WO2019173691A1

WO2019173691A1 - Methods and apparatus for formation of structured solder particles, and automated fabrication thereof

Info

Publication number: WO2019173691A1
Application number: PCT/US2019/021311
Authority: WO
Inventors: Fay Hua; Youngjin Kim; Mina YAGHMAZADEH
Original assignee: S&J Electronics, Llc
Priority date: 2018-03-09
Filing date: 2019-03-08
Publication date: 2019-09-12

Abstract

This invention discloses an improved apparatus and processing methods for fabrication of substantially uniform sized metal or alloy microspherical particles, enabled by advanced molten metal jetting device structures and processing methods, with the molten pool of metal in an atmosphere-controlled crucible, with a train of molten droplets ejected downward through at least one orifice. Pressure and vibration are applied to the source of molten metal. An environment of inert gas is substantially maintained to prevent oxidation of the particles or metal spheres.

Description

METHODS AND APPARATUS FOR FORMATION OF STRUCTURED SOLDER PARTICLES, AND AUTOMATED FABRICATION THEREOF

RELATED APPLICATIONS:

This application claims the benefit of U.S. Provisional Application No.62/640, 935 filed March 9, 2018 which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Disclosed is a method of spherical metal particle formation, more specifically, a method and apparatus for making substantially uniformly sized solder balls under control of a computer and microcontrollers.

BACKGROUND OF THE INVENTION

The production of metal droplets is useful in a variety of research and commercial applications. Such applications include metal powder production, rapid solidification research, spray forming of discrete parts, spray forming of strips, spray forming of metal-matrix composites and metal coating. One of the discrete parts used in the electronics packaging industry is solder balls, which are utilized for many types of packaging schemes. When used in electronic circuit related device packaging, it is absolutely required that all the solder balls associated with a surface be of as uniform size as possible. If the solder balls are not uniform in size, one solder ball can ruin an entire part. For example, in a flip chip type package, a large number of solder balls are used on one major surface of the package. The solder balls are mounted on the major surface of the package at electrical contact points. In use, to attach the package, the solder balls melt to form a connection of the flip chip to a substrate. If some of the solder balls are much larger than the other solder balls attached to the major surface of the solder bonded package, the package generally will be improperly spaced with respect to the substrate to which it is attached. In other words, the major surface will not be flat or parallel to the surface. The solder joint, when made, will also not be proper. Some may be long and weak while some others may be stronger, thus producing somewhat inconsistent attachment.

In the past, molten solder has been screened to form solder balls. The screen is used to produce a uniform volume for all the solder balls. Once screened, the molten solder forms balls based on surface tension. In another embodiment, solid solder is chopped into uniform bits. The uniform bits are melted and flowed or made molten to make uniform volumes of solder. The solder is then cooled in oil. The surface tension of the molten metal solder forms the solder into balls or spheres. The solder balls are cooled in a bath of oil. The oil also allows the surface tension to continue to act and keep the solder in balls or spheres geometry.

Generally, the spheres of solder are manufactured via sequential flow/quench or reflow processes and added to oil. This is then followed by degreasing and classification of the solder balls by size. When molten solder is placed in oil or grease as part of the manufacturing process, surface contamination or mishandling can aggravate sphere solderability. Sphere attachment onto a ball grid array (“BGA”) typically is achieved via vacuum-transfer or gravity-dispensing processes, and the spheres are held in place by flux or solder paste before reflow. After the solder balls are formed and washed or degreased, the resulting solder balls are inspected. In some instances the solder balls are graded and grouped by their sizes. Thus, once the solder balls are formed, additional processing steps including degreasing and sizing the solder balls are required. This adds to the complexity of manufacture of the solder balls. The solder balls also are more prone to having one solder ball being bigger than the others in a BGA application. Additionally, in carrying-out these manufacturing steps, time is wasted in cleaning the solder balls, inspecting them and sizing them.

In addition to the electronic device packaging, metal spheres are also useful for three dimensional (3D) printing. The 3D printing has been a blossoming technical field with many potential consumer and industrial applications. The size of global 3D printing metals market is estimated to be more than $100 million in year 2015, and is poised to grow in excess of $1 billion in coming decades.

For 3D printing, typically sphere-shaped plastics, ceramics or metals are utilized. Metal spheres have unique advantages as the final 3D printed finished products are mechanically superior in strength, toughness, and durability. Various end-use industries have been trying to incorporate metal 3D printers as mainstream manufacturing equipment in order to reduce their lead time and increase profitability, which is expected to drive the market. It is well known that 3D printing metals are widely utilized in sectors including aerospace & defense, automotive, and medical & dental. Titanium and its alloys, as well as aluminum alloys, due to their beneficial properties such as light weight and anti-corrosion characteristics, are widely used in the aerospace industry. Complicated shaped parts can be produced by 3D printing type, additive manufacturing.

In addition, 3D printing technology has been applied in medical applications for more than a decade, such as in dental and hip implants especially as custom prosthetics. The medical applications of 3D printing have grown considerably because the process can bypass the need for expensive machining to achieve a complex geometry. The current medical uses of 3D printing can include artificial organs and tissue fabrication, creating prosthetics, orthopaedic and dental implants, anatomical models, and for pharmaceutical research of drug discovery or delivery.

With regard to the metal sphere fabrication, some previous art patents and publications disclose more convenient methods of producing uniform diameter solder spheres using molten metal spray approach. See Chun, et al, US Patent No. 5,266,098,“Production of Charged Uniformly Sized Metal Droplets”, issued on November 30, 1993, article by Chun, Passow and Suh,“Droplet-Based Manufacturing”, CIRP Annals, Volume 42(1), pages 235-238 (1993), Tang, et al, US Patent No. 5,891,212,“Apparatus and Method for Making Uniformly”, issued on April 6, 1999, Chun, et al, US Patent No. 5,431,315,“Apparatus for Applying Uniform Metal Coatings”, issued on June 11, 1995, Gurer, et al, US Patent No. 7,030,039, “Method of Uniformly Coating a Substrate”, issued on April 18, 2006, Hayes, et al, US Patent No. 5,736,074,“Manufacture Of Coated Spheres”, issued on April 7, 1998. While these prior art methods describe a process of forming relatively uniform sized metal spheres, there are many aspects that the prior methods do not teach in order to make the process sufficiently reliable enough for commercial applications and for large-scale

manufacturability .

SUMMARY OF THE INVENTION

This invention discloses various improved processing methods and apparatus to enable more efficient production of uniform diameter metal spheres, as well as scaled-up, continuous or continual manufacturing of large quantity of metal spheres, as described in detail below.

The invention also discloses application of these improved methods for fabrication of not only metal spheres but also ceramic and plastic spheres. In addition, the invention disclosed targeted uses of such improved metal spheres for electronic packaging, for additive

manufacturing, and for biomedical implant applications.

Disclosed is a method and apparatus for fabrication of uniform sized metal or alloy microspherical particles, enabled by improved jetting device structures and processing methods for producing uniformly sized metal spheres from molten metals or alloys in a container and ejecting a train of molten droplets downward through one or more orifice enabled by applied gas pressure, which is aided by vibration for droplet formation and also aided by applying a positive or negative electrical charge on the liquefied metal droplets, wherein the high-frequency repeated vibration causes metal to form uniform diameter. More specifically, disclosed are improved device and methods for:

(A) Making the natural vibration frequency of the device tunable and adjustable by controlling the vertical position of the associated mass unit. (By changing the position of the movable mass, the mass distribution in the system is rearranged (e.g., the distance between the bottom mass and the upper mass gets closer or farther) and the redistribution of the mass also changes the moment of inertia of the assembly)

(B) Making the vertical vibration displacement less impeded by incorporating a laterally extended wing structure with elastomeric interfaces against supporting structural components to allow the vibration actuator to minimize vibration absorption and have an essentially full mechanical vibration.

(C) Enhancing the device cooling capability by cooling liquid circulation in the piezoelectric actuator system.

(D) Eliminating the leakage of coolant liquid in the piezo stack using alignment structure and added sealant structure.

(E) Continuously or continually adding additional metal or alloy in the form of molten metal instead of solid metal form, to the main crucible containing molten metal, utilizing separate molten metal preparation structures. (F) Supplying the molten metal to the crucible or transferring to a different chamber by using a routing pipe structure having a larger diameter orifice with the on-off supply of molten metal controlled by adjustable gas pressure from above the melt.

(G) Protecting the piezoelectric vibration transducer from the surrounding heated environment by continuously circulating water cooling or air cooling.

(H) Providing a thin foil layer orifice selected from metallic, ceramic or composite layer, for reduced molten metal leakage, reduced head loss, reduced temperature gradient, easier prevention of dirt and ease of producing smaller diameter orifice.

(I) Automatically sorting out unsatisfactory particles from good particles using upper funnel and the rotating chute channels.

(j) Rapidly cooling molten metal droplets using cold nitrogen or helium vapor to obtain a finer grain size, minimized collision with chamber wall, reduced equipment height, and increased throughput for the given process time.

(K) Adding a cap structure to reduce the probability of funnel path clogging by filtering out undesirable agglomerated particles.

(L) Installing oxygen filters to the molten metal jetting structure and to the molten droplet cooling chamber to produce higher quality metal sphere particles, with much reduced surface oxidation.

(M) Charging the chamber wall to repel and prevent molten particle collision with the wall.

(N) Adding a valve configuration and evacuation/inert gas supply structure for oxidation preventing particle retrieval and transfer.

(O) Installing an in-situ zig-zag chute channel array structure to enable a continuous sieving of particle size in the molten metal jetting and solidification chamber.

The spherical metal or alloy particles having produced by improved apparatus and processing methods listed above are useful for various industrial applications including, but not limited to, electronic packaging, additive manufacturing for components in aerospace technology, automobile engineering, biomedical technology medical implants, and various other consumer products.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages, nature and additional features of the invention will appear more fully upon consideration of the illustrative embodiments described in the accompanying drawings. Fig. 1 is a schematic diagram of a molten metal jetting to obtain spherical particles, according to an example embodiment.

Fig. 2 is a schematic diagram of a vibration actuator for molten metal jetting, according to an example embodiment.

Fig. 3 is a schematic diagram of a movable mass for changing the natural vibration frequency of the assembly in three different positions on the assembly, according to an example embodiment.

Fig. 4 is a schematic diagram showing a mounting structure of the vibration actuator on top of the jetting crucible, according to an example embodiment.

Fig. 5 is a cross-sectional schematic view of a piezo stack having a liquid cooling capability, according to an example embodiment.

Fig. 6 is an illustration of a molten metal feeding apparatus and method for adding molten metal to a crucible, according to an example embodiment.

Fig. 7 is a structure for feeding crucible control by adjusting the pressure, according to an

Fig. 8 is a schematic view detailing an integrated feeding channel and the vibration actuator, according to an example embodiment.

Figs. 9A-9D are schematic views of a thin foil configured orifice and method of assembly and use, according to an example embodiment..

