A method for reworking defective back-tin products

Abstract

The present invention provides a method for reworking defective products of back tin-brushing products. The method includes: establishing a physical model; obtaining the current height of the convex solder joints and the current radius of the ground plane of the convex solder joints after each grinding; obtaining a grinding function; grinding the defective convex solder joints to the height of the reworked convex solder joints, and according to the grinding function, obtaining the corresponding radius of the ground plane of the reworked convex solder joints; selecting a corresponding rework stencil; sleeving the rework stencil on the ground defective convex solder joints, pouring solder paste into the openings of the rework stencil, printing the solder paste on the ground defective convex solder joints and performing reflow soldering to complete the rework of the defective products of the back tin-brushing products. The present invention completes the rework of defective products by physical grinding, reduces the risk of electrical defects of the products and shortens the rework cycle of the products at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of flip-chip light-emitting diodes, and particularly relates to a method for reworking defective products of back-brush tin products. Background Art

[0002] Flip Chip Bonding (abbreviated as FCB) is a surface array chip interconnection technology with high interconnectivity and interconnect strength. The initial method is to prefabricate solder bumps at the flip-chip pads, and at the same time print solder paste onto the PCB substrate pads. Then, through a die bonder, the unit chips on it are inverted so that the convex solder joints of the unit chips are aligned with the PCB substrate pads and welded to form a chip and PCB substrate package connected by intermetallic compounds. This method meets the requirements of miniaturization of microelectronic devices, reduces costs at the same time, and creates a larger space for the development of technology. Nowadays, with the continuous improvement and enhancement of process technology, FCB will become one of the most advanced technologies in packaging technology.

[0003] However, due to the complex manufacturing process of the solder convex solder joints, defective and rework problems are likely to occur in the convex solder joints on the back-brush tin products after reflow soldering. The existing technology generally uses aqua regia for major rework, which not only lengthens the product rework cycle, but also shows a downward trend in the performance of the chips after rework. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for reworking defective products of back-brush tin products, which is used to solve the technical problems that manual intervention and adjustment are prone to errors, the labor cost is relatively high, and the efficiency is relatively low in the existing technology.

[0005] The invention provides the following technical solutions. A method for reworking defective products of back-brush tin products, characterized in that the method comprises the following steps:

[0006] Step 1: Establish a physical model for the convex solder joints of the back-brush tin products;

[0007] Step 2: Grind the convex solder joints successively from top to bottom with a preset grinding thickness each time, and according to the physical model, obtain the current height of the convex solder joints and the current grinding plane radius of the convex solder joints after each grinding;

[0008] Step 3: Perform quadratic function fitting on the current height of the convex solder joints and the current grinding plane radius of the convex solder joints after each grinding to obtain a grinding function;

[0009] Step 4: According to the situation of the defective convex solder joints in the defective back-brush tin products, select the corresponding grinding thickness, and calculate the rework convex solder joint height and the corresponding rework convex solder joint grinding plane radius of the defective convex solder joints;

[0010] Step Five: Select a corresponding rework stencil for returning the height of the convex solder joint from the rework convex solder joint height to the initial height according to the height of the rework convex solder joint and the radius of the ground plane of the rework convex solder joint.

[0011] Step Six: Put the rework stencil on the defective convex solder joint after grinding, pour solder paste into the openings of the rework stencil, print the solder paste on the defective convex solder joint after grinding and perform reflow soldering to complete the rework of the defective product of the back-brush tin product.

[0012] Compared with the prior art, the beneficial effects of the present application are as follows: By establishing a grinding function corresponding to the current height of the convex solder joint and the current radius of the ground plane of the convex solder joint, and determining the grinding thickness and the radius of the ground plane of the rework convex solder joint according to the actual situation, a corresponding rework stencil is selected and solder paste is poured for reflow soldering to complete the rework of the defective product. The present invention uses a physical rework method to complete the rework of the defective product of the back-brush tin product, reduces the risk of electrical defects of the product while shortening the rework cycle, and at the same time improves the yield of the entire back-brush tin product after reflow soldering, providing guarantee for the welding reliability of downstream packaging.

[0013] Preferably, Step One includes:

[0014] Select the convex solder joints of several back-brush tin products, fit their outer contours into a hemispherical structure, place the fitted hemispherical structure in a three-dimensional space coordinate system, coincide the center of the bottom surface of the hemispherical structure with the origin of the three-dimensional space coordinate system, and make the height direction of the hemispherical structure parallel to the Z-axis of the three-dimensional space coordinate system to complete the establishment of the physical model.

