Method and system for evaluating soldering quality of metal gate line and solder strips

Abstract

A method and system for evaluating the soldering quality of a metal gate line and solder strips, the method comprising: constructing a resistance model of a target object (100) to obtain a relational expression of resistance R between solder strips (130) of a preset spacing D of the target object (100), gate line resistance Rf per unit distance of a gate line (120), contact resistance Rc between the gate line (120) and the solder strips (130), and resistance Rr of the solder strips (130) extending out of the edge of a body (110); measuring resistance values R between the solder strips (130) of different spacings D; on the basis of measurement results, obtaining a relationship diagram between the resistance values R and the spacings D; and, on the basis of the relational expression and the relationship diagram, evaluating the soldering quality of the target object (100). The method and system for evaluating the soldering quality of a metal gate line and solder strips can improve soldering processes on the basis of evaluation results, so as to improve the soldering quality, thereby improving the performance of entire battery modules.

Description

Methods and systems for evaluating the welding quality of metal grid wires and solder strips Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a method and system for evaluating the welding quality of metal grid lines and solder strips. Background Technology

[0002] After the solar cells are manufactured, multiple cells need to be welded together to form a solar cell assembly, and then packaged to form a solar module. The quality of the weld affects the weld resistance, which in turn affects the performance of the entire solar module. Existing TLM contact resistance testing methods can only test the contact resistance of thin layers of material on the solar cells, and cannot test the contact resistance between the photovoltaic cell's metal grid lines and the solder ribbon. Since contact resistance reflects weld quality, the inability to know the weld resistance means that the overall weld quality of the solar module cannot be determined, and consequently, improvements to the entire weld process cannot be made to enhance the performance of the entire solar module. Summary of the Invention

[0003] One objective of the first aspect of this invention is to provide a method for evaluating the welding quality of metal grid lines and solder strips, thereby solving the problem in the prior art that the welding quality of the entire battery module cannot be known.

[0004] A second aspect of the present invention is to provide a welding quality assessment system for metal grid lines and solder strips.

[0005] In particular, the present invention also provides a method for evaluating the welding quality of metal grid lines and solder strips, for evaluating the welding quality of a target object, the target object including a battery cell, a battery string, or a finished solar cell; the target object includes a body, at least one grid line, and multiple parallel and spaced solder strips; the at least one grid line is disposed at the body; each solder strip is in contact with all the grid lines, and at least a portion of the solder strip extends outside the body;

[0006] The evaluation method includes:

[0007] A resistance model of the target object is constructed to obtain the relationship between the resistance R between the solder strips at a preset spacing D, the grid line resistance Rf per unit distance of the grid line, the contact resistance Rc between the grid line and the solder strip, and the resistance Rr of the solder strip extending from the edge of the body; wherein, the relationship is:

[0008] R = (D × Rf + 2Rc) / n + Rr;

[0009] The resistance value R between the solder strips with different spacings D is detected;

[0010] The relationship between the resistance value R and the spacing D is obtained based on the detection results; wherein, the relationship diagram is a line graph formed by connecting the corresponding points with the resistance value R as the vertical axis and the spacing D as the horizontal axis.

[0011] The welding quality of the target object is evaluated based on the stated formula and the stated diagram.

[0012] Optionally, the step of constructing the resistance model of the target object to obtain the relationship includes:

[0013] Obtain the corresponding circuit diagram based on the structure of the target object;

[0014] The relationship is derived from the circuit diagram.

[0015] Optionally, obtaining the corresponding circuit diagram based on the structure of the target object includes:

[0016] When the target object contains only n=1 gate lines, the circuit diagram includes a circuit formed by connecting a first resistor located in the body and a second resistor of the solder strip extending from the body in series; wherein, the first resistor is the sum of the resistance (D×Rf) of the gate line between two solder strips spaced D apart and the contact resistance 2Rc between the solder strip and the gate line.

[0017] Optionally, the step of obtaining the corresponding circuit diagram based on the structure of the target object includes:

[0018] When the target object contains n greater than 1 gate lines, the circuit diagram is formed by connecting a first resistor and a third resistor in series, then connecting the third resistor in parallel with the first resistor, then connecting the third resistor in series with the next third resistor, then connecting the third resistor in parallel with the next first resistor, and so on, until the last third resistor is connected in series with the last first resistor, and finally connecting the third resistor in series with the last first resistor, and finally connecting the third resistor in series with the second resistor. The first resistor is the sum of the resistance (D×Rf) of the gate line between two solder strips spaced D apart and the contact resistance 2Rc between the solder strip and the gate line; the second resistor is the resistance of the solder strip extending from the body; and the third resistor is the resistance 2Rs of the solder strip between two gate lines.

