Discrete carbon nanotubes for solder alloy integration

Abstract

Solder alloys with enhanced properties derived from incorporation of CNTs make use of debundled, dispersed, and functionalized carbon nanotubes uniformly distributed throughout the solder alloy matrix to yield an acceptable metal-matrix nanocomposite solder alloy. Neutral buoyancy of CNTs within solder alloys may be achieved by the endohedral functionalization process. This process involves filling the CNTs with dense metals, such as low-cost, high-density bismuth, as well as functional fillers like ferromagnetic and superparamagnetic metals and alloys, or thermally conductive materials like copper and silver, which may result in an offset of the lower density carbon shell, allowing the CNTs to remain suspended in solder alloys.

Description

5 PCT APPLICATIONDocket No. 33733.8DISCRETE CARBON NANOTUBES FOR SOLDER ALLOY INTEGRATION10 BACKGROUND OF THE INVENTION1. Field of the Invention

[0001] The present invention relates to carbon nanotubes, and more particularly to discrete carbon nanotubes with dual functionalization for solder alloy integration.2. Background and Related Art15

[0002] Carbon nanotubes (CNTs) may be used for a number of applications including, for example, energy storage devices (e.g. ultracapacitors, supercapacitors and batteries), field emitters, conductive films and wires, membrane filters, reinforcing agents in polymer composites, semiconductor substrates, device modelling, automotive parts, boat hulls,20 sporting goods, coatings, actuators, electromagnetic shields, and drug delivery.

[0003] Carbon nanotubes tend to clump together during the manufacturing process and clumped / bundled CNTs are extremely difficult to untangle. Untangled CNTs can produce much more uniform materials and are exponentially superior in performance than materials manufactured with clumped tubes.| (20041 Solder plays an important role in the electronics manufacturing industry. Traditional solder materials and techniques have been limited by issues such as low electrical conductivity relative to copper, low ampacity, electromigration failures, poor mechanical strength, insufficient thermal conductivity, and incompatibility with advanced manufacturing processes like radio frequency (RF) heating or magnetic manipulation. A need exists for5 solder alloys with enhanced properties to yield an acceptable metal-matrix nanocomposite solder alloy.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0005] The objects and features of the present invention will become more fully apparent from the following description, taken in conjunction with the accompanying drawings.10 Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0006] FIG. 1 shows a discrete carbon nanotube that is dual functionalized, in accordance with one15 or more embodiments of the present disclosure.

[0007] FIG. 2 depicts a solder bump with CNTs that are activated by an inductor coil, in accordance with one or more embodiments.

[0008] FIG. 3 depicts a diagram of an RF heated die with an induction coil that generates a magnetic field that may heat elements such as solder on or between a die and a substrate.[QHB09] FIG. 4 illustrates a method for preparing a solder integrated with discrete carbon nanotubes.DETAILED DESCRIPTION OF THE INVENTION

[0010] A description of embodiments of the present invention will now be given with some reference to the Figures. It is expected that the present invention may take many other forms and shapes, hence the following disclosure is intended to be illustrative and not limiting.[(2511] CNT materials may be used throughout the critical stack up of materials required for complete computer chips. Discrete carbon nanotubes may be sorted or synthesized with specific chirality to make individual transistors, memory or logic elements in the semiconductor circuit. For signal wires and power delivery, CNTs may be incorporated into5 semiconductor designs as a plurality of conductors or embedded in metals to form metalmatrix nanocomposites. When embedded in metals such as copper, aluminum, nickel, gold, titanium, tantalum, platinum, palladium; it is critical to have uniform distribution of metal- functionalized discrete carbon nanotubes dispersed in the metal matrix to transfer the best properties to the resulting composite. At the chip interconnect level, die-to-die, die-to-10 substrate, substrate-to-interposer connections are typically made with low melting point solder alloys. Similarly, in some embodiments solder alloys with enhanced properties derived from incorporation of CNTs make use of debundled, dispersed, and functionalized carbon nanotubes uniformly distributed throughout the solder alloy matrix to yield an acceptable metal-matrix nanocomposite solder alloy.| (10121 Many attempts to incorporate carbon nanotubes (CNTs) into solder have used clumped or agglomerated CNTs with limited surface modification to improve solid state dispersion of the nanotubes throughout the molten and solidified solder material. Some simple methods have been used such as ball milling precursor CNT and metal powders or using ultrasonic assisted dispersion of CNTs in molten solder. However, each method has20 shown limited ability to break up nanotube bundles in the metallic phase. Using dispersed discrete nanotube materials facilitates complete chemical functionalization of the nanotubes with adhesion promoting chemistry on the nanotube surface as well as better access to the nanotube core for endohedral filling.|0013 | One approach that has been used to incorporate CNTs into a solder alloy involves25 coating surfaces of CNTs with a metal or polymer to improve compatibility with a solder alloy. While this may address issues of adhesion, it does not solve the problem of buoyancy and typically does not add functional properties like magnetic responsiveness. Another common approach is the addition of various nanoparticles directly into the solder matrix to refine the grain structure and improve mechanical properties. However, these nanoparticle5 additions do not offer the same level of electrical and thermal conductivity improvements asCNTs.

