Circuit board and back drilling method thereof

Abstract

The invention discloses a circuit board and a back drilling method thereof, and the method comprises the steps: placing a to-be-drilled circuit board on a drilling machine platform, enabling a back drilling surface to be located at one side, away from the drilling machine platform, of a non-back drilling surface, and placing a conductive plate between a first metal layer and an induction mushroom head; the to-be-drilled circuit board comprises a first via hole, and the first via hole is located between the second metal layer and the non-drillable layer; a drill bit is controlled to move towards the conductive plate, and when it is detected that the drill bit makes contact with the conductive plate, the distance between the Z-axis direction original point of the main shaft of the drilling machine and the first metal layer is obtained as the first height; an insulating layer is placed between the conductive plate and the induction mushroom head, and the induction mushroom head is electrically connected with the second metal layer; the distance between the Z-axis direction original point of the main shaft of the drilling machine and the non-drillable layer is obtained as a second height; and according to the first height and the second height, carrying out drilling, electroplating and back drilling on the to-be-drilled circuit board to form the circuit board. According to the technical scheme, the back drilling precision and the back drilling quality can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of back drilling, and in particular to a circuit board and a back drilling method thereof. Background Art

[0002] Circuit boards are primarily used in communications equipment, large servers, medical electronics, military, and aerospace applications. Due to the high number of layers and thickness of PCBs, signal conduction between layers is typically achieved by drilling through holes and then electroplating. However, this design can result in severe signal loss during high-frequency, high-speed signal transmission. For example, on a 20-layer backplane, if a signal line only needs to connect from the first layer to the fifth layer, the copper in the hole walls between the sixth and twentieth layers is redundant. The presence of this copper in the hole walls can easily cause reflections, scattering, and delays in signal transmission. Therefore, backdrilling effectively removes the sections of the through holes that do not serve any connection or transmission function, thereby preventing reflections, scattering, and delays in signal transmission, which could cause signal distortion.

[0003] A circuit board includes multiple metal layers and dielectric layers between the metal layers. In the prior art, test holes are usually drilled in the edge area of ​​the circuit board to obtain the depth between the backdrill surface and the non-drillable layer, and this depth is used as the depth of the subsequent backdrilling. However, during the preparation of the circuit board, the dielectric layer may have a thickness deviation between the edge area and the middle area of ​​the circuit board due to the pressing of the flow adhesive, etc. To ensure that the non-drillable layer is not drilled through, a large safety distance must be reserved. This safety distance usually needs to cover the range of board thickness fluctuations, resulting in the residual length of the stump being too long after backdrilling, affecting signal transmission, or drilling through the non-drillable layer and causing an open circuit risk; or the backdrilling depth can be determined during the process of drilling a through hole, but this solution requires a large copper foil to be set in the non-drillable layer, which limits the application scenarios. In addition, this solution will cause the inner copper ring of the non-drillable layer to be exposed after backdrilling, resulting in reliability risks. Summary of the Invention

[0004] The present 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 backdrilling method for a circuit board, wherein the circuit board to be drilled includes a backdrilled surface and a non-backdrilled 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 backdrilled surface is a first metal layer, and the metal layer located on the non-backdrilled 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 of the circuit board includes:

[0007] 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 facing away from the drilling platform, and placing a conductive plate between the first metal layer and the inductive mushroom head; the circuit board to be drilled includes a first conductive via, which is located between the second metal layer and the non-drillable layer;

[0008] controlling the drill bit to move toward the conductive plate, and detecting that the drill bit contacts the conductive plate, obtaining a distance between an origin in the Z-axis direction of the main shaft of the drill and the first metal layer as a first height;

[0009] placing an insulating layer between the conductive plate and the inductive mushroom head, and electrically connecting the inductive mushroom head to the second metal layer;

[0010] Controlling the drill bit to move toward the non-drillable layer, and detecting when the drill bit contacts the non-drillable layer, obtaining a distance between the origin of the spindle Z-axis direction of the drill and the non-drillable layer as a second height;

[0011] According to the first height and the second height, drilling, electroplating, and back drilling are performed on the circuit board to be drilled to form a circuit board.

