Solder foams, nano-porous solders, foamed-solder bumps in chip packages, methods of assembling same, and systems containing same

A foamed solder or a nano-porous solder is formed on a substrate of an integrated circuit package. The foamed solder exhibits a low modulus that resists cracking during shock and dynamic loading. The foamed solder is used as a solder bump for communication between an integrated circuit device and external structures.

TECHNICAL FIELD

Embodiments relate generally to integrated circuit fabrication. More particularly, embodiments relate to solder materials and morphologies in connection with microelectronic devices.

TECHNICAL BACKGROUND

Solders are an important part of a packaged integrated circuit (IC). An IC die is often fabricated into a microelectronic device such as a processor. The solders complete couplings between the IC die and the outside world.

The increasing demands upon an IC to perform at high speeds and to not overheat presents problems for the solders. The increasing heat stresses in an IC package causes thermal stresses between the solders and the substrates to which the solder are bonded.

DETAILED DESCRIPTION

Embodiments in this disclosure relate to a foamed solder that is disposed upon an IC substrate. Embodiments also relate to foamed solder metallurgies that are useful to form closed-cell and reticulated solders.

The following description includes terms, such as upper, lower, first, second, etc. that are used for descriptive purposes only and are not to be construed as limiting. The embodiments of an apparatus or article described herein can be manufactured, used, or shipped in a number of positions and orientations.

Reference will now be made to the drawings wherein like structures will be provided with like suffix reference designations. In order to show the structures of various embodiments most clearly, the drawings included herein are diagrammatic representations of integrated circuit structures. Thus, the actual appearance of the fabricated structures, for example in a photomicrograph, may appear different while still incorporating the essential structures of the illustrated embodiments. Moreover, the drawings show only the structures necessary to understand the illustrated embodiments. Additional structures known in the art have not been included to maintain the clarity of the drawings.

FIG. 1is a computer-image depiction of a photomicrograph100that exhibits a foamed solder in a cellular-foamed morphology according to an embodiment. The photomicrograph depiction100includes a foamed solder bump110. The cellular-foamed morphology is depicted by a cellular chamber112and a cellular wall114. Accordingly, the cellular-foamed solder is substantially closed as to the fluid-permeable porosity in the foamed solder bump110.

FIG. 2is a computer-image depiction of a photomicrograph200that exhibits a foamed solder in a reticulated-foamed morphology according to an embodiment. The photomicrograph depiction200includes a foamed solder bump210. The reticulated-foamed morphology is depicted by a ganglia214of solder that is substantially open as to the fluid-permeable porosity in the foamed solder bump210.

Hereinafter, the foamed solder, whether it is a cellular-foamed morphology or a reticulated-foamed morphology, will be referred to a simply as “foamed solder”. The various embodiments of a cellular-foamed morphology or a reticulated-foamed morphology are applicable to all depictions in this disclosure unless explicitly declared otherwise.

In an embodiment, the foamed solder is a foamed solder of a first material, and the relative density of the foamed solder is in a range from about 0.1 to about 0.9. By “relative density”, it is meant that the density of the foamed solder is compared to a solid solder of the same material. A solid solder of the same material can be ascertained by review of the classical-physics densities of materials like pure metals and solders such as can be found in reference materials.

In an embodiment, the foamed solder of a first material has a relative density of about 0.5. In an embodiment, the foamed solder of a first material has a relative density of about 0.6. In an embodiment, the foamed solder of a first material has a relative density of about 0.7. In an embodiment, the foamed solder of a first material has a relative density of about 0.8.

One way to resist shock in an IC package is to improve the Young's modulus (m) of the solder in the solder bump. Under shock loading conditions that are carried out in IC package testing, strain rates can be on the order of about 102/sec for both dynamic and impact loadings. In an embodiment under this strain rate, foamed solder embodiments exhibit so-called strain-rate sensitivity. In other words, foamed solder embodiments become stronger with increasing strain rate. The strain rate sensitivity becomes significant at a high homologous temperature at which the embodied foamed-solder materials are subject to during operation. For example, with m of about 0.2, the strain rate of 102/sec increases yield strength to about 250 percent of quasi-static yield strength. Because of this discovery, under shock-loading conditions, plastic deformation is suppressed and stress-strain behavior of foamed solders diverges positively from classical stress-strain behavior of metals in quasi-static yield strength.

