A solder paste with a low void ratio, its preparation method and application in the packaging of electronic components

Abstract

The present invention relates to the technical field of solder pastes, and discloses a solder paste with a low void ratio, its preparation method, and its application in the encapsulation of electronic components. Its materials include metal powder, flux components, and additives; the metal powder: 96.5% tin, 3.0% silver, 0.5% copper. For the solder paste with a low void ratio, its preparation method, and its application in the encapsulation of electronic components, due to the adoption of fine metal powder treatment and specific flux configuration, the solder paste of the present invention can significantly reduce the void ratio in the solder joints during the welding process of electronic components. This low void ratio directly improves the mechanical strength and electrical stability of the solder joints, thereby providing higher connection reliability. Adding nano silver particles and carbon nanotubes as additives not only enhances the mechanical strength of the solder joints, but also optimizes the thermal conductivity and electrical conductivity. By using environmentally friendly rosin and silane coupling agent as activators and antioxidants.

Description

Technical Field

[0001] The present invention relates to the technical field of solder pastes, and in particular to a solder paste with a low void ratio, a preparation method thereof, and an application in the encapsulation of electronic components. Background Art

[0002] Solder paste is a material widely used in the field of electronic manufacturing. It is mainly used in surface mount technology to achieve the soldering connection between electronic components and printed circuit boards (PCBs). It is a paste-like substance composed of fine metal powders (usually based on tin, added with alloy elements such as silver and copper) and a series of chemical soldering aids.

[0003] Existing solder pastes have the problems of too high void ratio, poor thermal conductivity and mechanical strength. High void ratios often occur in solder pastes due to trapped gases or separation of solder paste components. Voids will significantly affect the mechanical strength and electrical performance of solder joints. Moreover, traditional solder pastes have insufficient welding strength due to uneven mixing of metal powders or inappropriate solder aid ratios, resulting in early failure of solder joints during use, increasing maintenance costs and affecting user satisfaction. Summary of the Invention

[0004] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract and the title. However, such simplifications or omissions shall not be used to limit the scope of the present invention.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A solder paste with a low void ratio, the materials thereof including metal powders, solder aid components and additives;

[0007] Metal powders: tin 96.5%, silver 3.0%, copper 0.5%;

[0008] Particle size range: 20 - 38 μm;

[0009] Solder aid components: polyethylene glycol (PEG) as binder 2.5%, environmentally friendly rosin as activator 0.5%, and high-efficiency antioxidant (including silane coupling agent) 0.1%;

[0010] Additives: nano silver particles (for enhancing welding strength and reducing void ratio) 1.0% and trace carbon nanotubes (for improving thermal conductivity and mechanical strength) 0.1%.

[0011] A preparation method of a solder paste with a low void ratio, including,

[0012] S1. Pretreatment of metal powders;

[0013] S2, Flux and additive configuration;

[0014] S3, Mix metal powder with flux;

[0015] S4, Defoaming and viscosity adjustment;

[0016] S5, Packaging.

[0017] As a further solution of the present invention: In the step S1, weigh Sn96.5Ag3.0Cu0.5 alloy: tin (96.5%), silver (3%), copper (0.5%). Weigh each element using a high-precision electronic scale, with the error controlled within ±0.1 g. Put all the metal powders into a ball mill in an argon atmosphere, set the ball milling speed at 400 revolutions per minute, and continuously ball mill for 24 hours to ensure that the metal particles are fully refined and evenly mixed;

[0018] Adopt the electroless plating method. Immerse the metal powder in a solution containing a silane coupling agent, control the temperature at room temperature (25°C), let it stand and react for 30 minutes, then take out the powder from the solution and put it into an oven at 60°C to dry for 4 hours to cure the surface treatment layer.

[0019] As a further solution of the present invention: In the step S2, calculate according to 2.5% of PEG, 0.5% of environmentally friendly rosin, and 0.1% of antioxidant. If the total mass is 1 kg, then weigh 25 g of PEG, 5 g of rosin, and 1 g of antioxidant respectively. After mixing evenly, heat to 60°C and continuously stir until completely dissolved;

[0020] Add 10 g of silver nanoparticles and 1 g of carbon nanotubes, and use a high-speed disperser to disperse at a speed of 5000 revolutions per minute for 30 minutes to ensure that the additives are fully dispersed in the flux without aggregation.

[0021] As a further solution of the present invention: In the step S3, under the condition of 40°C, slowly add the pretreated metal powder to the flux mixture, and use a stirrer to mix at a speed of 200 revolutions per minute for 60 minutes to ensure thorough fusion;

[0022] In the step S4, put the mixture into a vacuum defoaming machine, set the pressure at -0.1 MPa, and keep it for 30 minutes. Observe and record the defoaming effect to ensure that no significant bubbles are generated. If necessary, adjust the viscosity according to the results of the rheometer, and control the viscosity of the final product by appropriately increasing or decreasing the amount of PEG.

[0023] As a further solution of the present invention: in step S5, in a dust-free environment, the solder paste is filled into small containers and sealed for storage to avoid air contact and contamination. The printing performance is tested against the welding standard, and the completed solder joints are subjected to X-ray inspection, microstructure analysis, etc. to ensure that the solder joints have a low void rate and good mechanical properties.

[0024] As a further solution of the present invention: the particle size range of the metal powder is obtained through the following steps:

[0025] S11. Based on the setting of the rotation speed and time of the ball mill, calculate the average particle size of the metal powder, where the average particle size (D) is determined by the formula D = 20 + 18×(rotation speed / 400) 0.5 ×(time / 24) 1 Determine;

[0026] S12. Adjust the rotation speed and time of the ball mill so that the calculated average particle size (D) is greater than or equal to 20 μm and less than or equal to 38 μm;

[0027] S13. Verify the particle size distribution by sieving method to ensure that more than 90% of the metal powder particle sizes are within the range of 20 - 38 μm;

[0028] S14. If the particle size distribution does not meet the requirements, return to step S11 to readjust the rotation speed and time of the ball mill.

