Diamond copper block and method for milling grooves of diamond copper block in circuit board

Abstract

The present invention discloses a diamond copper block and a method for milling grooves in the diamond copper block in a circuit board. The method comprises the following steps: cutting a core board and a polypropylene sheet according to the size of the panel, and opening windows on the core board and the PP sheet at positions corresponding to the buried copper blocks; stacking the core board and the PP sheet in sequence as required to form a composite board, forming buried copper slots at the corresponding openings on the core board and the PP sheet, and then placing the diamond copper block in the buried copper slots; stacking a prepreg and an outer copper foil on both surfaces of the composite board in sequence, and pressing them together to form a multilayer board; performing controlled-depth milling on the side of the multilayer board adjacent to the copper paste at positions corresponding to the grooves, wherein the size of the milled groove is smaller than the size of the groove so that a copper layer remains on the groove wall and the groove bottom after the groove is milled; and then removing the copper layer on the groove wall and the groove bottom by etching. The method of the present invention solves the problem that groove milling cannot be performed on existing single-material diamonds using a whole block.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, in particular to a diamond copper block and a method for milling grooves on the diamond copper block in a circuit board. Background Art

[0002] With the continuous development of the electronic communications industry and automotive electronics, the requirements for related circuit board products are becoming higher and higher, and they tend to be miniaturized and multifunctional, so the requirements for the heat dissipation performance of circuit boards are becoming higher and higher.

[0003] The products with high heat dissipation performance in the industry are mainly distributed in the following production processes:

[0004] 1: Metal-based products. The raw material cost of such products is high, and it is difficult to produce multi-layer products.

[0005] 2: Thick copper products. This type of product has good heat dissipation effect. The main disadvantage is that it cannot produce precise wiring and the product has limitations.

[0006] 3: The thermal conductivity of buried copper blocks and buried ceramic (aluminum nitride, aluminum oxide) products is not enough to meet the ultra-high heat dissipation requirements in the industry, and the products have limitations.

[0007] The main manifestations are: (1) Copper blocks and ceramic blocks (aluminum nitride, aluminum oxide) used as heat sinks have limited thermal conductivity, so these products have a greater risk of delamination and explosion, and their service life is limited.

[0008] (2) The surface roughness of the copper block and ceramic block (aluminum nitride, aluminum oxide) heat sink is relatively small, and the bonding ability with the dielectric layer after pressing is insufficient. At the same time, the surface roughness of the heat sink is relatively small and the bonding ability with the solder mask and other coatings is insufficient. The risk of product failure is relatively high under long-term harsh environment.

[0009] (3) The thermal expansion coefficients of copper blocks and ceramic blocks (aluminum nitride, aluminum oxide) are fixed and cannot match the thermal expansion coefficients of prepregs, resin inks, and other insulating materials that are significantly different from those of the radiator. When the thermal expansion coefficient difference is too large, the product is prone to cracking and delamination, and other quality abnormalities. Therefore, there are certain restrictions on the selection of materials for embedded products.

[0010] Problems with existing processes: In addition to high costs, wiring layouts, and a series of problems with manufacturing processes, the high-heat dissipation performance products in the above industries are also unable to meet the thermal conductivity needs of electronic components with extremely high heat dissipation requirements, especially 5G RF chips. When high-heat generating components are working, metal substrates, thick copper plates, embedded copper blocks, and embedded ceramic blocks (aluminum nitride, aluminum oxide) can no longer meet their heat dissipation needs.

[0011] Diamond has an ultra-high thermal conductivity of up to 2000W / m·K, making it the highest known natural material. Embedding diamond within a circuit board offers excellent thermal conductivity and heat dissipation. However, diamond is difficult to manufacture in large sizes and difficult to shape. Existing circuit board production equipment is generally unable to directly mill grooves within embedded diamonds, making existing methods unable to meet the requirements for controlled-depth milling of embedded diamond grooves. Summary of the Invention

[0012] In view of the above-mentioned technical defects, the present invention provides a diamond copper block and a method for milling grooves of the diamond copper block in a circuit board. The diamond copper block formed by combining diamond and copper slurry can facilitate the milling operation when it is buried in the circuit board.

[0013] In the first aspect, in order to solve the above-mentioned technical problems, the present invention provides a diamond copper block used in circuit board production, comprising a block of diamond, wherein a groove is provided on one surface of the diamond at a position corresponding to the position to be milled, and the groove is filled with solidified copper slurry.

[0014] Furthermore, a tool is used to machine the groove on one surface of the diamond, and then copper slurry is filled in the groove and solidified to form a diamond copper block.