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

[0013] placing a first conductive metal foil between the insulating layer and the induction mushroom head, so that the first conductive metal foil is in contact and electrically connected with the induction mushroom head;

[0014] placing a second conductive metal foil between the drilling rig platform and the second metal layer, wherein the second conductive metal foil is in contact and electrically connected with the second metal layer;

[0015] One end of a 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 induction 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] Drilling a hole on the non-backdrilling surface of the circuit board to be drilled to the non-drillable layer to form a first hole;

[0019] The first hole is filled with conductive paste to form the circuit board to be drilled including the first conductive hole.

[0020] Optionally, drilling a hole to the non-drillable layer at the non-back drilling surface of the circuit board to be drilled to form a first hole, comprising:

[0021] drilling a hole at the non-back drilling surface; the depth of the hole is less than the theoretical thickness between the second metal layer and the non-drillable layer;

[0022] drilling to the non-drillable layer at the hole by a first laser to form the first hole.

[0023] Optionally, after drilling to the non-drillable layer at the hole by the first laser, further comprising:

[0024] removing part of the non-drillable layer in the hole by a second laser to form the first hole.

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

[0026] 0 μm < d1≤ 10 μm.

[0027] Optionally, the depth of the hole is S1, and the theoretical thickness between the second metal layer and the non-drillable layer is H1;

[0028] wherein, 0 mm < H1-S1≤ 0.2 mm.

[0029] Optionally, after filling the conductive paste in the first hole, further comprising:

[0030] polishing 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 as the second metal layer.

[0031] Optionally, according to the first height and the second height, drilling, electroplating, and back drilling the circuit board to be drilled to form a circuit board, comprising:

[0032] determining a back drilling depth according to the first height and the second height;

[0033] drilling a hole at the non-back drilling surface to remove the first via to form a through hole penetrating through the circuit board to be drilled;

[0034] electroplating the through hole to form a through via;

[0035] back drilling the through via according to the back drilling depth to form a circuit board;

[0036] wherein, the aperture of the through hole is r1, and the aperture of the first via is r2, r2 < r1.

[0037] Optionally, according to the first height and the second height, the back drilling depth is determined, comprising:

[0038] An actual drilling depth compensation value is obtained;

[0039] A height difference between the second height and the first height is calculated, and according to the height difference and the actual drilling depth compensation value, the back drilling depth is determined.

[0040] In a second aspect, the present application provides a circuit board prepared by the back drilling method of the first aspect.

[0041] The technical scheme provided by the present application comprises the following steps: placing the to-be-drilled circuit board on a drilling machine platform, with the back drilling surface located on the side away from the drilling machine platform of the non-back drilling surface, and placing a conductive plate between the first metal layer and the induction mushroom head; in the process of controlling the drill bit to move from the origin of the Z-axis direction of the main shaft of the drilling machine to the conductive plate, the first height between the origin of the Z-axis direction of the main shaft of the drilling machine and the first metal layer is obtained; placing an insulating layer between the conductive plate and the induction mushroom head, and electrically connecting the induction mushroom head and the second metal layer, and then controlling the drill bit to move to the non-drillable layer, the second height between the origin of the Z-axis direction of the main shaft of the drilling machine and the non-drillable layer is obtained; according to the first height and the second height, 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 is obtained; and then drilling, electroplating and back drilling are performed on the to-be-drilled circuit board, so that the precision and reliability of back drilling can be improved. The technical scheme of the present application can measure the actual thickness between the back drilling surface and the non-drillable layer according to the first height and the second height to perform depth control back drilling operation, reduces the drilling deviation caused by the non-uniformity of the thickness of the board or the medium layer, thereby improving the back drilling precision, reducing the residual stubs of back drilling, and improving the quality of back drilling. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 A structure schematic diagram of a to-be-drilled circuit board provided for an embodiment of the present application;

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

[0044] Figure 3 A process structure schematic diagram of preparing a circuit board provided for an embodiment of the present application;

[0045] Figure 4 A partial process structure schematic diagram of preparing a circuit board provided for an embodiment of the present application;

[0046] Figure 5 A process structure schematic diagram of preparing a to-be-drilled circuit board provided for an embodiment of the present application. DETAILED DESCRIPTION

[0047] The application will be described in further detail below with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the scope of the application. In addition, it should be noted that, for the sake of brevity, only structures related to the present application are shown and described in the drawings.