[0019] The resistance 2Rs of the solder strip between the two gate lines in the third resistor of the sub-unit is removed to form a circuit consisting of only n first resistors connected in parallel and then connected in series with the second resistor.

[0020] Optionally, the step of evaluating the welding quality of the target object based on the relationship formula and the relationship diagram includes:

[0021] The welding quality at different locations of the target object is evaluated based on the relationship diagram of the same target object.

[0022] Optionally, the step of evaluating the welding quality at different locations of the same target object based on the relationship diagram includes:

[0023] Determine whether the lines in the relationship diagram are straight lines;

[0024] If so, the welding quality is the same at different locations of the target object;

[0025] If not, the welding quality will vary at different locations on the target object.

[0026] Optionally, the step of evaluating the different welding quality at different locations of the target object further includes:

[0027] The positions of inflection points with included angles less than a preset angle are obtained from the lines in the relationship diagram.

[0028] When the protrusion of the inflection point faces upwards along the line, the welding quality at that point is greater than the welding quality at other points.

[0029] When the protrusion of the inflection point faces downwards from the line, the welding quality at that point is lower than that at other points.

[0030] Optionally, the step of evaluating the welding quality of the target object based on the relationship formula and the relationship diagram includes:

[0031] The welding quality of different target objects is evaluated based on the relationship diagrams of different target objects.

[0032] Optionally, the step of evaluating the welding quality of different target objects based on the relationship diagrams of different target objects includes:

[0033] Obtain a relationship diagram of the target object where the lines are straight lines;

[0034] Compare the intercepts of the straight lines and the vertical axis of the relationship diagrams for different target objects;

[0035] The welding quality of the target object with a larger intercept is less than that of the target object with a smaller intercept.

[0036] In particular, the present invention also provides a welding quality assessment system for metal grid lines and solder strips, comprising assessing the welding quality of the metal grid lines and solder strips of a target object according to the welding quality assessment method for metal grid lines and solder strips described above.

[0037] This solution constructs a resistance model to obtain the relationship between the resistance between solder strips with a preset spacing and the resistance of each component. The relationship shows a linear relationship between the resistance between solder joints with the preset spacing and the preset spacing itself. Furthermore, by detecting the resistance values ​​between solder strips with different spacings, a graph showing the relationship between resistance and spacing is obtained. After obtaining the graph, it can be determined from the formula that an ideal graph should be a straight line, with the slope being the grid resistance Rf per unit distance, and the intercept being the sum of the contact resistance Rc and the resistance Rr of the solder strip extending beyond the edge of the body. The resistance Rr of the solder strip extending beyond the edge of the body can be obtained through detection. Therefore, not only can the grid resistance Rf per unit distance be obtained, but the contact resistance Rc can also be calculated. Furthermore, by observing the graph, the welding quality of the target object can be evaluated, and the welding process can be improved based on the evaluation results to enhance welding quality and ultimately improve the performance of the entire battery module.

[0038] This solution analyzes the welding quality at different locations of the same target object or between different target objects, which can further improve the welding process, thereby enhancing the welding quality and improving the performance of the entire battery module.

[0039] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0040] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0041] Figure 1 is a schematic structural diagram of a target object according to a specific embodiment of the present invention;

[0042] Figure 2 is a schematic structural diagram of the target object according to another specific embodiment of the present invention.

[0043] Figure 3 is a schematic flowchart of a welding quality assessment method for metal grid lines and solder strips according to a specific embodiment of the present invention;

[0044] Figure 4 is a schematic flowchart of obtaining the relational expression by constructing the resistance model of the target object according to a specific embodiment of the present invention;

[0045] Figure 5 is a circuit diagram of a target object according to a specific embodiment of the present invention;

[0046] Figure 6 is a circuit diagram of the target object according to another specific embodiment of the present invention;

[0047] Figure 7 is a simplified circuit diagram of Figure 6;

[0048] Figure 8 is a schematic flowchart of evaluating the welding quality of different positions of a target object based on a relationship diagram of the same target object according to a specific embodiment of the present invention;

[0049] Figure 9 is a graph showing the relationship between resistance and spacing according to a specific embodiment of the present invention;

[0050] Figure 10 is a graph showing the relationship between resistance and spacing according to another specific embodiment of the present invention;

[0051] Figure 11 is a schematic flowchart of evaluating the welding quality of different target objects based on the relationship diagram of different target objects according to a specific embodiment of the present invention;

[0052] Figure 12 is a diagram showing the relationship between different target objects according to a specific embodiment of the present invention.