Figs. 10A-10D are schematic views that compare the cross-sectional view structure and reliability aspects of (a),(b) of a conventional orifice (prior art) to the cross-sectional view structure and reliability aspects of (c),(d) of the inventive thin foil orifice, according to an example embodiment.

Fig. 11A is a schematic showing the rotational channel arrangement, according to an example embodiment.

Fig. 11B is a three-dimensional perspective view of a machine construction including the rotational channel arrangement, according to an example embodiment.

Fig 12 is a schematic view of a liquid nitrogen evaporator for faster cooling of molten or solidified metal particles, according to an example embodiment..

Fig. 13. Center cap installed in order to prevent the funnel entrance from getting clogged by agglomerated particles or other unwanted particles.

Fig. 14 is a schematic diagram of an oxygen removing system, according to an example embodiment. Fig. 15 is a schematic diagram of a chamber lined with material that cam be charged, according to an example embodiment.

Fig.16. is a schematic diagrams of a particle retrieval system, and details of the collecting port, according to an example embodiment.

Fig. 17 is a set of illustrations showing the valve settings on both container and system port to transfer metal parts from container to the transport or transfer vessel substantially without particle oxidation, according to an example embodiment.

Fig. 18 is a schematic drawing showing the steps of engaging the particle transfer or transport bottle with the size-sorting sieve without exposing to the air.

Fig. 19 is a continuous sieving apparatus and method for particle size control, according to an example embodiment.

Fig. 20 is a schematic of printing, transferring or pick-and-place positioning of solder ball spheres (or particles) for electronic circuits or electronic packaging and the like, according to an example embodiment.

Fig. 21 is a schematic diagram depicting three-dimensional printing of bone implant parts using permanent or biodegradable alloy spheres, according to an example embodiment.

Fig. 22 is another schematic diagram for three-dimensional-printing-based, additive

manufacturing of assorted parts with spherical metal or alloy particles prepared by molten metal jetting process, according to an example embodiment.

It is to be understood that the drawings are for purposes of illustrating the concepts of the disclosure and are not to scale. Further, the drawings illustrate exemplary embodiments and do not represent limitations to the scope of the disclosure.

DETAILED DESCRIPTION

The present invention is directed to a process and apparatus for producing and

maintaining charged, substantially uniformly sized metal droplets which cool and solidify rapidly in the sealed chamber underneath to form uniformly sized metal spheres including solder balls.

The process of the present invention requires the use of a crucible within which a pool of molten metal is contained, an apparatus comprising a spray chamber and a droplet generator disposed within the spray chamber for producing charged uniformly sized metal droplets and preferably a monitoring system for observing and controlling the droplet formation process. The droplet generator generally comprises a crucible-like container for holding and liquefying a charge of metal or alloy, a vibration-generating structure such as piezoelectric actuator for forming uniformly sized metal droplets, and a charging apparatus for charging the metal droplets. The piezoelectric actuator is attached to an extension rod immersed in the molten metal to transfer piezo-generated vibration into the molten metal so that the high-frequency vibration leads to a train of mechanical pulses to make the molten metal repeated on-off ejected through one or more orifice holes located at the bottom of the crucible. The forming apparatus can also include at least one oscillating gas jet disposed outside the container at the point where the liquefied metal exits the container.

The process generally comprises liquefying metal in the container which has at least one droplet-forming spray orifice, electrically charging the liquefied metal, and forcing the liquefied metal through the at least one orifice and thereafter forming charged uniformly sized liquid metal droplets which maintain their uniform size and solidify into uniformly sized solder balls. The vibration transfer rod can be made of durable material that can withstand high temperature molten metal environment, such as stainless steel rod, superalloy rod, ceramic or glass rod, composite material rod or other mechanically and thermally robust material. The rod can be monolithic or can be split into branches if desired to spread the vibration to a large cross- sectional area.

In one embodiment the liquefied metal is formed into uniformly sized metal droplets by vibrating the liquid metal while it is in the container or crucible and forcing it out of an orifice in the container so as to form metal droplets. As the liquefied metal exits the at least one orifice as a jet, the imposed vibrations in the liquefied metal cause it to break up into uniformly sized metal droplets.

In both of these embodiments, the metal droplets may be charged by either charging the liquefied metal while it is in the container or by charging the droplets as or after they are formed after exiting the container.

After the metal or alloy droplets are formed, they continue their descent through the spray chamber to a collecting means such as a substrate or a container. The end use application of the metal droplets will, of course, determine the composition of the droplets and the substrate.

The metal droplets formed using the process and apparatus of the present invention are in each case of uniform size and shape; i.e. they are substantially spherical in shape and have diameters which vary in degree by no more than about ±5%, preferably by no more than about ±2%, still more preferably by no more than about ±1%, , and most preferably by no more than about ±0.5%. The metal droplets are formed having this uniformity without the need for any size classification procedures. As used herein "metal droplets" includes both liquid and solid metal droplets. The process of the present invention is capable of producing metal droplets having diameters which may be controlled to be within the range of from about 0.5 to 2,000 micro meters (um), preferably 1 to 500 micro-meters, more preferably 5 to 200 micro-meters depending upon the specific process conditions employed and the specific desired applications.

The process and apparatus of the present invention are useful in numerous end use applications including uniform powder production, rapid solidification research, spray forming of discrete parts, spray forming of strips, spray forming of metal matrix composites, and metal coating. The produced uniform-diameter metal or alloy particles can be utilized for electronic packaging, additive manufacturing, biomedical implant manufacturing and other industrial or consumer devices and applications.

Referring now to the drawings, the process and apparatus for use in carrying out the process will now be described. Shown in Fig. 1 is a schematic description of molten metal jetting to obtain spherical particles. The ultrasonic vibration transferred to the melt causes the molten metal in the crucible to be pushed through the orifice in a discrete way. The molten droplets get spheroidized during downfall motion within the inert atmosphere chamber because of the surface tension. The droplets eventually get solidified into round metallic particles which are then collected at the bottom of the chamber.

Fig. 1. Schematic description of molten metal jetting to obtain spherical particles. Molten metal in the crucible is pushed through the orifice in a discrete way via ultrasonic vibration, with the molten droplets getting spheroidized during downfall motion within the inert atmosphere chamber, which eventually get solidified into round particles. The crucible material for the liquid metal reservoir can be selected from, e.g., high temperature ceramics, SiC (silicon carbide), BN (boron nitride), or stainless steel or other high temperature durable metals or alloys. Some of these crucibles can be used for operations up to 3,000□ . The electrostatic charging makes the metal particles charged so that they repel against each other for minimal contact and

agglomeration.

Fig. 1 is a schematic diagram of a molten metal jetting apparatus 100 for obtaining spherical particles, according to an example embodiment. The molten metal jetting apparatus 100, includes a crucible 110 that holds liquid or molten metal 112. The crucible 110 includes a temperature control for controlling the temperature of the molten metal 112. The crucible 110 also includes an orifice 114 through which molten metal from the crucible 110 passes. The jetting apparatus 100 also includes a chamber 120 filed with an inert gas 122. The chamber 120 is in fluid communication with the crucible 110 via the orifice 114. The chamber 120 also includes a charging plate 124 located near the orifice 114. Droplets of metal are controllably formed and dropped past the charging plate 124. A charge is imparted on the metal droplets to keep them separated as they fall to the bottom of the chamber 120. At the bottom of the chamber 120 id a collection dish 130 where solidified droplets of metal are collected. Positioned within the crucible 110 is a piezoelectric vibrator system 140 including a vibration source 142 and a vibration transfer rod 144 that is connected to the vibration source 142 and extends into the crucible 110 and into the molten metal 112. The metal is liquid as it leaves the orifice 114 and solidifies as it falls through the chamber 110. A video monitoring system.150 monitors the size of the solidified droplets 160. Information regarding the size of the solidified droplets 160 of metal is used as part of a feedback control system to change the pressure of the gas 122 in the chamberl 10 and the rate of vibration of the vibration source 142 as well as the height of the liquid metal in the crucible 110. These are some of the factors that control the size of the metal ball formed in the molten jetting apparatus 100. The crucible material for the liquid metal reservoir can be selected from, e.g., stainless steel or other high temperature durable metals or alloys for fabrication of spheres from the low melting point (m.p.) metals or alloys, such as Sn, Sb, or Bi base solders, Ag-based braze alloys, Al-base, Mg-base or Zn-base alloys. For higher m.p. metals (e.g., above 900°C), high temperature ceramics, SiC (silicon carbide), BN (boron nitride), graphite or other nonmetallic crucibles can be utilized. Some of these crucibles can be used for operations up to 3,000□ .

The electrostatic charging (e.g., by applied DC voltage) makes the metal particles charged so that they repel against each other for minimal contact and agglomeration. The electrostatic charging plate can be positioned so as to minimize interference with falling metal droplets, for example, desirably having a split or hole-containing geometry.

The vibration assisted molten metal jetting process described above requires its own unique conditions that other conditions usually do not require therefore it is difficult to make the process continued for long period of time. The process utilizes a very small orifice that can be clogged easily if not carefully handled. A pressure differential across the orifice(s) between the molten metal container and the spray chamber of about 0.5 - 100 psi, preferably at least 3 psi is desired in order to release the molten metal and form a sprayable jet of molten metal. As the process requires a high pressure inside the molten metal container during the process, it is not trivial to add additional material or remove the product without releasing the pressure since the process requires very precise control of temperature, pressure and vibration. Any disturbance of these controls can cause size deviation of the product and instability of the process. Most of automated system adding additional material is done by adding solid state material, but adding solid raw material can induce system vibration and temperature disturbance. Adding molten liquid is challenging since the temperature of most of molten materials is quite high (many metals/alloys have their m.p. above l,000°C).

The process also requires vacuum pumping steps to remove unwanted gas molecules (oxygen, water vapor, etc) prior to metal sphere production (or after production). There are many commercial components that can endure either vacuum or pressurized condition, but there are not that many components that work in both conditions. The vibration actuator, which is usually made of peizo elements, is also vulnerable to heat since the longtime vibration itself during manufacturing as well as the presence of molten metal keeps supplying heat. The molten metal jetting process often constantly requires cleaning to remove the unwanted deposition of the material on the processing chamber.

Solidified metal spheres can be collected at the bottom of the spray chamber using a dish type container. Alternatively, an automatic, continuous /continual particle removable system (optionally using a loadlock or conveyer belt system) can be introduced to increase production output with minimal disturbance of the continuous jetting process.

Control of the particle size and uniformity is achieved through adjustment of the piezoelectric vibrator's frequency, and the pressure difference between the reactor and the collecting chamber. Also, if the pressure difference between the upper and lower chambers (molten metal chamber vs spray chamber) is reduced, e.g., from 40 psi to 10 psi, the particle size decreases.

