Sectional impedance measurement method for circuit board

Abstract

The invention discloses a circuit board sectional impedance measurement method, which is applied to a test circuit board, at least two impedance lines to be measured are arranged on the test circuit board, and all the impedance lines to be measured share one measurement point, and the method comprises the following steps: selecting one impedance line to be measured on the test circuit board as a target impedance line, the rest impedance lines to be measured are used as non-target impedance lines; forming an open circuit between all the non-target impedance lines and the measurement point; and measuring the impedance of the target impedance line at the measurement point position through the measurement probe. A destructive means is adopted to form an open circuit between all non-target impedance lines and a measurement point, so that only a path of a target impedance line exists on a test circuit board, and the impedance of the target impedance line is detected; different impedance lines to be measured are selected from different test circuit boards to serve as target impedance lines, impedance detection of all the impedance lines to be measured can be completed, independent measurement and monitoring of impedance of an overlapping area are achieved, and the detection problem caused by concentrated measurement points is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board measurement, and in particular to a circuit board segmented impedance measurement method. Background Art

[0002] In flexible circuit board (FPC) production, segmented impedance control is a key component in ensuring signal transmission performance. However, existing technologies often concentrate measurement points for multi-layer circuits in the same area, making it difficult for traditional instruments to independently measure the impedance of each segment. For example, when the impedance lines on the first and second sides of a circuit board overlap or approach each other, it becomes difficult to independently measure the impedance of each segment. This inability to detect impedance anomalies during the manufacturing process can easily lead to batches of defective products being shipped to the customer or entire batches being scrapped, resulting in costly losses. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a segmented impedance measurement method for a circuit board, so as to solve the problem that the impedance cannot be accurately detected due to the concentration of measurement points.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: A circuit board segmented impedance measurement method is applied to a test circuit board, wherein the test circuit board is provided with at least two impedance lines to be measured, and all the impedance lines to be measured share a measurement point. The method comprises: Selecting one of the impedance lines to be measured on the test circuit board as a target impedance line, and the remaining impedance lines to be measured as non-target impedance lines; forming an open circuit between all the non-target impedance lines and the measurement points; The impedance of the target impedance line is measured at the measurement point by a measuring probe.

[0005] The beneficial effects of the present invention are as follows: when impedance measurement is performed on a test circuit board on which multiple impedance lines to be measured exist and the multiple impedance lines to be measured overlap, the impedance lines to be measured other than the selected target impedance line are regarded as non-target impedance lines, and destructive means are used to form a circuit break between all non-target impedance lines and the measurement points, so that only the path of the target impedance line exists on the test circuit board, thereby realizing impedance detection of the target impedance line; thus, by selecting different impedance lines to be measured as target impedance lines on different test circuit boards, impedance detection of all impedance lines to be measured can be completed, independent measurement and monitoring of the impedance of the overlapping area can be realized, and the detection problem caused by the concentration of measurement points can be solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 This is a flowchart of the steps of a circuit board segmented impedance measurement method according to an embodiment of the present invention; Figure 2A schematic diagram of punching in a circuit board segmented impedance measurement method according to an embodiment of the present invention; Figure 3 Schematic diagram of another punching method for measuring segmented impedance of a circuit board according to an embodiment of the present invention. DETAILED DESCRIPTION

[0007] To illustrate the technical content, achieved objectives and effects of the present invention in detail, the following description is given in conjunction with the embodiments and accompanying drawings.

[0008] A circuit board segmented impedance measurement method is applied to a test circuit board, wherein the test circuit board is provided with at least two impedance lines to be measured, and all the impedance lines to be measured share a measurement point. The method comprises: Selecting one of the impedance lines to be measured on the test circuit board as a target impedance line, and the remaining impedance lines to be measured as non-target impedance lines; forming an open circuit between all the non-target impedance lines and the measurement points; The impedance of the target impedance line is measured at the measurement point by a measuring probe.

[0009] From the above description, it can be seen that the beneficial effect of the present invention is that: when impedance measurement is performed on a test circuit board where there are multiple impedance lines to be measured and the multiple impedance lines to be measured overlap, the impedance lines to be measured other than the selected target impedance line are regarded as non-target impedance lines, and destructive means are used to form a circuit break between all non-target impedance lines and the measurement points, so that only the path of the target impedance line exists on the test circuit board, thereby realizing impedance detection of the target impedance line; thus, by selecting different impedance lines to be measured as target impedance lines on different test circuit boards, the impedance detection of all impedance lines to be measured can be completed, and the independent measurement and monitoring of the impedance of the overlapping area can be realized, thereby solving the detection problem caused by the concentration of measurement points.