[0053] Explanation of reference numerals in the attached figures:

[0054] Target object - 100; Body - 110; Grid line - 120; Solder strip - 130; First resistor - 200; Second resistor - 300; Third resistor - 400. Detailed Implementation

[0055] In the description of this embodiment, it should be understood that the terms "length", "width", "height", "upper", "lower", "left", "right", "vertical", "horizontal", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0056] As a specific embodiment of the present invention, as shown in Figures 1 and 2, this embodiment provides a method for evaluating the welding quality of metal grid lines and solder strips. This evaluation method is used to assess the welding quality of a target object. Specifically, the target object in this embodiment can be a battery cell, a battery string, or a finished solar cell. Each target object 100 may include a body 110, at least one grid line 120, and multiple parallel and spaced solder strips 130. At least one grid line 120 is disposed at the body 110. Each solder strip 130 is in contact with all grid lines 120, and at least a portion of the solder strip 130 extends beyond the body 110.

[0057] Specifically, as shown in Figure 3, the evaluation method of this embodiment may include:

[0058] Step S100: Construct a resistance model of the target object 100, and obtain the relationship between the resistance R between the solder ribbons 130 at a preset spacing D of the target object 100, the grid line resistance Rf per unit distance of the grid line 120, the contact resistance Rc between the grid line 120 and the solder ribbon 130, and the resistance Rr of the solder ribbon 130 extending from the edge of the body 110; wherein, the relationship is:

[0059] R = (D × Rf + 2Rc) / n + Rr;

[0060] Step S200: Detect the resistance value R between solder strips 130 with different spacings D;

[0061] Step S300: Obtain the relationship diagram between resistance value R and spacing D based on the detection results; wherein, the relationship diagram is a line graph formed by connecting multiple points with resistance value R as the vertical axis and spacing D as the horizontal axis.

[0062] Step S400: Evaluate the welding quality of target object 100 based on the formula and diagram.

[0063] Specifically, in this embodiment, by constructing a resistance model, the relationship between the resistance between the solder strips 130 with a preset spacing and the resistance of each part is obtained. The relationship shows that the resistance between solder joints with a preset spacing is linearly related to the preset spacing. Then, by detecting the resistance values ​​between solder strips 130 with different spacings, a relationship graph between the resistance value and the spacing is obtained. After obtaining the relationship graph, it can be known from the relationship formula that the ideal relationship graph should be a straight line, and the slope of the line is the grid line resistance Rf per unit distance, the intercept is the sum of the contact resistance Rc and the resistance Rr of the solder strips 130 extending from the edge of the body 110, and the resistance Rr of the solder strips 130 extending from the edge of the body 110 can be obtained through detection. Therefore, not only can the grid line resistance Rf per unit distance be obtained, but the contact resistance Rc can also be calculated. Furthermore, by observing the relationship graph, the welding quality of the target object 100 can be evaluated, and the welding process can be improved based on the evaluation results to enhance the welding quality.

[0064] As a specific embodiment of the present invention, as shown in FIG4, step S100 of constructing the resistance model of the target object 100 to obtain the relational expression may include:

[0065] Step S110: Obtain the corresponding circuit diagram based on the structure of the target object 100;

[0066] Step S120: Obtain the relational expression based on the circuit diagram.

[0067] Specifically, step S110, which involves obtaining the corresponding circuit diagram based on the structure of the target object 100, may include:

[0068] When the target object 100 contains only n=1 grid lines 120, its target object (which can be a battery cell) structure is shown in Figure 1, and the circuit diagram is shown in Figure 5. At this time, the circuit diagram includes a circuit formed by connecting the first resistor 200 located inside the body 110 and the second resistor 300 of the solder strip 130 extending out of the body 110 in series. Among them, the first resistor 200 is the sum of the grid line resistance (D×Rf) between the two solder strips 130 that are separated by a distance D and the contact resistance 2Rc between the solder strip 130 and the grid line 120.

