Detection method for quickly grading hole precision of circuit board

Abstract

The invention relates to a detection method for rapidly performing circuit board hole precision grading, which comprises the steps of substrate preparation, circuit manufacturing, visual inspection and plate processing, specifically, four characteristic holes arranged in a 2 * 2 manner are required to be formed in the edge area of a substrate in the substrate preparation, and an observation ring is required to be formed in the edge area of a copper layer in the circuit manufacturing; the observation ring is composed of two large rings and two small rings, the inner diameter of each large ring is larger than that of each small ring, the ring centers of the two large rings and the ring centers of the two small rings are located at the four corners of the same standard square, and the ring centers of the two large rings are located at the two ends of the first diagonal line of the square. The ring centers of the two small rings are located at the two ends of the second diagonal line of the square. According to the invention, the blind through hole can be aligned by using the observation ring structure with a special structure, so that whether the product plate passes, is scrapped or needs to be detected again is distinguished, and the processing time is saved on the basis of ensuring the accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for quickly detecting the accuracy grading of circuit board holes. Background Art

[0002] In FPC production, blind vias (BVs) are key structures connecting different layers of circuits, and their quality directly impacts the electrical performance and reliability of the FPC. Currently, there are many challenges in inspecting BVs. Traditional inspection methods, such as manual visual inspection, are inefficient and prone to missed defects, while automated optical inspection (AOI) also needs to improve its accuracy in identifying minor defects.

[0003] The lack of effective auxiliary detection structures around existing FPC blind vias makes it difficult to quickly and accurately judge the quality of the blind vias during the inspection process, resulting in a high defective rate in production, increased production costs and production cycles.

[0004] Chinese patent CN104427792A discloses a method for manufacturing a multi-layer circuit board, in which a concentric circle pattern surrounding the same through-hole is formed to ensure the alignment accuracy between multiple stacked layers. However, each layer is only judged as pass or fail. If there are many stacked layers, the number of concentric circles will increase, and the entire alignment target will be larger, which is limited in its application to circuit boards with many layers. Because the larger the target range, the larger the visual inspection field will be, the greater the distance between the lens and the product will be, and the clarity of the final inspection will be reduced, and the accuracy of the inspection will be reduced.

[0005] Therefore, it is necessary to design a new detection method to avoid the above problems. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method for quickly grading the accuracy of circuit board holes, which can use a special structure of the observation ring structure to align the blind holes, so as to distinguish whether the product board is passed, scrapped or needs to be re-tested, saving processing time while ensuring accuracy.

[0007] The present invention achieves the above-mentioned object through the following technical solution: a method for quickly detecting the accuracy classification of circuit board holes, comprising the following steps: S1. Substrate preparation: Prepare a substrate with through holes or blind holes on its surface. Set four characteristic holes in a 2×2 arrangement in the edge area of the substrate, with the centers of the four characteristic holes located at the four corners of the same standard square; S2. Circuit Manufacturing: A copper layer is plated on the surface of the substrate to provide electrical continuity between the copper layers through which through-holes or blind vias pass, and then a circuit is formed by processing. The edge region of the copper layer has an observation ring, which is composed of two large rings and two small rings. The inner diameter of the large ring is larger than the inner diameter of the small ring. The centers of the two large rings and the centers of the two small rings are located at the four corners of the same standard square, with the centers of the two large rings located at the ends of the first diagonal of the square, and the centers of the two small rings located at the ends of the second diagonal of the square. The center of each characteristic hole is located within the inner circle of a large ring or a small ring. S3. Visual inspection: The observation ring is visually photographed. When the outer contours of all characteristic holes are within the inner circle of their respective rings, the multilayer circuit board is judged to be a qualified board. When the outer contours of the characteristic holes in the large ring are all within the inner circle of the large ring in which they are located, and the contours of the characteristic holes in any small ring intersect with the annular range of the small ring in which they are located, the multilayer circuit board is judged to be a suspect board. When the contours of the characteristic holes in any large ring intersect with the annular range of the large ring in which they are located, the multilayer circuit board is judged to be a defective board.

[0008] S4. Plate processing: Qualified plates are marked and flow into the next production link, defective plates are scrapped, and suspect plates are reviewed. Suspect plates that pass the review are processed as qualified plates, otherwise they are scrapped as defective plates.

[0009] Specifically, the side length of the standard square is 300-500 μm.

[0010] Furthermore, the inner diameter of the macroring is 130-200 μm larger than the aperture of the characteristic hole.

[0011] Furthermore, the inner diameter of the small ring is 40 μm smaller than the inner diameter of the large ring.

