Curved surface welding spot partition welding method based on laser ball mounting equipment

Abstract

The invention relates to the technical field of electronic packaging and welding, and provides a curved surface welding spot partition welding method based on laser ball mounting equipment, which comprises the following steps of: firstly judging a critical inclination angle of a curved surface substrate, and dividing welding spots capable of accepting deformation deviation into a plurality of curved surface areas to be welded according to the critical inclination angle; and equipment comprising a laser ball mounting module, a three-dimensional five-axis module and a vacuum chamber is constructed, so that the brazing filler metal balls fall in vacuum along the Z axis. Convection heat dissipation, oxidation and airflow disturbance are restrained through vacuum, so that a large working distance exceeding a threshold exists between a nozzle arranged in the area and a to-be-welded face, welding spot deposition in the area is completed only by controlling X-axis linear motion and Y-axis linear motion, and the nozzle collision problem is avoided. And the superposed substrate moves and rotates during cross-region. According to the method, a three-dimensional five-axis interconnection task is simplified into a two-dimensional equal-step linear beat, the welding spot position precision, the morphology and the metallurgical quality are considered, and the efficiency and the yield of complex curved surface packaging are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electronic packaging and welding technology, and particularly relates to a curved surface welding spot partition welding method based on a laser ball planting device. BACKGROUND

[0002] With the booming development of 5G communication, Internet of Things and artificial intelligence technology, electronic devices are rapidly evolving towards miniaturization, flexibility and multi-functional integration. Traditional rigid planar circuits have been difficult to meet the demand for complex curved surface circuits in the fields of intelligent wearable devices, biomedical electronics, aerospace, etc. due to their limitation in two-dimensional structure. Conformal electronics technology has become a key direction to break through this limitation because it can conform to any curved surface. However, there are great challenges in realizing high-density and high-reliability three-dimensional interconnection on curved substrates - both to ensure the stability of electrical performance and to avoid damage to heat-sensitive substrates during processing. The current mainstream electronic packaging interconnection technologies have obvious limitations. Traditional processes such as reflow soldering and wave soldering require overall heating, which not only has high energy consumption, but also produces thermal stress concentration on heat-sensitive materials (such as flexible polymer substrates), leading to substrate deformation or device failure. While low-temperature interconnection methods such as conductive adhesive bonding avoid thermal damage, they have problems such as unstable conductive performance and poor long-term reliability. Especially in the context of three-dimensional interconnection on complex curved surfaces, how to achieve micron-level precision of the solder positioning while ensuring the strength and air tightness of the metallurgical bonding has become a key technical bottleneck restricting the development of curved surface circuits. Compared with traditional processes such as reflow soldering and wave soldering, laser ball implantation soldering as a new type of laser micro-connection technology uses a high-energy density laser beam as a heating source to directly heat and melt pre-formed solder balls (40-760um in diameter) in a short time, forming micro-droplets, and depositing them on the welding position by nitrogen, and completing the metallurgical interconnection using the energy it carries. During the welding process, the laser power is low and the laser action time is milliseconds, which makes the heat input of the laser micro-droplet soldering process extremely small. At the same time, the implantation nozzle can be precisely positioned to the welding position to achieve local heating. Due to the small volume of the solder ball and the small amount of heat carried, its thermal cycle time is only tens of milliseconds, which makes the microstructure of the implantation solder joint fine and the mechanical properties good. Therefore, laser micro-droplet soldering technology has the characteristics of no need for pre-placed solder, local heating, fast heating and cooling, fine microstructure of solder joint, etc., and is expected to be applied to the three-dimensional packaging of functional devices on complex curved surface circuits. However, there are two main problems in the process of welding interconnection of curved surface devices. The first problem is the welding efficiency. Since the laser ball implantation process can only weld one solder joint at a time, a large part of the time is spent on the displacement of the laser ball implantation assembly and the workpiece when facing a large number of welding positions distributed on the curved surface, which greatly reduces the welding efficiency. At the same time, due to the working distance of the traditional laser ball implantation process being about 1mm during the welding process, there is a problem of nozzle and workpiece collision during movement, and excessive increase in working distance will cause the solder ball to randomly deviate and overcool in the air. The second problem is that the solder ball has a certain kinetic energy during the falling process, which makes it obtain a good solder joint morphology on the horizontal surface, but on the inclined surface, there is a problem of solder joint deviation and elongation caused by solder collision and rebound. APPLICATION CONTENT

[0003] In view of the deficiencies in the prior art, the present application provides a curved surface soldering point partition welding method and device based on a laser ball planting device, which can effectively reduce the soldering point deviation and elongation caused by the collision and rebound of the filler metal, and improve the welding efficiency and precision.

