Method for FPC interlayer alignment using cross hole and flexible circuit board

Abstract

This invention discloses a method for interlayer alignment of FPCs using cross-holes and a flexible circuit board, belonging to the field of flexible circuit board manufacturing technology. The method includes: before lamination, creating a cross-shaped alignment mark in the non-functional area of ​​the inner circuit layer; creating a cross-shaped alignment bracket with varying width and opening a window at the corresponding position on the outer circuit layer; after lamination and before curing, observing the fit between the alignment mark and the bracket through the window; judging the offset and alignment accuracy based on whether the alignment mark exceeds the edge of the bracket; determining high and low precision levels; and adjusting process parameters until qualified. This invention requires no precision testing instruments, can be operated by ordinary workers after 10-15 minutes of training, reduces single-piece inspection time to 8-12 seconds, lowers inspection costs, supports high and low precision dual-level inspection, adapts to RTR roll-to-roll production needs, has a low interlayer alignment defect rate, and is suitable for the large-scale production of various double / multi-layer FPCs.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board manufacturing, and more specifically to a method for interlayer alignment of FPC using cross holes 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 using cross-holes and a flexible circuit board. This interlayer alignment method is simple, quick, has a low operational 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 FPCs using cross-holes, which includes the following steps: S1. Before the lamination process of the flexible circuit board, alignment marks are made in the non-functional areas of the inner and outer circuit layers, respectively, where: S11. Create a star-shaped alignment mark in the non-functional area of ​​the inner circuit layer. The star-shaped alignment mark includes a first type of alignment mark with four orthogonal directions radiating from the center and a second type of alignment mark with four 45° directions. S12. A star-shaped alignment bracket is fabricated in the non-functional area of ​​the outer circuit layer. The star-shaped alignment bracket includes four first-type blocks in the same direction and four second-type blocks in the 45° direction, which correspond one-to-one with the star-shaped alignment mark. The width of the first-type blocks has a first preset difference from the width of the first-type alignment mark, and the width of the second-type blocks has a second preset difference from the width of the second-type alignment mark, and the second preset difference is greater than the first preset difference. The area of ​​the star-shaped alignment bracket corresponding to the star-shaped alignment mark is made into a window to observe the alignment mark matching status between the star-shaped alignment mark and the star-shaped alignment bracket. S2. After the inner and outer circuit layers are laminated and before lamination and curing, observe the alignment status of the cross-shaped alignment markers and the cross-shaped alignment blocks through the window area: If the relative offset of the first type of alignment markers in all orthogonal directions to their corresponding first type of blocks is ≤ 1 / 2 of the first preset value, the interlayer alignment accuracy is determined to be high precision qualified; if the relative offset of the first type of alignment markers in orthogonal directions to their corresponding first type of blocks is > 1 / 2 of the first preset value, but the relative offset of the second type of alignment markers in all 45° directions to their corresponding second type of blocks is ≤ 1 / 2 of the second preset value, the interlayer alignment accuracy is determined to be low precision qualified; if the relative offset in the 45° direction is > 1 / 2 of the second preset value, the interlayer alignment is determined to be unqualified; determine the interlayer offset direction according to the direction in which the second alignment markers exceed or protrude from the second type of blocks, and determine the offset magnitude according to the value of the relative offset exceeding the second preset difference value. S3. Adjust the alignment process parameters according to the offset direction and offset amount determined in step S2. After the adjustment is completed, repeat the verification operation in step S2 until the alignment accuracy is qualified.

