High-temperature dense-spacing tiny through hole welding spot laser welding method

Abstract

The invention relates to a high-temperature dense-spacing tiny through hole welding spot laser welding method, belongs to the technical field of laser welding, and solves one of the problems of poor welding performance, poor welding spot morphology consistency and dependence on manual operation in the prior art. According to the method, through the steps of selecting proper welding flux, setting the reasonable number and size of the spraying balls, setting the segmentation technology, conducting automatic welding and the like, high-temperature welding of dense-interval tiny through hole welding spots is achieved through the laser spraying ball automatic welding equipment, the welding performance is excellent, the welding spot morphology consistency is good, and deartialization is effectively achieved.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding, and in particular to a high-temperature, dense-pitch, tiny through-hole solder joint laser welding method. Background Art

[0002] In recent years, laser ball welding has been gradually applied to many fields such as high-speed data lines, flexible circuit boards and various connectors, but the solders used in these applications are almost all lead-free alloys or 6337 alloys (Pb 63 Sn 37 ), the corresponding solder joint structures are all PIN (needle) / PAD (pad) type or "L" type. For through-hole pin type solder joints that have high requirements on solder transmittance, laser ball welding has rarely been used.

[0003] The assembly requirements of existing dual-polarized antennas are constantly increasing with the product application environment, and the assembly rate of such antennas is extremely sensitive to the solder joint morphology, so the requirements for through-hole pin solder joints are also increasing. However, due to the special working environment, the high melting point of solder, poor solderability, the solder joints are affected by the structural space, and the aperture and pad are limited, the welding is difficult.

[0004] The existing technology mostly uses manual welding to weld through-hole pin-type solder joints, especially the welding of fine-pitch through-holes. There are problems such as high dependence on operators, poor consistency of solder joint morphology, and unstable welding performance, which have a great impact on the subsequent assembly effect and efficiency of the antenna. Summary of the invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a high-temperature, fine-pitch, micro-through-hole solder joint laser welding method to solve one of the problems existing in the prior art, namely, high operator dependence, poor solder joint morphology consistency, and unstable welding performance.

[0006] The present invention discloses a laser welding method for high-temperature fine-pitch micro-through-hole solder joint welding, comprising the following steps:

[0007] S1: Select the appropriate solder according to the working environment of the solder joint, and estimate the solder volume according to the through-hole size of the pad on the printed circuit board;

[0008] S2: Determine the diameter and number of spray balls based on the estimated solder volume;

[0009] S3: Determine the segmented process according to the number of spray balls;

[0010] S4: setting welding power, time and gas pressure parameters in the process window of the laser ball spraying automatic welding equipment according to the determined segmented process;

[0011] S5: Adjust the distance between the nozzle and the pad, and the laser ball spray automatic welding equipment automatically completes the welding to obtain the final product.

[0012] Specifically, the estimated solder volume in step S1 is v is the solder volume, r1 is the pad through-hole radius, h is the through-hole depth, and r2 is the pad radius.

[0013] Specifically, the number of sub-process sections of the segmented process in step S3 corresponds to the number of spray balls.

[0014] Specifically, the number of the spray balls in step S2 is 2 and the volumes of the 2 spray balls are equal.

[0015] Specifically, the diameter of the pad is 0.5 mm, the diameter of the through hole is 0.35 mm, the depth of the through hole is 0.544 mm, and the diameter of the spray ball is 0.4 mm.

[0016] Specifically, the segmentation process described in step S3 is:

[0017] The first spray ball: spray pressure: 3±0.5kPa; the first stage welding power is 90±10W, the welding time is 2±0.5ms; the second stage welding power is 30±10w, the welding time is 50±5ms;

[0018] The second spray ball: spray pressure: 2±0.5kPa; welding power 30±10w, welding time 10±2ms.

[0019] Specifically, the solder liquidus is ≥300°C.

[0020] Preferably, the solder is Sn5Pb 95 , the liquidus is 312℃.

[0021] Specifically, the distance between the welding nozzle and the welding pad is 1 to 3 times the diameter of the corresponding spray ball.

