A copper core ball and a preparation method and device thereof

Abstract

The application provides a copper core ball and a preparation method and device thereof. The preparation method of the copper core ball comprises the following steps: S1: preparing a copper block into a molten liquid, and extruding the molten liquid to form liquid drops in a nearly separated state at the pipe opening; S2: arranging a magnetic induction coil around the pipe opening separation point and falling track of the liquid drops, passing alternating current through the magnetic induction coil, and separating the liquid drops from the pipe opening and dropping along the falling track; and S3: sequentially cooling, grinding, screening and electroplating the liquid drops to obtain the copper core ball. The device for preparing the copper core ball comprises a mold groove, a capillary tube, a magnetic induction coil, an induction power source and a cooling tank. The application adopts the liquid drop magnetic induction separation and remelting technology to prepare a copper core ball with high roundness, thereby ensuring the stability and quality reliability of the electronic packaging interconnection space.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic component manufacturing, in particular to a copper core ball and a preparation method and device thereof. BACKGROUND

[0002] In recent years, with the miniaturization of electronic devices, in order to meet the market requirements of miniaturization, narrow spacing and multi-pin of electronic packaging, the size of the interconnection solder joint is continuously reduced, and the packaging technology represented by 3D stacked packaging emerges as the times require. 3D stacked packaging requires multiple thermal processes, and the traditional tin ball is easy to collapse, which cannot ensure the required space between PKGs, and is easy to cause bridging and cause short circuit of the pins, and has the problem of poor solder joint connection reliability. Therefore, the copper core tin-plated ball is used as the packaging material to ensure the required space between PKGs after reflow soldering.

[0003] In the process of 3D stacked packaging, the size consistency and roundness of the copper core ball play an absolute role in packaging quality. If different diameter solder balls with poor sphericity are used on the same electronic component, coplanarity problems will occur during packaging, which seriously affects the reliability of the solder joint and forms a solder joint defect. Therefore, the preparation of high roundness copper core ball is the key to solving the problem of maintaining the interconnection space of electronic packaging and product reliability. The traditional droplet forming method mainly cuts off the molten droplet adhesion force by external driving force, and applies magnetic force or vibration during the droplet separation process to quickly isolate the ball. However, this method is prone to form necking residues during droplet separation and condensation, and the external force will cause the ball to deform, the ball to be irregular, and the sphericity to be poor. In the process of chip packaging, poor sphericity is easy to cause the collapse of the solder joint, which cannot meet the use conditions. SUMMARY

[0004] The purpose of the present application is to prepare a high roundness copper core ball by using droplet magnetic induction separation and remelting technology, to ensure the stability and quality reliability of the interconnection space of electronic packaging.

[0005] To achieve the above purpose, the present application provides a preparation method of a copper core ball, comprising the following steps: S1: preparing a copper block into a molten liquid, and extruding the molten liquid to form a liquid droplet in a nearly separated state at the pipe opening; S2: setting a magnetic induction coil around the pipe opening separation point and the falling trajectory of the liquid droplet, the magnetic induction coil is connected to an alternating current, the liquid droplet is separated from the pipe opening and falls along the falling trajectory; S3: the liquid droplet is sequentially cooled, ground, screened and electroplated to obtain a copper core ball.

[0006] The application adopts magnetic induction segmentation remelting technology to prepare copper core ball with high roundness. The main method is as follows: when the liquid drops in the near separation state drop downward in the mold groove under the gas ramming, the magnetic induction coil of the induction power is installed around the falling segmentation point and the falling track, the magnetic induction segmentation remelting technology is used to promote the liquid drops in the near separation state to realize magnetic induction separation, reshape the spherical shape and realize no vibration deformation during segmentation.

[0007] Specifically, after the magnetic induction coil is supplied with alternating current, the alternating current generates alternating magnetic field through the magnetic induction coil, when the metal liquid drop is about to be separated, it is placed in the cutting alternating magnetic force line, so that the alternating current is generated in the metal liquid drop instantaneously, the induced current generates a closed control loop along the liquid drop to form eddy current, the eddy current makes the metal liquid drop spheroidize, and the atoms inside move at high speed in a random manner, collide and rub with each other to generate heat energy, so that the liquid drop is remelted. According to the volume and surface area formula, the surface area of the sphere is the smallest under the same volume, the surface tension generates an inward pulling force on the surface of the metal liquid drop, reduces the viscous force of the metal liquid drop, accelerates the separation of the liquid drop from the molten liquid in the capillary tube, and realizes self-separation; in addition, the surface tension has a branch force opposite to the gravity, so the shape of the sphere is not affected by the gravity, therefore, the metal liquid drop tends to be a high roundness sphere after remelting, and the spherical liquid drop prepared by the method is condensed to obtain a metal sphere with high roundness.

[0008] In any of the above technical solutions, S1 specifically comprises: S11: performing an electrolysis process on the copper block in the mold groove to obtain molten liquid; S12: under the action of nitrogen gas ramming and gravity, the molten liquid is extruded from the capillary tube to form liquid drops in the near separation state at the end of the capillary tube.