According to the invention, as the piezoelectric vibrator frequency is raised, e.g., from 10 kHz to 150 kHz, the particle size decreases, e.g., from 150 um to sub-50 um. The frequency of piezoelectric vibration (or magnetostrictive transducer induced vibration) affects not only the particle size but also affect the production rate, with the higher frequency producing faster jetting and increased volume of the metal sphere particles.

One of the unique aspects of this invention is the adjustability of vibrating frequency . In this invention, the vibration actuator can adjust its own natural frequency by altering the location of the moving mass. The natural frequency of the assembly can thus be adjusted, e.g., between 200 Hz and 200 KHz, with the adjustable range basically unlimited.

Fig. 2. Schematics of the vibration actuator for molten metal jetting. One configuration, according to the invention, is to provide a capability of self adjusting (or tuning) its natural frequency, e.g., by introducing a configuration of movable mass.

Fig. 2 is a schematic diagram of a vibration actuator 200 for molten metal jetting, according to an example embodiment. The vibration actuator 200 has several of the same components as the vibration system 100 shown in Fig. 1. The vibration actuator 200 includes several extra elements that will be described below. The vibration actuator 200 includes a frequency tuning structure 300 that includes a fixed mass 210 and a moveable mass 220. The fixed mass is attached or coupled to the vibration transferring rod 144. The moveable mass 220 is attached to the vibration source 142 and includes a mass movement mechanism 230. The moveable mass 220 includes an internally threaded opening 222 which rides on a threaded rod 224. A motor 230 rotates the threaded rod 224 and can move the moveable mass 222 to different positions, such as those shown in Fig. 3. The mass also includes at least one guide opening. As shown, the mass includes two guide openings (not shown in detail). Guide rods 240 are positioned between the vibration source 142 and a plate 242 a distance above the vibration source 142.

Shown in Fig. 2 is a more detailed schematics of the vibration actuator part for molten metal jetting. The number of piezo stack in Fig. 2 can be increased to be two or more in order to enhance the overall power and amplitude of piezo-induced mechanical vibration. The preferred number of piezo elements in the stack is at least 2, preferably at least 4, possibly up to 8. Multi layer, co-fired piezo stack can be used. The properties of each piezo unit or the multi-layer stack can be as follows. Electromechanical coupling coefficient (a numerical measure of the conversion efficiency between electrical and acoustic energy in piezoelectric materials) useful for the device in this invention is in the range of K_p (the coupling coefficient when the electrodes are perpendicular to the three axis) = ~ 0.5-0.7, K_t (the thickness coupling factor) = -0.3 - 0.5, K_3i (the coupling coefficient with the electrodes perpendicular to three axis and the applied stress or direction of piezo strain is along one direction) = -0.3 - 0.4.

The desired Piezoelectric constants values are— D₃₃ = -50- 800 xlO -12 m/v, D_3I = - 500 - -60 xl0 ¹²m/v, G₃₃ = -10- 30 xlO^_3Vm/N, G₃₁ = -20- -5 xlO^_3Vm/N. The desired static capacitance value, Cs = -200 pF - 20,000pF, and the desired range of resonant impedance,

Zm = -2- 200W.

This invention discloses many new aspects of molten metal spraying designs, apparatus structures, and methods of operation, with some examples listed and described below.

Invention A. Configuration Comprising Adjustable/ Tunable Natural Vibration Frequency

The disclosed invention contains several unique advantageous aspects in device design and functionality. One preferred configuration, according to the invention, is to provide a capability of self adjusting (or tuning) its natural frequency , as described in Fig. 3. Three different examples of movable mass positions are shown in the figure, (a) the movable mass in the lower position, (b) in the middle position, and (c) at the higher position. Having the movable mass at different locations changes the natural vibration frequency of the piezo assembly, which in turn changes the jet sprayed metal particle size and throughput of particle manufacturing. The movable mass configuration consists of a ball screw and motor that can linearly move the upper mass so that the system can achieve any desired natural frequency. The adjustability of the frequency by movable mass position, according to the invention, is by at least 5%, preferably at least 10%, even more preferably at least 20%.

Fig. 3 is a schematic diagram of the frequency tuning structure 300 with a movable mass 220 for changing the natural vibration frequency of the assembly 200 in three different positions on the assembly 200, according to an example embodiment. The three different examples of movable mass positions shows the movable mass in a lowered position near the piezo stack 142 (shown in Fig 3A), and the movable mass 220 at higher positions above the piezo stack or vibration source 142 (shown in Figs. 3B and 3C). Having the movable mass 220 at different locations changes the natural vibration frequency of the assembly 200.

Invention B. Free Movement and Full Displacement Capability

Another unique advantageous aspect of the invention is the design that allows a free movement of vibrating component with minimal restrictions which enables essentially full displacement capability for more powerful piezo actuation. Shown in Fig. 4(a) is the unique mounting structure of the vibration actuator on top of the jetting crucible. The extended wing is held by elastomers so that the vibration actuator can have full displacement. The alternative design of Fig. 4(b) configuration does not contain the frequency-self-tuning (movable mass) arrangement, however, this design still allows free movement and essentially full displacement for more powerful piezo actuation. The structure that allows both (up and down) sides of the end free to have displacement (typically one side of the piezo stack is constrained with solid fixture). As described in the figure, the wing structure (or flange) is extended from the body of the piezo stack, by at least 1 mm, preferably at least 5 mm, more preferably at least 1 cm. The wing structure allows freeing of both ends. Here the wing is held by compliant elastomers so as to minimize constraining of the displacement and to improve the vibration. The desired dimension of the compliant elastomer is about 0.4-20 mm thickness, preferably l~l0mm, even more preferably l.5~4mm thick.]

When one end is fixed to the supporting structure (which is conventional as in the prior arts), it is unavoidable to get the vibration transferred to the very rigid supporting structure thus overall effective mass becomes higher and some portion of vibration could be absorbed by the structure. Elastomeric holding, as in this invention, isolates the piezo stack (or vibration actuator) from the supporting structure with only slight damping, therefore the supporting structure does not either substantially absorb or constrain the vibration. The amount of the damping loss in the type of invention design, i.e., the use of extended wing structure and the introduction of elastomertic interfaces is reduced such that the invention device provides at least 20% more piezoelectgric vibration amplitude as compared to the prior art without such a design, preferably at least 50% more, even more preferably at least 75% more piezoelectric vibration amplitude.

Prior art approaches generally allow only about 10% of the piezo-induced amplitude to be transferred to the actual liquid or molten metal. This mounting method is advantageous as it allows a much improved degree of vibration transfer.

Fig. 4. Unique mounting structure of the vibration actuator on top of the jetting crucible. The extended wing is held by elastomers so that the vibration actuator can have full

displacement. Case (b) shows an alternative configuration without the frequency- self-tuning arrangement, which is still useful for some applications.

Fig. 4 is a schematic diagram showing a mounting structure 400 for the vibration actuatoror vibration source 142, according to an example embodiment. The mounting structure 400 is attached to the crucible 110. The mounting structure 400 includes an extended wing or flange 410, and a set of elastomer supports 420. The flange is connected to the vibration source 200. The mounting structure 400, the extended wing or flange 410, and the set of elastomer supports 420 each have openings (not shown) to allow an aligning rod 430 to pass therethrough. The support structure 400 includes a base 402 and a shoulder 404. The shoulder 404 is attached to the base 402 with a fastener 406 to form a pocket that captures the extended wing or flange 410 and the elastomer or elastomeric supports 420. The mounting structure can be used with the vibration actuator 100 or the vibration actuator 200 that includes the frequency tuning structure 300.

Invention C. Device Cooling Capability by Liquid Yet another unique advantageous design of this invention is the liquid cooling capability. This is schematically illustrated in Fig. 5. Fig. 5 is a cross-sectional schematic view of a piezo stack 500 having a liquid cooling capability, according to an example embodiment. The piezo stack 500 includes doughnut shaped disk 510 which surround the individual stacked components 520 of the piezo stack 142. The doughnut shaped disks 510 are sealed into place with a sealant, such as silicon or the like. A center clamp 530 includes a fastener shaft 532 which fits between the disks 510 and the piezo elements 520 to form a set of fluid channel 540. Having a cooling channel inside the piezo stack (or vibration actuator) would be advantageous and overheated device can be continuously or continually cooled so as to make the device performance more reliable and durable. The unique design in this invention calls for a use of doughnut shaped discs with a hole, in combination with a dimension of the center clamp intentionally smaller than the hole size so as to produce a gap between them. The gap so produced between the center clamp and the wall of each discs need to be at least 0.5 mm, preferably in the range of 0.5 - 2 mm, but less than 10 mm to avoid too loose a gap. (The coolant maintains the temperature of the piezo stack device at least 20°C, preferably 40°C below the Curie temperature of the piezo element.

Invention D. Alisnment Structure Introduced between Disks in Poezo Stack

The invention also introduces an alignment geometry that prevents misalignment of discs. This geometry, a step-like structure described in the circular inset of Fig. 5, is important since there is a gap between the center clamp and the holes of the doughnut shaped discs. The silicone elastomer seal (which has some fluidity yet with some reasonable viscosity) between the neighboring electrode in the piezo stack prevents coolant leaking. For tight seal, it is desirable to have the silicone sealant to be compressed by 0-40%, preferably 5-20% of original thickness of the silicone seal by the electrode. According to the invention, with the alignment structure and the incorporation of sealant structure (eliminate) the tendency for coolant liquid leakage

The surface of electrode that the silicone seal is facing is optionally treated to have some roughness to ensure that the silicone material does not slip out from the intended position.

Fig. 5. Schematic cross-sectional view of the piezo stack having a liquid cooling capability. Hollow center and the silicone sealing between the connection of the piezo element enables the liquid cooling. The alternate arrangement of doughnut shaped piezo disk elements and copper electrode disk elements can produce the hollow channel for cooling liquid channel.

Invention E. Convenient Molten Metal Feeding System for Continuous or Continual Metal Droplet Jettins

For continuous operation (or long-time operation) of the molten metal jetting process (spray solidification), an additional quantity of the raw material metal (or alloy) has to be supplied once the pre-loaded amount is almost used up. Adding solid metallic material tends to cause disturbance in ultrasonic mechanical vibration and droplet breaking up as the process requires precise control of vibration. Solid metal addition will also alter the temperature of the melt, which will affect the viscosity and flow of molten metal.

Feeding solid material undesirably alters the temperature of the metal within the jetting crucible. When a solid melts, the solid absorbs heat from its surrounding. Furthermore, the heat of the fusion (or latent heat) of most metals or alloys is usually much larger than the specific heat of the liquid state material (molten metal). Therefore, melting of solid metal inside the crucible undesirably lowers the temperature of the crucible, e.g., more than 20°C instantaneously. In comparison, feeding liquid molten material that is already melted in another crucible, and the temperature is matched to that of the main jetting device crucible melt temperature (with the feeding melt temperature set desirably within less than 20°C difference, preferably less than lO°C difference, more preferably less than 5°C difference), does not change the temperature of the jetting crucible much. Therefore the jet does not have to be stopped while adding the additional material.

