A method for interlayer alignment of FPC double / multilayer boards using continuous PADs and a flexible circuit board

Abstract

This invention discloses a method for interlayer alignment of FPC double / multilayer boards using continuous PADs and a flexible circuit board, belonging to the field of flexible circuit board manufacturing technology. The method includes: preparing continuous PAD patterns in the non-functional areas of each circuit layer before lamination; ensuring that the number and shape of PAD patterns are consistent between adjacent layers, and that the positioning PAD design reference positions coincide; wherein the spacing between side PAD units in one layer is shortened by a preset spacing value compared to the other layer; after lamination and bonding but before lamination curing, observing the overlap state of the patterns by transmitting light; determining the offset and alignment accuracy based on the overlapping PAD positions; and adjusting process parameters until qualified. This invention requires no precision testing instruments, can be operated by ordinary workers with simple training, reduces single-piece inspection time to 10-15 seconds, lowers inspection costs, provides high alignment accuracy, is adaptable to RTR roll-to-roll production requirements, has a low interlayer alignment defect rate, and is suitable for the large-scale production of various double / multilayer FPCs.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board manufacturing, specifically to a method for interlayer alignment of FPC double / multilayer boards using continuous PADs and a flexible circuit board. Background Technology

[0002] In the manufacturing of flexible printed circuit (FPC) double-layer / multilayer boards, interlayer alignment accuracy is one of the core indicators determining product quality and electrical performance reliability. Poor interlayer alignment accuracy can easily lead to problems such as signal interference, short circuits, or open circuits, directly affecting the product's reliability and lifespan, and even causing the product to be scrapped, increasing production costs.

[0003] Currently, the industry primarily relies on X-ACT or other precision scanning and alignment testing instruments to inspect the interlayer alignment accuracy of FPCs. However, this method has several unavoidable drawbacks in practical applications, especially for RTR roll-to-roll FPC products: First, the testing instruments have a high barrier to entry. Precision testing equipment demands highly skilled operators with specialized training, which conventional online operators and inspectors cannot meet. This makes it unsuitable for generalized, large-scale production scenarios, resulting in significant limitations. Second, the testing response speed is slow; the testing process for precision equipment is cumbersome, and the test results are often slow. The response speed is relatively slow, often requiring a long wait to obtain test data, which easily leads to the problem of "post-testing without timely remediation." At the same time, the waiting process for test results can cause work-in-process (WIP) to accumulate, affecting the production schedule. Thirdly, it has poor compatibility with RTR roll-to-roll FPC products. Unlike traditional large-panel modular FPC products, RTR roll-to-roll FPC products have a continuous roll structure, with a large number of products and strong continuity, resulting in a much higher sampling quantity for inspection than traditional products. If precision instruments are used for testing throughout the process, it will consume a lot of manpower, material resources and time, and the testing cost will increase significantly, which does not meet the economic requirements of large-scale production.

[0004] Therefore, there is an urgent need for a simple, fast, and easy-to-use method that can be adapted to the interlayer alignment accuracy of RTR roll-to-roll FPC products, so as to solve many of the drawbacks of precision instrument testing and ensure production efficiency and product quality. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method for interlayer alignment of FPC double / multilayer boards using continuous PADs and a flexible circuit board. This interlayer alignment method is simple, quick, has a low operating threshold, and a fast response speed. It is also compatible with RTR roll-to-roll FPC products, which can solve many drawbacks of precision instrument testing and ensure production efficiency and product quality.

[0006] To achieve the above objectives, this invention proposes a method for interlayer alignment of FPC double-layer / multilayer boards using continuous PADs, which includes the following steps: S1. Before the lamination process of the flexible circuit board, continuous PAD patterns are prepared in the non-functional areas of each circuit layer, wherein: S11. Create a first continuous PAD pattern in the non-functional area of ​​the first line layer. The first continuous PAD pattern includes at least three PAD units arranged at equal intervals, one of which is a positioning PAD with identification features, and the remaining PAD units are distributed on at least one side of the positioning PAD. S12. Prepare a second continuous PAD pattern in the non-functional area of ​​the second circuit layer. The second circuit layer is a circuit layer that is adjacent to the first circuit layer after lamination. The number and shape of the PAD units in the second continuous PAD pattern are the same as those in the first continuous PAD pattern. The design reference position of the positioning PAD in the second continuous PAD pattern coincides with the design reference position of the positioning PAD in the first continuous PAD pattern. The spacing between adjacent PAD units located on the side of the positioning PAD in the second continuous PAD pattern is shortened by a preset spacing value compared with the spacing between PAD units at the corresponding position in the first continuous PAD pattern. S2. After the first circuit layer and the second circuit layer are laminated and bonded together, but before lamination and curing, observe the overlap state of the two continuous PAD patterns by transmitting light: if the positioning PADs of the two continuous PAD patterns are completely overlapped, the interlayer alignment accuracy is deemed acceptable; if the overlapping PAD unit of the two continuous PAD patterns is located at the Nth position to the side of the positioning PAD, the interlayer offset is determined to be N times the accuracy threshold, where N is a positive integer; if the overlapping PAD unit of the two continuous PAD patterns is located at the (N+1)th or higher position to the side of the positioning PAD, the interlayer alignment accuracy is deemed unacceptable. S3. Adjust the alignment process parameters according to the offset direction and offset amount determined in step S2. After the adjustment is completed, repeat step S2 to verify until the alignment accuracy is qualified.

