Method and system for back drilling of multilayer circuit boards

Abstract

A method and system for manufacturing a multilayer circuit board are disclosed, comprising: electrically connecting a drilling device to a plated multilayer circuit board; cutting a first hole having a first diameter through a first layer of the plated multilayer circuit board; reciprocatingly extending a second cutting device into a cylindrical portion of the plated multilayer circuit board a first predetermined distance and retracting the cutting device a second predetermined distance less than the first predetermined distance to form a second hole. After each retraction, sensing electrical contact representing a closed circuit between the cutting device and the plated multilayer circuit board; if a closed circuit is sensed, determining whether the second hole has reached a desired depth of the contact layer; if the desired depth of the contact layer has not been reached, determining that an edge strip has been formed within the cylindrical portion.

Description

[0001] By incorporating via reference

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 006,538, filed April 7, 2020, entitled “Method for Backdrilling and Silver Detection,” the entire contents of which are incorporated herein by reference. Background Technology

[0003] Multilayer circuit boards and / or wiring boards are well known in the art. A multilayer circuit board is formed having multiple signal layers (conductive layers) arranged in a predetermined pattern. These signal layers are insulated from each other by dielectric layers. Therefore, a multilayer circuit board is formed by interleaved (e.g., alternating) signal layers and dielectric layers. Holes, or "vias," are formed through the multilayer circuit board and may be plated with a conductive material to connect one signal layer to another. After being formed, the plated vias typically extend from one main side of the multilayer circuit board to the opposite side of the multilayer circuit board.

[0004] In some cases, plated vias or holes include "stub portions" that extend away from the signal layer towards one side of a multilayer circuit board. In high-speed data transmission, these stubs can cause dispersion or other effects that compromise signal integrity, thus reducing the achievable bandwidth. Therefore, in electronic systems utilizing high-speed signals, it is desirable to remove these stub portions to improve the signal-to-noise ratio (SNR). Smaller stub portions generally result in better signal quality. Historically, stub portions of plated vias were removed using a process known as "back-drilling." In back-drilling, the stub portion of the plated via is removed by drilling it to a predetermined depth. However, in practice, the thickness of layers in a multilayer circuit board is not uniform, and the depth of signal layers also varies, which often alters the amount of stub portion that needs to be removed. Drilling too deep can disconnect the signal layer from the plated via or leave unreliable connections; while drilling too shallow can lead to a decrease in SNR due to the increased stub length.

[0005] In addition to the residual length described in the previous paragraph, copper chips or slivers may also remain in the drilled copper cylindrical section. When these chips attach to the copper cylindrical section, they will function as residual sections and cause problems similar to those caused by incorrectly drilled chips. These chips may be caused by misalignment between the back drill hole and the first (initial) drill (plating) hole, or by drill bit wobble in the main drill hole or back drill hole.

[0006] Therefore, there is a need for systems and processes that overcome problems related to the differences in layer thickness in multilayer circuit boards, in order to achieve reduced residual lengths and inspection strips. The currently disclosed inventive concept is aimed at such improved systems and methods. Attached Figure Description

[0007] To assist those skilled in the art in making and using the subject matter of this invention, reference has been made to the accompanying drawings, which are not intended to be drawn to scale. Similar reference numerals in the drawings are intended to refer to similar elements for consistency. For clarity, not every component is labeled in each view.

[0008] Figure 1 This is a schematic diagram of a system for back-drilling plated multilayer circuit boards constructed according to an embodiment of the present disclosure.

[0009] Figure 2 According to one embodiment of this disclosure Figure 1 A cross-sectional view of a multilayer circuit board, wherein a first drill hole extends through the signal layer of the plated multilayer circuit board.

[0010] Figure 3 According to one embodiment of this disclosure Figure 1 A cross-sectional view of a multilayer circuit board, showing a cutting device drilling a second hole that extends through multiple layers of the plated multilayer circuit board.

[0011] Figure 4 According to one embodiment of this disclosure Figure 3 A cross-sectional view of a multilayer circuit board, showing the cutting device retracting from the second drill hole so that the cutting device is no longer in contact with the cylindrical portion containing conductive material.

