Circuit board and back drilling method thereof

Abstract

The application discloses a circuit board and a back drilling method thereof. The back drilling method comprises the following steps: placing a to-be-drilled circuit board on a drilling machine platform, with a back drilling surface located on the side away from the drilling machine platform and a conductive plate placed between a first metal layer and an inductive mushroom head; the to-be-drilled circuit board comprises a first through hole located between a second metal layer and an un-drillable layer; a drill bit is controlled to move towards the conductive plate, and when the drill bit contacts the conductive plate, the distance between the origin of the Z-axis of the main shaft of the drilling machine and the first metal layer is obtained as a first height; an insulating layer is placed between the conductive plate and the inductive mushroom head, and the inductive mushroom head is electrically connected with the second metal layer; the distance between the origin of the Z-axis of the main shaft of the drilling machine and the un-drillable layer is obtained as a second height; and the to-be-drilled circuit board is drilled, electroplated and back drilled according to the first height and the second height, so as to form the circuit board. The technical scheme can improve the back drilling precision and quality.

Description

Technical Field

[0001] This invention relates to the field of back drilling technology, and more particularly to a circuit board and a back drilling method thereof. Background Technology

[0002] Circuit boards are mainly used in communication equipment, large servers, medical electronics, military, aerospace and other fields. Because circuit boards have many layers and are quite thick, they typically use through-hole drilling followed by electroplating to achieve signal conduction between layers. However, this design can lead to significant signal loss in high-frequency, high-speed signal transmission. For example, in a 20-layer backplane, if a signal line only needs to connect from layer 1 to layer 5, then the copper in the holes from layer 6 to layer 20 is redundant. The presence of this section of copper in the hole walls can easily cause signal reflection, scattering, and delay. Therefore, back-drilling essentially removes the through-hole sections that do not serve any connection or transmission function, avoiding signal reflection, scattering, and delay, and preventing signal distortion.

[0003] Circuit boards consist of multiple metal layers and dielectric layers between them. In existing technologies, test holes are typically drilled at the edges of the circuit board to obtain the depth between the back-drilling surface and the non-drillable layer, which is then used as the depth for subsequent back-drilling. However, during circuit board manufacturing, the dielectric layer thickness varies between the edge and center areas due to factors such as lamination and adhesive flow. To ensure the non-drillable layer is not drilled through, a large safety distance must be reserved. This safety distance typically needs to cover the thickness fluctuation range, resulting in excessively long residual spikes after back-drilling, affecting signal transmission, or even breaking through the non-drillable layer, leading to an open circuit risk. Alternatively, the back-drilling depth can be determined during through-hole drilling, but this solution requires a large copper layer on the non-drillable layer, limiting its application scenarios. Furthermore, this solution exposes the inner copper ring of the non-drillable layer after back-drilling, leading to reliability risks. Summary of the Invention

[0004] This invention provides a circuit board and a back-drilling method thereof, which can improve the back-drilling accuracy.

[0005] In a first aspect, the present invention provides a back-drilling method for a circuit board, wherein the circuit board to be drilled includes a back-drilling surface and a non-back-drilling surface, the circuit board to be drilled includes multiple metal layers and a dielectric layer located between two adjacent metal layers; the metal layer located on the back-drilling surface is a first metal layer, the metal layer located on the non-back-drilling surface is a second metal layer; the metal layer located between the first metal layer and the second metal layer includes a non-drillable layer.

[0006] The back drilling method for the circuit board includes:

[0007] The circuit board to be drilled is placed on the drilling platform, with the back-drilling surface located on the side of the non-back-drilling surface away from the drilling platform, and a conductive plate is placed between the first metal layer and the induction mushroom head; the circuit board to be drilled includes a first through hole, which is located between the second metal layer and the non-drillable layer.

[0008] The drill bit is controlled to move towards the conductive plate side, and when the drill bit contacts the conductive plate, the distance between the origin of the Z-axis direction of the drill spindle and the first metal layer is obtained as the first height.

[0009] An insulating layer is placed between the conductive plate and the sensing mushroom head, and the sensing mushroom head is electrically connected to the second metal layer.

[0010] Control the drill bit to move toward the impenetrable layer, and when the drill bit contacts the impenetrable layer, obtain the distance between the origin of the Z-axis of the drill spindle and the impenetrable layer as the second height;

[0011] Based on the first height and the second height, the circuit board to be drilled is drilled, electroplated, and back-drilled to form a circuit board.