[0004] In a first aspect, the present application provides a curved surface soldering point partition welding method based on a laser ball planting device, comprising: determining a critical inclination angle of the curved surface substrate, and dividing all soldering points on the curved surface substrate that can be deformed and deviated into the same to-be-welded curved surface area, and the inclination angle of the curved surface formed by all soldering points in the same to-be-welded curved surface area does not exceed the critical inclination angle; A laser ball planting device based on a three-dimensional five-axis vacuum platform is provided, the laser ball planting device comprises a laser ball planting module, a three-dimensional five-axis module and a vacuum chamber, the laser ball planting module is installed on the Z-axis of the three-dimensional five-axis module, the filler metal balls are in a vacuum environment of the vacuum chamber during falling; the three-dimensional five-axis module has five-axis movement of X, Y, Z axes and two rotation degrees of freedom, the five-axis movement is used to drive the laser ball planting module to any target position to adapt to laser ball planting soft soldering on a complex curved surface; When all soldering points divided into the same to-be-welded curved surface area accept welding of the laser ball planting device, the nozzle of the laser ball planting module has a large working distance from the to-be-welded surface distance exceeding a threshold value, only the X and Y axis plane movement of the laser ball planting device is controlled to complete soldering point deposition of all filler metal balls divided into the same to-be-welded curved surface area; when all soldering points divided into different to-be-welded curved surface areas accept welding of the laser ball planting device, the laser ball planting device is controlled by five-axis linkage to cross different to-be-welded curved surface areas to complete soldering point deposition of all filler metal balls in different to-be-welded curved surface areas.

[0005] In a second aspect, the present application provides a laser ball planting device using the above-mentioned curved surface soldering point partition welding method based on a laser ball planting device.

[0006] Compared with the prior art, the present application has the following beneficial effects: The application provides a curved surface soldering point partition welding method based on a laser ball planting equipment, which comprises the following steps: determining a critical inclination angle of a curved surface substrate, and dividing all soldering points on the curved surface substrate which can be deformed and deviated into a same to-be-welded curved surface area, and the inclination angle of the curved surface formed by all soldering points in the same to-be-welded curved surface area is not more than the critical inclination angle; setting a laser ball planting equipment based on a three-dimensional five-axis vacuum platform, wherein the laser ball planting equipment comprises a laser ball planting module, a three-dimensional five-axis module and a vacuum chamber, the laser ball planting module is installed on a Z-axis of the three-dimensional five-axis module, and solder balls are in a vacuum environment of the vacuum chamber during falling; the three-dimensional five-axis module has five-axis movement of X, Y and Z axes and two rotation degrees of freedom, and the five-axis movement is used to drive the laser ball planting module to any target position to adapt to laser ball planting and soft soldering on a complex curved surface; when all soldering points in the same to-be-welded curved surface area are subjected to welding by the laser ball planting equipment, the distance between a nozzle of the laser ball planting module and a to-be-welded surface is a large working distance exceeding a threshold value, only the X and Y axis plane movement of the laser ball planting equipment is controlled to complete soldering point deposition of all solder balls in the same to-be-welded curved surface area; when all soldering points in different to-be-welded curved surface areas are subjected to welding by the laser ball planting equipment, the laser ball planting equipment is controlled by five-axis linkage to cross different to-be-welded curved surface areas to complete soldering point deposition of all solder balls in different to-be-welded curved surface areas. In the application, the solder balls are in the vacuum environment of the vacuum chamber during falling, which can avoid excessive cooling of the solder balls due to convection heat exchange, excessive deviation of the solder balls due to environmental airflow disturbance and quality decline of the soldering points caused by oxidation of high-temperature molten solder balls, thereby breaking through the working distance limitation of the existing laser ball planting equipment and greatly increasing the distance between the nozzle and the to-be-welded surface. In addition, the three-dimensional five-axis module has five-axis movement of X, Y and Z axes and two rotation degrees of freedom, which can adapt to laser ball planting and soft soldering on a complex curved surface; when partition welding is performed, the soldering point inclination angle of all soldering points in a to-be-welded curved surface area is less than the critical inclination angle, the distance between the nozzle of the laser ball planting module and the to-be-welded surface is a large working distance exceeding a threshold value, only the X and Y axis plane movement of the laser ball planting equipment is controlled to complete soldering point deposition of all solder balls in the same to-be-welded curved surface area, and the nozzle and the workpiece do not collide, which greatly improves the welding efficiency; the laser ball planting equipment is controlled by five-axis linkage to cross different to-be-welded curved surface areas to complete soldering point deposition of all solder balls in different to-be-welded curved surface areas. By the method of the application, when large-scale soldering point forming processing is performed on a complex curved surface, the welding efficiency can be greatly improved while the soldering point deposition precision and forming appearance are ensured, and the frequent displacement of the laser ball planting assembly and the workpiece is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0007] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings: Fig. 1 is a front view and a top view of a laser ball placement device used in a curved surface solder joint partitioning welding method according to an embodiment of the application; Fig. 2 is a schematic diagram of two methods for quantifying the solder joint deformation offset of the predicted morphology of a solder joint on a curved surface substrate according to an embodiment of the application; Fig. 3 is a schematic diagram of the state of solder joint area division on a curved surface substrate according to an embodiment of the application. DETAILED DESCRIPTION