[0009] The copper block is prepared into molten liquid, and the electrolysis process is selected as a means to obtain the molten liquid. Since the melting point of copper is relatively high, the melting point is 1050-1100 DEG C, the molten liquid is often prepared by using ordinary heating means, which requires a very high temperature and has a high cost. The electrolysis method can not only ensure that the obtained metal molten liquid has high purity, but also ensure the connectability with other components in the preparation device, and realize the integration of preparation.

[0010] The nitrogen gas is injected into the mold groove, which can not only ensure that the molten liquid is not oxidized, but also can accelerate the extrusion of the molten liquid and improve the preparation efficiency.

[0011] In any of the above technical solutions, the liquid drop falls in the nitrogen atmosphere in S2.

[0012] The metal sphere is prepared in the nitrogen atmosphere, so that the molten liquid forms liquid drops at the end of the capillary tube under the wrapping of nitrogen, and the liquid drop is completely isolated from the surrounding air in the falling track to prevent the copper ball from being oxidized.

[0013] In any of the technical solutions above, S3 specifically comprises: S31: the liquid drop falls into the liquid nitrogen cooling tank to collect the spherical body; S32: the spherical body is ground, and then sequentially cleaned, dried, screened, and polished; and S33: the polished spherical body is first subjected to nickel plating layer treatment, and then subjected to solder layer treatment to obtain a copper core ball; wherein the solder layer comprises tin alloy.

[0014] The liquid nitrogen is used as the cooling agent of the liquid drop, which not only ensures that the liquid drop is rapidly cooled into a spherical body when falling into the cooling tank, but also avoids oxidation of the liquid drop due to reaction with other substances. The spherical body obtained by cooling is sent into a ball grinding machine for grinding to reduce the difference between the maximum diameter and the minimum diameter of the spherical body. The ground spherical body is cleaned and dried, and the spherical body of the required size is screened out from the inside for polishing. The purpose of polishing is to improve the roundness of the spherical body and to reduce the unevenness of the surface of the spherical body, thereby avoiding the formation of a metal compound between the nickel layer and the copper layer due to atomic mutual diffusion, and ensuring the performance of the product.

[0015] The polished spherical body is subjected to nickel plating layer treatment. On the one hand, the nickel layer can prevent the copper ball from being oxidized. On the other hand, the hardness of copper is small and easy to deform, and plating nickel on the surface of copper can improve the strength of the spherical body. In addition, plating nickel can prevent the migration of copper atoms and avoid copper coloration of the plating layer. Tin alloy is selected as the solder layer to be electroplated on the surface of the copper ball, which can avoid corrosion of the copper ball and realize solder joint interconnection through multiple heat processes due to the low melting point of the tin alloy.

[0016] In any of the technical solutions above, the thickness of the nickel layer is 2-4 μm; and / or the thickness of the solder layer is 5-60 μm; and / or the diameter of the copper core ball is 300-500 μm.

[0017] The selection of the appropriate thickness of the nickel layer and the solder layer can not only ensure that the copper core ball has a certain hardness, but also avoid oxidation and corrosion of the spherical body. The selection of the appropriate size of the copper core ball ensures the space required for electronic component packaging, and the copper core ball is not easy to collapse, that is, even after numerous heat processes, the copper core ball still exists in the solder pad and maintains the space.

[0018] In any of the technical solutions above, the roundness of the copper core ball is not higher than 3.5 μm.

[0019] In the packaging process of electronic components, the size consistency and roundness of the copper core ball play an absolute role in packaging quality. Different sizes and poor roundness of the solder balls can cause solder joint deviation and other phenomena in the packaging process, thereby causing equipment failure. The use of solder balls of different diameters and poor roundness on the same electronic component can cause coplanarity problems in the packaging process, seriously affecting the reliability of the solder joint and forming solder joint defects. Therefore, the copper core ball with close size and high roundness can ensure the stability of the packaging.

[0020] The application provides a copper core ball device, comprising a mold groove, a capillary tube, a magnetic induction coil, an induction power supply and a cooling tank; the magnetic induction coil is arranged between the mouth of the capillary tube and the upper end of the cooling tank, so that the liquid drop passes through the magnetic induction coil; the induction power supply is electrically connected with the magnetic induction coil, so that the magnetic induction coil generates an alternating magnetic field.

[0021] When the magnetic induction coil is supplied with alternating current, the magnetic induction coil generates an alternating magnetic field; when the metal liquid drop is extruded from the mouth and is in a state of being ready to be separated, the liquid drop at the mouth is in the cutting alternating magnetic field, so that an alternating current is generated in the metal liquid drop instantaneously. On one hand, the surface tension of the liquid drop generates an inward pulling force on the surface of the metal liquid drop, reduces the viscous force of the metal liquid drop, accelerates the separation of the liquid drop from the molten liquid in the capillary tube, and thus realizes self-separation; on the other hand, the induced current generates a closed control loop along the liquid drop to form an eddy current, the eddy current makes the metal liquid drop spheroidize, the atoms in the liquid drop move at a high speed in a random manner, the atoms collide with and rub against each other to generate heat energy, the liquid drop is melted again, and finally the copper ball with high roundness is prepared.

