Precision machining method of high-current-carrying copper block-embedded PCB (Printed Circuit Board)

Abstract

The invention discloses a precision processing method of a high-current-carrying copper-block-embedded PCB, and the method comprises the following steps: core board processing: providing a first core board and a second core board, carrying out the single-side etching of the first core board and the second core board, manufacturing an inner-layer circuit, and drilling rivet holes; carrying out browning treatment; a third core plate is provided, double-sided etching is carried out on the third core plate until a copper layer is completely removed to form the light plate, then the copper-embedded groove is formed in the light plate in a milling mode, and the size of the copper-embedded groove is equal to that of the copper-embedded block; the embedded copper block is pretreated, specifically, the surface of the embedded copper block is roughened, and the embedded copper block is coated with a micro-adhesive film; embedding the embedded copper block into the light plate, and then sequentially stacking the first core plate, the light plate and the second core plate and fixing through rivets; performing press fit; mechanical drilling; electroplating to enable the copper thickness of the hole wall to be greater than or equal to 30 microns and the copper thickness of surface copper to be greater than or equal to 72 microns; performing double-sided depth-controlled milling to the surface of the copper-embedded block, and feeding back the milling depth in real time through laser ranging; and bending the embedded copper block to complete the manufacturing of the power supply circuit board. According to the precise machining method of the high-current-carrying copper block-embedded PCB, high-precision embedding of the copper block, controllable pressing thickness and residual-glue-free machining are achieved, and the problems of current-carrying capacity and reliability of a traditional power line board are solved.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing technology, and specifically to a precision machining method for a high current-carrying copper-embedded PCB. Background Technology

[0002] Copper-embedded power supply circuit boards have a wide range of applications in the market, especially in 5G communication equipment. Due to their excellent heat dissipation performance and space-saving features, copper-embedded power supply circuit boards are increasingly used in devices requiring high-performance heat dissipation. With the popularization of 5G communication and the future advancement of 6G technology, the market demand for copper-embedded power supply circuit boards will further increase.

[0003] The main technical defects of existing copper-embedded power circuit boards are:

[0004] 1. Copper block embedding process: The traditional method uses resin to fill and fix the copper block, which easily leads to a mismatch in the thermal expansion coefficients of the copper block and the substrate, and delamination is easy after high-temperature pressing (defect rate > 15%).

[0005] 2. When laminating and stacking copper blocks on multi-layer core boards, it is difficult to control the total thickness tolerance within ±0.2mm (the conventional process fluctuates within ±0.35mm);

[0006] 3. Residual adhesive residue or damage to the copper block surface during controlled-depth milling requires an additional cleaning process and also affects high-current conduction performance.

[0007] Therefore, it is necessary to provide a new process to solve the above-mentioned technical problems. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a precision processing method for high current-carrying copper-embedded PCBs, which can achieve high-precision embedding of copper blocks, controllable lamination thickness and residue-free processing, thus solving the problems of current carrying capacity and reliability of traditional power cord boards.

[0009] The technical solution of this invention is:

[0010] A precision machining method for a high current-carrying copper-embedded PCB includes the following steps:

[0011] Step S1, Core board processing: Provide a first core board and a second core board, perform single-sided etching on the first core board and the second core board to create inner layer circuits, and drill rivet holes;

[0012] Step S2, browning treatment;

[0013] Step S3, fabricate a bare board and run out copper embedding grooves: provide a third core board, etch the third core board on both sides until the copper layer is completely removed to form a bare board, and then run out copper embedding grooves on the bare board. The size of the copper embedding grooves is equivalent to that of the copper embedding block.

[0014] Step S4, copper embedding block pretreatment: roughen the surface of the copper embedding block and apply a micro-adhesive film.

[0015] Step S5: Embed the copper block into the light plate, then stack the first core plate, the light plate and the second core plate in sequence and fix them with rivets;

[0016] Step S6, pressing: heating rate 2-5℃ / min, heating to 180℃, holding pressure 1.3-1.6MPa, holding time 90-120min;

[0017] Step S7: Mechanical drilling, with hole position accuracy controlled within ±25µm;

[0018] Step S8, electroplating, to make the copper thickness of the hole wall ≥30um and the copper thickness of the surface ≥72um;

[0019] Step S9: Double-sided controlled-depth milling is performed using a carbide milling cutter with a diameter of φ1.8mm, a rotation speed of 25,000rpm, a feed rate of 0.8-1.5m / min, and a single-sided milling depth of 1.0mm±0.1mm. During the milling process, the milling depth is fed back in real time by laser ranging to avoid damage to the copper block. The milling thickness alignment accuracy is ±25μm, and the residual adhesive defect rate is <0.1%.