This invention discloses a new, advantageous method and associated device structure for molten metal feeding into the crucible even while the ultrasonic jetting is still in progress, as illustrated in Fig. 6. Fig. 6 is an illustration of a molten metal feeding apparatus 600 and method for adding molten metal to a crucible 110, according to an example embodiment. The molten metal feeding apparatus 600 includes a first feeding crucible 610 and a second feeding crucible 620. Fluidly coupled to the first feeding crucible 610 and the main crucible 110 of the jetting apparatus 100, 200 is a first headed feeding channel 612. Fluidly coupled to the second feeding crucible 620 and the main crucible 110 of the jetting apparatus 100, 200 is a second heated feeding channel 622. The first headed feeding channel 612 and the second heated feeding channel 622 are shaped to receive molten metal from the first feeding crucible 610 and the second feeding crucible 620 and carry the molten metal to the inside wall of the main crucible 110. In this way, the liquid in the main crucible 110 will not be disturbed or minimally disturbed as the molten metal enters the main crucible of the jetting system 100, 200. The heat is controlled in each of the feeding crucibles 610, 620 to be substantially the same as the molten metal in the main crucible. The level of molten metal is also kept substantially the same during the operation of the jetting apparatus 100, 200. In this way, the pressure head of the molten metal as it acts on the orifice at the bottom of the main crucible 110 will remain submstantially the same. The molten metal feeding apparatus 600 also includes a vibration/feeding channel holding block 630, a cooling block 640 and a thermal insulative material or layer 650 between the vibration/feeding channel holding block 630 and the cooling block 640. The piezo stack abuts the cooling block 640 and serves to cool the piezo stack 142, 500

The advantage of the molten metal (or alloy) feeding is that adding liquid can minimize the change to the process condition. Feeding liquid continuously along the jetting crucible wall minimizes additional mechanical and thermal disturbance. The convenient molten metal feeding system for continuous or continual metal droplet jetting allows a much higher production per day of metallic microspheres by at least 20%, preferably at least 50%, even more preferably at least 200%, as the machine downtime for feedstock replacement or replenishment is drastically reduced.

According to the invention, the improved molten metal jetting structure combined with an added in situ hot liquid metal continuous supply allows a continuous jetting operation, without interruption, of at least 24 hrs, preferably at least at least 8 hrs, preferably at least 5 days, more preferably at least 30 days.

Fig. 6. Molten metal feeding structure and method (a) Overview of molten liquid transferring system comprising two feeding crucibles, (b) Molten metal feeding structure with a zoomed image of the feeding channel that allows the liquid to flow along the wall.

Shown in Fig. 6 is the molten metal feeding structure and method, with Fig. 6(a) schematically describing the overview of molten liquid transferring system comprising two feeding crucibles. There could be a single, two or multiple feeding crucibles individually operating at any given time, or simultaneously operating, e.g., for faster feeding or two or more separate metal melts fed to form an alloy molten bath. The schematic drawing in Fig. 6(b) illustrates a zoomed image of the feeding channel that allows the liquid to flow along the wall.

The cooling block 640 in Fig. 6 is to make sure that the piezoelectric transducer stack 142, 500 is not overheated. Either a passive metal heat dissipating structure or actively cooled (by circulating coolant or air) can be utilized. According to the invention, the piezo transducer stack heating is reduced by the cooling -block-incorporated structure, by at least 20%, preferably at least 50%.

Fig. 7. Detailed structure of the feeding crucible control by adjusting the pressure (a) Direct vertical release of molten metal, (b) Routing of molten metal through an upside-down, U- shape tube (a transfer tube). The Method 1 requires orifice with small diameter to prevent uncontrolled molten metal exiting through the orifice. Only with appropriately small diameter, the viscosity of the molten metal can be balanced with the gravity-induced pressure to keep the liquid from leaking downward. The Method 2, utilizing a bent routing tube, does not have such a problem, and can use a larger diameter as needed. The inset shows the molten metal jetting structure with the dotted circle region expanded as Fig. 7(b).

Fig. 7 is a molten metal flow system 700, 700’ which is astructure for feeding crucible control by adjusting the pressure, according to an example embodiment. The feeding crucible 610, 620, has an orifice 614, 624 that directs molten metal to a heated thermal channel (shown in Fig. 6). In one embodiment, the feeding crucible 610, 620 is pressurized. In this type of arrangement the size of the orifice 614, 624 is carefully controlled. In another embodiment of the molten metal flow system 700’, the feeding crucible 610, 620 is provided with a routing tube 710. One end 712 of the routing tube 710 is located in the molten metal in the feeding crucible 610, 620. The other end 714 forms an exit route out of the feeding crucible 610, 620.

Invention F. Structure Enablins Adjustable Pressure Feeding of Molten Metal to Allow Larser Diameter Supply of Molten Metal

Shown in Fig. 7 is a detailed structure of the feeding crucible control by adjusting the pressure. Hot molten metal flow control is not trivial. Conventional valves cannot be used for the molten metal flow control due to corrosion problem. There are a few molten metal pumps that can circulate hot liquid metal in a controlled manner, however, they are very expensive and complicated. Therefore, a simplified and easy-to-use molten metal flow system 700 is required. We disclose such a simple yet novel method that can control the hot liquid flow by simply applying a pressure so as to supply molten metal through a transfer tube that routes the molten metal upward first, followed by downward movement of the molten metal.

The feeding crucible that is shown in the Fig. 7(a) starts to squeeze out the molten metal through a bottom hole to the feeding channel when the gas pressure (e.g., Ar or N₂) is applied onto the top of the liquid level, and stops to do so when the pressure is relieved. Feeding crucible requires an ability to supply molten metal liquid material to the jetting crucible at least at the same or faster rate of jetting at the jetting crucible 110. In order to meet the condition, the feeding crucible 610, 620 needs to be larger (with at least 1-3 times larger orifice than that in the jetting crucible). The Method 1 in Fig. 7(a) is a simple method that can feed liquid to the feeding chamber while the Method 2 is a more advanced configuration. When the level of the liquid is high, the pressure of the liquid itself can cause start of feeding in the Method 1. In comparison, the Method 2 ensures to prevent the molten metal material flow and leakage by the height (and weight) of the material itself. The height of the transfer tube (upside-down reversed U channel) is higher than the height of the liquid so that the pressure of the liquid due to the liquid height itself cannot overcome the barrier. In Method 2, a much larger tube (a transfer tube) can be used which allows even faster feeding of molten metal as needed.

For the Method 1, the size of the orifice for the feeder can be 1-10 times larger than the orifice for the jetting. (1.5- 2 times larger dimension is preferred). For the Method 2 the size of the tube for the feeder can be as much as x40 time (in the range of xl - x40 times) of the orifice for the jetting. (x2 - xlO times is preferred) . For the Method 2 the height of the top of the feeding tube is 0-5 inches higher than the height of the maximum level of the molten metal liquid. (0.1 - 1 inch higher level is preferred). Applying and releasing of pressure starts and stops the feeding. Pressure of the feeding chamber during the feeding can be 0.1-50 psi (1-2 psi is preferred) higher than the jetting chamber pressure. According to the invention, the orifice diameter for the molten metal feeder is advantageously increased by at least 20%, preferably at least 50%. Invention G. Prevention of Actuator Getting Too Hot by Continuous Coolins

Fig. 8 is a schematic view detailing an integrated feeding channel and the vibration actuator 800, according to an example embodiment. The integrated feeding channel and the vibration actuator 800 includes the first headed feeding channel 612 and the second heated feeding channel 622. Each heating channel 612, 622 are shaped to receive molten metal from an associated first feeding crucible 610, 620 (see Fig. 6). The integrated feeding channel and the vibration actuator 800 includes a vibration/feeding channel holding block 630, a cooling block 640 and a thermal insulative material or layer 650 between the vibration/feeding channel holding block 630 and the cooling block 640. The piezo stack abuts the cooling block 640 and serves to cool the piezo stack 142, 500

Shown in Fig. 8 is a drawing that describes some details of the integrated feeding channel and the vibration actuator. This schematic design teaches two important aspects (i). The piezoelectric vibration transducer needs to be protected from the heat of hot, molten metal pipeline and storage crucibles nearby. In this invention, a cooling block is provided which is connected with chiller for continuous water cooling as needed. Or alternatively, air circulation may be utilized for continuous cooling (ii). In the vibration assisted molten metal jetting process, the vibration actuator is located at the center position of the jetting crucible which is the only opening of the jetting crucible. To add liquid state material to supply more metal to the crucible, an innovative arrangement is required. Unlike the conventional solid feeding approach which needs the complete stopping of the jetting operation during the period of supplying the material, this invention enables a continuous supply of liquid (molten metal) feeding without having to stop the jetting operation. For utilizing molten metal feeding system, thermal management aspects also need to be considered since the molten material is at a high

temperature, and various apparatus parts can become undesirably hot.

According to the invention, the ultrasonically activated, molten metal microsphere jetting system, with incorporated structure of continuous cooling (e.g., utilizing connection to a water chiller system or gas cooler system), can reduce the degree of heating from surrounding hot environment heating by at least 20%, preferably at least 50%.

Fig. 8. Details of the integrated feeding channel and the vibration actuator.

Invention H. Introduction of Thin Foil Orifice for Enhanced Jetting Reliability

Figs. 9A-9D are schematic views of a thin foil configured orifice and method of assembly and use, according to an example embodiment. Fig. 9A shows a first embodiment of an orifice 914 for the bottom of a crucible, such as crucibles 110, 610, 620. An orifice 914 is formed from a mechanical support 910 and thin foil 920 which is attached to the mechanical support 910 except at an area 916 proximate the orifice 914 itself. The area 916 is where the foil layer 920 is cantilevered off the edge of an orifice in the mechanical support 910. The result is an orifice 924 with a smaller diameter than the orifice 914 that is in the foil 920. The foil 920 is thinner thant the mechanical support 910. The thin foil orifice assembly of Fig. 9A is clamped to the bottom of a feeding crucible 610, 620 with a plurality of clamping bolts 930, as shown in Fig. 9C. Fig. 9D shows a variation in the crucible 110 which is a tapered edge 950 down to the orifice 924.

The clamped portion is sealed with a sealant 940. show an orifice

Yet another advantageous aspect of the present invention is the design and utilization of thin foil orifice. Traditional orifices are made on a relatively thick support material, often as a vertical hole path or as a tapered, gradually-diameter-reduced insert. Using a thin foil as a basis of one or multiple orifice(s) brings in many advantages but requires challenging mounting method. The multiple orifices can be arranged either in a linear fashion, circular, square or other arrangements.

Being a thin foil with a need to have some of the top surface open for access of the molten metal, the assembly of thin foil orifice into the jetting device is not a trivial matter.

