CN117123788B - A copper core sphere and its preparation method and apparatus - Google Patents
A copper core sphere and its preparation method and apparatusInfo
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- CN117123788B CN117123788B CN202311096752.8A CN202311096752A CN117123788B CN 117123788 B CN117123788 B CN 117123788B CN 202311096752 A CN202311096752 A CN 202311096752A CN 117123788 B CN117123788 B CN 117123788B
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Abstract
本发明提供了一种铜核球及其制备方法、装置。铜核球的制备方法包括以下步骤：S1：将铜块制备成熔融液，并将熔融液挤出，在管口形成近分离状态的液滴；S2：在液滴的管口分割点和下落轨迹的周围设置磁感线圈，磁感线圈通交流电，液滴与管口分离并沿着下落轨迹进行掉落；S3：将液滴依次进行冷却、研磨、筛选、电镀，得到铜核球。制备铜核球的装置包括：模槽、毛细管、磁感线圈、感应电源和冷却槽。本发明通过采用液滴磁感分割再熔技术，制备得到一种高真圆度的铜核球，保证电子封装互连空间的稳定性和质量可靠性。
This invention provides a copper core sphere and its preparation method and apparatus. The preparation method of the copper core sphere includes the following steps: S1: preparing a copper block into a molten liquid, and extruding the molten liquid to form a nearly separated droplet at the tube opening; S2: placing a magnetic induction coil around the droplet's tube opening segment and its falling trajectory, applying alternating current to the magnetic induction coil, causing the droplet to separate from the tube opening and fall along its falling trajectory; S3: sequentially cooling, grinding, screening, and electroplating the droplet to obtain the copper core sphere. The apparatus for preparing the copper core sphere includes: a mold groove, a capillary tube, a magnetic induction coil, an induction power supply, and a cooling tank. This invention, by employing droplet magnetic induction segmentation and remelting technology, prepares a copper core sphere with high sphericity, ensuring the stability and reliability of the interconnect space in electronic packaging.
Description
Technical Field
The invention relates to the technical field of electronic element manufacturing, in particular to a copper core ball and a preparation method and a device thereof.
Background
In recent years, with the increasing miniaturization of the volume of electronic devices, in order to meet the market demands of miniaturization, narrow pitch, and multi-pin electronic packages, the size of interconnect pads is continuously reduced, and packaging technologies typified by 3D stacked packages are being developed. The 3D stack package requires multiple thermal processes, and the space required between PKGs cannot be ensured due to the easy collapse of the conventional solder balls, and the short circuit of pins caused by bridging is also easy to occur, so that the problems of poor connection reliability of solder joints and the like exist. Therefore, copper core tin plating balls are used as packaging materials, and the space required between PKGs after reflow is ensured.
In the 3D stacking packaging process, indexes such as size consistency, roundness and the like of the copper core balls play an absolute role on packaging quality, and when solder balls with different diameters and poor sphericity are used on the same electronic component, coplanarity problem in the packaging process can be caused, the reliability of welding spots is seriously influenced, and welding spot defects are formed, so that the preparation of the high-roundness copper core balls is a key for solving the problem of electronic packaging interconnection space maintenance and product reliability. The traditional drop forming method cuts off the viscous force of molten drops mainly by a method of externally applying driving force, applies magnetic force or vibration and the like in the drop separation process to quickly isolate the spheres, but the method is easy to form necking residues when the drops are separated and condensed, and the externally applying force can cause the deformation of the spheres, the irregularity of the spheres and the poor sphericity. The sphericity is poor in the chip packaging process, the welding spots are easy to collapse, and the using conditions cannot be met.
Disclosure of Invention
The invention aims to prepare the copper nuclear sphere with high roundness by adopting a droplet magnetic induction segmentation remelting technology, so as to ensure the stability and the quality reliability of an electronic packaging interconnection space.
The invention provides a preparation method of a copper core ball, which comprises the following steps of S1, preparing a copper block into a molten liquid, extruding the molten liquid, forming liquid drops in a near-separation state at a pipe orifice, S2, arranging magnetic induction coils around a pipe orifice separation point and a falling track of the liquid drops, supplying alternating current to the magnetic induction coils, separating the liquid drops from the pipe orifice and falling along the falling track, and S3, cooling, grinding, screening and electroplating the liquid drops in sequence to obtain the copper core ball.
The invention adopts a magnetic induction segmentation remelting technology to prepare the copper core ball with high roundness. When the liquid drop in the near-separation state is subjected to gas stamping and downward dripping in a die cavity, magnetic induction coils of an induction power supply are additionally arranged at the periphery of a falling dividing point and a falling track, and the magnetic induction dividing remelting technology is utilized to promote the liquid drop in the near-separation state to realize magnetic induction self-separation, remodel the shape of a sphere and avoid vibration deformation during dividing.
