Method and device for efficiently preparing gold-tin soldering ball with uniform and controllable particle size

Abstract

The invention provides a method and a device for efficiently preparing gold-tin solder balls with uniform and controllable particle size, the device comprises a vacuum system, a liquid drop injection system, a particle collector, an image acquisition system and a liquid level control system, and the liquid drop injection system adopts a crucible fixed in a vacuum chamber as a container for containing gold-tin melt; a micropore piece provided with a round micropore is fixed to the bottom of a crucible and communicated with an inner cavity of the crucible, piezoelectric ceramics arranged at the top of the crucible drive a transmission rod in the crucible to vibrate and apply pressure to gold-tin melt, the gold-tin melt is jetted into liquid drops through the micropore, the liquid drops are rapidly solidified to form gold-tin soldering balls with the uniform particle size after dropping, and the gold-tin soldering balls are collected by a particle collector. And a gap between the outer edge of the bottom of the transmission rod and the micropore at the bottom of the crucible is 0.10-0.35 mm. The invention further discloses a method for preparing the gold-tin solder ball through the device, the gold-tin solder ball is successfully prepared through a pulse micropore jetting method, and the preparation efficiency and the preparation precision have leap-type progress.

Description

Technical Field

[0001] The present invention relates to the technical field of spherical metal particle preparation, and particularly to a method and device for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes. Background Art

[0002] With the increasingly miniaturized application scenarios of current electronic packaging and the harsh working environment, existing solder pads and solder pastes are difficult to meet the market demand. In high-power optoelectronic packaging, the gold-tin solder ball Au80Sn20 (Wt%) ensures that the optical surface is not contaminated by any means with its unique no-flux process. In vacuum packaging, if flux is used, the flux residues will degas and corrode the components in the cavity, and the no-flux process of Au80Sn20 (Wt%) just solves such problems.

[0003] Since the Au80Sn20 (Wt%) phase consists of a mixture of two intermetallic compounds, AuSn (δ) and Au5Sn (ζ'), the solder is quite hard and has high creep resistance. These properties are beneficial to maintaining stable positions during long-term operation life. At the same time, Au80Sn20 (Wt%) also has very high thermal conductivity and corrosion resistance, and has good reliability at high temperatures, and is very popular in electronic devices that require high stability, and is widely used in multiple fields such as microelectronics, optoelectronic packaging, and sensors.

[0004] However, due to the characteristics of the alloy itself, such as high melting point, complex composition, and easy oxidation, the preparation process of gold-tin solder balls faces many challenges. It is easily affected by oxidation and contamination during the preparation process, which will lead to a decline in welding performance. Therefore, melting and forming need to be carried out under inert gas protection or in a vacuum environment to reduce the occurrence of oxidation. At the same time, the purity of equipment and raw materials also needs to be strictly controlled. The surface finish and sphericity of the solder balls have a direct impact on welding performance. High-precision processing and treatment technologies need to be adopted during the preparation process to obtain high-quality solder balls. Especially in automated production, ensuring the size and shape consistency of each solder ball is an important challenge. Due to the high price of gold, how to reduce the preparation cost, improve the material utilization rate, optimize the production process and equipment on the premise of ensuring quality is also an issue that needs to be considered.

[0005] At present, the conventional preparation methods of solder balls include wire cutting and remelting method, atomization method, electro-deposition method, etc. Since Au80Sn20 (Wt%) is an intermetallic compound composed of two phases and is brittle in texture, it is difficult to ensure the uniformity of volume through wire cutting and remelting method, and thus it is difficult to process it into solder balls. When prepared by the atomization method, a large number of satellite droplets are contained, that is, small particle powders are attached to the powder particles, and there are also defects such as hollow powder bodies, which seriously affect the fluidity, powder spreading performance and denseness of the powder. In addition, it is very difficult to ensure the uniformity of droplets during the preparation of micro-droplets by traditional methods, the experimental parameters are difficult to control, and the problems such as poor production continuity need to be solved urgently. The process of forming a gold-tin alloy on a substrate by electro-deposition method in an electrolytic solution and then peeling to form solder balls has a slow production speed and low efficiency.