[0012] Furthermore, the ring width of the large ring and the small ring is 70-100 μm.

[0013] The beneficial effects of the technical solution of the present invention are: The present invention can utilize a special structure of the observation ring structure to align the blind through hole, thereby distinguishing whether the product board is passed, scrapped or needs to be re-inspected, saving processing time while ensuring accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the position relationship diagram between the characteristic hole and the observation ring in the design; Figure 2 This is a schematic diagram of the relative positions of the characteristic holes and the observation ring of a qualified plate in actual processing; Figure 3This is a schematic diagram of the relative positions of the characteristic hole and the observation ring of the suspect plate during actual processing; Figure 4 Schematic diagram of the relative positions of the characteristic hole and observation ring of the defective board in actual processing.

[0015] The following are marked in the figure: 1-characteristic hole; 2-observation ring, 21-large ring, 22-small ring; 3- Standard square. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below with reference to specific embodiments.

[0017] Example: A method for quickly detecting the accuracy of circuit board holes, comprising the following steps:

[0018] S1. Substrate preparation: prepare a substrate with through holes or blind holes on its surface, and set four characteristic holes 1 arranged in a 2×2 pattern in the edge area of the substrate. The centers of the four characteristic holes 1 are respectively located at the four corners of the same standard square 3.

[0019] In the substrate hole design, the relative positions of the four characteristic holes 1 are fixed, forming the first alignment pattern. This first alignment pattern also maintains a fixed position relative to the remaining through-holes and blind vias on the substrate. The standard square here specifies only a standard side length. The design interval should maintain a reasonable spacing between the characteristic holes 1 to facilitate coordination with the structure of the observation ring 2. In experience, the side length of the standard square 3 is 300-500 μm.

[0020] S2. Circuit manufacturing: A copper layer is plated on the surface of the substrate to make the copper layer through which the through holes or blind holes pass through conductive, and then the circuit is formed. The edge area of the copper layer has an observation ring 2, which is composed of two large rings 21 and two small rings 22. The centers of the two large rings 21 and the centers of the two small rings 22 are located at the four corners of the same standard square 3, and the centers of the two large rings 21 are located at the two ends of the first diagonal of the square, and the centers of the two small rings 22 are located at the two ends of the second diagonal of the square. The center of each characteristic hole 1 is located within the inner circle of a large ring 21 or a small ring 22.

[0021] Observation ring 2 is a second alignment pattern consisting of two large rings 21 and two small rings 22. This second alignment pattern is also fixed relative to the rest of the copper layer, so it serves as a representative representation of the copper layer and can be compared with the first alignment pattern to determine if the relative positional deviation is within an acceptable range. The standard square here is only dimensionally related to the previous standard square; during actual production, there may be some deviation in relative position, so it is used to determine alignment accuracy. The "bottom layer" and "top layer" here are relative terms, and the base circuit board itself may be a multi-layer circuit board. Throughout the entire circuit board manufacturing process, for the Nth circuit layer (N ≥ 2), it is the top layer, and the N-1th circuit layer is the bottom layer. For example, based on the manufacturing sequence, the second circuit layer is the top layer relative to the first circuit layer, but the bottom layer relative to the third circuit layer. After each circuit layer is completed, alignment testing is performed, so each set of alignment patterns is staggered on the board surface to prevent interference.

[0022] Based on current manufacturing processes, the minimum offset between the two circuit planes can be ±65µm. Therefore, the inner diameter of large ring 21 should be at least 130µm larger than that of feature hole 1. However, considering the space occupied by observation ring 2 on the board, the maximum diameter should not exceed 200µm. To achieve appropriate grading, the inner diameter of small ring 22 cannot differ significantly from that of large ring 21. Based on the above size constraints, an inner diameter difference of 40µm is appropriate.

[0023] S3. Visual inspection: Visually photograph the observation ring 2. When the outer contours of all characteristic holes 1 are within the inner circle of their respective rings (large ring 21 or small ring 22), the multi-layer circuit board is judged to be a qualified board; when the outer contours of the characteristic holes 1 in the large ring 21 are all within the inner circle of the large ring 21 in which they are located, and the contours of the characteristic holes 1 in any small ring 22 intersect with the annular range of the small ring 22 in which they are located, the multi-layer circuit board is judged to be a suspect board; when the contours of the characteristic holes 1 in any large ring 21 intersect with the annular range of the large ring 21 in which they are located, the multi-layer circuit board is judged to be a defective board.