[0010] Furthermore, the disconnecting all the non-target impedance lines from the measurement points includes: Punching and destroying each of the non-target impedance lines in turn so that a circuit is formed between each of the non-target impedance lines and the measuring point.

[0011] From the above description, it can be seen that a through hole is formed between the non-target impedance line and the measurement point by punching, and the formed through hole effectively forms a circuit break between the non-target impedance line and the measurement point, thereby effectively forming a circuit break between the non-target impedance line and the measurement point.

[0012] Furthermore, the disconnecting all the non-target impedance lines from the measurement points includes: Obtaining a boundary position of an overlapping area between each non-target impedance line and the target impedance line; A circuit is formed between the non-target impedance line and the measurement point at the junction position.

[0013] It can be seen from the above description that by forming a break at the boundary position of the overlapping area between the non-target impedance line and the target impedance line, the influence of the broken non-target impedance line on the measured target impedance line can be reduced.

[0014] Furthermore, the punching and destroying each of the non-target impedance lines in sequence includes: Punching is performed on the non-target impedance line to form at least one through hole with a hole diameter of 0.5 mm to 1.0 mm.

[0015] From the above description, it can be seen that by forming a through hole with an aperture size of 0.5mm-1.0mm, the size and number of the through holes can be selected according to the size of the test circuit board and the size of the non-target impedance line, thereby ensuring that a circuit is broken between the non-target impedance line and the measurement point while ensuring that the other end can be measured normally.

[0016] Furthermore, measuring the impedance of the target impedance line at the measurement point by using a measuring probe includes: The impedance of the target impedance line is measured by a four-wire method, and the measurement is repeated a preset number of times to obtain an average impedance value of the target impedance line.

[0017] From the above description, it can be seen that the four-wire method is used to measure the impedance of the target impedance line to obtain an accurate impedance value. And by taking the average of repeated measurements, errors in single measurements can be avoided, which may lead to inaccurate measurement results.

[0018] Furthermore, the test circuit board includes a semi-finished circuit board that has not been laminated with a steel sheet or a cover film.

[0019] From the above description, it can be seen that using a semi-finished circuit board that has not been bonded with a steel sheet or a covering film as a test circuit board can avoid the problem of not being able to select the area that needs to be damaged for punching after the steel sheet is bonded; and performing a punching test before covering the film can adjust the product when the test fails, avoiding batch scrapping of products.

[0020] Furthermore, it also includes: Randomly sampling a preset number of the semi-finished circuit boards from a production batch; Performing a circuit integrity check on each of the semi-finished circuit boards and determining whether it is qualified; The unqualified semi-finished circuit boards are removed to obtain a set of test circuit boards.

[0021] From the above description, it can be seen that the use of random sampling inspection not only improves the inspection efficiency and reduces the number of samples damaged; at the same time, during the measurement, the circuit integrity check of the semi-finished circuit board can effectively eliminate the open circuit and short circuit samples.

[0022] Furthermore, selecting one of the impedance lines to be measured as the target impedance line on the test circuit board includes: Different impedance lines are selected from the test circuit board set as the target impedance lines, and the number of the test circuit boards corresponding to each target impedance line is the same.

[0023] From the above description, it can be seen that according to the number of impedance lines to be measured on the test circuit board, different impedance lines to be measured are selected on each test circuit board for impedance measurement, and the number of test circuit boards corresponding to each impedance line to be measured is the same, so as to effectively detect the impedance value corresponding to each impedance line to be measured.

[0024] Furthermore, measuring the impedance of the target impedance line at the measurement point by using a measuring probe further includes: If the deviation rate of any of the target impedance lines is greater than the deviation threshold, the production batch is judged to be unqualified.

[0025] From the above description, it can be seen that the tolerance rate is calculated after the impedance value of the target impedance line is detected, and when the tolerance rate of any target impedance line on the test circuit board is greater than the tolerance threshold, it indicates that the products of the current production batch are unqualified, thereby effectively judging whether the products are qualified.

[0026] Furthermore, after determining that the production batch is unqualified, the method further includes: Tracing back and adjusting each process parameter of the production batch to obtain an adjusted production batch; The adjusted production batches are randomly sampled and tested again until they are qualified.

[0027] From the above description, it can be seen that when the products of the current production batch are unqualified, each process parameter is traced back and adjusted, and the products of the current production batch are optimized based on the adjusted process parameters. Sampling inspection is then carried out until they are qualified, thus avoiding the scrapping of the entire batch of products.