[0006] Therefore, how to efficiently and stably prepare Au80Sn20 (Wt%) solder balls has become an urgent problem to be solved in the current field of materials science and engineering. It is necessary to provide a new preparation device and method for gold-tin solder balls to solve the above problems. Summary of the Invention

[0007] According to the above-mentioned technical problems, a method and device for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes are provided. The present invention mainly utilizes a channel with an inverted trapezoidal shape arranged at the bottom of the crucible, so that the liquid surface formed by the gold-tin melt in the micropores has an increased curvature radius, and then the curvature radius of the liquid surface is reduced, so as to effectively control the additional pressure and improve the stability of the gold-tin melt during the spraying process; combined with computer adjustment and control, the prepared solder balls have high sphericity, consistent thermal history, controllable particle sizes, and high preparation efficiency, thus effectively solving the problems of poor uniformity and uneven particle size distribution in the preparation of gold-tin solder balls in the prior art.

[0008] The technical means adopted by the present invention are as follows:

[0009] An apparatus for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes includes a vacuum system for evacuating the vacuum chamber inside the apparatus, a droplet spraying system arranged at the top of the vacuum chamber, a particle collector arranged at the bottom of the vacuum chamber and on the same axis as the droplet spraying system, an image acquisition system arranged on the inner wall of the vacuum chamber, and a liquid surface control system arranged on one side of the droplet spraying system. The droplet spraying system uses a crucible fixed inside the vacuum chamber as a container for containing the gold-tin melt. A microporous plate with a circular micropore is fixed at the bottom of the crucible and is connected to the inner cavity of the crucible. A piezoelectric ceramic arranged at the top of the crucible drives a transmission rod inside the crucible to vibrate, applying pressure to the gold-tin melt to spray it into droplet shape through the micropore, and after dropping, it quickly solidifies to form gold-tin solder balls with uniform particle sizes and is collected by the particle collector. Among them, the gap between the outer edge of the bottom of the transmission rod and the micropore at the bottom of the crucible is between 0.10 - 0.35 mm.

[0010] Further, the Au—Sn melt is an Au80Sn20 alloy, which has a fixed surface tension in the molten state; the micropores on the microporous sheet are channels in an inverted trapezoidal shape, so that the liquid surface formed by the Au—Sn melt therein has an increased radius of curvature, thereby reducing the radius of curvature of the liquid surface, effectively controlling the additional pressure, and enhancing the stability of the Au—Sn melt during the spraying process.

[0011] Further, the channels of the inverted trapezoidal shape of the micropores are such that the inner wall of the pore groove is shaped to narrow downward, that is, gradually taper from the surface facing the crucible side to the surface where the liquid drops fall. The outer edge of the micropores of the micropores and the inner wall of the pore groove are in a stepped shape, increasing the resistance that needs to be overcome during the fluctuation of the Au—Sn melt liquid surface and reducing the liquid surface fluctuation.

[0012] Further, the prepared Au—Sn solder balls have a particle size of 50 - 400 μm, the thickness of the microporous sheet is 1.5 - 3 mm, the upper diameter of the micropores is 5 - 7 mm, the lower diameter of the micropores is 0.1 - 0.5 mm, the thickness of the outer edge of the micropores is 0.2 - 0.5 mm, and the length of the outer edge of the micropores is 0.5 - 3 mm.

[0013] Further, the inclination range of the inner wall of the pore groove is between 100° and 135°, and the liquid surface stability is the best.

[0014] Further, a heating coil is provided around the crucible, and an infrared thermometer is installed on the inner wall of the vacuum chamber and connected to a computer for monitoring and controlling the temperature in the vacuum chamber. The heating method of the present invention is induction heating. The materials for making the crucible and the microporous sheet are selected as high-purity graphite with good mechanical properties and high melting points, and the material of the transmission rod is selected as Al2O3 with high-temperature strength, meeting the requirements for preparing Au—Sn solder balls.

[0015] Further, the vacuum system includes a vacuum chamber, a molecular pump and a mechanical pump provided on the outer wall of the vacuum chamber. A chamber inlet pipe and a connecting pipe are further provided in the vacuum chamber. A balance valve is installed on one side of the connecting pipe connected to the vacuum chamber, and the other side of the connecting pipe is connected to the crucible. A crucible inlet pipe connected to the crucible is further provided in the vacuum chamber, and the other end of the crucible inlet pipe is connected to a differential pressure controller. The transmission rod and the differential pressure controller cooperate to control the frequency of liquid drop dripping.

[0016] Further, the liquid surface control system is used to adjust the liquid surface height in the crucible and the molten pool of the feeding device according to the set pressure difference parameter, wherein the feeding device is used to supply liquid metal to the crucible.