[0012] Figure 5 According to one embodiment of this disclosure Figure 4 A cross-sectional view of a multilayer circuit board shows the cutting device retracting from the second drill hole, so that the cutting device is no longer in contact with the cylindrical part, but is still in contact with the contact layer.

[0013] Figure 6 According to one embodiment of this disclosure Figure 4 A cross-sectional view of a plated multilayer circuit board, showing the cutting device at its final depth.

[0014] Figure 7 This is a cross-sectional view of a plated multilayer circuit board with edge strips formed in a cylindrical portion according to an embodiment of the present disclosure.

[0015] Figure 8 According to one embodiment of this disclosure Figure 7A cross-sectional view of a plated multilayer circuit board, wherein the cutting device retracts and contacts the edge strip formed in the cylindrical portion.

[0016] Figure 9A This is a cross-sectional view of a multilayer circuit board according to an embodiment of the present disclosure, wherein the cutting device partially retracts so that the cutting device does not contact the cylindrical portion.

[0017] Figure 9B This is a cross-sectional view of a multilayer circuit board according to an embodiment of the present disclosure, wherein the cutting device partially retracts but contacts the edge strip formed in the cylindrical portion.

[0018] Figure 10A and Figure 10B A top plan view of a contact pad having one or more conductive fingers constructed according to an embodiment of the present disclosure is shown. Detailed Implementation

[0019] Before explaining at least one embodiment of this disclosure in detail, it should be understood that this disclosure is not limited in its application to the details of the construction, experiments, exemplary data and / or arrangement of components set forth in the following description or shown in the accompanying drawings.

[0020] The systems and methods described in this disclosure can have other embodiments, or can be practiced or performed in various ways. Furthermore, it should be understood that the wording and terminology used herein are for descriptive purposes and should not be considered limiting.

[0021] The following detailed description refers to the accompanying drawings. The same reference numerals in different drawings may identify the same or similar elements.

[0022] As used herein, the terms “comprising,” “including,” “containing,” “having,” “owning,” and any variations thereof are intended to cover non-exclusive inclusion. For example, unless otherwise stated, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherently present therein.

[0023] Furthermore, unless explicitly stated otherwise, "or" refers to an inclusive "or" rather than a unique "or". For example, condition A or B satisfies any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); and both A and B are true (or exist).

[0024] Furthermore, the terms "a" or "an" are used to describe elements and components of the embodiments herein. This is merely for convenience and to give a general meaning to the inventive concept. The description should be understood to include one or more, and the singular includes the plural unless explicitly stated otherwise. Additionally, unless explicitly stated otherwise, the use of the term "a plurality of" conveys "more than one".

[0025] As used herein, any reference to “an embodiment,” “an embodiment,” “some embodiments,” “an example,” or “for example” means that a particular element, feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. The appearance of the phrases “in some embodiments” or “in an example” throughout the specification does not necessarily refer to the same embodiment.

[0026] The currently disclosed inventive concept includes a combination of multilayer circuit board design and progressive reciprocating back drill process, which utilizes dynamic electrosensing through a conductive cutting device to generate a process for controlling the length of the residual section and / or eliminating potential edge strips.

[0027] Now refer to the attached diagram, especially Figures 1 to 6 These views show a back-drilling system 2, which has a drilling device 4 for cutting or deep-hole drilling on a plated multilayer circuit board 10 to form a multilayer circuit board 10a (see...). Figure 6 ).

[0028] The plated multilayer circuit board 10 is provided with signal layers 12a-12h, contact layers 13, dielectric layers 14a-14h, orifices 16, and a cylindrical portion 18 with an outer diameter 19 made of conductive plating or material.

[0029] The method described herein can be performed before the outer layer of the plated multilayer circuit board 10a is etched or removed. In other words, all circuits on the plated multilayer circuit board 10 are short-circuited. The aperture 16 can be open and lined with a cylindrical portion 18 (e.g., Figure 1 (As shown). In other embodiments, the aperture 16 may be filled with a conductive material, or the cylindrical portion 18 may be filled with a non-conductive material. Once one or more back-drilling processes described herein have been performed, excess copper on the surface of the plated multilayer circuit board 10 may be removed using techniques such as etching, laser ablation, milling, etc.