[0048] Figure 1 A structure diagram of a circuit board to be drilled is provided for an embodiment of the present application, as shown in the figure, the circuit board to be drilled includes a back drilling surface A1 and a non-back drilling surface A2, and the circuit board to be drilled includes multiple metal layers 10 and dielectric layers 20 between adjacent two metal layers 10; the metal layer 10 located at the back drilling surface A1 is a first metal layer 101, and the metal layer 10 located at the non-back drilling surface A2 is a second metal layer 102; the metal layer 10 between the first metal layer 101 and the second metal layer 102 includes an un-drillable layer 103. The circuit board to be drilled includes a first via 31, and the first via 31 is located between the second metal layer 102 and the un-drillable layer 103. Figure 1

[0049] The back drilling surface A1 means the surface of the circuit board to be drilled, and the non-back drilling surface A2 means the surface opposite to the back drilling surface A1 of the circuit board to be drilled. The dielectric layer 20 can realize insulation protection between different metal layers 10, isolate different metal layers 10, and prevent electrical signal short circuit and signal interference.

[0050] Specifically, the un-drillable layer 103 is located between the first metal layer 101 and the second metal layer 102, and the un-drillable layer 103 needs to be electrically connected with the second metal layer 102. Generally, drilling is performed on the circuit board to be drilled to form a via penetrating through each metal layer 10 and each dielectric layer 20, then the surface of the via is electroplated with conductive material, and finally a back drilling drill bit is used to enter the via from the back drilling surface A1 to drill off the conductive material on the surface of the via between the un-drillable layer 103 and the first metal layer 101, so as to drill off the via segment that does not need to play any connection or transmission role, thereby avoiding problems such as reflection, scattering or delay of high-speed signal transmission. After back drilling, the un-drillable layer 103 will not be drilled off, so as to ensure that the un-drillable layer 103 can be electrically connected with the second metal layer 102 through the conductive material to realize signal transmission.

[0051] Figure 2 A flowchart of a back drilling method of a circuit board is provided for an embodiment of the present application, Figure 3 A process structure diagram for preparing a circuit board is provided for an embodiment of the present application, referring to Figure 2 and Figure 3 The back drilling method of the circuit board includes:

[0052] ​S101, place the circuit board to be drilled on the drilling machine platform, with the back drilling surface on the side away from the non-back drilling surface of the drilling machine 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 between the second metal layer 102 and the non-drillable layer 103. The drilling machine platform 40 is used to place the circuit board to be drilled. The conductive plate 41 includes a composite aluminum plate or other metal plate material, which can be set as needed and is not limited here.

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

[0055] S102, control the drill bit to move towards the conductive plate, and detect when the drill bit contacts the conductive plate, to obtain the distance between the origin of the main shaft Z-axis direction of the drilling machine and the first metal layer as the first height.

[0056] The origin L0 of the main shaft Z-axis direction of the drilling machine represents the position where the main shaft of the drilling machine rises to the highest point, and can also be defined as other positions, which are not limited in detail, as long as the main shaft of the drilling machine rises to the same height as the Z-axis origin when the drilling machine detects 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 can form a conductive loop, which will generate a weak current signal. During the movement of the drill bit 43 towards the conductive plate 41, when the current signal is obtained, the distance moved by the drill bit 43 is taken as the first movement distance, and the sum of the first movement distance and the thickness of the conductive plate 41 is taken as the first height h1. The thickness of the conductive plate 41 is stored in advance in the drilling machine, and after the first movement distance is obtained, the first height h1 can be calculated in the drilling machine.

[0058] S103, place an insulating layer between the conductive plate and the induction mushroom head, and make the induction 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 as needed and is not limited here.