[0022] Specifically, the diameter of the through hole of the pad is 0.3-0.4 mm, and the center distance between adjacent pads is 0.8-1 mm.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] 1. High-efficiency welding of high-temperature, dense-pitch, and tiny through-hole solder joints is achieved, with excellent welding performance. By reasonably selecting the diameter and number of the spray balls, the total volume of the spray balls matches the capacity of the through-hole pads, and the tin amount of the through-hole solder joints and the surface consistency of the solder joints are good; using a fiber laser and setting a reasonable spray pressure, time, and segmented process curve corresponding to the number of spray balls, fast and efficient welding is achieved, with good consistency of welding morphology, excellent welding performance, and fast welding reaction speed, and can achieve dense-pitch tiny solder hole welding.

[0025] 2. Eliminate manual labor and reduce dependence on operators. Laser welding uses fixed power, air pressure, and time to weld small through-hole solder joints with dense spacing, effectively avoiding individual differences in previous manual welding, and making the solder joint morphology more consistent.

[0026] 3. The welding is efficient and fast, and the heat affected range is small. In the past, the manual single soldering point took about 2s, but now a single soldering point is controlled within 70ms, which effectively avoids thermal damage to the pad and greatly reduces the risk of pad falling off and failure. It also plays an effective protective role for the solder joints of the jack components.

[0027] 4. Laser welding uses a φ0.4mm tiny spot to irradiate, which can achieve continuous welding of small welds with dense spacing, without weld defects such as continuous welding, remelting, and sharp edges.

[0028] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0030] Figure 1 A schematic diagram of the process of high-temperature, dense-pitch, micro-through-hole solder joint laser welding;

[0031] Figure 2 This is a schematic diagram of a 100% tinned pad through-hole in Example 1;

[0032] Figure 3 This is a photo of the initial state of the pad in Example 1;

[0033] Figure 4 This is a photo of the solder joint on the pad surface of Example 1;

[0034] Figure 5 This is a photo of the back side of the pad being tinned in Example 1;

[0035] Figure 6 is a metallographic image of a through-hole solder joint of Example 1;

[0036] Figure 7 This is a SEM photo of the through-hole solder joint of Example 1;

[0037] Figure 8 This is a photo of the solder joint on the pad surface of Comparative Example 1;

[0038] Fig. 9 This is a photo of the solder joint on the pad surface of Comparative Example 2;

[0039] Fig.10 This is a photo of the solder joint on the pad surface of Comparative Example 3. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0041] The present invention discloses a laser welding method for high-temperature fine-pitch micro-through-hole solder joint welding, comprising the following steps:

[0042] S1: Select the appropriate solder according to the working environment of the solder joint, and estimate the solder volume according to the through-hole size of the pad on the printed circuit board;

[0043] S2: Determine the diameter and number of spray balls based on the estimated solder volume;

[0044] S3: Determine the segmented process according to the number of spray balls;

[0045] S4: setting welding power, time and gas pressure parameters in the process window of the laser ball spraying automatic welding equipment according to the determined segmented process;

[0046] S5: Adjust the distance between the nozzle and the pad, and the laser ball spray automatic welding equipment automatically completes the welding to obtain the final product.

[0047] The present invention achieves 100% tinning rate and quick response welding of through-hole pads by setting appropriate spray ball diameter, quantity, segmented process and welding parameters, while ensuring the welding effect, avoiding thermal damage to the solder joints originally attached to the soldering ends of through-hole components and even the adverse effects of open welding.

[0048] In step S1, the solidus of the selected solder must be 10°C higher than the working environment to prevent the solder joint from melting during the working process and affecting reliability. The through hole size refers to the pad diameter, through hole depth, and through hole diameter. The estimated solder volume is the sum of the surface solder joint volume and the solder volume in the hole.

[0049] In step S2, the size and number of solder balls are determined based on the estimated solder volume and the conventional solder ball size mass conversion table in the industry. The spray ball sizes currently supported by common related equipment manufacturers are discrete values. According to the approximate size range of related standard parts in the application field of the present invention, spray ball diameters of 0.25, 0.29, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60 (unit: mm) can generally be selected, and the number of spray balls is determined based on the estimated solder volume and the volume of a single spray ball.

[0050] Before starting step S4 soldering, a layer of soldering flux needs to be applied on the surface of the pad (common practice in the industry), preferably a medium-active rosin-based flux (RMA type) specified in GB / T9491 that remains active above the solidus of the solder.