[0014] This disclosure introduces an approach to enhancing the properties of solder alloys through dual functionalization of discrete carbon nanotubes (CNTs). Neutral buoyancy of CNTs within solder alloys may be achieved by the endohedral functionalization process. This 10 process involves filling the CNTs with dense metals, such as low-cost, high-density bismuth, as well as functional fillers like ferromagnetic and superparamagnetic metals and alloys, or thermally conductive materials like copper and silver. The lower density carbon shell of the CNTs may be offset, allowing the CNTs to remain suspended in solder alloys with densities ranging from 7-9 g / cm3.| (1(5151 In some cases, exohedral functionalization is also employed to enhance the external surface of the CNTs, promoting improved adhesion and compatibility with solder materials. This may be achieved through a variety of methods, including covalent sidewall modification, non-covalent interactions, electroplating, plasma surface modification, and in- situ metallic bonding. The dual functionalization technique may yield a multitude of benefits, 20 including refined grain structure of the solder, improved mechanical properties, enhanced current carrying capacity, modification of surface tension, and overall precious metal reduction savings.

[0016] Furthermore, this process enables the development of functional solders with unique capabilities such as RF induction heating and magnetic shape manipulation, which open new 25 avenues for advanced soldering techniques. Additionally, the processes and compositions disclosed herein may contribute to carbon capture and present a way to offset the use of precious metals.

[0017] This disclosure arises from challenges faced in the electronics manufacturing industry, where soldering plays a role. This disclosure overcomes limitations of traditional5 soldering by improving the integration of carbon nanotubes (CNTs) with solder alloys. Using improved solder alloys integrated with CNTs as disclosed herein may improve chips generally since using upgraded materials as disclosed herein may yield better, faster, and more powerful chips.

[0018] One problem this disclosure solves is the tendency of CNTs to exhibit buoyancy in10 solder alloys due to their low density, which may lead to uneven distribution and diminished performance of the solder. This is addressed by endohedral functionalization of CNTs, where they are filled with dense metals to achieve neutral buoyancy. This allows for a homogeneous distribution of CNTs within the solder, leading to refined grain structures and an improvement in mechanical properties.100191 Another problem is a lack of adhesion and compatibility between CNTs and solder alloys, which hinders the mechanical strength and current-carrying capacity of the resulting solder joints. Exohedral functionalization techniques may be used to modify external surfaces of CNTs to enhance their adhesion to solder materials, which may also contribute to improved electrical performance and enable additional functionalities such as RF induction20 heat-ability and magnetic shape manipulation.

[0020] By addressing these problems, this disclosure provides solders with superior mechanical, thermal, and electrical properties, which can be tailored for specific applications in electronic manufacturing.100211 The disclosure transforms the properties of solder alloys by incorporating dual-25 functionalized discrete carbon nanotubes (CNTs), leveraging their unique structural and electrical properties. Two aspects of such dual functionalization include endohedral functionalization and exohedral functionalization. Endohedral functionalization may include dense metal incorporation, magnetic functional fillers, and thermal conductivity enhancers. Exohedral functionalization may include covalent sidewall modification, noncovalent5 functionalization, electroplating, plasma surface modification, and in-situ metallic bonding.These specific functionalization techniques help ensure that CNTs are prepared for integration into solder alloys, leading to solders that are not only mechanically robust and electrically conductive but also capable of adding functionalities like induction heating and magnetic responsiveness to the solder joints.[Q@22] Regarding dense metal incorporation as a function of endohedral functionalization, for neutral buoyancy, metals such as bismuth, which has a density of 9.78 g / cm3, are deposited inside the hollow cavities of CNTs through a capillary filling under vacuum conditions to draw the molten metal into the CNTs achieving a consistent fill ratio, leveraging the capillary forces that drive the metal into the nanotube. Other metals such as15 tungsten may be used to fill CNTs to achieve neutral buoyancy. Filling CNTs with dense metals such as bismuth or tungsten to match the density of common solder alloys may help ensure that the CNTs remain suspended within the molten solder without rising to the surface or sinking.