[0029] As a further solution of the present invention: in step S11, when the calculated average particle size (D) is less than 20 μm, increase the rotation speed of the ball mill;

[0030] When the calculated average particle size (D) is greater than 38 μm, reduce the rotation speed of the ball mill;

[0031] In step S12, if the adjusted average particle size (D) is still not within the range of 20 - 38 μm, further adjust the ball milling time, where the ball milling time (T) is determined by the formula T = 24×(38 - D) / (D - 20);

[0032] In step S13, if it is found that the particle size distribution does not meet the requirements after verification by sieving method, adjust the rotation speed and time of the ball mill according to the sieving results, where the rotation speed (R) is determined by the formula R = 400×(38 - D) max ) / (D min - 20) Determine, where D max and D min are the maximum and minimum particle sizes respectively;

[0033] In step S14, if the requirements for particle size distribution still cannot be met after multiple adjustments, it is necessary to check the working state of the ball mill or replace the metal raw materials to ensure that the particle size range of the final metal powder meets the standard of 2038μm.

[0034] An application of a solder paste in the packaging of electronic components, where the solder paste is applied to the Ball Grid Array (BGA) packaging technology.

[0035] As a further solution of the present invention: its application method is as follows:

[0036] (1) Preparation: Ensure that the surface of the printed circuit board (PCB) to be soldered and the bottom of the BGA component are clean and dust-free. Select a suitable solder paste printing template, and the template design should be based on the solder joint size and layout of the BGA component;

[0037] (2) Printing the solder paste: Use a printing machine or a manual squeegee to evenly distribute the precisely configured solder paste with a low void rate onto the predetermined solder joint positions on the PCB. By precisely controlling the printing pressure, speed, and angle, ensure that the solder paste transfer through the holes of the template is accurate;

[0038] (3) Placing the BGA component: Use a precise placement device (pick-and-place machine) to accurately place the BGA component on the corresponding position of the PCB printed with the solder paste;

[0039] (4) Reflow soldering: Send the PCB with the BGA component into the reflow oven and set a reasonable temperature curve according to the specific composition and performance of the solder paste;

[0040] (41) Preheating stage: The temperature gradually rises to expel the solvent in the solder paste;

[0041] (42) Liquid soldering stage: Reach the melting point of the solder paste to melt the metal powder and form a good soldering connection;

[0042] (43) Cooling stage: Slowly cool down to avoid solder joint stress

[0043] (5) Inspection and quality control: After reflow soldering, use X-ray inspection equipment to check the solder joints under the BGA component to verify whether the internal solder joints have a low void rate and are well-connected. For BGA components with key functions, electrical performance tests can also be carried out to ensure that the soldering does not affect the component performance.

[0044] As a further solution of the present invention: Step (2) printing the solder paste is based on the precise control of printing parameters, including:

[0045] Adjust the pressure P of the printing machine to the set range [Pmin, Pmax];

[0046] Control the printing speed V to be maintained within Vopt ± ΔV;

[0047] Determine that the printing angle θ meets the requirement of θopt ± Δθ;

[0048] Ensure that the solder paste transfer rate T satisfies the conditions within the interval [Tmin, Tmax].

[0049] As a further aspect of the present invention: The control of the placement of the BGA component in step (3) based on position accuracy includes:

[0050] Set the positioning accuracy E of the placement device to Eopt ± ΔE;

[0051] Confirm that the relative position deviation Δd between the BGA component and the PCB is less than the allowable maximum deviation Δd max ;

[0052] Adjust the vertical descent speed S of the placement head to Sopt ± ΔS;

[0053] Monitor the horizontal offset amounts Δx and Δy of the BGA component during the placement process to ensure that Δx 2 + Δy 2 < (Δd m ax) 2 .

[0054] As a further aspect of the present invention: The optimization of the reflow soldering in step (4) based on the temperature curve includes:

[0055] Control the rising rate R1 of the temperature T1 in the preheating stage to be within R1opt ± ΔR1;

[0056] The temperature T2 in the liquid soldering stage reaches Tmelt ± ΔTmelt, where Tmelt is the melting point of the solder paste;

[0057] Control the falling rate R3 of the temperature T3 in the cooling stage to be within R3opt ± ΔR3;

[0058] Monitor the actual temperature curve T(t) during the reflow soldering process to ensure that the deviation ΔT(t) between T(t) and the target temperature curve T t arget(t) satisfies |ΔT(t)| < ΔT m ax.

[0059] As a further aspect of the present invention: The detection and quality control in step (5) based on the evaluation of the solder joint void ratio includes:

[0060] Use an X-ray detection device to obtain a solder joint image I;

[0061] Apply an image processing algorithm to calculate the solder joint void ratio H;

[0062] Judge whether the solder joint void ratio H satisfies H ≤ Hmax, where Hmax is the maximum allowable value of the void ratio;

[0063] If H > Hmax, mark this solder joint as a non - qualified solder joint and record the position information Pfail.

[0064] Compared with the prior art, the beneficial effects of the present invention are:

[0065] Due to the adoption of fine metal powder treatment and specific flux configuration, the solder paste of the present invention can significantly reduce the void ratio in the solder joints during the welding process of electronic components. This low void ratio directly improves the mechanical strength and electrical stability of the solder joints, thus providing higher connection reliability. Adding nano - silver particles and carbon nanotubes as additives not only enhances the mechanical strength of the solder joints but also optimizes the thermal conductivity and electrical conductivity. By using environmentally friendly rosin and silane coupling agent as activator and antioxidant, the present invention not only meets the current stricter environmental requirements but also can effectively prevent the oxidation of the solder paste during storage and use, maintaining the stability and consistency of its performance. Description of the Drawings

[0066] Figure 1 It is the flow chart of the preparation method of the solder paste of the present invention;

[0067] Figure 2 It is the flow chart of the application method of the solder paste of the present invention in the encapsulation of electronic components;

[0068] Figure 3 It is the flow chart of the re - flow soldering method in the application of the solder paste of the present invention in the encapsulation of electronic components. Detailed Embodiments

[0069] To make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be made with reference to the accompanying drawings of the specification.

[0070] In the following description, many specific details are set forth to facilitate a thorough understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0071] Secondly, the so - called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not all refer to the same embodiment, nor is it a separate or selectively exclusive embodiment from other embodiments.