[0007] According to the present invention, a method for interlayer alignment of FPC using cross-holes abandons the traditional alignment method that relies on precision testing instruments. Through the combined design of a cross-shaped double-precision alignment mark and a differential width stop, the interlayer offset is transformed into a visually identifiable difference in the graphic fit. Alignment accuracy can be quickly determined without complex measurement calculations, significantly lowering the operational threshold; ordinary workers can operate the method after 10-15 minutes of simple instruction. Furthermore, the inspection efficiency is significantly improved, reducing the inspection time for a single product from 3-5 minutes with traditional precision instruments to 8-12 seconds, increasing the response speed by over 90%, avoiding work-in-process accumulation, and ensuring production progress. No additional precision testing equipment is required, and there is no need to pay high equipment maintenance costs. Online testing can be achieved for continuous roll-type RTR products. Rapid testing eliminates the need for extensive sampling, reducing manpower and material costs by over 65% and saving approximately 30,000-40,000 RMB annually, significantly lowering testing costs and adapting to large-scale production needs. Furthermore, its dual-precision design supports both ±25μm high-precision testing and ±50μm low-precision testing simultaneously, accommodating products with varying precision levels. The offset direction and amount are intuitively and accurately determined, facilitating timely adjustments and compensation to ensure interlayer alignment accuracy. Alignment accuracy testing can be completed before lamination and curing, allowing for timely adjustments to process parameters and preventing the scrapping of defective products after lamination, thus reducing production losses. Alignment markings are fabricated simultaneously with the conductive lines of the circuit layers, requiring no additional process steps or equipment modifications to existing FPC production lines, and can be directly integrated into existing production processes.

[0008] Optionally, in step S11, the star-shaped alignment mark is manufactured simultaneously with the conductive lines of the inner circuit layer, and the material of the star-shaped alignment mark is the same as that of the conductive lines; in step S12, the star-shaped alignment bracket is manufactured simultaneously with the conductive lines of the outer circuit layer, and the material of the star-shaped alignment bracket is the same as that 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, the first preset difference is 20μm~100μm; the second preset difference is 40μm~200μm.

[0011] Furthermore, the first preset difference is 50 μm; the second preset difference is 100 μm.

[0012] Optionally, when the flexible circuit board is a multilayer flexible circuit board with three or more layers, two sets of independent star-shaped alignment marks are provided on the same surface of the intermediate circuit layer, and the upper and lower circuit layers adjacent to the intermediate circuit layer are respectively provided with matching star-shaped alignment brackets to align with the two sets of star-shaped alignment marks on the same surface of the intermediate circuit layer.

[0013] Optionally, the two sets of star-shaped alignment marks are distributed at intervals at both ends of the process edge of the board along the feeding direction of the flexible circuit board, and the design parameters of the two sets of star-shaped alignment marks are the same.

[0014] Optionally, the width relationship between the first type of alignment mark in the orthogonal direction and its corresponding first type of stop is alternately set: wherein the width relationship between the first type of alignment mark on opposite sides and its corresponding first type of stop is opposite.

[0015] Optionally, the width relationship between the second type of alignment mark in the 45° direction and its corresponding second type of stop is alternately set, wherein the width relationship between the second type of alignment mark on opposite sides and its corresponding second type of stop is opposite.

[0016] 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.

[0017] The present invention also proposes a flexible circuit board with interlayer alignment markings, comprising at least one inner circuit layer and at least one outer circuit layer stacked together, wherein: The non-functional area of ​​the inner circuit layer is provided with a star-shaped alignment mark, which includes a first type of alignment mark in four orthogonal directions radiating from the center and a second type of alignment mark in four 45° directions; The non-functional area of ​​the outer circuit layer is provided with a star-shaped alignment bracket. The star-shaped alignment bracket includes four first-type blocks in the same direction and four second-type blocks in the 45° direction, which correspond one-to-one with the star-shaped alignment mark. The width of the first-type blocks and the width of the first-type alignment mark have a first preset difference, and the width of the second-type blocks and the width of the second-type alignment mark have a second preset difference, and the second preset difference is greater than the first preset difference. The area of ​​the star-shaped alignment bracket corresponding to the star-shaped alignment mark is provided with an opening, and the opening exposes the star-shaped alignment mark for observation of the alignment and fit status.

[0018] Optionally, the star-shaped alignment mark is made of the same material as the conductive circuit of the inner circuit layer; the star-shaped alignment bracket is made of the same material as the conductive circuit of the outer circuit layer.

[0019] Optionally, the first preset difference is 50 μm; the second preset difference is 100 μm.

[0020] Optionally, when the flexible circuit board is a multilayer flexible circuit board with three or more layers, two sets of independent star-shaped alignment marks are provided on the same surface of the intermediate circuit layer, and the upper and lower circuit layers adjacent to the intermediate circuit layer are respectively provided with matching star-shaped alignment brackets to align with the two sets of star-shaped alignment marks on the same surface of the intermediate circuit layer.