According to the invention, the drawing in Fig. 9 shows an innovative clamping method that utilizes the pressure for the upper side of orifice with a need to simply supporting the bottom portion of the thin foil. Without the pressure on the upper part of the thin foil, the foil does not have means of complete contact with the bottom support. However, the pressure of the gravity force of molten metal itself serves as the needed pressure over the top of the thin foil to keep the thin foil in place. Utilizing the pressure makes the clamping method very simple and enables thin foil as the orifice. The schematic drawing of Fig. 9(c) describes such a use of molten metal gravitational force to maintain the thin foil orifice layer flat, while Fig. 9(d) shows an alternative, more stabilized structure of utilizing a tapered structural holder component to compress the thin foil orifice layer and keep it in place.

The thin foil orifice structure, according to the invention, has several advantageous aspects as described below, with some additional advantages depicted in Fig. 10. Conventional micron sized orifices (such as sapphire) are made from a small solid ceramic disc and inserted into the middle portion of a plate which serves as the supporting structure. The thickness of the orifice-containing insert is hard to avoid in order to ensure the desired mechanical strength. If the insert is made thin, it can not be inserted without great complications. However, according to the invention, a thin foil structured orifice can be made usable by utilizing a flat-bottomed support. The bottom support approach in this invention can prevent undesirable deformation of the orifice and orifice-containing structure, and enables utilizing very thin foils as orifices. Small unsupported portion (hanging portion) near the orifice can maintain the shape because of small area (as the force is pressure x area).

Fig. 9. Thin foil configured orifice (a) Cross-sectional structure, (b) Method of assembly and using it for more reliable jetting of molten metal, (c) Use of molten metal gravitational force to maintain the thin foil orifice layer flat, (d) Use of tapered structural holder component to compress the thin foil orifice layer and keep it in place. In addition, conventional orifice that requires certain thickness is vulnerable to leakage and to blockage caused by any foreign particle type materials. The thin foil type orifice has much less chance of these problems as illustrated in Fig. 10. In addition, there are also other advantages in using the invention structure of thin foil orifice, such as less head loss across the orifice and less temperature difference between the melt above and the melt below across the orifice.

In fluid dynamics for the case of incompressible fluid being pressured and passed through a pipe, there is a pressure loss due to friction, which can be expressed by the well known Darcy- Weisbach equation. This an empirical equation, which relates the head loss (pressure loss) to geometrical and other parameters as expressed in the following equation;

Ah = f_D (L V²/D-2g)

where,

Ah is the head loss due to pipe friction over the given length of pipe (SI units: meter).

F_D is the Darcy friction factor (a dimensionless friction factor, a coefficient for resistance to fluid flow)

L is the pipe length in meter unit (orifice thickness in this case).

D is the hydraulic diameter in meter (internal diameter of the pipe).

V is the fluid flow average velocity in meter/sec.

G is the gravity force (9.81 meter/sec )

It is clear that if the pipe length L (height of the orifice in this case) is reduced by utilizing a thin foil material, there will be a substantial decrease in head loss, which will be another advantageous feature of this invention.

The unsupported portion (Fig. 9) can be 0.1 mm to 2 mm wide (0.2-1 mm is preferred) depends on the mechanical strength and durability of the foil, e.g., the Young’s modulus or yield strength of the foil. When the portion of the unsupported area is very small (e.g., 0.5 mm to 2 mm), even a thin foil can stand pressure without supporting. The desired material that can contain the thin foil orifice should have melting point of at least 600°C, and should exhibit essentially no solubility into the selected molten metal or alloy being processed for particle formation.

The thin foil material is selected from preferably high strength, corrosion-resistant metal or alloy materials, such as refractory metals (e.g., Ti, Mo, Zr, Nb, Mo, Hf, Ta, W or their alloys, an example being Ti-6%Al-4%Al alloy), stainless steels (304 type, 410 type or precipitation- hardenable stainless steels like 17-4 Stainless Steel containing l7%Cr and 4%Ni, Ni base superalloys (e.g., Inconel, Hastelloy, Haynes alloy), with an example being Inconel 625 having Ni-20%Cr-8%Mo-4%Ta. A ceramic or composite material can also be utilized. The desired thickness of the thin foil material is typically in the range of 10 um to 500 um, preferably 25 um to 200 um, even more preferably 50 - 150 um. The orifice in the thin foil can be in the range of 3 um to 200 um. In order to prepare smaller diameter metal or alloy spheres, the orifice diameter can be reduced, e.g., 5 - 50 um, which can be prepared using precision machining, patterned chemical etching method (e.g., using a mask), laser ablation processing, or other metal processing means.

Fig. 10. Comparison of cross-sectional view structure and reliability aspects of (a),(b), Conventional orifice (prior art) to (c),(d) Thin foil orifice (this invention). Figs. 9A-9D are schematic views of a conventional orifice (Figs 9 A and 9B) compared to a orifice which is thin foil configured orifice (Figs. 9C and 9D) and method of assembly and use, according to an example embodiment.. Figs 9 A and 9B show an orifice

Figs. 10A-10D are schematic views that compare the cross-sectional view structure and reliability aspects of a conventional orifice (Figs. lOA-lOB-prior art) to the cross-sectional view structure and reliability aspects of the inventive thin foil orifice (Figs. 10C-10D, according to an example embodiment. The thin foil orifice 924, 914 is shown and described more fully with respect to Figs. 9A and 9C above. The reference numbers and corresponding structure will not be repeated since doing so would be duplicative.

When molten metal is sent through the orifice, it is essential to have no leak of molten metal. Also important is that the orifice should remain clean with no obstacles to the flow of molten metal. Shown in Fig. 10(a) - (d) are the comparative cross-sectional description of the Conventional orifice (prior art) vs Thin foil orifice (this invention). Metal jetting often uses very high pressure, and hence any potential leaking point, e.g., as illustrated in Fig. 10(a), can adversely affect the process parameters and the outcome. Unwanted particles trapped in the path of the liquid metal movement for jetting are also undesirable. The thin foil orifice, according to the invention, can contribute to resolving these two issues since the potential leaking is minimized, and a trapping of dirt or other materials is also prevented in the case of thin foil orifice.

Another advantage of the thin foil orifice approach is that it also allows easier fabrication of orifice holes especially a smaller diameter holes which enables fabrication of finer spherical particles, e.g., smaller than 50 um, preferably smaller than 20 um, even smaller than 10 um diameter spherical particles.

Therefore the thin foil type orifice in this invention offers many advantages, including at least these five advantages of (i) reduced probability of liquid leakage [by at least 10%,

preferably at least 30%], (ii) reduced head loss (pressure loss) [by at least 10%, preferably at least 30%], (iii) reduced temperature differential or temperature gradient between the melt crucible vs fluid being ejected below across the orifice [by at least 10%, preferably at least 30%], (iv) easier prevention of trapping of dirt or other materials in the orifice [by at least 10%, preferably at least 30%], and (v) ease of fabricating smaller orifice to enable more convenient fabrication of finer diameter particles [smaller by at least 20%, preferably at least 50%].

Invention I. Rotational Channel Arrangement to A utomatically Sort Out Good vs

Unsatisfactory Particles

Fig. 11. Rotational channel arrangement, (a) schematic illustration, (b) three-dimensional view of detailed machine construction.

Fig. 11 A is a schematic showing a rotational channel recycling arrangement 1100 for sorting metal particles, according to an example embodiment. Fig. 11B is a three-dimensional perspective view of a recycling machine 1100 including the rotational channel arrangement, according to an example embodiment. The rotational channel recycling arrangement 1100 includes a funnel 1110 and a rotating gravitational channel or chute 1120. The recycling arrangement also includes a good parts bin 1130 and a bad parts bin 1140. The vision system 150 (shown in Fig. 1) determines if the spheres are good, or are bad (too big or too small).

Adjustments are made to the system to produce spheres of the specified size or good parts..

When the spheres are correctly sized, the rotating channel or chute 1120 delivers the spheres to chamber 1130. When the parts are bad, i.e. too big or too small, the rotating channel or chute 1120 delivers the spheres to a recycle chamber 1140 The collection dish 130 removes particles that are too small and particles that are too large to meet the specified size for the metal balls or spheres. The funnel directs the metal spheres formed to the rotating chute 1120. The rotating chute 1120 is controlled by the vision system 150. It should be understood that the chute may be closed until the chute 1120 can be moved to a new position. In some embodiments, the chute can be moved quickly to redirect the parts between chambers 1130 and 1140 without having to block the chute 1120. It is also understood that some good spheres might be found in the recycle bin 1140.

The metal or alloy particles have a reasonable particle size uniformity and generally spherical particle geometry. However, sometimes the jetting operation may not be ideal or some process parameters are not properly controlled, or there might be some mechanical or thermal disturbance. In such a case, some particles may not have the intended geometry for some period of time. It is desirable to make sure that such unsatisfactory and inferior particles do not get mixed with a batch of good particles.

According to the invention, such unwanted particles can be separated from the good particles, in situ, using the automated video camera or laser sensing apparatus, which provides instantaneous command to change the orientation of the particle transport channel.

This invention utilizes a gravity driven selecting channel with rotation of the chute path (or channel or shaft), see Fig. 11, to sort out the unsatisfactory particles, which makes the system simpler. The combination of the funnel and the rotating chute channel allows the inlet for the particles to be a fixed spot, and only change the location of outlet so that the filtered/sieved particles can be sent to different bins as needed. The chute can be made to have a linear, curved or spiral configuration. Bad particles or oversize/ undersize particles can be sorted out so that the main product exhibits uniformity in size and properties. The container bin at the end of the chute to collect the bad particles (called here as recycling or rework container) is equipped with a valve system (to salvage potentially bad particles or oversize/undersize particles) to allow the recycling of the material without exposing them to air or oxygen atmosphere so as to prevent/minimize undesirable particle surface oxidation.

Such re-routing of produced metallic microspheres based on quality inspection, using video or optical monitoring and feedback control, according to the invention, can have at least 2, preferably at least 3 routes (channels) for easier quality control in manufacturing.

Invention J. New Method and Apparatus for Faster Solidification of Molten Metal Droplets

Molten metal droplets jetted out from the jetting apparatus requires to be cooled to get converted into solid metal particles, with advantages of (i) finer grain size with stronger mechanical strength and toughness in the solidified metal [by at least 10%, preferably at least 30%]. An additional benefit is that (ii) the faster solidification [by at least 20%, preferably at least 50%] minimizes the undesirable collision of molten metal droplet with the chamber side wall which could deform the spherical particles to be less symmetrical, or some portion of molten metal to stick to the wall surface. When the metal droplets are large or at a very high temperature, complete cooling requires very long gravitational falling distance to provide sufficient time. This also forces the cooling chamber height to be taller, which increases the cost of chamber, and also reduces the manufacturing throughput, therefore, (iii) rapid solidification allows the chamber to be less tall for reduced equipment cost [by at least 20%, preferably at least 50%], faster throughput [by at least 20%, preferably at least 50%] and less space to pump with vacuum [by at least 20%, preferably at least 50%] for jetting preparation.