[0072] Embodiment 1

[0073] Please refer to Figure 1 , which is the first embodiment of the present invention. This embodiment provides a method for preparing a soldering paste with a low void ratio, specifically as follows:

[0074] S101: By accurately weighing each element in the Sn96.5Ag3.0Cu0.5 alloy, the accuracy of the metal powder composition is ensured. Use a high-precision electronic scale to weigh 96.5% tin, 3% silver, and 0.5% copper, with the error controlled within ±0.1 g. This step ensures that the composition ratio of the metal powder meets the requirements. Then, put all the metal powders into a ball mill in an argon atmosphere, set the ball milling speed at 400 revolutions per minute, and continuously ball mill for 24 hours to ensure that the metal particles are fully refined and evenly mixed. In addition, adopt the electroless plating method, immerse the metal powder in a solution containing a silane coupling agent, control the temperature at room temperature of 25 °C, let it stand and react for 30 minutes, and then take out the powder from the solution and put it into an oven at 60 °C to dry for 4 hours to cure the surface treatment layer. Assuming that 1 kg of metal powder needs to be prepared, then 965 g of tin powder, 30 g of silver powder, and 5 g of copper powder need to be weighed, and then processed according to the above steps. Through the above steps, the surface activity of the metal powder can be effectively improved, and the formation of voids during the subsequent welding process can be reduced;

[0075] S102: By accurately configuring the flux components and additives, the performance of the soldering paste is ensured. First, calculate according to 2.5% PEG, 0.5% environmentally friendly rosin, and 0.1% antioxidant. If the total mass is 1 kg, then weigh 25 g of PEG, 5 g of rosin, and 1 g of antioxidant respectively. After mixing evenly, heat to 60 °C and continuously stir until completely dissolved. Then, add 10 g of nano silver particles and 1 g of carbon nanotubes, and use a high-speed disperser to disperse at a speed of 5000 revolutions per minute for 30 minutes to ensure that the additives are fully dispersed and non-aggregated in the flux. For 1 kg of flux components, various components need to be accurately weighed according to the above ratio and ensure that they are evenly mixed. Through the above steps, the thermal conductivity and mechanical strength of the soldering paste can be effectively improved, and the void ratio can be reduced at the same time;

[0076] S103: By mixing the pretreated metal powder with the flux, the uniformity and stability of the soldering paste are ensured. Under the condition of 40 °C, slowly add the pretreated metal powder into the flux mixture, and use a stirrer to mix at a speed of 200 revolutions per minute for 60 minutes to ensure complete fusion. For 1 kg of metal powder, it needs to be evenly dispersed into the already prepared flux and ensure uniform mixing. Through the above steps, the separation between the metal powder and the flux can be effectively avoided, thereby reducing the formation of voids during the welding process;

[0077] S104: By degassing and viscosity adjustment, the applicability of the solder paste is ensured. The mixture is placed in a vacuum degassing machine, and a pressure of -0.1 MPa is set for 30 minutes. Observe and record the degassing effect to ensure that no significant bubbles are generated. When necessary, adjust the viscosity according to the rheometer results, and control the viscosity of the final product by appropriately increasing or decreasing the amount of PEG. If a large number of bubbles are found during degassing, it can be improved by extending the degassing time or increasing the vacuum degree. Through the above steps, the bubbles in the solder paste can be effectively reduced, the void rate during welding can be lowered, and the solder paste can have a suitable viscosity for printing and welding;

[0078] S105: By packaging and testing, the quality of the solder paste is ensured. In a dust-free environment, the solder paste is dispensed into small containers and sealed to avoid air contact and contamination. Conduct printing performance tests against welding standards, and perform X-ray inspection, microstructure analysis, etc. on the completed solder joints to ensure low void rate and good mechanical properties of the solder joints. The completed solder paste needs to be dispensed in a dust-free workshop, and each batch needs to be strictly tested to ensure that its performance meets the standards. Through the above steps, the quality of the solder paste can be effectively guaranteed, the void rate during welding can be reduced, and the mechanical strength and electrical properties of the solder joints can be improved;

[0079] S106: By precisely controlling the particle size range of the metal powder, the performance of the solder paste is ensured. Based on the set rotation speed and time of the ball mill, calculate the average particle size of the metal powder. By adjusting the rotation speed and time of the ball mill, the calculated average particle size is greater than or equal to 20 μm and less than or equal to 38 μm. Verify the particle size distribution by sieving method to ensure that more than 90% of the metal powder particle sizes are in the range of 20 - 38 μm. If the particle size distribution does not meet the requirements, adjust the rotation speed and time of the ball mill according to the sieving results. If the initially calculated average particle size is less than 20 μm, the rotation speed of the ball mill needs to be increased. If the average particle size is greater than 38 μm, then during actual operation, when this device is used, first, various raw materials need to be prepared according to the formula and ratio described in Claim 1, including metal powder, flux components, and additives. The composition of the metal powder strictly follows the ratio of Sn96.5Ag3.0Cu0.5 and is pretreated by a ball mill to ensure that the particle size range of the metal powder is between 20 - 38 μm. This particle size range is crucial for reducing the void rate of the solder joints. During the pretreatment process, the metal powder also needs to undergo electroless plating treatment to enhance its surface activity. Next, configure the flux components and additives according to the steps of Claims 2 - 8, and then mix them with the pretreated metal powder at a specific temperature and stirring speed to ensure that all components can be evenly dispersed. After mixing, degassing treatment is also required to remove the bubbles in the mixture, and adjust the viscosity of the solder paste as needed to make it suitable for subsequent printing processes.

[0080] The experimental data table of material ratio is as follows:

[0081]

[0082]

[0083] Example 2

[0084] Please refer to Figures 2-3 , which is the second embodiment of the present invention. This embodiment provides an application of solder paste with a low void ratio in the encapsulation of electronic components, specifically as follows:

[0085] S101: By ensuring that the surface of the printed circuit board (PCB) to be soldered and the bottom of the BGA component are clean and dust-free, an ideal soldering environment is first created. To achieve this goal, methods such as blowing with compressed air, ultrasonic cleaning, or chemical solvent cleaning are used to remove surface dirt and oxides. In addition, it is crucial to select a suitable solder paste printing template. The design of the template must precisely match the solder joint size and arrangement of the BGA component to ensure that the solder paste can be accurately placed at the desired positions. When designing the template, laser cutting or electroforming technology can be considered to manufacture the template. Both methods can provide high-precision openings, thus ensuring the correct dispensing of the solder paste. In addition, the template needs to be regularly maintained and cleaned to prevent uneven distribution of the solder paste caused by template blockage;