[0015] Furthermore, diamond powder is used to produce a block of diamond with the groove through an integral molding method, and then copper slurry is filled in the groove and solidified to form a diamond copper block.

[0016] In a second aspect, the present invention further provides a method for milling a groove on a diamond copper block in a circuit board, comprising the following steps:

[0017] S1. Cut out the core board and PP sheet according to the size of the panel, and make windows on the core board and PP sheet at the positions corresponding to the buried copper blocks;

[0018] S2, stacking the core plate and the PP sheet in sequence as required to form a laminated plate, forming buried copper slots at the corresponding window openings of the core plate and the PP sheet, and then placing the diamond copper block as described in any one of the first aspects into the buried copper slots;

[0019] S3, sequentially laminating a prepreg and an outer copper foil on both surfaces of the laminate, and then laminating them to form a multilayer board;

[0020] S4. Performing controlled-depth milling on the multilayer board at a position corresponding to the groove on the side adjacent to the copper paste, wherein the size of the milled groove is smaller than the size of the groove, so that copper layers remain on both the groove wall and the groove bottom after the groove is milled;

[0021] S5. Finally, the copper layer at the groove wall and the groove bottom is removed by etching to reveal the diamond groove wall and the groove bottom.

[0022] Furthermore, in step S4, the size of the groove during milling is 0.15 mm smaller than the size of the groove on one side, so that the thickness of the residual copper on the groove wall and the groove bottom after milling is both 0.15 mm.

[0023] Furthermore, in step S5, a film is applied to the multilayer board, and then the milled grooves are exposed by exposure and development, and the remaining copper layer at the groove walls and groove bottoms is removed by etching to expose the diamond groove walls and groove bottoms.

[0024] Furthermore, the following steps are included between steps S3 and S4:

[0025] S31. Perform drilling, copper deposition, full-board electroplating, outer layer circuit production and solder mask production processes on the multi-layer board in sequence.

[0026] Furthermore, the following steps are included between steps S3 and S4:

[0027] S31. On the multilayer board, drilling, first copper deposition, first full-board electroplating, back drilling, resin plugging, sanding, second copper deposition, second full-board electroplating, outer layer circuit production and solder mask production processes are carried out in sequence.

[0028] Furthermore, after step S5, the following steps are also included:

[0029] S6. Perform surface treatment on the multilayer board.

[0030] Furthermore, after step S6, the following steps are also included:

[0031] S7. Perform molding processing on the multilayer board to obtain a circuit board embedded with diamonds.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The diamond copper block provided in the present invention forms grooves at positions corresponding to milling grooves in the diamond embedded in the circuit board before the circuit board is manufactured, and copper slurry is filled in the grooves to make both surfaces of the diamond copper block flat. This avoids the problem of board bursting and board depression caused by the grooves when the diamond copper block is embedded in the inner layer of the circuit board for pressing.

[0034] Secondly, when the diamond copper block is buried inside the multilayer board by pressing, since the milling groove position is copper slurry, the groove processing equipment on the circuit board production line can conveniently mill the groove at the position of the corresponding groove, solving the problem that groove milling cannot be performed on a whole piece of single-material diamond in the existing process; and a copper layer remains on the groove wall and groove bottom during groove milling, avoiding the problem of tool breakage caused by direct contact between the tool and the diamond during groove milling. Then, by utilizing the etching resistance of diamond, the copper layer remaining on the groove wall and groove bottom is removed by etching to reveal the diamond on the groove wall and groove bottom, thereby producing a high-precision power amplifier groove, ensuring that the size of the controlled depth milling area meets the design requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the diamond copper block in the embodiment;

[0036] Figure 2 2 is a cross-sectional view of a diamond copper block in an embodiment. DETAILED DESCRIPTION

[0037] In order to more fully understand the technical content of the present invention, the technical solution of the present invention will be further introduced and illustrated in conjunction with specific embodiments below.

[0038] Example 1

[0039] like Figure 1-2 As shown in this embodiment, a diamond copper block for use in circuit board production comprises a block of diamond 1. A groove 10 is formed on one surface of the diamond 1 at a location corresponding to the location to be milled. Groove 10 is filled with solidified copper paste 2. Specifically, molten copper paste 2 is filled into groove 10 and then solidified, allowing the solidified copper paste to combine with the diamond to form a diamond copper block. The copper paste surface is flush with the diamond surface, resulting in a smooth surface. It will be appreciated that the depth and dimensions of the groove are consistent with those required for milling grooves in circuit board production.

