A detection circuit design method for arbitrary interlayer dielectric thickness

Abstract

The invention discloses a detection circuit design method for arbitrary interlayer dielectric thickness. Detection holes are added on a board, and the detection holes are connected with the conducting holes on each circuit layer, so as to form a multi-layer detection circuit connected inside and outside in parallel between the conducting holes and the detection holes. When back-drilling in the detection hole, a conducting loop is formed between a back-drilling machine and the detection hole to be back-drilled. In this way, after each parallel detection circuit is cut off, the resistance value on the loop will instantly increase by one or more times, so that the position point when drilling through each circuit layer can be identified. By identifying the detected multiple positions, the dielectric thickness from the outer layer to any inner layer and the dielectric thickness between any two adjacent inner layers can be calculated. Then, the back-drilling depth when back-drilling on the board can be set according to the detected dielectric thickness, so as to achieve the purpose of high-precision back-drilling.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a detection circuit design method for arbitrary interlayer dielectric thickness. Background Art

[0002] As the integration of electronic systems continues to increase, circuit boards are becoming more and more integrated and functional, so it is inevitable that the design density of PCBs will become higher and higher. In addition, there are more and more applications of high-speed interconnection, and the requirements for high-speed signals of products will become higher and higher, such as 5G / 6G communications, supercomputing, high-performance computing, cloud computing, big data, etc.

[0003] As the application of high-frequency and high-speed products has increased significantly, new requirements have been put forward for the integrity of high-speed digital signals. The transmission lines of high-speed circuits have very high requirements for signal integrity at high frequencies and high speeds. The control and implementation of signal integrity are strongly correlated with the impedance and insertion loss of the transmission lines. When the high-speed rate exceeds 25Gbps, the impact of insertion loss on signal integrity becomes increasingly greater. The length of the extra stubs at the high-speed vias directly affects the size of the insertion loss. In order to obtain better high-speed signal integrity, the length of the stubs needs to be controlled as small as possible.

[0004] In order to reduce the short piles, the existing technology is to use a back drilling process to back drill away part of the excess short piles of the high-speed via holes. Since there is a tolerance in the thickness of the dielectric between the layers on the board, the tolerance of the dielectric thickness of multiple layers is large; moreover, there are large differences in the thickness of each area of ​​the large-size circuit board. Generally, due to the different thickness of the board, the extreme difference in the thickness is large and will exceed 0.2mm, which has a great impact on the back drilling accuracy of the whole board. Therefore, it is necessary to first determine the dielectric thickness between any layers in each area of ​​the board before determining the specific back drilling depth control.

[0005] In order to improve the back drilling accuracy, it is necessary to measure the plate thickness in different areas for manual stacking. When back drilling, the first piece needs to be sliced ​​to confirm the dielectric thickness between layers. In actual production, it is difficult to determine the difference in dielectric thickness at different locations on the plate, which makes it difficult to perform plate thickness stacking. Moreover, the slices are local slices, and only local cross-sections can be seen. The dielectric thickness between any layers in each area cannot be well determined, nor can the plate thickness differences in each area be effectively distinguished. In addition, the influence of plate thickness tolerance on back drilling depth and back drilling short piles cannot be eliminated, and high-precision back drilling cannot be achieved. Summary of the invention

[0006] In view of the above-mentioned existing technical defects, the present invention provides a detection circuit design method that can be used to detect the thickness of any interlayer dielectric.

[0007] In a first aspect, in order to solve the above technical problems, the present invention provides a method for designing a detection circuit for arbitrary interlayer dielectric thickness, comprising the following steps:

[0008] S1. Provide a core board, both surfaces of which are copper surfaces, and at least one drilling position is provided on the edge and / or non-circuit area of ​​the core board, wherein the drilling position is a position where a hole needs to be drilled in subsequent processing;

[0009] S2, transferring the inner layer pattern on the film to the core board through a negative film process, wherein the inner layer pattern is connected to the drilling position;

[0010] S3, then remove the exposed copper on the core board by etching, and then strip the film to form inner layer circuits and pads connected to the inner layer circuits.

[0011] S4, pressing at least one core board and the outer copper foil together through a prepreg to form a multi-layer production board;

[0012] S5. Drilling via holes connecting the inner and outer layers on the production board and drilling detection holes at positions perpendicular to each drilling position, and exposing each inner layer circuit on the hole walls of the detection holes and the via holes;

[0013] S6. The holes are metalized by copper deposition and electroplating. The metalized via holes and detection holes are connected to all circuit layers of the production board to form a multi-layer detection circuit connected in parallel inside and outside between the via holes and the detection holes.

[0014] Furthermore, in step S2, the inner layer pattern includes a circuit pattern and a pad pattern at a corresponding drilling position, wherein the circuit pattern is connected to the pad pattern, and an outer diameter of the pad pattern is larger than an outer diameter of the drilling position.

[0015] Furthermore, in step S3, an inner layer circuit and a pad connected to the inner layer circuit are formed on the core board after etching; in step 5, the pad is exposed on the hole wall of the detection hole after drilling.

[0016] Furthermore, in step S2, the inner layer pattern includes a circuit pattern and a hole ring pattern arranged around the drilling position, wherein the circuit pattern is connected to the hole ring pattern.

[0017] Furthermore, in step S3, an inner layer circuit and an annular hole connected to the inner layer circuit are formed on the core board after etching; in step 5, an inner circumference of the annular hole is exposed on the hole wall of the detection hole after drilling.