[0030] The method described herein can use one or more contact layers 13 positioned relative to a target signal layer 12f as a reference to determine the depth to drill into a plated multilayer circuit board 10 to remove multiple portions of a cylindrical portion 18. The contact layers 13 are positioned inside the plated multilayer circuit board 10 and spaced at a known distance from the signal layer of interest (with which there is interest, exemplified herein by signal layer 12f). The contact layers 13 and signal layer 12f are electrically isolated by one or more dielectric layers 14f positioned between the contact layers 13 and signal layer 12f. In some embodiments, the contact layers 13 and signal layer 12f are electrically connected to the cylindrical portion 18. In these embodiments, as discussed herein, the contact layers 13 and signal layer 12f are electrically isolated once the contact layers 13 are disconnected from the cylindrical portion 13. The depth or thickness of the dielectric layers 14f represents the known distance between the signal layer 12f and the contact layers 13 and undergoes variations referred to as dielectric layer tolerances. These dielectric layer tolerances must be taken into account during the back-drilling process, as will be further described herein.

[0031] In some embodiments, contact layer 13 may be an antipad on the power / ground plane, which is removed during the back-drilling process described herein. In some embodiments, contact layer 13 may be a signal layer; however, signal layers are expensive real estate in plated multilayer circuit boards 10 and typically have no space in dense areas where back-drilling as described herein would generally be performed. As will be described in detail herein, contact layer 13 disposed on the back-drilling side of signal layer 12f forms a reference for detection by drilling apparatus 4.

[0032] The drilling device 4 is equipped with a spindle unit 30 supporting the cutting device 32 and a measuring unit 34. For example, the drilling device 4 can be a drill, a CNC milling machine, or a router. The cutting device 32 can be a drill bit, end mill, etc., and is constructed of conductive material. The cutting device 32 is configured to have a diameter 33. The diameter 33 of the cutting device 32 is larger than the outer diameter 19 of the cylindrical portion 18. This allows all conductive material in the cylindrical portion 18 to be removed when drilling the plated multilayer circuit board 10.

[0033] The measuring unit 34 is electrically connected to the plated multilayer circuit board 10 via wires 36 and is also electrically connected to the spindle unit 30 and / or the cutting device 32 to sense the contact or proximity between the cutting device 32 and the plated multilayer circuit board 10. It should be noted that in some embodiments, the plated multilayer circuit board 10 is fully plated and can be contacted at any location by the wires 36. Once the cutting device 32 contacts the conductive material of the signal layer 12a, the plated multilayer circuit board 10 is detected by the drilling device 4, and a pre-programmed action can be performed. For example, the pre-programmed action could be setting a first zero-point stop position, stopping and retracting, continuing drilling to a set depth and then retracting, or a combination thereof.

[0034] exist Figure 2 In Figure 9, the drilling apparatus 4 is not fully shown. However, those skilled in the art will recognize that the illustrated cutting device 32 is part of the drilling apparatus 4 described above and is connected to the drilling apparatus 4 to perform the methods and steps described herein. Furthermore, the back-drilling process described below can be applied to each cylindrical section 18 within a plated multilayer circuit board 10 having a residual portion to be removed. In this case, when the residual portion of a particular cylindrical section 18 has been removed, the spindle unit 30 and the cutting device 32 can retract and move laterally relative to the plated multilayer circuit board 10 to align the longitudinal axis of the cutting device 32 with another cylindrical section 18. The spindle unit 30, the cutting device 32, and / or the plated multilayer circuit board 10 can be moved laterally to align the longitudinal axis of the cutting device 32 with a center point within the cylindrical section 18. Once the longitudinal axis of the cutting device 32 is aligned with the center point within the cylindrical section 18, the back-drilling process can be repeated.

[0035] like Figure 2As shown, a portion of the cylindrical portion 18 is electrically isolated from the signal layer 12a by removing a portion of the signal layer 12a. This can be achieved by forming a borehole 40 that extends partially through the signal layer 12a into the dielectric layer 14a. The borehole 40 removes the conductive material of the signal layer 12a and a portion of the cylindrical portion 18. The diameter 42 of the borehole 40 is larger than the diameter 33 of the cutting device 32. In some embodiments, the diameter 42 is 0.05 mm to 0.2 mm larger than the diameter 33 of the cutting device 32. However, it should be noted that these measurements are provided only as examples, and the borehole 40 can have any diameter 42 larger than the diameter 33 of the cutting device 32, so that the diameter of the conductive material of the signal layer 12a removed ensures that the cutting device 32 will not contact the conductive material of the signal layer 12a. A cutting device (not shown) similar to the cutting device 32 can be used to cut the borehole 40, for example, a cutting device that can remove the conductive material of the signal layer 12a and a portion of the underlying dielectric layer 14a. In some embodiments, the conductive material of the signal layer 12a can be removed using techniques such as etching, laser ablation, or milling.