[0086] S102: By using a printing machine or a manual squeegee to evenly distribute the precisely configured low-void-ratio solder paste to the predetermined solder joint positions on the PCB, we ensure the accurate placement of the solder paste. During the printing process, it is necessary to precisely control the printing pressure, speed, and angle to ensure the accurate transfer of the solder paste through the holes of the template. The printing machine is usually equipped with a vision system to monitor the printing process to ensure that the thickness and shape of the solder paste meet the requirements. In addition, a squeegee hardness regulator can be used to adjust the hardness of the squeegee to adapt to solder paste with different viscosities. For manual printing, the operator needs to be specially trained to ensure the consistency and accuracy of each printing. Through these measures, the formation of voids in the solder paste during the printing process can be effectively reduced, thereby improving the welding quality and reliability;

[0087] S103: By using a precise placement device, a pick-and-place machine, to accurately place the BGA component at the corresponding position on the PCB printed with solder paste, we ensure the precise alignment between the BGA component and the PCB. The pick-and-place machine usually has a high-precision positioning system that can place the BGA component within a tolerance range of millimeters or even smaller. Some advanced pick-and-place machines are equipped with an optical alignment system that can automatically correct the position deviation of the BGA component before placement, ensuring that each solder joint can precisely correspond to the solder balls on the BGA component. In addition, the pick-and-place machine also has an automatic correction function that can compensate for the thermal expansion and deformation of the PCB during the heating process, further improving the placement accuracy;

[0088] S104: By feeding the PCB with the BGA component into the reflow oven and setting a reasonable temperature profile according to the specific composition and properties of the solder paste, a high-quality soldering effect is achieved. The reflow soldering process is divided into three main stages: the preheating stage, the liquid soldering stage, and the cooling stage. In the preheating stage, the temperature gradually rises to expel the solvent in the solder paste. This process requires a gentle heating rate to avoid the solder paste bursting and forming voids due to the rapid evaporation of the solvent. The preheating rate can be set between 1 - 3 °C / second to ensure the solvent is smoothly discharged from the solder paste. After entering the liquid soldering stage, the temperature reaches the melting point of the solder paste, causing the metal powder to melt and form a good soldering connection. In this stage, the temperature needs to be kept stable to ensure the solder flows sufficiently and forms a firm solder joint. For Sn63Pb37 solder paste, the melting point is 183 °C, so the peak temperature of the reflow oven should be set between 210 - 230 °C. Finally, in the cooling stage, the temperature needs to be slowly reduced to avoid generating stress inside the solder joints. The cooling rate can be controlled at 3 - 5 °C / second to ensure the stability of the internal structure of the solder joints. Through these precise temperature controls, the void rate in the solder joints can be effectively reduced, and the mechanical strength of the solder joints can be improved;

[0089] S105: By using X-ray inspection equipment to inspect the solder joints under the BGA component after reflow soldering, we ensure the soldering quality. X-ray inspection is a non-destructive inspection method that can clearly show the internal situation of the solder joints, including the presence or absence of voids and the connectivity of the solder joints. Use X-ray inspection equipment to evaluate the void rate of the solder joints. If the void rate is found to be too high, the soldering parameters or the solder paste formula need to be adjusted. In addition, for BGA components with critical functions, electrical performance tests can also be carried out to ensure that the soldering does not affect the component performance. By applying voltage and current to test the function of the BGA component, ensure that all solder joints are in good electrical connection states. Through these strict inspection procedures, the reliability and consistency of the final product can be ensured, thus solving the problems existing in traditional solder paste, such as too high void rate, poor thermal conductivity, and poor mechanical strength.

[0090] Next, describe the specific steps for precisely controlling the printing of solder paste in the application of solder paste in the encapsulation of electronic components based on printing parameters:

[0091] S201: Adjust the pressure of the printer: In the application of a solder paste in the encapsulation of electronic components, the present invention further defines that in step 2, the pressure P of the printer needs to be precisely controlled during the process of printing the solder paste to ensure that the solder paste can be evenly and fully filled into the solder pads. Specifically, the pressure P needs to be adjusted within the set range [Pmin, Pmax], where Pmin and Pmax are the minimum and maximum pressure values respectively. For a specific printing process, if Pmin is determined to be 0.5 kg / cm 2 and Pmax is 1.5 kg / cm 2 , then during the actual operation process, it should be ensured that the pressure of the printer is always within this range to avoid problems such as insufficient filling of the solder paste due to too low pressure or overflow of the solder paste due to too high pressure;

[0092] S202: Control the printing speed: To further improve the printing quality, it is also necessary to control the printing speed V to be maintained within the range of Vopt ± ΔV, where Vopt is the optimal printing speed and ΔV is the allowable speed fluctuation range. If Vopt is set to 10 mm / s and the maximum allowable deviation ΔV is ±2 mm / s, then during the actual printing process, the printing speed should be maintained between 8 mm / s and 12 mm / s, which can ensure that the solder paste will neither be unevenly distributed due to too fast a speed nor fail to complete printing before the solder paste solidifies due to too slow a speed;

[0093] S203: Determine the printing angle: In addition, the printing angle θ must also meet the requirements of θopt ± Δθ, where θopt is the optimal printing angle and Δθ is the allowable angle deviation. If θopt is set to 45° and the maximum allowable deviation Δθ is ±5°, then during the actual printing process, the printing angle should be maintained between 40° and 50°, which can ensure that the solder paste can be correctly transferred to the solder pads during printing and avoid uneven distribution or missing of the solder paste due to improper angle;

[0094] S204: Ensure the solder paste transfer rate: Finally, it is also necessary to ensure that the solder paste transfer rate T meets the conditions within the interval [Tmin, Tmax], where Tmin and Tmax are the minimum and maximum values of the solder paste transfer rate respectively. If Tmin is set to 80% and Tmax is set to 95%, then during the actual printing process, the solder paste transfer rate should be maintained between 80% and 95%, which helps to ensure that the solder paste can be effectively transferred from the stencil to the solder pads and at the same time avoid problems of too much or too little solder paste.