[0007] According to the present invention, a method for interlayer alignment of FPC double-layer / multilayer boards using continuous PADs is proposed. This method abandons the traditional alignment method that relies on precision testing instruments. Through differentiated continuous PAD (pad) pattern design between adjacent layers, the interlayer offset is transformed into a visually identifiable difference in the overlapping position of the patterns. Specifically, in the invalid area (non-functional area) outside the cells of adjacent FPC layers, continuous PAD patterns with a fixed spacing are set. The PAD patterns of adjacent layers adopt a "partial overlap, differentiated spacing" design. By finely adjusting the spacing, the interlayer offset is transformed into a difference in the overlapping position of the patterns, realizing the quantitative judgment of the offset. Alignment accuracy can be quickly judged without complex measurement calculations, significantly reducing the operational threshold. Ordinary workers can operate the system with simple guidance. Furthermore, the inspection efficiency is significantly improved, reducing the inspection time per unit from that of traditional precision instruments. The response time is reduced from 3-5 minutes to 10-15 seconds, increasing the response speed by over 90%, avoiding work-in-process accumulation and ensuring production progress; no additional purchase of precision testing equipment is required, and high equipment maintenance costs are eliminated, significantly reducing testing costs and adapting to the needs of large-scale production; for continuous roll-type RTR products, online rapid testing can be achieved, eliminating the need for large-scale sampling testing, reducing testing manpower and material resources consumption by over 60%, significantly reducing testing costs and adapting to the needs of large-scale production; in addition, through differentiated PAD graphic design, interlayer offset can be accurately quantified, with a testing accuracy basically consistent with traditional precision instruments, and the offset direction can be quickly determined, facilitating timely adjustments and compensation, ensuring interlayer alignment accuracy; alignment accuracy testing can be completed before lamination and curing, and process parameters can be adjusted in time to avoid scrapping defective products after lamination, reducing production losses.

[0008] Optionally, in step S1, the continuous PAD pattern is prepared simultaneously with the conductive lines of the corresponding circuit layer, and the material of the continuous PAD pattern is the same as the material of the conductive lines.

[0009] Optionally, in step S1, the non-functional area is any one or more combinations of the following: the edge of the flexible circuit board, the cutting interval area between functional units, the non-functional blank area of ​​the circuit layer, or the reserved area around the process positioning hole.

[0010] Optionally, in step S11, the remaining PAD units are symmetrically distributed on the left and right sides of the positioning PAD, and the positioning PAD is located in the center of the first continuous PAD pattern.

[0011] Optionally, in step S11, the identification feature of the positioning PAD is a graphic mark with a shape different from the other PAD units, and the graphic mark is any one of a circle, triangle, cross or number mark.

[0012] Optionally, in step S12, the preset spacing value ranges from 1μm to 20μm, and the preset spacing value is positively correlated with the allowable misalignment deviation between layers of the flexible circuit board.

[0013] Furthermore, in step S12, the preset spacing value is 10 μm.

[0014] Optionally, the accuracy threshold is set according to the alignment accuracy requirements of the flexible circuit board, and the value range is 1μm~50μm.

[0015] Furthermore, the accuracy threshold is 5 μm, in step S2: If the PAD unit of the two consecutive PAD graphics is located at the second position on the side of the positioning PAD, the interlayer offset is determined to be 10μm, which is within the acceptable range. If the PAD unit of two consecutive PAD graphics overlaps and is located at the third or more position to the side of the positioning PAD, the interlayer alignment accuracy is deemed unqualified.

[0016] Optionally, when the flexible circuit board is a multilayer flexible circuit board with three or more layers, the first continuous PAD pattern and the second continuous PAD pattern are prepared on the same surface of the intermediate circuit layer, and the upper and lower circuit layers adjacent to the intermediate circuit layer are provided with the corresponding first continuous PAD pattern or the second continuous PAD pattern according to the intermediate circuit layer for alignment.

[0017] Optionally, the flexible circuit board is an RTR tape-type flexible circuit board. In step S3, the alignment process parameters are adjusted by adjusting the correction device of the RTR tape conveyor, with the adjustment direction opposite to the offset direction and the adjustment range consistent with the offset amount.