[0008] In order to make the technical personnel in the art better understand the present application, the technical solutions in the embodiments will be clearly and completely described below with reference to the drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work should fall within the scope of protection of the present application.

[0009] Referring to Figs. 1-3 , the present application provides a curved surface solder joint partitioning welding method based on a laser ball placement device, comprising the following steps: determining a critical inclination angle of the curved surface substrate, and dividing all the solder joints with acceptable deformation offset on the curved surface substrate in the same to-be-welded curved surface region, the inclination angle of the curved surface formed by all the solder joints in the same to-be-welded curved surface region being not more than the critical inclination angle; setting a laser ball placement device based on a three-dimensional five-axis vacuum platform, the laser ball placement device comprising a laser ball placement module, a three-dimensional five-axis module, and a vacuum chamber, the laser ball placement module being installed on the Z-axis of the three-dimensional five-axis module, the solder balls being in a vacuum environment in the vacuum chamber during the falling process, so as to avoid excessive cooling of the solder balls due to convection heat exchange, excessive offset of the solder balls due to environmental airflow disturbance, and quality decline of the solder joints due to oxidation of the high-temperature molten solder balls; the three-dimensional five-axis module has five-axis movement with X, Y, Z axes and two rotational degrees of freedom, and the five-axis movement is used to drive the laser ball placement module to any target position, so as to adapt to laser ball placement soft soldering on a complex curved surface; For all the welding points divided in the same surface area to be welded, the nozzle of the laser ball placement module is set to a large working distance beyond the threshold distance from the surface to be welded, and only the X and Y axis linear motion is controlled to complete the deposition of all the welding points of the solder balls in the same surface area to be welded; for all the welding points divided in different surface areas to be welded, the laser ball placement module is controlled by five-axis linkage to cross different surface areas to be welded to complete the deposition of all the welding points of the solder balls in different surface areas to be welded.

[0010] It should be noted that in the embodiment, the critical inclination angle of the curved substrate is first determined, and the welding points are divided into several surface areas to be welded according to the acceptable deformation offset; the equipment comprising a laser ball placement module, a three-dimensional five-axis module and a vacuum chamber is configured; the distance between the nozzle and the surface to be welded is set to a large working distance beyond the threshold distance in the same area, and only the X and Y axis linear motion is controlled to complete the deposition of all the welding points in the area; when crossing the area, the movement and rotation of the curved substrate are superimposed, which can solve the problem of slow pace and low efficiency caused by frequent multi-axis linkage and path re-planning in the welding of large quantities of discrete welding points on curved surfaces, and at the same time, the mechanism of avoiding collision between the nozzle and the workpiece is clear and is guaranteed by the large working distance, and the morphology instability caused by air convection cooling, air flow disturbance and oxidation of the solder balls is inhibited by the vacuum chamber, realizing the decomposition of the three-dimensional interconnection task of discrete points into efficient pace organization of two-dimensional equal-step linear motion in the area, and significantly improving the output and yield per unit time of complex curved surface electronic packaging under the premise of ensuring safety gap and welding point quality consistency.