[0017] Further, the device further includes a pre-collection tray, which is movably installed between the droplet ejection system and the particle collector and is used for pre-collecting gold-tin solder balls. The image acquisition system is used to acquire images of the pre-collected gold-tin droplets and feedback them to the differential pressure controller to adjust the differential pressure to control the particle size.

[0018] The present invention also discloses a method for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes, which uses the above device and specifically includes the following steps:

[0019] (1) Loading raw materials: Fix the microporous sheet with micropores at the bottom of the crucible, add gold-tin alloy raw materials inside the crucible and the melting pool, and fix the crucible at the top of the vacuum chamber.

[0020] (2) Vacuum pumping: Open the balance valve on the connecting pipe, connect the crucible with the vacuum chamber, and use a mechanical pump and a molecular pump to pump the crucible and the vacuum chamber to a pressure lower than 10 -3 Pa, and fill it with an inert protective gas, such as Ar gas or He gas, and repeat it several times. Finally, make the pressure in the vacuum chamber reach one atmospheric pressure.

[0021] (3) Heating and melting raw materials: Use a heating coil to heat, melt the gold-tin alloy raw materials in the crucible and the melting pool, and use an infrared thermometer to monitor the heating temperature in real time. After the gold-tin alloy raw materials are melted, keep them warm for 10 - 25 minutes.

[0022] (4) Preparing gold-tin solder balls by pulsed microporous injection method: Close the balance valve on the connecting pipe, open the pre-collection tray, adjust the differential pressure controller to make the differential pressure between the crucible and the vacuum chamber stable at 0 - 100 kPa, use a signal generator to edit a pulsed signal and apply it to the piezoelectric ceramic. The piezoelectric ceramic generates a small displacement under the drive of the pulsed signal, and this small displacement acts on the gold-tin melt at the bottom of the crucible through the transmission rod, so that the liquid is ejected from the micropores to form gold-tin droplets.

[0023] (5) Obtaining droplets with uniform and controllable particle sizes: The computer uses image analysis software to calculate the droplet diameter according to the images of gold-tin droplets captured by the high-speed camera, and feeds it back to the differential pressure controller and the signal generator for parameter adjustment, so that the droplet diameter is always at the set value.

[0024] (6) Containerless rapid solidification: Close the pre-collection tray. The uniformly spherical gold-tin droplets formed by spraying exchange radiation heat and convective heat with the surrounding environment during the falling process, and finally solidify without a container to form gold-tin solder balls with uniform and controllable particle sizes.

[0025] (7) Raw material supply and liquid level control: The liquid level regulator of the liquid level control system can adjust the liquid level height in the crucible and the molten pool according to the parameter settings and the information fed back by the computer; the automatic feeding device automatically controls the supply of raw materials according to the changes of the gold-tin melt in the crucible and the molten pool fed back by the computer, realizing continuous production.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. By setting a microporous design with an inverted trapezoidal structure, that is, optimizing the parameters such as the upper diameter, lower diameter, thickness, and length of the micropores, the present invention makes the gold-tin melt form an upwardly curved liquid surface in the pores, effectively increasing the curvature of the liquid surface and reducing the radius of curvature of the liquid surface, so that the liquid surface is more difficult to fluctuate significantly, making the liquid flow more stable during the entire spraying process and the spraying accuracy higher. In addition, this structural design can also effectively alleviate the uneven disturbance caused by the periodic vibration of the piezoelectric ceramic driving the transmission rod, further improving the spraying consistency and repeatability of the gold-tin melt.

[0028] 2. The key to preparing micron-sized gold-tin solder balls with uniform and controllable particle sizes in the present invention lies in maintaining the stability of the pressure difference inside and outside the crucible and the consistency of the micro-displacements generated by the piezoelectric ceramics, which is easier to achieve compared with other forming methods and is not affected by external disturbances. Therefore, the thermal history of the particles is consistent, the sizes, sphericity, and microstructures of the microparticles are consistent, and the surfaces of the gold-tin solder balls are free of dirt and foreign objects, showing metallic luster, the solder balls are not adhered, not ellipsoidal, and have true roundness.

[0029] 3. The present invention uses a computer to analyze the particle size data in the images transmitted by the high-speed camera and dynamically adjusts the parameters of the pulse generator and the differential pressure controller, so that the particle sizes of the prepared particles are always within the set values. In addition, the device of the present invention can adjust the liquid level height in the crucible and the molten pool through the liquid level control system and automatically supply raw materials to achieve continuous production.