Specifically, after alternating current is supplied to the magnetic induction coil, alternating current passes through the magnetic induction coil to generate an alternating magnetic field, when a molten metal drop drops to be separated, the alternating magnetic field is placed in a cutting alternating magnetic line, so that alternating current is instantaneously generated inside the molten metal drop, an induction current generates a closed control loop along the drop to form eddy current, the eddy current spheroidizes the molten metal drop, atoms in the eddy current make high-speed irregular movement, and atoms collide and rub with each other to generate heat energy, so that the drop is melted again. After the metal liquid drop is remelted, according to the volume and surface area formula, the surface area of the sphere under the same volume is minimum, the surface tension generates an inward pulling force on the surface of the metal liquid drop, the viscous force of the metal liquid drop is reduced, the separation of the liquid drop and the molten liquid in the capillary tube is accelerated, and self-separation is realized.
In any technical scheme, the method specifically comprises the steps of S11, carrying out an electrolysis process on a copper block in a die cavity to obtain molten liquid, and S12, extruding the molten liquid from a capillary under the action of nitrogen stamping and self gravity to form liquid drops in a near-separation state at the tail end of the capillary.
Preparing copper blocks into molten liquid, selecting an electrolysis process as a means for obtaining the molten liquid, wherein the melting point of copper is 1050-1100 ℃ because of higher melting point of copper, and melting by adopting a common heating means usually requires higher temperature and higher cost; the electrolytic method can ensure the purity of the obtained metal melt to be higher, ensure the connectivity with other components in the preparation device and realize the integration of preparation.
Nitrogen is flushed into the die cavity, so that the molten liquid is not oxidized, and on the other hand, the extrusion of the molten liquid can be quickened by gas flushing, and the preparation efficiency is improved.
In any of the above embodiments, the droplets in S2 are dropped under a nitrogen atmosphere.
The preparation of the metal spheres is carried out under a nitrogen atmosphere, so that the molten liquid forms liquid drops at the tail end of the capillary under the wrapping of nitrogen, and complete isolation from surrounding air is ensured in the falling track of the liquid drops, thereby preventing the copper spheres from being oxidized.
In any technical scheme, the method specifically comprises the steps of S31, enabling liquid drops to fall into a liquid nitrogen cooling tank, collecting to obtain spheres, S32, grinding the spheres, then sequentially cleaning, drying, screening and polishing, S33, firstly carrying out nickel plating treatment on the polished spheres, and then carrying out solder plating treatment on the polished spheres to obtain copper nuclear spheres, wherein the components of the solder layers comprise tin alloy.
Liquid nitrogen is used as a liquid drop cooling agent, so that the liquid drops are rapidly cooled into spheres when falling into a cooling tank, and oxidation caused by reaction of the liquid drops with other substances can be avoided. And (3) conveying the cooled spheres into a sphere grinding machine for grinding, and reducing the difference between the maximum diameter and the minimum diameter of the spheres. The ball body after grinding is cleaned and dried, the ball body which is required to meet the size is screened out from the ball body after grinding, and the ball body is polished, so that the purpose of polishing is to improve the roundness of the ball body on one hand, and reduce the phenomenon of uneven surface of the ball body on the other hand, and avoid forming metal piece compounds due to mutual diffusion of atoms between a nickel layer and a copper layer, thereby ensuring the performance of products.
The polished ball is subjected to nickel plating treatment, on one hand, the nickel layer can ensure that the copper ball is not oxidized, on the other hand, the copper has smaller hardness and is easy to deform, the strength of the ball can be improved by plating nickel on the surface of the copper, and in addition, the migration of copper atoms can be prevented after the nickel plating, and the copper color of the plating layer can be avoided. Tin alloy is selected as a brazing filler metal layer to be electroplated on the surface of the copper ball, so that the copper ball is prevented from being corroded, and the tin alloy is used as a low-melting-point material, so that the welding point interconnection can be realized through multiple thermal processes.
In any of the above embodiments, the nickel layer has a thickness of 2 μm to 4 μm, and/or the brazing filler metal layer has a thickness of 5 μm to 60 μm, and/or the copper core sphere has a diameter of 300 μm to 500 μm.
The thicknesses of the nickel layer and the brazing filler metal layer are selected appropriately, so that the copper core ball can be guaranteed to have certain hardness, and oxidation and corrosion of the ball body can be avoided. The proper size of the copper core ball is selected, so that the space required by the encapsulation of the electronic element is ensured, the copper core ball is not easy to collapse, and even through the thermal process is performed for a plurality of times, the copper core ball still exists in the bonding pad and maintains the space.
In any of the above technical solutions, the roundness of the copper core sphere is not higher than 3.5 μm.
In the packaging process of electronic components, indexes such as size consistency, roundness and the like of copper core balls play an absolute role on packaging quality, and the phenomenon of welding spot deviation and the like in the packaging process can be caused by different sizes and poor roundness of solder balls, so that equipment is blocked, and when solder balls with different diameters and poor sphericity are used on the same electronic component, coplanarity in the packaging process can be caused, the reliability of welding spots is seriously influenced, and welding spot defects are formed. Therefore, the copper core ball with close size and high roundness can ensure the stability of the package.
The invention provides a copper nuclear sphere device which comprises a die groove, a capillary tube, a magnetic induction coil, an induction power supply and a cooling groove, wherein the magnetic induction coil is arranged between a tube orifice of the capillary tube and the upper end of the cooling groove so as to enable liquid drops to pass through the magnetic induction coil, and the induction power supply is electrically connected with the magnetic induction coil so as to enable the magnetic induction coil to generate an alternating magnetic field.