Fig 12 is a schematic view of a liquid nitrogen evaporator 1200 for faster cooling of molten or solidified metal particles as the particles fall though the chamber 120 (also shown in Fig. 1), according to an example embodiment.

In this invention, a new method of accelerating the molten droplet cooling process is devised, which utilizes relatively inexpensive liquid nitrogen (boiling temperature of -l96°C). The liquid nitrogen evaporator 1200 shown in Fig. 12 includes a nitrogen source 1212, a cryogenic regulator 1210, evaporating tube 1220 that can steadily evaporate liquid nitrogen and supply cold vapor nitrogen, and PID controlled relief valve 1230 positioned away from the evaporating site 1222. Using the evaporated cold nitrogen vapor has several advantages compared to using liquid nitrogen pool as a cooling method. Liquid nitrogen boils in an uncontrolled manner so that gas pressure inside the cooling chamber becomes unsteady and having a liquid form of nitrogen at the bottom of the cooling chamber makes it difficult to transfer the particles continuously to make room for additional particle synthesis. Evaporated liquid nitrogen can still have its temperature as low as -l80°C and the particle movement path can be operated in a dry environment without getting hindered by the presence of liquid.

Fig. 12. Liquid nitrogen evaporator for faster cooling of molten or solidified metal particles. It is also possible to utilize other vapors such as from liquid argon or liquid helium. It is well known that He or He-containing gas enables faster, more efficient quenching than other gases because of high specific heat and higher heat transfer coefficient.

Invention K. Center Can Design and Structure To Filter Out and Block Undesirable

Asslomerated Particles

Fig. 13 shows several views of a center cap 1300 installed in order to prevent the funnel 1110 entrance from getting clogged by agglomerated particles or other unwanted particles, according to an example embodiment. The center cap 1300, as installed for use, is separated from the funnel 1110 so that there is an open path 1310 to the funnel 1110 exit.

The solidified metal (or alloy) particles need to be collected near the bottom of the cooling chamber. Particle collecting system needs funnels to guide the particles to smaller path. If any agglomeration blocks the narrow path, the particle cannot flow anymore. Particle agglomeration often happens in the earlier stage of cooling so if the entrance to the narrow path is protected, there will be less clogging problem. The schematic in Fig. 13 shows the center cap that protects the entrance to the funnel from clogging. The right top shows the case of not having the center cap, Fig. 13(c) and the schematics in Fig. 13(b) and (d) show the case with the center cap. With the center cap, if one portion of the gap between the center cap and the funnel is blocked, there are other regions that are open. The top view at the bottom of the Fig. 13 shows such an open path. The invention reduced the probability of funnel path clogging [by at least 20%, preferably at least 50%] that would prevent or reduce the molten metal passage.

Invention L. Oxygen Purifying System to Prevent/Minimize Particle Oxidation

Fig. 14 is a jetting system 100, 500 that also includes an oxygen removing system 1400 to provide cleaner vacuum or inert gas atmosphere in the metal/alloy melting and transport system, according to an example embodiment. The oxygen removing system 1400 is placed in fluid communication with the gas inside the molten metal jetting system 100, 500. The oxygen removal system 1400 includes a container 1402 having a catalyst 1410 therein. The catalyst in this particular example embodiment, is copper. The container 1402 in the oxygen removing system 1400 (e.g., copper sieve) can be regenerated after some use by forming gas annealing heat treatment.

The molten metal sprayed particle synthesis system requires a precisely controlled pressure within the chamber. The integrating of an oxygen filter is not a trivial matter. In this invention system, because of continuous intentional bleeding of evaporated liquid nitrogen vapor in the cooling chamber, the low oxygen level can be maintained. Connecting the oxygen filter (that has catalyst) to the jetting aperture, Fig. 14, can protect the molten liquid. If connected to the cooling chamber, the molten metal droplets will experience a very low oxygen environment for higher quality metal sphere particles, with much less surface oxidation contamination [by at least 20%, preferably at least 50%].

Fig. 14. Oxygen removing system to provide cleaner vacuum or inert gas atmosphere in the metal/alloy melting and transport system. The catalyst in the oxygen removing system (e.g., copper sieve) can be regenerated after some use by forming gas annealing heat treatment.

Invention M. Chamber Wall Charsins Structure to Prevent Molten Particle Collision with the Chamber Wall

In vibration assisted jetting system, high voltage charging near the jetting orifice prevent particles merging in the middle of the cooling process by making particles repel each other by having same electrical polarity. However, the repulsion causes the jet diverge in some angles and this causes some of the molten particles to hit the side wall (interior wall) of the cooling chamber (such as a transparent glass tube chamber) to enable video monitoring of jetting process and quality). These wall-colliding molten metal particles sometimes stick to the wall and force frequent cleaning, which is undesirable. Some other particles that contacted the chamber wall but managed to be separated can become deformed and become unacceptably non-spherical.

Fig. 15 is a schematic diagram showing a chamber wall charging system 1500, according to an example embodiment. The interior of the chamber 110 is coated with a material coat 1520 that can be charged to prevent molten particle sphere hitting the chamber wall and getting deformed, and to keep the glass clean with minimal adhesion of molten metal pieces. The coating 1500 is charged with the same polarity as the particles so that the particles and coated portion of the interior wall are repelled from one another.

Fig. 15. Chamber wall charging to prevent molten particle sphere hitting the chamber wall and getting deformed, and to keep the glass clean with minimal adhesion of molten metal pieces.

Coating the side wall of the cooling chamber such as made of glass or quartz with transparent conductor material such as ITO (indium-tin-oxide) or ZnO, allows charging of high voltage (e.g., at least 200 volts, preferably >1,000 volts, even more preferably >3,000 volts) to the wall surface, still allowing visual or video monitoring of the jetting process. This is schematically illustrated in Fig. 15. Charging of the wall with the same polarity as the particles prevents the particles from hitting the wall, thus minimizing the probability formation of deformed or irregular shaped metal spheres [by at least 20%, preferably at least 50%] and also reduces the chance of glass wall getting dirty by molten metal hitting the wall [by at least 20%, preferably at least 50%].

Invention N. Method and Apparatus for Oxidation-Preventing Particle Retrieval and

Transfer

Shown in Fig.16 is a particle retrieval system 1600 and the details of the collecting port 1610 that is at the bottom of at least the chamber 1130 (see Fig. 11) where the good particles are collected. Most of the particle metal surface is vulnerable to oxidation if exposed to air. The particle retrieval system 1600 includes at least a first valve 1601 and a second valve 1602. The particle retrieval system 1600 also includes a purging system 1620, The double valve system 1601, 1602 with the purging ability 1620 shown in the figure enables the particle collection without exposing the particles to regular air for even a short time.

The schematics in Fig. 16 to Fig. 18 illustrate some detailed valve arrangements for convenient purging process to remove air/oxygen and enable clean particle transfer. The metal particles prepared by molten metal jetting, being handled by the oxygen-preventing particle retrieval and transfer method thus exhibits much reduced surface oxidation layer thickness [by at least 20%, preferably at least 50%].

Fig.16. (a) Particle retrieval system overview, and (b) the details of the collecting port.

Fig. 17. Valve on both container and system port to transfer to the transport vessel without particle oxidation. Basically, the bottom of the container 1130 for good parts is closed and another transfer container 1700 is connected to the container 1130. The valve 1602 and the purge valve 1620 can be opened to purge the transfer container 1700 and the inner portions proximate the various valves of contaminant gas. The purge valve 1620 is closed. The valve 1602 is open, the valve 1610 is opened to allow the particles in collection container 1130 to transfer to the transfer container 1700. All valves are then closed and the transfer container 1700 contains the metal particles with minimal exposure to oxidizing gases.

Fig. 18. How to engage the particle collecting bottle 1700 with the size-sorting sieve 1800 without exposing the particles within the bottle 1700 to the air.

Invention O. Method and Apparatus for Continuous Sieving of Particle Size Once the metallic particles are produced by molten metal jetting, the particle diameter size distribution needs to be tightly controlled by batch processing, or preferably by a continuous processing. This is to obtain a more accurate particle size range control, and also to remove unwanted oversize/undersize particles or defective particles with excellent process efficiency. An important issue is to ensure that no oxidation occurs on the particle surface during such sieving operations. The atmosphere in this process can be controlled to very low atmosphere, e.g., <100 ppm oxygen, preferably <30, more preferably <10 ppm.

Fig. 19 is a continuous sieving apparatus 1900 and method for particle size control, according to an example embodiment. The continuous sieving apparatus 1900 has a series of sieves used to separate the desired spheres 1910 from the spheres formed that are too large 1912 and those that are too small 1914. Three sieves are used. A first sieve 1920 has large openings that allow the right sized spheres 1910 and the too small spheres 1914 to pass. The first sieve 1920 is tilted so the too large spheres are placed in a recycle or reject bin 1950. A second sieve 1922 has smaller openings that those of the first sieve 1920. The second sieve 1922 is also slanted and has an output positioned over a container 1960 for receiving the right sized or target particles of the desired size 1910. The too small sized spheres 1914 pass through the second sieve 1922 and pass along a chute and exit into the reject or recycle bin 1950. The continuous sieving apparatus 1900 is vibrated during sorting to keep the particles moving through the continuous sieve.

Fig. 19. New continuous sieving method for particle size control. A zigzag arrangement of sieves with tilt angle is made to allow a continuous processing. The sieve with a large hole is positioned at the one end (near the beginning part of the particle downward movement).

Continuous particle size sorting (or sieving) is not easy for manufacturing. This invention disclosed industrially viable, low-cost particle sieving method, especially useful for molten metal jetting operation to obtain spherical microparticles with well defined diameter ranges. With the invention structure of in-situ continuous sieving, the overall manufacturing time for size sieving is reduced by at least 50%, preferably at least by a factor or 2.

According to the invention, an example sieving apparatus, e.g., a multi-stage zigzag arrangement (or spiral arrangement) of a multi-stage sieves with each having some tilting angle allows continuous processing as shown Fig. 19. The sieve with a larger hole (to pass larger diameter metal particles) is positioned at the one end. The surface of the zigzag arranged chutes is made to be very smooth so that the particles move/roll easily. If desired, the surface can be coated with a low friction coefficient layer such as diamond-like-carbon (DLC) or Teflon- containing coating. A mechanical or ultrasonic vibration is applied to the zigzag chutes so as to facilitate the movement of the particles with minimal stiction. The tilt angle for the chutes can be 10° to 70°, preferably 30 - 50° angle. The number of stages (chutes) can be further increased if desired.

Conventional sieves consist of a mesh and a side wall. The balls collected on the sieve needs to be poured out or suctioned with a vacuum device. This aspect makes continuous sieving difficult. In most of the systems, stopping and resuming of sieving is not an issue, however, this invention allows the desired continuous sieving processing. Such continuous sieving

substantially increases the throughput and reduces the cost and the time needed to accomplish desired particle sorting [by at least 20%, preferably at least 50%]. To eliminate the needs of pouring out or vacuum suction, as shown Fig. 19, the meshes having an opening at the one end of meshes are arranged in a zigzag shape, and the bottom has a slope with a very smooth surface. This sieving system can be either integrated into the main jetting unit, separately installed in additional chambers, or utilized as an independent, continuously operating, particle size sorting system.