[0011] It should be noted that the solder ball is in the vacuum environment of the vacuum chamber during falling, which can avoid excessive cooling of the solder ball due to convective heat transfer, excessive deviation due to environmental airflow disturbance, and quality decline of the welding spot caused by oxidation of the high-temperature molten solder ball, thereby breaking through the working distance limitation of the existing laser ball planting equipment and greatly increasing the distance between the nozzle and the surface to be welded. In addition, the three-dimensional five-axis module has five-axis movement of X, Y, Z axes and two rotation degrees of freedom, which can adapt to laser ball planting and soldering on complex curved surfaces; when partition welding is performed, the welding spot inclination angle of all welding spots in a curved surface region to be welded is less than the critical inclination angle, the distance between the nozzle of the laser ball planting module and the surface to be welded is a large working distance exceeding the threshold value, and only the X and Y axis plane movement of the laser ball planting equipment is controlled, so that the welding spot deposition of all solder balls in the same curved surface region to be welded can be performed without collision between the nozzle and the workpiece, thereby greatly improving the welding efficiency; the five-axis linkage is used to cross different curved surface regions to be welded to complete the welding spot deposition of all solder balls in different curved surface regions to be welded. Through the method of the present application, when large-scale welding spot forming is performed on a complex curved surface, the welding spot deposition accuracy and the formed appearance can be ensured while the frequent displacement of the laser ball planting assembly and the workpiece is greatly reduced, and the welding efficiency is improved.

[0012] Preferably, the inclination angle of the curved surface is the included angle between the falling direction of the solder and the normal direction of the curved surface to be welded, and the value is between 0°-70°.

[0013] Preferably, when determining the critical inclination angle of the curved surface substrate, the following steps are included: a numerical model is established according to the actual working condition of the curved surface substrate, and the inclination angle of the curved surface substrate in the numerical model is changed to obtain the welding spot predicted appearance on the curved surface substrate under different inclination angles; the welding spot deformation deviation of the welding spot predicted appearance on the curved surface substrate is quantified, the welding spot deformation deviation of the welding spot predicted appearance on the curved surface substrate obtained by quantification is compared with a preset welding spot deformation deviation acceptable range, and the critical inclination angle of the curved surface substrate is determined.

[0014] In this embodiment, a numerical model is established according to the actual working condition, the system changes the inclination angle of the curved surface to obtain the welding spot predicted appearance; the welding spot deformation deviation of the predicted appearance is quantified and compared with the preset acceptable interval, thereby determining the critical inclination angle of the curved surface substrate, which can solve the problems of strong subjectivity, high trial and error cost, poor migration to different curved surfaces, materials and pad designs caused by relying on experience or small sample welding to determine the weldable angle, and realize the measurability, traceability and reusability of the critical inclination criterion. Once the critical angle is objectified, the region division can be pre-positioned to the process planning stage, and the boundary conditions can be physically verified by using only X and Y linear motion in the region, thereby reducing the number of cross-region rotation and reset and ensuring that the deposited appearance and deviation are within the controlled range.

[0015] Preferably, the vacuum chamber is connected with a vacuum pump, which provides 10 2 -10 -1 Pa or 10 -1 -10 -5 Pa or above, the vacuum chamber is a good airtight sealing space to reach a preset airtight level.

[0016] In this embodiment, the ball placement is carried out in the vacuum chamber with good airtightness, and the falling process is in 10 2 -10 -1 Pa or 10 -1 -10 -5 Pa or above, which can solve the problems of excessive cooling caused by convective heat exchange when the solder ball flies in the air, random deviation caused by environmental airflow disturbance, and oxidation film growth caused by high temperature exposure, and realize the triple steady-state control of the droplet heat, trajectory and surface state. Vacuum inhibits convection and turbulence, so that the microspheres with small heat carrying capacity still maintain appropriate fluidity before reaching the pad, and regular wetting shape and dense metallurgical bonding are more easily obtained by local heating of the substrate; limited oxidation also reduces the probability of inclusion and crack initiation. Therefore, under different normal directions and local curvature changes of the curved surface, the repeatability and strength of the solder joint morphology can still be maintained, which provides quality assurance for the efficiency strategy of subsequent X and Y plane high-speed scanning in the region.

[0017] Preferably, the ball placement module of the laser ball placement module is connected with a gas flow meter, and the gas flow meter is connected with a vacuum pump for communication, and the vacuum pump clears the previous data in the gas flow meter after each start, so as to ensure that the gas flow meter calculates the amount of nitrogen discharged from the nozzle after the last working of the vacuum pump.