[0012] Optionally, electrically connecting the sensing mushroom head to the second metal layer includes:

[0013] A first conductive metal foil is placed between the insulating layer and the sensing mushroom head so that the first conductive metal foil makes contact and electrical connection with the sensing mushroom head;

[0014] A second conductive metal foil is placed between the drilling platform and the second metal layer, and the second conductive metal foil is electrically connected to the second metal layer.

[0015] One end of the third conductive metal foil is electrically connected to the first conductive metal foil, and the other end of the third conductive metal foil is electrically connected to the second conductive metal foil, so that the sensing mushroom head is electrically connected to the second metal layer through the first conductive metal foil, the third conductive metal foil, and the second conductive metal foil.

[0016] Optionally, before placing the circuit board to be drilled on the drilling platform, the method further includes:

[0017] Provide the original circuit board to be drilled;

[0018] Drill a hole to the non-drillable layer on the non-back-drillable surface of the original circuit board to be drilled to form the first hole;

[0019] The first hole is filled with conductive paste to form the circuit board to be drilled, which includes the first through hole.

[0020] Optionally, drilling a hole to the non-drillable layer on the non-back-drillable surface of the original circuit board to form a first hole includes:

[0021] A hole is drilled on the non-back-drilling surface; the depth of the hole is less than the theoretical thickness between the second metal layer and the impenetrable layer.

[0022] The first laser is used to drill through the impenetrable layer at the borehole location to form the first hole.

[0023] Optionally, after drilling to the impenetrable layer at a borehole using a first laser, the method further includes:

[0024] A second laser is used to remove part of the impenetrable layer located within the first borehole to form the first hole.

[0025] Optionally, the depth of the impenetrable layer removed by the second laser is d1;

[0026] 0μm<d1≤10μm.

[0027] Optionally, the depth of the borehole is S1, and the theoretical thickness between the second metal layer and the impenetrable layer is H1;

[0028] Where 0mm

[0029] Optionally, after filling the first hole with conductive paste, the method further includes:

[0030] The surface of the conductive paste facing away from the first metal layer is polished so that the surface of the conductive paste facing away from the first metal layer is on the same horizontal plane as the second metal layer.

[0031] Optionally, based on the first height and the second height, the circuit board to be drilled is subjected to drilling, electroplating, and back drilling to form a circuit board, including:

[0032] Determine the back drilling depth based on the first height and the second height;

[0033] Drill a hole on the non-back-drilling surface to remove the first through hole, thereby forming a through hole through the circuit board to be drilled;

[0034] The through hole is electroplated to form a through-hole;

[0035] The through-hole is back-drilled according to the back-drilling depth to form a circuit board;

[0036] Wherein, the diameter of the through hole is r1, the diameter of the first through hole is r2, and r2 < r1.​

[0037] Optionally, determining the back-drilling depth based on the first height and the second height includes:

[0038] Obtain the actual drilling depth compensation value;

[0039] Calculate the height difference between the second height and the first height, and determine the back-drilling depth based on the height difference and the actual drilling depth compensation value.

[0040] Secondly, the present invention provides a circuit board manufactured using the back-drilling method described in the first aspect.

[0041] The technical solution provided by this invention involves placing the circuit board to be drilled on a drilling platform, with the back-drilling surface located on the side of the non-back-drilling surface away from the drilling platform. A conductive plate is placed between the first metal layer and the induction mushroom head. During the process of controlling the drill bit to move from the origin of the drilling machine's spindle Z-axis towards the conductive plate, a first height between the origin of the drilling machine's spindle Z-axis and the first metal layer is obtained. An insulating layer is placed between the conductive plate and the induction mushroom head, and the induction mushroom head is electrically connected to the second metal layer. During the process of controlling the drill bit to move towards the non-drillable layer, a second height between the origin of the drilling machine's spindle Z-axis and the non-drillable layer is obtained. Based on the first and second heights, the distance between the first metal layer and the non-drillable layer can be determined, and the actual depth between the back-drilling surface and the non-drillable layer can be obtained. Drilling, electroplating, and back-drilling of the circuit board to be drilled can then be performed, improving the accuracy and reliability of back-drilling. The technical solution of the present invention can perform controlled-depth back-drilling operation by measuring the actual thickness between the back-drilling surface and the undrillable layer based on the first height and the second height. This reduces drilling deviation caused by uneven plate thickness or medium layer thickness, thereby improving back-drilling accuracy, reducing back-drilling residue, and improving back-drilling quality. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of a circuit board to be drilled, provided in an embodiment of the present invention;