[0022] In any of the above technical solutions, the mold groove is provided with an air inlet stamping port for introducing nitrogen; the diameter of the mouth is 0.15mm-0.25mm; and the slope of the inner wall of the mouth and the capillary tube is 115°-125°.

[0023] The air inlet stamping port is arranged at the upper end of the mold groove, and the gas is punched into the groove to apply pressure to the molten liquid, so as to facilitate the extrusion of the molten liquid. The slope of the inner wall of the mouth and the capillary tube can ensure that the diameter of the obtained liquid drop is slightly larger than the diameter of the capillary tube.

[0024] In any of the above technical solutions, the length of the magnetic induction coil from the mouth to the cooling tank is 8m-12m; and the frequency of the induction power supply is 70kHz-90kHz.

[0025] The trajectory range of the liquid drop is from the mouth segmentation point to the falling trajectory, and the magnetic induction coil is arranged around the trajectory range, so as to ensure that the liquid drop undergoes a sufficient remelting process to obtain a ball with high roundness. At the mouth segmentation point, the liquid drop is in a state of being nearly separated, and under the action of the magnetic induction coil supplied with alternating current, the surface tension of the liquid drop generates an inward pulling force on the surface of the metal liquid drop, reduces the viscous force of the metal liquid drop, accelerates the separation of the liquid drop from the molten liquid in the capillary tube, and thus realizes self-separation.

[0026] When the magnetic induction coil is supplied with alternating current, the alternating current generates an alternating magnetic field through the magnetic induction coil, and when the metal liquid droplet is falling for separation, the metal liquid droplet is placed in the cutting alternating magnetic force line, so that the alternating current is generated in the metal liquid droplet instantaneously, the induced current generates a closed control loop along the liquid droplet to form an eddy current, the eddy current makes the metal liquid droplet spheroidize, and the atoms in the metal liquid droplet move at a high speed in a random manner, the atoms collide and rub with each other to generate heat energy, so that the liquid droplet is melted again.

[0027] The application provides a copper core ball, and the copper core ball is obtained by using the preparation method in any one of the preceding technical solutions, so that the copper core ball has the beneficial effects in any one of the preceding technical solutions, which will not be repeated here.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] The application adopts the magnetic induction separation and remelting technology to separate and remelt the falling copper core ball. In the process of separating the liquid droplet, the magnetic induction is used for separation, and under the condition of no vibration or external force, the liquid droplet is separated without necking and residual, and the formed ball is not deformed; after the liquid droplet is separated, the liquid droplet is melted again, and the liquid droplet is mainly affected by the surface tension, the surface tension generates an inward pulling force on the surface of the liquid droplet, and the liquid droplet is separated into a ball instantaneously, and the copper core ball prepared after condensation has no necking and residual, has high true circularity, and has a shiny surface. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and / or additional aspects and advantages of the application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

[0031] Figure 1 A true circularity comparison diagram of the copper core ball provided for the embodiment 1 of the application;

[0032] Figure 2 A structure schematic diagram of the copper core ball provided for the embodiment 1 of the application;

[0033] Figure 3 A true circularity electron microscope test diagram of the copper core ball provided for the embodiment 1 of the application;

[0034] Figure 4 A true circularity electron microscope test diagram of the copper core ball provided for the embodiment 1 of the application;

[0035] Figure 5 A preparation device diagram of the copper core ball provided for the embodiment of the application.

[0036] BRIEF DESCRIPTION OF DRAWINGS

[0037] 1-device; 2-mold groove; 3-capillary; 4-magnetic induction coil; 5-induction power supply; 6-cooling tank; 7-air inlet stamping port. DETAILED DESCRIPTION

[0038] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0039] 3D package requires multiple thermal processes, and the traditional material is tin ball for solder joint interconnection. However, after multiple reflow, the tin ball melts, and the weight of the multi-layer electronic components easily causes the tin ball to collapse, which leads to the inability to ensure the required space between the PKGs, and easily causes bridging and short circuit of the pins, and has the problem of poor solder joint connection reliability.

[0040] The biggest feature of the copper core solder ball is to ensure the required space between the PKGs after reflow. The copper core ball is composed of copper as the core and tin alloy plated on the surface. The melting point of copper is high, which is 1050-1100°C, and it will not melt in the solder packaging temperature range. Therefore, even after numerous thermal processes, the copper ball still exists in the solder pad and maintains the space, which is convenient for accommodating other electronic components for packaging, so as to realize high-density 3D packaging. The surface tin alloy can be subjected to multiple thermal processes for solder joint interconnection. The size and roundness of the copper core solder ball may cause the solder joint to deviate during the packaging process, thereby causing equipment failure.