[0020] Step S10: Bend the copper block to complete the power circuit board fabrication.

[0021] Further, in step S1, the first core board includes a first core board copper foil and a second core board copper foil, the second core board includes a third core board copper foil and a fourth core board copper foil, and the second core board copper foil and the third core board copper foil are etched to form inner layer circuits, and the line width / line spacing of the inner layer circuits is ≥100um.

[0022] Furthermore, the rivet hole diameter is 2.5mm-3.5mm.

[0023] Furthermore, in step S2, the micro-etching amount of the browning treatment is 0.8-1.2 μm, and the thickness of the browning film is 0.3-0.5 μm.

[0024] Further, in step S3, the thickness of the light plate is 1.0 mm, the thickness of the copper-embedded block is 1.0 mm ± 0.02 mm, the depth of the copper-embedded groove is 1.0 mm ± 0.02 mm, and the size of the contact surface between the copper-embedded groove and the copper-embedded block is the size of the copper-embedded block ± 0.05 mm.

[0025] Furthermore, in step S4, the surface roughness of the copper-embedded block Ra = 1.2-1.5 μm, the micro-adhesive film is a polyimide film with a thickness of 50 μm and a temperature resistance of ≥200℃.

[0026] Furthermore, in step S8, pulse electroplating is employed, wherein:

[0027] The concentrations of each component in the plating solution are as follows: Cu2 + 60~80g / L, H2SO4180~220g / L, Cl-40~80ppm;

[0028] The plating solution temperature is 20-30℃, and the plating solution is stirred by air or mechanical means.

[0029] When the through-hole has a low depth-to-diameter ratio (DPR) ≤ 8:1, the current density is 2–4 A / dm. 2 The duty cycle is 20%-30%, the frequency is 100-300Hz, and the electroplating time is 60-90 minutes; when the through hole has a high aspect ratio (thickness-to-diameter ratio > 8:1), the current density is 4-6 A / dm. 2 The electroplating time is 90 min to 60 min.

[0030] Furthermore, in step S10, the bent copper block is annealed at a temperature of 150-170℃ for 30 minutes.

[0031] Compared with the prior art, the precision processing method for high current-carrying copper-embedded PCBs provided by the present invention has the following advantages:

[0032] I. The precision processing method of the high current-carrying copper-embedded PCB of the present invention uses single-sided etching for the first core board and the second core board to form single-sided circuit protection, and uses open copper grooves to embed the copper blocks, which can reduce the deformation of the lamination and the warpage rate is <0.15%, which is better than the warpage of traditional double-sided etching (the warpage of traditional through-face etching is more than 0.3%), and the lamination thickness tolerance is ±0.2mm.

[0033] II. The precision processing method for high-current-carrying copper-embedded PCBs of the present invention improves the alignment accuracy of the copper blocks through interlayer alignment and lamination control. Specifically, the use of rivets to fix the stacked layers results in an interlayer offset ≤25μm, which is superior to the alignment accuracy of traditional rivetless processes (typically interlayer offset >50μm). By optimizing lamination parameters—heating rate 2-5℃ / min, heating to 180℃, holding pressure 1.3-1.6MPa, and holding time 90-120min—the lamination thickness tolerance is ±0.2mm (compared to the traditional lamination thickness tolerance of ±0.35mm), with a measured range of only 0.1mm for a board thickness of 3.2mm.

[0034] Third, the precision processing method of the high current-carrying copper-embedded PCB of the present invention adopts a combination of rivet fixing and open board slotting, which enhances the interlayer bonding force, reduces the risk of delamination, and reduces the defect rate from 15% to 0.1%.

[0035] IV. The precision processing method for high current-carrying copper-embedded PCBs of the present invention eliminates the need for laser drilling and special filler materials compared with existing technologies, reducing costs by approximately 25%; the residual adhesive residue area at the edge of the copper-embedded block is <0.01mm. 2 The residual adhesive defect rate is <0.1%.

[0036] V. The precision processing method of the high current-carrying copper-embedded PCB of the present invention has a bending angle tolerance of ±0.5° and a current carrying capacity of up to 50A (temperature rise <15°), which is better than the 30A limit of traditional PCBs. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the circuit board structure obtained by the precision machining method of the high current-carrying copper-embedded block PCB of the present invention;

[0039] Figure 2 yes Figure 1 A schematic diagram of the structure of the optical board in the circuit board described above;

[0040] Figure 3 yes Figure 1 The diagram shown illustrates the connection between the bare board and the copper-embedded block in the circuit board.

[0041] Figure 4 yes Figure 3 The diagram shows the structure of the copper-embedded block. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below.