[0040] In one embodiment, the diamond copper block is manufactured by machining the groove on a surface of the diamond using a tool, and then filling the groove with copper slurry and solidifying the slurry to form the diamond copper block.

[0041] In another embodiment, the diamond copper block is manufactured by using diamond powder in combination with a forming mold and manufacturing a block of diamond with the groove by an integrated molding method such as hot isostatic pressing, and then filling the groove with copper slurry and solidifying it to form a diamond copper block.

[0042] In one embodiment, the length and width of the diamond are both 38 mm.

[0043] In one embodiment, the length of the groove is 21.21±0.1 mm, and the width is 10.42±0.1 mm.

[0044] Example 2

[0045] The method for manufacturing a circuit board with a diamond copper block embedded therein shown in this embodiment includes the following processing steps in sequence:

[0046] (1) Cutting: Cut out several core boards according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the thickness of the copper layer on both surfaces of the core board is 0.5oz.

[0047] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, use a vertical coating machine to coat the photosensitive film, the film thickness of the photosensitive film is controlled at 8μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler), and the inner layer circuit pattern is formed after development; inner layer etching, the exposed and developed core board is etched to etch the inner layer circuit, and the inner layer line width is measured to be 3mil; inner layer AOI, and then check the inner layer circuit for defects such as open and short circuits, circuit gaps, and circuit pinholes. Defective products will be scrapped, and products without defects will be sent to the next process.

[0048] (3) Windowing: Windows are opened at the positions corresponding to the buried copper blocks on the core board and the PP sheet; the size of the window on one side is 0.075 to 0.2 mm larger than the size of the buried copper block.

[0049] (4) Lamination: Lay the core plate and the PP sheet in sequence as required to form a laminated plate, and form buried copper slots at the corresponding openings of the core plate and the PP sheet, and then place the diamond copper block described in the embodiment into the buried copper slots.

[0050] (5) Lamination: The browning speed is determined by the thickness of the bottom copper. The semi-cured sheet and the outer copper foil are sequentially laminated on both surfaces of the laminate. Then, the laminate is pressed in a vacuum laminator under appropriate lamination conditions according to the Tg of the sheet material to form a multilayer board.

[0051] (6) Drilling: Based on existing drilling technology, drilling is performed on the multilayer board according to design requirements.

[0052] (6) Copper plating: A thin layer of copper is deposited on the board surface and the hole wall using the chemical copper plating method. The backlight test is level 10, and the thickness of the copper plating in the hole is 0.5μm.

[0053] (7) Full board electroplating: The multi-layer board is electroplated throughout the board according to the design requirements to increase the thickness of the hole copper and the board surface copper layer.

[0054] (8) Production of outer circuit (negative process): Transfer of outer pattern, coating of photosensitive film on multilayer board with vertical coating machine, thickness of photosensitive film controlled at 8μm, using fully automatic exposure machine, exposure of outer circuit with 5-6 grid exposure ruler (21 grid exposure ruler), forming outer circuit pattern after development; outer layer etching, etching the exposed and developed multilayer board to produce outer circuit, outer line width measured at 3mil; outer layer AOI, then check the outer circuit for defects such as open and short circuit, circuit gap, circuit pinhole, etc., scrap the defective ones, and send the non-defective ones to the next process.

[0055] (9) Solder mask and silk screen characters: After silk screen printing solder mask ink on the surface of the multilayer board, it is sequentially processed through pre-curing, exposure, development and heat curing to solidify the solder mask ink into a solder mask layer; specifically, the solder mask ink and the characters on the TOP surface are added with "UL mark", so that a layer is coated on the circuits and substrates that do not need to be soldered to prevent bridging between circuits during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time beautify the appearance.

[0056] (10) Milling groove: Controlled depth milling groove is performed at the position of the corresponding groove on the side of the multilayer board adjacent to the copper paste. The size of the milling groove is smaller than the size of the groove so that copper layer remains on the groove wall and groove bottom after milling.

[0057] In one embodiment, the size of the groove during milling is 0.15 mm smaller than the size of the groove on one side, so that the thickness of the residual copper on the groove wall and the groove bottom after milling is 0.15 mm.

[0058] (11) Etching: A film is applied to the multilayer board, and then the milling groove is exposed through exposure and development. The board surface outside the milling groove area is covered with a film for protection, and then the remaining copper layer at the groove wall and groove bottom is removed by etching to reveal the diamond groove wall and groove bottom, forming a release groove.