After the magnetic induction coil is electrified with alternating current, the magnetic induction coil generates an alternating magnetic field, and when the metal liquid drop extrusion pipe orifice is in a state to be separated, liquid drops at the pipe orifice are in cutting alternating magnetic lines, so that alternating current is instantaneously generated inside the metal liquid drops. On one hand, the surface tension of the liquid drop is promoted to generate an inward pulling force action on the surface of the metal liquid drop, the viscous force of the metal liquid drop is reduced, the separation of the liquid drop and the molten liquid in the capillary tube is accelerated, and further self-separation is realized, on the other hand, induced current generates a closed control loop along the liquid drop to form vortex, the vortex enables the metal liquid drop to be spheroidized, atoms in the vortex move at a high speed in a random manner, and the atoms collide and rub with each other to generate heat energy, so that the liquid drop is molten again, and finally the copper ball with high roundness is prepared.
In any of the above technical schemes, the die cavity is provided with an air inlet punching opening for introducing nitrogen, and/or the caliber of the pipe orifice is 0.15mm-0.25mm, and/or the inclination of the pipe orifice and the inner wall of the capillary tube is 115 degrees to 125 degrees.
The air inlet punching opening is arranged at the upper end of the die cavity, and air is punched into the die cavity to apply pressure to the molten liquid, so that the molten liquid is extruded conveniently. The inclination of the pipe orifice and the inner wall of the capillary tube is set, so that the diameter of the obtained liquid drop is ensured to be slightly larger than the caliber of the capillary tube.
In any of the above technical schemes, the length of the magnetic induction coil from the pipe orifice to the cooling tank is 8m-12m, and/or the frequency of the induction power supply is 70kHz-90kHz.
The track range of the liquid drop is from the pipe orifice division point to the falling track, and a magnetic induction coil is arranged around the track range to ensure that the liquid drop passes through a full remelting process so as to obtain a sphere with high roundness. At the pipe orifice dividing point, the liquid drop is in a near-separation state, under the action of an electromagnetic induction coil electrified with alternating current, the surface tension of the liquid drop is promoted to generate an inward pulling force action on the surface of the metal liquid drop, the viscous force of the metal liquid drop is reduced, the separation of the liquid drop and the molten liquid in the capillary is accelerated, and further the self-separation is realized.
After the magnetic induction coil is electrified with alternating current, the alternating current generates an alternating magnetic field through the magnetic induction coil, when the molten metal drops fall down to be separated, the molten metal drops are placed in the cutting alternating magnetic lines, so that alternating current is instantaneously generated inside the molten metal drops, the induced current generates a closed control loop along the drops to form eddy currents, the eddy currents enable the molten metal drops to be spheroidized, atoms in the eddy currents move at high speed irregularly, and the atoms collide and rub with each other to generate heat energy, so that the drops are molten again.
The invention provides a copper core ball, which is obtained by adopting the preparation method according to any one of the technical schemes, so that the copper core ball has the beneficial effects according to any one of the technical schemes and is not repeated herein.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts a magnetic induction segmentation remelting technology to segment and remelt the fallen copper core spheres. The method comprises the steps of separating liquid drops, namely separating the liquid drops by utilizing magnetic induction, under the condition of no external force such as vibration, no necking residue exists during the separation of the liquid drops, forming spheres which are not deformed, and melting the liquid drops again after the separation of the liquid drops, wherein the liquid drops are mainly subjected to the action of surface tension, the surface tension generates an inward pulling force on the surfaces of the liquid drops, the liquid drops are instantaneously condensed and separated into spheres, and the copper nuclear spheres prepared after condensation have no necking residue, so that the copper nuclear spheres have high roundness and surface gloss.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 is a graph showing the comparison of the roundness of the copper core ball according to example 1 of the present invention;
fig. 2 is a schematic structural diagram of a copper core ball according to embodiment 1 of the present invention;
FIG. 3 is a graph of the true roundness electron microscope test of the copper core sphere provided in embodiment 1 of the present invention;
fig. 4 is a true roundness electron microscope test chart of the copper core sphere provided in embodiment 1 of the present invention;
fig. 5 is a diagram of a preparation apparatus for copper core balls according to an embodiment of the present invention.
Reference numerals illustrate:
1-device, 2-die cavity, 3-capillary, 4-magnetic induction coil, 5-induction power supply, 6-cooling cavity and 7-inlet punching opening.
Detailed Description
In order that the above-recited objects, features and advantages of the present invention will become more apparent, a more particular description of embodiments of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The 3D stack package needs multiple heat processes, the traditional material is that solder balls are used for carrying out welding spot interconnection, but after multiple reflow soldering, the solder balls are molten, at the moment, the weight of the multi-layer electronic part is easy to lead the solder balls to collapse, so that the space required between PKGs can not be ensured, bridging is easy to cause short circuit of pins, and the problems of poor reliability of welding spot connection and the like exist.