[0060] Specifically, by setting the insulating layer 44, the induction mushroom head 42 is prevented from being electrically connected with 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 with the second metal layer 102, since the second metal layer 102 is electrically connected with the un-drillable layer 103 through the first through hole 31, when the drill bit 43 contacts the un-drillable layer 103, the drill bit 43, the un-drillable layer 103, the first through hole 31, the second metal layer 102, and the induction mushroom head 42 can form an electrically connected loop to generate a current signal.

[0061] It should be noted that the implementation manner of electrically connecting the induction mushroom head 42 with the second metal layer 102 can be set according to actual needs. In an optional embodiment, referring to Figure 3 the induction mushroom head 42 is electrically connected with the second metal layer 102, including: placing a first conductive metal foil 451 between the insulating layer 44 and the induction mushroom head 42, so that the first conductive metal foil 451 is in contact with the induction mushroom head 42 for electrical connection; placing a second conductive metal foil 452 between the drill platform 40 and the second metal layer 102, the second conductive metal foil 452 being in contact with the second metal layer 102 for electrical connection; and setting one end of a third conductive metal foil 453 to be electrically connected with the first conductive metal foil 451, and the other end of the third conductive metal foil 453 to be electrically connected with the second conductive metal foil 452, so that the induction mushroom head 42 is electrically connected with 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 can include conductive materials such as copper, which can be set according to actual needs.

[0063] Specifically, the second conductive metal foil 452 is in contact with the side surface of the second metal layer 102 away from the first metal layer 101, and since the second conductive metal foil 452 and the second metal layer 102 can both realize electrical signal transmission, the second conductive metal foil 452 and the second metal layer 102 can transmit electrical signals to each other after being in contact. Correspondingly, the first conductive metal foil 451 and the induction mushroom head 42 are in contact for electrical connection. 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, and enable the induction mushroom head 42 to be electrically connected with the un-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 can be understood that the first conductive metal foil 451, the second conductive metal foil 452 and the third conductive metal foil 453 can be integrally arranged or electrically connected by welding, and can be arranged according to actual needs, which is not limited specifically herein.

[0065] S104, control the drill bit to move to the un-drillable layer, and detect the distance between the origin of the main shaft Z-axis direction of the drilling machine and the un-drillable layer when the drill bit contacts the un-drillable layer as a second height.

[0066] Specifically, the drill bit 43 starts drilling from the origin L0 of the main shaft direction of the drilling machine along the Z-axis direction, and when the drill bit 43 contacts the un-drillable layer 103, the drill bit 43, the un-drillable layer 103, the first through hole 31, the second metal layer 102 and the induction mushroom head 42 form an electrical connection path to generate an electric current signal. When the electric current signal is obtained, the distance moved by the drill bit 43 is taken as the second movement distance, and the sum of the second movement distance and the thickness of the second conductive metal foil 452 is taken as the second height h2. Preferably, the diameter of the drill bit 43 is the same as the diameter of the through hole 32.

[0067] S105, according to the first height and the second height, drilling, electroplating and back drilling are performed on the circuit board to be drilled to form the circuit board.

[0068] Specifically, the first through hole 31 can be accessed from the non-back drilling side A2 to remove the first through hole 31, and at least the second metal layer 102 and the un-drillable layer 103 overlapping 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 the drill bit 43 is arranged to enter the through hole 32 from the back drilling side A1, and the back drilling depth is the sum of the difference between the second height h2 and the first height h1 and the actual drilling depth compensation value to remove the electroplated layer on the side of the un-drillable layer 103 away from the second metal layer 102 to form the circuit board.

[0069] The technical scheme provided by the present application places the circuit board to be drilled on the drilling machine platform, the back drilling side is located on the side away from the drilling machine platform of the non-back drilling side, and a conductive plate is placed between the first metal layer and the induction mushroom head. In the process of controlling the drill bit to move from the origin of the main shaft Z-axis direction of the drilling machine to the conductive plate, the first height between the origin of the main shaft Z-axis direction of the drilling machine 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 with the second metal layer. In the process of controlling the drill bit to move to the un-drillable layer, the second height between the origin of the main shaft Z-axis direction of the drilling machine and the un-drillable layer is obtained. According to the first height and the second height, the distance between the first metal layer and the un-drillable layer can be determined, that is, the actual depth between the back drilling side and the un-drillable layer is obtained. Drilling, electroplating and back drilling are performed on the circuit board to be drilled, which can improve the depth control accuracy of back drilling and improve the reliability of back drilling.