[0018] The present invention also proposes a flexible circuit board with interlayer alignment markings, comprising at least two stacked circuit layers, wherein: The non-functional area of ​​the first line layer is provided with a first continuous PAD pattern. The first continuous PAD pattern includes at least three PAD units arranged at equal intervals, one of which is a positioning PAD with identification features, and the remaining PAD units are distributed on at least one side of the positioning PAD. A second continuous PAD pattern is provided in the non-functional area of ​​the second line layer adjacent to the first line layer. The number and shape of the PAD units in the second continuous PAD pattern are the same as those in the first continuous PAD pattern. The design reference position of the positioning PAD in the second continuous PAD pattern coincides with the design reference position of the positioning PAD in the first continuous PAD pattern. The spacing between adjacent PAD units located on the side of the positioning PAD in the second continuous PAD pattern is shortened by a preset spacing value compared to the spacing between PAD units at the corresponding position in the first continuous PAD pattern.

[0019] Optionally, the preset spacing value is 10 μm.

[0020] Optionally, the remaining PAD units of the first continuous PAD graphic are symmetrically distributed on the left and right sides of the positioning PAD, and the positioning PAD is located in the center of the first continuous PAD graphic.

[0021] Optionally, the non-functional area is any one or more combinations of the following: the edge of the flexible circuit board, the cutting interval area between functional units, the non-functional blank area of ​​the circuit layer, or the reserved area around the process positioning hole.

[0022] Optionally, the flexible circuit board includes three or more stacked circuit layers, with the first continuous PAD pattern and the second continuous PAD pattern disposed on the same surface of the middle circuit layer, which are respectively used to align with the continuous PAD patterns of the adjacent upper and lower circuit layers.

[0023] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of a method for interlayer alignment of FPC double / multilayer boards using continuous PADs according to the present invention. Figure 2 This is a schematic diagram of the design of the continuous PAD graphic in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of continuous PAD patterns that overlap and are properly aligned on the left side in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of continuous PAD patterns that overlap and are properly aligned on the right side in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of a series of PAD patterns that overlap on the left side and are misaligned in Embodiment 1 of the present invention. Figure 6 This is a physical image of a continuous PAD graphic in Embodiment 1 of the present invention, showing that the alignment is correct and there is no offset. Figure 7 This is a physical image of a continuous PAD graphic in Embodiment 1 of the present invention, which is correctly aligned but has an offset. Figure 8 This is a photograph of a continuous PAD pattern with misalignment in Embodiment 1 of the present invention. Figure 9 This is a schematic diagram of the continuous PAD graphic design in Embodiment 2 of the present invention; Figure 10This is a schematic diagram of the flexible circuit board in Embodiment 3 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0026] This application is based on the inventor's considerations regarding the following: Existing FPC interlayer alignment detection relies on precision scanning and alignment detection instruments such as X-ACT. The specific detection process involves placing the FPC product on the testing platform of a precision instrument, scanning the interlayer pattern to obtain complex alignment data, and then analyzing and calculating the interlayer offset to determine if it meets accuracy requirements. In addition to the shortcomings mentioned in the background art, this method also suffers from cumbersome detection procedures, high instrument maintenance costs (approximately 20,000-30,000 RMB per year), large instrument size, and space occupation, further limiting its application in large-scale production. Furthermore, traditional visual alignment markers can only determine whether there is an offset, but cannot quantify the offset amount, making it difficult to guide precise adjustments of process parameters and unsuitable for the continuous detection requirements of RTR roll-to-roll production.

[0027] To address these issues, this application proposes a continuous PAD alignment method and structure that solves the problems of high operational threshold, slow response speed, and high inspection cost of traditional precision instruments, as well as the inability of traditional visual alignment markers to quantify offsets and poor compatibility with RTR processes. It is also compatible with existing FPC circuit manufacturing processes, achieving high precision, high efficiency, and low operational threshold for interlayer alignment inspection.