[0028] The circuit board segmented impedance measurement method provided by the present invention can be applied to segmented impedance detection scenarios of circuit boards, such as segmented impedance detection in the production of FPC (Flexible Printed Circuit) and RFPC (Rigid-Flex Printed Circuit). It is used to solve the problem of inaccurate detection caused by concentrated measurement points and effectively reduce the risk of batch scrapping. The following is an explanation through specific implementation methods: Example 1 A method for measuring segmented impedance on a circuit board is disclosed. The method is applied to a circuit board with at least two impedance lines to be measured, all of which share a common measurement point. For example, in a three-layer board, where the L1 and L3 surfaces are the front and back sides, each provided with an impedance line, connected to the same output measurement port via connected vias. The output measurement port can be located on either the L1 or L3 surfaces. Consequently, the impedance lines on the L1 and L3 surfaces overlap or are too closely spaced, concentrating the measurement points in the same area. This makes it impossible for traditional instruments to independently measure the impedance of each segment.

[0029] Please refer to Figure 1 , the method comprising: S0, measurement sample screening S01. Before attaching the steel sheet or cover film to the flexible circuit board, a preset number of semi-finished circuit boards are randomly sampled from the production batch. Punching holes in the areas requiring damage after attaching the steel sheet becomes difficult, so this process must be performed before attaching the steel sheet. Furthermore, the first piece of circuitry completed before the cover film is attached allows for quick confirmation of whether the customer's impedance control requirements are met. If punching and testing are performed after the cover film is attached, and the test fails to meet customer requirements, the product will need to be scrapped in bulk. By controlling quality risks at the semi-finished product stage, the problem of being unable to rework the finished product can be avoided.

[0030] S02. Perform a circuit integrity check on each semi-finished circuit board and determine whether it is qualified; remove unqualified semi-finished circuit boards to obtain a test circuit board set, ensuring that the samples have no visually visible circuit defects; for example, use a microscope to check the circuit integrity and remove open or short circuit samples. The preset number of randomly selected circuit boards needs to be greater than the number of circuit boards to be measured to avoid an insufficient number of samples for measurement after removing unqualified semi-finished circuit boards; alternatively, perform integrity checks simultaneously with random sample selection until the number of samples obtained meets the sample quantity requirement, for example, randomly select ≥10 qualified semi-finished circuit boards from the production batch as test samples.

[0031] S1. Select one impedance line to be measured on the test circuit board as the target impedance line, and the remaining impedance lines to be measured as non-target impedance lines; wherein, when measuring different target impedance lines, different test circuit boards need to be selected; therefore, different impedance lines need to be selected as target impedance lines in the test circuit board set, and the number of test circuit boards corresponding to each target impedance line is the same. Figure 2 as well as Figure 3 As shown in the figure, the left side shows the first impedance line to be measured, set on the L1 surface; the right side shows the second impedance line to be measured, set on the L3 surface, connected to the same output measurement port through a via. Taking the measurement of the first impedance line as an example, the first impedance line is selected as the target impedance line, and the second impedance line is the non-target impedance line. For example, there are 5 samples for each of the first and second impedance lines, for a total of 10 samples.

[0032] S2. Disconnect all the non-target impedance lines from the measurement point. Specifically, punch each non-target impedance line in turn to disconnect all the non-target impedance lines from the measurement point. That is, disconnect all impedance lines other than the first impedance line from the output measurement port. In an optional embodiment, the intersection position of each non-target impedance line and the overlapping area of ​​the target impedance line is obtained; a circuit is formed between the non-target impedance line and the measurement point at the intersection position, and the circuit is formed by punching the non-target impedance line in the direction of punching, forming at least one through hole with a hole diameter of 0.5mm-1.0mm, for example, the hole diameter is 0.8mm (adjusted according to the line spacing), ensuring that only the non-target impedance line is interrupted and the adjacent lines are not damaged. Figure 2 As shown, when the first impedance line needs to be measured, a circuit board is taken out and two through holes are punched at the intersection of the second impedance line and the first impedance line using a CNC precision punching machine, so that a circuit is formed between the second impedance line and the output measurement port; wherein, the positioning accuracy of the CNC precision punching machine is: ±0.05mm, and the rotation speed is: 10000-15000rpm. Figure 3 As shown, when the second impedance line needs to be measured, another circuit board is removed and two through-holes are formed at the intersection of the first and second impedance lines, thereby creating a circuit break between the first impedance line and the output measurement port. In other words, the holes are punched deep through the non-target impedance line to form a physical breakpoint, thus creating a circuit break between the non-target impedance line and the measurement point.

[0033] S3. Measure the impedance of the target impedance line at the measurement point using a measuring probe. When measuring impedance, secure the punched sample to an insulating measuring fixture, connect the target impedance line to a high-precision impedance meter, and measure the impedance value of the target impedance line. Simultaneously, measure the impedance of the target impedance line using a four-wire method, and repeat the measurement a preset number of times to obtain the average impedance value of the target impedance line. For example, repeat the measurement three times for each impedance segment and take the average value. Simultaneously, record the minimum, maximum, average, and deviation rate data for multiple samples as a segmented impedance test report.

