Back-drilled composite cover plate for controlling drilling depth of circuit board and processing method thereof

Abstract

The present invention relates to a back-drilled composite cover plate and a processing method for controlling the drilling depth of a circuit board. With the promotion of 4G, 5G and future 6G communications, the back-drilling process will become an indispensable manufacturing process in the production process of circuit boards for communications, wherein the back-drilled composite cover plate comprises a processing surface insulating layer, a conductive layer carrier and a conductive layer; the conductive layer carrier and the conductive layer are combined by electroplating, vacuum evaporation deposition or coating; the processing surface insulating layer and the conductive layer carrier are combined by bonding, laminating or pressing; due to the use of a composite structure, the present invention can make the selection range of the processing surface insulating layer material wider under the premise of ensuring the drilling accuracy. For example, the use of insulating and environmentally friendly materials that are both high-temperature resistant and not prone to drill wire can not only improve the high-temperature resistance of the back-drilled composite cover plate, but also avoid the back-drilled composite cover plate from generating drill wire during the drilling process, which is adhered to the drill bit and blocks the chip groove of the drill bit, and is suitable for the rapid drilling process.

Description

Technical Field

[0001] The invention relates to the field of drilling holes in communication circuit boards, and in particular to a back-drilled composite cover plate for controlling the drilling depth of circuit boards and a processing method thereof. Background Art

[0002] The back drilling process is to remove the conductive layer part of the conductive through-hole that does not transmit signals by mechanical drilling after copper deposition, so as to eliminate the antenna effect of this part, ensure the strength and stability of the electrical signal, and facilitate high-frequency and high-speed signal transmission, especially for circuit boards used in 4G and 5G, as well as future 6G communication equipment.

[0003] At present, there are mainly two types of back-drilling cover plates for circuit boards:

[0004] 1. A copper-clad laminate with a single-sided copper coating of 0.1-0.3 mm is used, the copper surface is used as a conductive layer 10 with a thickness of 15-35 microns, and the back surface is used as an insulating layer 20. The conductive layer 10 and the insulating layer 20 are combined by hot pressing.

[0005] The disadvantages of using this drilling cover are: A: copper foil (conductive layer) is expensive; B: the copper foil needs to be roughened to form an effective bond with the insulating layer after lamination, resulting in uneven or pinhole contact between the copper foil and the insulating layer, with a tolerance of 5 microns (such as Figure 1 C: The thickness tolerance of the copper foil itself caused by the hot pressing process.

[0006] Based on the above tolerances, the thickness tolerance of the conductive layer 20 of the single-sided copper clad laminate (such as Figure 1 As shown in area B of FIG, the depth of the hole is within the range of plus or minus 10-15 microns. When the depth of the hole is controlled on the circuit board, the accuracy of the hole depth control is difficult to control, which affects the product quality.

[0007] 2. Use 0.01-0.05mm single-sided aluminum-clad aluminum plate, with the aluminum surface as the conductive layer, the thickness is generally 10-50 microns, and the back side as the insulating layer.

[0008] This material has been described in the invention patent (patent number CN205764024U) and the invention patent (application number 201610564610.3), and the conductive layer and the insulating layer are also combined by lamination.

[0009] The advantage of using this aluminum-clad laminate as a drilling cover plate is that the cost is lower than that of a single-sided copper-clad laminate. However, because of the use of a hot pressing process, the conductive layer needs to be surface roughened or specially treated to improve the adhesion because metal and organic matter do not adhere to each other. This results in a thickness tolerance of 10-15 microns in the conductive layer, affecting the control accuracy of the depth drilling of the circuit board. At the same time, due to the influence of debris, bumps or pinholes are formed on the surface, affecting the depth control accuracy of the back drilling.

[0010] Therefore, the company applied for two patents with patent numbers 201720787182.0 and 201880041327.X in 2017 and 2018 respectively. The processing surface insulation layer and the conductive layer are combined by electroplating, vacuum evaporation deposition or coating. Although the thickness tolerance of the conductive layer of the drilling cover plate can be reduced to less than 1 micron, the thickness tolerance of the conductive layer is reduced. However, for the efficient production of metal vacuum evaporation or coating, the insulation layer requires rolled insulation material, and the surface roughness of the processing surface insulation layer is required to be less than 5 microns. These requirements limit the selection range of the processing surface insulation layer material to those with surface roughness. Smooth and relatively high-temperature resistant organic materials (for example: PI or PTFE materials, with a thickness of 0.10-0.35 mm and a relative temperature resistance of 250-280 degrees) make the selection range of processing surface insulation layer materials relatively narrow, and the drill wire is easy to stick to the drill needle during drilling, clogging the drill needle chip groove, thereby increasing the friction between the drill needle and the circuit board during drilling, and further increasing the drill bit temperature; at the same time, when drilling at high speed, the drilling speed can reach 100 holes / minute per minute, causing the drill bit temperature to reach a high temperature of 300-450 degrees Celsius. Due to the high temperature resistance of the material, the existing drilling cover plate cannot be used in the high-speed drilling process. Summary of the invention

[0011] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a back-drilled composite cover plate and a processing method for controlling the drilling depth of a circuit board, which can make the selection range of the processing surface insulation layer material wider and is suitable for high-speed drilling processes.

