profile 3 did not sinter the material sufficiently. Profile 3 did not sinter due to the fact that the peak temperature of 150 °C was too low for silver to sinter. Thus, the adhesion measurements were only done for profiles 2 and 4. The paste lot used for this experiment is from Lot #3. The results are as shown in Table 5 below.
Table 5: Die Shear Adhesion Results for Lot 3
Figure imgf000014_0001
Adhesion strength were done with 100 x 100 mils die
As shown in Table 5, 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, however, gave good adhesion at a peak temperature of 200 °C. The adhesion was significantly lower at 180 °C. Note how the failure mode for Profile 2 is on the die/paste interface while that of Profile 4 was on the paste substrate interface. This shows that the lower cure profile for Profile 4 had less sintering and therefore, failed within the material. 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.
The adhesion of Lot #4 was then tested using Profile 2. The results are shown in Table 6 below. Table 6: Die Shear Adhesion Results for Lot #4
Figure imgf000015_0001
Adhesion strength were done with 100 x 100 mils die.
As shown in Table 6, the adhesion for the silver spot plated surface was the highest, followed by the bare copper surface. In this experiment, the nickel plated surface showed a minimal amount of adhesion. This particular lot of material, however, 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.
Analysis and Conclusion
Three varieties of this material were mixed, and the viscosity has been found to be dependent on the mixing ratio of their organic content. All the pastes were able to sinter. Four different profiles for sintering were used. It was found that the silver flakes could sinter at 180 °C or higher. The volume resistivity of the sintered materials was found to be lower than silver filled epoxy adhesives but comparable to the conductivity of silver glass and solder. The adhesion of these pastes was mainly dependent on the temperature. It was also dependent on the surface they adhere to. In particular, a metallized die surface (e.g., with silver) would be a better surface. Apart from the die surface, the material was not able to sinter well onto nickel-plated surfaces but had good adhesion to silver spot plated surfaces.
While the present invention has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto.

Claims

What is claimed is:
1. 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.
2. The heat transfer material of claim 1 which is substantially absent of solvents and binders.
3. The heat transfer material of claim 1 which has a storage modulus of from about 10 GPa or less.
4. The heat transfer material of claim 1 which has an electrical resistance of from about 1 x 10 "6 ohm/ cm to about lx 10 "4 ohm/cm.
5. The heat transfer material of claim 1 wherein the flakes have a thickness of from about 0.1 μm to about 2 μm and a diameter of from about 3 μm to about 100 μm.
6. The heat transfer material of claim 1 wherein the flakes comprise a metal selected from the group consisting of aluminum, copper, lead, zinc, tin, gold, palladium and alloys and combinations thereof.
7. A microelectronic device which comprises a layer of the heat transfer material of claim 1.
8. A microelectronic device which comprises a microchip, a heat spreader on the . microchip and a layer of the heat transfer material of claim 1 attached between the microchip and the heat spreader.
9. 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.
10. The method of claim 9 further comprising the subsequent step of attaching a layer of the heat transfer material to a microchip.
11. The method of claim 9 further comprising the subsequent step of attaching a layer of the heat transfer material between a microchip and a heat spreader.
12 . The method of claim 9 further comprising the subsequent step of attaching the heat transfer material to a microchip, and attaching a second surface of the heat transfer material to a heat spreader.
13. The method claim 9 wherein the flakes comprise a metal selected from the group consisting of aluminum, copper, lead, zinc, tin, gold, palladium and alloys and combinations thereof.
14. The method of claim 9 wherein the flakes comprise silver.
15. The method of claim 9 wherein the flakes have a thickness of from about 0.1 μm to about 2 μm and a diameter of from about 3 μm to about 100 μm.
16. The method of claim 9 wherein the solvent comprises a volatile organic solvent.
17. The method of claim 9 wherein the volatile organic solvent is selected from the group consisting of ethanol, propanol and butanol.
18. The method of claim 9 wherein the volatile organic solvent comprises butanol.
19. The method of claim 9 wherein the flakes are heated at a temperature ranging from about 100°C to about 200°C.
20. 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.
PCT/US2001/032544 2001-10-18 2001-10-18 Electrically conductive thermal interface WO2003041165A2 (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
CA002454155A CA2454155A1 (en) 2001-10-18 2001-10-18 Electrically conductive thermal interface
EP01988123A EP1436835A2 (en) 2001-10-18 2001-10-18 Electrically conductive thermal interface
KR1020047001319A KR100782235B1 (en) 2001-10-18 2001-10-18 Sintered Metal Flake
CNA2007100968120A CN101038795A (en) 2001-10-18 2001-10-18 Conductive paste and heat diffusion material
PCT/US2001/032544 WO2003041165A2 (en) 2001-10-18 2001-10-18 Electrically conductive thermal interface
JP2003543099A JP4202923B2 (en) 2001-10-18 2001-10-18 Thermally conductive material, microelectronic device, method of forming thermally conductive material, and method of conducting and removing heat from a microchip
CNB018235581A CN1319162C (en) 2001-10-18 2001-10-18 Current conducting and heat conducting interface
US10/483,370 US7083850B2 (en) 2001-10-18 2001-10-18 Electrically conductive thermal interface
TW091124081A TW578180B (en) 2001-10-18 2002-10-18 Sintered metal flakes

