Automobile 77GHZ millimeter wave radar board PCB and preparation method thereof

Abstract

The invention provides an automobile 77GHZ millimeter wave radar board PCB, which comprises a PCB main body, and is characterized in that the PCB main body is composed of a first dielectric layer, a first conductive layer, a second dielectric layer, a second conductive layer, a third dielectric layer and a third conductive layer which are stacked in sequence; the first dielectric layer and the third dielectric layer are both made of a modified polytetrafluoroethylene material; the second dielectric layer is made of an epoxy resin-based composite material with high heat-conducting property; the first conductive layer, the second conductive layer and the third conductive layer are all made of high-purity electrolytic copper foil; blind buried holes are arranged among the first conductive layer, the second conductive layer and the third conductive layer. According to the invention, the PCB main body adopts the modified polytetrafluoroethylene material, the high-purity electrolytic copper foil and the chemical nickel-gold plating process, so that the transmission loss of high-frequency signals is remarkably reduced, the signal transmission quality is improved, the high-precision requirement of 77GHZ millimeter-wave radar on signal transmission can be met, and the detection distance and precision of the radar are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of PCB board, and particularly relates to an automobile 77GHZ millimeter wave radar board PCB and a preparation method thereof. BACKGROUND

[0002] The automobile 77GHz millimeter wave radar system is a high-frequency radar device, which is mainly used for vehicle ranging, speed detection and direction recognition, and is a core component of an intelligent driving auxiliary system (such as ACC cruise and AEB active brake). In the automobile 77GHZ millimeter wave radar system, the PCB as a key carrier directly affects the radar detection accuracy and reliability.

[0003] At present, the traditional PCB has many problems: firstly, the dielectric constant and dielectric loss tangent value of the conventional substrate material used are high, and when the 77GHZ high-frequency signal is transmitted, the signal is seriously attenuated, which limits the radar detection distance and reduces the accuracy; secondly, the interlayer alignment accuracy of the multilayer PCB is insufficient, and the via interconnection reliability is poor, which is prone to signal transmission interruption, short circuit and other faults; thirdly, the existing PCB heat dissipation structure design is unreasonable, and the heat generated by the electroplated element cannot be dissipated in time, which leads to high working temperature of the element, performance degradation or even damage.

[0004] Therefore, it is urgent to develop a high-performance PCB suitable for automobile 77GHZ millimeter wave radar and a preparation method thereof. SUMMARY

[0005] In order to solve the above technical problems, the application provides an automobile 77GHZ millimeter wave radar board PCB and a preparation method thereof. By using a new material, optimizing the structure design and innovating the preparation process, the signal transmission loss is reduced, the interlayer alignment accuracy and via interconnection reliability are improved, and the heat dissipation performance is enhanced, so as to improve the overall performance and stability of the radar board PCB.

[0006] An automobile 77GHZ millimeter wave radar board PCB comprises a PCB main body, which is composed of a first dielectric layer, a first conductive layer, a second dielectric layer, a second conductive layer, a third dielectric layer and a third conductive layer which are sequentially stacked.

[0007] Preferably, the first dielectric layer and the third dielectric layer both adopt a modified polytetrafluoroethylene material.

[0008] Preferably, the second dielectric layer adopts an epoxy resin-based composite material with high heat dissipation performance.

[0009] Preferably, the first conductive layer, the second conductive layer and the third conductive layer all adopt high-purity electrolytic copper foil.

[0010] Preferably, the first conductive layer, the second conductive layer and the third conductive layer are provided with blind buried holes, which realize the function of electrical connection.

[0011] Preferably, the edge of the PCB body is provided with a metal heat dissipation frame, which is connected with the ground circuit of the first conductive layer, the second conductive layer and the third conductive layer, and the metal heat dissipation frame is made of aluminum alloy material with high thermal conductivity.

[0012] A preparation method of the automobile 77GHZ millimeter wave radar board PCB is as follows:

[0013] Step one: medium layer preparation,

[0014] The first step is finished medium layer preparation, and the second step is second medium layer preparation.

[0015] Step two: conductive layer making,

[0016] The first step is conductive layer making, and the second step is nickel-gold plating processing.

[0017] Step three: blind buried hole making,

[0018] The first step is drilling, and the second step is roughening treatment.