Advantageously, there are various valves associated with the droplet formation apparatus, as they can be computer controlled or remote controlled to be opened and closed during the jetting process as needed. The valves are also utilized to control vacuum evacuation of various chambers or to pressurize during the jetting process.

The invention system also utilizes a video camera or optical sensor systems to measure the molten metal sphere synthesis and jetting processes as part of a feedback control loop to keep the particle size, speed of jetting and other parameters, which allows automated manufacturing and continuous production of spherical metal particles.

Applications of spherical metal particles made by the molten metal jetting

Spherical particles of solders, including Pb-free solders such as based on Sn-Ag, Sn-Ag- Cu, Sn-Cu, Sn-Sb, In-Sn, Bi-Sn or other variations of binary, ternary or more complex solder compositions, are useful for electronic packaging or assembly or circuit layers. Sphere attachment onto a ball grid array (BGA) typically is achieved via vacuum-transfer or gravity dispensing processes, and the spheres are held in place by flux or solder paste before reflow, e.g., to obtain a periodic array of solder spheres. After the solder balls are formed and washed or degreased, the resulting solder balls are inspected. The solder balls also are more prone to having one solder ball being bigger than the others in a BGA application. The spherical solder balls manufactured in a more controlled way, according to the invention, are more uniform and cleaner so that electronic packaging applications can be performed in a more reliable and inexpensive manner. Due to the more uniform solder particle size, the particles made by the method and apparatus described in this invention are useful for 3D printed or transferred solder circuit formation (See Fig. 20(a) and (b)) using a solder ball containing paste placed using a print head 2000. The paste can be used to make circuit paths 2002, for example. Solder balls 2010 can also be printed on a substrate in a similar fashion. Of course the solder balls formed could also be placed by a pick and place machine.

Aside from solder base metals, other metal spheres such as various other Sn-base, Mg- base, Al-base , Zn-base, Ti-base, Cu-base, Ni-base, or Fe-base alloy spheres can be reliably fabricated by the molten metal jetting process described in this invention. These alloy spheres are also useful for three dimensional (3D) printing for additive manufacturing. The 3D printing has been a blossoming technical field with many potential consumer and industrial applications. The size of global 3D printing metals market is expected to grow to the level of $1 billion in coming decades.

Fig. 21 is a schematic diagram depicting three-dimensional printing of bone implant parts using permanent or biodegradable alloy spheres, according to an example embodiment. A 3-D print head 2120 is provided with a paste or solvent 2100 of metal spheres 2110. The metal spheres 2110 and paste or solvent 2100 are ejcted from the print head 2100 using a piezo electro or thermally actuated release.

Metal spheres have unique advantages as the final 3D printed finished products are mechanically superior in strength, toughness, and durability. Various end-use industries have been trying to incorporate metal 3D printers as mainstream manufacturing equipment in order to reduce their lead time and increase profitability, which is expected to drive the market. It is well known that 3D printing metals are widely utilized in sectors including aerospace & defense, automotive, and medical & dental fields. Titanium and its alloys, as well as aluminum alloys, due to their beneficial properties such as light weight and anti-corrosion characteristics, are widely used in the aerospace industry. Complicated shaped parts can be produced by 3D printing type, additive manufacturing (see Fig. 21 and Fig. 22).

In addition, 3D printing technology has been applied in medical applications for more than a decade, such as in dental and hip implants especially as custom prosthetics. The medical applications of 3D printing have grown considerably because the process can bypass the need for expensive machining to achieve a complex geometry (see Fig. 21). The current medical uses of 3D printing can include artificial organs and tissue fabrication, creating prosthetics, orthopaedic and dental implants, anatomical models, and for pharmaceutical research of drug discovery or delivery.

Fig. 20. Printing, transferring or pick-and-place positioning of solder ball spheres (or particles) for electronic circuits or electronic packaging such as flip-chip bonding of device layers.

Fig. 21 Three dimensional printing of bone implant parts using permanent or

biodegradable alloy spheres.

Fig. 22 is another schematic diagram for three-dimensional-printing-based, additive manufacturing of assorted parts with spherical metal or alloy particles prepared by molten metal jetting process, according to an example embodiment. As shown in Fig. 22A, a complicated mechanical piece, such as a gear 220 is printed using 3D printing as discussed with respect to Fig. 21. Fig. 22B shows a 3D printing scheme of spherical metal or alloy particles prepared by molten metal jetting, via DLMS (Direct Metal Laser Sintering) or related powder bed fusion processes such as SLS (Selective Laser Sintering) or SLM (Selective Laser Melting), electron beam sintering or melting. This has an advantage over traditional powder metal making of parts in that the metal particles are substantially free of oxides and other contaminants. The result is stronger parts when compared to powder metal parts formed by sintering.

Fig. 22. Three-dimensional-printing-based, additive manufacturing of complicated machine parts, electronic device parts, or biomedical implant parts with spherical metal or alloy particles prepared by molten metal jetting process (a) additive printing, (b) 3D printing scheme of spherical metal or alloy particles prepared by molten metal jetting, via DLMS (Direct Metal Laser Sintering) or related powder bed fusion processes such as SLS (Selective Laser Sintering) or SLM (Selective Laser Melting), electron beam sintering or melting.

In summary, this specification describes numerous embodiments of the invention. The various embodiments cover various apparatus useful for jetting molten metal or alloy to form spherical particles, and associated methods. Industrially desirable manufacturing approaches including continuous or continual molten metal jetting operations are also disclosed. Some of the various embodiments are listed below. It is contemplated that these individual embodiments as well as any combination of the listed embodiments are among the inventions contemplated by this specification. All these combinations are contemplated as inventions. It should be noted that the listing below is not exhaustive. Other inventions contemplated may be one or more of the embodiments listed below along with portions of the above specification.

Some of the embodiments include the following.

Embodiment 1. An apparatus for producing uniformly sized metal spheres from molten metals or alloys in a container and the ejecting a train of molten droplets downward through one or more orifice enabled by applied gas pressure, which is aided by mechanical, magneto strictive or piezoelectric vibration for droplet formation and also aided by applying a positive or negative electrical charge on the liquefied metal droplets, wherein the high-frequency repeated vibration causes metal to form uniform diameter, spherical metal droplets with the diameter variation of less than 5%.

Embodiment 2. The metal sphere producing apparatus of Embodiment 1 wherein the natural vibration frequency of the device is made tunable and adjustable and the inertia is changeable by controlling the vertical position of the associated mass unit to alter the distribution of the mass. [Invention #A incorporated]

Embodiment 3. The apparatus of Embodiment 2 wherein the vibration frequency is alterable by at least 5%, preferably at least by 20%. [Invention #A incorporated]

Embodiment 4. The metal sphere producing apparatus of Embodiment 1 wherein the vertical vibration displacement is made to be less impeded by incorporating a laterally extended wing structure with elastomeric interfaces against supporting structural components to allow the vibration actuator to minimize vibration absorption and have an essentially full mechanical vibration, with the overall vibration intensity improved by at least 20%, preferably at least 50%. [Invention #B incorporated]

Embodiment 5. The metal sphere producing apparatus of Embodiment 1 wherein the liquid droplet producing apparatus has a device cooling capability by cooling liquid circulation in the piezoelectric actuator system. [Invention #C incorporated]

Embodiment 6. The metal sphere producing apparatus of Embodiment 5 wherein the hollow center together with silicone sealing between the connections of the piezo element enables secure liquid cooling, with the piezo stack cooling enables the temperature to be at least 5°C lower, preferably at least 20°C lower. [Invention #C incorporated]

Embodiment 7. The metal sphere producing apparatus of Embodiment 1 wherein disk-shaped piezoelectric transducers and copper disks are alternately stacked with an alignment structure and a sealant is applied to minimize leakage of coolant liquid, with the tendency for coolant leakage reduced by at least 20%, preferably at least 50%. [Invention #D incorporated]

Embodiment 8. The metal sphere producing apparatus of Embodiment 1 wherein the apparatus comprises separate molten metal preparation structures to continuously or continually add additional metal or alloy in the form of molten metal instead of solid metal form, to the main crucible containing molten metal. [Invention #E incorporated]

Embodiment 9. The metal sphere producing apparatus of Embodiment 8 wherein;

— A continuous jetting operation, without interruption, is enabled for at least 8 hrs, preferably at least 5 days, even more preferably at least 30 days.

— The temperature of the molten metal or alloy to be fed is matched to that of the main jetting device crucible melt temperature within less than 20°C difference, preferably less than l0°C difference, more preferably less than 5°C difference, and a much accelerated production of metallic microspheres is accomplished at a faster rate by at least 20%, preferably at least 50%, even more preferably at least 200%. [Invention #E incorporated]

Embodiment 10. The metal sphere producing apparatus of Embodiment 1 wherein the molten metal is supplied to the crucible or transferred to a different chamber by using a routing pipe structure having a larger diameter orifice with the on-off supply of molten metal controlled by adjustable gas pressure from above the melt. [Invention #F incorporated]

Embodiment 11. The metal sphere producing apparatus of Embodiment 10 wherein the size of the routing pipe orifice for the feeder is at least 2 times larger, preferably at least 10 times larger than the regular orifice for the jetting, with the pressure of the feeding chamber during the feeding is at least 0.5 psi, preferably at least 2 psi higher than the jetting chamber pressure, with the manufacturing throughput in the ultrasonically activated system is increased by at least 20%, preferably at least 50%. [Invention #F incorporated] Embodiment 12. The metal sphere producing apparatus of Embodiment 1 wherein the piezoelectric vibration transducer is protected from the surrounding heated environment by continuously circulating water cooling or air cooling. [Invention #G incorporated]

Embodiment 13. The metal sphere producing apparatus of Embodiment 12 wherein the incorporated structure of continuous cooling reduces the degree of heating from surrounding hot environment by at least 20%, preferably at least 50%. [Invention #G incorporated]

Embodiment 14. The metal sphere producing apparatus of Embodiment 1 wherein the molten metal ejecting orifice is made from a thin foil layer selected from metallic, ceramic or composite layer. [Invention #H incorporated]

Embodiment 15. The metal sphere producing apparatus of Embodiment 14 wherein the thin foil orifice has:

— a thickness in the range of 10 um to 500 um, preferably 25 um to 200 um, even more preferably 50 - 150 um,

— with the orifice diameter in the range of 3 um to 200 um, with the orifice dimension prepared using precision machining, patterned chemical etching method, or laser ablation processing,

— exhibiting at least one of the following five advantages of (i) reduced probability of liquid leakage by at least 10%, preferably at least 30%, (ii) reduced head loss (pressure loss) by at least 10%, preferably at least 30%, (iii) reduced temperature differential or temperature gradient between the melt crucible vs fluid being ejected below across the orifice by at least 10%, preferably at least 30%, (iv) easier prevention of trapping of dirt or other materials in the orifice by at least 10%, preferably at least 30%, and (v) ease of fabricating smaller orifice to enable more convenient fabrication of finer diameter particles smaller by at least 20%, preferably at least 50%. [Invention #H incorporated]

Embodiment 16. The metal sphere producing apparatus of Embodiment 1 wherein rotational channels are added to automatically sort out good particles separated from unsatisfactory particles and send [Invention #1 incorporated]

Embodiment 17. The metal sphere producing apparatus of Embodiment 16 wherein the combination of the upper funnel and the rotating chute channels below allows to separate acceptable particles and unsatisfactory particles (of poor quality or oversized/ undersized), with the unsatisfactory particles saved without surface oxidation for efficient remelting. [Invention #1 incorporated]

Embodiment 18. The metal sphere producing apparatus of Embodiment 1 wherein a continuous supply mechanism is structured so that cold nitrogen vapor or helium vapor is utilized to rapidly solidify the ejected molten metal droplets. [Invention #J incorporated] Embodiment 19. The metal sphere producing apparatus of Embodiment 18 wherein the continuous cooling vapor device enables to achieve;

— (i) A finer grain size in the solidified metal with stronger mechanical strength and toughness in the solidified metal by at least 10%, preferably at least 30%.