[0018] Furthermore, in step S1, the core board is divided into a plurality of parts in equal or unequal ways in the long side and / or short side directions, and at least one drilling position is provided in the board edge and / or non-circuit area of ​​each part.

[0019] Furthermore, in step S6, the detection hole in each part is connected to the conductive hole closest thereto.

[0020] Furthermore, after step S6, the following steps are also included:

[0021] S7. Fix the production board on the table of the back drilling machine, lead out two signal lines on the back drilling machine that are respectively connected to its control system, and the other end of one of the signal lines is connected to the drill bit on the back drilling machine, the blade diameter of the drill bit is larger than the aperture of the detection hole, and the other signal line is connected to the copper surface on the production board to form a conductive detection circuit between the production board and the back drilling machine.

[0022] In a second aspect, the present invention further provides another method for designing a detection circuit for arbitrary interlayer dielectric thickness, comprising the following steps:

[0023] S10, providing a core board, both surfaces of which are copper surfaces, and providing at least one set of detection modules on the edge and / or non-circuit area of ​​the core board, each set of detection modules including two adjacent drilling positions and a wire connecting the two drilling positions, wherein the drilling positions are positions where drilling is required in subsequent processing;

[0024] S20, transferring the inner layer pattern on the film to the core board through a negative film process, wherein the inner layer pattern includes a wire pattern corresponding to the wires in each group of detection modules;

[0025] S30, then removing the exposed copper on the core board by etching, and then stripping the film to form an inner layer circuit and a wire connecting two drilling positions in each group of detection modules;

[0026] S40, pressing at least one core board and an outer copper foil together through a prepreg to form a multi-layer production board;

[0027] S50, drilling detection holes at positions perpendicular to each drilling position on the production board, and exposing each layer of wires on the walls of the detection holes;

[0028] S60, metallizing the holes by copper deposition and electroplating, so that the two detection holes in each group of detection modules are connected to the wires in each inner layer, so as to form a multi-layer detection circuit connected inside and outside in parallel between the two detection holes in each group of detection modules.

[0029] Furthermore, in step S20, the inner layer pattern also includes a pad pattern at the corresponding drilling position or a hole ring pattern arranged around the drilling position, wherein the wire pattern in the same group of detection modules is connected to the pad pattern or the hole ring pattern, and the outer diameter of the pad pattern is larger than the outer diameter of the drilling position; in step S30, inner layer circuits, wires, pads and pads or hole rings are formed on the core board after etching; in step 50, the pad or hole ring is exposed on the hole wall of the detection hole after drilling.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] In the method of the present invention, by adding detection holes on the board, and connecting the detection holes with the conductive holes on each circuit layer, a multi-layer detection circuit connected inside and outside is formed between the conductive holes and the detection holes. When back-drilling in the detection hole, a conductive loop is formed between the back-drilling machine and the detection hole to be back-drilled. In this way, after each layer of the parallel detection circuit is cut off, the resistance value on the loop will instantly increase by one or more times, so that the position point when drilling through each circuit layer can be identified, and the dielectric thickness from the outer layer to any inner layer and the dielectric thickness between any two adjacent inner layers can be calculated by identifying the detected multiple positions. In this way, the back-drilling depth when back-drilling on the board can be set according to the detected dielectric thickness, so as to achieve the purpose of high-precision back-drilling; similarly, by setting at least one detection hole at each position on the board, the dielectric thickness at each location can be detected, so that the board thickness difference in each area can be effectively distinguished. First, regional back-drilling can be realized, and second, the dielectric thickness detected at each location can be used to calculate the average value, and then the specific back-drilling depth is determined by the average value, so as to reduce the influence of factors such as board thickness tolerance when back-drilling the production board.

[0032] Additional aspects and advantages of the present invention will be given in part in the following description, which will become obvious from the following description, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the electroplating on the board in Example 1;

[0034] Figure 2 This is a schematic diagram of placing the production board behind the back drilling machine in Example 1;

[0035] Figure 3 This is a schematic diagram of back drilling at a detection hole on a production board in Example 1;

[0036] Figure 4 This is a schematic diagram of the electroplating on the board in Example 2;

[0037] Figure 5 A schematic diagram of placing the production board behind the back drilling machine in Example 2;

[0038] Figure 6 This is a schematic diagram of back drilling at the detection hole on the production board in Example 2. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0041] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0042] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0043] Example 1

[0044] The present embodiment shows a method for manufacturing a circuit board, which includes a detection circuit design method for detecting the thickness of any interlayer dielectric, a detection process using the detection circuit, and a back drilling process. The method can realize high-precision manufacturing of back drilling holes and high-precision control of short piles. Taking the manufacturing of a ten-layer circuit board and drilling back drilling holes through seven layers of circuits as an example, the method includes the following processing steps in sequence:

[0045] (1) Cutting: Four core boards are cut according to the size of 520mm×620mm. The thickness of the core board is 0.5mm, and the thickness of the copper layer on both surfaces of the core board is 0.5oz. According to the design requirements, several positions for drilling holes after pressing are reserved on the board edges and non-circuit areas on both surfaces of each core board. These positions are called drilling positions.

[0046] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, a photosensitive film is coated on the core board with a vertical coating machine, the film thickness of the photosensitive film is controlled to be 8μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler). After development, the inner layer circuit pattern is formed, and the inner layer circuit pattern includes a pad pattern or annular hole pattern with an outer diameter larger than the drilling position; inner layer etching, the exposed and developed core board is etched to form the inner layer circuit, and a pad or annular hole 30 is made on both surfaces of the four core boards at the positions corresponding to all the drilling positions. In addition, the pad or annular hole 30 is connected to the inner layer circuit 40 (such as Figure 1 As shown in the figure, pads or hole rings are used to facilitate the connection between the hole wall copper layer at the later drilling position and the inner layer circuit. The inner layer line width is measured to be 3mil; inner layer AOI, and then check the inner layer circuit for open short circuits, circuit gaps, circuit pinholes and other defects. Defective products are scrapped and non-defective products are sent to the next process.