[0069] Specifically, when the target object has only one grid line 120, the structure of the target object (as shown in Figure 1) consists of two solder ribbons 130 and one grid line 120. A detection device is connected between the two extended solder ribbons 130 to detect the resistance. Thus, the formed circuit (as shown in Figure 5) consists of the contact resistance 2Rc between the solder ribbon 130 and the grid line 120, the grid line resistance (D×Rf) between the two solder ribbons 130, and the resistance Rr of the extended solder ribbon 130 connected in series. In this circuit diagram, the first resistor 200 only includes the grid line resistance between the two solder ribbons 130 and the contact resistance between the grid line 120 and the solder ribbon 130. The relationship can be: R = (D×Rf + 2Rc) / n + Rr, where n = 1.

[0070] Specifically, step S110, which involves obtaining the corresponding circuit diagram based on the structure of the target object 100, may include:

[0071] When the target object 100 contains n+1 gate lines 120, the structure is shown in Figure 2. The circuit diagram at this time is shown in Figure 6. The circuit diagram is formed by connecting the first resistor 200 and the third resistor 400 in series, then connecting them in parallel with the first resistor 200, then connecting them in series with the next third resistor 400, then in parallel with the next first resistor 200, and so on, until the last third resistor 400 is connected in series with the last first resistor 200. Finally, the circuit is connected in series with the second resistor 300. Here, the first resistor 200 is the sum of the resistance (D×Rf) of the gate line between two solder ribbons spaced D apart and the contact resistance 2Rc between the solder ribbon 130 and the gate line 120. The second resistor 300 is the resistance of the solder ribbon 130 extending from the body 110. The third resistor 400 is the resistance 2Rs of the solder ribbon 130 between two gate lines 120. At this time, the relationship can be R=[(D×Rf+2Rc]]. n +2Rs×(D×Rf+2Rc) n-1 ] / [n×(D×Rf+2Rc) n-1 +2Rs× (n-1) × (D×Rf+2Rc) n-2 ]+ Rr, where n is an integer greater than 1.

[0072] By removing the resistance 2Rs of the solder strip 130 between the two gate lines 120 in the third resistor 400 of the sub-unit, a circuit is formed consisting of only n first resistors 200 connected in parallel, and then connected in series with the second resistor 300 (as shown in Figure 7). At this time, the relationship after removing the resistance 2Rs of the solder strip 130 between the two gate lines 120 becomes R = (D × Rf + 2Rc) / n + Rr, where n is an integer greater than 1.

[0073] In this embodiment, when there are multiple grid lines 120 in the target object 100, the structure of the target object consists of multiple parallel grid lines 120 and two solder ribbons 130 that are in contact with all of the grid lines 120. The circuit formed when the detection device detects the resistance between two solder ribbons 130 is shown in Figure 6. This circuit consists of a first resistor 200 connected in series with a third resistor 400, then connected in parallel with the first resistor 200, then connected in series with the next third resistor 400, then in parallel with the next first resistor 200, and so on, until the last third resistor 400 is connected in series with the last first resistor 200. Finally, this circuit is connected in series with a second resistor 300. Since the resistance 2Rs of the solder ribbon 130 between the two grid lines 120 is negligible compared to the contact resistance 2Rc, the circuit diagram can be simplified by removing the resistance 2Rs of the solder ribbon 130 between the two grid lines 120 in the third resistor 400. Thus, a circuit is formed consisting of n first resistors of 200Ω connected in parallel, and then connected in series with the second resistor of 300Ω, as shown in Figure 7. The final equation can be combined with the equation for n=1 to form:

[0074] R = (D × Rf + 2Rc) / n + Rr; where n is a natural number.

[0075] As a specific embodiment of the present invention, step S400 of evaluating the welding quality of the target object 100 based on the relational formula and relational diagram may include:

[0076] Step S410: Evaluate the welding quality at different positions of the target object 100 based on the relationship diagram of the same target object 100.

[0077] As a specific embodiment of the present invention, as shown in FIG8, step S410, which evaluates the welding quality of different positions of the target object 100 based on the relationship diagram of the same target object 100, includes:

[0078] Step S411: Determine whether the lines in the relationship diagram are straight lines;

[0079] If yes, proceed to step S412; otherwise, proceed to step S413.

[0080] Step S412: The welding quality is the same at different positions of the target object 100;

[0081] In step S413, the welding quality varies at different locations on the target object 100.

[0082] Specifically, if the welding quality is the same at each location, the contact resistance of the solder strip 130 and the grid line 120 at each location will be the same, thus forming a straight line (as shown in Figure 9). Of course, in actual resistance testing, there will be errors. Within the allowable error range, the line can be considered a straight line or a near-straight line, or the angle at the inflection point can be close to 180°, for example, greater than 165°. Therefore, by observing whether the lines in the relationship diagram are straight lines, one can determine whether the welding quality at different locations of the target object 100 is the same.