In an embodiment, the foamed solder is a copper-based solder such as pure copper, copper-tin, copper-tin-lead, copper-tin-silver, copper-tin-bismuth, copper-tin-indium and others. In an embodiment, the foamed solder is a nickel-based solder such as pure nickel, nickel-tin, nickel-tin-lead, nickel-tin-silver, nickel-tin-bismuth, nickel-tin-indium and others. In an embodiment, the foamed solder is a nickel-titanium shape-memory alloy such as NITINOL®, manufactured by Johnson-Matthey of Wayne, Pa. NITINOL® is a nickel-titanium alloy that exhibits superplastic behavior. In an embodiment, the foamed solder is a tin-based solder such as pure tin, tin-nickel, tin-lead, tin-indium, tin-lead-nickel, tin-nickel-silver, and others. In an embodiment, the foamed solder is an indium-based solder such as pure indium, indium-tin, indium-lead, indium-lead-nickel, indium-nickel-silver, and others. Other foamed solders can be used depending upon the application.

FIG. 3is an elevational cross-section of an article300that includes a foamed solder core316of a first material and a solder shell318of a second material upon a substrate320according to an embodiment. In an embodiment, the substrate320is an IC die. In an embodiment, the substrate320is a mounting substrate such as a printed-wiring board. The foamed solder core316is depicted schematically, and it can be either of a cellular-foamed solder or a reticulated-foamed solder according to an embodiment. As depicted, the foamed solder includes a cellular chamber312and a cellular wall314such as the cellular-foamed solder bump110depicted inFIG. 1.

The foamed solder core316and the solder shell318make up a solder bump310according to an embodiment. The substrate320includes a bond pad322according to an embodiment. In an embodiment, the bond pad322exhibits elongated columnar grain morphology that is characteristic of a plating process. The bond pad322includes a flash layer324such as a gold flash layer324upon a copper bond pad322according to an embodiment. In an embodiment, the solder bump310exhibits a modulus in a range between about 0.2 and about 0.7.

In an embodiment, the solder shell318is an intermetallic derivative of the foamed solder core316. The intermetallic derivative can be any composition that intermingles with the foamed solder core316under processing conditions such as reflow, to form an intermetallic material. In an example embodiment, the solder shell318is a nickel-tin intermetallic and the foamed solder core is nickel or a nickel alloy.

In an embodiment, the foamed solder core316has a diameter326of unity, and the thickness328of the solder shell318has a thickness that is in a range from about 1 percent of unity to about 100 percent of unity. In an embodiment, the solder shell318has a thickness that is in a range from about 5 percent of unity to about 20 percent of unity. In an embodiment, the solder shell318has a thickness that is in a range from about 6 percent of unity to about 19 percent of unity.

In an embodiment, the size of the solder bump310, and therefore the approximate dimensions of the foamed solder core316and the solder shell318can be ascertained by the size of the bond pad322. In an embodiment, the bond pad322is about 106 micrometers (μm). In an embodiment, the diameter326of the solder core316and twice the thickness328of the solder shell318also is about 106 μm. Other dimensions can be selected depending upon the application.

FIG. 4is an elevational cross-section of an article400that includes a foamed solder sphere410and an intermediate solder layer430upon a substrate420according to an embodiment. In an embodiment, the substrate420is an IC die. In an embodiment, the substrate420is a mounting substrate such as a printed-wiring board. The foamed solder sphere410is depicted schematically, and it can be either of a cellular-foamed solder or a reticulated-foamed solder according to an embodiment. The substrate420includes a bond pad422according to an embodiment. In an embodiment, the bond pad422exhibits elongated columnar grain morphology that is characteristic of a plating process. The bond pad422includes a flash layer424such as a gold flash layer424upon a copper bond pad422according to an embodiment. Above the foamed solder sphere410is located an upper substrate432and a bond pad434according to an embodiment. In an embodiment, the upper substrate432is an IC die. In an embodiment, the upper substrate432is a mounting substrate such as a printed wiring board. In an embodiment, the solder sphere410exhibits a modulus in a range between about 0.2 and about 0.7.