[0051] Specifically, the estimated solder volume in step S1 is v is the solder volume, r1 is the pad through hole radius, h is the through hole depth, and r2 is the pad radius. The first half of the formula The second half is the formula for calculating the through-hole volume. The formula for calculating the volume of a hemisphere with a radius of r2, which is the radius of the pad, is used to preliminarily estimate the solder volume, so there is no need to make corrections for the volume of the through hole occupied by the socket and the solder joint morphology that is not a standard hemisphere. In fact, since the socket occupies part of the volume in the through hole, and the solder joint morphology is a spherical crown with a volume smaller than that of a standard hemisphere, even considering the small amount of solder passing through the printed circuit board, the estimated solder volume is still excessive. It has been verified experimentally that a good welding effect can be achieved when the total volume of the spray ball (volume of a single spray ball * number of spray balls) is 75% to 100% of the estimated solder volume.

[0052] Specifically, the number of sub-process sections of the segmented process corresponds to the number of spray balls. The number of sub-process sections of the segmented process is equal to the number of spray balls, and the process parameter setting of a specific single sub-process section is closely related to the process goal that the corresponding spray ball needs to achieve. For example, if the preset technical goal of a spray ball is to complete the perforation and tinning, then the welding power in the parameter setting of the sub-process section should ensure that the spray ball can be fully melted and the spray pressure is sufficient to enable the spray ball to complete the perforation and tinning.

[0053] It is worth emphasizing that a single sub-process segment may contain multiple welding stages. For example, in Example 1, the sub-process segment corresponding to the first spraying of the solder ball contains two welding stages, which respectively achieve the technical goals of solder penetration and tinning and surface solder joint formation.

[0054] Preferably, the number of spray balls described in step S2 is 2 and the volumes of the 2 spray balls are equal. When determining the size and number of the spray balls according to the through-hole aperture of the pad and the estimated solder volume, it is also necessary to consider that the more spray balls there are, the greater the thermal shock to the pad; and single spray ball welding is prone to produce large bubbles, which leads to poor tinning. Experiments have shown that the welding effect is optimal when the number of laser spray balls is 2. The spray balls sprayed first complete the tinning of the through-holes, and the spray balls sprayed later form solder joints on the surface of the pad. In addition, according to the inherent characteristics of the solder box and the solder spraying device of the laser spray ball welding related equipment, the spray ball size is a preset standard value, and the size of the spray balls sprayed during the welding process is the same within the tolerance range, that is, the spraying of solder balls of different sizes is not supported during the rapid welding process.

[0055] Specifically, the diameter of the pad is 0.5 mm, and the diameter of the through hole of the pad is 0.3-0.4 mm, for example, the through hole diameter is 0.35 mm, and the through hole depth is 0.544 mm. According to the above-determined number of laser spray balls is 2, the spray ball diameter is obtained by querying the solder ball size mass conversion table as 0.4 mm. That is, the spray ball diameter is obtained by querying the solder ball size mass conversion table based on the estimated solder volume and when the number of spray balls is 2.

[0056] Specifically, the segmentation process described in step S3 is:

[0057] The first spray ball: spray pressure: 3±0.5kPa; the first stage welding power is 90±10W, the welding time is 2±0.5ms; the second stage welding power is 30±10w, the welding time is 50±5ms;

[0058] The second spray ball: spray pressure: 2±0.5kPa; welding power 30±10w, welding time 10±2ms.

[0059] The spray ball pressure refers to the pressure difference between the nitrogen filled in the pump head and the outside world. It is adjusted by the gas proportional valve of the pump head. This parameter controls the pressure difference between the inside and outside of the nozzle cavity when spraying the ball, as well as the oxygen content of the gas around the nozzle mouth. It affects the accuracy of the spray ball landing point, the degree of oxidation on the solder joint surface, and the temperature of the solder ball and solder joint during welding. If the air pressure is too high, the accuracy of the spray ball position will be worse, which may cause the top of the solder joint to be inclined. In severe cases, most of the spray ball will fall outside the pad area, resulting in the solder joint being completely unformed. If the air pressure is too low, it can be observed that the nozzle has obvious flames, serious dust accumulation, thickening of the oxide layer on the solder joint surface, and even cracks on the solder joint surface. After testing, the first spray ball can achieve full tinning and take into account the landing point accuracy when the spray pressure is in the range of 3±0.5kPa; the second spray ball does not need to pass through the through hole, so the spray pressure can be in the range of 2±0.5kPa.