[0015] Preferably, Step Two includes:

[0016] Obtain the number of grinding times n according to the ratio of the initial height of the convex solder joint to the preset grinding thickness, grind the convex solder joint with the preset grinding thickness from top to bottom for a total of n times. Calculate the current height of the convex solder joint each time after grinding, and import the current height of the convex solder joint after each grinding into the physical model to obtain the current radius of the ground plane of the convex solder joint after each grinding.

[0017] Preferably, in Step Two, the convex solder joint is ground by a grinding machine, and the grinding wheel speed of the grinding machine is 1200 r / min to 1800 r / min.

[0018] Preferably, in Step Three, the grinding function is used to characterize the corresponding relationship between the current height of the convex solder joint and the current radius of the ground plane of the convex solder joint, and the expression of the grinding function is: y = ax 2 + bx + c, where a, b, and c are all constants, x is the current radius of the ground plane of the convex solder joint, and y is the current height of the convex solder joint.

[0019] Preferably, step four includes:

[0020] According to the situation of the defective convex solder joints in the defective products of the back-brush tin products, select the corresponding grinding thickness H1, obtain the initial height H2 of the defective convex solder joints, and calculate the rework convex solder joint height H3 = H2 - H1 of the defective convex solder joints according to the grinding thickness H1 and the initial height H2. Grind the defective convex solder joints to the rework convex solder joint height through a grinding machine, and substitute the rework convex solder joint height into the grinding function to obtain the corresponding rework convex solder joint grinding plane radius.

[0021] Preferably, in step five, the length and width of the opening of the rework stencil are equal to twice the rework convex solder joint grinding plane radius.

[0022] Preferably, in step five, the thickness of the rework stencil is greater than the initial height of the defective convex solder joints.

[0023] Preferably, in step six, the steps of printing solder paste on the ground defective convex solder joints and performing reflow soldering include:

[0024] Feed the solder paste into the preheating zone and preheat it to 40°C - 150°C, then feed it into the constant temperature zone and keep it at a constant temperature of 150°C - 190°C for 60S - 120S. Finally, feed it into the soldering zone and solder it at a temperature above 230°C for 30S - 90S. After soldering is completed, let it stand and cool for a preset time to complete the rework of the defective products of the back-brush tin products.

[0025] Preferably, after step six, the method further includes:

[0026] Package the reworked back-brush tin products on a bracket and perform a thrust test. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is a flowchart of the method for reworking defective products of back-brush tin products provided by the first embodiment of the present invention;

[0029] Figure 2 It is a flowchart of the method for reworking defective products of back-brush tin products provided by the second embodiment of the present invention.

[0030] The present invention will be described in detail below with reference to the drawings. Specific embodiments

[0031] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the embodiments of the present invention and should not be construed as limiting the present invention.

[0032] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0033] Embodiment 1

[0034] In an embodiment of the present invention, as Figure 1 shown, a method for reworking defective back-tin-plated products includes the following steps:

[0035] Step 1: Establish a physical model for the convex solder joints of the back-tin-plated products;

[0036] In this embodiment, several convex solder joints of the back-tin-plated products are selected, and their outer contours are fitted into a hemispherical structure according to the outer contours of the several convex solder joints. Then, the fitted hemispherical structure is placed in a three-dimensional space coordinate system, with the center of the bottom surface of the hemispherical structure coinciding with the origin of the three-dimensional space coordinate system and the height direction of the hemispherical structure parallel to the Z-axis of the three-dimensional space coordinate system, thus completing the establishment of the physical model;

[0037] Specifically, according to the shape of the convex solder joints of the back-tin-plated products, a three-dimensional model thereof is constructed and presented in three-dimensional software. By establishing the physical model, it is convenient to obtain the grinding thickness and the radius of the ground plane of the convex solder joints after grinding in the subsequent steps;

[0038] At the same time, in this embodiment, the convex solder joints are hemispherical structures, and the physical model is a hemispherical physical model. In the actual construction process of the physical model, the convex solder joints can be approximately regarded as a hemisphere. Correspondingly, when establishing the physical model, a convex solder joint physical model in the form of a hemispherical structure should be established according to the shape of the convex solder joints.