[0095] Next, describe the specific steps for controlling the placement accuracy of BGA components in the application of solder paste in the packaging of electronic components:

[0096] S301: Set the positioning accuracy of the placement device: By adjusting the mechanical system or software parameters of the placement device, set the positioning accuracy E to the optimal value Eopt and allow a certain error range ΔE. This step ensures that the placement device can accurately align with the predetermined position, reducing position deviations caused by mechanical vibrations or other factors;

[0097] S302: Confirm the relative position deviation between the BGA component and the PCB: Measure the relative position deviation Δd between the BGA component and the printed circuit board PCB through a vision inspection system or other sensors, and ensure that this deviation is less than the pre-set maximum allowable deviation Δd max , which helps to avoid soldering defects caused by excessive position deviations;

[0098] S303: Adjust the vertical descent speed of the placement head: According to factors such as the weight, size of the BGA component, and the surface characteristics of the PCB, adjust the vertical descent speed S of the placement head to the optimal value Sopt and allow a certain range of fluctuations ΔS. This can ensure that the BGA component is placed smoothly on the PCB, reducing the impact on the component;

[0099] S304: Monitor the horizontal offset of the BGA component: During the placement process, continuously monitor the horizontal offsets Δx and Δy of the BGA component relative to the predetermined position, and ensure that the sum of the squares of the offsets in these two directions is less than the square of the maximum allowable deviation Δd_max. If the offset is found to exceed the allowable range, the placement strategy needs to be adjusted in a timely manner to ensure that the BGA component is accurately placed at the specified position;

[0100] These steps together constitute strict control over the placement accuracy of BGA components, thereby improving the reliability and efficiency in the process of electronic component packaging.

[0101] Next, describe the specific steps for optimizing the reflow soldering based on the temperature curve in the application of solder paste in the packaging of electronic components:

[0102] S401: Ensure uniform heating of the solder paste by precisely controlling the temperature rise rate in the preheating stage. Specifically, in the preheating stage, the temperature rise rate R1 of temperature T1 is strictly controlled near an optimal value R1 opt, and the allowable deviation range is ±ΔR1. This can avoid solder paste oxidation or component damage caused by local overheating and ensure uniform temperature distribution in the entire welding area;

[0103] S402: By precisely controlling the temperature during the liquid soldering stage, ensure that the solder paste can fully melt and form good solder joints. At this stage, the temperature T2 needs to reach the melting point Tmelt of the solder paste ± ΔTmelt, which is crucial for forming stable and reliable solder joints. Because if the temperature is too low, the solder paste may not fully melt, while if the temperature is too high, it may cause excessive solder diffusion or form a poor intermetallic compound layer;

[0104] S403: Ensure the quality of the solder joints by controlling the temperature drop rate during the cooling stage. During the cooling stage, the temperature drop rate R3 of the temperature T3 is controlled within the range of R3opt ± ΔR3. Rapid cooling helps to form a fine grain structure, thereby improving the mechanical strength and reliability of the solder joints, while slow cooling helps to reduce the stress inside the solder joints and prevent crack generation;

[0105] S404: During the entire reflow soldering process, monitor the actual temperature curve Tt in real time and compare it with the pre-set target temperature curve T t arget(t) to ensure that the deviation ΔTt between the two is always less than the maximum allowable deviation ΔTmax. The monitoring mechanism can be implemented through temperature sensors installed inside the reflow oven. Once the detected deviation exceeds the allowable range, the system will automatically adjust the heating power or other parameters to correct the temperature curve, thereby ensuring the quality control of the soldering process.

[0106] Next, describe the specific steps regarding the detection and quality control of the void ratio of solder joints in the application of solder paste in the packaging of electronic components:

[0107] S501: Obtain the solder joint image I through an X-ray detection device. This process involves placing the packaged electronic component under the X-ray detection device and using the ability of X-rays to penetrate materials to capture the internal structure image of the solder joint. The X-ray detection device is usually equipped with a high-resolution imaging system that can clearly display the details inside the solder joint, including possible void areas;

[0108] S502: Calculate the void ratio H of the solder joint by applying image processing algorithms. After obtaining the X-ray image of the solder joint, the image needs to be analyzed to determine the proportion of voids inside the solder joint. This step includes image preprocessing such as denoising, enhancing contrast, etc., void area recognition, and calculating the proportion of the void area to the entire solder joint area. Modern image processing software or custom-developed algorithms can automatically complete these tasks, thus quickly and accurately obtaining the void ratio H of the solder joint;

[0109] S503: Determine whether the void ratio H of the solder joint satisfies H ≤ H ma, where Hmax is the maximum allowable value of the void ratio. Set a maximum allowable void ratio threshold Hmax according to industry standards or the requirements of specific applications. Then compare the calculated actual void ratio H with Hmax. If H is greater than Hmax, it indicates that there is a quality problem with the solder joint. Otherwise, the solder joint is considered qualified;

[0110] S504: If H > H max , then mark this solder joint as a non - qualified solder joint and record the position information P fail , once it is found that the void ratio of the solder joint exceeds the allowable maximum value, it is necessary to mark this solder joint for subsequent processing. At the same time, record the position information P of the non - qualified solder joint fail , which is crucial for tracking problem solder joints, analyzing the reasons, and improving the process flow. The data can be stored in a database for quality control and statistical analysis.

[0111] Next, describe the specific steps regarding the electrical performance test of BGA components in the application of solder paste in the encapsulation of electronic components:

[0112] S601: Start the electrical performance test process by applying a standard test signal S to the BGA (Ball Grid Array) component. This standard test signal S is usually an electrical signal with known characteristics, such as a sine wave or pulse signal with a specific frequency and amplitude, used to simulate the input signal under actual working conditions;

[0113] S602: Proceed to the next step by measuring the output response signal R of the BGA component. Use precision measuring equipment, such as an oscilloscope or a network analyzer, etc., to ensure that the details of the output signal can be accurately captured;

[0114] S603: Calculate the signal distortion degree D, that is, the degree of difference between the input signal S and the output signal R. This can be completed by comparing parameters such as their waveforms, phases, amplitudes, etc. If the signal distortion degree D exceeds the pre - set maximum allowable distortion degree Dmax, it is considered that there is a quality problem with this BGA component;

[0115] S604: If the signal distortion degree D is greater than the maximum allowable distortion degree Dmax, then determine that this BGA component is unqualified and record the specific failure type Ffail;

[0116] In actual operation, a signal generator can be used to generate a standard test signal S and apply it to a pin of the BGA component. Then, an oscilloscope is used to simultaneously monitor the signal changes on this pin and the corresponding output pin to obtain the output response signal R. By comparing the waveforms of the input signal S and the output signal R, the signal distortion degree D can be calculated. If it is found that the distortion degree exceeds the preset threshold Dmax, it is necessary to further check whether there are problems such as poor soldering in the BGA component and record the specific fault type for subsequent analysis and improvement.