[0030] In summary, the particles prepared by the present invention have the advantages of uniform and controllable particle sizes, high sphericity, and strong process controllability, improving the preparation accuracy, and meeting the needs of continuous industrial production. The production efficiency is increased several times compared with the previous preparation methods.

[0031] For the above reasons, the present invention is particularly suitable for wide promotion in technical fields such as high-precision electronic packaging. Brief Description of the Drawings

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 Schematic diagram of the device for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes provided by the present invention.

[0034] Figure 2 For Figure 1 Schematic diagram of the structure of the micro-hole plate.

[0035] Figure 3 For Figure 2 Schematic cross-sectional view of the micro-holes in the micro-hole plate.

[0036] Figure 4 Schematic diagram of the contact between the micro-holes of the micro-hole plate and the molten alloy droplets in the prior art.

[0037] Figure 5 Schematic diagram of the contact between the micro-holes of the micro-hole plate provided by the present invention and the gold-tin melt.

[0038] Figure 6 Scanning electron microscope image of the gold-tin solder balls with uniform and controllable particle sizes prepared by the pulsed micro-hole injection method in Example 1. Among them, the particle size of the gold-tin solder balls is 55μm ± 5μm.

[0039] Figure 7 Scanning electron microscope image of the gold-tin solder balls with uniform and controllable particle sizes prepared by the pulsed micro-hole injection method in Example 2. Among them, the particle size of the gold-tin solder balls is 200μm ± 5μm.

[0040] Figure 8 Scanning electron microscope image of the gold-tin solder balls with uniform and controllable particle sizes prepared by the pulsed micro-hole injection method in Example 3. Among them, the particle size of the gold-tin solder balls is 300μm ± 5μm.

[0041] In the figure: 1. Piezoelectric ceramic; 2. Transmission rod; 3. Connecting pipe; 4. Balance valve; 5. Melting pool; 6. Liquid level regulator; 7. Feeding device; 8. Infrared thermometer; 9. U-shaped connecting pipe; 10. Micro-hole plate; 11. Micro-hole; 12. Molecular pump; 13. Mechanical pump; 14. Chamber inlet pipe; 15. Droplet; 16. Particle collector; 17. Gold-tin solder ball; 18. Vacuum chamber; 19. Pre-collection tray; 20. Bracket; 21. High-speed camera; 22. Crucible; 23. Heating coil; 24. Differential pressure controller; 25. Computer; 26. Crucible inlet pipe; 27. Signal generator; 28. Gold-tin melt; 29. Inner wall of the hole groove; 30. Outer edge of the micro-hole. Detailed implementation mode

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0043] As Figure 1 shown, the present invention provides a device for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes, mainly including a vacuum system for evacuating the vacuum chamber 18 in the device, a droplet injection system arranged at the top of the vacuum chamber 18, a particle collector 16 arranged at the bottom of the vacuum chamber 18 and on the same axis as the droplet injection system, an image acquisition system (the present invention uses a high-speed camera 21) arranged on the inner wall of the vacuum chamber 18, and a liquid level control system arranged on one side of the droplet injection system. The droplet injection system uses a crucible 22 fixed inside the vacuum chamber 18 as a container for containing the gold-tin melt 28. A microporous plate 10 with a circular micropore 11 (as Figure 2 shown) is fixed at the bottom of the crucible 22 and is connected to the inner cavity of the crucible 22. A piezoelectric ceramic 1 arranged at the top of the crucible 22 drives a transmission rod 2 inside the crucible 22 to vibrate, applying pressure to the gold-tin melt 28 to be ejected into the shape of droplets 15 through the micropore 11. After dropping, it quickly solidifies to form gold-tin solder balls 17 with uniform particle sizes and is collected by the particle collector 16. Among them, the gap between the outer edge of the bottom of the transmission rod 2 and the micropore 11 at the bottom of the crucible 22 is between 0.10 - 0.35 mm.

[0044] The gold-tin melt 28 in the present invention is an Au80Sn20 alloy and has a fixed surface tension in the molten state; mainly the microporous plate 10 is regulated and improved. Specifically, as Figure 3 shown, the micropore 11 on the microporous plate 10 is a channel in the shape of an inverted trapezoid, that is, the inner wall 29 of the pore groove is in a shape that narrows downward, that is, it gradually tapers from the surface facing the crucible 22 to the surface where the droplets 15 drip. The inclination range of the inner wall 29 of the pore groove is between 100° - 135°, and the liquid level stability is the best.