[0012] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a back-drilled composite cover plate for controlling the drilling depth of a circuit board, comprising a processing surface insulating layer, a conductive layer carrier and a conductive layer placed in sequence from top to bottom; the conductive layer carrier and the conductive layer are combined by electroplating, vacuum evaporation deposition or coating; the processing surface insulating layer and the conductive layer carrier are combined by bonding, laminating or pressing.

[0013] Preferably, the thickness of the conductive layer is 0.001-5.0 microns.

[0014] Preferably, the conductive layer is a metal conductive layer, a metal alloy conductive layer or a metal-organic mixture conductive layer.

[0015] Preferably, the conductive layer carrier is a current blocking insulating layer or an electrical signal blocking insulating layer, and its thickness is between 1 micron and 100 microns.

[0016] Preferably, the surface roughness of the conductive layer carrier is less than 5 microns.

[0017] Preferably, the processing surface insulation layer is made of an insulating and environmentally friendly material that is resistant to high temperatures and is not prone to producing drill wires.

[0018] The present invention also provides a method for processing a back-drilled composite cover plate for controlling the drilling depth of a circuit board, comprising the following steps:

[0019] S1: forming a conductive layer on the bottom surface of the conductive layer carrier by electroplating, vacuum evaporation deposition or coating;

[0020] S2: The top surface of the conductive layer carrier is then combined with the processing surface insulating layer by bonding, laminating or pressing to finally form a back-drilled composite cover plate.

[0021] Preferably, the step of "forming a conductive layer on the bottom surface of the conductive layer carrier by electroplating" specifically includes:

[0022] placing the conductive layer carrier in an electroplating tank;

[0023] Electricity is applied to the bottom surface of the conductive layer carrier to form a conductive layer on the surface.

[0024] Preferably, the step of "forming a conductive layer on the bottom surface of the conductive layer carrier by vacuum evaporation deposition" specifically includes:

[0025] placing the conductive layer carrier in a vacuum;

[0026] vaporize the conductive material in a vacuum;

[0027] The vaporized conductive material solidifies on the bottom surface of the conductive layer carrier to form a conductive layer.

[0028] Preferably, the step of "forming a conductive layer on the bottom surface of the conductive layer carrier by coating" specifically includes:

[0029] Coating a conductive material on the bottom surface of the conductive layer carrier;

[0030] The conductive material is dried, chemically and photocured to form a conductive layer.

[0031] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0032] 1. Compared with the single-sided copper-clad cover plate and the single-sided aluminum-clad cover plate, the present invention does not use a high-temperature hot pressing process (temperature 160-200 degrees Celsius, duration 60-180 minutes); instead, a vacuum evaporation, electroplating or coating process is used to produce a conductive layer, which saves energy consumption and reduces the cost of the conductive layer;

[0033] 2. Due to the composite structure, the present invention can retain the high-precision advantages of the previous generation of patented products of the company (patent number 201720787182.0 and patent number 201880041327.X), by changing the original processing surface insulation layer to a conductive layer carrier, the thickness is reduced to less than 50 microns, and the high precision of the thickness and surface roughness of the conductive layer is maintained; experiments show that the total drilling depth error of the back-drilled composite cover plate is plus or minus 2 microns, which is significantly improved compared to the total error of plus or minus 12 microns of the copper-clad or aluminum-clad back-drilled cover plate. This error mainly comes from the sum of the surface roughness of the insulating layer and the thickness error of the conductive layer;

[0034] 3. Due to the composite structure adopted in the present invention, the high-precision advantages of the previous generation of patented products of the company (patent number 201720787182.0 and patent number 201880041327.X) can be retained. On the premise of the high precision advantages, the present invention can make the selection range of the insulating layer material of the processing surface wider. For example, the insulating environmentally friendly material that is both resistant to high temperature and not easy to produce drill wire (such as kraft paper mainly composed of wood fiber) is selected as the insulating layer material of the processing surface. It can not only improve the high temperature resistance of the back-drilled composite cover plate, but also avoid the back-drilled composite cover plate from producing drill wire during the drilling process, which adheres to the drill bit and blocks the chip groove of the drill bit, thereby improving the quality and reliability of drilling. It is suitable for the process of rapid drilling (about 100 holes per minute). Taking 3500 holes as an example, using the back-drilled composite cover plate and the rapid drilling process of 200,000 rotation speed can reduce the processing time from 60 minutes to 35 minutes, and can nearly double the drilling speed, so that the utilization rate of expensive drilling equipment is doubled.

