WO2019009790A1

WO2019009790A1 - A method of manufacturing a metal matrix and graphene fiber composite based thermal interface material

Info

Publication number: WO2019009790A1
Application number: PCT/SE2018/050710
Authority: WO
Inventors: Johan LIU
Original assignee: Sht Smart High-Tech Ab
Priority date: 2017-07-07
Filing date: 2018-06-28
Publication date: 2019-01-10

Abstract

There is provided a method for manufacturing a thermal interface material, the method comprising:forming (100) a porous mat comprising graphene fibers; heating (102) the mat to form a graphite fiber matwhere the graphene based fibers exhibits a turbostratic crystal structure; metal plating (104) of the graphite fiber mat; and metal infiltration (106) of the metal plated graphite fiber mat.

Description

A METHOD OF MANUFACTURING A METAL MATRIX AND GRAPHENE FIBER COMPOSITE BASED THERMAL INTERFACE MATERIAL

Field of the Invention

The present invention relates to field of microelectronics packaging, and especially thermal interface materials in which heat dissipation is a crucial issue.

Background of the Invention

The ever increasing demand of faster and more efficient electronic processors and devices has become a serious worldwide concern. In essence, the more powerful a processor is, the more energy is consumed and as a consequence the more heat is generated which has to be removed from the integrated circuit to the ambient in order to both optimize its efficiency and not damage the board and components. A thermal interface material is a crucial component for cooling of microelectronics. It is placed in the form of a thermally conductive film in between two components to facilitate heat transfer in between. One such potential application is between an active component and a cooling device, or between a chip and a heat spreader. A high thermal conductivity interface as thermal interface material is needed to make it possible to have more sophisticated and faster microprocessors for the next generation electronic devices and gadgets.

It is known to use a composite structure comprising a porous polymer fiber and a bulk metal as a thermal interface material, see SE531018. A porous polymer fiber network is infiltrated with molten metal to form a composite film structure with arbitrary thickness.

However, the polymer fibers typically used in this application have a very low thermal conductivity, which limits the total composite thermal conductivity. Summary

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved method for manufacturing a high thermal conductivity interface material.

According to a first aspect of the invention, there is provided a method for manufacturing a thermal interface material. The method comprises: forming a porous mat comprising graphene based fibers; heating said mat to form a graphite fiber mat where the graphene based fibers exhibits a turbostratic crystal structure; metal plating of said graphite mat; and metal infiltration of the metal plated graphite mat.

Graphene fibers have been shown to have very high thermal conductivity, in excess of 1000-2000 W/mK, and the present invention aims to implement graphene fibers into the metal to form composite structure in order to increase the total composite thermal conductivity. Using this concept, a new composite based thermal interface material with a thermal conductivity as high as 1400-1500 W/mK (lateral plan) and over 60 W/mK (vertical plan) is provided.

Moreover, it has been found that a graphite fiber mat with turbostratic alignment between adjacent graphene layers within the graphene based fibers exhibits a greatly improved in-plane thermal conductivity in comparison to known graphene-based and graphite heat spreading materials. The improved thermal conductivity can be explained by a reduced phonon scattering as a result of weaker interlayer binding for the turbostratic structure. In comparison, the strong interlayer binding between the ordered graphene layers in graphite can lead to severe phonon interfacial scattering and reduce the thermal conductivity of graphite films.

According to one embodiment of the invention, the mat comprising graphene based fibers is formed to be a porous mat comprising openings having a size in the range of 0.1 urn to 10um to allow a flow of metal into the mat. Thereby, metal infiltration is simplified and it can be ensured that the metal fully infiltrates the porous mat. According to one embodiment of the invention, the method further comprises coating the mat comprising graphene based fibers with a first layer comprising Ti and a second layer comprising at least one metal selected from the group comprising Ni, Au and Pt. The Ti layers binds to the to bind the carbon of the graphene fiber and the second metal layer comprising Ni, Au or Pt to bond the metal used to infiltrate the porous mat to form a the thermal interface material.

According to a second aspect of the invention, there is provided a thermal interface material comprising a metal infiltrated graphite mat based on continuous graphene based fibers, wherein the graphite mat exhibits a turbostratic crystal structure such a first graphene layer is shifted with respect to a second adjacent graphene layer to prevent formation of a regular graphite lattice structure.

Effects and features of the second aspect of the invention are analogous to the advantages discussed above in relation to the first aspect.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

Fig 1 is a flow chart outlining the general steps of a method according to an embodiment of the invention.

Detailed Description of Example Embodiments

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout.

Fig. 1 is a flow chart outlining the general steps of a method according to the present invention. The method comprises forming 100 a mat

comprising graphene fibers, heating 102 the mat to form a graphite fiber mat where the graphene based fibers exhibits a turbostratic crystal lattice structure, metal plating 104 of the graphite mat, and metal infiltration 106 of the metal plated graphite mat. The described heating step realigns the graphene layers of the graphene based fibers to achieve a turbostratic alignment between adjacent graphene layers in the graphene based fiber. The method may also comprise pressing the film at high pressure.