[0117] Next, describe the specific steps for the application of solder paste in the packaging of electronic components:

[0118] S701: Measure the roughness of the surface of the printed circuit board (PCB) and the flatness of the bottom of the ball grid array (BGA) component using appropriate detection tools or equipment to obtain initial evaluation data, which will be used to determine the most suitable cleaning method subsequently. A surface profilometer can be used to measure the roughness of the PCB surface, and a microscope can be used to check the flatness of the bottom of the BGA component;

[0119] S702: Compare the obtained data with the preset first threshold and second threshold to decide which cleaning method to adopt. If the roughness of the PCB surface is less than the first threshold and the flatness of the bottom of the BGA component is greater than the second threshold, it indicates that the surface is relatively clean, and at this time, a gentle cleaning method can be adopted, such as gently wiping with a soft brush or blowing with compressed air. On the contrary, if the roughness of the PCB surface is greater than or equal to the first threshold or the flatness of the bottom of the BGA component is less than or equal to the second threshold, it indicates that a more thorough cleaning treatment is required, and at this time, a strong cleaning method should be adopted, such as cleaning with a solvent or ultrasonic cleaning, etc.;

[0120] S703: After completing the cleaning process, measure the roughness of the PCB surface and the flatness of the bottom of the BGA component again using the same detection tools or equipment to verify whether the cleaning effect meets the expected standard. If the data after cleaning meets the set standard, the next soldering operation can be continued. If not, the cleaning needs to be repeated until the requirements are met. This process ensures that the surface conditions before soldering can support high-quality soldering operations.

[0121] Next, describe the application of solder paste in the packaging of electronic components, especially the specific steps regarding the selection of a suitable solder paste printing template:

[0122] S801: First, according to the solder joint size and layout of the BGABall Grid Array component, template design is carried out, which involves detailed measurement of the solder joints on the BGA component to determine the diameter of the solder joints. The solder joint diameter is one of the key factors determining the template aperture size, so accurate measurement is required;

[0123] S802: Next, calculate the distance between the solder joints. The solder joint pitch refers to the distance between the centers of two adjacent solder joints. This parameter is crucial for determining the template aperture because it directly affects whether the solder paste can be accurately placed at the predetermined position without overflow or shortage;

[0124] S803: Then, determine the size of the template aperture according to the proportional relationship between the solder joint pitch and the solder joint diameter. Specifically, if the ratio of the solder joint pitch to the solder joint diameter is less than a preset third threshold, the template aperture size is set to the solder joint diameter minus a fourth threshold. Conversely, if the ratio of the solder joint pitch to the solder joint diameter is greater than or equal to the third threshold, the template aperture size is set to the solder joint diameter minus a fifth threshold. The third, fourth, and fifth thresholds here are all preset values based on practical experience and are used to ensure that the solder paste can be correctly and evenly distributed to each solder joint.

[0125] Illustrate the technical implementation method of the above steps by an example:

[0126] S801: Suppose we have a BGA component with a solder joint diameter of 0.5 mm. To obtain accurate measurement results, a high-precision microscope or a special measurement tool can be used for measurement, and the diameter of each solder joint is recorded;

[0127] S802: Continuing with the above example, assume that the measured solder joint pitch is 0.8 mm. To calculate the solder joint pitch, the same measurement tool can be used to measure the distance between the centers of two adjacent solder joints;

[0128] S803: Suppose the third threshold is set to 1.6, that is, the ratio of the solder joint pitch to the solder joint diameter, the fourth threshold is 0.1 mm, and the fifth threshold is 0.05 mm. According to the calculation, the ratio of the solder joint pitch to the solder joint diameter is 1.6 (0.8 / 0.5 = 1.6), which is exactly equal to the third threshold. Therefore, the template aperture size should be set to the solder joint diameter minus the fifth threshold, that is, 0.45 mm (0.5 - 0.05 = 0.45). The template aperture designed in this way can ensure that the solder paste is neither too much nor too little during the printing process, thus improving the welding quality and reliability.

[0129] Next, describe the specific steps of the application of solder paste in the encapsulation of electronic components:

[0130] S901: By using a precisely configured solder paste with a low void ratio, in one embodiment of the present invention, an application of a solder paste in the encapsulation of electronic components, the step of printing the solder paste includes using a printing machine or a manual squeegee to evenly distribute the precisely configured solder paste with a low void ratio to the predetermined solder joint positions on the PCB (printed circuit board). The process requires precise control to ensure that the solder paste can accurately fill the pores of the stencil and form a uniform solder paste layer on the PCB surface. To achieve this goal, key parameters in the printing process need to be adjusted, including printing pressure, speed, and angle;

[0131] S902: Ensure the accuracy of solder paste transfer by adjusting the printing pressure, speed, and angle. During the printing process, first, the printing pressure needs to be adjusted. If it is detected that the printing pressure is less than the preset sixth threshold, then the printing pressure needs to be increased to ensure that the solder paste can fully fill the stencil pores and be transferred to the PCB. Next, the printing speed needs to be adjusted. If the printing speed is greater than the preset seventh threshold, then the printing speed needs to be reduced to avoid uneven distribution caused by excessive solder paste flow. Finally, the printing angle also needs to be adjusted. If the deviation of the printing angle is greater than the preset eighth threshold, then the printing angle needs to be corrected to ensure that the solder paste can be accurately transferred to the predetermined position. These adjustments can be automatically completed by the control system of the printing machine or manually adjusted by the operator;

[0132] S903: Confirm the even distribution of the solder paste by checking the solder paste transfer situation again. After completing the above parameter adjustments, it is necessary to check the solder paste transfer situation again to confirm whether the solder paste has been evenly distributed on the predetermined solder joint positions of the PCB. This step can be completed by visual inspection or using an automated detection device. If it is found that the solder paste distribution is uneven, it may be necessary to further adjust the printing parameters until the requirements are met. Once it is confirmed that the solder paste is evenly distributed, the subsequent encapsulation process steps can be continued.

[0133] Next, describe the specific steps regarding the placement of the BGA component in the application of a solder paste in the encapsulation of electronic components:

[0134] S1001: Accurately place the ball grid array (BGA) component onto the designated position on the printed circuit board (PCB) that has already been printed with solder paste through a precise placement device, usually called a pick - and - place machine. Highly precise operation is required to ensure the alignment accuracy between the BGA component and the PCB. During the placement process, a vision inspection system will be used to measure the relative position deviation between the BGA component and the PCB;

[0135] S1002: If the alignment error data obtained through measurement shows that the error exceeds the pre-set ninth threshold, that is, the alignment accuracy is insufficient, the fine-tuning function of the pick-and-place machine needs to be used to adjust the position of the BGA component until the error is reduced to an acceptable range. This adjustment process requires multiple iterations, and the alignment error needs to be re-measured after each adjustment until the error meets the requirements.