[0039] Step 2: Grind the convex solder joints successively from top to bottom with a preset grinding thickness each time, and according to the physical model, obtain the current height of the convex solder joints and the current radius of the ground plane of the convex solder joints after each grinding;

[0040] Specifically, starting from the top of the convex solder joint, the convex solder joint is ground once according to a preset grinding thickness each time, and the number of grinding times is determined according to the ratio relationship between the preset grinding thickness and the initial thickness of the convex solder joint. At the same time, after each grinding, since the convex solder joint is a hemispherical structure, after grinding, a circle appears on its ground plane, that is, the top surface. And as the number of grinding times increases, the radius of its ground plane will gradually increase, and this grinding process can be reflected in the physical model. That is, from the vertex position of the physical model, a plane is set downward at a distance equal to the grinding thickness, and the physical model is truncated on the Z-axis, and this truncated plane is the ground plane after grinding. At the same time, the radius of the ground plane can be directly obtained on the physical model;

[0041] In this embodiment, this step is specifically as follows:

[0042] Obtain the number of grinding times n according to the ratio of the initial height of the convex solder joint to the preset grinding thickness. Grind the convex solder joint from top to bottom each time with the preset grinding thickness for a total of n times. After each grinding, calculate the current height of the convex solder joint, and import the current height of the convex solder joint after each grinding into the physical model to obtain the current grinding plane radius of the convex solder joint after each grinding;

[0043] In the process of specifically obtaining the current grinding plane radius of the convex solder joint, each grinding process is reflected in the physical model. That is, in the first grinding process, a thickness of X is ground. That is, at the vertex position of the physical model, draw a plane or a straight line parallel to the ground of the physical model of the convex solder joint, translate this straight line or plane downward by a distance of X, and determine the functional formula of this straight line or plane. According to the intersection points of this straight line or plane and the physical model, for the straight line functional formula, there are two intersection points between this straight line and the physical model. Calculate half of the distance between the two intersection points to calculate the current grinding plane radius of the convex solder joint. For the plane functional formula, there are countless intersection points between this plane and the physical model, but the intersection points between the two form a circle, and this circle is the ground plane. Just calculate the radius of this circle to calculate the current grinding plane radius of the convex solder joint;

[0044] And so on. In the subsequent grinding process, just continue to translate the plane or straight line parallel to the ground of the physical model of the convex solder joint downward by a distance equal to the preset grinding thickness, and then according to the intersection points between the straight line or plane and the physical model, the current height of the convex solder joint and the current grinding plane radius of the convex solder joint after each grinding can be calculated;

[0045] Specifically, the initial height of the convex solder joint is 80 um, and the preset grinding thickness is 10 um. Correspondingly, the number of grinding times n = 8. Then, in the grinding process of the convex solder joint, 8 grinding processes are required. The specific data of the current height of the convex solder joint and the current grinding plane radius of the convex solder joint are shown in Table 1:

[0046] Table 1 Current height data of convex solder joints and current radius data of ground flat surfaces of convex solder joints

[0047]

[0048] Meanwhile, during the specific grinding process, the convex solder joints are ground by a grinding machine table, and the rotational speed of the grinding wheel of the grinding machine table is 1200 r / min to 1800 r / min, preferably 1500 r / min. The feed rate of the grinding machine table is related to the preset grinding thickness.

[0049] Step 3: Perform quadratic function fitting on the current height of the convex solder joint and the current radius of the ground flat surface of the convex solder joint after each grinding to obtain a grinding function.

[0050] Specifically, since the physical model is a hemispherical structure and there is a certain functional relationship between the current height of the convex solder joint and the current radius of the ground flat surface of the convex solder joint, in this step, the data in Table 1 are subjected to quadratic fitting to obtain a quadratic function, that is, the grinding function. At the same time, due to the symmetry of the hemispherical structure of the physical model, the fitting of this grinding function satisfies the functional relationship between the actual current height of the convex solder joint and the current radius of the ground flat surface of the convex solder joint, and the authenticity is relatively high.

[0051] In this embodiment, the grinding function is used to characterize the corresponding relationship between the current height of the convex solder joint and the current radius of the ground flat surface of the convex solder joint, and the expression of the grinding function is: y = ax 2 + bx + c, where a, b, and c are all constants, x is the current radius of the ground flat surface of the convex solder joint, and y is the current height of the convex solder joint.