[0083] Specifically, in this embodiment, if the welding quality is the same at different locations of the same target object 100, then the welding resistance at different locations is also the same. This is ultimately reflected in the relationship diagram as the line intercepting the vertical axis being the same. If the relationship diagram of the entire target object 100 is a straight line, it indicates that the slope of each place is consistent, and the intercept of the straight line formed is also consistent, indicating that the welding quality is the same.

[0084] When the resulting relationship diagram is not a straight line (as shown in Figure 10), the slope and intercept at different positions may also be different, which in turn represents different welding quality at different positions.

[0085] The steps for assessing the different weld quality at different locations on target object 100 also include:

[0086] Based on the lines in the relationship diagram, identify the positions of inflection points with angles less than a preset value;

[0087] When the protruding part of the inflection point faces upwards along the line, the welding quality at that point is greater than that at other points.

[0088] When the protruding part of the inflection point faces downwards from the line, the welding quality at that point is lower than that at other points.

[0089] More specifically, by connecting different points, the value at locations with varying welding quality will deviate from the straight line. Connecting multiple points in this way creates a broken line. Within the error range, if the angle 'a' at the inflection point of the broken line is close to 180°, it can be considered a straight line. Only when the angle 'a' at the inflection point is less than a preset angle is it considered to be due to welding quality issues. Specifically, in this embodiment, the preset angle can be approximately 165°.

[0090] If the protruding part of the inflection point faces upwards from the line, it indicates that the detected resistance value is greater than the normal resistance value. Since the contact resistance is connected in parallel in the circuit, this means the contact resistance is lower, indicating better weld quality at this location. Conversely, if the protruding part of the inflection point faces downwards from the line, it indicates that the detected resistance value is lower than the normal resistance value, meaning the weld resistance is higher, further indicating poorer weld quality at this location.

[0091] As a specific embodiment of the present invention, step S400 of evaluating the welding quality of the target object 100 based on the relational formula and relational diagram includes:

[0092] Step S420: Evaluate the welding quality of different target objects 100 based on the relationship diagram of different target objects 100.

[0093] Specifically, as shown in Figure 11, step S420, which evaluates the welding quality of different target objects 100 based on the relationship diagrams of different target objects, includes:

[0094] Step S421: Obtain the relationship diagram of the target object 100 where the lines are straight lines;

[0095] Step S422: Compare the intercepts of the straight lines in the relationship diagrams of different target objects 100;

[0096] In step S423, the welding quality of the target object 100 with a larger intercept is less than that of the target object 100 with a smaller intercept.

[0097] Specifically, when evaluating the welding quality of different target objects 100, it is possible to observe whether the lines in the relationship graph are straight. For non-straight welded batteries, the reasons for the stability of the weld and further improvements can be analyzed separately. For the straight lines in the relationship graph of different target objects 100, the intercept of the line with the vertical axis yields the contact resistance of that target object 100, thus obtaining the welding resistance of different target objects (as shown in Figure 12). By comparing the contact resistance of different target objects 100, the welding quality of different target objects 100 can be evaluated. By comparing the welding processes of different target objects 100, directions for improvement can be found to enhance the performance of the battery module.

[0098] Generally, since the intercept of the straight line is the sum of the contact resistance and the resistance of the solder strip 130, and the resistance of the solder strip 130 is generally the same, a target object 100 with a larger intercept indicates a larger contact resistance, and its welding quality is worse than that of a target object 100 with a smaller intercept (i.e., lower contact resistance). By comparing the welding process of the target object 100 with poor welding quality, we can analyze areas for improvement and enhance the performance of the solar cells.

[0099] Furthermore, the resistance per unit length of the gate line 120 can be determined from the slope in the relationship diagram of the target object 100, thereby evaluating the quality of the gate line 120. The fabrication process of the gate line 120 can be adjusted based on its resistance to improve the performance of the target object.

[0100] This embodiment analyzes the welding quality at different locations of the same target object 100 or the welding quality between different target objects to further improve the welding process, thereby enhancing the welding quality and improving the performance of the entire battery module.

[0101] As a specific embodiment of the present invention, this embodiment also provides a welding quality assessment system for metal grid lines 120 and solder strips 130. This assessment system may include assessing the welding quality of the metal grid lines 120 and solder strips 130 of the target object 100 according to the welding quality assessment method for metal grid lines 120 and solder strips 130 described above.