[0024] The design idea of the present invention is that the two large rings 21 and the two characteristic holes 1 inside them are regarded as a group to limit a relatively wide error range, and the two small rings 22 and the other two characteristic holes 1 inside them are regarded as a group to limit a relatively narrow error range. The two groups of alignment methods are integrated in a very close position so that they can be detected by the same visual inspection. Therefore, according to the overlap of the two groups of alignment methods, the actual product boards can be divided into three categories.

[0025] In order to clearly identify the structure of the observation ring 2, the large ring 21 and the small ring 22 must have a clear color contrast with the surrounding area. If the ring width is too narrow, it will cause inconvenience in identification, so the ring width must be 70~100um.

[0026] S4. Plate processing: Qualified plates are marked and flow into the next production link, defective plates are scrapped, and suspect plates are reviewed. Suspect plates that pass the review are processed as qualified plates, otherwise they are scrapped as defective plates.

[0027] After multi-layer circuit boards are categorized, qualified boards are those with errors clearly within the accuracy range, while defective boards are those with errors clearly outside the accuracy range. These two categories account for the largest proportion, allowing for a direct judgment in a single test, saving time. However, a small number of finished boards are considered suspect, and their qualification remains uncertain. To avoid increased scrap costs, these boards undergo additional testing steps. Once they are confirmed as qualified, they can continue to be processed.

[0028] like Figure 2 As shown, although the standard square of the observation ring 2 does not overlap with the standard squares determined by the four characteristic holes 1, the outlines of all characteristic holes 1 are within the inner circle of their respective rings, so this product board is a qualified board and can be directly processed to the next production link.

[0029] like Figure 3 As shown, for the two large rings 21, their corresponding characteristic holes 1 are within their inner circle range, but the characteristic hole 1 in one of the small rings 21 deviates too much. This product board should be treated as a suspect board for secondary judgment and then corresponding processing should be made.

[0030] like Figure 4 As shown, one of the characteristic holes 1 has deviated from the inner circle range of its corresponding large ring 21. This product board must be a defective board and can be directly scrapped.

[0031] In summary, the present invention can utilize the special structure of the observation ring structure to align the blind through hole, thereby distinguishing whether the product board is passed, scrapped or needs to be re-inspected, saving processing time while ensuring accuracy.

[0032] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for quickly detecting the accuracy of circuit board holes, characterized in that the steps include: S1. Substrate preparation: A basic circuit board having a substrate is manufactured. Four characteristic holes arranged in a 2×2 pattern are provided in the edge area of the substrate, and the centers of the four characteristic holes are located at the four corners of the same standard square; S2. Circuit Manufacturing: A copper layer is plated on the surface of the substrate to provide electrical continuity between the copper layers through which through-holes or blind vias pass, and then a circuit is formed by processing. The edge region of the copper layer has an observation ring, which is composed of two large rings and two small rings. The inner diameter of the large ring is larger than the inner diameter of the small ring. The centers of the two large rings and the centers of the two small rings are located at the four corners of the same standard square, with the centers of the two large rings located at the ends of the first diagonal of the square, and the centers of the two small rings located at the ends of the second diagonal of the square. The center of each characteristic hole is located within the inner circle of a large ring or a small ring. S3. Visual inspection: The observation ring is visually photographed. When the outer contours of all characteristic holes are within the inner circle of their respective rings, the multilayer circuit board is judged to be a qualified board. When the outer contours of the characteristic holes in the large ring are all within the inner circle of the large ring in which they are located, and the contours of the characteristic holes in any small ring intersect with the annular range of the small ring in which they are located, the multilayer circuit board is judged to be a suspect board. When the contours of the characteristic holes in any large ring intersect with the annular range of the large ring in which they are located, the multilayer circuit board is judged to be a defective board. S4. Plate processing: Qualified plates are marked and flow into the next production link, defective plates are scrapped, and suspect plates are reviewed. Suspect plates that pass the review are processed as qualified plates, otherwise they are scrapped as defective plates.

2. The method for rapidly detecting circuit board hole accuracy classification according to claim 1, characterized in that: The side length of the standard square is 300-500 μm.

3. The method for rapidly detecting circuit board hole accuracy classification according to claim 2, characterized in that: The inner diameter of the large ring is 130-200 μm larger than the aperture of the characteristic hole.

4. The method for rapidly detecting circuit board hole accuracy classification according to claim 3, characterized in that: The inner diameter of the small ring is 40 μm smaller than the inner diameter of the large ring.

5. The method for rapidly detecting circuit board hole accuracy classification according to claim 1, characterized in that: The ring width of the large ring and the small ring is 70-100 μm.

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