[0018] In this embodiment, the gas pipe of the laser ball placement module is connected with the gas flow meter and communicates with the vacuum pump, and the previous data of the flow meter is cleared after each vacuum cycle, and only the amount of nitrogen discharged from the nozzle after the last cycle is calculated, which can solve the problems of difficult accurate accounting of nitrogen protection and boosting amount in batch and batch, leading to unrepeatable droplet stress and flying amount, thereby causing deposition deviation and solder joint morphology fluctuation, realize the process measurement and tracking of segmenting, clearing and recalculating the corresponding nitrogen dose of each vacuum cycle section. Once the amount of nitrogen is quantified, it can be related to quality control such as center deviation of solder joint, contact angle and elongation rate, and a data-based process window is formed; at the same time, overblowing is avoided to cause energy consumption to rise and the solder ball to be supercooled. Finally, stable falling trajectory and landing point consistency are obtained without sacrificing vacuum protection and exhaust cleanliness, which supports higher qualified number per unit time for straight-line rhythm in the region.

[0019] Preferably, the vacuum degree in the vacuum chamber is monitored in real time by a vacuum degree sensor, and the air pressure in the vacuum chamber is automatically adjusted when the vacuum degree is lower than a threshold. In this case, the vacuum degree sensor is arranged in the vacuum chamber for detecting the vacuum degree, and the vacuum chamber is connected to a vacuum pump through a vacuum pump air pipe. When the vacuum degree in the vacuum chamber is lower than the threshold, the vacuum pump is started, and when the vacuum degree reaches the threshold, the vacuum pump is stopped.

[0020] In this embodiment, the vacuum degree sensor is arranged in the vacuum chamber to detect the vacuum degree in real time and control the vacuum pump in linkage: the pump is started when the vacuum degree is lower than a threshold, and the pump is stopped when the vacuum degree reaches the threshold. This can solve the problem of uncertain cooling rate of molten droplets and surface tension state caused by vacuum fluctuation, thereby coupling the wetting and contact angle fluctuation of the welding point, and realize closed-loop stable pressure control and energy-saving control of the environmental pressure. The steady-state vacuum keeps the heat exchange boundary condition experienced by the solder ball consistent, avoiding the morphology drift of the same formula but different batches; the threshold control reduces the frequent start and stop of the pump and energy waste, so that the equipment can still maintain a uniform microenvironment when running straight at high speed in a long time region.

[0021] Preferably, the laser ball placement module is used to place solder balls with a diameter of 50-1200 microns.

[0022] Preferably, when determining the critical tilt angle of the curved substrate, the determination condition of the critical tilt angle is the degree of welding point offset or deformation at different tilt angles; when the degree of welding point offset or deformation at a certain tilt angle reaches a threshold, the corresponding angle is the critical tilt angle.

[0023] Preferably, when determining the critical tilt angle of the curved substrate, the determination condition of the critical angle is the degree of welding point center offset at different tilt angles; when the degree of welding point center offset at a certain tilt angle reaches a threshold, the corresponding angle is the critical tilt angle.

[0024] In this embodiment, the degree of welding point center offset at different tilt angles is used as the critical angle criterion, and when the center offset reaches a threshold, the corresponding angle is defined as the critical tilt angle, which can solve the problem of uncontrollable positioning accuracy caused by subjective judgment based on appearance or estimation of indirect indicators such as contact line length, and realize the determination of the weldable boundary based on the landing point error, which is a direct quantitative indicator that determines the reliability of interconnection. With the threshold of center offset, the area with significant normal change on the curved surface can be excluded from the cross-region strategy, and the area with controlled offset can be included in the high-speed beat of only X and Y linear motion, thereby maximizing the coverage rate of linear motion and minimizing the number of rotations from the path planning level, and achieving a compromise and optimization of efficiency and quality in the same index system.

[0025] Preferably, when judging the critical tilt angle of the curved substrate, the critical angle judging condition is the difference of the contact angle of the solder joint at different tilt angles; when the difference of the advancing angle and receding angle of the contact angle of the solder joint at a certain tilt angle reaches a threshold value, the corresponding angle is the critical tilt angle.

[0026] In the embodiment, the difference between the advancing angle and receding angle of the contact angle of the solder joint at different tilt angles is taken as the critical angle criterion, and when the difference reaches a threshold value, the critical tilt angle is defined, which can solve the problem of only focusing on the landing point coordinates and ignoring the risk of wetting symmetry and interfacial tension gradient, avoid the appearance of elongation, tear drop or upwarping on the back slope and other morphology defects on the tilted surface, and realize the process boundary control with the core of wetting mechanical stability. The difference of the contact angle directly reflects the tension unevenness of the flow front and the withdrawal boundary, and once the threshold value is exceeded, it is easy to induce false welding, bridging or air tightness defects; as the criterion, the high-risk area of wetting asymmetry can be classified into the cross-region process step, and the area with good symmetry can be used for fast-paced deposition with only X and Y linear motion. Finally, while the efficiency is not reduced, the symmetry of the solder joint morphology, metallurgical density and subsequent air tightness, fatigue life are all included in the quantitative constraints, realizing the integrated optimization of appearance, structure and reliability of the curved interconnection.