[0036] The back-drilling depth of the plated multilayer circuit board 10 depends on the position of the contact layer 13 relative to the signal layer 12f on the cross-section of the plated multilayer circuit board 10. The goal is to ensure that any remaining fragments are as short as possible and as consistent as possible when manufacturing multiple plated multilayer circuit boards 10. In other words, the differences between plated multilayer circuit boards 10 produced in a batch and between plated multilayer circuit boards 10 produced in different batches will be minimized.

[0037] To determine the depth of the contact layer 13 in the plated multilayer circuit board 10, a progressive reciprocating drilling technique is used in conjunction with inductive sensing. The progressive reciprocating drilling technique is achieved by lowering or extending the cutting device 32 into the borehole 16 and sensing the potential on the cylindrical portion 18 and / or the contact layer 13 using the cutting device 32. Once the drilling system 4 senses contact between the cutting device 32 and the cylindrical portion 18, the drilling system 4 lowers or extends the cutting device 32 a predetermined distance. Once the cutting device 32 reaches this predetermined distance, it retracts a predetermined distance to break the contact between the cutting device 32 and the cylindrical portion 18 (e.g., ...). Figure 4 (As shown), this is sensed by the drilling device 4. This cycle, starting from the previous depth, is repeated, and another predetermined distance of the cylindrical portion 18 is removed. This process is repeated until the contact is not broken when the cutting device 32 retracts, indicating that the cutting device 32 is contacting the contact layer 13 (as shown). Figure 5 (As shown). Once contact layer 13 is detected, the predetermined back-off distance determines the depth accuracy.

[0038] With the cutting device 32 located at the contact layer 13, the drilling system 4 references the depth and determines the distance for the next cut. Taking into account dielectric layer tolerances, the drilling system 4 determines the distance for the next cut based on the known depth or thickness of the dielectric layer 14f. The next cut ensures electrical isolation between the contact layer 13 and the signal layer 12f. Any cylindrical portion 18 remaining above the signal layer 12f after the next cut is referred to as the remnant 50 (e.g., ...). Figure 6 As shown, it has a residual length of 52. As mentioned above, the larger the residual length 52, the greater the interference. Therefore, in order to improve the signal-to-noise ratio in electronic systems utilizing high-speed signals, it may be desirable to perform one or more other cuts to get closer to the signal layer 12f, which will reduce the residual length 52.

[0039] Using the method described herein, the residual length 52 can be reduced because the contact layer 13 serves as a reference or second zero point. Using this second zero point, when determining the final drilling depth, only the layer tolerance between the contact layer 13 and the signal layer 12f must be considered. For example, in Figures 1 to 6 In the example shown, there is only one dielectric layer 14f between the contact layer 13 and the signal layer 12f. Therefore, when determining the final drilling depth, only one set of dielectric layer tolerances must be considered, thus allowing for a small residual length 52.

[0040] In contrast, when using existing methods, the layer tolerances of the six signal layers (signal layers 12a-12e and contact layer 13, in this case contact layer 13 is a signal layer) and the dielectric layer tolerances of the six dielectric layers (dielectric layers 14a-14f) must be taken into account, which is more likely to result in 1) a longer residual depth; or 2) an increased chance that signal layer 12f will be damaged or cut off during drilling.

[0041] It should be noted that when designing multilayer circuit boards, designers can choose contact layers that are further away from the target signal layer, as long as a safe isolation can be formed. In this document, the term "safe isolation" refers to the minimum distance between the remnant and the contact layer that forms a sufficiently large barrier without causing CAF / EM failure. However, in the case of edge strips, the contact layer should not be too far from the target signal layer so that the edge strips can be detected using the methods described below.