[0047] In a specific implementation case, 1-100 drilling positions, preferably 2-9, can be set on the edge of the core board and / or non-circuit area. The drilling positions are generally evenly distributed at various positions of the core board to facilitate the subsequent back-drilling detection. The dielectric thickness at various positions on the board from the board surface to any layer can be obtained, and by calculating the average dielectric thickness at each position, the thickness difference of each area on the board can be eliminated as much as possible, and the influence of the board thickness tolerance on the back-drilling depth and back-drilling short piles can be reduced.

[0048] In a specific implementation case, in order to avoid the large difference in board thickness between regions and the inability to reduce the impact of back drilling on the entire board by calculating the average dielectric thickness, the core board can be designed by dividing the region first, and then detection holes are set in each region to obtain the dielectric thickness and average from the board surface of the region to any inner layer after pressing, and this is used as the reference value for back drilling in the region, that is, the back drilling depth of each region may be the same or different when back drilling on the entire board, and will vary with the difference in board thickness between regions; specifically: the core board is divided into multiple parts in equal or unequal manner in the long side and / or short side direction, and 1-100 drilling positions are provided at the board edge and / or non-line area of ​​each part of the core board, preferably 2-9.

[0049] (3) Lamination: The browning speed is based on the browning thickness of the bottom copper. The four core boards, the prepreg, and the outer copper foil are stacked in sequence as required. The drilling positions on the four core boards correspond to each other and overlap up and down. The thickness of the outer copper foil is preferably 0.5 oz. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to press the laminated boards to form a ten-layer production board. Both surfaces of the production board are copper surfaces, and there are eight layers of inner circuits inside. One surface of the production board is the back-drilled surface to be drilled, that is, the first circuit layer, and the other surface is the non-back-drilled surface, that is, the tenth circuit layer.

[0050] (4) Drilling: According to the existing drilling technology, drilling is performed on the production board according to the design requirements to drill the conductive holes 10 for connecting the inner and outer layer circuits and drill the detection holes 20 at the position perpendicular to each drilling position. The diameter of the detection hole is smaller than the outer diameter of the pad or the same as the inner diameter of the hole ring, so that the pad or the hole ring 30 (such as Figure 1 shown).

[0051] (5) Copper plating: A thin layer of copper is deposited on the board surface and hole wall by chemical copper plating. The backlight test is level 10. The copper thickness in the hole is 0.5 μm. The metallized via holes and detection holes are connected to all circuit layers of the production board to form a multi-layer detection circuit connected inside and outside in parallel between the via holes and the detection holes, such as Figure 1 As shown, a detection circuit that can be used to detect the thickness of any interlayer dielectric is obtained; of course, no matter the core board is designed in a divided area or a partial area, each detection hole is generally connected to the conductive hole closest to it.

[0052] (6) Full-board electroplating: Full-board electroplating is performed at a current density of 18 ASF for 60 minutes to thicken the copper layer on the hole and the board surface.

[0053] (7) Medium thickness detection: specifically including the following steps:

[0054] a. Figure 2 As shown, the production board 1 is first fixed on the table of the back drilling machine, with its back drilling surface located at the uppermost side and serving as the first circuit layer, and the non-back drilling surface located at the lowermost side and serving as the tenth circuit layer. Two signal lines 3 are led out from the back drilling machine and connected to its control system respectively, that is, one end of the two signal lines is connected to the control system 2, and the other end of one of the signal lines is connected to the drill bit on the back drilling machine, that is, an electrical connection is formed. Of course, the connection relationship cannot affect the rotation of the drill bit. The blade diameter of the drill bit is adapted to the designed hole diameter of the back drilling hole, that is, the blade diameter of the drill bit is larger than the outer diameter of the detection hole, so that the copper layer of the hole wall can be ensured to be removed during back drilling. The other signal line 3 is connected to the copper surface on the production board 1, that is, through the conduction of the control system, the copper surface and the drill bit are connected, but no loop is formed at the initial stage before back drilling; the control system of the back drilling machine is a servo control system.

[0055] Preferably, a presser foot 4 is provided on the back drilling machine, which can move up and down and abut against the surface of the production board 1. The signal line 3 is connected to the copper layer on the surface of the production board 1 through the presser foot 4. The connection using the presser foot is convenient and universal.

[0056] In a specific implementation case, a clamp (not shown in the figure) that can be clamped on the surface of the production board is provided on the back drilling machine, and the signal line is connected to the copper layer on the surface of the production board through the clamp.

[0057] b. Figure 3 As shown, the drill bit 5 is controlled to back-drill the detection holes one by one. When the drill bit contacts the board surface, a loop is formed between the detection hole of the production board and the drill bit through two signal lines and the copper layer on the production board, so that the change of resistance value during the drill bit back-drilling can be monitored. When the drill bit continues to drill and detects for the first time that the resistance value is instantly doubled or more, the control system records this time as the reference zero point. When the drill bit continues to drill until the second time it is detected that the resistance value is instantly doubled or more, it is recorded as the end point of the second layer, and the dielectric thickness from the outer layer to the second layer can be obtained. When the drill bit continues to drill until the third time it is detected that the resistance value is instantly doubled or more, it is recorded as the end point of the third layer, and the dielectric thickness from the outer layer to the third layer and the dielectric thickness from the second layer to the third layer can be obtained. By analogy, the dielectric thickness from the outer layer to any inner layer and the dielectric thickness between any two adjacent inner layers can be obtained in sequence during the process of the drill bit continuing to drill.