[0028] Specifically, refer to Figure 1 This application proposes a method for interlayer alignment of FPC double-layer / multilayer boards using continuous PADs, which includes the following steps: S1. Before the lamination process of the flexible circuit board, continuous PAD patterns are prepared in the non-functional areas of each circuit layer, wherein: S11. Create a first continuous PAD pattern in the non-functional area of ​​the first line layer. The first continuous PAD pattern includes at least three PAD units arranged at equal intervals, one of which is a positioning PAD with identification features, and the remaining PAD units are distributed on at least one side of the positioning PAD. S12. Prepare a second continuous PAD pattern in the non-functional area of ​​the second circuit layer. The second circuit layer is a circuit layer that is adjacent to the first circuit layer after lamination. The number and shape of the PAD units in the second continuous PAD pattern are the same as those in the first continuous PAD pattern. The design reference position of the positioning PAD in the second continuous PAD pattern coincides with the design reference position of the positioning PAD in the first continuous PAD pattern. The spacing between adjacent PAD units located on the side of the positioning PAD in the second continuous PAD pattern is shortened by a preset spacing value compared with the spacing between PAD units at the corresponding position in the first continuous PAD pattern. S2. After the first circuit layer and the second circuit layer are laminated and bonded together, but before lamination and curing, observe the overlap state of the two continuous PAD patterns by transmitting light: if the positioning PADs of the two continuous PAD patterns are completely overlapped, the interlayer alignment accuracy is deemed acceptable; if the overlapping PAD unit of the two continuous PAD patterns is located at the Nth position to the side of the positioning PAD, the interlayer offset is determined to be N times the accuracy threshold, where N is a positive integer; if the overlapping PAD unit of the two continuous PAD patterns is located at the (N+1)th or higher position to the side of the positioning PAD, the interlayer alignment accuracy is deemed unacceptable. S3. Adjust the alignment process parameters according to the offset direction and offset amount determined in step S2. After the adjustment is completed, repeat step S2 to verify until the alignment accuracy is qualified.

[0029] According to the present invention, a method for interlayer alignment of FPC double-layer / multilayer boards using continuous PADs is proposed. This method abandons the traditional alignment method that relies on precision testing instruments. Through differentiated continuous PAD (pad) pattern design between adjacent layers, the interlayer offset is transformed into a visually identifiable difference in the overlapping position of the patterns. Specifically, in the invalid area (non-functional area) outside the cells of adjacent FPC layers, continuous PAD patterns with a fixed spacing are set. The PAD patterns of adjacent layers adopt a "partial overlap, differentiated spacing" design. By finely adjusting the spacing, the interlayer offset is transformed into a difference in the overlapping position of the patterns, realizing the quantitative judgment of the offset. Alignment accuracy can be quickly judged without complex measurement calculations, significantly reducing the operational threshold. Ordinary workers can operate the system with simple guidance. Furthermore, the inspection efficiency is significantly improved, reducing the inspection time per unit from that of traditional precision instruments. The response time is reduced from 3-5 minutes to 10-15 seconds, increasing the response speed by over 90%, avoiding work-in-process accumulation and ensuring production progress; no additional purchase of precision testing equipment is required, and high equipment maintenance costs are eliminated, significantly reducing testing costs and adapting to the needs of large-scale production; for continuous roll-type RTR products, online rapid testing can be achieved, eliminating the need for large-scale sampling testing, reducing testing manpower and material resources consumption by over 60%, significantly reducing testing costs and adapting to the needs of large-scale production; in addition, through differentiated PAD graphic design, interlayer offset can be accurately quantified, with a testing accuracy basically consistent with traditional precision instruments, and the offset direction can be quickly determined, facilitating timely adjustments and compensation, ensuring interlayer alignment accuracy; alignment accuracy testing can be completed before lamination and curing, and process parameters can be adjusted in time to avoid scrapping defective products after lamination, reducing production losses.

[0030] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0031] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0032] Example 1: Interlayer alignment method for double-layer FPC The method for interlayer alignment of FPC double-layer boards using continuous PADs provided in this embodiment includes the following steps: S1. Continuous PAD graphic preparation Before the lamination process of the flexible circuit board, continuous PAD patterns are prepared in the non-functional areas of the first and second circuit layers respectively. In this embodiment, the non-functional areas are selected from the edge of the FPC, which is 0.5mm away from the cutting path of the functional unit, so as not to affect the normal function of the product.

[0033] S11, Reference Figure 2 A first continuous PAD pattern 11 is fabricated along the edge of the first circuit layer. This first continuous PAD pattern comprises several equally spaced rectangular PAD units. The central PAD unit is a first positioning PAD 111 with a triangle marking at the end of the rectangle. The remaining PAD units are symmetrically distributed on the left and right sides of the first positioning PAD 111, serving as first side PAD units 112. The spacing between two adjacent first side PAD units 112 is 50 μm. The first continuous PAD pattern 11 is fabricated synchronously with the conductive lines of the first circuit layer through exposure, development, and etching processes. The material is copper, consistent with the conductive lines, requiring no additional processing steps. In other words, a continuous PAD pattern (i.e., the first continuous PAD pattern 11) with a fixed spacing is designed within the invalid area outside the units of the first circuit layer (areas that do not affect the normal function of the product). The PAD pattern adopts a rectangular structure, with a fixed spacing between adjacent PADs. A special graphic mark is designed on the PAD in the middle of the continuous PAD (clearly distinguishing it from other rectangular PADs for easy positioning by operators), serving as a positioning PAD.