[0019] Step four: lamination and pressing,

[0020] The first step is stacking, and the second step is hot pressing.

[0021] Step five: metal heat dissipation frame installation, a mounting groove is milled on the edge of the PCB body, the pre-prepared aluminum alloy metal heat dissipation frame is embedded into the mounting groove, and the metal heat dissipation frame is firmly connected with the ground circuit of the first conductive layer, the second conductive layer and the third conductive layer through welding process.

[0022] Preferably, in the first step of the first step of step one, for the first medium layer and the third medium layer, modified polytetrafluoroethylene resin and nano-sized silicon dioxide particles are mixed in a high-speed mixer to form a uniform mixture, and then a flow casting process is adopted to form a medium layer green body with a thickness of 0.15mm, and then sintering is performed to obtain a finished medium layer, i.e. the first medium layer and the third medium layer.

[0023] In the second step of step one, for the second medium layer, epoxy resin and aluminum nitride ceramic particles are mixed in a planetary mixer to form a uniform composite slurry, and a pressing forming process is adopted to press to form a second medium layer with a thickness of 0.1mm.

[0024] Preferably, in the first step of step two, the conductive layer is prepared by uniformly coating the prepared medium layer with photoresist, forming a circuit pattern through exposure and development processes, plating high-purity electrolytic copper foil on the circuit pattern protected by the photoresist by electroplating copper process, forming a conductive layer, and then removing the remaining photoresist by a photoresist removal process.

[0025] In the second step of step two, the surface of the conductive layer is subjected to a chemical nickel-gold plating process, which is performed in the order of chemical nickel plating and chemical gold plating, and the thickness of the nickel layer and the gold layer is strictly controlled.

[0026] Preferably, in the first step of step three, according to the design requirements, ultraviolet laser drilling technology is used to drill holes at the positions where blind holes or buried holes are required, forming blind holes or buried holes.

[0027] In the second step of step three, the blind and buried holes are subjected to roughening treatment, and then the hole walls are thickened by chemical copper plating process to make the copper layer thickness of the hole walls meet the design requirements.

[0028] Preferably, in the first step of step four, the prepared medium layers and conductive layers are stacked in the designed order, and an appropriate amount of prepreg is placed between the layers.

[0029] In the second step of step four, the stacked plate is placed in a hot press to heat and press, so that the layers are tightly combined to form a complete PCB main body.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] 1. In the present application, the PCB main body is prepared by using modified polytetrafluoroethylene material and high-purity electrolytic copper foil, and chemical nickel-gold plating process, which significantly reduces the high-frequency signal transmission loss, improves the signal transmission quality, and meets the high-precision requirements of 77GHz millimeter wave radar for signal transmission, thereby improving the detection distance and precision of the radar.

[0032] 2. In the present application, the second medium layer uses high-thermal-conductivity epoxy resin-based composite material, which, in combination with the metal heat dissipation frame at the edge of the PCB main body, forms an efficient heat dissipation channel, which can quickly dissipate the heat generated by the PCB main body during operation, reduce the working temperature of the components, ensure the performance and service life of the electronic components, and improve the reliability and stability of the PCB main body.

[0033] 3. In the present application, laser drilling technology is used to make blind and buried holes, and the hole walls are subjected to chemical copper plating thickening treatment, which improves the interlayer alignment accuracy and via interconnection reliability, reduces the occurrence of signal transmission interruption, short circuit and other faults, and ensures the stability and reliability of signal transmission.

[0034] 4. In the application, the innovative preparation process can precisely control the structure and performance of the PCB, improve the qualified rate and production efficiency of the product, and is conducive to realizing large-scale production, from the preparation of the dielectric layer to the preparation of the conductive layer, and then to the lamination and pressing. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a schematic structural diagram of a PCB body of the application.

[0036] Figure 2 is a schematic structural diagram of a sectional structure of the PCB body of the application.

[0037] Figure 3 is a process diagram of the preparation method of the application.

[0038] Figure 4 is a process diagram of the preparation of the dielectric layer of the application.

[0039] Figure 5 is a process diagram of the preparation of the conductive layer of the application.

[0040] Figure 6 is a process diagram of the preparation of the blind via of the application.