In an embodiment, the intermediate solder layer430is a reflowed solder that is denser than the foamed solder sphere410. In an embodiment, reflowing of the intermediate solder layer430is carried out at a temperature that is below the liquidus temperature of the foamed solder sphere410. For example, the intermediate solder layer430begins as nano-particulates of copper in a paste matrix, and the foamed solder sphere410is a prepared sphere with a melting temperature that is at or near the classical-physics melting temperature of elemental copper. During reflow of the intermediate solder layer430, the average grain size of the copper is no greater than about 20 μm according to an embodiment.

In an embodiment, the foamed solder sphere410has a diameter426in a range from about 25 μm to about 200 μm. In an embodiment, the foamed solder sphere410has a diameter426of about 106 μm. In an embodiment, the size of the foamed solder sphere410can be ascertained by the size of the bond pad422. In an embodiment, the bond pad422is about 106 μm. Other dimensions can be selected depending upon the application.

In an embodiment, the intermediate solder layer430is formed upon the substrate420by using a nano-particulate solder paste matrix. In an embodiment, the nano-particulate solder paste includes metal particles, about 100 percent of which pass the 20 nanometer (nm) screening, and the matrix includes a paste such as a fluxing agent and a volatile component.

In an embodiment, the intermediate solder layer430includes the nano-particulate solder paste including copper particles, and the foamed solder sphere includes copper. Also, the bond pad422includes copper and the flash layer424is not present. In an embodiment, the intermediate solder layer430includes the nano-particulate solder paste including nickel particles, and the foamed solder sphere includes nickel. Also, the bond pad422includes nickel and the flash layer424is not present. In an embodiment, the intermediate solder layer430includes the nano-particulate solder paste of a shape-memory alloy such as nickel-titanium alloy particles, and the foamed solder sphere also includes the shape-memory alloy. Also, the bond pad422includes the shape-memory alloy and the flash layer424is not present. In an embodiment, the intermediate solder layer430includes the nano-particulate solder paste including metal particles of a first type, and the foamed solder sphere includes the same metal of the same first type. Also, the bond pad422includes the same metal of the same first type and the flash layer424is not present.

Processing of the intermediate solder layer430includes heating the nano-particulate containing solder paste to a low temperature at which the solder particles begin to reflow. Because the solder paste matrix substantially protects the nano-particulates in the intermediate solder layer430from corrosive and/or oxidative influences, the intermediate solder layer430can resist substantial grain growth during reflow. In an embodiment, the intermediate solder layer430after reflow has an average grain size in a range from about 50 nm to about 20 μm.

In an embodiment, the intermediate solder layer430before reflow includes a particle having a size in a range from about 2 nm to 50 nm. In an embodiment, the intermediate solder layer430includes a particle having a size in a range from about 10 nm to about 30 nm. In an embodiment, the intermediate solder layer430includes a particle having a size in a range of about 98% less than or equal to about 20 nm.

Because of the particle size embodiments, nucleation of the metal particles of the intermediate solder layer430causes a transition from solid to solidus, and the transition can be initiated at about 400° C. or lower. For example, gold can experience a solid-to-solidus transition at about 300° C.

In an embodiment, the intermediate solder layer430includes a melting temperature equal to or below about 400° C. Depending upon the metal type and the particle size, the intermediate solder layer430can have a change in melting temperature of several hundred degrees. For example, solid gold has a classical-physics melting temperature of about 1064° C. When gold is formed into a nano-particulate intermediate solder layer430as set forth herein, the melting temperature can be reduced to about 300° C. This solid-to-solidus temperature lowering is useful for all the nano-particulate solder composition embodiments set forth in this disclosure.

Where the intermediate solder layer430and the foamed solder sphere410are of different metals or different alloys, an intermetallic region431can form therebetween. In an embodiment, the intermediate solder layer430is a copper-tin-indium solder and the foamed solder sphere410is copper metal. The intermetallic region431in this embodiment is a copper-tin intermetallic material.