[0060] If the power is too large and the welding time is too long, the solder joint will be subjected to excessive heat, the temperature will be too high, the glue layer between the pad metal and the substrate will be damaged, and the pad will fall off. At the same time, the amount of tin penetration is too large, the amount of tin in the front welding is insufficient, the appearance is poor, and the solder joint at the welding end is thermally damaged or even open. If the power is too small and the time is too short, the welding heat is insufficient, the amount of tin in the solder joint is small, the tin ball is not fully melted when it is sprayed out, and it sticks to the suction nozzle. When it falls on the pad, the solder joint surface is pointed, the wettability is poor, and the solder joint is raw. After testing, the first spray ball uses a welding power of 90±10W and a welding time of 2±0.5ms; a second welding power of 30±10w and a welding time of 50±5ms; the second spray ball uses a welding power of 30±10w and a welding time of 10±2ms. The process parameter settings can achieve high-quality welding.

[0061] The first section of the welding of the spray ball is to achieve solder melting and sufficient penetration of tin, so the welding power is relatively large. On the other hand, in order to prevent thermal damage to the material, the welding time is strictly controlled at about 2ms.

[0062] The present invention overcomes the problems of large heat source area, unstable welding performance and poor welding morphology consistency in manual welding by setting a segmented process (corresponding to step S3) that gradually reduces welding power, spray pressure and time, and adopts laser ball spray automatic welding equipment for welding. Specifically, the liquidus line of the solder is ≥300°C. This method can be widely used in the welding and assembly of dual-polarized antenna components. For example, such antennas need to work in a high temperature environment of about 280°C, and various electronic components need to be welded at a high density on the printed circuit board. Therefore, it is necessary to select a solder with a liquidus line of not less than 300°C for welding to avoid problems such as melting of solder joints under working conditions.

[0063] Preferably, the solder is Sn5Pb 95 , and its liquidus is 312°C. Compared with other high-temperature solders, this type of solder has stronger solderability, better solder joint wettability, and is conducive to subsequent metallographic analysis and SEM analysis.

[0064] Specifically, the distance between the welding nozzle and the welding pad is 1 to 3 times the corresponding laser spray ball diameter, preferably 2 times the laser spray ball diameter. The distance between the welding nozzle and the welding pad is set according to the common industry standards to ensure the stability of the welding effect.

[0065] Specifically, the through hole diameter of the pad is 0.3-0.4 mm, and the center distance between adjacent pads is 0.8-1 mm. Exemplarily, the through hole diameter can be 0.31 mm, 0.32 mm, 0.33 mm, 0.34 mm, 0.35 mm, 0.36 mm, 0.37 mm, 0.38 mm, 0.39 mm; the center distance between adjacent pads on the printed board can be 0.85 mm, 0.90 mm, 0.95 mm. The setting of the through hole diameter and the pad center distance is preset by the designer before the printed board is prepared according to the electrical performance requirements.

[0066] Specific examples and comparative examples:

[0067] The conventional parameters of the laser automatic welding equipment used in all the following embodiments and comparative examples are shown in Table 1:

[0068] Table 1 General parameters of laser automatic welding equipment

[0069]

[0070]

[0071] Embodiment 1:

[0072] Step 1: For the dual-polarized antenna working environment at 300°C, select the solder alloy composition as Sn5Pb 95 , liquidus 312℃.

[0073] Step 2: The pad diameter is 0.5mm, the pad thickness is 18μm, the through hole diameter of the pad is 0.35mm, the through hole depth is 0.544mm (the through hole depth is the sum of the printed circuit board thickness and the pad thickness, and the printed circuit board thickness is 0.526mm), and the center distance between adjacent pad holes is 0.8mm.

[0074] like Figure 2 As shown in the figure, the estimated solder volume after 100% tinning can be estimated to be 0.085mm 3 .

[0075] Step 3: Estimated solder volume is 0.085mm 3 , you can spray 3 spray balls with a diameter of 0.35mm, 2 spray balls with a diameter of 0.4mm, or 1 spray ball with a diameter of 0.5mm. The test shows that the more spray balls there are, the greater the thermal shock to the pad, and a single spray ball soldering is prone to produce large bubbles, which leads to poor tinning. Finally, it is preferred to spray 2 spray balls with a diameter of 0.4mm as the single-hole pad spray ball solder. Figure 5 As shown in the figure, the first spray ball completes the tinning of the through hole, and the second spray ball completes the solder joint morphology on the pad surface. This ensures that the morphology of continuous solder joints is consistent and the quality deviation of the solder ball is less than 1%.