[0021] 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

[0022] Figure 1 This is a flowchart illustrating a method for interlayer alignment of FPC using cross-holes according to the present invention. Figure 2 This is a schematic diagram of the design of the cross-shaped alignment mark of the present invention; Figure 3 This is a schematic diagram of the design of the outer cross-shaped alignment bracket of the present invention; Figure 4 This is a schematic diagram of the high-precision alignment qualification state of Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the alignment low-precision qualified state in Embodiment 1 of the present invention. Figure 6 This is a schematic diagram of the misalignment state in Embodiment 1 of the present invention; Figure 7 This is a physical image of the high-precision alignment condition in Embodiment 1 of the present invention; Figure 8 This is a physical image of the alignment in a qualified low-precision state according to Embodiment 1 of the present invention; Figure 9 This is a physical image of the misalignment state in Embodiment 1 of the present invention; Figure 10 This is a schematic diagram of the flexible circuit board in Embodiment 3 of the present invention. Detailed Implementation

[0023] 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.

[0024] 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 defects mentioned in the background art, this method also suffers from cumbersome detection procedures, high instrument maintenance costs, and space requirements, further limiting its application in large-scale production. Traditional visual alignment markers can only determine if there is an offset, but cannot quantify the offset, making it difficult to guide precise adjustments to process parameters. Furthermore, they are mostly designed for a single accuracy level, failing to adapt to the detection needs of products with different accuracy levels.

[0025] To address these issues, this application proposes a cross-hole 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, lack of multi-precision range adaptation, and poor compatibility with RTR processes. At the same time, it is compatible with existing FPC circuit manufacturing processes, realizing the interlayer alignment inspection requirements of high precision, high efficiency, and low operational threshold.

[0026] Specifically, refer to Figure 1 This application proposes a method for interlayer alignment of FPCs using cross-holes, which includes the following steps: S1. Before the lamination process of the flexible circuit board, alignment marks are made in the non-functional areas of the inner and outer circuit layers, respectively, where: S11. Create a star-shaped alignment mark in the non-functional area of ​​the inner circuit layer. The star-shaped alignment mark includes a first type of alignment mark with four orthogonal directions radiating from the center and a second type of alignment mark with four 45° directions. S12. A star-shaped alignment bracket is fabricated in the non-functional area of ​​the outer circuit layer. The star-shaped alignment bracket includes four first-type blocks in the same direction and four second-type blocks in the 45° direction, which correspond one-to-one with the star-shaped alignment mark. The width of the first-type blocks has a first preset difference from the width of the first-type alignment mark, and the width of the second-type blocks has a second preset difference from the width of the second-type alignment mark, and the second preset difference is greater than the first preset difference. The area of ​​the star-shaped alignment bracket corresponding to the star-shaped alignment mark is made into a window to observe the alignment mark matching status between the star-shaped alignment mark and the star-shaped alignment bracket. S2. After the inner and outer circuit layers are laminated and before lamination and curing, observe the alignment status of the cross-shaped alignment markers and the cross-shaped alignment blocks through the window area: If the relative offset of the first type of alignment markers in all orthogonal directions to their corresponding first type of blocks is ≤ 1 / 2 of the first preset difference, the interlayer alignment accuracy is determined to be high precision qualified; if the relative offset of the first type of alignment markers in orthogonal directions to their corresponding first type of blocks is > 1 / 2 of the first preset difference, but the relative offset of the second type of alignment markers in all 45° directions to their corresponding second type of blocks is ≤ 1 / 2 of the second preset difference, the interlayer alignment accuracy is determined to be low precision qualified; if the relative offset in the 45° direction is > 1 / 2 of the second preset difference, the interlayer alignment is determined to be unqualified; determine the interlayer offset direction according to the direction in which the alignment markers exceed or protrude from the blocks, and determine the offset magnitude according to the value of the relative offset exceeding the preset difference. S3. Adjust the alignment process parameters according to the offset direction and offset amount determined in step S2. After the adjustment is completed, repeat the verification operation in step S2 until the alignment accuracy is qualified.