[0136] S1003: Once the alignment error between the BGA component and the PCB is adjusted to be less than or equal to the ninth threshold, that is, the required alignment accuracy is achieved, the BGA component can be maintained at the current position. After the position adjustment is completed, the alignment error is measured again to finally confirm the accuracy of the placement, ensuring that the BGA component can be correctly aligned with the solder joints on the PCB, thereby guaranteeing the quality and reliability of the subsequent soldering process.

[0137] Next, describe the specific steps in the preheating stage of the reflow soldering process in the application of solder paste in the packaging of electronic components:

[0138] S1101: Monitor the temperature change during the preheating process by measuring the temperature rise rate. This process can be achieved through temperature sensors installed in the reflow oven. These sensors can monitor and record the temperature change situation in the preheating stage in real time. The data of the temperature sensors is transmitted to the control system, and the control system calculates the actual temperature rise rate according to the set program.

[0139] S1102: Calculate the solvent evaporation rate by analyzing the solder paste composition and environmental conditions. It is necessary to determine the solvent evaporation rate of different types of solder paste at a specific temperature through experiments in advance and store this data in the database. When actual soldering is carried out, the control system will call the corresponding data and calculate the actual solvent evaporation rate in combination with the current temperature conditions.

[0140] S1103: Compare the proportional relationship between the temperature rise rate and the solvent evaporation rate. The control system compares the calculated temperature rise rate with the solvent evaporation rate. If it is found that the ratio of the temperature rise rate to the solvent evaporation rate is less than the tenth threshold, that is, a pre-set safety ratio, it is considered that the solvent evaporation may be insufficient. At this time, the control system will automatically extend the preheating time to ensure that the solvent can be completely evaporated. On the contrary, if the ratio of the temperature rise rate to the solvent evaporation rate is greater than or equal to the tenth threshold, it is considered that the solvent evaporation is sufficient, and the control system will appropriately shorten the preheating time to improve production efficiency.

[0141] Through the above steps, the time in the preheating stage can be effectively controlled to ensure that the solvent in the solder paste can be fully evaporated, thereby improving the soldering quality and production efficiency.

[0142] In the actual operation process, when this device is used, the application of solder paste in the electronic component packaging starts with the preparation work, that is, ensuring that the surface of the printed circuit board (PCB) to be soldered and the bottom of the BGA component are clean and dust-free, and selecting a suitable solder paste printing template. The design of this template needs to be based on the solder joint size and layout of the BGA component to ensure that the solder paste can accurately cover the predetermined solder joint positions during the subsequent printing process. Subsequently, a solder paste with a low void rate is evenly distributed onto the PCB using a printing machine or a manual squeegee. This process requires precise control of the printing pressure, speed, and angle to ensure that the solder paste can be accurately transferred onto the solder joints of the PCB. Next, a BGA component is accurately placed on the corresponding position of the PCB printed with solder paste using a precise placement device such as a pick-and-place machine. This step is crucial for ensuring the precise alignment between the BGA component and the PCB. After that, the PCB with the BGA component is sent into a reflow soldering furnace for soldering. The reflow soldering process is divided into three main stages: the preheating stage, the liquid soldering stage, and the cooling stage. The preheating stage is to remove the solvent in the solder paste, and the liquid soldering stage is to reach the melting point of the solder paste to melt the metal powder to form a good soldering connection. Finally, in the cooling stage, the solder joints will slowly cool down to avoid generating internal stress. After completing the reflow soldering, inspection and quality control are also required. This step uses X-ray inspection equipment to check the solder joints under the BGA component to verify whether the solder joints have a low void rate and good connectivity inside. For some BGA components with key functions, additional electrical performance tests will also be carried out to ensure that the soldering process does not affect the overall performance of the component. The whole process reflects a highly coordinated workflow from the selection of solder paste to printing, placement, soldering, and finally to the final quality control, ensuring the high quality and reliability of the electronic component packaging.

[0143]

[0144]

[0145]

[0146] Conclusion: Through the processes of precise weighing, ball milling, and electroless plating, the uniform refinement and good surface treatment of the metal powder (Sn96.5Ag3.0Cu0.5 alloy) are ensured. The ball milling process effectively reduces the size of the metal particles and achieves the specified particle size distribution (20 - 38 μm), which is crucial for improving the reliability and solder joint quality during the soldering process.

[0147] The correct proportioning and uniform dispersion of the flux and additives, especially silver nanoparticles and carbon nanotubes, play a significant role in enhancing the welding strength and reducing the void ratio. Stirring at 60 °C ensures the complete dissolution of PEG, rosin, and antioxidant, while a high-speed disperser ensures a uniform distribution without aggregation;

[0148] Under the condition of 40 °C, the metal powder was slowly added to the flux mixture, and an appropriate stirring speed and time were used to ensure the thorough fusion of the mixture, which is particularly important for ensuring the integrity and performance stability of the final product.