[0076] Step 4: Fix the printed circuit board to the special tooling and clamp it to the welding equipment. The round copper wire to be welded needs to be trimmed flush with the welding pad before welding.

[0077] Step 5: Set the spray ball welding parameters as shown in Table 2. The process window of welding power is ±10 W. The laser welding equipment uses a 150 W fiber laser.

[0078] Table 2 Welding process parameters

[0079]

[0080] Step 6: Adjust the distance between the nozzle and the pad. The height between the nozzle and the pad is generally 1 to 3 solder ball diameters. In this embodiment, the distance between the nozzle and the pad is set to 2 solder ball diameters, that is, 0.8 mm.

[0081] Step seven, laser ball spray welding is performed on the fine-pitch through-hole solder joints according to the above process.

[0082] Solder joint morphology Figure 5 and Figure 6 As shown in the figure, according to IPC-TM-650 and GB / T 16594-2008, a professional testing agency was commissioned to observe the solder joints with a metallographic microscope and measure the thickness of the IMC with a SEM. The inspected solder joints have no abnormalities such as non-wetting and cracking, the tin-lead two-phase distribution and diffusion are uniform, the solder filling degree in the through-hole is 100%, and there is obvious IMC generation between the round copper wire and the printed circuit board pad in the SEM photo. The IMC layer generates tin-silver alloy on the round copper wire side and tin-copper alloy on the pad side. The IMC thickness is 1-2μm and the morphology is uniform. This analysis verifies that the quality of the solder joints is qualified, and the morphology of continuous solder joints is highly consistent, which greatly improves the production capacity of this type of antenna.

[0083] The solder joints have good appearance wetting, and the wetting angle is no more than 90 degrees. The solder joints are observed at 100 times magnification through a microscopic inspection device (capable of 360-degree inspection). There are no pinholes, pulled tips, and other poor appearances. The height difference between solder joints is no more than 0.2mm, and there is no bridging between solder joints and no raw solder joints.

[0084] Embodiment 2:

[0085] The first solder ball welding power and time settings are:

[0086] The first stage: 80W / 2ms; the second stage: 20W / 50ms, and the other steps and parameter settings are the same as those in Example 1. The solder joint morphology is qualified, and the amount of tin on the bottom is slightly less than that in Example 1.

[0087] Embodiment 3:

[0088] The ejection pressure of the second solder ball was set to 2.5 kPa, and the remaining steps and parameter settings were the same as those in Example 1. The solder joint morphology was qualified because the second solder ball mainly affected the external solder joints, and the ejection pressure increased, resulting in a slightly flat top and a wetting angle close to 90 degrees.

[0089] Comparative Example 1:

[0090] The laser power corresponding to the first solder ball is increased to 120W, and the other parameters and operations are exactly the same as those in Example 1. Figure 8 As shown in the figure, due to excessive power, the pad lifted up and the solder joint failed.

[0091] Comparative Example 2:

[0092] Use 3 φ0.35mm solder balls, and the soldering process curve is set as:

[0093] The first solder ball: the ejection pressure is 3kPa, the welding power and time are: 90W / 2ms for the first stage and 30W / 50ms for the second stage.

[0094] The second solder ball: the ejection pressure is 2 kPa, the welding power is 30 W, and the welding time is 10 ms;

[0095] The third solder ball: the ejection pressure is 2 kPa, the welding power is 30 W, and the welding time is 10 ms.

[0096] Other parameters and operations are exactly the same as those in Example 1. Fig. 9 As shown in the figure, since the amount of solder is equivalent to two φ0.4mm solder balls, the solder joint morphology is similar. However, due to the three solder balls, the soldering time is longer, the thermal shock to the pad is large, the proportion of pad shedding increases significantly, and due to the small diameter of the solder ball, the solder joint cannot cover the outer edge of the pad.

[0097] Comparative Example 3:

[0098] A φ0.5 mm solder ball was used, the spray pressure was 3 kPa, the welding power and time were: first stage: 90 W / 2 ms; second stage: 30 W / 60 ms, and other parameters and operations were exactly the same as in Example 1.

[0099] The volume of one φ0.5mm solder ball is equivalent to that of two φ0.4mm solder balls, but the void ratio inside the solder joint after soldering is higher for one φ0.5mm solder ball. Fig.10 As shown, large pores are easily generated on the surface of the solder joint, or large bubbles are formed due to the incomplete release of gas during the welding process. Such solder joints are prone to bursting bubbles on the surface of the solder joints after temperature changes and vibration shocks, and the solder joint quality is unqualified.