[0043] It should be noted that the descriptions of these embodiments are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] A precision machining method for a high current-carrying copper-embedded PCB includes the following steps:

[0045] Step S1, Core board processing: Provide a first core board and a second core board, perform single-sided etching on the first core board and the second core board to create inner layer circuits, and drill rivet holes;

[0046] Specifically, the first core board includes first core board copper foil L1 and second core board copper foil L2, the second core board includes third core board copper foil L3 and fourth core board copper foil L4, the first core board copper foil L1 and fourth core board copper foil L4 are fully copper, and the second core board copper foil L2 and third core board copper foil L3 are etched to create inner layer circuits, the line width / spacing of the inner layer circuits is ≥100um;

[0047] The rivet hole diameter is 2.5mm-3.5mm, with a positional accuracy of ±20um.

[0048] Step S2, browning treatment;

[0049] Specifically, the micro-etching amount of the browning treatment is 0.8-1.2 μm, and the thickness of the browning film is 0.3-0.5 μm. The browning treatment can enhance the interlayer bonding force.

[0050] Step S3, fabricate a bare board and run out copper embedding grooves: provide a third core board, etch the third core board on both sides until the copper layer is completely removed to form a bare board, and then run out copper embedding grooves on the bare board. The size of the copper embedding grooves is equivalent to that of the copper embedding block.

[0051] In this embodiment, the thickness of the light board is 1.0mm, the thickness of the copper inlay block is 1.0mm±0.02mm, the depth of the copper inlay groove is 1.0mm±0.02mm (reserving space for pressurization and adhesive flow), and the size of the contact surface between the copper inlay groove and the copper inlay block is the size of the copper inlay block ±0.05mm (gap compensation).

[0052] Step S4, copper embedding block pretreatment: roughen the surface of the copper embedding block and apply a micro-adhesive film.

[0053] Specifically, the surface roughness of the copper-embedded block is Ra = 1.2-1.5 μm, and the micro-adhesive film is a polyimide film with a thickness of 50 μm and a temperature resistance of ≥200℃. The polyimide film is applied to the non-contact surface of the copper-embedded block.

[0054] Step S5: Embed the copper block into the light plate, then stack the first core plate, the light plate and the second core plate in sequence and fix them with rivets;

[0055] The rivets are stainless steel rivets with a diameter that matches the rivet hole.

[0056] Step S6, pressing: heating rate 2℃ / min, heating to 180℃, holding pressure 1.5MPa, holding time 90min;

[0057] Step S7: Mechanical drilling with a hole diameter of 3.0mm / 6.6mm. Carbide drill bits are used for drilling the copper block area, and the hole position accuracy is controlled within ±25um.

[0058] Step S8, electroplating, to make the copper thickness of the hole wall ≥30um and the copper thickness of the surface ≥72um;

[0059] Specifically, the process begins with chemical copper plating, achieving a copper layer thickness ≥0.4µm and a backlight level ≥9.5. Following this, pattern electroplating is performed using pulse electroplating. The electroplating process is as follows:

[0060] The concentrations of each component in the plating solution are as follows: Cu2 + 60~80g / L, H2SO4180~220g / L, Cl-40~80ppm;

[0061] The plating bath temperature is 20-30℃ to control ion mobility and deposition rate; and the plating bath is agitated with air or mechanically to reduce concentration variations.

[0062] When the through-hole has a low aspect ratio (i.e., thickness-to-diameter ratio ≤ 8:1), the current density is 2–4 A / dm. 2 The duty cycle is 20%-30%, the frequency is 100-300Hz, and the electroplating time is 60-90 minutes. When the through-hole has a high aspect ratio (i.e., thickness-to-diameter ratio > 8:1), such as in an HDI board, the current density is 4-6 A / dm. 2 The electroplating time is 90 min to 60 min.

[0063] Step S9: Double-sided depth control milling is performed to the surface of the copper block, and the milling depth is fed back in real time through laser ranging.

[0064] Specifically, double-sided milling uses a carbide milling cutter with a diameter of 1.8mm and a speed of 25,000rpm. For different copper block thicknesses (0.8-1.2mm), the feed rate is adjusted to 0.8-1.5m / min, and the single-sided milling depth is 1.0mm±0.1mm.

[0065] Then, through residual adhesive testing, the area of ​​residual adhesive residue at the edge of the copper-embedded block was <0.01mm. 2 .

[0066] Step S10: Bend the copper-embedded block to complete the power circuit board fabrication;

[0067] The bent copper block is then annealed at a temperature of 150-170℃ for 30 minutes; the V-groove angle tolerance is ±0.5° and the bending radius is 1.0mm ±0.05mm.