FIG. 5is an elevational cross-section of an article500that includes a foamed-solder elongate pad510upon a substrate520according to an embodiment. The foamed-solder elongate pad510is depicted schematically, and it can be either of a cellular-foamed solder or a reticulated-foamed solder according to an embodiment. The substrate520includes a bond pad522according to an embodiment. In an embodiment, the bond pad522exhibits elongated columnar grain morphology that is characteristic of a plating process. The bond pad522includes a flash layer524such as a gold flash layer524upon a copper bond pad522according to an embodiment. In an embodiment, the foamed-solder elongate pad510exhibits a modulus in a range between about 0.2 and about 0.7.

In an embodiment, the foamed-solder elongate pad510is prepared with an intermediate solder layer536that can be the same material of any intermediate solder layer436depicted and described inFIG. 4. Further according to an embodiment, the nano-particulate metal of the intermediate solder layer536can be processed to reflow at a temperature that is significantly lower than the classical-physics solidus temperature of the metal.

In an embodiment, the foamed-solder elongate pad510has a characteristic dimension526in a range from about 25 μm to about 200 μm. In an embodiment, the foamed-solder elongate pad510has a characteristic dimension526of about 106 μm. In an embodiment, the size of the foamed-solder elongate pad510can be ascertained by the size of the bond pad522. In an embodiment, the bond pad522is about 106 μm. Other dimensions can be selected depending upon the application.

In an embodiment, the intermediate solder layer536is formed upon the substrate520by using a nano-particulate solder paste matrix. In an embodiment, the nano-particulate solder paste includes metal particles, about 100 percent of which pass the 20 nm screening, and the matrix includes a paste such as a fluxing agent and a volatile component.

In an embodiment, the intermediate solder layer536includes the nano-particulate solder paste including copper particles, and the foamed-solder elongate pad510includes copper. Also, the bond pad522includes copper and the flash layer524is not present. In an embodiment, the intermediate solder layer536includes the nano-particulate solder paste including nickel particles, and the foamed-solder elongate pad510includes nickel. Also, the bond pad522includes nickel and the flash layer524is not present. In an embodiment, the intermediate solder layer536includes the nano-particulate solder paste of a shape-memory alloy such as nickel-titanium alloy particles, and the foamed-solder elongate pad510also includes the shape-memory alloy. In an embodiment, the intermediate solder layer536includes the nano-particulate solder paste including metal particles of a first type, and the foamed-solder elongate pad510includes the same metal of the same first type. Also, the bond pad522includes the same metal of the same first type and the flash layer524is not present.

Processing of the intermediate solder layer536includes heating the nano-particulate containing solder paste to a low temperature at which the solder particles begin to reflow. Because the solder paste matrix substantially protects the nano-particulates in the intermediate solder layer536from corrosive and/or oxidative influences, the intermediate solder layer536can resist substantial grain growth during reflow. In an embodiment, the intermediate solder layer536after reflow has an average grain size in a range from about 50 nm to less than or equal to about 20 μm.

In an embodiment, the intermediate solder layer536before reflow includes a particle having a size in a range from about 2 nm to 50 nm. In an embodiment, the intermediate solder layer536includes a particle having a size in a range from about 10 nm to about 30 nm. In an embodiment, the intermediate solder layer536includes a particle having a size in a range of about 98% less than or equal to about 20 nm.

FIG. 6is a process depiction600of forming a foamed solder according to an embodiment. Processing begins by first intermingling a foamed solder precursor611with a compressible gas613. In an embodiment, the foamed solder precursor611is a metal particulate. In an embodiment, the compressible gas613is inert to the metal of the foamed solder precursor. In an embodiment, the compressible gas613is argon.

In an embodiment, the foamed solder precursor611includes a metallic surfactant that facilitates the formation of the foamed solder. In an embodiment, the foamed solder611composition includes, by weight percent, approximately Sn-10In-0.6Cu. In this depiction, the foamed solder precursor611composition includes about 10 percent indium, about 0.6 percent copper, and the balance tin. Other impurities may be present, based upon the specific feedstocks obtained and the chemical purities thereof.

InFIG. 6, the foamed solder precursor611is placed into a can638as is known in the metal-consolidation art. The filled can638is then processed by compressing to achieve a high-pressure can639that contains the foamed solder precursor611and the compressible gas613. In an embodiment, the high-pressure can639is achieved by hot-isostatic pressing (HIPing) as is known in the metal-consolidation art. After HIPing, the high-pressure can639is further heated without significantly restrictive external pressure, and the high-pressure can639expands such that a metal foam610is formed that includes a metal chamber612and a metal wall614if the foamed solder is a cellular-foamed solder. Alternatively after HIPing, the high-pressure can639is further heated without significantly restrictive external pressure, and the high-pressure can639expands such that a metal foam610′ is formed that includes a metal ganglia614′ that is formed if the foamed solder is a reticulated-foamed solder.