[0045] The outer edge 30 of the micropore of the micropore 11 and the inner wall 29 of the pore groove are in a stepped shape, so that the liquid level formed by the gold-tin melt 28 in it has an increased radius of curvature (as Figure 5 shown), thereby reducing the radius of curvature of the liquid level, effectively controlling the additional pressure, increasing the resistance that needs to be overcome during the fluctuation of the liquid level of the gold-tin melt 28, reducing the liquid level fluctuation, and improving the stability of the gold-tin melt 28 during the injection process.

[0046] When the particle size of the prepared Au—Sn solder balls 17 is 50 - 400 μm, the thickness of the micro-hole sheet 10 is 1.5 - 3 mm, the upper diameter of the micro-holes 11 is 5 - 7 mm, the lower diameter of the micro-holes 11 is 0.1 - 0.5 mm, the thickness of the outer edge 30 of the micro-holes is 0.2 - 0.5 mm, and the length of the outer edge 30 of the micro-holes is 0.5 - 3 mm.

[0047] Specifically, during the vibration of the piezoelectric ceramic 1 driving the transmission rod 2, the transmission rod 2 drives the molten alloy liquid surface to fluctuate, thereby affecting the spraying stability (as Figure 4 shown). Due to the trapezoidal inverted structure design of the micro-holes 11, the curvature of the Au—Sn melt 28 increases, that is, the radius of curvature of the curved liquid surface caused by capillary action decreases. The additional pressure F of the curved liquid surface can be expressed by the Laplace equation:

[0048]

[0049] where F is the Laplace pressure; γ is the surface tension (usually in N / m); R1 and R2 are the two radii of curvature of the curved surface, which are related to the bending of the liquid surface. Since the gap decreases, that is, R1 and R2 decrease accordingly, and γ is the surface tension of the molten Au80Sn20, which is a fixed value here. As Figure 5 shown, when R1 and R2 decrease, the Laplace pressure F of the curved liquid surface increases. When the Au—Sn melt 28 is disturbed by driving the transmission rod 2, the resistance overcome when the liquid surface fluctuates upward is greater, that is, the molten liquid surface tends to have smaller fluctuations, thereby making the spraying process more stable.

[0050] Furthermore, a heating coil 23 is provided outside the crucible 22. The infrared thermometer 8 is installed on the inner wall of the vacuum chamber 18 and is connected to the computer 25 for monitoring and controlling the temperature in the vacuum chamber 18. The heating method of the present invention is induction heating. The materials for making the crucible 22 and the micro-hole sheet 10 are selected as high-purity graphite with good mechanical properties and high melting points, and the material of the transmission rod 2 is selected as Al2O3 with high-temperature strength, meeting the requirements for preparing the Au—Sn solder balls 17.

[0051] The vacuum system includes a vacuum chamber 18, a molecular pump 12 and a mechanical pump 13 provided on the outer wall of the vacuum chamber 18. A chamber inlet pipe 14 and a connecting pipe 3 are further provided in the vacuum chamber 18. A balance valve 4 is installed on the side of the connecting pipe 3 connected to the vacuum chamber 18, and the other side of the connecting pipe 3 is connected to the crucible 22. A crucible inlet pipe 26 connected to the crucible 22 is further provided in the vacuum chamber 18. The other end of the crucible inlet pipe 26 is connected to a differential pressure controller 24. The transmission rod 2 and the differential pressure controller 24 cooperate to control the dripping frequency of the liquid droplets 15.

[0052] The liquid level control system is used to adjust the liquid level height in the crucible and the molten pool 5 of the feeding device according to the set pressure difference parameter. Among them, the feeding device 7 is used to replenish the liquid metal in the crucible 22.

[0053] The device further includes a pre-collection tray 19, which is movably installed between the droplet spraying system and the particle collector 16 through a bracket 20 for pre-collecting the AuSn solder balls 17. The image acquisition system is used to acquire the images of the pre-collected AuSn droplets and feedback them to the differential pressure controller 24 to adjust the differential pressure control particle size.

[0054] The present invention also discloses a method for efficiently preparing AuSn solder balls with uniform and controllable particle sizes. Using the above device, it specifically includes the following steps:

[0055] (1) Loading raw materials: Fix the microporous sheet 10 with micropores 11 at the bottom of the crucible 22. Add AuSn alloy raw materials inside the crucible 22 and the molten pool 5, and fix the crucible 22 at the top of the vacuum chamber 18.