[0052] Therefore, substituting the parameters in Table 1 into the expression of the grinding function for fitting, it can be known that the expression of the grinding function is y = -0.0021x 2 - 0.2802x + 81.941, that is, a = -0.0021, b = -0.2802, and c = 81.941.

[0053] Step 4: According to the situation of defective convex solder joints in the defective products of back-brush soldering, select the corresponding grinding thickness, and calculate the rework convex solder joint height and the corresponding rework convex solder joint ground flat surface radius of the defective convex solder joints.

[0054] In this embodiment, according to the situation of the defective convex solder joints in the defective back-tin products, the corresponding grinding thickness H1 is selected, the initial height H2 of the defective convex solder joints is obtained, and the rework convex solder joint height H3 = H2 - H1 of the defective convex solder joints is calculated according to the grinding thickness H1 and the initial height H2. The defective convex solder joints are ground to the rework convex solder joint height by a grinding machine, and the rework convex solder joint height is substituted into the grinding function to obtain the corresponding rework convex solder joint grinding plane radius;

[0055] Among them, generally, all the convex solder joints need to be ground flat, that is, the grinding thickness needs to reach 80um, and the corresponding rework convex solder joint grinding plane radius needs to reach 142.5um. However, due to possible corresponding errors in actual observation and calculation, that is, after reserving an error range of ±2.5um, the rework convex solder joint grinding plane radius is 137.5um.

[0056] Step Five: According to the rework convex solder joint height and the rework convex solder joint grinding plane radius, select the corresponding rework stencil for returning the convex solder joint from the rework convex solder joint height to the initial height;

[0057] Specifically, since in the previous steps, the rework convex solder joint height and the rework convex solder joint grinding plane radius have been determined, where the rework convex solder joint height is 80um and the rework convex solder joint grinding plane radius is 137.5um, when selecting the rework stencil, the opening size and thickness of the rework stencil need to be determined according to the rework convex solder joint height and the rework convex solder joint grinding plane radius;

[0058] In this embodiment, the length and width of the opening of the rework stencil are equal to twice the rework convex solder joint grinding plane radius. Therefore, the actual length and width of the opening of the rework stencil are 137.5um to ensure that the final grinding plane of the convex solder joint can be within the opening range of the rework stencil. At the same time, the thickness of the rework stencil is greater than the initial height of the defective convex solder joint. Therefore, the thickness of the rework stencil is 95um, so as to ensure that the convex solder joint after rework can return to the original initial height of 80um;

[0059] At the same time, since a printing stencil is required during the forming process of the convex solder joint, and when printing the convex solder joint, it is necessary to ensure that the length and width of the opening of the printing stencil are equal to twice the bottom radius of the convex solder joint, and the thickness of the rework stencil is greater than the final height of the convex solder joint, that is, the size and position of the printing stencil and the rework stencil are the same. Therefore, to ensure the opening consistency between the rework stencil and the printing stencil, there is no need to prepare a rework stencil, and the original printing stencil can be used to replace the rework stencil. In this way, the printing stencil can be used normally, and at the same time, the function of the rework stencil is taken into account, realizing the method of "using one stencil for two purposes".

[0060] Step 6: Place the rework stencil on the defective convex solder joints after grinding them flat, pour solder paste into the openings of the rework stencil, print the solder paste on the defective convex solder joints after grinding them flat, and perform reflow soldering to complete the rework of defective products of the back-brush tin products;

[0061] Specifically, place the ground surface of the defective convex solder joints at the opening positions of the rework stencil, pour the corresponding solder paste, print the solder paste and perform reflow soldering at the same time to ensure that the convex solder joints can form a dome-shaped structure to ensure the appearance consistency before and after rework;

[0062] In this embodiment, the step of printing the solder paste on the defective convex solder joints after grinding them flat and performing reflow soldering includes:

[0063] Send the solder paste into the preheating zone to be preheated to 40°C - 150°C, then send it into the constant temperature zone and keep it at a constant temperature of 150°C - 190°C for 60S - 120S. Finally, send it into the soldering zone and solder it at a temperature above 230°C for 30S - 90S. After soldering is completed, let it stand and cool for a preset time to complete the rework of defective products of the back-brush tin products;