[0068] In this invention, the core board used is FR4 with a Tg ≥ 170℃; the copper inlay block is C1100 pure copper with a thickness of 1.0mm; the press is a vacuum hot press with a pressure accuracy of ±0.5kg / cm. 2 The milling machine is a CNC precision milling machine with an accuracy of ±0.05mm.

[0069] In this embodiment, the process parameter requirements and actual measurement parameters are as follows:

[0070] 1. Pressing thickness: 3.2mm, based on 10 sets of measured data, the thickness ranges from 3.16 to 3.26mm;

[0071] 2. The copper thickness of the hole wall is ≥30um, and the actual measured copper thickness of the hole wall is 32-35um. Ten copper slices were taken from the hole, and the range was 0.3um.

[0072] 3. Bending: 90°, actual measurement 89.8-90.6°.

[0073] The precision machining method for high-current-carrying copper-embedded PCBs of the present invention, and the resulting circuit boards, compared with those produced by existing processes, show the following technical advantages:

[0074] index Traditional crafts This invention Lamination thickness tolerance ±0.35 ±0.2mm Copper block alignment accuracy ±50um ±25um Residual adhesive defect rate 5％ ＜0.1％ Bending angle tolerance ±3° ±0.5° Current carrying capacity 30A (temperature rise 25℃) 50A (temperature rise < 15°C)

[0075] Please refer to the following: Figures 1 to 4 ,in Figure 1 This is a schematic diagram of the circuit board structure obtained by the precision machining method of the high current-carrying copper-embedded block PCB of the present invention; Figure 2 yes Figure 1 A schematic diagram of the structure of the optical board in the circuit board described above; Figure 3 yes Figure 1 The diagram shown illustrates the connection between the bare board and the copper-embedded block in the circuit board. Figure 4 yes Figure 3 The diagram shows the structure of the copper-embedded block. The copper-embedded power circuit board of this embodiment includes a multilayer circuit board 1 formed by lamination, a through hole 2 formed through the multilayer circuit board 1, a first copper plating layer 3 deposited on the wall of the through hole 2, and a second copper plating layer 4 and a third copper plating layer 5 deposited on the surface of the outer copper foil of the multilayer circuit board 1, and outer circuitry is designed on the second copper plating layer 4 and the third copper plating layer 5.

[0076] The multilayer circuit board 1 includes a first core board 11, a bare board 12, and a second core board 13 stacked in sequence, and a copper inlay block 14 with one end embedded in the bare board 12 and the other end extending out of the bare board. The first core board 1, the bare board 2, and the second core board 3 are fixed by rivets and then pressed together.

[0077] The first core board 11 and the second core board 12 are FR4 core boards. Specifically, the first core board 11 includes an epoxy resin material layer 111, a first core board copper foil L1 and a second core board copper foil L2 stacked on both sides of the first epoxy resin material layer 111; the second core board 13 includes a second epoxy resin material layer 131, a third core board copper foil L3 and a fourth core board copper foil L4 stacked on both sides of the second epoxy resin material layer 131. The first core board copper foil L1 and the fourth core board copper foil L4 are entirely copper, while the second core board copper foil L2 and the third core board copper foil L3 are etched to create inner layer circuitry, with a linewidth / spacing of ≥100µm.

[0078] The first copper plating layer 3 is a hole wall copper layer with a thickness ≥30um; the second copper plating layer 4 is deposited on the surface of the first core board copper foil L1; and the third copper plating layer 5 is deposited on the surface of the fourth core board copper foil L4 with a thickness ≥72um.

[0079] The bare board 12 is formed by double-sided etching of the core board, and neither side of the bare board 12 contains copper foil. A copper embedding groove 121 is formed on the bare board 12. In this embodiment, the thickness of the copper embedding block 14 is 1.0mm ± 0.02mm, the groove depth of the copper embedding groove 121 is 1.0mm ± 0.02mm, the size of the contact surface between the copper embedding groove 121 and the copper embedding block 14 is equal to the size of the copper embedding block ± 0.05mm, and the position of the copper embedding block does not shift after it is embedded in the copper embedding groove.

[0080] Micro-adhesive film 141 is attached to the opposite sides of the copper embedding block 14. The micro-adhesive film 141 is a polyimide film with a thickness of 50 μm. The sides of the copper embedding block covered with the micro-adhesive film are the non-contact surfaces with the copper embedding groove, that is, the opposite sides in the thickness direction.

[0081] The copper inlay 14 extends beyond the bare plate and is bent to form a bent portion 142. The bending radius of the bent portion 142 is 1.0 mm ± 0.05 mm.