[0027] According to the present invention, a method for interlayer alignment of FPC using cross-holes abandons the traditional alignment method that relies on precision testing instruments. Through the combined design of a cross-shaped double-precision alignment mark and a differential width stop, the interlayer offset is transformed into a visually identifiable difference in the graphic fit. Alignment accuracy can be quickly determined without complex measurement calculations, significantly lowering the operational threshold; ordinary workers can operate the method after 10-15 minutes of simple instruction. Furthermore, the inspection efficiency is significantly improved, reducing the inspection time for a single product from 3-5 minutes with traditional precision instruments to 8-12 seconds, increasing the response speed by over 90%, avoiding work-in-process accumulation, and ensuring production progress. No additional precision testing equipment is required, and there is no need to pay high equipment maintenance costs. Online testing can be achieved for continuous roll-type RTR products. Rapid testing eliminates the need for extensive sampling, reducing manpower and material costs by over 65% and saving approximately 30,000-40,000 RMB annually, significantly lowering testing costs and adapting to large-scale production needs. Furthermore, its dual-precision design supports both ±25μm high-precision testing and ±50μm low-precision testing simultaneously, accommodating products with varying precision levels. The offset direction and amount are intuitively and accurately determined, facilitating timely adjustments and compensation to ensure interlayer alignment accuracy. Alignment accuracy testing can be completed before lamination and curing, allowing for timely adjustments to process parameters and preventing the scrapping of defective products after lamination, thus reducing production losses. Alignment markings are fabricated simultaneously with the conductive lines of the circuit layers, requiring no additional process steps or equipment modifications to existing FPC production lines, and can be directly integrated into existing production processes.

[0028] 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.

[0029] 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.

[0030] Example 1: Interlayer alignment method for double-layer FPC The method for interlayer alignment of FPC double-layer boards using cross holes provided in this embodiment includes the following steps: S1. Alignment Marker Production Before the lamination process of the flexible circuit board, alignment marks are made in the non-functional areas of the inner and outer 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.

[0031] S11, Reference Figure 2 A star-shaped alignment mark is fabricated along the edge of the inner layer circuitry. This star-shaped alignment mark consists of eight radiating alignment marks (solid copper arms). The four orthogonal first-type alignment arms have widths of 250μm (top), 200μm (right), 200μm (bottom), and 250μm (left), respectively. The four 45° second-type alignment arms have widths of 200μm (top right), 200μm (bottom right), 300μm (bottom left), and 300μm (top left), respectively. The star-shaped alignment marks are fabricated synchronously with the conductive lines of the inner layer circuitry through exposure, development, and etching processes. The material is copper, consistent with the conductive lines, requiring no additional processing steps. In other words, within the ineffective area outside the cells of the inner layer circuitry (the area that does not affect the normal function of the product), a design is implemented... Figure 2 The crosshair alignment markers shown are of the following dimensions. The crosshair alignment markers include four orthogonal first-type alignment markers (i.e., positive crosshair alignment markers) and four 45° second-type alignment markers (i.e., oblique crosshair alignment markers). The intersection of the oblique crosshair alignment markers coincides with the intersection of the positive crosshair alignment markers, and the oblique crosshair alignment markers form a 45° angle with the positive crosshair alignment markers.