In an embodiment, the filled can638is not HIPed, but rather it is first heated to cause sintering of the foamed solder precursor611as is understood in the metal-consolidation art. Sintering does not cause a complete reflow of the foamed solder precursor, rather, a nucleation of contact points640between two occurrences of the foamed solder precursor611. Second heating of the foamed solder precursor611forms a metal foam such that first sintering and second heating expansion of the foamed solder occurs. In an embodiment, the first sintering achieves a foamed solder such that a metal foam610is a cellular-foamed solder. Alternatively, the first heating achieves a foamed solder such that a metal foam610′ with a metal ganglia614′ is formed.

In an embodiment, the filled can638is first consolidated without significant external heating, and second heated to cause the solder precursor611to expand. In an embodiment, the second heating achieves a foamed solder such that a metal foam610is a cellular-foamed solder. Alternatively, the second heating achieves a foamed solder such that a metal foam610′ with a metal ganglia614′ is formed.

Other techniques are usable to form the foamed solder. In an embodiment, investment casting is used as is known in the art. In an embodiment, melt processing is used along with the decomposition of metal hydride, which forms a gas that creates the porosity in the foamed solder. In an embodiment, powder processing is used that exploits the decomposition of the metal hydride. In an embodiment, a polymer prefoam is used as a temporary support structure to support the foamed solder as it solidifies, after which the polymer prefoam is driven off.

In an embodiment, metal powder is packed into a can, which is outgassed and then pressurized with argon gas. The can is HIPed to consolidate the metal powder. After consolidation, the can is heated to expand the entrapped gas by creep of the surrounding matrix in the HIPed powder. This technique is available to produce porous metals with bulk densities in a range from about 0.6 to about 0.8. The size and distribution of pores may be precisely controlled using appropriate gas pressure, metal surfactant content, heating time, temperature, and other parameters.

In an embodiment after forming of the metal foam610or the metal foam610′, the metal foam (hereinafter “metal foam610”) is further processed to prepare a solder bump. In an embodiment, the metal foam610is first extruded without destroying the foamed quality, and it is cut as wire into short sections by a heading machine until the wire is substantially cubical or solid cylindrical. Processing of the substantially cubical or solid cylindrical pieces of foamed solder includes tumbling to achieve a more spherical shape, or grinding in a mill. In an embodiment, autogenous grinding of the substantially cubical or solid cylindrical foamed solder is done in a tumbling mill. In an embodiment, semi-autogenous grinding of the substantially cubical or solid cylindrical foamed solder is done in a tumbling mill with the presence of a first amount of grinding media such as ceramic balls. In an embodiment, mill-grinding of the substantially cubical or solid cylindrical foamed solder is done in a tumbling mill with a second amount of grinding media that is greater than the first amount of grinding media. In an embodiment after first grinding the foamed solder to achieve a spherical shape, surface finishing is carried out in a less extreme tumbling environment.

Once the foamed solder core or the foamed solder sphere is made, the solder is coated on the foamed solder by electroplating according to an embodiment. Reference is again made toFIG. 3. Where the foamed solder core316is a shape-memory foam, a nickel plating process is carried out to create enhanced wettability between the shape-memory alloy and the bond pad322. Where the flash layer324is present, the plating process can be eliminated according to an embodiment.

FIG. 7is a flow chart that describes a process flow according to various embodiments.

At710, the process includes forming a foamed solder precursor in a can along with an intermingled gas.

At720, the process includes pressing the can. The process can include isostatic pressing or HIPing.

At730, the process includes heating the can under conditions to cause the foamed solder precursor to form a cellular foam or a reticulated foam. In an embodiment, the process terminates at720.

At740, the process includes forming the foamed solder into a foamed solder ball or into a foamed-elongate solder pad.

At750, a process embodiment includes forming an intermediate solder layer on a bond pad. In an embodiment, the intermediate solder layer is a nano-particulate solder preform.