[0041] Figure 7 is a process diagram of the lamination and pressing of the application.

[0042] In the drawings:

[0043] 1, PCB body; 11, first dielectric layer; 12, first conductive layer; 13, second dielectric layer; 14, second conductive layer; 15, third dielectric layer; 16, third conductive layer; 17, metal heat dissipation frame. DETAILED DESCRIPTION

[0044] The application will be specifically described below with reference to the drawings, such as Figure 1 and Figure 2 shown, a 77GHz millimeter wave radar board PCB for an automobile includes a PCB body 1 composed of a first dielectric layer 11, a first conductive layer 12, a second dielectric layer 13, a second conductive layer 14, a third dielectric layer 15, and a third conductive layer 16 stacked in sequence.

[0045] In the embodiment, specifically, the first dielectric layer 11 and the third dielectric layer 15 both use modified polytetrafluoroethylene (PTFE) material, the modified polytetrafluoroethylene (PTFE) material is modified by adding nano-sized silicon dioxide particles, the mass fraction of the nano-sized silicon dioxide particles is 15%, the dielectric constant of the material is reduced to 2.3, the dielectric loss tangent value is less than 0.002, and the high-frequency signal transmission loss is effectively reduced.

[0046] In the embodiment, specifically, the second dielectric layer 13 adopts an epoxy resin-based composite material with high thermal conductivity, the epoxy resin-based composite material uniformly disperses aluminum nitride ceramic particles with a mass fraction of 30% in the epoxy resin, and the thermal conductivity reaches 3.5 W / (m·K), which can quickly conduct the heat generated during the operation of the PCB.

[0047] In the embodiment, specifically, the first conductive layer 12, the second conductive layer 14, and the third conductive layer 16 all adopt high-purity electrolytic copper foil, the copper content is not less than 99.98%, and a chemical nickel-gold plating process is adopted on the surface of the copper foil, the thickness of the nickel layer is 3-5 μm, and the thickness of the gold layer is 0.1-0.3 μm, which reduces the line resistance, improves the oxidation resistance, and improves the signal transmission quality.

[0048] In the embodiment, specifically, blind buried holes are arranged between the first conductive layer 12, the second conductive layer 14, and the third conductive layer 16, the blind buried holes realize electrical connection, the blind buried holes are made by laser drilling technology, the aperture is 0.15 mm, the roughness Ra of the hole wall is ≤0.5 μm, the stability and reliability of signal transmission are ensured, and the inner wall of the blind buried hole is thickened by chemical copper plating process, so that the thickness of the copper layer of the hole wall is uniformly 25 μm.

[0049] In the embodiment, specifically, a metal heat dissipation frame 17 is arranged at the edge of the PCB main body 1, the metal heat dissipation frame 17 is connected with the ground line of the first conductive layer 12, the second conductive layer 14, and the third conductive layer 16, the metal heat dissipation frame 17 adopts aluminum alloy material with high thermal conductivity, and the thickness is 1.5 mm, which enhances the heat dissipation capacity of the PCB.

[0050] In the embodiment, combined with the accompanying drawings, Figure 3 As shown in the drawings, a preparation method of a 77GHz millimeter wave radar board PCB for an automobile is as follows:

[0051] S1: dielectric layer preparation,

[0052] S11: finished product dielectric layer preparation; S12: second dielectric layer preparation;

[0053] S2: conductive layer making,

[0054] S21: making a conductive layer; S22: nickel-gold plating processing;

[0055] S3: blind buried hole making,

[0056] S31: drilling; S32: roughening treatment;

[0057] S4: lamination and pressing,

[0058] S41: stacking; S42: hot pressing.

[0059] S5: metal heat dissipation frame installation, milling installation groove on the edge of the PCB main body 1, embedding the pre-prepared aluminum alloy metal heat dissipation frame 17 into the installation groove, and firmly connecting the metal heat dissipation frame 17 with the ground circuit of the first conductive layer 12, the second conductive layer 14 and the third conductive layer 16 through the welding process.