[0149] The above is the preferred embodiment of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A method for preparing a solder paste with low void ratio, The materials of the solder paste with low void ratio include metal powder, flux components and additives; Metal powder: tin 96.5%, silver 3.0%, copper 0.5%; Particle size range: 20-38μm; The flux components are: 2.5% polyethylene glycol as a binder, 0.5% environmentally friendly rosin as an activator, and 0.1% high-efficiency antioxidant containing a silane coupling agent; Additives: 1.0% of nano silver particles to improve welding strength and reduce void ratio, and 0.1% of trace carbon nanotubes to improve thermal conductivity and mechanical strength. The method for preparing a solder paste with low void ratio comprises: S1. Metal powder pretreatment; S2, flux and additive configuration; In step S2, according to 2.5% PEG, 0.5% environmentally friendly rosin and 0.1% antioxidant, if the total mass is 1kg, 25g PEG, 5g rosin and 1g antioxidant are weighed respectively, and after uniform distribution, they are heated to 60°C and stirred continuously until completely dissolved; Add 10g of nanosilver particles and 1g of carbon nanotubes, and use a high-speed disperser to disperse them at a speed of 5000 rpm for 30 minutes to ensure that the additives are fully dispersed in the flux without aggregation; S3, mixing metal powder and flux; Slowly add the pre-treated metal powder to the flux mixture at 40°C and mix using a blender at 200 rpm for 60 minutes to ensure thorough blending; The particle size range of the metal powder is obtained by the following steps: S11. Calculate the average particle size of the metal powder based on the speed and time setting of the ball mill, where the average particle size (D) is calculated by the formula D = 20 + 18 × (speed / 400) 0.5 ×(time / 24) 1 Sure; S12, adjusting the rotation speed and time of the ball mill so that the calculated average particle size (D) is greater than or equal to 20 μm and less than or equal to 38 μm; S13, verify the particle size distribution by sieving method to ensure that more than 90% of the metal powder particle size is within the range of 2038μm; S14, if the particle size distribution does not meet the requirements, return to step S11 to readjust the speed and time of the ball mill; In the step S11, when the calculated average particle size (D) is less than 20 μm, the rotation speed of the ball mill is increased; When the calculated average particle size (D) is greater than 38 μm, reduce the speed of the ball mill; In the step S12, if the adjusted average particle size (D) is still not within the range of 20-38 μm, the ball milling time is further adjusted, wherein the ball milling time (T) is determined by the formula T=24×(38D) / (D20); In step S13, if the particle size distribution does not meet the requirements after verification by the screening method, the speed and time of the ball mill are adjusted according to the screening results, wherein the speed (R) is calculated by the formula R = 400 × (38D max ) / (D min 20) Determine, where D max and D min are the maximum and minimum particle sizes, respectively; In step S14, if the particle size distribution requirement cannot be met after multiple adjustments, it is necessary to check the working state of the ball mill or replace the metal raw material to ensure that the particle size range of the final metal powder meets the standard of 20-38 μm; S4, degassing and viscosity adjustment; Place the mixture in a vacuum degassing machine and set the pressure to -0.1 MPa for 30 minutes. Observe and record the degassing effect to ensure that no significant bubbles are generated. If necessary, adjust the viscosity according to the rheometer results. Control the viscosity of the final product by appropriately increasing or decreasing the amount of PEG. S5. Packaging; In the step S1, weigh Sn96.5Ag3.0Cu0.5 alloy: 96.5% tin, 3% silver, and 0.5% copper, use a high-precision electronic scale to weigh each element, and the error is controlled within ±0.1g, put all the metal powders into a ball mill in an argon atmosphere, set the ball milling speed to 400 rpm, and continue ball milling for 24 hours to ensure that the metal particles are fully refined and evenly mixed; Using a chemical plating method, the metal powder is immersed in a solution containing a silane coupling agent, the temperature is controlled at room temperature of 25°C, and the reaction is allowed to stand for 30 minutes. The powder is then taken out of the solution and placed in an oven at 60°C for 4 hours to dry in order to solidify the surface treatment layer.

2. The method for preparing a solder paste with low void ratio according to claim 1, characterized in that: In step S5, the solder paste is divided into small containers in a dust-free environment and sealed to avoid air contact and contamination. The printing performance test is carried out according to the welding standard, and the completed solder joints are subjected to X-ray inspection and microstructure analysis to ensure that the solder joints have low void rate and good mechanical properties.

3. An application of a solder paste in electronic component packaging, comprising the solder paste with low void ratio according to claim 1, characterized in that: The solder paste is applied to Ball Grid Array packaging technology, including: (1) Preparation: Ensure that the PCB surface to be soldered and the bottom of the BGA component are clean and dust-free, and select a suitable solder paste printing template. The template design should be based on the solder joint size and arrangement of the BGA component; (2) Printing solder paste: Use a printer or a manual scraper to evenly distribute the precisely configured low voiding solder paste to the predetermined solder joint locations on the PCB. By precisely controlling the printing pressure, speed, and angle, ensure that the solder paste transfer through the holes of the template is accurate. Step (2) printing solder paste based on precise control of printing parameters, including: Adjust the pressure P of the printing press to the set range [Pmin, Pmax]; Control the printing speed V to be within Vopt±ΔV; Determine that the printing angle θ meets the requirement of θopt±Δθ; Ensure that the solder paste transfer rate T meets the conditions within the interval [Tmin, Tmax]; (3) Placing BGA components: Use a precision pick-and-place machine to accurately place the BGA components on the corresponding position of the PCB printed with solder paste; Step (3) BGA component placement based on positional accuracy control includes: Set the positioning accuracy E of the placed device to Eopt±ΔE; Confirm that the relative position deviation Δd between the BGA component and the PCB is less than the maximum allowable deviation Δd max ; Adjust the vertical descent speed S of the placement head to Sopt±ΔS; Monitor the horizontal offset Δx and Δy of BGA components during placement to ensure Δx 2 +Δy 2 <(Δd m ax) 2 ; (4) Reflow soldering: Send the PCB with BGA components into the reflow soldering furnace and set a reasonable temperature curve according to the specific composition and performance of the solder paste; (41) Preheating stage: The temperature is gradually increased to drive out the solvent in the solder paste; (42) Liquid welding stage: reaching the melting point of the solder paste, melting the metal powder to form a good welding connection; (43) Cooling stage: Slowly cool down to avoid solder joint stress; Step (4) reflow soldering based on the optimization of the temperature curve, including: The rising rate R1 of the temperature T1 in the preheating stage is controlled at R1opt±ΔR1; The temperature T2 in the liquid soldering stage reaches Tmelt±ΔTmelt, where Tmelt is the melting point of the solder paste; The decreasing rate R3 of the temperature T3 in the cooling stage is controlled at R3opt±ΔR3; Monitor the actual temperature curve T(t) during reflow soldering to ensure that T(t) is consistent with the target temperature curve T t The deviation ΔT(t) of arget(t) satisfies |ΔT(t)|<ΔT m ax; (5) Inspection and quality control: After reflow soldering, use X-ray inspection equipment to inspect the solder joints under the BGA components to verify whether the void rate inside the solder joints is low and the connectivity is good. For BGA components with key functions, electrical performance tests can also be performed to ensure that soldering does not affect component performance; Step (5) Inspection and quality control is based on the evaluation of solder joint void rate, including: Using X-ray inspection equipment to obtain solder joint image I; Apply image processing algorithm to calculate the void ratio H of solder joints; Determine whether the void rate H of the solder joint satisfies H≤Hmax, where Hmax is the maximum allowable void rate value; If H>Hmax, the solder joint is marked as a failed solder joint and the position information Pfail is recorded.

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