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2001/032544 WO2003041165A2 (en) 2001-10-18 2001-10-18 Electrically conductive thermal interface

Publications (2)

Publication Number Publication Date
WO2003041165A2 true WO2003041165A2 (en) 2003-05-15
WO2003041165A3 WO2003041165A3 (en) 2003-07-24

Family

ID=21742921

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2001/032544 WO2003041165A2 (en) 2001-10-18 2001-10-18 Electrically conductive thermal interface

Country Status (7)

Country Link
EP (1) EP1436835A2 (en)
JP (1) JP4202923B2 (en)
KR (1) KR100782235B1 (en)
CN (2) CN101038795A (en)
CA (1) CA2454155A1 (en)
TW (1) TW578180B (en)
WO (1) WO2003041165A2 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005107487A (en) * 2003-09-26 2005-04-21 Samsung Sdi Co Ltd Display device and plasma display device
US9812624B2 (en) 2008-01-17 2017-11-07 Nichia Corporation Method for producing conductive material, conductive material obtained by the method, electronic device containing the conductive material, light-emitting device, and method for producing light-emitting device

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TW200923975A (en) * 2007-10-12 2009-06-01 Cheil Ind Inc Composition for fabrication of electrode, electrode fabricated using the same, plasma display panel, and associated methods
CN101319775B (en) * 2008-07-18 2010-06-09 东莞东海龙环保科技有限公司 High thermal conductivity flexible sealant of power type LED lamp
EP2405449B1 (en) * 2009-03-06 2017-08-16 Toyo Aluminium Kabushiki Kaisha Electrically conductive paste composition and electrically conductive film formed by using the same
EP2612755B1 (en) * 2010-08-31 2019-03-20 Sekisui Polymatech Co., Ltd. Thermally conductive sheet
US10000670B2 (en) * 2012-07-30 2018-06-19 Henkel IP & Holding GmbH Silver sintering compositions with fluxing or reducing agents for metal adhesion
EP3294799B1 (en) 2015-05-08 2024-09-04 Henkel AG & Co. KGaA Sinterable films and pastes and methods for the use thereof
CN113632219A (en) * 2019-03-20 2021-11-09 住友电木株式会社 Thermally conductive composition and semiconductor device
CN112207481A (en) * 2020-09-09 2021-01-12 中山大学 Low-temperature pressureless sintering micron silver soldering paste and preparation method and application thereof
CN113492281A (en) * 2021-05-27 2021-10-12 中山大学 Micron silver soldering paste directly sintered on bare copper at low temperature and without pressure, and preparation method and application thereof

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63140292A (en) * 1986-11-30 1988-06-11 Chuo Denki Kogyo Kk Porous-type heat radiator
CN1019760B (en) * 1987-06-11 1992-12-30 国家机械工业委员会上海材料研究所 Method for making porous elements from spherical metal powders
JPH07118701A (en) * 1993-10-22 1995-05-09 Katayama Tokushu Kogyo Kk Flaky metal powder, metallic porous body and production of the powder
JPH08213026A (en) * 1994-11-28 1996-08-20 Katayama Tokushu Kogyo Kk Metallic porous body for battery electrode substrate, battery plate, and manufacture thereof
JP3166060B2 (en) * 1995-12-11 2001-05-14 三菱マテリアル株式会社 Heat dissipation sheet
US5738936A (en) * 1996-06-27 1998-04-14 W. L. Gore & Associates, Inc. Thermally conductive polytetrafluoroethylene article
JP4174088B2 (en) * 1997-07-14 2008-10-29 住友ベークライト株式会社 Conductive resin paste and semiconductor device manufactured using the same