[0058] In the above, the dielectric thickness from the reference zero point to each end point s = v·tn·h, where v is the drilling speed of the drill bit, t is the back drilling time from the reference zero point to each end point, n is the number of inner layer circuit layers drilled during back drilling, and h is the copper thickness of the inner layer circuit; the dielectric thickness between any two adjacent inner layers = the difference in dielectric thickness from the reference zero point to the two adjacent end points.

[0059] In the above, when the drill bit continues to drill down and cuts off the connection between the copper layer on the board surface and the copper layer on the hole wall, it is equivalent to forming an instantaneous open circuit state between the board surface and the copper layer of the back-drilled detection hole, and its resistance is close to the maximum value, but the loop is still connected because the drill bit is in contact with the board surface and the copper layer in the hole. At this time, the resistance is not the maximum value, and the resistivity of the drill bit is generally greater than the resistivity of copper. Therefore, the instantaneous resistance value when drilling off will be twice or more than twice that before drilling off. Similarly, when drilling off the connection between the wire in the drilled layer and the copper layer of the detection hole, the instantaneous resistance value will also be twice or more than twice that before drilling off; the drill bit is preferably made of steel alloy.

[0060] In the above, the back drilling machine can select a schmoll drilling machine, and the control system on the back drilling machine provides a constant voltage U to the circuit formed when the drill bit is back drilling. When the drill bit is back drilling, the resistance value in the circuit is constantly changing, so the current I in the circuit is also constantly changing, and the schmoll drilling machine can monitor the specific changes of the current in the circuit, and calculate the real-time resistance value R=voltage U / current I under the condition that the voltage remains unchanged, and then determine whether a certain line layer has been drilled through by the change in resistance value; of course, the constant voltage U provided is generally 12-24V.

[0061] c. After all the detection holes on the board are back-drilled, the dielectric thickness from the outer layer to any inner layer at each detection hole on the production board and the dielectric thickness between any two adjacent inner layers are obtained, so as to determine the dielectric thickness difference and board thickness difference in each area of ​​the board. First, the purpose of board thickness stacking can be achieved. Second, when the production board is not partitioned, the average value of the dielectric thickness from the outer layer to the same inner layer at all detection holes can be calculated, and then the average value is used to determine the actual back-drilling depth in the later stage, which can try to eliminate the influence of the board thickness difference in each area on the back-drilling. Third, when the production board is partitioned, the average value of the dielectric thickness from the outer layer to the same inner layer at all detection holes in each part can be calculated, and then the actual back-drilling depth in the later stage can be determined by the average value calculated in the part, so as to achieve regional division and perform back-drilling according to different back-drilling parameters, and completely eliminate the influence of the board thickness difference in each area on the back-drilling.

[0062] (8) Back drilling: When the production board is not designed with partitions, the average value of the dielectric thickness from the outer layer to the seventh layer at all the detection holes calculated in step c plus the compensation value is used as the actual back drilling depth of the back drilling holes in the production board, that is, the conductive holes to be back drilled on the production board are back drilled according to the actual back drilling depth obtained; similarly, when the production board is designed with partitions, the average value of the dielectric thickness from the outer layer to the seventh layer at all the detection holes in each part is calculated plus the compensation value as the actual back drilling depth of the back drilling holes in the board in that part, that is, the conductive holes to be back drilled in each part are back drilled according to the actual back drilling depth obtained; wherein the compensation value is not greater than 50% of the dielectric thickness between the seventh layer and the eighth layer, that is, when back drilling, after drilling through the seventh circuit layer, the further drilling down does not exceed half of the dielectric thickness of the lower layer, so as to minimize the length of the residual pile between the drilled layer and the non-drilled layer.

[0063] Preferably, in addition to the percentage calculation method described above, the compensation value can also be calculated based on the accuracy of the back drilling machine, the tolerance of the dielectric thickness between the drilled layer and the non-drilled layer, and the minimum length value of the stub based on the reliability of the line connection performance; for example, the average dielectric thickness between the seventh layer and the eighth layer of the entire board or a part thereof is detected to be 0.14 mm, the accuracy of the back drilling machine is ±0.025 mm, the length of the stub should be ≥0.05 mm, and the compensation value = 0.14-0.025-0.05 = 0.065 mm. In this way, the length of the stub is controlled between 0.05-0.13 mm after back drilling, which can meet the requirement of making the back drilling stub as small as possible when the high-speed transmission rate exceeds 50 Gbps.

[0064] Preferably, since the dielectric thickness from the copper layer to the seventh layer on the board surface does not include the copper thickness of each layer, in order to avoid the influence of the copper thickness during back drilling, the actual back drilling depth may also be added with the copper thickness of each layer drilled through.

[0065] (9) Production of outer circuits (positive film process): Transfer of outer pattern, using fully automatic exposure machine and positive circuit film, with 5-7 grid exposure ruler (21 grid exposure ruler) to complete the exposure of outer circuit, after development, the outer circuit pattern is formed on the production board; electroplating of outer pattern, and then copper plating and tin plating on the production board respectively, setting the electroplating parameters according to the required copper thickness, copper plating is 1.8ASD current density electroplating for 60 minutes on the whole board, tin plating is 1.2ASD current density electroplating for 10 minutes, tin thickness is 3-5μm; then stripping, etching and tin stripping are carried out in turn, and the outer circuit is etched on the production board, and the copper thickness of the outer circuit is greater than or equal to 70μm; outer layer AOI, using automatic optical inspection system, by comparing with CAM data, detect whether the outer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc.