The copper core solder ball is characterized in that the space required between PKGs after reflow soldering can be ensured, the copper core ball is formed by taking a copper material as a core and adopting a surface tin-plated alloy, the melting point of copper is high, the melting point of copper is 1050-1100 ℃, and the copper core solder ball cannot be melted in a soldering tin packaging temperature region, so that even though the copper core solder ball is subjected to numerous thermal processes, the copper core solder ball still exists in a bonding pad and maintains the space, and the space is convenient for accommodating other electronic parts for packaging, so that the high-density 3D packaging is facilitated, and the surface tin alloy can be subjected to welding point interconnection through multiple thermal processes. The solder joint offset and other phenomena in the packaging process can be caused by the different sizes and the true roundness difference of the copper core solder balls, so that equipment obstruction is caused.
The copper core ball is prepared by tin plating on the surface of the copper ball, but the copper core ball prepared by an atomization method and a plasma gasification method has the problems of different particle size, poor roundness and the like, and the quality reliability of the copper core ball prepared by a mechanical ball milling method is poor. The prior mature technology is that a ball is prepared by a liquid drop forming method, the liquid metal is conveyed to a pipe orifice through a capillary, a molten drop is slowly formed at the tail end of the pipe orifice, the molten drop is necked down under the action of gravity along with the increase of the volume of the molten drop, the height of the molten drop is gradually increased under the reverse action of the viscosity force of the liquid and the gravity, the minimum neck width is gradually reduced, and the molten drop falls off and is condensed into a ball. In order to make the sphericity higher and reduce necking residues of the viscous force of the molten drops, external field driving such as vibration, pneumatic, magnetic force and the like is generally needed to realize rapid separation of the liquid drops. The method has the defects that when the height of the molten drops is gradually increased, the formed sphere shape is deviated along with the occurrence of condensation and crystallization of the molten drops, when an external driving force is applied to separate the sphere, the shape of the metal sphere in a crystallization state is changed, so that the roundness of the sphere is reduced, and meanwhile, the separated necking remains, so that the surface of the sphere is irregular.
Therefore, the invention adopts the magnetic induction segmentation remelting technology to segment and remelt the fallen copper core spheres. The method comprises the steps of separating liquid drops, namely separating the liquid drops by utilizing magnetic induction, under the condition of no external force such as vibration, no necking residue exists during the separation of the liquid drops, forming spheres which are not deformed, and melting the liquid drops again after the separation of the liquid drops, wherein the liquid drops are mainly subjected to the action of surface tension, the surface tension generates an inward pulling force on the surfaces of the liquid drops, the liquid drops are instantaneously condensed and separated into spheres, and the copper nuclear spheres prepared after condensation have no necking residue, so that the copper nuclear spheres have high roundness and surface gloss.
The embodiment of the invention provides a preparation method of a copper nuclear ball, which comprises the following steps of S1, preparing a copper block into a molten liquid, extruding the molten liquid, forming liquid drops in a near-separation state at a pipe orifice, S2, arranging magnetic induction coils around a pipe orifice separation point and a falling track of the liquid drops, leading the magnetic induction coils to apply alternating current, separating the liquid drops from the pipe orifice and falling along the falling track, and S3, cooling, grinding, screening and electroplating the liquid drops in sequence to obtain the copper nuclear ball.
The copper core ball with high roundness is prepared by adopting a magnetic induction segmentation remelting technology. When the liquid drop in the near-separation state is subjected to gas stamping and downward dripping in the die cavity, a magnetic induction coil of an induction power supply is additionally arranged around a falling dividing point and a falling track, and the magnetic induction dividing remelting technology is utilized to promote the liquid drop in the near-separation state to realize magnetic induction self-separation, remodel the shape of the sphere and avoid vibration deformation during dividing, so that the metal sphere with high roundness is finally obtained.
In some embodiments of the present invention, S1 specifically includes S11 of performing an electrolysis process on a copper block in a die cavity to obtain a molten liquid, and S12 of extruding the molten liquid from a capillary under the action of nitrogen gas stamping and self gravity to form droplets in a near-separation state at the end of the capillary.
Preparing copper blocks into molten liquid, selecting an electrolysis process as a means for obtaining the molten liquid, wherein the melting point of copper is 1050-1100 ℃ because of higher melting point of copper, and melting by adopting a common heating means usually requires higher temperature and higher cost; the electrolytic method can ensure the purity of the obtained metal melt to be higher, ensure the connectivity with other components in the preparation device and realize the integration of preparation. Nitrogen is flushed into the die cavity, so that the molten liquid is not oxidized, and on the other hand, the extrusion of the molten liquid can be quickened by gas flushing, and the preparation efficiency is improved. Preferably, the oxygen content set in the nitrogen atmosphere is not higher than 0.001%.
In some embodiments of the present invention, the drop in S2 is dropped under a nitrogen atmosphere.
The preparation of the metal spheres is carried out under a nitrogen atmosphere, so that the molten liquid forms liquid drops at the tail end of the capillary under the wrapping of nitrogen, and complete isolation from surrounding air is ensured in the falling track of the liquid drops, thereby preventing the copper spheres from being oxidized.
In some embodiments of the invention, S3 specifically comprises S31, wherein liquid drops fall into a liquid nitrogen cooling tank to obtain spheres, S32, wherein the spheres are ground and then sequentially cleaned, dried, screened and polished, S33, the polished spheres are firstly subjected to nickel plating and then are subjected to solder plating to obtain copper core spheres, and the components of the solder layers comprise tin alloy.