[0042] Now for reference Figures 7 to 8 The diagram shows a multilayer circuit board 80 in which a drilled hole 82 is formed as described above to remove a portion of the cylindrical portion 84 to a minimum distance from the reference target signal layer 86. However, in this case, the axis 90 of the drilled hole 82 is not aligned or coaxial with the axis 94 of the cylindrical portion 84. This misalignment results in the formation of a strip 96 in the conductive material of the cylindrical portion 84. Since a portion of the strip 96 contacts the signal layer 86, the strip 96 causes signal dispersion, which must be eliminated.

[0043] The edge strip 96 may also be generated / formed, for example, by the oscillation of the cutting device 32, the deflection of the cutting device 32, or the oscillation of the spindle unit 30.

[0044] Using the inventive concept disclosed herein, there are three methods for detecting conductive strips 96. First, as... Figure 7 As shown, after the borehole 82 is drilled to a known or expected depth that has passed through the contact layer 88, the strip 96 will short-circuit the contact layer 88 with the signal layer 86.

[0045] Second, such as Figure 8 As shown, when the cutting device 32 retracts above the contact layer 88 and the circuit remains closed, this indicates the presence of the edge strip 96. The depth of the contact layer 88 can be stored in the drilling system 4 for statistical analysis to determine, for example, the depth that the contact layer 88 should reach or the retraction depth at which there should no longer be contact.

[0046] Figure 9A and Figure 9B A multilayer circuit board 100a is shown, which is constructed similarly to the multilayer circuit board 10a described above, except that the multilayer circuit board 100a does not have a contact layer. The drilling system 4 can be used as described above. Therefore, for the sake of brevity, reference will be made to... Figure 9A and Figure 9B The drilling system 4 is described below. As described above, the drilling system 4 performs reciprocating drilling on the plated multilayer circuit board 100. Each time the cutting device 32 retracts, as... Figure 9A As shown, an open circuit should be formed between the cylindrical portion 110 and the cutting device 32. If a strip 112 is formed in the cylindrical portion 110, continuity is measured during the retraction of the cutting device 32, indicating the presence of the strip 112. Measurements during retraction can be performed at multiple positions along the entire length of the back drill portion.

[0047] Now for reference Figure 10A and Figure 10B The diagram shows contact pads 120 and 130. For example, contact pads 120 and 130 can be formed in the contact layers 13 and 88 described above, aligned with orifices. When contact layers 13 and 88 are formed of a solid conductive material such as copper, the capacitance of signal layers 12f and 86 increases. Increasing the distance between contact layers 13 and 88 and signal layers 12f and 86 reduces capacitance, but also reduces the accuracy of determining the stub length as described above. To reduce capacitance, contact layers 13 and 88 can be formed with one or more conductive fingers 122 and 132 (in... Figure 10A and Figure 10B(Only one of each of the pads is marked) is contact pad 120 and 130. The reduced surface area of ​​contact pads 120 and / or 130 reduces the capacitance between contact layers 13 and 88 and signal layers 12f and 86, thereby allowing for a smaller spacing between signal layer 12f or 86 and contact layer 13 or 88.

[0048] The following is a list of numbered non-limiting illustrative embodiments of the inventive concept disclosed herein.

[0049] 1. A method for back-drilling a plated multilayer circuit board, comprising:

[0050] Electrically connect the drilling device to the plated multilayer circuit board;

[0051] The first cutting device of the drilling apparatus, having a first diameter, extends until the first layer of the plated multilayer circuit board is sensed;

[0052] The first cutting device is extended a predetermined distance through the first layer of the plated multilayer circuit board to form a first drill hole;

[0053] A second cutting device having a second diameter smaller than the first diameter is extended into the first drill hole until it senses contact with the cylindrical portion of the plated multilayer circuit board;

[0054] The second cutting device is repeatedly extended into the cylindrical portion by a first predetermined distance and retracted by a second predetermined distance less than the first predetermined distance to form a second borehole;

[0055] After each retraction, the electrical contact representing the closed circuit between the cutting device and the plated multilayer circuit board is sensed;

[0056] If a closed circuit is detected, it is determined whether the second borehole has reached the expected depth of the contact layer; and

[0057] If the expected depth of the contact layer is not reached, it is determined that an edge strip has been formed in the cylindrical portion.