[0064] Among them, the heating rate of the preheating zone is between 1 and 3, and the heating time is between 30S and 120S. After heating to a certain temperature, send it into the constant temperature zone and keep it at a constant temperature for a certain time. After keeping it for a certain time, it needs to be heated to the welding required temperature, and the heating time required for this heating process is 30S - 60S. Finally, perform soldering on it, and its specific soldering temperature is about 240°C. In the actual reflow soldering process, after soldering is completed, the defective products of the back-brush tin products after soldering need to be sent into the cooling zone to stand and cool, and the cooling rate can be slightly greater than the heating rate of the preheating zone to achieve rapid cooling of the defective products of the back-brush tin products. After cooling is completed, the solder paste changes from the initial liquid state to a fixed state, and at the same time, the fixed solder paste replaces the convex solder joints ground in the previous step, so that it returns from the height of the rework convex solder joints to its initial height before grinding to meet the product consistency before and after rework.

[0065] The advantage of this first embodiment is that by establishing a grinding function corresponding to the current height of the convex solder joints and the current radius of the ground surface of the convex solder joints, and according to the actual situation, determining the grinding thickness and the radius of the ground surface of the rework convex solder joints, selecting the corresponding rework stencil and pouring solder paste for reflow soldering to complete the rework of defective products. The present invention uses a physical rework method to complete the rework of defective products of the back-brush tin products, reduces the risk of electrical defects of the products, shortens the rework cycle, and at the same time improves the yield of the entire back-brush tin products after reflow soldering, providing guarantee for the welding reliability of downstream packaging.

[0066] Embodiment 2

[0067] In the second embodiment of the present invention, asFigure 2 As shown in Figure 2 , a method for reworking defective back-tin-plated products, the method comprising the following steps

[0068] Step 1: Establish a physical model for the convex solder joints of the back-tin-plated products;

[0069] Step 2: Grind the convex solder joints successively from top to bottom with a preset grinding thickness each time, and according to the physical model, obtain the current height of the convex solder joints and the current radius of the grinding plane of the convex solder joints after each grinding;

[0070] Step 3: Perform quadratic function fitting on the current height of the convex solder joints and the current radius of the grinding plane of the convex solder joints after each grinding to obtain a grinding function;

[0071] Step 4: According to the situation of the defective convex solder joints in the defective back-tin-plated products, select the corresponding grinding thickness, calculate the height of the reworked convex solder joints of the defective convex solder joints according to the grinding thickness, grind the defective convex solder joints to the height of the reworked convex solder joints, and according to the grinding function, obtain the corresponding radius of the grinding plane of the reworked convex solder joints;

[0072] Step 5: Select the corresponding rework stencil according to the height of the reworked convex solder joints and the radius of the grinding plane of the reworked convex solder joints;

[0073] Step 6: Put the rework stencil on the ground defective convex solder joints, pour solder paste into the openings of the rework stencil, print the solder paste on the ground defective convex solder joints and perform reflow soldering to complete the rework of the defective back-tin-plated products

[0074] Step 7: Package the reworked back-tin-plated products on a bracket for a thrust test;

[0075] Specifically, after the test is completed, according to the test results, judge whether the thrust test result is higher than the customer's required thrust. If the thrust test result is higher than the customer's required thrust, the next process can be entered. If the thrust test result is not higher than the customer's required thrust, repeat the above steps 1 to 6 until the thrust test result is higher than the customer's required thrust;

[0076] The difference between the first embodiment and the second embodiment is that by adding a process of packaging the reworked back-tin-plated products on a bracket for a thrust test, so as to verify whether the reworked back-tin-plated products meet the customer's requirements, and the specific experimental data is shown in Table 2 below:

[0077] Table 2 Thrust test data

[0078]

[0079] For the convenience of comparison, in this embodiment, the back tinning qualified products and the back tinning rework products are also introduced for comparison. From the comparison results, it can be seen that the thrust test data of the back tinning rework products obtained by the rework processing method provided in this embodiment and the back tinning qualified products have little difference, and both can meet the actual needs of customers.

[0080] The advantage of the second embodiment compared with the first embodiment is that by adding the step of thrust test, it can further reflect that the rework processing method provided by the present invention can reduce the product nonconformance risk, and at the same time, it can also prevent the nonconforming products after rework from flowing into the market.