Liquid nitrogen is used as a liquid drop cooling agent, so that the liquid drops are rapidly cooled into spheres when falling into a cooling tank, and oxidation caused by reaction of the liquid drops with other substances can be avoided. And (3) conveying the cooled spheres into a sphere grinding machine for grinding, so that the difference value between the maximum diameter and the minimum diameter of the spheres is reduced, the true roundness of the spheres is further improved, and the true roundness of the spheres is ensured to be not higher than 3.5 mu m. The ball body after grinding is cleaned and dried, the ball body which is required to meet the size is screened out from the ball body after grinding, and the ball body is polished, so that the purpose of polishing is to improve the roundness of the ball body on one hand, and reduce the phenomenon of uneven surface of the ball body on the other hand, and avoid forming metal piece compounds due to mutual diffusion of atoms between a nickel layer and a copper layer, thereby ensuring the performance of products.
The polished ball is subjected to nickel plating treatment, on one hand, the nickel layer can ensure that the copper ball is not oxidized, on the other hand, the copper has smaller hardness and is easy to deform, the strength of the ball can be improved by plating nickel on the surface of the copper, and in addition, the migration of copper atoms can be prevented after the nickel plating, and the copper color of the plating layer can be avoided. It should be noted that the surface of the sphere needs to be kept with a certain roughness so that the nickel layer can be firmly attached to the surface of the sphere, and the sphere is not easy to fall off.
The composition of the solder layer comprises a tin alloy, preferably a tin-copper alloy, a tin-silver-copper alloy, a tin-gold alloy. Tin alloy is selected as a brazing filler metal layer to be electroplated on the surface of the copper ball, so that the copper ball is prevented from being corroded, and the tin alloy is used as a low-melting-point material, so that the welding point interconnection can be realized through multiple thermal processes.
In some embodiments of the invention, the nickel layer has a thickness of 2 μm to 4 μm, and/or the braze layer has a thickness of 5 μm to 60 μm, and/or the copper core sphere has a diameter of 300 μm to 500 μm.
Preferably, the nickel plating layer treatment and the solder plating layer treatment are carried out in an electroplating mode, and the proper thickness of the nickel layer and the solder layer is selected, so that the copper core ball can be ensured to have certain hardness, and oxidation and corrosion of the ball can be avoided. Preferably, the nickel layer has a thickness of 2.5 μm to 3.5 μm and the brazing filler metal layer has a thickness of 8 μm to 50 μm. The proper size of the copper core ball is selected, so that the space required by the encapsulation of the electronic element is ensured, the copper core ball is not easy to collapse, and even through the thermal process is performed for a plurality of times, the copper core ball still exists in the bonding pad and maintains the space. Preferably, the copper core sphere has a diameter of 350 μm to 450 μm. The person skilled in the art can choose a suitable coating thickness according to his own needs.
In some embodiments of the invention, the copper core sphere has a roundness of not more than 3.5 μm.
In the packaging process of electronic components, indexes such as size consistency, roundness and the like of copper core balls play an absolute role on packaging quality, and the phenomenon of welding spot deviation and the like in the packaging process can be caused by different sizes and poor roundness of solder balls, so that equipment is blocked, and when solder balls with different diameters and poor sphericity are used on the same electronic component, coplanarity in the packaging process can be caused, the reliability of welding spots is seriously influenced, and welding spot defects are formed. Therefore, the copper core ball with close size and high roundness can ensure the stability of the package.
The embodiment of the invention also provides a copper core ball device 1, which comprises a die cavity 2, a capillary tube 3, a magnetic induction coil 4, an induction power supply 5 and a cooling groove 6, wherein the magnetic induction coil 4 is arranged between the orifice of the capillary tube 3 and the upper end of the cooling groove 6 so as to enable liquid drops to pass through the magnetic induction coil 4, and the induction power supply 5 is electrically connected with the magnetic induction coil 4 so as to enable the magnetic induction coil 4 to generate an alternating magnetic field.
As shown in fig. 5, the cooling tank 6 is disposed at the lower end opposite to the orifice of the capillary tube 3, and is used for receiving and collecting the dropped copper balls, a magnetic induction coil 4 is disposed between the orifice of the capillary tube 3 and the upper end of the cooling tank 6, the magnetic induction coil 4 is connected with an induction power supply 5 of alternating current, the magnetic induction coils 4 are densely distributed, and the dropped liquid drops pass through the inside of the magnetic induction coils 4 and finally drop into the cooling tank 6 to form spheres with high roundness.
After the magnetic induction coil 4 is electrified with alternating current, the magnetic induction coil 4 generates an alternating magnetic field, and when the metal liquid drop extrusion pipe orifice is in a state to be separated, the liquid drop at the pipe orifice is in a cutting alternating magnetic force line, so that alternating current is instantaneously generated inside the metal liquid drop. On one hand, the surface tension of the liquid drop is promoted to generate an inward pulling force action on the surface of the metal liquid drop, the viscous force of the metal liquid drop is reduced, the separation of the liquid drop and the molten liquid in the capillary tube is accelerated, and further self-separation is realized, on the other hand, induced current generates a closed control loop along the liquid drop to form vortex, the vortex enables the metal liquid drop to be spheroidized, atoms in the vortex move at a high speed in a random manner, and the atoms collide and rub with each other to generate heat energy, so that the liquid drop is molten again, and finally the copper ball with high roundness is prepared.