[0070] Optionally, during the process of controlling the drill bit to move towards the conductive plate, the moving distance of the drill bit can be acquired, and the electrical signal corresponding to the current moving distance can be acquired. The speed of the drill bit can be a constant value, and the drill system can determine the moving distance of the drill bit according to the time length of the drill bit movement. The acquisition method of the moving distance of the drill bit can also be other methods, which are not limited here. 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 mushroom head 42 does not form an electrical connection loop with the drill bit 43, and thus 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 loop with the induction mushroom head 42 through the conductive plate 41, and thus a small current signal is generated. The moving distance corresponding to this time is taken as the first height h1.

[0071] Optionally, during the process of controlling the drill bit to move towards the non-drillable layer, the moving distance of the drill bit can be acquired, and the electrical signal corresponding to the current moving distance can be acquired. The speed of the drill bit can be a constant value, and the drill system can determine the moving distance of the drill bit according to the time length of the drill bit movement. The acquisition method of the moving distance of the drill bit can also be other methods, which are not limited here. 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 mushroom head 42 does not form an electrical connection loop with the non-drillable layer 103, and thus 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 loop with the induction mushroom head 42 through the non-drillable layer 103, and thus a small current signal is generated. The moving distance corresponding to this time is taken as the second height h2.

[0072] In an optional embodiment, Figure 4 A partial process structure schematic diagram for preparing a circuit board is provided for the embodiment of the present application, as shown in Figure 4 According to the first height and the second height, the circuit board to be drilled is drilled, electroplated, and back drilled to form a circuit board, including: determining a back drilling depth according to the first height and the second height; drilling a hole on a non-back drilling surface to drill off the first through hole to form a through hole penetrating through the circuit board to be drilled; electroplating the through hole to form a through via; and back drilling the through via according to the back drilling depth to form the circuit board.

[0073] The back drilling depth is determined according to the first height and the second height, including obtaining an actual drilling depth compensation value, calculating a 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. The actual drilling depth compensation value can be determined according to an actual back drilling process. Specifically, after the through hole 32 is electroplated with conductive material, the surface of the first metal layer 101 will also be electroplated with conductive material, and the thickness k1 of the conductive material needs to be added to the calculation of the actual drilling depth compensation value. In addition, a drill bit tip angle compensation k2 is generated during the drilling process. A conductive plate is usually placed on the side of the to-be-drilled circuit board away from the drilling machine platform during drilling to protect the to-be-drilled circuit board and serve as a conductive connection. The thickness k3 of the conductive plate is also added to the calculation of the actual back drilling depth. In addition, the residual stub length k4 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, and 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, further improving the accuracy of back drilling.

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

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

[0076] Reference Figure 4 and Figure 5The aperture of the through hole 32 is r1, the aperture of the first through hole 31 is r2, the through hole 32 is a plated through hole before back drilling, and the aperture needs to meet the aperture requirement of the back drilling metallization hole part, and the first through hole 31 is an auxiliary hole for electrically connecting the non-drillable layer 103 and the second metal layer 102 in the through hole 32 before the through hole 32 is formed, and the first through hole 31 needs to be drilled to form the through hole 32 after the actual depth of the back drilling surface A1 to the non-drillable layer 103 is detected. By setting the aperture r2 of the first through hole 31 to be smaller than the aperture r1 of the through hole 32, when the actual depth of the back drilling surface A1 to the non-drillable layer 103 is detected at the back drilling hole position, the aperture of the first through hole 31 is greater than the aperture of the through hole 32, which can avoid the actual aperture of the through hole 32 exceeding the theoretical design aperture when the through hole 32 is drilled subsequently, thereby meeting the aperture requirement of the through hole 32.