[0041] The copper ball is plated with tin, but the copper core balls prepared by the atomization method and the plasma gasification method have the problems of different particle sizes and poor roundness. The copper core balls prepared by the mechanical ball milling method have poor quality reliability. The more mature technology is the liquid drop forming method. The liquid drop forming method is to transport the metal liquid to the pipe mouth through the capillary tube, slowly form a droplet at the end of the pipe mouth, and gradually increase the height of the droplet under the action of gravity as the volume of the droplet increases. The minimum neck width gradually decreases, so that it falls off and condenses into a ball. In order to make the sphericity higher and reduce the necking residue of the droplet viscous force, an external field driving such as vibration, pneumatic, magnetic force, etc. is usually used to realize the rapid separation of the droplet. The disadvantage is that when the height of the droplet gradually increases, the droplet condensation and crystallization occur, and the shape of the formed ball body deviates; the driving force also changes the shape of the metal ball body which is in the process of crystallization, causing the roundness of the ball body to decrease; at the same time, the necking residue also makes the surface of the ball body irregular.

[0042] Therefore, the application adopts magnetic induction segmentation remelting technology to segment and remelt the falling copper core ball. In the process of droplet separation, the magnetic induction is used for segmentation, and under the condition of no external force such as vibration, there is no necking residual in the process of droplet separation, and the formed ball is not deformed; after the droplet is segmented, it is remelted again, the droplet is mainly affected by the surface tension, the surface tension generates an inward pulling force on the surface of the droplet, and the droplet is separated into a ball in an instant, and the copper core ball prepared after condensation has no necking residual, high roundness and a shiny surface.

[0043] The embodiment of the application provides a preparation method of a copper core ball, which comprises the following steps: S1, preparing a copper block into a molten liquid, and extruding the molten liquid to form a droplet in a nearly separated state at the pipe opening; S2, arranging a magnetic induction coil around the pipe opening segmentation point and the falling track of the droplet, passing alternating current through the magnetic induction coil, and making the droplet separate from the pipe opening and fall along the falling track; and S3, sequentially cooling, grinding, screening and electroplating the droplet to obtain the copper core ball.

[0044] By adopting the magnetic induction segmentation remelting technology, the copper core ball with high roundness is prepared. When the droplet in the nearly separated state is pressed downward by gas in the mold groove, the magnetic induction coil of the induction power supply is arranged around the falling segmentation point and the falling track, the magnetic induction segmentation remelting technology is used to promote the droplet in the nearly separated state to realize magnetic induction self-separation, reshape the spherical shape and have no vibration deformation in the segmentation process, and finally the metal ball with high roundness is obtained.

[0045] In some embodiments of the application, S1 specifically comprises: S11, performing an electrolysis process on the copper block in the mold groove to obtain a molten liquid; and S12, extruding the molten liquid from the capillary under the action of nitrogen gas pressing and self gravity to form a droplet in a nearly separated state at the end of the capillary.

[0046] The copper block is prepared into a molten liquid, and the electrolysis process is selected as a means to obtain the molten liquid. Since the melting point of copper is relatively high, the melting point is 1050-1100 DEG C, and the use of ordinary heating means for melting often requires a very high temperature, which has a high cost. The electrolysis method used in the application can not only ensure that the purity of the obtained metal molten liquid is high, but also ensure the connectability with other components in the preparation device, and realize the integration of preparation. Nitrogen gas is injected into the mold groove, which can prevent the molten liquid from being oxidized, and the gas pressing can accelerate the extrusion of the molten liquid and improve the preparation efficiency. Preferably, the oxygen content in the nitrogen atmosphere is not higher than 0.001%.

[0047] In some embodiments of the application, the droplet falls in the nitrogen atmosphere in S2.

[0048] Preparation of the metal sphere is carried out under a nitrogen atmosphere, the molten liquid forms droplets at the end of the capillary under the wrapping of nitrogen, and it is ensured that the droplets are completely isolated from the surrounding air in the falling track to prevent the copper ball from being oxidized.

[0049] In some embodiments of the present application, S3 specifically comprises: S31: the droplets fall into a liquid nitrogen cooling tank to collect the spheres; S32: the spheres are ground, and then sequentially cleaned, dried, screened, and polished; S33: the polished spheres are first subjected to a nickel layer plating treatment, and then subjected to a solder layer plating treatment to obtain a copper core sphere; wherein the solder layer comprises a tin alloy.

[0050] Liquid nitrogen is used as the coolant of the droplets, which not only ensures that the droplets are rapidly cooled into spheres when falling into the cooling tank, but also avoids oxidation of the droplets due to reaction with other substances. The spheres obtained by cooling are sent into a sphere grinding machine for grinding to reduce the difference between the maximum diameter and the minimum diameter of the spheres, further improve the roundness of the spheres, and ensure that the roundness is not higher than 3.5 μm. The ground spheres are cleaned, dried, and screened to obtain the desired spheres of a certain size for polishing. The purpose of polishing is to improve the roundness of the spheres and reduce the unevenness of the surface of the spheres, thereby avoiding the formation of metal compounds between the nickel layer and the copper layer due to atomic mutual diffusion, and ensuring the performance of the product.