[0058] 2. A method for back-drilling a plated multilayer circuit board according to illustrative embodiment 1, wherein the expected depth of the contact layer is equal to the number of signal layers preceding the contact layer plus the number of dielectric layers in the plated multilayer circuit board.

[0059] 3. A method for back-drilling a plated multilayer circuit board according to illustrative embodiment 1 or 2, wherein the contact layer further includes contact pads, the contact pads including one or more conductive fingers aligned with the second drill hole.

[0060] 4. A method for back-drilling a plated multilayer circuit board according to any one of illustrative embodiments 1 to 3, wherein the method further includes extending the second cutting device into the cylindrical portion a third predetermined distance in response to determining that the second drill hole has reached the expected depth of the contact layer.

[0061] 5. A method for manufacturing a circuit board, comprising:

[0062] Using a cutting device, a progressive reciprocating drill is used to back-drill the cylindrical portion of the plated circuit board from the first side to form a drill hole, and the cylindrical portion is removed in a direction toward the second side of the plated circuit board.

[0063] During the progressive reciprocating drilling, the contact layer within the plated circuit board is positioned by monitoring the conductivity between the cutting device and the contact layer. The contact layer is positioned at a predetermined distance from the signal layer, and is closer to the first side of the circuit board blank than the signal layer.

[0064] The cutting device extends beyond the contact layer by a predetermined distance.

[0065] 6. The method according to illustrative embodiment 5, wherein the method further includes retracting the cutting device from the borehole after extending the cutting device beyond the contact layer by a predetermined distance.

[0066] 7. The method according to illustrative embodiment 5 or 6, wherein the cutting device is a first cutting device, and the method further includes the step of extending a second cutting device from a first side of the circuit board into the cylindrical portion before back-drilling the cylindrical portion of the plated multilayer circuit board.

[0067] 8. The method according to any one of illustrative embodiments 5 to 7, wherein back drilling of the cylindrical portion of the plated multilayer circuit board includes forming a drill hole having a first portion and a second portion, the first portion having a first diameter and the second portion having a second diameter, the first diameter being larger than the second diameter.

[0068] 9. The method according to illustrative embodiment 8, wherein the first portion intersects with the first side of the plated multilayer circuit board.

[0069] 10. The method according to illustrative embodiment 8, wherein the cutting device is a first cutting device, and the method further includes forming the first portion of the drill hole using a second cutting device.

[0070] 11. The method according to any one of illustrative embodiments 5 to 10, wherein the step of extending the residual portion of the cylindrical section from the signal layer toward the contact layer and extending the cutting device beyond the contact layer by the predetermined distance reduces the length of the residual portion.

[0071] 12. The method according to illustrative embodiment 11, wherein the cutting device is extended beyond the predetermined distance of the contact layer to remove the residual portion.

[0072] 13. The method according to any one of illustrative embodiments 5 to 12, wherein the predetermined distance is a first predetermined distance, and the progressive reciprocating drilling includes reciprocatingly extending the cutting device into the cylindrical portion a second predetermined distance and retracting the cutting device a third predetermined distance less than the second predetermined distance.

[0073] 14. The method according to any one of illustrative embodiments 5 to 13, wherein positioning the contact layer by monitoring the conductivity between the cutting device and the contact layer is further defined as positioning the contact layer by detecting a closed circuit when the cutting device retracts.

[0074] 15. The method according to any one of illustrative embodiments 5 to 14, wherein positioning the contact layer by monitoring the conductivity between the cutting device and the contact layer is further defined as positioning the contact layer by detecting a closed circuit while extending the cutting device.

[0075] 16. A method for manufacturing a multilayer circuit board, comprising:

[0076] Electrically connect the drilling device to the plated multilayer circuit board;

[0077] For each of the one or more cylindrical portions within the plated multilayer circuit board to be back-drilled, back-drilling is performed in the following manner:

[0078] Remove a first portion of the conductive layer on the outer surface of the plated multilayer circuit board in order to isolate the cylindrical portion of the plated multilayer circuit board to be back-drilled from the conductive layer.