[0060] In the embodiment, the preparation of the first medium layer 11 and the third medium layer 15 in S11 of S1 is shown in FIG. 2. The modified polytetrafluoroethylene resin and the nano-sized silicon dioxide particles are mixed in a high-speed mixer to form a uniform mixture, and then a flow casting process is used to form a medium layer green body with a thickness of 0.15 mm. After sintering, the first medium layer 11 and the third medium layer 15 are obtained. Figure 4

[0061] In the embodiment, the preparation of the second medium layer 13 in S12 of S1 is shown in FIG. 3. The epoxy resin and the aluminum nitride ceramic particles are mixed in a planetary mixer to form a uniform composite slurry, and then a pressing process is used to press the second medium layer 13 with a thickness of 0.1 mm.

[0062] In the embodiment, the preparation of the first medium layer 11 and the third medium layer 15 in S11 of S1 is shown in FIG. 2. The modified polytetrafluoroethylene resin and the nano-sized silicon dioxide particles are mixed in a high-speed mixer to form a uniform mixture, and then a flow casting process is used to form a medium layer green body with a thickness of 0.15 mm. After sintering, the first medium layer 11 and the third medium layer 15 are obtained. Figure 5

[0063] In the embodiment, the preparation of the first medium layer 11 and the third medium layer 15 in S11 of S1 is shown in FIG. 2. The modified polytetrafluoroethylene resin and the nano-sized silicon dioxide particles are mixed in a high-speed mixer to form a uniform mixture, and then a flow casting process is used to form a medium layer green body with a thickness of 0.15 mm. After sintering, the first medium layer 11 and the third medium layer 15 are obtained.

[0064] In the embodiment, the preparation of the first medium layer 11 and the third medium layer 15 in S11 of S1 is shown in FIG. 2. The modified polytetrafluoroethylene resin and the nano-sized silicon dioxide particles are mixed in a high-speed mixer to form a uniform mixture, and then a flow casting process is used to form a medium layer green body with a thickness of 0.15 mm. After sintering, the first medium layer 11 and the third medium layer 15 are obtained. Figure 6

[0065] In the embodiment, the preparation of the first medium layer 11 and the third medium layer 15 in S11 of S1 is shown in FIG. 2. The modified polytetrafluoroethylene resin and the nano-sized silicon dioxide particles are mixed in a high-speed mixer to form a uniform mixture, and then a flow casting process is used to form a medium layer green body with a thickness of 0.15 mm. After sintering, the first medium layer 11 and the third medium layer 15 are obtained.

[0066] In the embodiment, the preparation of the first medium layer 11 and the third medium layer 15 in S11 of S1 is shown in FIG. 2. The modified polytetrafluoroethylene resin and the nano-sized silicon dioxide particles are mixed in a high-speed mixer to form a uniform mixture, and then a flow casting process is used to form a medium layer green body with a thickness of 0.15 mm. After sintering, the first medium layer 11 and the third medium layer 15 are obtained. Figure 7 ​​​As shown, in S41 of S4, the prepared first dielectric layer 11, first conductive layer 12, second dielectric layer 13, second conductive layer 14, third dielectric layer 15 and third conductive layer 16 are sequentially stacked in the designed order, and an appropriate amount of prepreg (PP sheet) is placed between the layers.

[0067] In this embodiment, specifically, in S42 of S4, the stacked board is placed in a hot press for hot pressing, so that the layers are tightly combined to form a complete PCB main body 1.

[0068] Example 1:

[0069] In S11 of S1, for the first dielectric layer 11 and the third dielectric layer 15, 850 g of modified polytetrafluoroethylene resin and 150 g of nano-sized silicon dioxide particles are weighed, and the modified polytetrafluoroethylene resin and the nano-sized silicon dioxide particles are mixed in a high-speed mixer at a speed of 1000 r / min for 3 hours to form a uniform mixture, and then a flow casting process is used to prepare a dielectric layer green body with a thickness of 0.15 mm under the conditions of a temperature of 280℃ and a pressure of 8 MPa, and then the dielectric layer green body is sintered at a high temperature of 350℃ for 2 hours to obtain the finished dielectric layer, i.e., the first dielectric layer 11 and the third dielectric layer 15.

[0070] In S12 of S1, for the second dielectric layer 13, 700 g of epoxy resin and 300 g of aluminum nitride ceramic particles are weighed, and the epoxy resin and the aluminum nitride ceramic particles are mixed in a planetary mixer at a speed of 500 r / min for 2 hours to form a uniform composite slurry, and then a compression molding process is used to prepare a second dielectric layer 13 with a thickness of 0.1 mm under the conditions of a temperature of 180℃ and a pressure of 10 MPa for 1.5 hours.