[0027] Further, referring to Fig. 2 In the embodiment, the difference between the advancing angle and receding angle of the contact angle of the solder joint at different tilt angles is taken as the critical angle criterion, and when the difference reaches a threshold value, the critical tilt angle is defined, which can solve the problem of only focusing on the landing point coordinates and ignoring the risk of wetting symmetry and interfacial tension gradient, avoid the appearance of elongation, tear drop or upwarping on the back slope and other morphology defects on the tilted surface, and realize the process boundary control with the core of wetting mechanical stability. The difference of the contact angle directly reflects the tension unevenness of the flow front and the withdrawal boundary, and once the threshold value is exceeded, it is easy to induce false welding, bridging or air tightness defects; as the criterion, the high-risk area of wetting asymmetry can be classified into the cross-region process step, and the area with good symmetry can be used for fast-paced deposition with only X and Y linear motion. Finally, while the efficiency is not reduced, the symmetry of the solder joint morphology, metallurgical density and subsequent air tightness, fatigue life are all included in the quantitative constraints, realizing the integrated optimization of appearance, structure and reliability of the curved interconnection.

[0027] Further, referring to Fig. 2 In the embodiment, the difference between the advancing angle and receding angle of the contact angle of the solder joint at different tilt angles is taken as the critical angle criterion, and when the difference reaches a threshold value, the critical tilt angle is defined, which can solve the problem of only focusing on the landing point coordinates and ignoring the risk of wetting symmetry and interfacial tension gradient, avoid the appearance of elongation, tear drop or upwarping on the back slope and other morphology defects on the tilted surface, and realize the process boundary control with the core of wetting mechanical stability. The difference of the contact angle directly reflects the tension unevenness of the flow front and the withdrawal boundary, and once the threshold value is exceeded, it is easy to induce false welding, bridging or air tightness defects; as the criterion, the high-risk area of wetting asymmetry can be classified into the cross-region process step, and the area with good symmetry can be used for fast-paced deposition with only X and Y linear motion. Finally, while the efficiency is not reduced, the symmetry of the solder joint morphology, metallurgical density and subsequent air tightness, fatigue life are all included in the quantitative constraints, realizing the integrated optimization of appearance, structure and reliability of the curved interconnection.

[0028] Further, referring to Fig. 2 Fig. 6b, the solder deformation offset of the predicted morphology of the solder joint on the curved substrate is quantified, including: measuring the solder advancing angle θ a and the receding angle θ r , quantifying the solder deformation offset of the predicted morphology of the solder joint on the curved substrate by the difference θ a - θ r的 between the advancing angle θ a and the receding angle θ r ; the solder advancing angle θ a is the angle between the edge of the solder at the bottom of the slope of the curved substrate and the slope of the curved substrate, and the solder advancing and receding angle θ r is the angle between the edge of the solder at the top of the slope of the curved substrate and the slope of the curved substrate. It should be noted that in the laser ball placement process, the solder ball will often have a morphology offset when deposited on an inclined curved surface due to its falling kinetic energy, which is manifested as elongation or offset of the solder joint along the slope, resulting in asymmetric fitting of the front and rear edges of the solder joint to the curved surface. θ a characterizes the angle between the front of the solder joint (metal flow direction) and the slope, and if the solder flows smoothly and spreads well, the advancing angle is small; θ r characterizes the angle between the rear of the solder joint (solder retraction end) and the slope, and if the solder has difficulty climbing the slope or accumulates, the receding angle is larger; therefore, the larger the difference θ a - θ r , the more severe the deformation of the solder joint and the stronger the non-uniformity of the spread. This parameter can intuitively reflect the asymmetric morphology of the solder joint affected by the slope of the curved surface, and is helpful for quantitatively judging whether the solder joint is within the process acceptance range. Compared with the linear distance quantification based on coordinate measurement of x / D, the angle difference θ a - θ r as a dimensionless geometric index does not depend on the absolute size of the ball or the nozzle coordinate system, and has stronger universality for different specifications of solder and different process platforms, and can be used as a rapid evaluation index for multi-curvature welding areas to predict the solder joint qualification rate in advance and guide the optimization and adjustment of zoning planning. a The angle difference θ r , together with the critical offset angle threshold (for example: θ a - θ r ≤ 20°) as an acceptable morphology deformation criterion, can further refine the division criteria of each region and enhance the consistency of the solder joints within the region.