[0051] The polished spheres are subjected to a nickel layer plating treatment. On the one hand, the nickel layer can prevent the copper ball from being oxidized. On the other hand, the hardness of copper is small and easy to deform, and plating nickel on the surface of copper can improve the strength of the spheres. In addition, plating nickel can prevent the migration of copper atoms and avoid copper coloration of the plating layer. It should be noted that a certain roughness is required on the surface of the spheres to enable the nickel layer to be firmly attached to the surface of the spheres and prevent the nickel layer from falling off.

[0052] The solder layer comprises a tin alloy, which is preferably a tin-copper alloy, a tin-silver-copper alloy, or a tin-gold alloy. The tin alloy is selected as the solder layer to be plated on the surface of the copper ball to prevent corrosion of the copper ball, and the tin alloy as a low-melting-point material can be subjected to multiple heat processes to realize interconnection of the solder joints.

[0053] In some embodiments of the present application, the thickness of the nickel layer is 2 μm-4 μm; and / or the thickness of the solder layer is 5 μm-60 μm; and / or the diameter of the copper core sphere is 300 μm-500 μm.

[0054] Preferably, electroplating is used for both the nickel plating and solder plating processes. Selecting appropriate thicknesses for the nickel and solder layers not only ensures the copper core ball has a certain degree of hardness but also prevents oxidation and corrosion. Preferably, the nickel layer thickness is 2.5μm-3.5μm, and the solder layer thickness is 8μm-50μm. Choosing appropriate copper core ball dimensions ensures sufficient space for electronic component packaging, and the copper core ball is less prone to disintegration; even after numerous thermal processes, it remains within the pads and maintains its space. Preferably, the diameter of the copper core ball is 350μm-450μm. Those skilled in the art can select appropriate plating thicknesses according to their needs.

[0055] In some embodiments of the present invention, the sphericity of the copper core sphere is not higher than 3.5 μm.

[0056] In the packaging process of electronic components, the dimensional consistency and roundness of the copper core balls play an absolute role in the packaging quality. Inconsistent solder ball size and poor roundness can lead to solder joint misalignment during packaging, causing equipment failure. Using solder balls of different diameters and with poor sphericity on the same electronic component can cause coplanarity problems during packaging, seriously affecting solder joint reliability and resulting in solder joint defects. Therefore, copper core balls with similar dimensions and high roundness can ensure packaging stability.

[0057] An embodiment of the present invention also provides a device 1 for forming a copper core ball, comprising: a mold groove 2, a capillary tube 3, a magnetic induction coil 4, an induction power supply 5, and a cooling tank 6; wherein, the magnetic induction coil 4 is disposed between the opening of the capillary tube 3 and the upper end of the cooling tank 6, so that the droplet passes through the magnetic induction coil 4; the induction power supply 5 is electrically connected to the magnetic induction coil 4 to generate an alternating magnetic field.

[0058] like Figure 5 As shown, the cooling tank 6 is located at the lower end opposite to the opening of the capillary tube 3, and is used to collect the falling copper balls. A magnetic induction coil 4 is provided between the opening of the capillary tube 3 and the upper end of the cooling tank 6. The magnetic induction coil 4 is connected to the AC induction power supply 5. The magnetic induction coil 4 is densely arranged, and the falling droplets pass through the inside of the magnetic induction coil 4 and finally fall into the cooling tank 6 to form highly rounded spheres.

[0059] When the magnetic induction coil 4 is supplied with alternating current, the magnetic induction coil 4 generates alternating magnetic field. When the metal liquid droplet is at the separating state, the liquid droplet at the pipe orifice is in the cutting alternating magnetic force line, so that the alternating current is generated in the metal liquid droplet instantaneously. On one hand, the surface tension of the liquid droplet generates an inward pulling force on the surface of the metal liquid droplet, reduces the viscous force of the metal liquid droplet, accelerates the separation of the liquid droplet from the molten liquid in the capillary tube, and then realizes self-separation; on the other hand, the induced current generates a closed control loop along the liquid droplet to form eddy current. The eddy current makes the metal liquid droplet spheroidize, and the atoms in the liquid droplet move at high speed in a random manner, collide and rub with each other to generate heat energy, so that the liquid droplet is melted again, and finally the copper ball with high roundness is prepared.

[0060] In some embodiments of the present application, the mold groove 2 is provided with an air inlet port 7 for introducing nitrogen; and / or the diameter of the pipe orifice is 0.15mm-0.25mm; and / or the inner wall slope of the pipe orifice and the capillary tube 3 is 115°-125°.

[0061] Specifically, the mold groove 2 is used to contain the metal molten liquid. The electrolytic device can be arranged in the mold groove 2 to realize the process effect of preparing the molten liquid while extruding the liquid droplet, or the prepared molten liquid can be introduced into the mold groove 2 for preparation. The air inlet port 7 is arranged at the upper end of the mold groove 2, and the gas is rushed into the groove to apply pressure to the molten liquid, facilitating the extrusion of the molten liquid. The bottom of the mold groove 2 is provided with at least one capillary tube 3 for forming a liquid droplet with a size.