[0023] To incorporate ferromagnetic or superparamagnetic properties for magnetic functional 20 fillers, materials such as iron, cobalt, nickel, ferrites, carbonyl iron, or ferromagnetic alloys can be introduced into the CNTs. These metals can be in the form of nanoparticles which are embedded inside the CNTs using a solution-based filling process, where the nanotubes are dispersed in a metal salt solution followed by a reduction process. Additionally, the metallic or magnetic core may be formed first in the shape of a nanorod or nanowire, and a graphitic 25 shell or carbon nanotube may be grown on top of the already formed core.

[0024] For improving and enhancing thermal conductivity in a CNT, materials like copper or silver can be introduced into CNTs. One approach is the electrochemical deposition method, where the CNTs are first sensitized and then immersed in a metal salt solution. An electric field drives the ions into the CNTs where they are reduced and deposited.

[0025] Regarding covalent sidewall modification for exohedral functionalization, this could involve attaching functional groups such as carboxyl (-COOH) or hydroxyl (-OH) to the CNT sidewalls using acid treatment which introduces defects and functional groups to the CNT surface, allowing for further reactions with the solder material. Other covalent modifications include nitrogen doping of the nanotube sidewall, thiolation with sulfur, phosphidation, and10 metallic substitution of carbon in the side wall with metals including but not limited to copper, tin, nickel, cobalt, rhodium, nickel, palladium, and platinum.

[0026] Referring to noncovalent functionalization, utilizing 7t-7i stacking interactions, polymers or surfactants can be absorbed onto the surface of CNTs to enhance solubility and dispersion in the solder matrix without disrupting the sp2bonding of the carbon atoms,15 maintaining electrical properties.

[0027] For electroplating, a thin layer of metal such as tin or silver may be electroplated onto the CNT surface to improve the wetting properties with solder. This may be done by activating the CNT surface with a catalyst or chemically functionalized sidewall group and immersing it in a plating solution while applying a current. Electroless plating methods may20 also be used to deposit a thin layer of metal onto the surface of functionalized CNTs.

[0028] To accomplish plasma surface modification, argon or oxygen plasma may be used to introduce functional groups onto the CNT surface. This increases the surface energy of the CNTs, improving their compatibility with the solder alloy. Metallic sputtering may also be used to deposit thin layers of adhesion promoting interfaces on the nanotube sidewall.

[0029] Regarding in-situ metallic bonding, by mixing CNTs with solder powder followed by a sintering process, a metallurgical bond can be formed between the CNTs and the solder particles, helping to ensure a strong mechanical interlock once the solder is reflowed. Chemically reactive metallic components are added to the solder alloy to facilitate a chemical reaction during solder reflow whereby the reactive metallic atoms (e.g., Titanium (Ti),5 Cerium (Ce), Lanthanum (La), Gallium (Ga), Magnesium (Mg)) form strong bonds with active groups present on the nanotube sidewall.