[0066] (10) Solder mask and silk screen characters: After silk screen printing solder mask ink on the surface of the production board, it is sequentially subjected to pre-curing, exposure, development and heat curing treatment to solidify the solder mask ink into a solder mask layer; specifically, the solder mask ink and the characters on the top surface are added with "UL mark", so that a layer is coated on the circuits and substrates that do not need to be soldered to prevent bridging between circuits during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time beautify the appearance; the production process of the solder mask layer includes the following steps:

[0067] (11) Surface treatment (nickel-gold immersion): The copper surface of the pad at the solder mask opening is chemically treated to uniformly deposit nickel and gold layers of a certain required thickness. The thickness of the nickel layer is 3-5 μm; the thickness of the gold layer is 0.05-0.1 μm.

[0068] (12) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0069] (13) Molding: According to the existing technology and the design requirements, the circuit board is manufactured with a shape tolerance of + / -0.05mm.

[0070] (14) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0071] (15) FQA: Re-test the circuit board’s appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. to see if they meet customer requirements.

[0072] (16) Packaging: According to the packaging method and packaging quantity required by the customer, the circuit boards are sealed and packed with desiccant and humidity card before shipment.

[0073] Example 2

[0074] The present embodiment shows a method for manufacturing a circuit board, which includes a detection circuit design method for detecting the thickness of any interlayer dielectric, a detection process using the detection circuit, and a back drilling process. The method can realize high-precision manufacturing of back drilling holes and high-precision control of short piles. Taking the manufacturing of a ten-layer circuit board and drilling back drilling holes through seven layers of circuits as an example, the method includes the following processing steps in sequence:

[0075] (1) Cutting: Four core boards are cut according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the thickness of the copper layer on both surfaces of the core board is 0.5oz. According to the design requirements, several groups of detection modules are reserved on the board edges and non-circuit areas on both surfaces of the four core boards. Each group of detection modules includes two adjacent drilling positions and a wire connecting the two drilling positions. The drilling positions are the positions where holes need to be drilled after pressing.

[0076] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, a photosensitive film is coated on the core board with a vertical coating machine, the film thickness of the photosensitive film is controlled to be 8μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler). After development, the inner layer circuit pattern is formed, and the inner layer circuit pattern includes the wire pattern corresponding to the wire in each group of detection modules; inner layer etching, the exposed and developed core board is etched to form the inner layer circuit, and a pad or hole ring 30 is made on both surfaces of the four core boards at the positions corresponding to all the drilling positions. In addition, the two pads or hole rings in each group of detection modules are connected through the wire 50 made on the same layer (such as Figure 5 As shown in the figure, the copper layers of the hole walls at the two drilling positions of the same group of inspection modules are connected by using pads or hole rings. The inner layer line width is measured to be 3mil; inner layer AOI, and then check the inner layer circuit for open short circuits, circuit gaps, circuit pinholes and other defects. Defective products will be scrapped and non-defective products will be sent to the next process.

[0077] In a specific implementation case, 1-100 groups of detection modules can be set at the edge of the core board and / or non-line area, preferably 2-9 groups. The detection modules are generally evenly distributed at various positions of the core board to facilitate the subsequent back-drilling detection. The dielectric thickness at various positions on the board from the board surface to any layer can be obtained, and by calculating the average dielectric thickness at each position, the thickness difference of each area on the board can be eliminated as much as possible, and the influence of the board thickness tolerance on the back-drilling depth and back-drilling short piles can be reduced.

[0078] In a specific implementation case, in order to avoid the large difference in board thickness between regions and the inability to reduce the impact of back drilling on the entire board by calculating the average dielectric thickness, the core board can be first designed by dividing the region, and then a detection module is set on each region and the average dielectric thickness of the region is calculated after pressing, which is used as the reference value of the back drilling depth of the region, that is, the back drilling depth of each region may be the same or different when back drilling is performed on the entire board, and will vary with the difference in board thickness between regions; specifically: the core board is divided into multiple parts in equal or unequal manner in the long side and / or short side direction, and 1-100 groups of detection modules are provided at the board edge and / or non-line area of ​​each part of the core board, preferably 2-9 groups.

[0079] (3) Lamination: The browning speed is based on the browning thickness of the bottom copper. The four core boards, the prepreg, and the outer copper foil are stacked in sequence as required. The drilling positions on the four core boards correspond to each other and overlap up and down. The thickness of the outer copper foil is preferably 0.5 oz. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to press the laminated boards to form a ten-layer production board. Both surfaces of the production board are copper surfaces, and there are eight layers of inner circuits inside. One surface of the production board is the back-drilled surface to be drilled, that is, the first circuit layer, and the other surface is the non-back-drilled surface, that is, the tenth circuit layer.

[0080] (4) Drilling: Based on the existing drilling technology, drilling is performed on the production board according to the design requirements, thereby drilling through holes in the board for connecting the inner and outer layer circuits, and drilling detection holes 20 (such as Figure 5 As shown), the diameter of the detection hole is smaller than the outer diameter of the pad or is the same as the inner diameter of the hole ring, so that the pad or the hole ring is exposed on the hole wall of the detection hole. One detection hole in the same group of detection modules is used as a hole for back drilling detection later, and the other is used as a conductive hole of the loop.