In some embodiments of the invention, the die cavity 2 is provided with an inlet punch 7 for introducing nitrogen gas and/or the orifice has a caliber of 0.15mm to 0.25mm and/or the orifice has a slope of 115 ° to 125 ° from the inner wall of the capillary 3.
Specifically, the die cavity 2 is used for containing molten metal, an electrolysis device can be selectively arranged in the die cavity 2to realize the technical effect of extruding liquid drops while preparing molten metal, and the molten metal prepared in advance can be introduced into the die cavity 2 for preparation. The air inlet punching opening 7 is arranged at the upper end of the die cavity 2, and air is punched into the die cavity to apply pressure to the molten liquid, so that the molten liquid is extruded conveniently. At least one capillary 3 is provided at the bottom of the die cavity 2 for forming droplets of a desired size.
The purpose of the scheme is to prepare copper nuclear spheres with the diameter of 300-500 mu m, so that the caliber of a nozzle is designed to be 0.15-0.25 mm, preferably 0.18-0.22 mm, the diameter of the obtained liquid drop is slightly larger than that of a capillary, the inclination of the nozzle to the inner wall of the capillary is 115-125 degrees, preferably 118-122 degrees. The pipe orifice is a liquid drop dividing point, the inclination is the angle between the plane of the pipe orifice and the inner wall of the conical pipe head, and a person skilled in the art can select proper caliber and inclination according to the required size of the copper core ball.
For example, nitrogen is flushed into the space of the apparatus containing the molten metal at a suitable gas flow rate to ensure smooth extrusion of the molten metal, preferably at a flow rate of 0.8mm 3/s-5mm3/s, more preferably at a flow rate of 1.5mm 3/s-4mm3/s. When the preparation of copper core balls is started, the molten liquid is difficult to flow out from a pipe orifice due to certain viscosity, so that larger gas punching is needed to help the molten liquid flow out, and in the subsequent extrusion process, the flow resistance of the molten liquid is reduced due to certain dynamic viscosity among the molten liquid, so that the strength of the gas punching can be properly reduced. Preferably, the nitrogen gas is stamped to 60Pa-100Pa when the melt is initially discharged, and 10Pa-50Pa when the melt is stably discharged. Further preferably, the nitrogen gas is stamped to 70Pa-90Pa when the melt is initially discharged, and 20Pa-40Pa when the melt is stably discharged.
In some embodiments of the invention, the length of the magnetic induction coil 4 from the nozzle to the cooling bath 6 is 8m-12m, and/or the frequency of the inductive power supply 5 is 70kHz-90kHz.
Specifically, the track range of the liquid drop is from the pipe orifice division point to the falling track, and the magnetic induction coil 4 is arranged around the track range, so that the liquid drop is ensured to undergo a sufficient remelting process, and a sphere with high roundness is obtained. At the pipe orifice dividing point, the liquid drop is in a near-separation state, under the action of the magnetic induction coil 4 which is electrified with alternating current, the surface tension of the liquid drop is promoted to generate an inward pulling force action on the surface of the metal liquid drop, the viscous force of the metal liquid drop is reduced, the separation of the liquid drop and the molten liquid in the capillary 3 is accelerated, and further the self-separation is realized. The length of the magnetic induction coil 4 from the nozzle to the cooling tank 6 is 8m to 12m, and further preferably 9m to 11m.
The electromagnetic induction heating is to generate an alternating magnetic field by utilizing an alternating electric field, the heated object cuts the magnetic field to generate eddy current to heat the object, and an induction power supply 5, a magnetic induction coil 4 and falling liquid drops are required to form a complete induction heating system. The electromagnetic induction heating has the advantages of quick heating, good energy-saving effect and high intelligent degree. When the output power of the induction power supply 5 is constant, the higher the frequency, the faster the heating speed, and the heating depth is reduced under the same heating time, so that the proper induction frequency is required to be selected to ensure the heating speed and the certain heating depth of the liquid drops. Preferably, the magnetic induction coil 4 adopts an induction power supply 5 with the frequency of 70kHz-90kHz, and the high-frequency induction heating power supply is suitable for rapid heating of thin layers or finer grains, and more preferably, the frequency of the induction power supply 5 is 75kHz-85kHz.
It should be noted that, the power of one induction power supply 5 is limited, and the power required by the magnetic induction coil 4 in this scheme cannot be satisfied, so that a plurality of induction power supplies 5 can be additionally installed, the power of the induction power supply 5 can be preferably 300kW or 400kW, the induction power supply 5 is an alternating current, and a person skilled in the art can select the power size and the assembly number of the induction power supply 5 according to his own needs. Furthermore, it is required that the induction power supply device is selected so as to satisfy a heating depth, preferably a heating depth from the surface to the inside of not less than 0.2mm to 2mm, more preferably a heating depth of not less than 0.3mm to 1.5mm.