— (ii) The faster solidification rate by at least 20%, preferably at least 50% minimizes the undesirable collision of molten metal droplet with the chamber side wall to prevent deformation of spherical particles to be less symmetrical, or some portion of molten metal to stick to the wall surface.

— (iii) Rapid solidification allows the chamber to be less tall for reduced equipment cost by at least 20%, preferably at least 50%, faster throughput by at least 20%, preferably at least 50% and less space to pump with vacuum by at least 20%, preferably at least 50% for jetting preparation. [Invention #J incorporated]

Embodiment 20. The metal sphere producing apparatus of Embodiment 1 wherein a cap structure is installed to filter out undesirable agglomerated particles to prevent blockage of the particle path. [Invention #K incorporated]

Embodiment 21. The metal sphere producing apparatus of Embodiment 20 wherein the presence of the cap structure reduces the probability of funnel path clogging by at least 20%, preferably at least 50%. [Invention #K incorporated]

Embodiment 22. The metal sphere producing apparatus of Embodiment 1 wherein a oxygen filter is installed and connected to the molten metal jetting structure and to the molten droplet cooling chamber. [Invention #L incorporated]

Embodiment 23. The metal sphere producing apparatus of Embodiment 22 wherein the oxygen filter is installed and connected to the molten metal jetting structure to produce higher quality metal sphere particles, with much reduced surface oxidation contamination by at least 20%, preferably at least 50%. [Invention #L incorporated]

Embodiment 24. The metal sphere producing apparatus of Embodiment 1 wherein a chamber wall charging structure is added to repel and prevent molten particle collision with the wall. [Invention #M incorporated]

Embodiment 25. The metal sphere producing apparatus of Embodiment 24 wherein the chamber wall coated with optically transparent conducting oxide, and is charged to 100 - 5,000 volts DC reducing the probability of formation of deformed or irregular shaped metal spheres by at least 20%, preferably at least 50% and also reducing the chance of glass wall getting dirty by molten metal hitting the wall by at least 20%, preferably at least 50%. [Invention #M

incorporated] Embodiment 26. The metal sphere producing apparatus of Embodiment 1 wherein a valve configuration and evacuation/inert gas supply structure are added for oxidation-preventing particle retrieval and transfer is enabled. [Invention #N incorporated]

Embodiment 27. The metal sphere producing apparatus of Embodiment 26 wherein the oxidation-preventing particle retrieval and transfer structure enables the molten metal jetted metal particles to exhibit much reduced surface oxidation layer thickness by at least 20%, preferably at least 50%. [Invention #N incorporated]

Embodiment 28. The metal sphere producing apparatus of Embodiment 1 wherein an in-situ zig-zag chute channel array structure is added to enable a continuous sieving of particle size in the molten metal jetting and solidification chamber. [Invention #0 incorporated]

Embodiment 29. The metal sphere producing apparatus of Embodiment 28 wherein the in-situ zig-zag chute channel array structure for continuous size sieving enables;

— Mechanical or ultrasonic vibration to the zigzag chutes to facilitate the movement of the particles with minimal sticking with the chute tilt angle preferably in the range of 30 - 50° angle.

— An exposure of the freshly solidified metal particles to a very low oxygen-containing atmosphere of at most less than 100 ppm oxygen.

— The overall manufacturing time for size sieving is reduced by at least 50%, preferably at least by a factor or 2.

— The surface of the zigzag arranged chutes is optionally made to be very smooth so that the particles move/roll easily, with a low friction coefficient coating selected from diamond-like- carbon (DLC) or Teflon-containing coating.

— A substantially increased throughput and reduced cost and the time of particle sorting by at least 20%, preferably at least 50%. To eliminate the needs of pouring out or vacuum suction, as shown Fig. 19, the meshes having an opening at the one end of meshes are arranged in a zigzag shape, and the bottom has a slope with a very smooth surface. [Invention #0 incorporated]

Embodiment 30 - Embodiment 45. Various methods for fabricating spherical metal or alloy particles, corresponding to the apparatus Embodiments 1 - 30. (as described in Fig. 1 to Fig.

19).

Embodiment 46 - 50. Article including electronic products, automobile products, aerospace products, biomedical producrs, and comsumer products comprising spherical particles made by processing methods of Embodiment 30 - Embodiment 45. Embodiment 51. Use of the spherical metal or alloy particles fabricated by the molten metal jetting apparatus and methods of Embodiments 1-45, for electronic solder packaging.

Embodiment 52. The application of the spherical metal or alloy particles in Embodiment 46, wherein the solder packaging is ball grid array connection of circuits.

Embodiment 53. Use of the spherical metal or alloy particles fabricated by the molten metal jetting apparatus and methods of Embodiments 1-45, for additive manufacturing of complicated metal parts.

Embodiment 54. The application of the spherical metal or alloy particles in Embodiment 48, wherein the additive manufacturing is three dimensional packaging.

Embodiment 55. The application of the spherical metal or alloy particles in Embodiment 48, wherein the additive manufacturing is for aerospace parts, automobile parts or biomedical parts.

Embodiment 56. The application of the spherical metal or alloy particles in Embodiment 48, wherein the additive manufacturing is for medical implants including dental, hip, knee or other orthopaedic implants for human or animal body.

The foregoing description of the specific embodiments reveals the general nature of the invention sufficiently that others can, by applying current knowledge, readily modify and/or adapt for various applications without departing from the concept, and therefore such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Accordingly, the invention is intended to embrace all such alternatives, modifications, equivalents and variations as fall within the spirit and broad scope of the appended claims.

Claims

We claim:

1. A metal sphere producing apparatus for producing substantially uniform sized metal spheres from molten metal comprising:

a crucible for holding molten metal, the crucible including at least one orifice therein;

a chamber in fluid communication with the crucible, the chamber including an opening proximate the at least one orifice, and including a droplet charging apparatus;

a vibration system associated with the crucible; and

pressurized gas within the container, molten droplets passing through the at least one orifice and into the chamber, substantially uniform diameter molten droplets formed by controlling the gas pressure in the crucible and by controlling the vibrations formed by the vibration system, the droplet charging apparatus placing an electrical charge on the metal droplets as they pass through the chamber.

2. The metal sphere producing apparatus of Claim 1 wherein the vibration system includes a movable mass, the vibration frequency of the vibration system adjustable by repositioning the moveable mass to alter the distribution of the mass.

3. The metal sphere producing apparatus of Claim 2 wherein the vibration system further comprises a lateral wing structure with elastomeric interfaces abutting supporting structural components to lessen vibration absorption by the supporting structural components.

4. The metal sphere producing apparatus of Claim 1 wherein the vibration system is cooled by a cooling liquid circulation apparatus.

5. The metal sphere producing apparatus of Claim 1 further comprising a molten metal feeding apparatus in fluid communication with the crucible, the molten metal feeding apparatus controllably delivering molten metal to the crucible.

6. The metal sphere producing apparatus of Claim 5 wherein the metal sphere producing apparatus can produce metal spheres substantially continuously in the range 0.12 days to 30 days.

7. The metal sphere producing apparatus of Claim 1 wherein the at least one molten metal ejecting orifice is comprised of a thin foil layer having a thickness in the range of 10 um to 500 um.

8. The metal sphere producing apparatus of Claim 1 further comprising a vision system for monitoring the size of the spheres formed, the vision system positioned in the chamber.

9 The metal sphere producing apparatus of Claim 8 further comprising rotational channels positioned in the chamber, the rotational channels separating acceptable metal spheres from unsatisfactory metal spheres based on input from the vision system.

10. The metal sphere producing apparatus of Claim 1 wherein a cooling gas is injected into the chamber to rapidly solidify the molten metal droplets.

11. The metal sphere producing apparatus of Claim 1 further comprising:

a plurality of rotating chute channels for separating acceptable metal spheres and unsatisfactory metal spheres, the unsatisfactory metal spheres captured in a container without being exposed to oxygen to prevent surface oxidation for efficient remelting; and

a funnel which catches the metal spheres and delivers them to the plurality of rotating chute channels.

12. The metal sphere producing apparatus of Claim 11 further comprising a cap structure associated with the funnel, the cap structure preventing an agglomerated particle blocking the path out of the funnel.

13. The metal sphere producing apparatus of Claim 1 further comprising a chamber wall charging structure which is electrically charged to repel the charged metal droplets and prevent collision with the chamber wall.

14. The metal sphere producing apparatus of Claim 1 further comprising a valve configuration and evacuation/inert gas supply structure that substantially prevents oxidation of metal spheres removed form the chamber.

15. The metal sphere producing apparatus of Claim 1 further comprising an in-situ chute channel array structure for sieving metal spheres, the in-situ chute channel array structure positioned in the chamber.

16. A method of forming metal spheres comprising

controllably vibrating a crucible containing molten metal, the crucible having at least one orifice therein, the vibration causing a droplet of molten metal to pass through the orifice and into a chamber;

electrically charging the droplet of molten metal;

adding a cooling gas to the chamber to remove heat from the molten droplet, the droplet solidifying as it falls through the chamber.

17. The method of claim 16 further comprising pressurizing the atmosphere volume above the crucible.

18. The method of claim 16 further comprising providing a substantially inert atmosphere in the chamber and the volume around the crucible.

19. The method of claim 18 further comprising using valving to remove produced metal spheres from the chamber without exposing the metal spheres to oxygen.

20. Products made from the metal spheres produced by the methods of claim 16-19.

21. The method of claim 20 wherein the metal spheres are added to a paste, the paste including the metal spheres used to print lines of paste and metal spheres on a substrate.