At752, the process includes forming a foamed-solder such as a foamed solder bump or a foamed solder elongate pad on the intermediate solder layer.

At754, the process includes reflowing the intermediate solder layer to bond to the foamed solder. In an embodiment, the process terminates at754.

FIG. 8is a process depiction800of forming a nano-porous solder according to an embodiment. Processing begins by first intermingling a foamed solder precursor811with a blowing agent813. In an embodiment, the foamed solder precursor811is a metal particulate that has an average particle diameter in a range from about 5 nm to about 50 nm. In an embodiment, the foamed solder precursor811is a metal particulate that has an average particle diameter in a range from about 10 nm to about 40 nm. In an embodiment, the foamed solder precursor811is a metal particulate that has an average particle diameter in a range from about 15 nm to about 30 nm. In an embodiment, the foamed solder precursor811is a metal particulate that has an average particle diameter that is about 99% passing 20 nm and about 98% larger than about 5 nm.

In an embodiment, the blowing agent813is a metal hydride such as titanium hydride (TiH2). In an embodiment, the blowing agent813is a metal hydride such as zirconium hydride (ZrH2). In an embodiment, the blowing agent813is a metal hydride such as hafnium hydride (HfH2). In an embodiment, the blowing agent813is a refractory metal hydride, represented as RH2. In an embodiment, the blowing agent813substantially matches the particle size distribution of the foamed solder precursor.

In an embodiment, the foamed solder precursor811includes a metallic surfactant that facilitates the formation of the foamed solder. In an embodiment, the foamed solder precursor811composition includes, by weight percent, approximately Sn-10In-0.6Cu. In this depiction, the foamed solder precursor811composition includes about 10 percent indium, about 0.6 percent copper, and the balance tin. Other impurities may be present, based upon the specific feedstocks obtained and the chemical purities thereof.

InFIG. 8, the foamed solder precursor811and the blowing agent813is placed into a mixing vessel838, for example, such as is known in the metal-comminution arts. The mixing vessel838is then operated by blending the foamed solder precursor811and the blowing agent813to achieve a precursor-blowing agent mixture.

In an embodiment, the precursor-blowing agent mixture is compressed in an axial-compression die840. Compression dies are used, for example, in the powder metallurgy consolidation art. An anvil842receives a precursor-blowing agent mixture844and is pressed into the anvil842by a ramrod846. After axial pressing an axially pressed pellet848is the result.

In an embodiment, the precursor-blowing agent mixture is compressed in an extrusion die850. Extrusion is known, for example, in the powder metallurgy extrusion art. The precursor-blowing agent mixture844and is pressed into the extrusion die850by a ramrod846. After extrusion, an extruded pellet852is the result.

In an embodiment, either the axially pressed pellet848or the extruded pellet852is a nano-porous solder precursor that is further processed such as rolling to achieve rolled sheet stock854or856. In an embodiment, the pellet or the rolled sheet stock is stamped from pellet or rolled stock, into substantially spherical pellets of a nano-porous solder precursor for further processing.

Processing of the substantially cubical or solid cylindrical pieces of the nano-porous solder precursor from a pressed or extruded pellet includes tumbling to achieve a more spherical shape, or grinding in a mill. In an embodiment, autogenous grinding of the nano-porous solder precursor is done in a tumbling mill. In an embodiment, semi-autogenous grinding of the nano-porous solder precursor is done in a tumbling mill with the presence of a first amount of grinding media such as ceramic balls. In an embodiment, mill-grinding of the nano-porous solder precursor is done in a tumbling mill with a second amount of grinding media that is greater than the first amount of grinding media. In an embodiment after first grinding the nano-porous solder precursor to achieve a spherical shape, surface finishing is carried out in a less extreme tumbling environment.

After forming the nano-porous solder precursor into a desired shape, the desired shape is further processed under heating to achieve a nano-porous solder858.

FIG. 9Ais an elevational cross-section of an article900during processing of a nano-porous solder according to an embodiment. A pellet910, such as a nano-porous solder precursor, is disposed on a mounting substrate920. In an embodiment, the mounting substrate920is a board. In an embodiment, the mounting substrate920is a die. In an embodiment, the mounting substrate920includes a bond pad922. In an embodiment, an upper substrate932includes an upper substrate bond pad934, and the upper substrate932is also in contact with the pellet910.