[0034] S12. Prepare a second continuous PAD pattern 21 on the corresponding board edge of the second circuit layer. The second circuit layer is the circuit layer adjacent to the first circuit layer after lamination. The number and shape of the PAD units in the second continuous PAD pattern 21 are completely consistent with the first continuous PAD pattern 11. It also contains several PAD units. The center is a second positioning PAD 211 with a rectangle and a triangle mark at the end. The two sides are second side PAD units 212. The design reference position of the second positioning PAD 211 coincides with the design reference position of the first positioning PAD 111. The spacing between two adjacent second side PAD units 212 is shortened by a preset spacing value of 5 μm compared with the spacing between two adjacent first side PAD units 112. That is, the adjacent spacing of the second side PAD units 212 is 45 μm. In other words, a fixed-spaced continuous PAD pattern (i.e., the second continuous PAD pattern 21) is designed at the corresponding position on the adjacent layers of the FPC (corresponding to the upper or lower layer of the first line layer). The PAD pattern and number are completely consistent with the first continuous PAD pattern 11, only the fixed spacing between adjacent PADs is adjusted, that is, the spacing between the PADs on both sides (except for the specially marked PAD in the middle) is shortened by 5 μm, while the position of the specially marked PAD in the middle remains unchanged, ensuring that the two layers of PAD patterns partially overlap. For example, Figure 2As shown, the orientations of the triangular marks on the first positioning PAD 111 and the second positioning PAD 211 can be opposite.

[0035] S2. Alignment accuracy detection After laminating and bonding the first circuit layer and the second circuit layer and before curing by lamination, observe the overlapping state of the continuous PAD patterns of the two layers through light transmission under a backlight source. That is, by observing the overlapping degree of the continuous PAD patterns of adjacent two layers, judge and quantify the interlayer offset data of the product. Without complex measurement, it is visually distinguishable. If the positioning PADs of the continuous PAD patterns of the two layers completely overlap, it is determined that the interlayer alignment accuracy is qualified; if the overlapping PAD unit of the continuous PAD patterns of the two layers is at the Nth position on the side of the positioning PAD, it is determined that the interlayer offset is N times the accuracy threshold, where N is a positive integer; if the overlapping PAD unit of the continuous PAD patterns of the two layers is at the N + 1th position and above on the side of the positioning PAD, it is determined that the interlayer alignment accuracy is unqualified.

[0036] Specifically, assume that the interlayer alignment accuracy requirement of the FPC product is ±10 μm. When converted into the requirement for graphic coincidence, it is that when the middle special mark PAD (i.e., the positioning PAD) in the continuous PAD patterns of the two layers completely overlaps and is consistent with the original design intention, it is determined that the interlayer alignment accuracy is qualified (PASS). At this time, the two circuit layers meet the original specification requirements and no adjustment is required. That is, if the second positioning PAD 211 and the first positioning PAD 111 completely overlap, it is determined that the interlayer alignment accuracy is qualified and there is no offset, and it can directly enter the lamination process. For a specific physical diagram, reference can be made to Figure 6 The first continuous PAD pattern is provided with 5 PAD units, and the second continuous PAD pattern is also provided with 5 PAD units; the second positioning PAD 211 is aligned with the first positioning PAD 111. At this time, the product can be regarded as completely aligned, and the alignment accuracy is extremely high, fully meeting the production requirements of high-precision products.

[0037] The judgment of the offset amount is: when the overlapping PAD is at the second PAD unit on the left or right side of the middle special mark PAD (i.e., the positioning PAD), it is the maximum acceptance range. At this time, it can be directly judged that the overall graphic offset amount is 10 μm; among them, when the overlapping PAD is at the second PAD unit on the left side of the special mark, it is determined that the interlayer graphic is offset 10 μm to the left; when the overlapping PAD is at the second PAD unit on the right side of the special mark, it is determined that the interlayer graphic is offset 10 μm to the right.

[0038] Specifically refer to Figure 3If the PAD unit of the two consecutive PAD patterns (i.e. the first consecutive PAD pattern 11 and the second consecutive PAD pattern 21) is located at the second position to the left of the first positioning PAD 111, the leftward offset between the layers is determined to be 2×5μm=10μm, where 5μm is the preset accuracy threshold of this embodiment. An offset of ≤10μm is within the qualified range and can directly enter the lamination process or be finely adjusted before lamination.

[0039] refer to Figure 4 If the overlapping PAD unit of two consecutive PAD patterns (i.e., the first consecutive PAD pattern 11 and the second consecutive PAD pattern 21) is located at the second position to the right of the first positioning PAD 111, the rightward offset between the layers is determined to be 10μm, which is within the acceptable range. The lamination process can proceed directly, or it can be finely adjusted before lamination. For a specific physical image, please refer to... Figure 7 Of the five PAD units, including the positioning PAD, one PAD unit is aligned, as indicated by the green arrow in the figure. At this point, the graphic offset is 10μm, which basically meets the production requirements of high-precision products.