[0100] Comparative Example 4:

[0101] Three φ0.4mm solder balls are used, and the specific process parameters are set as follows:

[0102] The first solder ball: the ejection pressure is 3kPa, the welding power and time are: 90W / 2ms for the first stage and 30W / 50ms for the second stage.

[0103] The second solder ball: the ejection pressure is 2kPa, the welding power and time are 30W / 10ms;

[0104] The third solder ball: the ejection pressure is 2kPa, the welding power and time are 30W / 10ms.

[0105] Other parameters and operations are exactly the same as those in Example 1. The volume of the three φ0.4 mm solder balls is too large, and the wetting angle of the solder joint morphology is greater than 90 degrees. Due to the large volume of the solder, it is easy to form bridges between the solder joints. In addition, due to the long heating process, the pad is easy to fall off, and the solder joint is unqualified.

[0106] Comparative Example 5:

[0107] Except that the laser power of the second solder ball was reduced to 10W, other parameters and operations were exactly the same as those in Example 1. The solder joint surface wetting of this comparative example was poor, the solder joint was not smooth, some positions were raw, and the solder joint quality was poor and unqualified.

[0108] The present invention preferably uses two tin balls (spray balls) for through-hole welding. The first tin ball mainly fills the inside of the through-hole and the non-welding surface with tin. The first tin ball completes the welding solder and is basically flush with the pad surface; the second ball completes the solder joint morphology forming on the pad surface. Microscopic photos and metallographic inspections show that no damage to the pad structure was found. The total volume of solder should be equivalent to the capacity of the pad and the through-hole. Too much solder can easily cause the solder joint morphology wetting angle to be greater than 90 degrees and the bridging between solder joints to be unqualified. Too little solder cannot completely cover the pad, or the non-welding surface is less than 100% tinned. The laser power, time, and air pressure are within the scope of the present invention, and the solder volume is appropriate, which can significantly improve the solder joint yield rate and meet production requirements.

[0109] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A laser welding method for high temperature, fine pitch, micro through hole solder joint welding, characterized in that: The following steps are involved: S1: Select the appropriate solder according to the working environment of the solder joint, and estimate the solder volume according to the through-hole size of the pad on the printed circuit board; S2: Determine the diameter and number of spray balls based on the estimated solder volume; S3: Determine the segmented process according to the number of spray balls; S4: setting welding power, time and gas pressure parameters in the process window of the laser ball spraying automatic welding equipment according to the determined segmented process; S5: Adjust the distance between the nozzle and the pad, and the laser ball spray automatic welding equipment automatically completes the welding to obtain the final product.

2. The laser welding method according to claim 1, characterized in that: The estimated solder volume in step S1 is v is the solder volume, r1 is the pad through-hole radius, h is the through-hole depth, and r2 is the pad radius.

3. The laser welding method according to claim 1, characterized in that: The number of sub-process sections of the segmented process corresponds to the number of spray balls.

4. The laser welding method according to claim 1, characterized in that: The number of spray balls in step S2 is 2 and the volumes of the two spray balls are equal.

5. The laser welding method according to claim 4, characterized in that: The diameter of the pad is 0.5 mm, the diameter of the through hole is 0.35 mm, the depth of the through hole is 0.544 mm, and the diameter of the spray ball is 0.4 mm.

6. The laser welding method according to claim 4 or 5, characterized in that: The segmentation process described in step S3 is: The first spray ball: spray pressure: 3±0.5kPa; the first stage welding power is 90±10W, the welding time is 2±0.5ms; the second stage welding power is 30±10w, the welding time is 50±5ms; The second spray ball: spray pressure: 2±0.5kPa; welding power 30±10w, welding time 10±2ms.

7. The laser welding method according to claim 1, characterized in that: The solder liquidus is ≥300°C.

8. The laser welding method according to claim 1, characterized in that: The solder is Sn5Pb 95 .

9. The laser welding method according to claim 1, characterized in that: The distance between the welding nozzle and the welding pad is 1 to 3 times the diameter of the corresponding spray ball.

10. The laser welding method according to claim 1, characterized in that: The through hole diameter of the pad is 0.3-0.4 mm, and the center distance between adjacent pads is 0.8-1 mm.

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