[0081] (5) Copper plating: A thin layer of copper is deposited on the board surface and the hole wall by chemical copper plating. The backlight test is level 10. The thickness of the copper plating in the hole is 0.5 μm. In addition to forming a connection between the metallized detection holes on the board surface, the two detection holes in the same detection module are also connected at any inner circuit layer to form an internal and external parallel multi-layer detection circuit between the two detection holes in each detection module, such as Figure 5 shown.

[0082] (6) Full-board electroplating: Full-board electroplating is performed at a current density of 18 ASF for 60 minutes to thicken the copper layer on the hole and the board surface.

[0083] (7) Medium thickness detection: specifically including the following steps:

[0084] a. Figure 5As shown, the production board is first fixed on the table of the back drilling machine, with its back drilling surface located at the uppermost side and serving as the first circuit layer, and the non-back drilling surface located at the lowermost side and serving as the tenth circuit layer. Two signal lines 3 are led out from the back drilling machine and connected to its control system respectively, that is, one end of the two signal lines is connected to the control system 2, and the other end of one of the signal lines is connected to the drill bit on the back drilling machine, that is, an electrical connection is formed. Of course, the connection relationship cannot affect the rotation of the drill bit. The blade diameter of the drill bit is adapted to the designed hole diameter of the back drilling hole, that is, the blade diameter of the drill bit is larger than the outer diameter of the detection hole, so that the copper layer of the hole wall can be ensured to be removed during back drilling. The other signal line 3 is connected to the copper surface on the production board 1, that is, through the conduction of the control system, the copper surface and the drill bit are connected, but no loop is formed at the beginning before back drilling; the control system of the back drilling machine is a servo control system.

[0085] Preferably, a presser foot 4 is provided on the back drilling machine, which can move up and down and abut against the surface of the production board 1. The signal line 3 is connected to the copper layer on the surface of the production board 1 through the presser foot 4. The connection using the presser foot is convenient and universal.

[0086] In a specific implementation case, a clamp (not shown in the figure) that can be clamped on the surface of the production board is provided on the back drilling machine, and the signal line is connected to the copper layer on the surface of the production board through the clamp.

[0087] b. Figure 6 As shown, the drill bit 5 is controlled to back-drill one of the detection holes of each group of detection modules. When the drill bit contacts the board surface, a loop is formed between the detection hole of the production board and the drill bit through two signal lines and the copper layer on the production board to monitor the change in resistance value when the drill bit is back-drilling. When the drill bit continues to drill and detects for the first time that the resistance value is instantly doubled or more, the control system records this time as the reference zero point. When the drill bit continues to drill until the second time it is detected that the resistance value is instantly doubled or more, it is recorded as the end point of the second layer, and the dielectric thickness from the outer layer to the second layer can be obtained. When the drill bit continues to drill until the third time it is detected that the resistance value is instantly doubled or more, it is recorded as the end point of the third layer, and the dielectric thickness from the outer layer to the third layer and the dielectric thickness from the second layer to the third layer can be obtained. By analogy, the dielectric thickness from the outer layer to any inner layer and the dielectric thickness between any two adjacent inner layers can be obtained in sequence during the process of the drill bit continuing to drill.

[0088] In the above, the dielectric thickness from the reference zero point to each end point s = v·tn·h, where v is the drilling speed of the drill bit, t is the back drilling time from the reference zero point to each end point, n is the number of inner layer circuit layers drilled during back drilling, and h is the copper thickness of the inner layer circuit; the dielectric thickness between any two adjacent inner layers = the difference in dielectric thickness from the reference zero point to the two adjacent end points.

[0089] c. After back-drilling of one of the detection holes of all the detection modules on the board, the dielectric thickness from the outer layer to any inner layer at each detection module on the production board and the dielectric thickness between any two adjacent inner layers are obtained, so as to determine the dielectric thickness difference and board thickness difference at each area on the board. Firstly, the purpose of board thickness stacking can be achieved. Secondly, when the production board is not partitioned, the average value of the dielectric thickness from the outer layer to the same inner layer at all the detection modules can be calculated, and then the actual back-drilling depth in the later stage can be determined by the average value, which can eliminate the influence of the board thickness difference in each area on the back-drilling as much as possible. Thirdly, when the production board is partitioned, the average value of the dielectric thickness from the outer layer to the same inner layer at all the detection modules in each part can be calculated, and then the actual back-drilling depth in the later stage can be determined by the average value calculated in the part, so as to achieve regional division and perform back-drilling according to different back-drilling parameters, which can completely eliminate the influence of the board thickness difference in each area on the back-drilling.

[0090] (8) Back drilling: When the production board is not designed with partitions, the average value of the dielectric thickness from the outer layer to the seventh layer at all detection modules calculated in step c plus the compensation value is used as the actual back drilling depth of the back drilling holes in the production board, that is, the conductive holes to be back drilled on the production board are back drilled according to the actual back drilling depth obtained; similarly, when the production board is designed with partitions, the average value of the dielectric thickness from the outer layer to the seventh layer at all detection holes in each part is calculated plus the compensation value as the actual back drilling depth of the back drilling holes in the board in that part, that is, the conductive holes to be back drilled in each part are back drilled according to the actual back drilling depth obtained; wherein the compensation value is not greater than 50% of the dielectric thickness between the seventh layer and the eighth layer, that is, when back drilling, after drilling through the seventh circuit layer, the further drilling down does not exceed half of the dielectric thickness of the lower layer, so as to minimize the length of the residual pile between the drilled layer and the non-drilled layer.