[0071] In S21 of S2, high-purity electrolytic copper foil is plated on the circuit pattern protected by the photoresist, and the copper layer has a thickness of 35μm.

[0072] In S22 of S2, the surface of the conductive layer is subjected to chemical nickel plating and gold plating in sequence, and the thicknesses of the nickel layer and the gold layer are strictly controlled. In the chemical nickel plating solution, the concentration of nickel sulfate is 40 g / L, and the concentration of sodium hypophosphite is 30 g / L. The temperature is controlled at 85℃, and the nickel plating time is 20 minutes to obtain a nickel layer with a thickness of about 4μm. In the chemical gold plating solution, the concentration of potassium cyanide is 3 g / L, and the concentration of potassium citrate is 20 g / L. The temperature is controlled at 45℃, and the gold plating time is 5 minutes to obtain a gold layer with a thickness of about 0.2μm.

[0073] In the S31 drilling in S3, according to the design requirement, the ultraviolet laser drilling technology with a wavelength of 355 nm is used to drill at the position where the blind buried hole is needed to be made, to form a blind hole or a buried hole, and the hole diameter is 0.15 mm;

[0074] In the S32 roughening treatment in S3, the blind buried hole is subjected to roughening treatment, and then the hole wall is subjected to copper plating thickening by using the chemical copper plating process, so that the copper layer thickness of the hole wall reaches the design requirement, the chemical roughening is carried out by using a potassium permanganate solution, the temperature is 60 DEG C, and the time is 10 minutes, then the hole wall is subjected to copper plating thickening by using the chemical copper plating process, the copper sulfate concentration in the chemical copper plating solution is 20 g / L, the formaldehyde concentration is 10 mL / L, the temperature is controlled at 30 DEG C, and the copper plating time is 30 minutes, so that the copper layer thickness of the hole wall uniformly reaches 25 mu m.

[0075] In the S41 stacking in S4, the prepared first dielectric layer 11, the first conductive layer 12, the second dielectric layer 13, the second conductive layer 14, the third dielectric layer 15 and the third conductive layer 16 are sequentially stacked in the designed order, and an appropriate amount of prepreg (PP sheet) is placed between the layers, and the thickness of the prepreg is 0.08 mm.

[0076] In the S42 hot pressing in S4, the stacked plate is placed in a hot press, and is hot pressed at a temperature of 220 DEG C and a pressure of 15 MPa for 4 hours, so that the layers are tightly combined to form a complete PCB main body 1.

[0077] In S5, a mounting groove with a depth of 1.5 mm and a width of 2 mm is milled on the edge of the PCB main body 1, a pre-prepared aluminum alloy metal heat dissipation frame 17 is embedded into the mounting groove, and the metal heat dissipation frame 17 is firmly connected with the ground lines of the first conductive layer 12, the second conductive layer 14 and the third conductive layer 16 through a soldering process.

[0078] The performance test of the PCB prepared in Example 1 shows that, at a frequency of 77 GHz, the signal transmission loss is reduced by 32%, the thermal resistance is reduced by 40%, and in the via interconnection reliability test, after 1000 thermal cycles (-40 DEG C-125 DEG C), there is no open circuit, short circuit or other failure phenomenon, and the product qualification rate reaches 98%.

[0079] The technical solutions described in the present application, or the technical solutions designed by those skilled in the art inspired by the technical solutions of the present application, which achieve the above technical effects, are all within the protection scope of the present application.

Claims

1. A PCB board for a 77GHz millimeter-wave radar in automobiles, characterized in that, It includes a PCB body (1), which is composed of a first dielectric layer (11), a first conductive layer (12), a second dielectric layer (13), a second conductive layer (14), a third dielectric layer (15), and a third conductive layer (16) stacked in sequence.

2. The automotive 77GHz millimeter-wave radar PCB as described in claim 1, characterized in that, The first dielectric layer (11) and the third dielectric layer (15) are both made of modified polytetrafluoroethylene material; the second dielectric layer (13) is made of epoxy resin-based composite material with high thermal conductivity.