[0030] Regarding incorporation of the functionalized discrete carbon nanotubes into the solder alloy, several methods are taught. Simple mixing of functionalized CNTs into molten solder baths in a crucible or other mixing vessel is possible. Advanced mixing methods may10 include incorporating high shear or ultrasonic dispersion equipment. Shear mixing of solder alloys with CNTs may be accomplished with high energy mixing blades, rotor-stator mixers, high-pressure homogenization, magnetic stirring, or high-speed planetary mixers. Ultrasonic energy may be applied to molten solder and CNT baths to further assist in mixing and wetting of CNTs into the solder alloy. CNT’s may also be incorporated into solder alloys with solid-15 state powder metallurgy methods. These methods include mixing functionalized CNT powder and the solder alloy powder with high energy, high pressure or high heat equipment such as a ball mill, cryogenic mill, hot isostatic pressing, spark plasma sintering, hot or cold extrusion, explosive compaction. Alternatively, CNTs may be dispersed into flux or solder paste in the flux phase and may either remain in the flux or migrate into the solder alloy through wetting.20 CNT’s may also be incorporated into solder alloys through co-electrodeposition of CNTs and solder alloys in plating baths. In this method, functionalized discrete carbon nanotubes are dispersed into an electroplating bath containing the necessary metallic ion species and other additives such as brighteners, levels, and suppressors and the CNTs are co-deposited along with the metal atoms to yield a uniform solder alloy metal matrix nanocomposite. Typical25 metals include tin, silver, copper, lead, bismuth, antimony, and indium, and alloys such as SAC 305, SnAg, SnCu, SnSb, SnBi, SnPb, SnAgCuZn, and SnAgCuMn. Plating baths may be prepared using water as the solvent, or for advanced plating techniques, organic solvents such as room temperature ionic liquids (RTILs) and deep eutectic solvents (DESs) may be used to have more control over the electrochemical reduction window.[0® 1] As discussed herein, the present disclosure incorporates a process of dual functionalization of CNTs to improve their integration with solder alloys for electronic applications. In some cases, CNTs that have been functionalized may be integrated with solder alloys in a paste that can be applied to semiconductors, microchips, printed circuit boards (PCBs), and any other circuitry that may require assembling of electrical components10 and / or wiring. In one or more embodiments, CNTs may comprise a weight of a solder alloy that is integrated with the CNTs of between 1% and 50%, or in some cases between 5% and 25%. Some embodiments of the present disclosure may include discrete carbon nanotubes, endohedral functionalization of such discrete CNTs, and / or exohedral functionalization of discrete CNTs. In some embodiments, a prerequisite for preparing a homogenous carbon15 nanotube metal matrix composite is debundling and dispersing the carbon nanotube starting material. The nanotubes may be either single wall, double wall or multi-wall. When these materials are synthesized, they tend to form dense intertangled bundles of carbon nanotubes that are difficult to disperse into another matrix. To facilitate the subsequent functionalization steps and dispersion process in the solder metal matrix, discrete carbon nanotubes are20 prepared by detangling bundles of CNTs.

[0032] Exohedral functionalization may include surface modification for adhesion which may include sidewall functionalization of CNTs to help ensure proper adhesion to the solder matrix. Acid treatment to introduce carboxyl groups onto the CNT surface may help accomplish such sidewall functionalization and surface modification.[ (2B3 ] In some embodiments, enhancements for endohedral functionalization may include functional fillers such as ferromagnetic materials (e.g., iron nanoparticles) which may impart additional properties such as responsiveness to magnetic fields or RF induction heating, thus expanding the utility of the solder. In one or more embodiments, variations for exohedral functionalization may include advanced surface coatings. Implementing methods such as5 noncovalent functionalization with surfactants or electroplating with solder-compatible metals may further enhance the dispersion and bonding of CNTs within the solder.

[0034] In some embodiments, tinned carbon nanotubes may be prepared and analyzed under scanning electron microscopy (SEM). In further embodiments, endohedral CNTs may be filled with iron cobalt. Furthermore, in some embodiments, a magnetic nanoparticle solder10 alloy such as SAC305 may be prepared and melted with RF induction heating equipment.

[0035] In one or more embodiments, CNTs within a SAC solder alloy (e.g., SAC305 solder alloy) may be filled with bismuth to maintain a neutral buoyancy within the solder. Such an embodiment meets certain industry standards for lead-free soldering and may also exhibit superior mechanical and thermal properties. The nanotubes may be exohedral functionalized15 for enhanced compatibility with tin, and tin plated prior to preparing a SAC305 metal matrix composite in a solder pot via simple melt mixing.

[0036] In some embodiments, an RF-responsive solder composite may include a version of a CNT-infused solder alloy that utilizes a combination of ferromagnetic or superparamagnetic fillers within CNTs to create a solder composite that is responsive to RF fields for induction 20 soldering, representing an advancement in soldering technology.

[0037] Certain features of the present disclosure help ensure that the CNTs are compatible with and enhance the base properties of solder alloys. This is enabled by discrete and debundled carbon nanotubes that form an effective dispersion in the metal matrix and stay well dispersed via neutral buoyancy and full wettability. Certain other features and25 embodiments may provide pathways for additional functionalities, tailored to specific applications within the realm of electronic manufacturing and assembly. Some embodiments embody successful integration of various features as disclosed.

[0038] The scope of the disclosure is not limited to the embodiments as specifically disclosed herein, but may be expanded to include any and all combinations of endohedral and5 exohedral functionalization as disclosed herein. In some embodiments, endohedral functionalization of a CNT may include filling the CNT with a dense metal as well as a magnetic core such that neutral buoyancy and magnetic responsiveness for the CNTs within the solder alloy is achieved.