[0062] The purpose of the present application is to prepare a copper core ball with a diameter of 300μm-500μm, so the diameter of the pipe orifice is designed to be 0.15mm-0.25mm, preferably 0.18mm-0.22mm; the diameter of the obtained liquid droplet is slightly larger than the diameter of the capillary tube, and the inner wall slope of the pipe orifice and the capillary tube is 115°-125°, preferably 118°-122°. The pipe orifice is the liquid droplet separation point, and the slope is the angle between the pipe orifice plane and the inner wall of the conical pipe head. Those skilled in the art can select appropriate diameter and slope according to the size of the required copper core ball.

[0063] For example, nitrogen is rushed into the device space containing the metal molten liquid. The appropriate gas flow rate can ensure the smooth extrusion of the metal molten liquid. Preferably, the flow rate of nitrogen is 0.8mm 3 / s-5mm 3 / s, more preferably, the flow rate of nitrogen is 1.5mm 3 / s-4mm 3When the preparation of copper core ball is started, the molten liquid is not easy to flow out from the pipe orifice due to its viscosity, so a larger gas ram is needed to help the molten liquid flow out; in the subsequent extrusion process, the dynamic viscosity between the molten liquids exists, which reduces the flow resistance of the molten liquid, so the strength of the gas ram can be appropriately reduced. Preferably, when the molten liquid initially flows out, the nitrogen ram is 60 Pa-100 Pa; when the molten liquid stably flows out, the nitrogen ram is 10 Pa-50 Pa. Further preferably, when the molten liquid initially flows out, the nitrogen ram is 70 Pa-90 Pa; when the molten liquid stably flows out, the nitrogen ram is 20 Pa-40 Pa.

[0064] In some embodiments of the present application, the length of the magnetic induction coil 4 from the pipe orifice to the cooling tank 6 is 8 m-12 m; and / or the frequency of the induction power source 5 is 70 kHz-90 kHz.

[0065] Specifically, the trajectory range of the liquid droplet is from the pipe orifice division point to the falling trajectory, and the magnetic induction coil 4 is arranged around it to ensure that the liquid droplet undergoes sufficient remelting process to obtain a high-true roundness ball. At the pipe orifice division point, the liquid droplet is in a near-separation state, and under the action of the magnetic induction coil 4 with alternating current, the surface tension of the liquid droplet generates an inward pulling force on the surface of the metal liquid droplet, reduces the viscous force of the metal liquid droplet, and accelerates the separation of the liquid droplet from the molten liquid in the capillary tube 3, thereby realizing self-separation. The length of the magnetic induction coil 4 from the pipe orifice to the cooling tank 6 is 8 m-12 m, and the further preferred length is 9 m-11 m.

[0066] Electromagnetic induction heating is to use alternating electric field to generate alternating magnetic field, the heated object cuts the magnetic field, generates eddy current and heats itself; a complete induction heating system is composed of induction power source 5, magnetic induction coil 4 and falling liquid droplet. The advantage of electromagnetic induction heating is fast heating, good energy saving effect and high intelligentization. When the output power of the induction power source 5 is constant, the higher the frequency, the faster the heating speed, and under the same heating time, the heating depth will be reduced, so the appropriate induction frequency needs to be selected to ensure the heating speed while ensuring the heating depth of the liquid droplet. Preferably, the magnetic induction coil 4 of the present application uses an induction power source 5 with a frequency of 70 kHz-90 kHz, and the high-frequency induction heating power is suitable for thin layer or more refined grain rapid heating; more preferably, the frequency of the induction power source 5 is 75 kHz-85 kHz.

[0067] It should be noted that the power of an induction power supply 5 is limited and cannot meet the power required by the magnetic induction coil 4 in the present scheme, therefore multiple induction power supplies 5 can be installed, and the power of the induction power supply 5 can be preferably 300 kW, 400 kW, the induction power supply 5 is an alternating current, and those skilled in the art can select the power size and installation number of the induction power supply 5 according to their own needs. In addition, the selected induction power supply device needs to meet a certain heating depth, preferably, the heating depth from the surface to the inside is not less than 0.2 mm-2 mm, more preferably, the heating depth is not less than 0.3 mm-1.5 mm.

[0068] Embodiment 1

[0069] The embodiment of the present application provides a preparation method of copper core balls, comprising the following steps:

[0070] S1: electrolyzing a copper block in a mold groove to obtain a molten liquid.

[0071] S2: introducing nitrogen gas from the top end of the mold groove downward, under the action of nitrogen gas ramming and self gravity, the molten liquid is extruded from the capillary tube, and a liquid drop in a nearly separated state is formed at the end of the capillary tube; wherein the flow rate of the nitrogen gas is 0.8 mm / s, the ramming pressure of the nitrogen gas when the molten liquid initially flows out is 60 Pa, and the ramming pressure of the nitrogen gas when the molten liquid stably flows out is 10 Pa. 3

[0072] S3: installing a magnetic induction coil capable of passing alternating current at the liquid drop separation position of the capillary tube, so that the heating depth of the liquid drop is not less than 0.2 mm, the liquid drop separates from the pipe opening and falls through the magnetic induction coil, and the falling trajectory of the liquid drop through the magnetic induction coil is 10 m.