[0035] 4. The processing surface insulation layer of the present invention is made of insulating and environmentally friendly materials that are resistant to high temperatures and not prone to producing drill wires. Compared with the aluminum-clad single-sided cover plate made mainly of phenolic resin and kraft paper and the copper-clad back-drilled cover plate made mainly of epoxy resin and glass fiber, the present invention is more environmentally friendly and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The technical solution of the present invention is further described below in conjunction with the accompanying drawings:

[0037] Attached Figure 1 A schematic diagram of a drilling entry plate produced by pressing or bonding in the prior art;

[0038] Attached Figure 2 The figure is a schematic diagram of the back-drilled composite cover plate for controlling the drilling depth of a circuit board according to the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0040] Attached Figure 2 The back-drilled composite cover plate for controlling the drilling depth of a circuit board according to the present invention comprises a processing surface insulating layer 1, a conductive layer carrier 2 and a conductive layer 3 placed in sequence from top to bottom; the conductive layer carrier 2 and the conductive layer 3 are combined by electroplating, vacuum evaporation deposition or coating; the processing surface insulating layer 1 and the conductive layer carrier 2 are combined by bonding, laminating or pressing; the thickness of the conductive layer 3 is 0.001-5.0 microns; the conductive layer 3 is a metal conductive layer, a metal alloy conductive layer or a metal organic mixture conductive layer, specifically an aluminum conductive layer or an aluminum alloy conductive layer; the conductive layer carrier 2 is a current blocking insulating layer or an electrical signal blocking insulating layer, and its thickness is between 1 micron and 100 microns; the surface roughness of the conductive layer carrier 2 is less than 5 microns (refer to Figure 2 C area in the processing surface); wherein the thickness of the processing surface insulating layer 1, the conductive layer carrier 2 and the conductive layer 3 are adjusted according to actual needs.

[0041] The back-drilled composite cover plate described in the present invention can make the selection range of materials for the insulating layer 1 of the processing surface wider. For example, if an insulating and environmentally friendly material that is both resistant to high temperatures and not prone to producing drill wires is selected as the insulating layer material of the processing surface (such as kraft paper mainly composed of wood fibers), it can not only improve the high temperature resistance of the back-drilled composite cover plate, but also prevent the back-drilled composite cover plate from producing drill wires during the drilling process, which adhere to the drill bit and block the chip groove of the drill bit, thereby improving the quality and reliability of drilling. It is also environmentally friendly and economical, and is suitable for rapid drilling (about 100 holes per minute) technology. Taking 3500 holes as an example, using a back-drilled composite cover plate and a 200,000 rpm rapid drilling process can reduce the processing time from 60 minutes to 35 minutes, and can nearly double the drilling speed, thereby doubling the utilization rate of expensive drilling equipment.

[0042] Implementation Cases:

[0043] 1. Electroplating

[0044] According to a general electroplating method, the conductive layer carrier 2 can be placed in an electroplating device, and a current can be passed through one side to form a conductive layer on the conductive layer. The thickness of the conductive layer can be adjusted by adjusting the current and the electroplating time.

[0045] 2. Vacuum evaporation deposition

[0046] The conductive layer carrier 2 is placed in a vacuum, and the conductive material is vaporized by heating or plasma sputtering on the side where the conductive layer needs to be formed. After the conductive material is vaporized, it re-solidifies on the insulating material side with a lower temperature to form a conductive layer.

[0047] 3. Coating method

[0048] One side of the conductive layer carrier 2 is coated with a coating having conductive properties, wherein the coating contains glue that can adhere to the insulating material, and after drying, a stable conductive layer-conductive layer carrier composite is formed.

[0049] The present invention also provides a method for processing a back-drilled composite cover plate for controlling the drilling depth of a circuit board, comprising the following steps:

[0050] S1: forming a conductive layer 3 on the bottom surface of the conductive layer carrier 2 by electroplating, vacuum evaporation deposition or coating;

[0051] S2: The top surface of the conductive layer carrier 2 is then combined with the processing surface insulating layer 1 by bonding, laminating or pressing, and finally a back-drilled composite cover plate is manufactured.