[0079] The cutting device is repeatedly extended into the cylindrical portion by a first predetermined distance and then retracted by a second predetermined distance less than the first predetermined distance to form a hole;

[0080] After each retraction, the electrical contact representing the closed circuit between the cutting device and the plated multilayer circuit board is sensed; and

[0081] In response to sensing the closed circuit after the second cutting device retracts, the cutting device extends a second predetermined distance into the cylindrical portion, the second predetermined distance being equal to the thickness of at least one dielectric layer located between the contact layer and the target signal layer minus the dielectric layer tolerance.

[0082] 17. A method of manufacturing a multilayer circuit board according to illustrative embodiment 16, wherein the expected depth of the contact layer is equal to the number of signal layers preceding the contact layer plus the number of dielectric layers in the plated multilayer circuit board.

[0083] 18. A method of manufacturing a multilayer circuit board according to illustrative embodiment 16 or 17, wherein the contact layer further includes contact pads, the contact pads including one or more conductive fingers aligned with the second drill hole.

[0084] 19. A method of manufacturing a multilayer circuit board according to any one of illustrative embodiments 16 to 18, wherein the method further comprises removing a second portion of the conductive layer of the plated multilayer circuit board after back-drilling the one or more cylindrical portions within the plated multilayer circuit board.

[0085] 20. A plated multilayer circuit board, comprising:

[0086] A multilayer circuit board has a first side and a second side, and a cylindrical portion extending from the first side toward the second side, the cylindrical portion being constructed of a conductive material. The multilayer circuit board further includes a contact layer between the first side and the second side, a signal layer between the first side and the second side, and a dielectric layer located between the signal layer and the contact layer. The contact layer and the signal layer are constructed of at least one conductive material and are spaced apart by a known distance.

[0087] It is electrically connected to the cylindrical portion.

[0088] It is clear from the above description that the inventive concepts(one or more) disclosed herein are well adapted to achieve the purposes mentioned herein and to obtain the advantages inherent in the inventive concepts(one or more) mentioned herein and disclosed herein. Although exemplary embodiments of the inventive concepts(one or more) disclosed herein have been described for the purposes of this disclosure, it should be understood that many modifications can be made within the spirit of the inventive concepts(one or more) disclosed herein that are readily apparent to those skilled in the art.

Claims

1. A method for back-drilling a plated multilayer circuit board, comprising: Electrically connect the drilling device to the plated multilayer circuit board; The first cutting device of the drilling apparatus, having a first diameter, extends until the first layer of the plated multilayer circuit board is sensed; The first cutting device is extended a predetermined distance through the first layer of the plated multilayer circuit board to form a first drill hole; A second cutting device having a second diameter smaller than the first diameter is extended into the first drill hole until it senses contact with the cylindrical portion of the plated multilayer circuit board; The second cutting device is repeatedly extended into the cylindrical portion by a first predetermined distance and retracted by a second predetermined distance less than the first predetermined distance to form a second borehole; After each retraction, the electrical contact representing the closed circuit between the cutting device and the plated multilayer circuit board is sensed; If a closed circuit is detected, it is determined whether the second drill hole has reached the expected depth of the contact layer of the plated multilayer circuit board. as well as If the expected depth of the contact layer is not reached, it is determined that an edge strip has been formed in the cylindrical portion.

2. The method for back drilling of plated multilayer circuit boards according to claim 1, characterized in that, The expected depth of the contact layer is equal to the number of signal layers preceding the contact layer plus the number of dielectric layers in the plated multilayer circuit board.

3. The method for back drilling of plated multilayer circuit boards according to claim 1, characterized in that, The contact layer further includes contact pads, which include one or more conductive fingers aligned with the second drill hole.

4. The method for back drilling of a plated multilayer circuit board according to any one of claims 1 to 3, characterized in that, The method further includes, in response to determining that the second borehole has reached the expected depth of the contact layer, extending the second cutting device a third predetermined distance into the cylindrical portion.