[0073] S4: the liquid drop falls into a liquid nitrogen cooling tank to collect high-true-roundness spherical bodies.

[0074] S5: sending the spherical bodies into a ball grinding machine for grinding, and then sequentially cleaning, drying, screening and polishing.

[0075] S6: the polished spherical bodies are first treated with a nickel plating layer, then cleaned and treated with a solder plating layer to obtain copper core balls; wherein the thickness of the nickel layer is 2 μm, the thickness of the solder plating layer is 5 μm, and the diameter of the copper core ball is 300 μm.

[0076] S7: performing plating layer detection on the copper core balls with the solder plating layer, and packaging the finished products after passing the detection.

[0077] As Figure 1 and Figure 2 shown, the diameters of the copper core balls prepared in Embodiment 1 are 300 μm, and it can be observed that the true roundness of each copper core ball is high, and the difference in the true roundness of each copper core ball is small.

[0078] As​Figure 3 and Figure 4 As shown in the figure, the copper core ball with a diameter of 300 μm is prepared by example 1, and the roundness is tested by the diameter method, that is, roundness = (D max -D min ) / 2, D max is the maximum diameter of the copper core ball, and D min is the minimum diameter of the copper core ball. By calculation, the roundness of the copper core ball in the three examples is 1.75 μm, 2.85 μm, 3.2 μm, Figure 3 respectively, and the roundness of the copper core ball in the fourth example is 3.1 μm. It can be seen that the roundness of the copper core ball with a diameter of 300 μm prepared is less than 3.5 μm. In summary, the roundness of the copper core ball prepared by the preparation method of the present application is higher. Figure 4

[0079] Example 2

[0080] The embodiment of the present application provides a preparation method of a copper core ball, comprising the following steps:

[0081] S1: performing an electrolysis process on the copper block in a mold groove to obtain a molten liquid.

[0082] S2: introducing nitrogen gas from the top end of the mold groove downward, and under the action of nitrogen gas ramming and its own gravity, the molten liquid is extruded from the capillary tube to form a liquid drop in a nearly separated state at the end of the capillary tube; wherein the flow rate of the nitrogen gas is 3 mm 3 / s, the ramming of the nitrogen gas when the molten liquid initially flows out is 80 Pa, and the ramming of the nitrogen gas when the molten liquid stably flows out is 30 Pa.

[0083] S3: installing a magnetic induction coil that passes alternating current at the liquid drop separation position of the capillary tube, so that the heating depth of the liquid drop is not less than 1.1 mm, and the liquid drop separates from the pipe opening and falls through the magnetic induction coil, and the falling track of the liquid drop through the magnetic induction coil is 10 m.

[0084] S4: the liquid drop falls into a liquid nitrogen cooling tank to collect a high-roundness ball.

[0085] S5: sending the ball into a ball grinder for grinding, and then sequentially performing cleaning, drying, screening and polishing.

[0086] S6: performing nickel layer plating treatment on the polished ball, and then performing solder layer plating treatment after cleaning to obtain a copper core ball; wherein the thickness of the nickel layer is 3 μm, the thickness of the solder layer is 30 μm, and the diameter of the copper core ball is 400 μm.

[0087] S7: performing plating layer detection on the copper core ball with the plated solder layer, and performing finished product packaging after passing the detection.

[0088] Example 3

[0089] ​An embodiment of the present invention provides a method for preparing copper core spheres, comprising the following steps:

[0090] S1: Electrolyze the copper block in the mold to obtain molten liquid.

[0091] S2: Nitrogen gas is introduced downwards from the top of the mold cavity. Under the pressure of the nitrogen gas and its own gravity, the molten liquid is extruded from the capillary, forming nearly separated droplets at the end of the capillary; the flow rate of nitrogen gas is 5 mm. 3 / s, the nitrogen pressure is 100Pa when the molten liquid initially flows out, and the nitrogen pressure is 50Pa when the molten liquid flows out steadily.

[0092] S3: Install an alternating current magnetic coil at the droplet separation point of the capillary tube so that the heating depth of the droplet is not less than 2mm. The droplet separates from the tube opening and falls through the magnetic coil. The trajectory of the droplet falling through the magnetic coil is 10m.

[0093] S4: The droplets fall into the liquid nitrogen cooling tank and are collected to obtain highly spherical spheres.

[0094] S5: The spheres are fed into a ball grinding machine for grinding, and then washed, dried, screened and polished in sequence.

[0095] S6: The polished sphere is first plated with a nickel layer, then cleaned and plated with a brazing filler layer to obtain a copper core sphere; wherein the thickness of the nickel layer is 4μm, the thickness of the brazing filler layer is 60μm, and the diameter of the copper core sphere is 500μm.

[0096] S7: Conduct plating inspection on the copper core balls after the brazing layer has been plated. If the plating is qualified, package the finished product.