[0043] Figure 2 A flowchart illustrating a back-drilling method for a circuit board provided in an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of a process structure for manufacturing a circuit board according to an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of a partial process structure for manufacturing a circuit board according to an embodiment of the present invention;

[0046] Figure 5 This is a schematic diagram of a process structure for preparing a circuit board to be drilled, provided in an embodiment of the present invention. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0048] Figure 1 This is a schematic diagram of the structure of a circuit board to be drilled according to an embodiment of the present invention, as shown below. Figure 1 As shown, the circuit board to be drilled includes a back-drilling surface A1 and a non-back-drilling surface A2. The circuit board to be drilled includes multiple metal layers 10 and a dielectric layer 20 located between two adjacent metal layers 10. The metal layer 10 located on the back-drilling surface A1 is a first metal layer 101, and the metal layer 10 located on the non-back-drilling surface A2 is a second metal layer 102. The metal layer 10 located between the first metal layer 101 and the second metal layer 102 includes a non-drillable layer 103. The circuit board to be drilled includes a first via 31, which is located between the second metal layer 102 and the non-drillable layer 103.

[0049] During back drilling, the drill bit needs to enter the circuit board to be drilled from the back drilling surface A1 side to drill away the conductive sections of the through holes that do not serve a connection or transmission function. The non-back drilling surface A2 refers to the surface of the circuit board to be drilled that is opposite to the back drilling surface A1. The dielectric layer 20 can provide insulation protection between different metal layers 10, isolate different metal layers 10, and prevent short circuits and signal interference.

[0050] Specifically, the non-drillable layer 103 is located between the first metal layer 101 and the second metal layer 102. The non-drillable layer 103 needs to be electrically connected to the second metal layer 102. Typically, the circuit board to be drilled is drilled to form through-holes penetrating each metal layer 10 and each dielectric layer 20. Then, conductive material is electroplated onto the surface of the through-holes. Finally, a back-drilling tool is used to enter the through-hole from the back-drilling surface A1 to remove the conductive material on the surface of the through-hole located between the non-drillable layer 103 and the first metal layer 101. This removes the through-hole segment that does not serve any connection or transmission function, avoiding problems such as reflection, scattering, or delay in high-speed signal transmission. After back-drilling, the non-drillable layer 103 is not removed, ensuring that it can be electrically connected to the second metal layer 102 through the conductive material, thus enabling signal transmission.

[0051] Figure 2 This is a flowchart of a back-drilling method for a circuit board provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of a process structure for fabricating a circuit board according to an embodiment of the present invention, with reference to... Figure 2 and Figure 3 The back-drilling methods for circuit boards include:

[0052] S101. Place the circuit board to be drilled on the drilling platform, with the back-drilling surface located on the side of the non-back-drilling surface away from the drilling platform, and place a conductive plate between the first metal layer and the induction mushroom head.

[0053] The circuit board to be drilled includes a first through-hole 31, which is located between the second metal layer 102 and the non-drillable layer 103. The drilling platform 40 is used to place the circuit board to be drilled. The conductive plate 41 includes metal plates such as composite aluminum plates, which can be set according to actual needs and are not specifically limited here.

[0054] Specifically, by placing a conductive plate 41 on the side of the first metal layer 101 away from the second metal layer 102, in addition to its conductive connection function, it can also play a role in positioning support, heat dissipation and protection during drilling, thereby improving drilling quality and avoiding problems such as hole deviation or burrs at the hole opening.

[0055] S102. Control the drill bit to move towards the conductive plate, and when the drill bit contacts the conductive plate, obtain the distance between the origin of the drill spindle Z-axis and the first metal layer as the first height.

[0056] The origin L0 of the drilling rig's spindle Z-axis direction represents the position of the drilling rig spindle when it rises to its highest point. Of course, it can also be defined as other positions, and there are no restrictions on the specifics, as long as it can ensure that the drilling rig spindle rises to the same height as the Z-axis origin when it is probing the depth.