[0032] S12, Reference Figure 3A cross-shaped alignment bracket is fabricated on the corresponding edge of the outer circuit layer. This bracket includes eight blocks distributed in the same direction, each corresponding to a cross-shaped alignment mark. The widths of the first-type blocks in four orthogonal directions are 200μm (top), 250μm (right), 250μm (bottom), and 200μm (left), respectively. The width difference between these blocks and the corresponding first-type alignment arms is 50μm (i.e., the first preset difference is 50μm). The widths in the orthogonal directions are alternately arranged: on the top side, the width of the inner first-type alignment arm (250μm) is greater than the width of the outer first-type block (200μm); on the bottom side, the width of the inner first-type alignment arm (200μm) is less than the width of the outer first-type block (250μm); and on the left side, the width of the inner first-type alignment arm (250μm) is greater than the width of the outer first-type block. The width of the first type of stop is 200μm. On the right side, the width of the inner first type of alignment arm is 200μm, which is smaller than the width of the outer first type of stop, which is 250μm. That is, the width relationship between the two sides is opposite. The widths of the second type of stop in the four 45° directions are 300μm (upper right), 300μm (lower right), 200μm (lower left), and 200μm (upper left), respectively. The width difference with the corresponding second type of alignment arm is 100μm (that is, the second preset difference is 100μm). The width relationship in the 45° direction is also alternately set: the width of the second type of alignment arm on the upper right and lower right sides is 200μm, which is smaller than the width of the second type of stop, which is 300μm. The width of the second type of alignment arm on the lower left and upper left sides is 300μm, which is larger than the width of the second type of stop, which is opposite. The area corresponding to the star-shaped alignment mark on the outer layer of the X-shaped alignment bracket has a window, slightly larger than the star-shaped alignment mark. This allows direct observation of the alignment between the inner and outer star-shaped alignment marks. In other words, the outer visible layer is designed based on the inner star-shaped alignment mark, ensuring concentric alignment between the outer and inner star-shaped alignment brackets, and that the overlapping area's trace dimensions have a fixed difference from the inner layer. The outer star-shaped alignment bracket is made of the same material as the FPC traces (copper), ensuring graphic stability and legibility.

[0033] S2, Alignment accuracy detection After the inner and outer circuit layers are laminated and before lamination and curing, the alignment status of the cross-shaped alignment marks and cross-shaped alignment blocks within the windowed area is observed under sufficient light with the naked eye or a 10x magnifying glass. That is, by observing the fit between adjacent alignment marks, the interlayer offset data of the product can be judged and quantified. No complex measurements are required; the result is intuitive and easily identifiable. Taking a first preset difference of 50μm and a second preset difference of 100μm in this embodiment as examples, the corresponding alignment accuracy judgment criteria are as follows: If the relative offset of the first - type alignment arms in all orthogonal directions from their corresponding first - type stoppers is ≤ 25 μm (i.e., 1 / 2 of the first preset difference of 50 μm), the inter - layer alignment accuracy is determined to be qualified with high precision. That is to say, when the first - type alignment arms in all orthogonal directions cooperate with the corresponding first - type stoppers, the two sides of the alignment arms do not exceed the edge of the stopper or the side of the stopper does not expose the coverage range of the alignment arm, and the overall offset is ≤ ±25 μm, meeting the requirements of high - precision products, and it can directly enter the lamination process. The specific cooperation status can be referred to Figure 4 , when there is no situation where the unilateral edge of the inner - layer positive cross exceeds the edge of the outer - layer circuit at the border part between the inner - layer positive cross and the outer - layer positive cross, the inter - layer alignment accuracy is determined to be qualified. At this time, the accuracy deviation in the X - axis and Y - axis directions of the inner and outer layers is controlled within ±25 μm; this standard can be customized to adjust the size difference of the different - layer circuits according to the actual accuracy requirements of the product (for example, if the accuracy requirement is ±20 μm, the size difference can be adjusted to 40 μm). The physical diagram of the high - precision qualified state is as Figure 7 shown.

[0034] If there is a relative offset of the first - type alignment arms in an orthogonal direction from their corresponding first - type stoppers > 25 μm (i.e., 1 / 2 of the first preset difference of 50 μm), but the relative offset of all second - type alignment arms in the 45° direction from their corresponding second - type stoppers is ≤ 50 μm (i.e., 1 / 2 of the second preset difference of 100 μm), the inter - layer alignment accuracy is determined to be qualified with low precision. That is to say, when there is an obvious offset in the positive - cross direction (the side of the alignment arm exceeds the edge of the stopper or the side of the stopper exposes), but the alignment arms in the oblique - cross direction still completely fall within the width range of the corresponding stoppers without edge exceeding, the inter - layer deviation is in the range of ±25 μm to ±50 μm, and it can be directly laminated or laminated after fine - tuning according to the product accuracy requirements. The specific cooperation status can be referred to Figure 5 , when the positive - cross alignment does not meet the requirements (i.e., there is a situation where the unilateral edge exceeds the edge of the different - layer circuit), the oblique - cross alignment is used for backup judgment, and the accuracy requirement is reduced; it can be known from the width difference of 100 μm between the inner - layer oblique - cross and the outer - layer oblique - cross that when there is no situation where the unilateral edge of the inner - layer oblique - cross exceeds the edge of the outer - layer circuit at the border part between the inner - layer oblique - cross and the outer - layer oblique - cross, the inter - layer alignment accuracy is determined to be within the acceptable range. At this time, the accuracy deviation in the X - axis and Y - axis directions of the inner and outer layers is controlled within ±50 μm; this standard can also be customized according to the actual needs of the product. The physical diagram of the low - precision qualified state is as Figure 8 shown.