The graphene fibers may be continuous graphene fibers.

The continuous graphene fibers may have a length between 0.1 and

100cm.

Forming a mat comprising graphene based fibers may comprise spinning to form a mat comprising randomly oriented fibers

Forming a mat comprising graphene fibers may comprise weaving to form a mat having regularly oriented fibers.

Heating the mat may comprise forming graphite at a temperature in the range from 1000 and up to 3300°C.

The graphite fibers may have a diameter between 0,01 mm and 1 mm.

The graphene fibers may be created from exfoliated graphene oxide. The graphene fiber mat may advantageously form a porous graphene fiber matrix comprising openings having a size in the range of 0.1 to 10 um in diameter that allows the flows of the metal into the fiber mat. The porous graphene fiber matrix may further be coated with a combination of metals selected from the group comprising of Ti, Ni, Au and Pt. The coating improves the metal infiltration by improving the adhesion of the metal to the carbon based material.

The main aim of this invention is to combine high thermal conductivity graphene fibers with a metal phase matrix to form a composite material to be used as thermal interface material. The present description covers the methodology and manufacturing method of graphene fiber based thermal interface material.

The graphene fiber is produced from exfoliated graphene or graphene oxide (GO) flakes using various spinning methods such as wet spinning, dry jet spinning or eiectrospinning. Graphene fibers used in this invention are arranged in a mat, using a woven or non-woven structure.

A typical fiber production method is according to a simple process of dry-jet wet spinning where first the high concentration of a viscous mixture of graphene and graphene oxide present in the plastic syringe (~ 20mg/ml) exhibited a fully nematic liquid crystal (LC) structure resulting directly from a highly exfoliated and large GO sheets. The latter mixture was spun through a range of spinneret diameters of 0.08 to 0.16 mm. In order to provide additional alignments for the LC, an air gap of 3cm was included between the tip and the coagulation bath that contained a solution of 10%CaCl2 and was rotated with a speed of 20rpm to provide a further drawing of the gel-like fiber within the bath and thus resulting in an additional alignment of the sheets an improvement of the mechanical properties of the fibers. The as-spun fibers were then washed with ethanol and dried at 60deg C for 30min.

In order to enhance the wetting between molten metal and graphene fibers, the fibers are subsequently functionalized by deposition of a wetting agent such as Ag, Cu, Au, Ni, Pd, Ti, Pt or a combination thereof. It can be deposited by various methods such as sputtering or chemical deposition.

The resulting coated graphene fiber mat is subsequently infiltrated by a molted metal alloy under pressure. The process may advantageously be chosen according to a previously described process, see WO2015176761 . The metal phase infiltrated material may be chosen among alloys such as Sn, Sn-based, In, In-based and Bi and Bi-based systems. In particular: AgCu, SnBi, SnBiAg, SnAgCu, SnZn, In, BiSnAg and InSnBi. A thermal conductivity of 1400-1500 W/mK in the lateral plan and over 60 W/mK in the vertical plan can be expected.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the method may be omitted,

interchanged or arranged in various ways, the method yet being able to perform the functionality of the present invention.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1 . Method for manufacturing a thermal interface material, the method comprising:

forming (100) a porous mat comprising graphene based fibers;

heating (102) said mat to form a graphite fiber mat where the graphene based fibers exhibits a turbostratic crystal structure;

metal plating (104) of said graphite fiber mat; and

metal infiltration (106) of the metal plated graphite fiber mat.

2. The method according to claim 1 , wherein the mat comprising graphene based fibers is formed to be a porous mat comprising openings having a size in the range of 0.1 urn to 10um to allow a flow of metal into the mat.

3. The method according to claim 1 or 2, wherein the graphene fibers are continuous graphene based fibers.

4. The method according to claim 3, wherein the continuous graphene fibers have a length between 0, 1 and 100cm.

5. The method according to any one of the preceding claims, wherein forming a mat comprising graphene based fibers comprises spinning to form a mat comprising randomly oriented fibers

6. The method according to any one of claims 1 to 4, wherein forming a mat comprising graphene fibers comprises weaving to form a mat having regularly oriented fibers.

7. The method according to any one of the preceding claims, wherein heating said mat comprises forming graphite at a temperature in the range between 1000 to 3200°C.

8. The method according to any one of the preceding claims, wherein said graphite fibers have a diameter between 0.1 pm and 1 mm.

9. The method according to any one of the preceding claims, wherein said graphene fibers are created from exfoliated graphene oxide.

10. The method according to any one of the preceding claims, further comprising coating the mat comprising graphene based fibers with a first layer comprising Ti and a second layer comprising at least one metal selected from the group comprising Ni, Au and Pt.

1 1 . A thermal interface material comprising a metal infiltrated graphite mat based on continuous graphene based fibers, wherein the graphite mat exhibits a turbostratic crystal structure such a first graphene layer is shifted with respect to a second adjacent graphene layer to prevent formation of a regular graphite lattice structure.