[0056] (2) Evacuating: Open the balance valve 4 on the connecting pipe 3. The crucible 22 is connected to the vacuum chamber 18. Use the mechanical pump 13 and the molecular pump 12 to evacuate the crucible 22 and the vacuum chamber 18 to less than 10 -3 Pa, and fill it with an inert protective gas, such as Ar gas or He gas, and repeat it several times. Finally, make the pressure in the vacuum chamber 18 reach one atmosphere.

[0057] (3) Heating and melting raw materials: Use the heating coil 23 to heat to melt the AuSn alloy raw materials in the crucible 22 and the molten pool 5. Use an infrared thermometer to monitor the heating temperature in real time. After the AuSn alloy raw materials are melted, keep them warm for 10 - 25 minutes.

[0058] (4) Preparing AuSn solder balls by pulsed microporous spraying method: Close the balance valve 4 on the connecting pipe, open the pre-collection tray 19, adjust the differential pressure controller 24 to make the differential pressure between the crucible 22 and the vacuum chamber 18 stable at 0 - 100 kPa. Use a signal generator to edit a pulsed signal and apply it to the piezoelectric ceramic 1. The piezoelectric ceramic 1 generates a small displacement under the drive of the pulsed signal. This small displacement acts on the AuSn melt 28 at the bottom of the crucible 22 through the transmission rod 2, so that the liquid sprays out from the micropores to form AuSn droplets.

[0059] (5) Obtaining droplets with uniform and controllable particle sizes: The computer uses the image analysis software Winroof 2018 (Mitani Corporation) to calculate the droplet diameter based on the images of Au-Sn droplets captured by the high-speed camera 21. After feeding back to the differential pressure controller 24 and the signal generator 27, parameter adjustment is carried out. The signal generator 27 outputs a preset reference waveform to drive the ceramics controlled by the piezoelectric ceramics 1 to generate mechanical oscillations, and then drives the ceramic transmission rod 2 to perform high-frequency reciprocating motion. To ensure the dynamic performance of the system, the present invention adopts a dual-channel oscilloscope monitoring scheme: the original output end of the signal source and the vibration feedback end of the actuator are synchronously connected to the oscilloscope to form an excitation-response comparison observation interface. This real-time dual-trace waveform comparison mechanism can intuitively present the phase difference and amplitude deviation, so as to replace the process parameters to timely adjust the diameter of the Au-Sn droplets. In addition, the existence of the pressure difference inside and outside the crucible will assist the unstable liquid surface state of the Au-Sn alloy at the micropores to reach the most easily ejected stable liquid surface state, thus ensuring the stability and uniformity of the solder ball ejection.

[0060] (6) Containerless rapid solidification: Close the pre-collection tray 19. The uniformly spherical Au-Sn droplets formed by spraying exchange radiation heat and convective heat with the surrounding environment during the falling process, and finally solidify without a container to form Au-Sn solder balls 17 with uniform and controllable particle sizes;

[0061] (7) Raw material supply and liquid level control: The liquid level regulator 6 of the liquid level control system can adjust the liquid level heights in the crucible 22 and the molten pool 5 through the U-shaped connecting pipe 9 according to the parameter settings and the information fed back by the computer; the feeding device 7 automatically controls the supply of raw materials according to the changes of the Au-Sn melt 28 in the crucible 22 and the molten pool 5 fed back by the computer to achieve continuous production.

[0062] Example 1

[0063] The Au-Sn solder balls are prepared by using the device for efficiently preparing Au-Sn solder balls with uniform and controllable particle sizes provided by the present invention. Specifically, the microporous sheet 10 and the crucible 22 are fixed. The thickness of the microporous sheet 10 is 2.2 mm, the upper diameter of the micropores is 5 mm, the lower diameter of the micropores is 0.05 mm, the thickness of the outer edge 30 of the micropores is 0.2 mm, and the length of the outer edge 30 of the micropores is 1.94 mm. The inclination angle of the inner wall 29 of the hole groove is set to 105°.

[0064] Add the gold-tin alloy into crucible 22 and the molten pool 5. After the gold-tin alloy is fully melted by the heating system, then apply high-frequency reciprocating vibration to the drive rod 2 through a preset pulse waveform, and adjust the gap between the outer edge of the bottom of the drive rod 2 and the micropores at the bottom of the crucible to 0.2 mm, ensuring that the bottom of the drive rod 2 is within the gold-tin melt 28. Turn on the switch of the piezoelectric ceramic 1, set the frequency to 100 Hz, and the rod 2 then drives the gold-tin melt 28 to break through the Laplace pressure F at the micropores 11 to achieve the ejection of the droplets 15. The prepared gold-tin solder balls are as Figure 6 shown. The particle size is 55 μm ± 5 μm. It can be seen that the surface of the prepared gold-tin solder balls has no dirt or foreign objects, shows a metallic luster, the solder balls have no adhesion and no ellipsoid shape, and no screening is required. The roundness reaches 95%.