[0057] Specifically, when the drill bit 43 contacts the conductive plate 41, the drill bit 43, the conductive plate 41, and the induction mushroom head 42 form a conductive circuit, generating a weak current signal. During the movement of the drill bit 43 towards the conductive plate 41, when the current signal is detected, the distance the drill bit 43 has moved is taken as the first moving distance, and the sum of the first moving distance and the thickness of the conductive plate 41 is taken as the first height h1. The thickness of the conductive plate 41 is pre-stored in the drilling rig, and the first height h1 can be calculated in the drilling rig after the first moving distance is obtained.

[0058] S103. Place an insulating layer between the conductive plate and the sensing mushroom head, and make the sensing mushroom head electrically connected to the second metal layer.

[0059] The insulating layer 44 includes insulating materials such as insulating kraft paper, which can be set according to actual needs, and no specific limitation is made here.

[0060] Specifically, by setting an insulating layer 44, the induction mushroom head 42 is prevented from being electrically connected to the conductive plate 41, so that no current signal is generated when the drill bit 43 contacts the conductive plate 41. By setting the induction mushroom head 42 to be electrically connected to the second metal layer 102, since the second metal layer 102 is electrically connected to the non-drillable layer 103 through the first through hole 31, when the drill bit 43 contacts the non-drillable layer 103, the drill bit 43, the non-drillable layer 103, the first through hole 31, the second metal layer 102 and the induction mushroom head 42 can form an electrical connection circuit and generate a current signal.

[0061] It should be noted that the method of electrically connecting the sensing mushroom head 42 to the second metal layer 102 can be set according to actual needs. In an optional embodiment, refer to... Figure 3 The method for electrically connecting the sensing mushroom head 42 to the second metal layer 102 includes: placing a first conductive metal foil 451 between the insulating layer 44 and the sensing mushroom head 42, so that the first conductive metal foil 451 and the sensing mushroom head 42 are in contact and electrically connected; placing a second conductive metal foil 452 between the drilling platform 40 and the second metal layer 102, so that the second conductive metal foil 452 and the second metal layer 102 are in contact and electrically connected; and setting one end of a third conductive metal foil 453 to be electrically connected to the first conductive metal foil 451, and the other end of the third conductive metal foil 453 to be electrically connected to the second conductive metal foil 452, so that the sensing mushroom head 42 is electrically connected to the second metal layer 102 through the first conductive metal foil 451, the third conductive metal foil 453 and the second conductive metal foil 452.

[0062] The first conductive metal foil 451, the second conductive metal foil 452, and the third conductive metal foil 453 may include conductive materials such as copper, and can be configured according to actual needs.

[0063] Specifically, the second conductive metal foil 452 contacts the surface of the second metal layer 102 opposite to the first metal layer 101. Since both the second conductive metal foil 452 and the second metal layer 102 can transmit electrical signals, they can transmit electrical signals to each other after contact. Correspondingly, the first conductive metal foil 451 and the sensing mushroom head 42 are electrically connected. The extension direction of the third conductive metal foil 453 is parallel to the thickness direction of the circuit board to be drilled, so as to electrically connect the first conductive metal foil 451 and the second conductive metal foil 452 through the third conductive metal foil 453, so that the sensing mushroom head 42 can be electrically connected to the non-drillable layer 103 through the first conductive metal foil 451, the third conductive metal foil 453, the second conductive metal foil 452, the second metal layer 102, and the first through hole 31.

[0064] It is understood that the first conductive metal foil 451, the second conductive metal foil 452 and the third conductive metal foil 453 can be integrally set or electrically connected by welding or other means. They can be set according to actual needs, and no specific limitation is made here.

[0065] S104. Control the drill bit to move towards the unpenetrable layer, and when the drill bit contacts the unpenetrable layer, obtain the distance between the origin of the drill spindle Z-axis and the unpenetrable layer as the second height.

[0066] Specifically, the drill bit 43 is controlled to start drilling downwards from the origin L0 of the drill spindle along the Z-axis. When the drill bit 43 contacts the non-drillable layer 103, the drill bit 43, the non-drillable layer 103, the first through hole 31, the second metal layer 102, and the induction mushroom head 42 form an electrical connection path, generating a current signal. The distance the drill bit 43 moves when the current signal is obtained is taken as the second moving distance, and the sum of the second moving distance and the thickness of the second conductive metal foil 452 is taken as the second height h2. Preferably, the cutting diameter of the drill bit 43 is the same as the diameter of the through hole 32.