[0040] refer to Figure 5 If the overlapping PAD unit of two consecutive PAD patterns (i.e., the first consecutive PAD pattern 11 and the second consecutive PAD pattern 21) is located at the third position to the left of the first positioning PAD 111, the interlayer offset is determined to be 15 μm, which is greater than the maximum allowable offset of 10 μm required by the accuracy threshold. Therefore, the interlayer alignment accuracy is deemed unqualified, and process adjustments are required. Alternatively, if the two consecutive PAD patterns (i.e., the first consecutive PAD pattern 11 and the second consecutive PAD pattern 21) do not have overlapping PAD units, the interlayer alignment accuracy is deemed unqualified, and process adjustments are required. For specific physical diagrams, please refer to [reference needed]. Figure 8 If none of the five PAD units, including the positioning PAD, are aligned, the graphic offset exceeds 10 μm, which is completely unacceptable and needs to be adjusted before generation.

[0041] The detection process in this embodiment takes only 10 seconds to complete, requires no professional operators, and can be operated independently by ordinary workers after a short training period. The detection accuracy rate is over 99%. It should be noted that when making the above judgment and observation, the line of sight must be kept perpendicular to the product surface, and tilting the view is strictly prohibited to prevent visual deviation.

[0042] S3. Process Adjustment and Verification Based on the accuracy judgment results of step S2 above, determine the offset direction (left or right) and offset amount of the interlayer pattern (≤10μm can be finely adjusted or not adjusted, >10μm requires large adjustment).

[0043] Specifically, based on the judgment result of step S2, if the offset direction is to the left and the offset amount is 15μm, adjust the alignment process parameters: for RTR tape-type FPC production equipment, adjust the correction device of the RTR tape conveyor to adjust the conveying position to the right by 15μm; after the adjustment, select the adjusted product, and observe the overlap of the continuous PAD pattern again according to the accuracy judgment step of step S2 above. Confirm that any of the five adjacent PAD units, including the middle special mark PAD (i.e., positioning PAD), are completely overlapped. After the alignment accuracy is judged to be qualified, normal production is resumed; if it is still not qualified, repeat the above adjustment-verification steps until the accuracy requirements are met. Among them, the RTR tape-type FPC production equipment and the correction device are existing equipment used to prepare RTR tape-type FPC products, and will not be described in detail here.

[0044] Example 2: Interlayer alignment method for three-layer FPC This embodiment is largely the same as Embodiment 1, and the similarities will not be described in detail. The difference is that this embodiment involves the interlayer alignment of a three-layer flexible circuit board, including the upper circuit layer, the middle circuit layer, and the lower circuit layer. The specific alignment method is as follows: Two independent sets of continuous PAD patterns are fabricated side-by-side on the same surface of the intermediate circuit layer. One set is the first continuous PAD pattern 11, which is used for alignment with the upper adjacent circuit layer; the other set is the second continuous PAD pattern 21, which is used for alignment with the lower adjacent circuit layer. The first continuous PAD pattern 11 is consistent with the design rules of the first continuous PAD pattern in Example 1, and the second continuous PAD pattern 21 is consistent with the design rules of the second continuous PAD pattern in Example 1 (that is, the adjacent spacing of the PAD units on both sides of the second continuous PAD pattern 21 is shortened by 5μm, except for the positioning PAD).

[0045] The upper circuit layer creates a second continuous PAD pattern 21 to align with the first continuous PAD pattern 11 of the middle circuit layer, and the lower circuit layer creates a first continuous PAD pattern 11 to align with the second continuous PAD pattern 21 of the middle circuit layer.

[0046] After lamination, the overlap of the first continuous PAD pattern 11 and the second continuous PAD pattern 21 of each group of adjacent layers is checked. After all adjacent layers are aligned and qualified, the lamination process is carried out.

[0047] This embodiment eliminates the need for additional alignment markers for multilayer boards. Alignment detection of all adjacent layers can be achieved using only one set of graphic rules, simplifying the alignment process of multilayer boards and adapting to the production needs of multilayer FPCs.