3. The automotive 77GHz millimeter-wave radar PCB as described in claim 1, characterized in that, The first conductive layer (12), the second conductive layer (14), and the third conductive layer (16) are all made of high-purity electrolytic copper foil.

4. The automotive 77GHz millimeter-wave radar PCB as described in claim 1, characterized in that, A blind via is provided between the first conductive layer (12), the second conductive layer (14), and the third conductive layer (16), and the blind via enables electrical connection.

5. The automotive 77GHz millimeter-wave radar PCB as described in claim 1, characterized in that, The edge of the PCB body (1) is provided with a metal heat dissipation frame (17). The metal heat dissipation frame (17) is connected to the grounding line of the first conductive layer (12), the second conductive layer (14) and the third conductive layer (16). The metal heat dissipation frame (17) is made of aluminum alloy material with high thermal conductivity.

6. A method for manufacturing a 77GHz millimeter-wave radar PCB for automobiles according to any one of claims 1-5, characterized in that, The fabrication method of the PCB board for the 77GHz millimeter-wave radar in this vehicle is as follows: Step 1: Dielectric layer preparation The first step is the preparation of the finished dielectric layer; the second step is the preparation of the second dielectric layer. Step 2: Fabrication of the conductive layer. The first step is to create a conductive layer; the second step is to perform nickel-gold plating. Step 3: Fabrication of blind boreholes. The first step is drilling. Step 2: Roughening process; Step 4: Lamination and pressing, The first step is: stacking; Step 2: Hot pressing. Step 5: Install the metal heat sink frame. Mill a mounting groove on the edge of the PCB body (1), embed the pre-prepared aluminum alloy metal heat sink frame (17) into the mounting groove, and firmly connect the metal heat sink frame (17) to the grounding lines of the first conductive layer (12), the second conductive layer (14) and the third conductive layer (16) through a welding process.

7. The method for fabricating a 77GHz millimeter-wave radar PCB for automobiles as described in claim 6, characterized in that, In the first step of the preparation of the finished dielectric layer, for the first dielectric layer (11) and the third dielectric layer (15), the modified polytetrafluoroethylene resin and nano-sized silica particles are mixed in a high-speed mixer to form a uniform mixture. Then, a casting molding process is used to form a dielectric layer green blank with a thickness of 0.15 mm. After sintering, the finished dielectric layers, namely the first dielectric layer (11) and the third dielectric layer (15), are obtained. In the second step of step one, the preparation of the second dielectric layer, for the second dielectric layer (13), epoxy resin and aluminum nitride ceramic particles are mixed in a planetary mixer to form a uniform composite slurry, and then pressed using a pressing molding process to form a second dielectric layer (13) with a thickness of 0.1 mm.

8. The method for fabricating a 77GHz millimeter-wave radar PCB for automobiles as described in claim 6, characterized in that, In the first step of step two, the conductive layer is fabricated by uniformly coating photoresist on the surface of the prepared dielectric layer, forming a circuit pattern through exposure and development processes, and then using an electroplating copper process to plate high-purity electrolytic copper foil on the circuit pattern protected by the photoresist to form a conductive layer. Finally, the remaining photoresist is removed through a photoresist removal process. In the second step of step two, the nickel-gold plating process involves electroless nickel-gold plating on the surface of the conductive layer, proceeding sequentially with electroless nickel plating and electroless gold plating, while strictly controlling the thickness of the nickel and gold layers.

9. The method for manufacturing a 77GHz millimeter-wave radar PCB for automobiles as described in claim 6, characterized in that, In the first step of step three, according to the design requirements, ultraviolet laser drilling technology is used to drill holes at the locations where blind holes need to be made, forming blind holes or buried holes. In the second roughening process of step three, the blind buried via is roughened, and then the copper plating process is used to thicken the copper layer on the via wall so that the copper layer thickness on the via wall meets the design requirements.

10. The method for manufacturing a 77GHz millimeter-wave radar PCB for automobiles as described in claim 6, characterized in that, In the first step of step four, the prepared dielectric and conductive layers are stacked in the designed order, and an appropriate amount of prepreg is placed between the layers. In the second step of step four, hot pressing, the stacked board material is placed in a hot press to press the layers tightly together to form a complete PCB body (1).

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