[0067] S105. Based on the first height and the second height, drill holes, electroplate, and back-drill the circuit board to be drilled to form a circuit board.

[0068] Specifically, the first through hole 31 can be entered from the non-back-drilling surface A2 side to remove the first through hole 31, as well as at least the second metal layer 102 and the non-drillable layer 103 overlapping with the first through hole 31, to form a through hole 32. Then, the surface of the through hole 32 is electroplated to form an electroplated layer. Then, a drill bit 43 is set to enter the through hole 32 from the back-drilling surface A1 side. The back-drilling depth is the difference between the second height h2 and the first height h1, plus the sum of the actual drilling depth compensation value, to remove the electroplated layer located on the side of the non-drillable layer 103 away from the second metal layer 102, to form a circuit board.

[0069] The technical solution provided by this invention involves placing the circuit board to be drilled on a drilling platform, with the back-drilling surface located on the side of the non-back-drilling surface away from the drilling platform. A conductive plate is placed between the first metal layer and the induction mushroom head. During the process of controlling the drill bit to move from the origin of the drilling machine's spindle Z-axis towards the conductive plate, a first height between the origin of the drilling machine's spindle Z-axis and the first metal layer is obtained. An insulating layer is placed between the conductive plate and the induction mushroom head, and the induction mushroom head is electrically connected to the second metal layer. During the process of controlling the drill bit to move towards the non-drillable layer, a second height between the origin of the drilling machine's spindle Z-axis and the non-drillable layer is obtained. Based on the first and second heights, the distance between the first metal layer and the non-drillable layer can be determined, i.e., the actual depth between the back-drilling surface and the non-drillable layer is obtained. Drilling, electroplating, and back-drilling of the circuit board to be drilled can then be performed, improving the depth control accuracy and reliability of back-drilling.

[0070] Optionally, during the process of controlling the drill bit to move towards the conductive plate, the distance the drill bit moves, and the corresponding electrical signal, can be acquired. The drill bit's movement speed can be a constant value, and the drilling rig system can determine the distance the drill bit moves based on the duration of its movement. Other methods can also be used to acquire the drill bit's movement distance; these are not specifically limited here. (Reference) Figure 3 A small voltage signal can be applied to the drill bit so that when the drill bit 43 is not in contact with the conductive plate 41, the sensing mushroom head 42 does not form an electrical connection circuit with the drill bit 43, so no electrical signal can be detected; when the drill bit 43 is in contact with the conductive plate 41, the drill bit 43 can form an electrical connection circuit with the sensing mushroom head 42 through the conductive plate 41, thereby generating a small current signal, and the corresponding moving distance at this time is taken as the first height h1.

[0071] Optionally, during the movement of the drill bit towards the impenetrable layer, the distance the drill bit travels and the corresponding electrical signal can be acquired. The drill bit's speed can be a constant value, and the drilling rig system can determine the distance traveled by the drill bit based on the duration of its movement. Other methods can also be used to acquire the drill bit's distance; these are not specifically limited here. (Reference) Figure 3 A small voltage signal can be applied to the drill bit so that when the drill bit 43 is not in contact with the non-drillable layer 103, the sensing mushroom head 42 does not form an electrical connection circuit with the non-drillable layer 103, so no electrical signal can be detected; when the drill bit 43 is in contact with the non-drillable layer 103, the drill bit 43 can form an electrical connection circuit with the sensing mushroom head 42 through the non-drillable layer 103, thereby generating a small current signal, and the corresponding movement distance at this time is taken as the second height h2.

[0072] In an alternative embodiment, Figure 4 This is a schematic diagram of a partial process structure for manufacturing a circuit board according to an embodiment of the present invention, as shown below. Figure 4 As shown, based on a first height and a second height, drilling, electroplating, and back drilling are performed on the circuit board to be drilled to form a circuit board, including: determining the back drilling depth based on the first height and the second height; drilling on the non-back drilling surface to remove the first through hole to form a through hole penetrating the circuit board to be drilled; electroplating the through hole to form a through through hole; and back drilling the through through hole according to the back drilling depth to form a circuit board.