[0052] Preferably, the step of “forming the conductive layer 3 on the bottom surface of the conductive layer carrier 2 by electroplating” specifically includes:

[0053] Placing the conductive layer carrier 2 in an electroplating tank;

[0054] Electricity is applied to the bottom surface of the conductive layer carrier 2 to form a conductive layer 3 on the surface.

[0055] Preferably, the step of “forming the conductive layer 3 on the bottom surface of the conductive layer carrier 2 by vacuum evaporation deposition” specifically includes:

[0056] placing the conductive layer carrier 2 in a vacuum;

[0057] Heating or plasma sputtering a conductive material in a vacuum to vaporize the conductive material;

[0058] The vaporized conductive material solidifies on the bottom surface of the conductive layer carrier 2 to form a conductive layer 3 .

[0059] Preferably, the step of "forming the conductive layer 3 on the bottom surface of the conductive layer carrier 2 by coating" specifically includes:

[0060] Coating a conductive material on the bottom surface of the conductive layer carrier 2;

[0061] The conductive material is dried, chemically and photocured to form a conductive layer 3 .

[0062] When performing deep drilling: the moment the metal drill bit contacts the aluminum conductive layer 3, the starting point of drilling is accurately determined, thereby reducing the depth tolerance of the deep drilling and improving the hole position accuracy of the deep drilling; during the processing, when conductor debris adheres to the drill bit, the insulating layer can prevent the conductor debris from contacting the aluminum conductive layer 3, and the electrical signal is transmitted when and only when the drill bit drills through the insulating layer and contacts the aluminum conductive layer 3; due to the use of aluminum or aluminum alloy, the processing cost is low, and the depth control accuracy is extremely high, thereby improving the quality of the deep drilling of the product.

[0063] The above are only specific application examples of the present invention and do not constitute any limitation on the protection scope of the present invention. Any technical solution formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention.

Claims

1. A back-drilled composite cover plate for controlling the drilling depth of a circuit board, characterized in that: It comprises a processing surface insulating layer, a conductive layer carrier and a conductive layer which are placed in sequence from top to bottom; The conductive layer carrier and the conductive layer are combined by electroplating, vacuum evaporation deposition or coating; The processing surface insulating layer and the conductive layer carrier are combined by bonding, laminating or pressing; The processing surface insulation layer is made of an insulating and environmentally friendly material that is both resistant to high temperatures and not prone to producing drill wires; The conductive layer carrier is a current blocking insulating layer or an electrical signal blocking insulating layer, and its thickness is between 1 micron and 100 microns.

2. The back-drilled composite cover plate for controlling the drilling depth of a circuit board according to claim 1, characterized in that: The thickness of the conductive layer is 0.001-5.0 microns.

3. The back-drilled composite cover plate for controlling the drilling depth of a circuit board according to claim 1, characterized in that: The conductive layer is a metal conductive layer, a metal alloy conductive layer or a metal-organic mixture conductive layer.

4. The back-drilled composite cover plate for controlling the drilling depth of a circuit board according to claim 1, characterized in that: The surface roughness of the conductive layer carrier is less than 5 microns.

5. A method for processing a back-drilled composite cover plate for controlling the drilling depth of a circuit board, used for processing the back-drilled composite cover plate for controlling the drilling depth of a circuit board according to claim 1, characterized in that: The following steps are involved: S1: forming a conductive layer on the bottom surface of the conductive layer carrier by electroplating, vacuum evaporation deposition or coating; S2: The top surface of the conductive layer carrier is then combined with the processing surface insulating layer by bonding, laminating or pressing to finally form a back-drilled composite cover plate.

6. A method for processing a back-drilled composite cover plate for controlling the drilling depth of a circuit board according to claim 5, characterized in that: The step of "forming a conductive layer on the bottom surface of the conductive layer carrier by electroplating" specifically includes: placing the conductive layer carrier in an electroplating tank; Electricity is applied to the bottom surface of the conductive layer carrier to form a conductive layer on the bottom surface.

7. A method for processing a back-drilled composite cover plate for controlling the drilling depth of a circuit board according to claim 5, characterized in that: The step of "forming a conductive layer on the bottom surface of the conductive layer carrier by vacuum evaporation deposition" specifically includes: placing the conductive layer carrier in a vacuum; vaporize the conductive material in a vacuum; The vaporized conductive material solidifies on the bottom surface of the conductive layer carrier to form a conductive layer.

8. The method for processing a back-drilled composite cover plate for controlling the drilling depth of a circuit board according to claim 5, characterized in that: The step of "forming a conductive layer on the bottom surface of the conductive layer carrier by coating" specifically includes: Coating a conductive material on the bottom surface of the conductive layer carrier; The conductive material is dried, chemically and photocured to form a conductive layer.

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