[0065] Example 2

[0066] Using the preparation method of the present invention, different from Example 1, the thickness of the microporous sheet 10 is 0.22 mm, the upper diameter of the micropores is 5 mm, the lower diameter of the micropores is 0.2 mm, the thickness of the outer edge 30 of the micropores is 0.2 mm, and the length of the outer edge 30 of the micropores is 1.25 mm. The inclination angle of the inner wall 29 of the hole groove is 120°. Further control the particle size of the gold-tin solder balls by adjusting the preset pulse waveform. The prepared gold-tin solder balls are as Figure 7 shown. The particle size is 200 μm ± 5 μm, no screening is required, and the roundness reaches 96%.

[0067] Example 3

[0068] Different from Example 1, the thickness of the microporous sheet 10 is 0.22 mm, the upper diameter of the micropores is 5 mm, the lower diameter of the micropores is 0.3 mm, the thickness of the outer edge 30 of the micropores is 0.2 mm, and the length of the outer edge 30 of the micropores is 0.35 mm. The inclination range of the inner wall 29 of the hole groove is 135°. Further control the particle size of the gold-tin solder balls by adjusting the preset pulse waveform. The prepared gold-tin solder balls are as Figure 8 shown. The particle size is 300 μm ± 5 μm, no screening is required, and the roundness reaches 96%.

[0069] It can be seen from Example 1-3 and the pictures of the prepared gold-tin solder balls that in the device of the present invention, by systematically increasing the inclination angle of the side walls of the inverted trapezoidal structure in the microporous sheet, the curvature radius values R1 and R2 of the molten metal liquid surface can be effectively increased. This hydrodynamic design significantly increases the value of the Laplace pressure F, thereby forming a stronger surface tension constraint effect during the micro-droplet ejection process. This dynamic balance mechanism can effectively suppress the fluctuation amplitude of the molten metal liquid surface, making the particle size distribution of the obtained Au80Sn20 solder ball products more uniform.

[0070] In summary, the particles prepared by using the device and method of the present invention have uniform and controllable particle sizes, high sphericity, and controllable processes, greatly improving the preparation accuracy, and can meet the needs of continuous industrial production. The production efficiency is doubled compared with the previous preparation methods.

[0071] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A device for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes, comprising a vacuum system for evacuating a vacuum chamber in the device, a droplet ejection system arranged at the top of the vacuum chamber, a particle collector arranged at the bottom of the vacuum chamber and on the same axis as the droplet ejection system, an image acquisition system arranged on the inner wall of the vacuum chamber, and a liquid level control system arranged on one side of the droplet ejection system, characterized in that: The droplet injection system uses a crucible fixed inside a vacuum chamber as a container for holding a gold-tin melt, and a microporous sheet with circular micropores is fixed to the bottom of the crucible and communicated with the inner cavity of the crucible. The piezoelectric ceramic arranged on the top of the crucible drives the transmission rod inside the crucible to vibrate, and applies pressure to the gold-tin melt to be sprayed through the micropores into droplets. After dripping, it quickly solidifies to form gold-tin solder balls with uniform particle size and is collected by a particle collector, wherein the gap between the outer edge of the bottom of the transmission rod and the micropores at the bottom of the crucible is between 0.10-0.35 mm.

2. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle size according to claim 1, characterized in that: The gold-tin melt is an Au80Sn20 alloy, which has a fixed surface tension in a molten state; the micropores on the microporous sheet are inverted trapezoidal channels, so that the liquid surface formed by the gold-tin melt has an increased curvature radius, thereby reducing the curvature radius of the liquid surface, achieving effective control of the additional pressure, and improving the stability of the gold-tin melt during the injection process.

3. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle size according to claim 2, characterized in that: The inverted trapezoidal channel of the micropore is in a shape in which the inner wall of the pore groove narrows downward, that is, it gradually shrinks from the surface facing the crucible to the surface on the side where the liquid droplets fall, and the outer edge of the micropore and the inner wall of the pore groove are stepped, thereby increasing the resistance that the gold-tin melt liquid level needs to overcome during the fluctuation process, thereby reducing the liquid level fluctuation.

4. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle size according to claim 3, characterized in that: The particle size of the prepared gold-tin solder ball is 50-400 μm, the thickness of the microporous sheet is 1.5-3 mm, the upper diameter of the micropore is 5-7 mm, the lower diameter of the micropore is 0.1-0.5 mm, the thickness of the micropore outer edge is 0.2-0.5 mm, and the length of the micropore outer edge is 0.5-3 mm.

5. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle size according to claim 4, characterized in that: The inclination range of the inner wall of the hole groove is between 100° and 135°.

6. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle size according to claim 1, characterized in that: A heating coil is arranged on the periphery of the crucible, and an infrared thermometer is installed on the inner wall of the vacuum chamber and is connected to a computer for monitoring and controlling the temperature in the vacuum chamber.

7. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle size according to claim 1, characterized in that: The vacuum system includes a vacuum chamber, a molecular pump and a mechanical pump arranged on the outer wall of the vacuum chamber, a chamber air inlet pipe and a connecting pipe are also provided in the vacuum chamber, a balancing valve is installed on the side of the connecting pipe connected to the vacuum chamber, and the other side of the connecting pipe is connected to the crucible, and a crucible air inlet pipe connected to the crucible is also provided in the vacuum chamber, and the other end of the crucible air inlet pipe is connected to a differential pressure controller, and the transmission rod and the differential pressure controller cooperate to control the frequency of droplet dripping.

8. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle size according to claim 1, characterized in that: The liquid level control system is used to adjust the liquid level in the crucible and the feeding device molten pool according to the set pressure difference parameter, wherein the feeding device is used to replenish the liquid metal in the crucible.

9. The device for efficiently preparing gold-tin solder balls with uniform and controllable particle sizes according to claim 1, characterized in that: The device also includes a pre-collection plate, which is movably installed between the droplet injection system and the particle collector and is used for pre-collecting gold-tin solder balls. The image acquisition system is used to collect the pre-collected gold-tin droplet images and feed them back to the differential pressure controller to adjust the differential pressure to control the particle size.

10. A method for efficiently preparing gold-tin solder balls with uniform and controllable particle size, characterized in that: The device according to any one of claims 1 to 9 comprises the following steps: (1) Loading the raw materials: Fixing a microporous sheet with micropores at the bottom of the crucible, adding gold-tin alloy raw materials into the crucible and the molten pool, and fixing the crucible on the top of the vacuum chamber; (2) Vacuuming: Open the balance valve on the connecting pipe, connect the crucible to the vacuum chamber, and use a mechanical pump and a molecular pump to evacuate the crucible and the vacuum chamber to less than 10 -3 Pa, and fill with inert protective gas Ar gas or He gas, repeat several times, and finally make the pressure in the vacuum chamber reach one atmosphere; (3) Heating and melting the raw materials: using a heating coil to heat the gold-tin alloy raw materials in the crucible and the molten pool to melt, using an infrared thermometer to monitor the heating temperature in real time, and keeping the gold-tin alloy raw materials warm for 10-25 minutes after they melt; (4) Preparation of gold-tin solder balls by pulse micropore injection method: close the balance valve on the connecting pipe, open the pre-collection plate, adjust the differential pressure controller to stabilize the differential pressure between the crucible and the vacuum chamber at 0-100 kPa, use the signal generator to edit the pulse signal and apply it to the piezoelectric ceramic. The piezoelectric ceramic generates a small displacement under the driving action of the pulse signal. This small displacement is acted on the gold-tin melt at the bottom of the crucible by the transmission rod, so that the liquid is ejected from the micropores to form gold-tin droplets; (5) Obtaining droplets with uniform and controllable particle size: The computer uses image analysis software to calculate the droplet diameter based on the image of the gold-tin droplet taken by the high-speed camera, and then feeds it back to the differential pressure controller and signal generator to adjust the parameters so that the droplet diameter is always at the set value; (6) Container-free rapid solidification: The pre-collection tray is closed, and the uniform spherical gold-tin droplets formed by spraying exchange heat with the surrounding environment through radiation and convection during the falling process, and finally solidify without a container to form gold-tin solder balls with uniform and controllable particle size; (7) Raw material supply and liquid level control: The liquid level regulator of the liquid level control system can adjust the liquid level in the crucible and the molten pool according to the parameter settings and information fed back by the computer; the feeding device automatically controls the supply of raw materials according to the changes in the gold-tin melt in the crucible and the molten pool fed back by the computer to achieve continuous production.

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