[0048] Example 3: Flexible circuit board with interlayer alignment markings refer to Figure 10The flexible circuit board with interlayer alignment marks in this embodiment includes a first circuit layer, a second circuit layer, and a third circuit layer stacked together: The first circuit layer has a first continuous PAD pattern 11 on the edge of the board, which includes several PAD units arranged at equal intervals. The center is a positioning PAD, and there are several rectangular side PAD units on the left and right sides. The spacing between adjacent side PAD units is 50μm. The second circuit layer has a second continuous PAD pattern 21 and a first continuous PAD pattern 11 at the corresponding board edge process edge position. The number and shape of the PAD units in the second continuous PAD pattern 21 are consistent with the first continuous PAD pattern 11 of the first circuit layer. The design reference position of the positioning PAD coincides with the first positioning PAD. The adjacent spacing of the side PAD units is 45μm, which is 5μm shorter than the side PAD spacing of the first continuous PAD pattern 11. Then, the first continuous PAD pattern 11 of the second circuit layer is consistent with the first continuous PAD pattern 11 of the first circuit layer.

[0049] The third circuit layer has a second continuous PAD pattern 21 on the corresponding board edge process edge, which is consistent with the second continuous PAD pattern 21 of the second circuit layer.

[0050] The continuous PAD pattern surface is not covered with solder mask, making it easy to observe the overlapping state by transmitting light.

[0051] The flexible circuit board in this embodiment can quickly detect the interlayer alignment accuracy without relying on precision instruments, which is suitable for large-scale production needs. The alignment mark is set on the edge of the board and the process edge, so there is no residue after subsequent cutting, which does not affect the appearance and function of the product.

[0052] In summary, according to the embodiments of the present invention, the interlayer alignment method for the FPC double-layer / multi-layer board has prominent detection efficiency and cost advantages. Through the differential pitch design of continuous PADs on adjacent layers, the abstract offset amount is converted into the difference in the overlapping position of the graphics that can be visually recognized. Not only can it quickly judge whether it is qualified, but it can also accurately quantify the offset direction and offset value, providing a clear basis for the adjustment of process parameters and avoiding the efficiency loss caused by blind adjustment. For the continuous production characteristics of the RTR reel-to-reel FPC, online dynamic detection and linkage adjustment of the deviation correction device can be realized, fully adapting to the high-speed continuous operation requirements of reel-to-reel production, and significantly improving the product yield. The continuous PAD graphics and the conductive lines of the circuit layer are prepared synchronously, with the same material as the conductive lines. There is no need to add additional process steps, and there is no need to modify the equipment of the existing FPC production line, and it can be directly integrated into the existing production process. The PAD graphics are set in non-functional areas such as the board edge process edge and the cutting interval area, without occupying the effective functional space of the product. There is no residue after subsequent cutting, which does not affect the electrical performance and appearance of the product, and can be directly applied to the production scenarios of various FPC products such as double-layer, multi-layer, and RTR reel-to-reel, with strong versatility. The detection link is set before lamination curing, which can timely detect the alignment deviation and adjust the process parameters, avoiding the scrapping of unqualified products after lamination and reducing the production loss rate.

[0053] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0054] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "multiple" means two or more unless otherwise specifically defined.

[0055] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0058] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for interlayer alignment of FPC double-layer / multilayer boards using continuous PADs, characterized in that, Includes the following steps: S1. Before the lamination process of the flexible circuit board, continuous PAD patterns are prepared in the non-functional areas of each circuit layer, wherein: S11. Create a first continuous PAD pattern in the non-functional area of ​​the first line layer. The first continuous PAD pattern includes at least three PAD units arranged at equal intervals, one of which is a positioning PAD with identification features, and the remaining PAD units are distributed on at least one side of the positioning PAD. S12. Prepare a second continuous PAD pattern in the non-functional area of ​​the second circuit layer. The second circuit layer is a circuit layer that is adjacent to the first circuit layer after lamination. The number and shape of the PAD units in the second continuous PAD pattern are the same as those in the first continuous PAD pattern. The design reference position of the positioning PAD in the second continuous PAD pattern coincides with the design reference position of the positioning PAD in the first continuous PAD pattern. The spacing between adjacent PAD units located on the side of the positioning PAD in the second continuous PAD pattern is shortened by a preset spacing value compared with the spacing between PAD units at the corresponding position in the first continuous PAD pattern. S2. After the first circuit layer and the second circuit layer are laminated and bonded together, but before lamination and curing, observe the overlap state of the two continuous PAD patterns by transmitting light: if the positioning PADs of the two continuous PAD patterns are completely overlapped, the interlayer alignment accuracy is deemed acceptable; if the overlapping PAD unit of the two continuous PAD patterns is located at the Nth position to the side of the positioning PAD, the interlayer offset is determined to be N times the accuracy threshold, where N is a positive integer; if the overlapping PAD unit of the two continuous PAD patterns is located at the (N+1)th or higher position to the side of the positioning PAD, the interlayer alignment accuracy is deemed unacceptable. S3. Adjust the alignment process parameters according to the offset direction and offset amount determined in step S2. After the adjustment is completed, repeat step S2 to verify until the alignment accuracy is qualified.