[0091] Preferably, in addition to the percentage calculation method mentioned above, the compensation value can also be calculated based on the accuracy of the back drilling machine, the dielectric thickness between the seventh layer and the eighth layer, and the minimum length value of the stub based on the reliability of the line connection performance; for example, the average dielectric thickness between the seventh layer and the eighth layer of the entire board or a part is detected to be 0.14mm, the accuracy of the back drilling machine is ±0.025mm, the length of the stub should be ≥0.05mm, the compensation value = 0.14-0.025-0.05 = 0.065mm, so that the length of the stub is controlled between 0.05-0.13mm after back drilling, which can meet the requirement of making the back drilling stub as small as possible when the high-speed transmission rate exceeds 50Gbps.

[0092] Preferably, since the dielectric thickness from the copper layer to the seventh layer on the board surface does not include the copper thickness of each layer, in order to avoid the influence of the copper thickness during back drilling, the actual back drilling depth may also be added with the copper thickness of each layer drilled through.

[0093] (9) Production of outer circuits (positive film process): Transfer of outer pattern, using fully automatic exposure machine and positive circuit film, with 5-7 grid exposure ruler (21 grid exposure ruler) to complete the exposure of outer circuit, after development, the outer circuit pattern is formed on the production board; electroplating of outer pattern, and then copper plating and tin plating on the production board respectively, setting the electroplating parameters according to the required copper thickness, copper plating is 1.8ASD current density electroplating for 60 minutes on the whole board, tin plating is 1.2ASD current density electroplating for 10 minutes, tin thickness is 3-5μm; then stripping, etching and tin stripping are carried out in turn, and the outer circuit is etched on the production board, and the copper thickness of the outer circuit is greater than or equal to 70μm; outer layer AOI, using automatic optical inspection system, by comparing with CAM data, detect whether the outer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc.

[0094] (10) Solder mask and silk screen characters: After silk screen printing solder mask ink on the surface of the production board, it is sequentially subjected to pre-curing, exposure, development and heat curing treatment to solidify the solder mask ink into a solder mask layer; specifically, the solder mask ink and the characters on the top surface are added with "UL mark", so that a layer is coated on the circuits and substrates that do not need to be soldered to prevent bridging between circuits during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time beautify the appearance; the production process of the solder mask layer includes the following steps:

[0095] (11) Surface treatment (nickel-gold immersion): The copper surface of the pad at the solder mask opening is chemically treated to uniformly deposit nickel and gold layers of a certain required thickness. The thickness of the nickel layer is 3-5 μm; the thickness of the gold layer is 0.05-0.1 μm.

[0096] (12) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0097] (13) Molding: According to the existing technology and the design requirements, the circuit board is manufactured with a shape tolerance of + / -0.05mm.

[0098] (14) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0099] (15) FQA: Re-test the circuit board’s appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. to see if they meet customer requirements.

[0100] (16) Packaging: According to the packaging method and packaging quantity required by the customer, the circuit boards are sealed and packed with desiccant and humidity card before shipment.

[0101] Above Figures 1 to 6In the diagram, the bold lines on the circuit board are the copper layers.

[0102] In addition to being applicable to high-precision back drilling, the method for detecting the thickness of the interlayer dielectric in the above two embodiments can also be applied to high-precision impedance design. A detection hole or a detection module can be designed at the area where the impedance line passes to detect whether the thickness of the interlayer dielectric at the impedance line meets the design requirements. Based on the result, it can be determined whether to adjust the design of the thickness of the interlayer dielectric at the impedance line during pressing, thereby greatly reducing the reduction in impedance design accuracy caused by inaccurate dielectric thickness.

[0103] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for designing a detection circuit for arbitrary interlayer dielectric thickness, characterized in that: The following steps are involved: S1. Provide a core board, both surfaces of which are copper surfaces, and at least one drilling position is provided on the edge and / or non-circuit area of ​​the core board, wherein the drilling position is a position where a hole needs to be drilled in subsequent processing; S2, transferring the inner layer pattern on the film to the core board through a negative film process, wherein the inner layer pattern is connected to the drilling position; S3, then remove the exposed copper on the core board by etching, and then strip the film to form an inner layer circuit and a pad connected to the inner layer circuit; S4, pressing at least one core board and the outer copper foil together through a prepreg to form a multi-layer production board; S5. Drilling via holes connecting the inner and outer layers on the production board and drilling detection holes at positions perpendicular to each drilling position, and exposing each inner layer circuit on the hole walls of the detection holes and the via holes; S6. The holes are metalized by copper deposition and electroplating. The metalized via holes and detection holes are connected to all circuit layers of the production board to form a multi-layer detection circuit connected in parallel inside and outside between the via holes and the detection holes; S7, fix the production board on the table of the back drilling machine, lead out two signal lines on the back drilling machine that are respectively connected to its control system, and the other end of one of the signal lines is connected to the drill bit on the back drilling machine, the blade diameter of the drill bit is larger than the aperture of the detection hole, and the other signal line is connected to the copper surface on the production board, so that a conductive detection circuit is formed between the production board and the back drilling machine; S8. Back-drill the detection holes one by one with a drill bit, wherein the resistivity of the drill bit is greater than the resistivity of copper. When the drill bit contacts the board surface, a conductive loop is formed between the drill bit and the detection hole to be back-drilled through the signal line, so that the resistance value change during the drill bit back-drilling can be monitored. When the drill bit continues to drill and detects that the resistance value is instantly doubled or more for the first time, this time is recorded as the reference zero point. When the drill bit continues to drill until the resistance value is instantly doubled or more for the second time, it is recorded as the end point of the second layer, and the dielectric thickness from the outer layer to the second layer can be obtained. When the drill bit continues to drill until the resistance value is instantly doubled or more for the third time, it is recorded as the end point of the third layer, and the dielectric thickness from the outer layer to the third layer and the dielectric thickness from the second layer to the third layer can be obtained. By analogy, the dielectric thickness from the outer layer to any inner layer and the dielectric thickness between any two adjacent inner layers can be obtained in sequence during the drill bit continuing to drill.