[0073] The process of determining the back drilling depth based on the first and second heights includes obtaining the actual drilling depth compensation value, calculating the height difference between the second and first heights, and determining the back drilling depth based on the height difference and the actual drilling depth compensation value. The actual drilling depth compensation value can be determined based on the actual back drilling process. Specifically, after electroplating conductive material on the through hole 32, conductive material will also be electroplated on the surface of the first metal layer 101. The thickness k1 of this conductive material needs to be added to the calculation of the actual drilling depth compensation value. In addition, the drill bit tip angle compensation k2 will be generated during the drilling process. During drilling, a conductive plate is usually placed on the side of the circuit board to be drilled away from the drilling platform to protect the circuit board to be drilled and to provide conductive connection. The thickness k3 of the conductive plate is also added to the calculation of the actual back drilling depth. In addition, the required length k4 of the residual pile is also added to the calculation of the actual drilling depth compensation value. The actual drilling depth compensation value is k1+k2+k3-k4. The height difference h3 between the second height h2 and the first height h1 is calculated. The sum of the height difference h3 and the actual drilling depth compensation value, i.e., h3+(k1+k2+k3-k4), is used as the back drilling depth to further improve the accuracy of back drilling.

[0074] The first height h1 represents the distance between the origin L0 of the drilling rig spindle Z-axis and the surface of the first metal layer 101 facing away from the second metal layer 102. The second height h2 represents the distance between the origin L0 of the drilling rig spindle Z-axis and the surface of the non-drillable layer 103 facing away from the second metal layer 102. The height difference between the second height h2 and the first height h1 represents the distance between the surface of the first metal layer 101 facing away from the second metal layer 102 and the surface of the non-drillable layer 103 facing away from the second metal layer 102. This distance is the actual thickness h3 from the back-drilling surface to the non-drillable layer, so as to improve the depth control accuracy of subsequent back-drilling.

[0075] Specifically, after determining the actual thickness h3 from the back-drilling surface to the non-drillable layer, the first through-hole 31 can be drilled from the non-back-drilling surface A2 to form a through-hole 32 penetrating the circuit board to be drilled. After plasma descaling of the through-hole 32, conductive material is electroplated on the inner surface of the through-hole 32 to form a through-hole. Since only the non-drillable layer 103 needs to be electrically connected to each metal layer 10 on the side of the non-drillable layer 103 away from the first metal layer 101, back-drilling can be performed on the through-hole on the back-drilling surface A1. The height difference between the second height h2 and the first height h1 is calculated, and the sum of this height difference and the actual drilling depth compensation value is used as the back-drilling depth, thereby improving the back-drilling accuracy.

[0076] refer to Figure 4 and Figure 5The diameter of the through hole 32 is r1, and the diameter of the first through hole 31 is r2. The through hole 32 serves as an electroplated through hole before back drilling, and its diameter must meet the diameter requirements of the metallized portion of the back drilling. The first through hole 31, before the formation of the through hole 32, serves as an auxiliary hole for electrically connecting the non-drillable layer 103 and the second metal layer 102 in the through hole 32. After the actual depth detection from the back drilling surface A1 to the non-drillable layer 103 is completed, it needs to be drilled away to form the through hole 32. By setting the diameter r2 of the first through hole 31 to be smaller than the diameter r1 of the through hole 32, when detecting the actual depth from the back drilling surface A1 to the non-drillable layer 103 at the back drilling position, it is possible to avoid the diameter of the first through hole 31 being larger than the diameter of the through hole 32, which would cause the actual diameter of the through hole 32 to exceed the theoretical design diameter when drilling the through hole 32 subsequently, thus meeting the diameter requirements of the through hole 32.

[0077] Based on the above embodiments, this embodiment of the invention describes the situation before the circuit board to be drilled is placed on the drilling platform, such as... Figure 5 As shown, the method of forming the circuit board to be drilled includes: providing a circuit board to be drilled; drilling a hole to an un-drillable layer on the non-back-drilling surface of the circuit board to be drilled to form a first hole 310; filling the first hole 310 with conductive paste to form a circuit board to be drilled including a first through hole 31.

[0078] The conductive paste can be made of copper, gold, silver or aluminum, etc., and can be set according to actual needs. No specific limit is made here.

[0079] Specifically, the original circuit board to be drilled includes multiple metal layers 10 and a dielectric layer 20 located between two adjacent metal layers 10. A drill bit is used to drill from the non-back-drilling side A2 to remove the dielectric layer 20 and the metal layer 10 located between the second metal layer 102 and the non-drillable layer 103, forming a first hole 310. Then, conductive copper paste is filled into the first hole 310 to form a first through hole 31, so that the non-drillable layer 103 can be electrically connected to the second metal layer 102 through the first through hole 31.