[0082] The copper-embedded power circuit board also includes a first heat dissipation hole 6 formed through the second copper plating layer 4 and the first core board 11, and a second heat dissipation hole 7 formed through the third copper plating layer 5 and the second core board, and the first heat dissipation hole 6 and the second heat dissipation hole 7 are distributed on two opposite sides of the copper-embedded block 14. There can be multiple first heat dissipation holes 6 and second heat dissipation holes.

[0083] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations made to these embodiments without departing from the principles and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A precision machining method for a high current-carrying copper-embedded PCB, characterized in that, Includes the following steps: Step S1, Core board processing: Provide a first core board and a second core board, perform single-sided etching on the first core board and the second core board to create inner layer circuits, and drill rivet holes; Step S2, browning treatment; Step S3, fabricate a bare board and run out copper embedding grooves: provide a third core board, etch the third core board on both sides until the copper layer is completely removed to form a bare board, and then run out copper embedding grooves on the bare board. The size of the copper embedding grooves is equivalent to that of the copper embedding block. Step S4, copper embedding block pretreatment: roughen the surface of the copper embedding block and apply a micro-adhesive film. Step S5: Embed the copper block into the light plate, then stack the first core plate, the light plate and the second core plate in sequence and fix them with rivets; Step S6, pressing: heating rate 2-5℃ / min, heating to 180℃, holding pressure 1.3-1.6MPa, holding time 90-120min; Step S7: Mechanical drilling, with hole position accuracy controlled within ±25µm; Step S8, electroplating, to make the copper thickness of the hole wall ≥30um and the copper thickness of the surface ≥72um; Step S9: Double-sided controlled-depth milling is performed using a carbide milling cutter with a diameter of φ1.8mm, a rotation speed of 25,000rpm, a feed rate of 0.8-1.5m / min, and a single-sided milling depth of 1.0mm±0.1mm. During the milling process, the milling depth is fed back in real time by laser ranging to avoid damage to the copper block. The alignment accuracy after milling is ±25μm, and the residual adhesive defect rate is <0.1%. Step S10: Bend the copper block to complete the power circuit board fabrication.

2. The precision machining method for high current-carrying copper-embedded PCB according to claim 1, characterized in that, In step S1, the first core board includes a first core board copper foil and a second core board copper foil, the second core board includes a third core board copper foil and a fourth core board copper foil, and the second core board copper foil and the third core board copper foil are etched to form inner layer circuits, and the line width / line spacing of the inner layer circuits is ≥100um.

3. The precision machining method for high current-carrying copper-embedded PCB according to claim 2, characterized in that, The rivet hole diameter is 2.5mm-3.5mm.

4. The precision machining method for high current-carrying copper-embedded PCB according to claim 1, characterized in that, In step S2, the micro-etching amount of the browning treatment is 0.8-1.2 μm, and the thickness of the browning film is 0.3-0.5 μm.

5. The precision machining method for a high current-carrying copper-embedded PCB according to claim 1, characterized in that, In step S3, the thickness of the light plate is 1.0 mm, the thickness of the copper inlay block is 1.0 mm ± 0.02 mm, the depth of the copper inlay groove is 1.0 mm ± 0.02 mm, and the size of the contact surface between the copper inlay groove and the copper inlay block is equal to the size of the copper inlay block ± 0.05 mm.

6. The precision machining method for a high current-carrying copper-embedded PCB according to claim 1, characterized in that, In step S4, the surface roughness of the copper-embedded block is Ra = 1.2-1.5 μm, and the micro-adhesive film is a polyimide film with a thickness of 50 μm and a temperature resistance of ≥200℃.

7. The precision machining method for a high current-carrying copper-embedded PCB according to claim 1, characterized in that, In step S8, pulse electroplating is used, wherein: The concentrations of each component in the plating solution are as follows: Cu2 + 60~80g / L, H2SO4180~220g / L, Cl-40~80ppm; The plating solution temperature is 20-30℃, and the plating solution is stirred by air or mechanical means. When the through-hole has a low depth-to-diameter ratio (≤8:1), the current density is 2–4 A / dm. 2 The duty cycle is 20%-30%, the frequency is 100-300Hz, and the electroplating time is 60-90 minutes; when the through-hole has a high aspect ratio (thickness-to-diameter ratio > 8:1), the current density is 4-6 A / dm. 2 The electroplating time is 90 min to 60 min.

8. The precision machining method for a high current-carrying copper-embedded PCB according to claim 1, characterized in that, In step S10, the bent and embedded copper block is annealed at a temperature of 150-170℃ for 30 minutes.

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