[0097] like Figure 5 As shown, the present invention provides a device 1 for forming copper core spheres, comprising: a mold trough 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 mold trough 2 is provided with an air inlet 7 for introducing nitrogen gas; the capillary tube 3 is disposed at the bottom of the mold trough 2 for extruding molten liquid; the magnetic induction coils 4 are densely arranged in a longitudinal position from the opening of the capillary tube 3 to the opening of the cooling tank 6, allowing droplets to pass through the magnetic induction coils 4; the induction power supply 5 is connected to the magnetic induction coils 4 to generate an alternating magnetic field; the cooling tank 6 is longitudinally opposite to the capillary tube 3 to collect falling droplets. The device provided by the present invention will be further described below with reference to specific embodiments.

[0098] Example 4

[0099] The embodiment of the present application provides a copper core ball device 1, the caliber of the nozzle is 0.15mm; the inner wall slope of the nozzle and the capillary 3 is 115 °; wherein the frequency of an induction power supply 5 is 70 kHz, the power is 300 kW, and the induction power supply 5 is alternating current.

[0100] Example 5

[0101] The embodiment of the present application provides a copper core ball device 1, the caliber of the nozzle is 0.20mm; the inner wall slope of the nozzle and the capillary 3 is 120 °; wherein the frequency of an induction power supply 5 is 80 kHz, the power is 300 kW, and the induction power supply 5 is alternating current.

[0102] Example 6

[0103] The embodiment of the present application provides a copper core ball device 1, the caliber of the nozzle is 0.25mm; the inner wall slope of the nozzle and the capillary 3 is 125 °; wherein the frequency of an induction power supply 5 is 90 kHz, the power is 400 kW, and the induction power supply 5 is alternating current.

[0104] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a copper core ball, characterized by, The method comprises the following steps: S1: preparing a copper block into a molten liquid, and extruding the molten liquid to form liquid drops in a near-separation state at the tube opening; S2: arranging a magnetic induction coil around the tube opening separation point and falling track of the liquid drops, the magnetic induction coil being supplied with alternating current, the liquid drops being separated from the tube opening and falling along the falling track; S3: sequentially cooling, grinding, screening and electroplating the liquid drops to obtain copper core balls; S1 specifically comprises: S11: performing an electrolysis process on the copper block in a mold groove to obtain the molten liquid; S12: under the action of nitrogen gas ramming and self gravity, the molten liquid is extruded from the capillary tube to form the liquid drops in a near-separation state at the end of the capillary tube; S3 specifically comprises: S31: the liquid drops fall into a liquid nitrogen cooling tank to collect the spherical bodies; The true circularity of the copper core balls is not higher than 3.5 μm; The magnetic induction coil is arranged between the tube opening of the capillary tube and the upper end of the cooling tank, so that the liquid drops pass through the magnetic induction coil; and the induction power source is electrically connected with the magnetic induction coil, so that the magnetic induction coil generates an alternating magnetic field.

2. The production method according to claim 1, characterized by, The length of the magnetic induction coil from the tube opening to the cooling tank is 8 m-12 m; 3. The preparation method according to claim 1, characterized in that, The frequency of the induction power source is 70 kHz-90 kHz; and the magnetic induction coil makes the heating depth of the liquid drops not less than 2 mm. The liquid drops fall in a nitrogen atmosphere in S2. S3 specifically comprises: S31: the liquid drops fall into a liquid nitrogen cooling tank to collect the spherical bodies; S32: grinding the spherical bodies, and then sequentially cleaning, drying, screening and polishing the spherical bodies; S33: performing nickel plating on the polished spherical bodies, and then performing solder plating on the nickel-plated spherical bodies to obtain the copper core balls; The solder plating layer comprises tin alloy.

4. The preparation method according to claim 3, wherein: The thickness of the nickel plating layer is 2 μm-4 μm; and / or 5. A device (1) for use in a production method as claimed in any one of claims 1 to 4, characterized in that The thickness of the solder plating layer is 5 μm-60 μm; and / or The diameter of the copper core balls is 300 μm-500 μm. The device (1) comprises: a mold groove (2), a capillary tube (3), a magnetic induction coil (4), an induction power source (5) and a cooling tank (6); The magnetic induction coil (4) is arranged between the tube opening of the capillary tube (3) and the upper end of the cooling tank (6), so that the liquid drops pass through the magnetic induction coil (4); and the induction power source (5) is electrically connected with the magnetic induction coil (4), so that the magnetic induction coil (4) generates an alternating magnetic field.

6. The device (1) according to claim 5, wherein: The mold groove (2) is provided with a gas ramming port (7) for introducing nitrogen; and / or The diameter of the tube opening is 0.15 mm-0.25 mm; and / or The inner wall slope of the tube opening and the capillary tube (3) is 115°-125°.

7. The device (1) according to claim 5, wherein: The length of the magnetic induction coil (4) from the tube opening to the cooling tank (6) is 8 m-12 m; and / or The frequency of the induction power source (5) is 70 kHz-90 kHz.

Images