[0080] Optionally, a hole is drilled to a non-drillable layer on the non-back-drillable side of the original circuit board to form a first hole, including drilling a hole on the non-back-drillable side; the depth of the hole is less than the theoretical thickness between the second metal layer and the non-drillable layer; a first laser drilling method is used to drill to the non-drillable layer at the hole to form the first hole.

[0081] The theoretical thickness between the second metal layer and the non-drillable layer refers to the thickness set in the design of the circuit board to be drilled. Optionally, the depth of a drill hole is S1, and the theoretical thickness between the second metal layer and the non-drillable layer is H1; where 0mm < H1 - S1 ≤ 0.2mm.

[0082] Specifically, during the actual fabrication process, the actual thickness of the dielectric layer 20 may deviate due to factors such as adhesive flow during pressing. Furthermore, the drilling process is also affected by the precision of the drilling equipment. Therefore, by setting the difference between the theoretical thickness H1 between the second metal layer 102 and the non-drillable layer 103 and the drilling depth S1 to be greater than 0 and less than or equal to 0.2 mm, the drilling depth is made less than the theoretical thickness H1 between the second metal layer 102 and the non-drillable layer 103. This avoids drilling through the non-drillable layer 103, preventing the non-drillable layer 102 from forming a conductive connection with the second metal layer 102.

[0083] Specifically, after drilling a hole to a depth S1 from the non-back-drilling side of the circuit board to be drilled, residual dielectric material may remain in the hole. This residual substrate and adhesive residue at the bottom of the hole can be cleaned using a first laser. The first laser may include laser types that cannot drill away the metal layer 10, such as CO2 lasers, and can be set according to actual needs; no specific limitations are made here.

[0084] Optionally, after drilling to the impenetrable layer 103 at a borehole using the first laser, a second laser can be used to remove part of the impenetrable layer 103 located in the borehole to form the first hole 310.

[0085] The second type of laser includes laser types such as UV lasers that can remove metal layers.

[0086] Specifically, a second laser is used to laser process the non-drillable layer 103 in a drill hole to remove part of the thickness of the non-drillable layer 103. This allows the conductive paste to reliably contact the non-drillable layer 103 after the drill hole is subsequently filled with conductive paste, thereby improving the reliability of the conductive connection between the second metal layer 102 and the non-drillable layer 103.

[0087] Optionally, the depth of the impenetrable layer 103 removed by the second laser is d1; 0 μm < d1 ≤ 10 μm.

[0088] Specifically, if the depth d1 of the impenetrable layer 103 removed by the second laser is greater than 10 μm, it may penetrate the impenetrable layer 103. After filling a drilled hole with conductive slurry, the impenetrable layer 103 may not be able to conduct through to the second metal layer 102. Therefore, by setting the depth d1 of the impenetrable layer 103 removed by the second laser to be within 0 μm to 10 μm, it is possible to ensure that the resin residue in a drilled hole is completely removed, improving the reliable contact between the subsequent conductive slurry and the impenetrable layer 103, while avoiding penetration of the impenetrable layer 103, which would prevent it from conducting through to the second metal layer 102 and thus making it impossible to detect the second height.

[0089] Optionally, after filling the first hole with conductive paste, the surface of the conductive paste facing away from the first metal layer is further polished, so that the surface of the conductive paste facing away from the first metal layer is at the same horizontal plane as the second metal layer. In this way, the conductive paste extending beyond the surface of the second metal layer is removed through the polishing process, improving the flatness of the non-back-drilled surface A2 and improving the accuracy of determining the subsequent back-drilling depth.

[0090] Based on the same inventive concept, the present invention provides a circuit board, which is manufactured using the back-drilling method of the circuit board provided in any embodiment of the present invention, and has the same beneficial effects as the above method, which will not be repeated here.