[0077] On the basis of the above-mentioned embodiments, the present embodiment illustrates the case before the to-be-drilled circuit board is placed on the drilling machine platform, as shown in FIG. 1, the forming method of the to-be-drilled circuit board comprises the following steps: Figure 5 As shown in FIG. 1, the forming method of the to-be-drilled circuit board comprises the following steps: providing a to-be-drilled circuit original board; drilling from a non-back drilling surface to a non-drillable layer to form a first hole 310; and filling conductive paste in the first hole 310 to form a to-be-drilled circuit board comprising a first through hole 31.

[0078] Optionally, the conductive paste comprises copper, gold, silver or aluminum, which can be set according to actual needs, and is not limited here.

[0079] Specifically, the to-be-drilled circuit board original board comprises a plurality of metal layers 10 and a dielectric layer 20 between adjacent two metal layers 10. A drill bit is used to drill from the non-back drilling surface A2 side to drill away the dielectric layer 20 and the metal layer 10 between the second metal layer 102 and the non-drillable layer 103 to form the first hole 310, and then conductive copper paste is filled into the first hole 310 to form the first through hole 31, so that the non-drillable layer 103 can be conductively connected with the second metal layer 102 through the first through hole 31.

[0080] Optionally, the drilling from the non-back drilling surface to the non-drillable layer to form the first hole comprises the following steps: drilling a first hole; the depth of the first hole is less than the theoretical thickness between the second metal layer and the non-drillable layer; and using a first laser to drill to the non-drillable layer at the first hole to form the first hole.

[0081] Optionally, the depth of the first hole is S1, and the theoretical thickness between the second metal layer and the non-drillable layer is H1; wherein 0mm

[0082] Specifically, in the actual preparation process, the medium layer 20 has a deviation in the actual pressing thickness due to pressing and glue flow, etc. In addition, in the drilling process, it is also affected by the accuracy 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 depth of the drilling is less than the theoretical thickness H1 between the second metal layer 102 and the non-drillable layer 103, which can avoid drilling through the non-drillable layer 103 and cannot form a conductive connection between the non-drillable layer 102 and the second metal layer 102.

[0083] Specifically, after drilling a hole from the non-back drilling surface to the circuit board to be drilled according to the drilling depth S1, the medium material may be left in the hole. The remaining substrate and hole bottom glue left in the hole can be completely removed by the first laser. The first laser includes CO2 laser and other laser types that cannot drill the metal layer 10. The first laser can be set according to actual needs, which is not limited here.

[0084] Optionally, after drilling to the non-drillable layer 103 at the hole by the first laser, a second laser can be used to remove part of the non-drillable layer 103 in the hole to form the first hole 310.

[0085] The second laser includes UV laser and other laser types that can remove the metal layer.

[0086] Specifically, the second laser is used to laser process the non-drillable layer 103 in the hole to remove part of the thickness of the non-drillable layer 103. After filling the conductive paste in the hole later, the conductive paste can reliably contact the non-drillable layer 103, and the reliability of the conductive connection between the second metal layer 102 and the non-drillable layer 103 is improved.

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

[0088] Specifically, if the depth d1 of the non-drillable layer 103 removed by the second laser is greater than 10 μm, the non-drillable layer 103 may be drilled, and after filling the conductive paste in the hole later, the non-drillable layer 103 may not be in conductive connection with the second metal layer 102. Therefore, by setting the depth d1 of the non-drillable layer 103 removed by the second laser to be within 0 μm ~ 10 μm, the resin glue in the hole can be completely removed, the conductive paste can reliably contact the non-drillable layer 103, and the non-drillable layer 103 is prevented from being drilled, which prevents the non-drillable layer 103 from being in conductive connection with the second metal layer 102, and thus the second height cannot be detected.

[0089] Optionally, after filling the conductive paste in the first hole, the method further comprises polishing a 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 horizontal plane as the second metal layer. In this way, the conductive paste beyond the surface of the second metal layer is removed by the polishing process, improving the flatness of the non-back-drilling surface A2 and improving the accuracy of the subsequent determination of the back-drilling depth.

[0090] Based on the same inventive concept, the present application provides a circuit board prepared by the back-drilling method of the circuit board provided by any of the embodiments of the present application, which has the same beneficial effects as the above method, which will not be described here.