5. A method for manufacturing a circuit board, comprising: Using a cutting device, a progressive reciprocating drill is used to back-drill the cylindrical portion of the plated circuit board from the first side to form a drill hole, and the cylindrical portion is removed in a direction toward the second side of the plated circuit board. During the progressive reciprocating drilling, the contact layer is positioned by monitoring the conductivity between the cutting device and the contact layer located within the plated circuit board. The contact layer is positioned at a predetermined distance from the signal layer and is closer to the first side of the circuit board blank than the signal layer. as well as The cutting device extends beyond the contact layer by a predetermined distance; Wherein, the predetermined distance is a first predetermined distance, and the progressive reciprocating drilling includes reciprocatingly extending the cutting device into the cylindrical portion a second predetermined distance and retracting the cutting device a third predetermined distance less than the second predetermined distance; and During the progressive reciprocating drilling, after each retraction, the electrical contact representing the closed circuit between the cutting device and the plated circuit board is sensed. If a closed circuit is sensed, it is determined whether the drilling has reached the expected depth of the contact layer. If the expected depth of the contact layer has not been reached, it is determined that an edge strip has been formed in the cylindrical portion.

6. The method according to claim 5, characterized in that, The method further includes retracting the cutting device from the borehole after extending the cutting device beyond a predetermined distance from the contact layer.

7. The method according to claim 5, characterized in that, The cutting device is a first cutting device, and the method further includes the step of extending a second cutting device from the first side of the circuit board into the cylindrical portion before back-drilling the cylindrical portion of the plated circuit board.

8. The method according to any one of claims 5 to 7, characterized in that, Back-drilling the cylindrical portion of the plated circuit board includes forming a drill hole having a first portion and a second portion, the first portion having a first diameter and the second portion having a second diameter, the first diameter being larger than the second diameter.

9. The method according to claim 8, characterized in that, The first portion intersects with the first side of the plated circuit board.

10. The method according to claim 8, characterized in that, The cutting device is a first cutting device, and the method further includes forming the first portion of the drill hole using a second cutting device.

11. The method according to any one of claims 5 to 7, characterized in that, The step of extending the residual portion of the cylindrical section from the signal layer toward the contact layer and extending the cutting device beyond the predetermined distance of the contact layer reduces the length of the residual portion.

12. The method according to claim 11, characterized in that, The cutting device extends beyond the predetermined distance of the contact layer to remove the remaining portion.

13. The method according to any one of claims 5 to 7, characterized in that, Positioning the contact layer by monitoring the conductivity between the cutting device and the contact layer is further defined as positioning the contact layer by detecting a closed circuit when the cutting device retracts.

14. The method according to any one of claims 5 to 7, characterized in that, Positioning the contact layer by monitoring the conductivity between the cutting device and the contact layer is further defined as positioning the contact layer by detecting a closed circuit while extending the cutting device.

15. A method for manufacturing a multilayer circuit board, comprising: Electrically connect the drilling device to the plated multilayer circuit board; For each of one or more cylindrical portions within the plated multilayer circuit board to be back-drilled, back-drilling is performed in the following manner: Remove a first portion of the conductive layer on the outer surface of the plated multilayer circuit board in order to isolate the cylindrical portion of the plated multilayer circuit board to be back-drilled from the conductive layer. The cutting device is repeatedly extended into the cylindrical portion by a first predetermined distance and then retracted by a second predetermined distance less than the first predetermined distance to form a hole; After each retraction, the electrical contact representing the closed circuit between the cutting device and the plated multilayer circuit board is sensed; If a closed circuit is detected, it is determined whether the drill hole has reached the expected depth of the contact layer of the plated multilayer circuit board. as well as If the expected depth of the contact layer is not reached, it is determined that a strip has been formed in the cylindrical portion. If the expected depth of the contact layer is reached, the cutting device is extended into the cylindrical portion by a third predetermined distance, the third predetermined distance being equal to the thickness of at least one dielectric layer located between the contact layer and the target signal layer minus the dielectric layer tolerance.

16. The method for manufacturing a multilayer circuit board according to claim 15, characterized in that, The expected depth of the contact layer is equal to the number of signal layers preceding the contact layer plus the number of dielectric layers in the plated multilayer circuit board.

17. The method for manufacturing a multilayer circuit board according to claim 15, characterized in that, The contact layer further includes contact pads, which include one or more conductive fingers aligned with the drill hole.

18. The method of manufacturing a multilayer circuit board according to any one of claims 15 to 17, characterized in that, The method further includes removing a second portion of the conductive layer of the plated multilayer circuit board after back drilling has been performed on the one or more cylindrical portions within the plated multilayer circuit board.

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