[0059] (12) Surface treatment (nickel-gold immersion): A nickel layer and a gold layer of a certain required thickness are uniformly deposited on the wall and bottom of the power amplifier slot and the copper surface of the solder pad at the solder mask window position through chemical principles. The thickness of the nickel layer is: 3-5μm; the thickness of the gold layer is: 0.05-0.1μm.

[0060] (13) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0061] (14) Molding: According to the existing technology and the design requirements, the circuit board is made with a shape tolerance of + / -0.05mm.

[0062] (15) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0063] (16) FQA: Re-test the appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness of the circuit board to see if they meet the customer's requirements.

[0064] (17) Packaging: According to the packaging method and packaging quantity required by the customer, the circuit board is sealed and packed, and desiccant and humidity card are placed before shipment.

[0065] Example 3

[0066] The manufacturing method of a circuit board with a diamond copper block embedded therein shown in this embodiment is basically the same as the method described in Example 2, except that steps (7) and (8) further include back drilling, resin plugging, sanding, second copper deposition and second full-board electroplating.

[0067] Among them, back drilling is to back drill at the hole position that needs to be back drilled to form a back drilled hole; then the back drilled hole is plugged with resin and solidified, and then the resin protruding from the hole is removed by sanding the board with a sand belt to make the board surface level; a layer of copper is plated on the resin surface of the hole through the second copper deposition and the second full-board electroplating.

[0068] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for milling a groove on a diamond copper block in a circuit board, characterized in that: The diamond copper block comprises a block of diamond, a surface of the diamond having a groove formed thereon at a position corresponding to a groove to be milled, the groove being filled with copper slurry, and the method comprising the following steps: S1. Cut out the core board and PP sheet according to the size of the panel, and make windows on the core board and PP sheet at the positions corresponding to the buried copper blocks; S2, stacking the core plate and the PP sheet in sequence as required to form a laminated board, forming buried copper slots at the corresponding window openings of the core plate and the PP sheet, and then placing the diamond copper block into the buried copper slots; S3, sequentially laminating a prepreg and an outer copper foil on both surfaces of the laminate, and then laminating them to form a multilayer board; S4. Performing controlled-depth milling on the multilayer board at a position corresponding to the groove on the side adjacent to the copper paste, wherein the size of the milled groove is smaller than the size of the groove, so that copper layers remain on both the groove wall and the groove bottom after the groove is milled; S5. Finally, the copper layer at the groove wall and the groove bottom is removed by etching to reveal the diamond groove wall and the groove bottom.

2. The method for milling a groove of a diamond copper block in a circuit board according to claim 1, characterized in that: The groove is machined on one surface of the diamond using a tool, and then the groove is filled with copper slurry and solidified to form a diamond copper block.

3. The method for milling a groove on a diamond copper block in a circuit board according to claim 1, characterized in that: Diamond powder is used to produce a block diamond with the groove through an integrated molding method, and then copper slurry is filled in the groove and solidified to form a diamond copper block.

4. The method for milling a groove on a diamond copper block in a circuit board according to claim 1, wherein: In step S4, the size of the groove during milling is 0.15 mm smaller than the size of the groove on one side, so that the thickness of the residual copper on the groove wall and the groove bottom after milling is both 0.15 mm.

5. The method for milling a groove on a diamond copper block in a circuit board according to claim 4, characterized in that: In step S5, a film is applied to the multilayer board, and then the milled grooves are exposed by exposure and development, and the remaining copper layer at the groove walls and groove bottoms is removed by etching to expose the diamond groove walls and groove bottoms.

6. The method for milling a groove of a diamond copper block in a circuit board according to any one of claims 1 to 5, characterized in that: The following steps are also included between steps S3 and S4: S31. Perform drilling, copper deposition, full-board electroplating, outer layer circuit production and solder mask production processes on the multi-layer board in sequence.

7. The method for milling a groove on a diamond copper block in a circuit board according to any one of claims 1 to 5, characterized in that: The following steps are also included between steps S3 and S4: S31. On the multilayer board, drilling, first copper deposition, first full-board electroplating, back drilling, resin plugging, sanding, second copper deposition, second full-board electroplating, outer layer circuit production and solder mask production processes are carried out in sequence.

8. The method for milling a groove on a diamond copper block in a circuit board according to claim 1, wherein: After step S5, the following steps are also included: S6. Perform surface treatment on the multilayer board.

9. The method for milling a groove on a diamond copper block in a circuit board according to claim 8, characterized in that: After step S6, the following steps are also included: S7. Perform molding processing on the multilayer board to obtain a circuit board embedded with diamonds.

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