[0091] Note that the above are only preferred embodiments of the present application and the technical principles applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and those skilled in the art can make various obvious changes, re-adjustments, mutual combinations and substitutions without departing from the scope of the present application. Therefore, although the present application has been described in more detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the inventive concept, and the scope of the present application is determined by the scope of the appended claims.

Claims

1. A back drilling method for a circuit board, characterized in that: The circuit board to be drilled includes a back-drilled surface and a non-back-drilled surface, and 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-drilled surface is a first metal layer, and the metal layer located on the non-back-drilled 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; The back drilling method of the circuit board comprises: 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 facing away from the drilling platform, and placing a conductive plate between the first metal layer and the inductive mushroom head; the circuit board to be drilled includes a first conductive via, which is located between the second metal layer and the non-drillable layer; controlling the drill bit to move toward the conductive plate, and detecting that the drill bit contacts the conductive plate, obtaining a distance between an origin of a spindle Z-axis direction of the drill 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 to the second metal layer; Controlling the drill bit to move toward the non-drillable layer, and detecting when the drill bit contacts the non-drillable layer, obtaining a distance between the origin of the spindle Z-axis direction of the drill and the non-drillable layer as a second height; According to the first height and the second height, drilling, electroplating, and back drilling are performed on the circuit board to be drilled to form a circuit board.

2. The back drilling method of a circuit board according to claim 1, wherein: The method of electrically connecting the inductive mushroom head to the second metal layer comprises: placing a first conductive metal foil between the insulating layer and the induction mushroom head, so that the first conductive metal foil is in contact and electrically connected with the induction mushroom head; placing a second conductive metal foil between the drilling rig platform and the second metal layer, wherein the second conductive metal foil is in contact and electrically connected with the second metal layer; One end of a 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 induction 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, wherein: Before placing the circuit board to be drilled on the drilling platform, the method further comprises: Provide the original circuit board to be drilled; Drilling a hole on the non-backdrilling surface of the circuit board to be drilled to the non-drillable layer to form a first hole; The first hole is filled with conductive paste to form the circuit board to be drilled including the first conductive hole.

4. The back drilling method of a circuit board according to claim 3, wherein: Drilling a hole on the non-backdrilling surface of the circuit board to be drilled to the non-drillable layer to form a first hole includes: Drilling a hole on the non-backdrilled surface; the depth of the hole is less than the theoretical thickness between the second metal layer and the non-drillable layer; A first laser is used to drill into the non-drillable layer at the drilling hole to form the first hole.

5. The back drilling method of a circuit board according to claim 4, characterized in that: After drilling the non-drillable layer at the drill hole using the first laser, the method further includes: A second laser is used to remove a portion of the non-drillable layer within the first drill hole to form the first hole.

6. The back drilling method of a circuit board according to claim 5, characterized in that: The depth of the non-drillable layer removed by the second laser is d1; 0μm<d1≤10μm.

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

8. The back drilling method of a circuit board according to claim 6, wherein: After the conductive paste is filled into the first hole, the method further includes: A 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 located at the same level as the second metal layer.

9. The back drilling method of a circuit board according to claim 1, wherein: Drilling, electroplating, and backdrilling the circuit board to be drilled according to the first height and the second height to form a circuit board, including: determining a backdrilling depth according to the first height and the second height; Drilling on the non-backdrilled surface to remove the first conductive hole to form a through hole penetrating the circuit board to be drilled; electroplating the through hole to form a through via; backdrilling the through via holes according to the backdrill depth to form a circuit board; The diameter of the through hole is r1, the diameter of the first conductive hole is r2, and r2<r1.

10. The back drilling method of a circuit board according to claim 9, characterized in that: Determining a backdrilling depth according to the first height and the second height includes: Get the actual drilling depth compensation value; A height difference between the second height and the first height is calculated, and the backdrilling depth is determined according to the height difference and the actual drilling depth compensation value.

11. A circuit board, characterized in that: The circuit board is manufactured by the back drilling method of any one of claims 1 to 10.

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