[0035] If there is a relative offset of the second - type alignment arms in the 45° direction from their corresponding second - type stoppers > 50 μm (i.e., 1 / 2 of the second preset difference of 100 μm), the inter - layer alignment accuracy is determined to be unqualified, and the inter - layer offset > ±50 μm, and production needs to be stopped immediately for adjustment. The specific cooperation status can be referred to Figure 6The orientation of both the directional and diagonal crosses is significantly off, making it completely unacceptable. A photograph of the unacceptable item is shown below. Figure 9 As shown.

[0036] The offset direction is determined by the direction in which the alignment arm extends beyond or protrudes from the stop block. If the alignment arm extends upward beyond the stop block edge, the interlayer pattern is considered to be offset upward; if it extends downward, it is considered to be offset downward; if it extends to the left, it is considered to be offset to the left; and if it extends to the right, it is considered to be offset to the right. The offset magnitude is calculated by the value by which the relative offset exceeds the first or second preset difference. The offset direction and offset magnitude together form the basis for subsequent process adjustments.

[0037] The detection process in this embodiment takes only 8-12 seconds to complete, requires no professional operators, and can be operated independently by ordinary workers after 10-15 minutes of simple training. 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.

[0038] S3. Process Adjustment and Verification Based on the accuracy judgment results of step S2 above, the offset direction (up, down, left, right) and offset amount of the interlayer pattern are determined (≤±25μm no adjustment is needed, ±25μm~±50μm can be finely adjusted or not adjusted, >±50μm requires significant adjustment).

[0039] Specifically, based on the judgment result of step S2, if the offset direction is upward and the offset amount is 60μm, 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 downward by 60μm; after adjustment, select 3-5 adjusted products, and observe the matching status of the star-shaped alignment mark and star-shaped alignment stop in the window area again according to the accuracy judgment steps in step S2 above. After confirming that the alignment accuracy meets the requirements, resume normal production; if it is still not qualified, repeat the above adjustment-verification steps until the accuracy requirements are met; if it still cannot be qualified after multiple adjustments, check the design dimensions or window position of the star-shaped alignment mark and star-shaped alignment stop to eliminate design or process defects. The RTR tape-type FPC production equipment and correction device are existing equipment used for manufacturing RTR tape-type FPC products, and will not be described in detail here.

[0040] 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 cross-shaped alignment marks are fabricated side by side at both ends of the same surface of the intermediate circuit layer along the material feeding direction. The first alignment mark set is used to align with the upper adjacent circuit layer, and the second alignment mark set is used to align with the lower adjacent circuit layer. The design parameters of the two sets of cross-shaped alignment marks are the same as those of the cross-shaped alignment marks in Example 1 (i.e., including four first-type alignment arms in orthogonal directions and four second-type alignment arms in 45° directions, with the size and width difference set the same as in Example 1).

[0041] A cross-shaped alignment bracket with a window is made at the corresponding position on the upper line layer to align with the first alignment bracket group on the middle line layer; a cross-shaped alignment bracket with a window is made at the corresponding position on the lower line layer to align with the second alignment bracket group on the middle line layer.

[0042] After lamination, the alignment of the cross-shaped alignment marks and cross-shaped alignment blocks of each group of adjacent layers is checked. After all adjacent layers are aligned and qualified, the lamination process is carried out.

[0043] 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.