[0091] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A back-drilling method of a circuit board, characterized by, A to-be-drilled circuit board includes a back-drilling surface and a non-back-drilling surface, and includes a plurality of metal layers and a dielectric layer between two adjacent metal layers; The metal layer located on the back-drilling surface is a first metal layer, and the metal layer located on the non-back-drilling surface is a second metal layer; The metal layers between the first metal layer and the second metal layer include an un-drillable layer; A back-drilling method of the circuit board includes: placing the to-be-drilled circuit board on a drilling machine platform, with the back-drilling surface located on the side away from the non-back-drilling surface of the drilling machine platform, and placing a conductive plate between the first metal layer and an inductive mushroom head; the to-be-drilled circuit board includes a first through-hole, which is located between the second metal layer and the un-drillable layer; controlling a drill bit to move towards the conductive plate, and detecting when the drill bit contacts the conductive plate, to obtain a distance between the origin of the Z-axis of the main shaft of the drilling machine and the first metal layer as a first height; placing an insulating layer between the conductive plate and the inductive mushroom head, and electrically connecting the inductive mushroom head and the second metal layer; controlling the drill bit to move towards the un-drillable layer, and detecting when the drill bit contacts the un-drillable layer, to obtain a distance between the origin of the Z-axis of the main shaft of the drilling machine and the un-drillable layer as a second height; drilling, electroplating, and back-drilling the to-be-drilled circuit board according to the first height and the second height, to form a circuit board.

2. The back drilling method of a circuit board according to claim 1, characterized by, electrically connecting the inductive mushroom head and the second metal layer includes: placing a first conductive metal foil between the insulating layer and the inductive mushroom head, so that the first conductive metal foil is in contact with the inductive mushroom head for electrical connection; placing a second conductive metal foil between the drilling machine platform and the second metal layer, so that the second conductive metal foil is in contact with the second metal layer for electrical connection; electrically connecting one end of a third conductive metal foil to the first conductive metal foil, and electrically connecting the other end of the third conductive metal foil to the second conductive metal foil, so that the inductive mushroom head is electrically connected to the second metal layer through the first conductive metal foil, the third conductive metal foil, and the second conductive metal foil.

3. The back drilling method of a circuit board according to claim 1, characterized by, Before placing the to-be-drilled circuit board on the drilling machine platform, the method further includes: providing a to-be-drilled circuit board; drilling the non-back-drilling surface of the to-be-drilled circuit board to the un-drillable layer to form a first hole; filling the first hole with conductive paste to form the to-be-drilled circuit board including the first through-hole.

4. The back drilling method of a circuit board according to claim 3, wherein Drilling the non-back-drilling surface of the to-be-drilled circuit board to the un-drillable layer to form a first hole includes: drilling a hole in the non-back-drilling surface; the depth of the hole is less than the theoretical thickness between the second metal layer and the un-drillable layer; drilling the hole to the un-drillable layer using a first laser to form the first hole.

5. The back drilling method of a circuit board according to claim 4, wherein After drilling the hole to the un-drillable layer using a first laser, the method further includes: removing part of the un-drillable layer in the hole using a second laser to form the first hole.

6. The back drilling method of a circuit board according to claim 5, wherein The depth of the second laser removing the non-drillable layer is d1; 0 μm < d1 ≤ 10 μm.

7. The back drilling method of a circuit board according to claim 4, wherein The depth of the first hole is S1, and the theoretical thickness between the second metal layer and the non-drillable layer is H1; 0 mm < H1-S1 ≤ 0.2 mm.

8. The back drilling method of a circuit board according to claim 6, wherein After filling the conductive paste in the first hole, further comprising: Grinding the side surface of the conductive paste away from the first metal layer, so that the side surface of the conductive paste away from the first metal layer is at the same level with the second metal layer.

9. The back drilling method of a circuit board according to claim 1, wherein According to the first height and the second height, drilling, electroplating, back drilling the to-be-drilled circuit board to form a circuit board, comprising: According to the first height and the second height, determining the back drilling depth; Drilling on the non-back drilling surface to drill the first via to form a through hole through the to-be-drilled circuit board; Electroplating the through hole to form a through via; According to the back drilling depth, back drilling the through via to form a circuit board; Wherein, the aperture of the through hole is r1, and the aperture of the first via is r2, r2 < r1.

10. The back drilling method of a circuit board according to claim 9, wherein According to the first height and the second height, determining the back drilling depth, comprising: Obtaining an actual drilling depth compensation value; Calculating the height difference between the second height and the first height, and determining the back drilling depth according to the height difference and the actual drilling depth compensation value.

11. A circuit board, characterized by The circuit board is prepared by the back drilling method of any one of claims 1-10. The circuit board is prepared by the back drilling method of any one of claims 1-10.

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