[0029] Preferably, the solder balls used to complete the solder joint deposition of all solder balls in the same to-be-welded curved surface region and to complete the solder joint deposition of all solder balls in different to-be-welded curved surface regions are SnAgCu, SnBi, SnPb, SnAu, SnIn, InPb, etc.

[0030] Preferably, when establishing the numerical model according to the actual working condition of the curved substrate, the following steps are included: establishing a calculation domain according to the inclination angle, the curvature of the curved substrate, and the diameter of the solder ball used; after the calculation domain is established, material properties are assigned according to the actual welding material used; after the material properties are assigned, boundary conditions related to the predicted morphology of the welding spot are set, and the numerical model is established; when assigning material properties according to the actual welding material used, the actual welding material used includes the type of solder ball used and the range of protective gas; the boundary conditions related to the predicted morphology of the welding spot include the nitrogen gas pressure inlet condition of the laser ball planting equipment, the pressure outlet condition, the heat exchange and wetting condition of the inner wall of the nozzle of the laser ball planting equipment, the heat exchange and wetting condition of the device pad welded with the curved substrate, the heat exchange and wetting condition of the solder resist area of the device pad welded with the curved substrate, the heat exchange and wetting condition of the curved substrate pad, and the heat exchange and wetting condition of the solder resist area of the curved substrate. It should be noted that the calculation domain is established by the inclination angle + curvature + solder ball diameter of the curved substrate, which truly reflects the three-dimensional space form of the welding spot deposition surface. Combined with the input of actual material properties and boundary conditions, the following coupled processes can be simulated, including but not limited to: cooperative simulation between heat, flow, gas, wetting, surface tension and other physical fields; considering the whole process of solder ball melting, flying, contacting, spreading and solidification, simulating the dynamic forming behavior of the welding spot; integrating comprehensive working conditions such as material type (such as SAC305), protective atmosphere (such as nitrogen purity and pressure), device structure (nozzle thermal boundary), etc. Such high-precision modeling helps to predict whether the welding spot in different areas can achieve the target morphology and offset tolerance in advance, providing data support for subsequent area division. By setting the nitrogen inlet pressure, outlet boundary, heat exchange / wetting characteristics of the inner wall of the nozzle and the substrate in different areas, the scheme in this embodiment can simulate the flying speed and landing point offset of the solder ball under different gas pressure / nozzle structures, evaluate the difference in solder melting / solidification rate under different heat exchange conditions, predict the final height, wetting angle, etc. of the welding spot, and identify the possible cold welding, virtual welding, and continuous welding areas. This series of settings greatly enhances the adaptability of the model to different material levels and local structure designs in real-world applications. At the same time, in the scheme provided in this embodiment, since complete material properties and boundary conditions are introduced, the model can construct an adaptive process window under the support of parameter scanning or optimization algorithm. For example: evaluating the best forming range under different nitrogen pressure and laser power combinations; comparing the effects of different solder ball types (such as SAC105, SAC305) on welding spot offset and spreading; optimizing the nozzle inner wall structure and flow field distribution to reduce the morphology distortion caused by jet offset. This not only helps to improve the efficiency of initial process development, but also can be used for simulation verification before actual production, reducing experimental cost and failure rate.

[0031] Preferably, the surface formed by all the welding points in one of the curved surface regions to be welded corresponds to one critical inclination angle, and the surface formed by all the welding points in the other of the curved surface regions to be welded corresponds to another critical inclination angle, so that all the welding points on the curved surface substrate are divided into a plurality of sub-surfaces, each of which corresponds to one critical inclination angle. It should be noted that in actual three-dimensional packaging or flexible electronic layout, the curved surface substrate often does not have a single curvature or consistent inclination angle, but has structural features such as multi-region curvature mutation and slope distribution difference. For example, the cylindrical surface and transition slope in wearable devices, and the complex curved surface distribution in medical probes or aviation structures. In the scheme provided in this embodiment, by assigning an independent critical inclination angle to each sub-surface, the welding point division can be more detailed, flexible and adaptive, and high-quality welding of special-shaped complex devices can be supported.