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005107487A (en) * 2003-09-26 2005-04-21 Samsung Sdi Co Ltd Display device and plasma display device
US9812624B2 (en) 2008-01-17 2017-11-07 Nichia Corporation Method for producing conductive material, conductive material obtained by the method, electronic device containing the conductive material, light-emitting device, and method for producing light-emitting device
US10573795B2 (en) 2008-01-17 2020-02-25 Nichia Corporation Method for producing conductive material, conductive material obtained by the method, electronic device containing the conductive material, light-emitting device, and method for producing light-emitting device
US10950770B2 (en) 2008-01-17 2021-03-16 Nichia Corporation Method for producing an electronic device
US11652197B2 (en) 2008-01-17 2023-05-16 Nichia Corporation Method for producing an electronic device

Also Published As

Publication number Publication date
JP4202923B2 (en) 2008-12-24
EP1436835A2 (en) 2004-07-14
CN101038795A (en) 2007-09-19
WO2003041165A3 (en) 2003-07-24
KR20040051582A (en) 2004-06-18
CN1545731A (en) 2004-11-10
JP2005509293A (en) 2005-04-07
TW578180B (en) 2004-03-01
CA2454155A1 (en) 2003-05-15
CN1319162C (en) 2007-05-30
KR100782235B1 (en) 2007-12-05

Similar Documents

Publication Publication Date Title
US7083850B2 (en) Electrically conductive thermal interface
CN107921541B (en) Bonded body and semiconductor device
CA2355171C (en) Method of applying a phase change thermal interface material
CN107949447B (en) Copper paste for bonding, method for producing bonded body, and method for producing semiconductor device
CN100373998C (en) Power assembly and method for manufacturing the same
KR20190062377A (en) Film-like adhesive, method of manufacturing semiconductor package using film-like adhesive
CN110498384B (en) Microelectronic module including thermally extended layer and method of making same
JP6848549B2 (en) Copper paste for bonding and semiconductor devices
WO2009131913A2 (en) Thermal interconnect and interface materials, methods of production and uses thereof
KR100782235B1 (en) Sintered Metal Flake
KR20180050714A (en) Copper paste for bonding, method of manufacturing a bonded body, and method of manufacturing a semiconductor device
CN107914006B (en) Conductive paste for bonding
US7608324B2 (en) Interface materials and methods of production and use thereof
WO2002096636A1 (en) Interface materials and methods of production and use thereof
CN111799251B (en) Power discrete device adopting multi-chip stacking structure and preparation method thereof
Bai et al. Low-temperature sintering of nanoscale silver pastes for high-performance and highly-reliable device interconnection
US20230260959A1 (en) Method for manufacturing composite structure and method for fabricating semiconductor device
JP2006059905A (en) Semiconductor device manufacturing method
JP2001523047A (en) Non-conductive heat dissipator components
Löwer et al. Sinter adhesive-new horizons in semiconductor packaging
Markov et al. Thermal characterisation of LTCC frontend modules with integrated power amplifiers for wireless LAN application
CN117461120A (en) Conductive paste, cured product, and semiconductor device

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A2

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NO NZ PL PT RO RU SD SE SG SI SK SL TJ TM TR TT TZ UA UG US UZ VN YU ZA ZW

AL Designated countries for regional patents

Kind code of ref document: A2

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZW AM AZ BY KG KZ MD RU TJ TM AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
WWE Wipo information: entry into national phase

Ref document number: 10483370

Country of ref document: US

Ref document number: 2454155

Country of ref document: CA

WWE Wipo information: entry into national phase

Ref document number: 2003543099

Country of ref document: JP

WWE Wipo information: entry into national phase

Ref document number: 2001988123

Country of ref document: EP

WWE Wipo information: entry into national phase

Ref document number: 1020047001319

Country of ref document: KR

WWE Wipo information: entry into national phase

Ref document number: 20018235581

Country of ref document: CN

WWP Wipo information: published in national office

Ref document number: 2001988123

Country of ref document: EP

点击 这是indexloc提供的php浏览器服务,不要输入任何密码和下载