Example 1
The embodiment of the invention provides a preparation method of a copper core ball, which comprises the following steps:
s1, carrying out an electrolysis process on the copper block in a die cavity to obtain molten liquid.
And S2, introducing nitrogen downwards from the top end of the die cavity, extruding the molten liquid from the capillary under the action of nitrogen stamping and self gravity, and forming liquid drops in a near-separation state at the tail end of the capillary, wherein the flow rate of the nitrogen is 0.8mm 3/S, the stamping of the nitrogen is 60Pa when the molten liquid initially flows out, and the stamping of the nitrogen is 10Pa when the molten liquid stably flows out.
And S3, adding a magnetic induction coil which is electrified with alternating current at a liquid drop separation position of the capillary tube, so that the heating depth of the liquid drop is not less than 0.2mm, separating the liquid drop from a pipe orifice, and enabling the liquid drop to fall through the magnetic induction coil, wherein the falling track of the liquid drop through the magnetic induction coil is 10m.
And S4, the liquid drops fall into a liquid nitrogen cooling tank, and a sphere with high roundness is obtained through collection.
And S5, conveying the spheres into a ball grinder for grinding, and then sequentially cleaning, drying, screening and polishing.
And S6, firstly carrying out nickel plating treatment on the polished ball, cleaning and then carrying out solder plating treatment on the ball to obtain the copper core ball, wherein the thickness of the nickel layer is 2 mu m, the thickness of the solder layer is 5 mu m, and the diameter of the copper core ball is 300 mu m.
And S7, carrying out plating detection on the copper core balls plated with the brazing filler metal layer, and packaging finished products after the copper core balls are qualified.
As shown in FIGS. 1 and 2, by comparing the respective copper core balls having a diameter of 300 μm prepared in example 1, it was observed that the degree of roundness of the respective copper core balls was high and the difference in degree of roundness of the respective copper core balls was small.
As shown in fig. 3 and 4, the copper core ball with a diameter of 300 μm was obtained in example 1, the roundness was measured by the diameter method, the roundness= (D max-Dmin)/2,Dmax is the maximum diameter of the copper core ball, D min is the minimum diameter of the copper core ball, the roundness of the copper core ball in fig. 3 is 1.75 μm, 2.85 μm and 3.2 μm, respectively, and the roundness of the copper core ball in fig. 4 is 3.1 μm, so that the prepared copper core ball with a diameter of 300 μm has a roundness of less than 3.5 μm.
Example 2
The embodiment of the invention provides a preparation method of a copper core ball, which comprises the following steps:
s1, carrying out an electrolysis process on the copper block in a die cavity to obtain molten liquid.
And S2, introducing nitrogen downwards from the top end of the die cavity, extruding the molten liquid from the capillary under the action of nitrogen stamping and self gravity, and forming liquid drops in a near-separation state at the tail end of the capillary, wherein the flow speed of the nitrogen is 3mm 3/S, the stamping of the nitrogen is 80Pa when the molten liquid initially flows out, and the stamping of the nitrogen is 30Pa when the molten liquid stably flows out.
And S3, adding a magnetic induction coil which is electrified with alternating current at a liquid drop separation position of the capillary tube, so that the heating depth of the liquid drop is not less than 1.1mm, separating the liquid drop from a pipe orifice, and enabling the liquid drop to fall through the magnetic induction coil, wherein the falling track of the liquid drop through the magnetic induction coil is 10m.
And S4, the liquid drops fall into a liquid nitrogen cooling tank, and a sphere with high roundness is obtained through collection.
And S5, conveying the spheres into a ball grinder for grinding, and then sequentially cleaning, drying, screening and polishing.
And S6, firstly carrying out nickel plating treatment on the polished ball, cleaning and then carrying out solder plating treatment on the ball to obtain the copper core ball, wherein the thickness of the nickel layer is 3 mu m, the thickness of the solder layer is 30 mu m, and the diameter of the copper core ball is 400 mu m.
And S7, carrying out plating detection on the copper core balls plated with the brazing filler metal layer, and packaging finished products after the copper core balls are qualified.
Example 3
The embodiment of the invention provides a preparation method of a copper core ball, which comprises the following steps:
s1, carrying out an electrolysis process on the copper block in a die cavity to obtain molten liquid.
And S2, introducing nitrogen downwards from the top end of the die cavity, extruding the molten liquid from the capillary under the action of nitrogen stamping and self gravity, and forming liquid drops in a near-separation state at the tail end of the capillary, wherein the flow speed of the nitrogen is 5mm 3/S, the stamping of the nitrogen is 100Pa when the molten liquid initially flows out, and the stamping of the nitrogen is 50Pa when the molten liquid stably flows out.
And S3, adding a magnetic induction coil which is electrified with alternating current at a liquid drop separation position of the capillary tube, so that the heating depth of the liquid drop is not less than 2mm, separating the liquid drop from a pipe orifice, and enabling the liquid drop to fall through the magnetic induction coil, wherein the falling track of the liquid drop through the magnetic induction coil is 10m.
And S4, the liquid drops fall into a liquid nitrogen cooling tank, and a sphere with high roundness is obtained through collection.
And S5, conveying the spheres into a ball grinder for grinding, and then sequentially cleaning, drying, screening and polishing.