2. The method for designing a detection circuit for arbitrary interlayer dielectric thickness according to claim 1, characterized in that: In step S2, the inner layer pattern includes a circuit pattern and a pad pattern at a corresponding drilling position, wherein the circuit pattern is connected to the pad pattern, and an outer diameter of the pad pattern is larger than an outer diameter of the drilling position.

3. The method for designing a detection circuit for arbitrary interlayer dielectric thickness according to claim 2, characterized in that: In step S3, an inner layer circuit and a pad connected to the inner layer circuit are formed on the core board after etching; in step 5, the pad is exposed on the hole wall of the detection hole after drilling.

4. The method for designing a detection circuit for arbitrary interlayer dielectric thickness according to claim 1, characterized in that: In step S2, the inner layer pattern includes a circuit pattern and a hole ring pattern arranged around the drilling position, wherein the circuit pattern is connected to the hole ring pattern.

5. The method for designing a detection circuit for arbitrary interlayer dielectric thickness according to claim 4, characterized in that: In step S3, an inner layer circuit and an annular hole connected to the inner layer circuit are formed on the core board after etching; in step 5, an inner circumference of the annular hole is exposed on the hole wall of the detection hole after drilling.

6. The method for designing a detection circuit for arbitrary interlayer dielectric thickness according to any one of claims 1 to 5, characterized in that: In step S1, the core board is divided into a plurality of parts in equal or unequal ways in the long side and / or short side direction, and at least one drilling position is provided in the board edge and / or non-circuit area of ​​each part.

7. The method for designing a detection circuit for arbitrary interlayer dielectric thickness according to claim 6, characterized in that: In step S6, the detection hole in each part is connected to the conductive hole closest thereto.

8. A method for designing a detection circuit for arbitrary interlayer dielectric thickness, characterized in that: The following steps are involved: S10, providing a core board, both surfaces of which are copper surfaces, and providing at least one set of detection modules on the edge and / or non-circuit area of ​​the core board, each set of detection modules including two adjacent drilling positions and a wire connecting the two drilling positions, wherein the drilling positions are positions where drilling is required in subsequent processing; S20, transferring the inner layer pattern on the film to the core board through a negative film process, wherein the inner layer pattern includes a wire pattern corresponding to the wires in each group of detection modules; S30, then removing the exposed copper on the core board by etching, and then stripping the film to form an inner layer circuit and a wire connecting two drilling positions in each group of detection modules; S40, pressing at least one core board and an outer copper foil together through a prepreg to form a multi-layer production board; S50, drilling detection holes at positions perpendicular to each drilling position on the production board, and exposing each layer of wires on the walls of the detection holes; S60, metalizing the holes by copper deposition and electroplating, so that the two detection holes in each group of detection modules are connected to the wires in each inner layer, so as to form a multi-layer detection circuit connected inside and outside in parallel between the two detection holes in each group of detection modules; S70, fix the production board on the table of the back drilling machine, lead out two signal lines on the back drilling machine that are respectively connected to its control system, and the other end of one of the signal lines is connected to the drill bit on the back drilling machine, the blade diameter of the drill bit is larger than the aperture of the detection hole, and the other signal line is connected to the copper surface on the production board, so that a conductive detection circuit is formed between the production board and the back drilling machine; S80, back-drill one of the detection holes of each group of detection modules by using a drill bit, wherein the resistivity of the drill bit is greater than the resistivity of copper. When the drill bit contacts the board surface, a loop is formed between the detection hole of the production board and the drill bit through two signal lines and the copper layer on the production board, so as to monitor the change of resistance value when the drill bit is back-drilling. When the drill bit continues to drill down and detects for the first time that the resistance value is instantly doubled or more, this time is recorded as the reference zero point. When the drill bit continues to drill down until the second time that the resistance value is instantly doubled or more, it is recorded as the end point of the second layer, and the dielectric thickness from the outer layer to the second layer can be obtained. When the drill bit continues to drill down until the third time that the resistance value is instantly doubled or more, it is recorded as the end point of the third layer, and the dielectric thickness from the outer layer to the third layer and the dielectric thickness from the second layer to the third layer can be obtained. By analogy, the dielectric thickness from the outer layer to any inner layer and the dielectric thickness between any two adjacent inner layers can be obtained in sequence during the process of the drill bit continuing to drill down.

9. The method for designing a detection circuit for arbitrary interlayer dielectric thickness according to claim 8, characterized in that: In step S20, the inner layer pattern also includes a pad pattern at the corresponding drilling position or a hole ring pattern arranged around the drilling position, wherein the wire pattern in the same group of detection modules is connected to the pad pattern or the hole ring pattern, and the outer diameter of the pad pattern is larger than the outer diameter of the drilling position; in step S30, inner layer circuits, wires, pads and pads or hole rings are formed on the core board after etching; in step S50, the pad or hole ring is exposed on the hole wall of the detection hole after drilling.

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