[0102] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. A method for evaluating the welding quality of metal grid lines and solder strips, characterized in that, The material is used to evaluate the welding quality of a target object, which includes a battery cell, a battery string, or a finished solar cell. Each target object includes a body, at least one grid line, and multiple parallel and spaced weld strips. The at least one grid line is located on the body. Each of the solder strips is in contact with all of the gate lines, and at least a portion of the solder strips extends beyond the body. The evaluation method includes: A resistance model of the target object is constructed to obtain the relationship between the resistance R between the solder strips at a preset spacing D, the grid line resistance Rf per unit distance of the grid line, the contact resistance Rc between the grid line and the solder strip, and the resistance Rr of the solder strip extending from the edge of the body; wherein, the relationship is: R = (D × Rf + 2Rc) / n + Rr; The resistance value R between the solder strips with different spacings D is detected; The relationship between the resistance value R and the spacing D is obtained based on the detection results; wherein, the relationship diagram is a line graph formed by connecting the corresponding points with the resistance value R as the vertical axis and the spacing D as the horizontal axis. The welding quality of the target object is evaluated based on the stated formula and the stated diagram.

2. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 1, characterized in that, The steps for constructing the resistance model of the target object to obtain the relationship include: Obtain the corresponding circuit diagram based on the structure of the target object; The relationship is derived from the circuit diagram.

3. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 2, characterized in that, The steps for obtaining the corresponding circuit diagram based on the structure of the target object include: When the target object contains only n=1 gate lines, the circuit diagram includes a circuit formed by connecting a first resistor located in the body and a second resistor of the solder strip extending from the body in series; wherein, the first resistor is the sum of the resistance (D×Rf) of the gate line between two solder strips spaced D apart and the contact resistance 2Rc between the solder strip and the gate line.

4. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 2, characterized in that, The steps for obtaining the corresponding circuit diagram based on the structure of the target object include: When the target object contains n greater than 1 gate lines, the circuit diagram is formed by connecting a first resistor and a third resistor in series, then connecting the third resistor in parallel with the first resistor, then connecting the third resistor in series with the next third resistor, then connecting the third resistor in parallel with the next first resistor, and so on, until the last third resistor is connected in series with the last first resistor, and finally connecting the third resistor in series with the last first resistor, and finally connecting the third resistor in series with the second resistor. The first resistor is the sum of the resistance (D×Rf) of the gate line between two solder strips spaced D apart and the contact resistance 2Rc between the solder strip and the gate line; the second resistor is the resistance of the solder strip extending from the body; and the third resistor is the resistance 2Rs of the solder strip between two gate lines. The third resistor 2Rs of the sub-unit is removed to form a circuit consisting of only n first resistors connected in parallel and then connected in series with the second resistor.

5. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 1, characterized in that, The steps for evaluating the welding quality of the target object based on the relationship formula and the relationship diagram include: The welding quality at different locations of the target object is evaluated based on the relationship diagram of the same target object.

6. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 5, characterized in that, The steps for evaluating the welding quality at different locations of the same target object based on the relationship diagram include: Determine whether the lines in the relationship diagram are straight lines; If so, the welding quality is the same at different locations of the target object; If not, the welding quality will vary at different locations on the target object.

7. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 1, characterized in that, The steps for assessing the different welding quality at different locations of the target object also include: The positions of inflection points with included angles less than a preset angle are obtained from the lines in the relationship diagram. When the protrusion of the inflection point faces upwards along the line, the welding quality at that point is greater than the welding quality at other points. When the protrusion of the inflection point faces downwards from the line, the welding quality at that point is lower than that at other points.

8. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 1, characterized in that, The steps for evaluating the welding quality of the target object based on the relationship formula and the relationship diagram include: The welding quality of different target objects is evaluated based on the relationship diagrams of different target objects.

9. The method for evaluating the welding quality of metal grid lines and solder strips according to claim 8, characterized in that, The steps for evaluating the welding quality of different target objects based on the relationship diagrams of different target objects include: Obtain a relationship diagram of the target object where the lines are straight lines; Compare the intercepts of the straight lines and the vertical axis of the relationship diagrams for different target objects; The welding quality of the target object with a larger intercept is less than that of the target object with a smaller intercept.

10. A welding quality assessment system for metal grid wires and solder strips, characterized in that, The method includes evaluating the welding quality of the metal grid lines and solder strips of a target object according to any one of claims 1-9.

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