[0081] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for reworking defective products of back-tin-plated products, characterized in that, The method includes the following steps: Step 1: Establish a physical model for the convex solder joints of the back-tin-brushing products. Step 2: Grind the convex solder joints downwards one by one with a preset grinding thickness each time, and according to the physical model, obtain the current height of the convex solder joints and the current radius of the grinding plane of the convex solder joints after each grinding. Step 3: Perform quadratic function fitting on the current height of the convex solder joints and the current radius of the grinding plane of the convex solder joints after each grinding to obtain a grinding function. Step 4: According to the situation of the defective convex solder joints in the defective back-tin-brushing products, select the corresponding grinding thickness, and calculate the rework height of the defective convex solder joints and the corresponding rework radius of the grinding plane of the convex solder joints. Step 5: According to the rework height of the convex solder joints and the rework radius of the grinding plane of the convex solder joints, select the corresponding rework stencil for returning the convex solder joints from the rework height back to the initial height. Step 6: Put the rework stencil on the ground defective convex solder joints, pour solder paste into the openings of the rework stencil, print the solder paste on the ground defective convex solder joints and perform reflow soldering to complete the rework of the defective back-tin-brushing products. Among them, Step 1 includes: Select the convex solder joints of several back-tin-brushing products, fit their outer contours into a hemispherical structure according to several of the convex solder joints, place the fitted hemispherical structure in a three-dimensional space coordinate system, coincide the center of the bottom surface of the hemispherical structure with the origin of the three-dimensional space coordinate system, and make the height direction of the hemispherical structure parallel to the Z-axis of the three-dimensional space coordinate system to complete the establishment of the physical model. In the third step, the flattening function is used to characterize the corresponding relationship between the current height of the convex solder joint and the current radius of the flattened surface of the convex solder joint, and the expression of the flattening function is: y = ax 2 + bx + c, where a, b, and c are all constants, x is the current radius of the flattened surface of the convex solder joint, and y is the current height of the convex solder joint.

2. The method for reworking defective products of the back-tin-plated product according to claim 1, characterized in that, Step 2 includes: Obtain the number of grinding times n according to the ratio of the initial height of the convex solder joints to the preset grinding thickness. Grind the convex solder joints downwards one by one with a preset grinding thickness each time for a total of n times. Calculate the current height of the convex solder joints each time after grinding, and import the current height of the convex solder joints after each grinding into the physical model to obtain the current radius of the grinding plane of the convex solder joints after each grinding.

3. The method for reworking defective products of the back tin-plated product according to claim 2, characterized in that, In Step 2, the convex solder joints are ground by a grinding machine platform, and the grinding wheel speed of the grinding machine platform is 1200 r / min to 1800 r / min.

4. The method for reworking defective products of the back-tin-plated product according to claim 1, characterized in that, Step 4 includes: According to the situation of the defective convex solder joints in the defective back-tin-brushing products, select the corresponding grinding thickness H1, obtain the initial height H2 of the defective convex solder joints, and calculate the rework height H3 = H2 - H1 of the defective convex solder joints according to the grinding thickness H1 and the initial height H2. Grind the defective convex solder joints to the rework height by a grinding machine platform, and substitute the rework height into the grinding function to obtain the corresponding rework radius of the grinding plane of the convex solder joints.

5. The method for reworking defective products of the back-tin-plated product according to claim 1, characterized in that, In Step 5, the length and width of the opening of the rework stencil are equal to twice the rework radius of the grinding plane of the convex solder joints.

6. The method for reworking defective products of the back-tin-plated product according to claim 1, characterized in that, In Step 5, the thickness of the rework stencil is greater than the initial height of the defective convex solder joints.

7. The method for reworking defective products of the back-tin-plated product according to claim 1, characterized in that, In Step 6, the step of printing the solder paste on the ground defective convex solder joints and performing reflow soldering includes: Feed the solder paste into the preheating zone and preheat it to 40°C - 150°C. Then, feed it into the constant temperature zone and keep it at a constant temperature of 150°C - 190°C for 60S - 120S. Finally, feed it into the soldering zone and solder it at a temperature above 230°C for 30S - 90S. After soldering is completed, let it stand and cool for a preset time to complete the rework of defective back-brush tin products.

8. The method for reworking defective products of the back tin-plated product according to claim 1, wherein, After the step six, the method further includes: Package the reworked back-brush tin product on a bracket for a thrust test.

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