[0034] S4. Process Quality Assessment: If the deviation rate of any target impedance line exceeds the deviation threshold, the production batch is deemed unqualified. The deviation threshold is set to 10%, i.e., the first impedance segment requirement is 100±10Ω; the second impedance segment requirement is 100±10Ω.

[0035] If all impedance sections in all samples meet the required standards (i.e., the tolerance rate is ≤10%), the batch is deemed to be operating normally and can be transferred to subsequent processes. If the tolerance rate of any section exceeds 10%, the batch is deemed unqualified and production is immediately suspended. Each process parameter of the batch is then traced back and adjusted to obtain an adjusted batch. Random sampling of the adjusted batch is then retested until it meets the required standards.

[0036] In summary, the circuit board segmented impedance measurement method provided by the present invention performs segmented impedance measurement in the semi-finished stage of the circuit board. When impedance measurement is performed on a test circuit board where there are multiple impedance lines to be measured and the multiple impedance lines to be measured overlap, the impedance lines to be measured other than the selected target impedance line are used as non-target impedance lines, and destructive means are used to form a circuit break between all non-target impedance lines and the measurement points, so that only the path of the target impedance line exists on the test circuit board, thereby realizing impedance detection of the target impedance line; thus, by selecting different impedance lines to be measured as target impedance lines on different test circuit boards, impedance detection of all impedance lines to be measured can be completed, and segmented independent measurement and monitoring of the impedance of the overlapping area can be realized, thereby solving the detection problem caused by the concentration of measurement points, timely discovering impedance anomalies in the process, and effectively reducing the risk of batch scrapping.

[0037] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A circuit board segmented impedance measurement method, characterized in that: Applied to a test circuit board, the test circuit board is provided with at least two impedance lines to be measured, and all the impedance lines to be measured share a measuring point. The method includes: Selecting one of the impedance lines to be measured on the test circuit board as a target impedance line, and the remaining impedance lines to be measured as non-target impedance lines; forming an open circuit between all the non-target impedance lines and the measurement points; The impedance of the target impedance line is measured at the measurement point by a measuring probe.

2. A circuit board segmented impedance measurement method according to claim 1, characterized in that: The disconnecting of all the non-target impedance lines from the measurement points comprises: Punching and destroying each of the non-target impedance lines in turn so that a circuit is formed between each of the non-target impedance lines and the measuring point.

3. A circuit board segmented impedance measurement method according to claim 1 or 2, characterized in that: The disconnecting of all the non-target impedance lines from the measurement points comprises: Obtaining a boundary position of an overlapping area between each non-target impedance line and the target impedance line; A circuit is formed between the non-target impedance line and the measurement point at the junction position.

4. A circuit board segmented impedance measurement method according to claim 2, characterized in that: The punching and destroying of each of the non-target impedance lines in sequence comprises: Punching is performed on the non-target impedance line to form at least one through hole with a hole diameter of 0.5 mm to 1.0 mm.

5. The circuit board segmented impedance measurement method according to claim 1, characterized in that: Measuring the impedance of the target impedance line at the measurement point by using a measuring probe includes: The impedance of the target impedance line is measured by a four-wire method, and the measurement is repeated a preset number of times to obtain an average impedance value of the target impedance line.

6. The circuit board segmented impedance measurement method according to claim 1, characterized in that: The test circuit board includes a semi-finished circuit board that has not been bonded with a steel sheet or a cover film.

7. A circuit board segmented impedance measurement method according to claim 6, characterized in that: Also includes: Randomly sampling a preset number of the semi-finished circuit boards from a production batch; Performing a circuit integrity check on each of the semi-finished circuit boards and determining whether it is qualified; The unqualified semi-finished circuit boards are removed to obtain a set of test circuit boards.

8. A circuit board segmented impedance measurement method according to claim 7, characterized in that: The step of selecting one of the impedance lines to be measured as the target impedance line on the test circuit board includes: Different impedance lines are selected from the test circuit board set as the target impedance lines, and the number of the test circuit boards corresponding to each target impedance line is the same.

9. A circuit board segmented impedance measurement method according to claim 8, characterized in that: Measuring the impedance of the target impedance line at the measurement point by using a measuring probe further includes: If the deviation rate of any of the target impedance lines is greater than the deviation threshold, the production batch is judged to be unqualified.

10. A circuit board segmented impedance measurement method according to claim 9, characterized in that: After determining that the production batch is unqualified, the following steps are further included: Tracing back and adjusting each process parameter of the production batch to obtain an adjusted production batch; The adjusted production batches are randomly sampled and tested again until they are qualified.

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