And S6, firstly carrying out nickel plating treatment on the polished ball, cleaning and then carrying out solder plating treatment on the ball to obtain the copper core ball, wherein the thickness of the nickel layer is 4 mu m, the thickness of the solder layer is 60 mu m, and the diameter of the copper core ball is 500 mu m.
And S7, carrying out plating detection on the copper core balls plated with the brazing filler metal layer, and packaging finished products after the copper core balls are qualified.
As shown in fig. 5, the present invention provides a copper core ball device 1 comprising a die cavity 2, a capillary tube 3, a magnetic induction coil 4, an induction power supply 5 and a cooling tank 6. The upper end of the die cavity 2 is provided with an air inlet punching opening 7 for introducing nitrogen, the capillary tube 3 is arranged at the bottom of the die cavity 2 and used for extruding molten liquid, the magnetic induction coils 4 are densely distributed and arranged at the longitudinal positions from the pipe orifice of the capillary tube 3 to the notch of the cooling groove 6 so as to enable liquid drops to pass through the magnetic induction coils 4, the induction power supply 5 is connected with the magnetic induction coils 4 so as to enable the magnetic induction coils 4 to generate an alternating magnetic field, and the cooling groove 6 is longitudinally opposite to the capillary tube 3 so as to enable the cooling groove 6 to collect the falling liquid drops. The apparatus provided by the present invention is further described below in connection with specific embodiments.
Example 4
The embodiment of the invention provides a copper nuclear sphere device 1, wherein the caliber of a tube orifice is 0.15mm, the inclination of the tube orifice and the inner wall of a capillary tube 3 is 115 degrees, the frequency of one induction power supply 5 is 70kHz, the power is 300kW, and the induction power supply 5 is alternating current.
Example 5
The embodiment of the invention provides a copper nuclear sphere device 1, wherein the caliber of a tube orifice is 0.20mm, the inclination of the tube orifice and the inner wall of a capillary tube 3 is 120 degrees, the frequency of one induction power supply 5 is 80kHz, the power is 300kW, and the induction power supply 5 is alternating current.
Example 6
The embodiment of the invention provides a copper nuclear sphere device 1, wherein the caliber of a tube orifice is 0.25mm, the inclination of the tube orifice and the inner wall of a capillary tube 3 is 125 degrees, the frequency of one induction power supply 5 is 90kHz, the power is 400kW, and the induction power supply 5 is alternating current.
It should be noted that the above-mentioned embodiments are merely for illustrating the technical solution of the present invention, and not for limiting the same, and although the present invention has been described in detail with reference to the above-mentioned embodiments, it should be understood by those skilled in the art that the technical solution described in the above-mentioned embodiments may be modified or some technical features may be equivalently replaced, and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solution of the embodiments of the present invention.
Claims (7)
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| JP2005066557A (en) * | 2003-08-27 | 2005-03-17 | Kyocera Corp | Method and apparatus for producing fine particles |
| CN105609437A (en) * | 2016-01-05 | 2016-05-25 | 重庆群崴电子材料有限公司 | Preparation method of gold-plated copper sphere or nickel and tin-plated copper sphere for three-dimensional (3D) package |
| CN106449422A (en) * | 2016-08-31 | 2017-02-22 | 大丰市德讯科技有限公司 | Preparation method of copper-core solder ball |
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| US4715878A (en) * | 1987-03-12 | 1987-12-29 | Gte Products Corporation | Process for producing finely divided spherical glass powders |
| DE4022648C2 (en) * | 1990-07-17 | 1994-01-27 | Nukem Gmbh | Method and device for producing spherical particles from a liquid phase |
| EP1286789A4 (en) * | 2000-05-22 | 2004-06-16 | Univ California | HIGH SPEED MANUFACTURE OF VERY SMALL SCALE METAL MICROSPHERES |
| US6562099B2 (en) * | 2000-05-22 | 2003-05-13 | The Regents Of The University Of California | High-speed fabrication of highly uniform metallic microspheres |
| CN104493186B (en) * | 2014-11-26 | 2017-06-27 | 大连理工大学 | A kind of preparation device and preparation method of uniform spherical microparticles |
| DE102019122000A1 (en) * | 2019-08-15 | 2021-02-18 | Ald Vacuum Technologies Gmbh | Method and device for dividing an electrically conductive liquid |
| CN114082969A (en) * | 2021-11-30 | 2022-02-25 | 中机凯博表面技术江苏有限公司 | A plasma remelting system and process for thermal spraying ultrafine powder |
| CN114850483B (en) * | 2022-04-28 | 2024-02-13 | 北华航天工业学院 | A device and method for quickly and efficiently screening uniform solder balls |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2005066557A (en) * | 2003-08-27 | 2005-03-17 | Kyocera Corp | Method and apparatus for producing fine particles |
| CN105609437A (en) * | 2016-01-05 | 2016-05-25 | 重庆群崴电子材料有限公司 | Preparation method of gold-plated copper sphere or nickel and tin-plated copper sphere for three-dimensional (3D) package |
| CN106449422A (en) * | 2016-08-31 | 2017-02-22 | 大丰市德讯科技有限公司 | Preparation method of copper-core solder ball |
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