Processing of the pellet910is reflowed in a thermal environment as illustrated by the dashed line936as a hot space such as an oven.

In an embodiment, the pellet910includes a nano-particulate foamed solder precursor in any size distribution range set forth in this disclosure. Similarly, a blowing agent is also present, substantially uniformly blended such as to facilitate expansion of the pellet910during reflow. In an embodiment, heating of the pellet910is carried out in a temperature range from about 150° C. to about 260° C. In an embodiment during reflow, the blowing agent liberates gas, such as hydrogen from a metal hydride. As the nano-porous solder precursor begins to nucleate at solidus reflow, a balance is struck between surface tension on nascent nano-sized gas bubbles and on grain growth from the nano-sized particles of the foamed solder precursor. Consequently, grain sizes that overcome the dimensions of the nascent nano-sized gas bubbles are avoided.

In an embodiment, reflow is carried out under an overpressure such as a HIPing environment, but the temperature is in the range from about 150° C. to about 260° C. In this embodiment, the overpressure is balanced against the nascent pressure of liberated gases, while the other balances of reflowing solder wetting and even the gravitational effect of the nascent nano-sized gas bubbles rising during reflow. In an embodiment, the nascent nano-sized gas bubbles in the reflowing solder is substantially in the Stokes flow regime, which includes creeping flow.

FIG. 9Bis an elevational cross-section of the article depicted inFIG. 9Aafter further processing of the nano-porous solder according to an embodiment. The article901has been processed such that nanopores have formed in the reflowed pellet911, one of which is designated with the reference numeral909. In an embodiment, the degree of porosity of the reflowed pellet911is in a range from about 1% to about 70%. In an embodiment, the relative density of the reflowed pellet911is in a range from about 0.1 to about 0.9. By “relative density”, it is meant that the density of the reflowed pellet911is compared to a solid solder of the same material. In an embodiment, the reflowed pellet911has a relative density of about 0.5. In an embodiment, the foamed solder reflowed pellet911has a relative density of about 0.6. In an embodiment, the reflowed pellet911has a relative density of about 0.7. In an embodiment, the reflowed pellet911has a relative density of about 0.8.

FIG. 10is a process flow diagram1000for processing a nano-porous solder precursor according to an embodiment.

At1010, the process includes blending a nano-solder precursor and a blowing agent.

At1020, the process includes compacting the nano-solder precursor and the blowing agent into a foamed solder precursor.

At1030, the process includes placing the nano-solder precursor upon one of a mounting substrate and a die.

At1040, the process includes expanding the nano-solder precursor to achieve a nano-porous solder.

FIG. 11is a cut-away elevation that depicts a computing system1100according to an embodiment. One or more of the foregoing embodiments of the foamed solder bumps, foamed solder elongate pads, or nano-porous solder spheres may be utilized in a computing system, such as a computing system1100ofFIG. 11. Hereinafter any foamed solder bumps, foamed solder elongate pads, or nano-porous solder spheres embodiments alone or in combination with any other embodiment is referred to as an embodiment(s) configuration.

The computing system1100includes at least one processor (not pictured), which is enclosed in a package1110, a data storage system1112, at least one input device such as a keyboard1114, and at least one output device such as a monitor1116, for example. The computing system1100includes a processor that processes data signals, and may include, for example, a microprocessor, available from Intel Corporation. In addition to the keyboard1114, the computing system1100can include another user input device such as a mouse1118, for example.

For purposes of this disclosure, a computing system1100embodying components in accordance with the claimed subject matter may include any system that utilizes a microelectronic device system, which may include, for example, at least one of the foamed solder bumps, foamed solder elongate pads, or nano-porous solder spheres embodiments that is coupled to data storage such as dynamic random access memory (DRAM), polymer memory, flash memory, and phase-change memory. In this embodiment, the embodiment(s) is coupled to any combination of these functionalities by being coupled to a processor. In an embodiment, however, an embodiment(s) configuration set forth in this disclosure is coupled to any of these functionalities. For an example embodiment, data storage includes an embedded DRAM cache on a die. Additionally in an embodiment, the embodiment(s) configuration that is coupled to the processor (not pictured) is part of the system with an embodiment(s) configuration that is coupled to the data storage of the DRAM cache. Additionally in an embodiment, an embodiment(s) configuration is coupled to the data storage1112.