[0039] Simultaneous endohedral and exohedral functionalization of CNTs is distinctive,10 addressing both buoyancy and compatibility with solder simultaneously. Additionally, achieving neutral buoyancy in solder alloys address the density disparity between CNTs and solder alloys, which may lead to uneven distribution of CNTs with the solder. Incorporating functional fillers such as ferromagnetic and superparamagnetic materials inside CNTs is a solution that adds multifunctionality to solders, such as targeted RF induction heat-ability and15 magnetic manipulation, which are not commonly found in conventional solders.

[0040] In some embodiments, the filler metals and magnetic cores are permanently encapsulated in the CNTs and are configured to never be released from the CNTs. In other embodiments, filler metals and magnetic cores inserted into the CNTs using endohedral functionalization may be configured to be removed at a later time.[CfflMl] FIG. 1 depicts a discrete carbon nanotube, in accordance with one or more embodiments of the present disclosure. In some embodiments, the carbon nanotube in FIG. 1 is shown in three progressive configurations. The first configuration is a carbon nanotube that has been untangled and dispersed from a tangle of carbon nanotubes, which renders the carbon nanotube discrete and ready for functionalization. A group of discrete CNTs may25 enhance electrical conductivity and minimize electromigration as compared to clumped CNTs. Furthermore, discrete CNTs may function as a diffusion barrier between a magnetic core (e.g., of the second configuration shown in FIG. 1) and the solder matrix. Additionally, a discrete CNT may function as a template for a magnetic core to optimize induction heating.[0(542] The second configuration is a carbon nanotube that has gone through an endohedral functionalization process with ferromagnetic or superparamagnetic materials deposited within the CNT. Such a magnetic core may act as a susceptor to maximize a specific absorption rate (SAR) for a solder metal matrix composite. The magnetic core may also offset nanotube intrinsic density for buoyancy neutral nanotubes in solder. The third configuration is a CNT10 that has undergone an exohedral functionalization process which may improve surface properties of the CNT including adhesion, dispersion, wettability, etc.

[0043] FIG. 2 depicts a solder bump with CNTs that are activated by an inductor coil, in accordance with one or more embodiments. As shown in FIG. 2, there may be an array of solder bumps, where each solder bump may have integrated CNTs that are functionalized in15 one of the ways disclosed herein. The diagram in FIG. 2 depicts that a solder bump may be activated by an inductor coil which generates a magnetic field. The CNTs in FIG. 2 may include magnetic cores that are responsive to magnetic fields. Such cores may be activated (e.g., vibrate within the CNT) to generate localized heat while avoiding that the surrounding bumps or areas of the chip are subjected to heat.|OT441 A metal matrix nanocomposite solder alloy composition and method for making the same. Some embodiments comprise a solder metal matrix having a first density. In some embodiments the solder metal matrix also includes a plurality of discrete carbon nanotubes having a second density approximately equal to the first density to provide the discrete carbon nanotubes with a neutral buoyancy in the metal matrix nanocomposite solder alloy25 composition. In some embodiments of the solder composition the discrete carbon nanotubes are distributed in the solder metal matrix in a substantially uniform distribution. In some embodiments the second density is a combined density of the discrete carbon nanotubes and a second material. In some embodiments the second density is dense metal incorporation as a function of endohedral functionalization, for neutral buoyancy. In some embodiments the5 endohedral functionalization may include a heavy metal deposited inside the hollow cavities of discrete carbon nanotubes through a capillary filling under vacuum conditions to draw a molten metal into the discrete carbon nanotubes. In some embodiments the discrete carbon nanotubes may include may include fill ratio of metal in the discrete carbon nanotubes. In some embodiments the solder composition may include the discrete carbon nanotubes10 modified through exohedral functionalization. In some embodiments the discrete carbon nanotubes are functionalized to respond to radio frequency induction heat-ability.

[0045] General aspects in some embodiments include the metal matrix nanocomposite solder alloy composition also includes a solder metal matrix having a first density; a plurality of dual functionalized discrete carbon nanotubes filled with a material with a second density that15 makes the discrete carbon nanotubes neutrally buoyant in the solder metal matrix.