[0032] It should be noted that the present embodiment also provides a laser ball planting device, which uses the curved surface welding point partition welding method based on the laser ball planting device.

[0033] 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 that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for partitioned welding of curved surface weld points based on laser ball-planting equipment, characterized in that, include: Determine the critical tilt angle of the curved substrate, divide all the solder joints with acceptable solder joint deformation and displacement on the curved substrate into the same curved surface region to be soldered, and the tilt angle of the surface formed by all the solder joints divided into the same curved surface region to be soldered does not exceed the critical tilt angle. A laser ball-planting device based on a three-dimensional five-axis vacuum platform is set up. The laser ball-planting device includes a laser ball-planting module, a three-dimensional five-axis module, and a vacuum chamber. The laser ball-planting module is installed on the Z-axis of the three-dimensional five-axis module. The solder ball is in the vacuum environment of the vacuum chamber during its descent. The three-dimensional five-axis module has five-axis motion with X, Y, Z axes and two rotational degrees of freedom. The five-axis motion is used to drive the laser ball-planting module to any target position to adapt to laser ball-planting soft soldering on complex curved surfaces. When all solder joints in the same surface area to be soldered are being welded by the laser ball-planting device, the distance between the nozzle of the laser ball-planting module and the surface to be soldered is a large working distance exceeding the threshold. Only the X and Y axis planar movements of the laser ball-planting device are controlled to complete the solder joint deposition of all solder balls in the same surface area to be soldered. When all solder joints in different surface areas to be soldered are being welded by the laser ball-planting device, the laser ball-planting device is controlled across different surface areas to be soldered through a five-axis linkage to complete the solder joint deposition of all solder balls in different surface areas to be soldered.

2. The method for partitioned welding of curved surface weld points based on laser ball-planting equipment as described in claim 1, characterized in that, The inclination angle of the curved surface is the angle between the direction of the solder falling and the normal of the curved surface to be soldered, and its value is between 0° and 70°.

3. The method for partitioned welding of curved surface weld points based on laser ball-planting equipment as described in claim 1, characterized in that, Determining the critical tilt angle of a curved substrate includes: establishing a numerical model based on the actual working conditions of the curved substrate, and changing the tilt angle of the curved substrate within the numerical model to obtain the predicted solder joint morphology on the curved substrate at different tilt angles; quantifying the solder joint deformation offset of the predicted solder joint morphology on the curved substrate, comparing the quantized solder joint deformation offset of the predicted solder joint morphology on the curved substrate with a preset acceptable range of solder joint deformation offset, and determining the critical tilt angle of the curved substrate.

4. The method for partitioned welding of curved surface weld points based on laser ball-planting equipment as described in claim 1, characterized in that, The vacuum chamber is connected to a vacuum pump, which provides 10... 2 -10 -1 Medium vacuum degree of Pa or 10 -1 -10 -5 The vacuum chamber is a high vacuum level of over Pa, and is a well-sealed space with good airtightness to achieve a preset airtightness level.

5. The method for partitioned welding of curved surface weld points based on laser ball-planting equipment as described in claim 1, characterized in that, The vacuum level inside the vacuum chamber is monitored in real time by a vacuum sensor, and the air pressure inside the vacuum chamber is automatically adjusted when the vacuum level is lower than the threshold.

6. The method for partitioned welding of curved surface weld points based on laser ball-planting equipment as described in claim 1, characterized in that, The laser ball-planting module uses 50-1200 micrometer solder balls for ball planting.

7. The method for partitioned welding of curved surface weld points as described in any one of claims 1-6, characterized in that, When determining the critical tilt angle of a curved substrate, the criteria for determining the critical tilt angle are the degree of solder joint offset and deformation at different tilt angles; when the degree of solder joint offset or deformation reaches a threshold at a certain tilt angle, the corresponding angle is the critical tilt angle.

8. The method for partitioned welding of curved surface weld points based on laser ball-planting equipment as described in claim 1, characterized in that, When completing solder joint deposition for all solder balls in the same solderable surface area and when completing solder joint deposition for all solder balls in different solderable surface areas, the solder balls used are SnAgCu, SnBi, SnPb, SnAu, SnIn, or InPb series solder balls.

9. A laser-assisted ball-planting device, characterized in that, The laser ball-planting equipment uses the curved surface weld point partitioning welding method based on the laser ball-planting equipment as described in any one of claims 1-8.

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