In an embodiment, the computing system1100can also include a die that contains a digital signal processor (DSP), a micro controller, an application specific integrated circuit (ASIC), or a microprocessor. In this embodiment, the embodiment(s) configuration is coupled to any combination of these functionalities by being coupled to a processor. For an example embodiment, a DSP (not pictured) is part of a chipset that may include a stand-alone processor and the DSP as separate parts of the chipset on the board1120. In this embodiment, an embodiment(s) configuration is coupled to the DSP, and a separate embodiment(s) configuration may be present that is coupled to the processor in the package1110. Additionally in an embodiment, an embodiment(s) configuration is coupled to a DSP that is mounted on the same board1120as the package1110. It can now be appreciated that the embodiment(s) configuration can be combined as set forth with respect to the computing system1100, in combination with an embodiment(s) configuration as set forth by the various embodiments of the foamed solder bumps, foamed solder elongate pads, or nano-porous solder spheres within this disclosure and their equivalents.

FIG. 12is a schematic of a computing system according to an embodiment. The electronic system1200as depicted can embody the computing system1100depicted inFIG. 11, but the electronic system is depicted more generically. The electronic system1200incorporates at least one electronic assembly1210, such as an IC package illustrated inFIGS. 3-5. In an embodiment, the electronic system1200is a computer system that includes a system bus1220to electrically couple the various components of the electronic system1200. The system bus1220is a single bus or any combination of busses according to various embodiments. The electronic system1200includes a voltage source1230that provides power to the integrated circuit1210. In some embodiments, the voltage source1230supplies current to the integrated circuit1210through the system bus1220.

The integrated circuit1210is electrically coupled to the system bus1220and includes any circuit, or combination of circuits according to an embodiment. In an embodiment, the integrated circuit1210includes a processor1212that can be of any type. As used herein, the processor1212means any type of circuit such as, but not limited to, a microprocessor, a microcontroller, a graphics processor, a digital signal processor, or another processor. Other types of circuits that can be included in the integrated circuit1210are a custom circuit or an ASIC, such as a communications circuit1214for use in wireless devices such as cellular telephones, pagers, portable computers, two-way radios, and similar electronic systems. In an embodiment, the processor1210includes on-die memory1216such as SRAM. In an embodiment, the processor1210includes on-die memory1216such as eDRAM.

In an embodiment, the electronic system1200also includes an external memory1240that in turn may include one or more memory elements suitable to the particular application, such as a main memory1242in the form of RAM, one or more hard drives1244, and/or one or more drives that handle removable media1246such as diskettes, compact disks (CDs), digital video disks (DVDs), flash memory keys, and other removable media known in the art.

In an embodiment, the electronic system1200also includes a display device1250, an audio output1260. In an embodiment, the electronic system1200includes a controller1270, such as a keyboard, mouse, trackball, game controller, microphone, voice-recognition device, or any other device that inputs information into the electronic system1200.

As shown herein, integrated circuit1210can be implemented in a number of different embodiments, including an electronic package, an electronic system, a computer system, one or more methods of fabricating an integrated circuit, and one or more methods of fabricating an electronic assembly that includes the integrated circuit and the foamed-solder embodiments as set forth herein in the various embodiments and their art-recognized equivalents. The elements, materials, geometries, dimensions, and sequence of operations can all be varied to suit particular packaging requirements.

It can now be appreciated that foamed-solder embodiments set forth in this disclosure can be applied to devices and apparatuses other than a traditional computer. For example, a die can be packaged with an embodiment(s) configuration, and placed in a portable device such as a wireless communicator or a hand-held device such as a personal data assistant and the like. Another example is a die that can be packaged with an embodiment(s) configuration and placed in a vehicle such as an automobile, a locomotive, a watercraft, an aircraft, or a spacecraft.

It will be readily understood to those skilled in the art that various other changes in the details, material, and arrangements of the parts and method stages which have been described and illustrated in order to explain the nature of this invention may be made without departing from the principles and scope of the invention as expressed in the subjoined claims.