[0044] Example 3: Flexible circuit board with interlayer alignment markings refer to Figure 10 The flexible circuit board with interlayer alignment marks in this embodiment includes an inner circuit layer and an outer circuit layer stacked together: The inner circuit layer has a star-shaped alignment mark on the edge of the board, which includes eight solid copper arms radiating from the center. The widths of the first type of alignment arms in four orthogonal directions are 250μm (top), 200μm (right), 200μm (bottom), and 250μm (left), respectively. The widths of the second type of alignment arms in four 45° directions are 200μm (top right), 200μm (bottom right), 300μm (bottom left), and 300μm (top left). The outer circuit layer is equipped with a star-shaped alignment bracket, which contains eight blocks that correspond one-to-one with the star-shaped alignment mark and are distributed in the same direction. The widths of the first type of blocks in the four orthogonal directions are 200μm (top), 250μm (right), 250μm (bottom), and 200μm (left), respectively, with a width difference of 50μm from the corresponding first type of alignment arm. The widths of the second type of blocks in the four 45° directions are 300μm (upper right), 300μm (lower right), 200μm (lower left), and 200μm (upper left), respectively, with a width difference of 100μm from the corresponding second type of alignment arm. The area of ​​the star-shaped alignment bracket corresponding to the star-shaped alignment mark is provided with an opening, which exposes the inner star-shaped alignment mark and is used to observe the matching state between the star-shaped alignment mark and the star-shaped alignment bracket.

[0045] 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.

[0046] In summary, according to embodiments of the present invention, the provided FPC interlayer alignment method offers significant advantages in both inspection efficiency and cost. Through the combined design of a cross-shaped double-precision alignment mark and a differential width stop, the abstract offset is transformed into a visually identifiable difference in graphic alignment. This not only allows for rapid determination of conformity but also precisely quantifies the offset direction and value, providing a clear basis for process parameter adjustments and avoiding efficiency losses caused by blind adjustments. For the continuous production characteristics of RTR roll-to-roll FPCs, online dynamic inspection and coordinated adjustment of the correction device can be achieved, fully adapting to the high-speed continuous operation requirements of roll-to-roll production, significantly improving product yield. The alignment markings are manufactured simultaneously with the conductive lines of the circuit layer, using the same material. No additional processing steps or equipment modifications to existing FPC production lines are required; they can be directly integrated into existing production processes. The alignment markings are placed in non-functional areas such as the board edge, process edge, and cutting interval, without occupying effective functional space. They leave no residue after subsequent cutting and do not affect the product's electrical performance or appearance. They can be directly applied to the production of various FPC products, including double-layer, multi-layer, and RTR roll-to-roll types, demonstrating strong versatility. The inspection process is set before lamination and curing, allowing for timely detection of alignment deviations and adjustment of process parameters, preventing the scrapping of defective products after lamination and reducing production loss.

[0047] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," 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 this 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 limitations on this invention.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 using cross-holes, characterized in that, Includes the following steps: S1. Before the lamination process of the flexible circuit board, alignment marks are made in the non-functional areas of the inner and outer circuit layers, respectively, where: S11. Create a star-shaped alignment mark in the non-functional area of ​​the inner circuit layer. The star-shaped alignment mark includes a first type of alignment mark with four orthogonal directions radiating from the center and a second type of alignment mark with four 45° directions. S12. A star-shaped alignment bracket is fabricated in the non-functional area of ​​the outer circuit layer. The star-shaped alignment bracket includes four first-type blocks in the same direction and four second-type blocks in the 45° direction, which correspond one-to-one with the star-shaped alignment mark. The width of the first-type blocks has a first preset difference from the width of the first-type alignment mark, and the width of the second-type blocks has a second preset difference from the width of the second-type alignment mark, and the second preset difference is greater than the first preset difference. The area of ​​the star-shaped alignment bracket corresponding to the star-shaped alignment mark is made into a window to observe the alignment mark matching status between the star-shaped alignment mark and the star-shaped alignment bracket. S2. After the inner and outer circuit layers are laminated and before lamination and curing, observe the alignment status of the cross-shaped alignment markers and the cross-shaped alignment blocks through the window area: If the relative offset of the first type of alignment markers in all orthogonal directions to their corresponding first type of blocks is ≤ 1 / 2 of the first preset value, the interlayer alignment accuracy is determined to be high precision qualified; if the relative offset of the first type of alignment markers in orthogonal directions to their corresponding first type of blocks is > 1 / 2 of the first preset value, but the relative offset of the second type of alignment markers in all 45° directions to their corresponding second type of blocks is ≤ 1 / 2 of the second preset value, the interlayer alignment accuracy is determined to be low precision qualified; if the relative offset in the 45° direction is > 1 / 2 of the second preset value, the interlayer alignment is determined to be unqualified; determine the interlayer offset direction according to the direction in which the second alignment markers exceed or protrude from the second type of blocks, and determine the offset magnitude according to the value of the relative offset exceeding the second preset difference value. S3. Adjust the alignment process parameters according to the offset direction and offset amount determined in step S2. After the adjustment is completed, repeat the verification operation in step S2 until the alignment accuracy is qualified.