2. The interlayer alignment method as described in claim 1, characterized in that, In step S1, the continuous PAD pattern is prepared simultaneously with the conductive lines of the corresponding circuit layer, and the material of the continuous PAD pattern is the same as that of the conductive lines.

3. The interlayer alignment method as described in claim 1, characterized in that, In step S1, the non-functional area is any one or more combinations of the following: the edge of the flexible circuit board, the cutting interval area between functional units, the non-functional blank area of ​​the circuit layer, or the reserved area around the process positioning hole.

4. The interlayer alignment method as described in claim 1, characterized in that, In step S11, the remaining PAD units are symmetrically distributed on the left and right sides of the positioning PAD, and the positioning PAD is located in the center of the first continuous PAD pattern.

5. The interlayer alignment method as described in claim 1, characterized in that, In step S11, the identification feature of the positioning PAD is a graphic mark with a shape different from the other PAD units. The graphic mark can be any one of a circle, triangle, cross, or number mark.

6. The interlayer alignment method as described in claim 1, characterized in that, In step S12, the preset spacing value ranges from 1μm to 20μm, and the preset spacing value is positively correlated with the allowable misalignment deviation between layers of the flexible circuit board.

7. The interlayer alignment method as described in claim 6, characterized in that, In step S12, the preset spacing value is 10 μm.

8. The interlayer alignment method as described in claim 1, characterized in that, The accuracy threshold is set according to the alignment accuracy requirements of the flexible circuit board, and the value range is 1μm~50μm.

9. The interlayer alignment method as described in claim 8, characterized in that, The accuracy threshold is 5μm. In step S2: If the PAD unit of the two consecutive PAD graphics is located at the second position on the side of the positioning PAD, the interlayer offset is determined to be 10μm, which is within the acceptable range. If the PAD unit of two consecutive PAD graphics overlaps and is located at the third or more position to the side of the positioning PAD, the interlayer alignment accuracy is deemed unqualified.

10. The interlayer alignment method as described in claim 1, characterized in that, When the flexible circuit board is a multilayer flexible circuit board with three or more layers, two independent continuous PAD pattern groups are arranged side by side on the same surface of the intermediate circuit layer, namely the first continuous PAD pattern and the second continuous PAD pattern. The upper and lower circuit layers adjacent to the intermediate circuit layer are set with the corresponding second continuous PAD pattern or the first continuous PAD pattern according to the intermediate circuit layer, so as to cooperate and align with the two pattern groups on the same surface of the intermediate circuit layer.

11. The interlayer alignment method as described in claim 1, characterized in that, The flexible circuit board is an RTR tape-type flexible circuit board. In step S3, the alignment process parameters are adjusted as follows: the correction device of the RTR tape conveyor is adjusted, the adjustment direction is opposite to the offset direction, and the adjustment range is consistent with the offset amount.

12. A flexible circuit board with interlayer alignment markings, characterized in that, Includes at least two stacked circuit layers, wherein: The non-functional area of ​​the first line layer is provided with a first continuous PAD pattern. The first continuous PAD pattern includes at least three PAD units arranged at equal intervals, one of which is a positioning PAD with identification features, and the remaining PAD units are distributed on at least one side of the positioning PAD. A second continuous PAD pattern is provided in the non-functional area of ​​the second line layer adjacent to the first line layer. The number and shape of the PAD units in the second continuous PAD pattern are the same as those in the first continuous PAD pattern. The design reference position of the positioning PAD in the second continuous PAD pattern coincides with the design reference position of the positioning PAD in the first continuous PAD pattern. The spacing between adjacent PAD units located on the side of the positioning PAD in the second continuous PAD pattern is shortened by a preset spacing value compared to the spacing between PAD units at the corresponding position in the first continuous PAD pattern.

13. The flexible circuit board with interlayer alignment markings as described in claim 12, characterized in that, The preset spacing value is 10μm.

14. The flexible circuit board with interlayer alignment markings as described in claim 12, characterized in that, The remaining PAD units of the first continuous PAD pattern are symmetrically distributed on the left and right sides of the positioning PAD, and the positioning PAD is located in the center of the first continuous PAD pattern.

15. The flexible circuit board with interlayer alignment markings as described in claim 12, characterized in that, The non-functional area is any one or more combinations of the following: the edge of the flexible circuit board, the cutting interval area between functional units, the non-functional blank area of ​​the circuit layer, or the reserved area around the process positioning hole.

16. The flexible circuit board with interlayer alignment markings as described in claim 12, characterized in that, The flexible circuit board includes three or more stacked circuit layers. Two independent continuous PAD pattern groups are arranged side by side on the same surface of the middle circuit layer. These are the first continuous PAD pattern and the second continuous PAD pattern, which are respectively matched and aligned with the continuous PAD patterns of the adjacent upper and lower circuit layers.

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