[0046] Implementations may also include one or more of the following features. In some embodiments the solder composition where the discrete carbon nanotubes are filled with bismuth. In some embodiments the material may include an rf-responsive solder composite.In some embodiments the material may include a dense metal and a magnetic material such20 that the discrete nanotubes are neutrally buoyant and magnetic responsiveness. In some embodiments the dual functionalization further may include endohedral functionalization of at least one of a dense metal, magnetic functional filler or a thermal conductivity enhancers. In some embodiments the dual functionalization further may include exohedral functionalization of at least one of covalent sidewall modification, noncovalent25 functionalization, electroplating, plasma surface modification, and in-situ metallic bonding.

[0047] Implementations of the described composition and methods may include a method of preparing a metal matrix nanocomposite solder alloy. In some embodiments The method also includes using an endohedral functionalization technique to fill discrete carbon nanotubes having an interior surface and an exterior surface with a material having a density5 approximately equal to a metal solder alloy; and mixing the functionalized discrete carbon nanotubes into a molten solder bath.

[0048] Implementations may include one or more of the following features. In some embodiments the method of the mixing may comprise dispersing the discrete carbon nanotubes into flux or solder paste in a flux phase. In some embodiments the method may10 include using an exohedral functionalization technique to modify the discrete carbon nanotube exterior surface to improve adhesion between the discrete carbon nanotubes and the solder composition. In some embodiments the material further may include a combination of ferromagnetic or superparamagnetic fillers.

[0049] The present invention may be embodied in other specific forms without departing15 from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. All changes which come within the meaning and range of equivalency of any claims are to be embraced within their scope.

Claims

What is claimed is:

1. A metal matrix nanocomposite solder alloy composition comprising: a solder metal matrix having a first density: a plurality of discrete carbon nanotubes having a second density approximately equal to the first density to provide the discrete carbon nanotubes with a neutral buoyancy in the metal matrix nanocomposite solder alloy composition.

2. The solder composition of claim 1 wherein the discrete carbon nanotubes are distributed in the solder metal matrix in a substantially uniform distribution.

3. The solder composition of claim 1 wherein the second density is a combined density of the discrete carbon nanotubes and a second material.

4. The solder composition of claim 1 wherein the second density is dense metal incorporation as a function of endohedral functionalization, for neutral buoyancy.

5. The solder composition of claim 4 wherein the endohedral functionalization comprises a heavy metal deposited inside the hollow cavities of discrete carbon nanotubes through a capillary filling under vacuum conditions to draw a molten metal into the discrete carbon nanotubes.

6. The solder composition of claim 5 wherein the discrete carbon nanotubes comprise consistent fill ratio of metal in the discrete carbon nanotubes.

7. The solder composition of claim 1 further comprising the discrete carbon nanotubes modified through exohedral functionalization.

8. The solder composition of claim 7 wherein the discrete carbon nanotubes are functionalized to respond to radio frequency induction heat-ability.

9. A metal matrix nanocomposite solder alloy composition comprising: a solder metal matrix having a first density; a plurality of dual functionalized discrete carbon nanotubes filled with a material with a second density that makes the discrete carbon nanotubes neutrally buoyant in the solder metal matrix.

10. The solder composition of claim 9 wherein the discrete carbon nanotubes are filled with bismuth.

11. The solder composition of claim 9 wherein the material comprises an RF-responsive solder composite.

12. The solder composition of claim 9 wherein the material comprises a dense metal and a magnetic material such that the discrete nanotubes are neutrally buoyant and magnetic responsiveness.

13. The solder composition of claim 9 wherein the dual functionalization further comprises endohedral functionalization of at least one of a dense metal, magnetic functional filler or a thermal conductivity enhancers.

14. The solder composition of claim 9 wherein the dual functionalization further comprises exohedral functionalization of at least one of covalent sidewall modification, noncovalent functionalization, electroplating, plasma surface modification, and in-situ metallic bonding.

15. A method of preparing a metal matrix nanocomposite solder alloy composition comprising: using an endohedral functionalization technique to fill discrete carbon nanotubes having an interior surface and an exterior surface with a material having a density7approximately equal to a metal solder alloy; and mixing the functionalized discrete carbon nanotubes into a molten solder bath.

16. The method of claim 15 wherein the mixing further comprising dispersing the discrete carbon nanotubes into flux or solder paste in a flux phase.

17. The method of claim 15 further comprising using an exohedral functionalization technique to modify the discrete carbon nanotube exterior surface to improve adhesion between the discrete carbon nanotubes and the solder composition.

18. The method of claim 15 wherein the material further comprises a combination of ferromagnetic or superparamagnetic fillers.

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