2. The method as described in claim 1, characterized in that, In step S11, the star-shaped alignment mark is manufactured simultaneously with the conductive lines of the inner circuit layer, and the material of the star-shaped alignment mark is the same as that of the conductive lines; in step S12, the star-shaped alignment bracket is manufactured simultaneously with the conductive lines of the outer circuit layer, and the material of the star-shaped alignment bracket is the same as that of the conductive lines.

3. The 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 method as described in claim 1, characterized in that, The first preset difference is 20μm~100μm; the second preset difference is 40μm~200μm.

5. The method as described in claim 4, characterized in that, The first preset difference is 50 μm; the second preset difference is 100 μm.

6. The 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 sets of independent star-shaped alignment marks are set on the same surface of the middle circuit layer, and the upper and lower circuit layers adjacent to the middle circuit layer are respectively provided with matching star-shaped alignment brackets to align with the two sets of star-shaped alignment marks on the same surface of the middle circuit layer.

7. The method as described in claim 6, characterized in that, The two sets of star-shaped alignment marks are distributed at intervals at both ends of the process edge of the board along the feeding direction of the flexible circuit board, and the design parameters of the two sets of star-shaped alignment marks are the same.

8. The method as described in claim 1, characterized in that, The width of the first type of alignment mark in the orthogonal direction and its corresponding first type of stop are alternately set: the width of the first type of alignment mark on opposite sides and its corresponding first type of stop are opposite.

9. The method as described in claim 1, characterized in that, The width of the second type of alignment mark in the 45° direction and its corresponding second type of stop are alternately set, wherein the width of the second type of alignment mark on opposite sides and its corresponding second type of stop are opposite.

10. The 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.

11. A flexible circuit board with interlayer alignment markings, characterized in that, It includes at least one inner circuit layer and at least one outer circuit layer stacked together, wherein: The non-functional area of ​​the inner circuit layer is provided with a star-shaped alignment mark, which includes a first type of alignment mark in four orthogonal directions radiating from the center and a second type of alignment mark in four 45° directions; The non-functional area of ​​the outer circuit layer is provided with a star-shaped alignment bracket. The star-shaped alignment bracket includes four first-type blocks in the same direction and four second-type blocks in the 45° direction, which correspond one-to-one with the star-shaped alignment mark. The width of the first-type blocks and the width of the first-type alignment mark have a first preset difference, and the width of the second-type blocks and the width of the second-type alignment mark have a second preset difference, and the second preset difference is greater than the first preset difference. The area of ​​the star-shaped alignment bracket corresponding to the star-shaped alignment mark is provided with an opening, and the opening exposes the star-shaped alignment mark for observation of the alignment and fit status.

12. The flexible circuit board with interlayer alignment markings as described in claim 11, characterized in that, The cross-shaped alignment mark is made of the same material as the conductive circuit of the inner circuit layer; the cross-shaped alignment bracket is made of the same material as the conductive circuit of the outer circuit layer.

13. The flexible circuit board with interlayer alignment markings as described in claim 11, characterized in that, The first preset difference is 50 μm; the second preset difference is 100 μm.

14. The flexible circuit board with interlayer alignment markings as described in claim 11, characterized in that, When the flexible circuit board is a multilayer flexible circuit board with three or more layers, two sets of independent star-shaped alignment marks are set on the same surface of the middle circuit layer, and the upper and lower circuit layers adjacent to the middle circuit layer are respectively provided with matching star-shaped alignment brackets to align with the two sets of star-shaped alignment marks on the same surface of the middle circuit layer.

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