HDI circuit board and manufacturing method thereof, millimeter wave radar sensor

Abstract

The present invention discloses an HDI circuit board and a manufacturing method thereof, and a millimeter wave radar sensor, the manufacturing method comprising the following steps: laminating at least two layers of a first circuit substrate to form an inner circuit board; laminating the inner circuit board and a second circuit substrate to form an HDI circuit board; wherein the thickness of the metal layer on the first surface of the HDI circuit board is greater than the thickness of the metal layer on the second surface; using different etching liquid spray pressures, etching the first surface and the second surface at the same time, so as to form circuits on the first surface and the second surface; wherein the different etching liquid spray pressures are set according to the thickness of the metal layer on the first surface and the second surface, respectively. In the above manner, the present application can provide technical support for providing low-cost, small-size antennas for millimeter wave radars.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit boards, and in particular to an HDI circuit board and a manufacturing method thereof, and a millimeter wave radar sensor. Background Art

[0002] Compared with cameras and lidars, the advantages of millimeter-wave radars are: 1) All-weather and all-day working characteristics, regardless of day or night, not restricted by weather conditions, and can work normally even in rainy and snowy days; 2) Strong environmental adaptability, can still work normally in adverse weather conditions, strong penetration ability, rain, fog, dust, etc. have little interference to millimeter-wave radars; 3) Strong speed and distance measurement capabilities.

[0003] Therefore, if cost and size are not considered, millimeter-wave radar can use patch antennas (small size, medium performance, medium cost) or external whip antennas (large size, high performance, high cost). However, PCB (printed circuit board) antennas are the lowest cost, smallest size, and can achieve sufficient performance if designed properly. Summary of the invention

[0004] The main technical problem solved by the present invention is to provide an HDI circuit board and a manufacturing method thereof, and a millimeter-wave radar sensor, so as to provide technical support for providing a low-cost, small-size antenna for millimeter-wave radar.

[0005] In order to solve the above technical problems, a technical solution adopted by the present invention is to provide a method for manufacturing an HDI circuit board, the method for manufacturing the circuit board comprising: laminating at least two layers of first circuit substrates to form an inner circuit board; laminating the inner circuit board and a layer of second circuit substrate to form an HDI circuit board; wherein the thickness of the metal layer on the first surface of the HDI circuit board is greater than the thickness of the metal layer on the second surface; using different etching liquid spray pressures, etching the first surface and the second surface at the same time, so as to form circuits on the first surface and the second surface; wherein the different etching liquid spray pressures are set according to the metal layer thicknesses of the first surface and the second surface, respectively.

[0006] Wherein, before laminating at least two layers of first circuit substrates to form an inner layer circuit board, the method includes: pre-treating each of the first circuit substrate and the second circuit substrate through inner layer pre-treatment, inner layer exposure, and inner layer etching processes to form circuits on the surface of each of the first circuit substrate and the second circuit substrate.

[0007] Among them, after laminating at least two layers of first circuit substrates to form an inner circuit board, the method includes: making a first blind hole and a first through hole at a preset position of the inner circuit board; and performing copper electroplating on the first blind hole and the first through hole to make the metal layers in the inner circuit board interconnected.

[0008] Wherein, the making of the first blind hole and the first through hole at the preset position of the inner circuit board comprises: using laser drilling to open a first blind hole at a first preset position of the first circuit substrate located at the bottom layer of the inner circuit board, and using mechanical drilling to open a first through hole at a second preset position of the inner circuit board; the copper plating of the first blind hole and the first through hole to make the metal layers in the inner circuit board interconnected comprises: forming a thin metal layer on the hole walls of the first blind hole and the first through hole respectively; electroplating the first blind hole and plugging the first through hole with vacuum resin to fill the first blind hole and the first through hole; wherein the depression formed by the filled first blind hole and the bottom surface of the inner circuit board is less than 25 μm.

[0009] Wherein, laminating at least two layers of first circuit substrates to form an inner circuit board includes: superimposing at least one first insulating layer between two adjacent layers of the first circuit substrates; and pressing all the first circuit substrates after superimposing the first insulating layer to form the inner circuit board; laminating the inner circuit board and a layer of second circuit substrate to form an HDI circuit board includes: superimposing at least one second insulating layer between the inner circuit board and the second circuit substrate; and pressing the inner circuit board and the second circuit substrate after superimposing the second insulating layer to form an HDI circuit board; wherein, the materials of the first insulating layer and the second insulating layer are the same or different.

[0010] Wherein, before stacking at least one first insulating layer between two adjacent layers of the first circuit substrate, the method includes: milling grooves at corresponding positions of each layer of the first circuit substrate, the first insulating layer and the second insulating layer, so that the formed inner circuit board has a groove for accommodating the metal base; stacking at least one second insulating layer between the inner circuit board and the second circuit substrate includes: stacking at least one second insulating layer on the top layer of the inner circuit board; placing the metal base in the groove, and stacking the second circuit substrate on the second insulating layer; wherein the transverse cross-section of the metal base is a first rectangle, the corners of the first rectangle are right angles, the transverse cross-section of the groove is a second rectangle, the corners of the second rectangle are oblique angles, and the right angle is opposite to the oblique angle.

[0011] Wherein, after laminating the inner layer circuit board and a second circuit substrate to form an HDI circuit board, the method includes: making a second blind hole and a second through hole at a preset position of the HDI circuit board; and performing copper electroplating on the second blind hole and the second through hole to make the metal layers in the HDI circuit board interconnected.

[0012] Wherein, making the second blind hole and the second through hole at the preset position of the HDI circuit board comprises: using laser drilling to open the second blind hole at the third preset position of the second circuit substrate located at the top layer of the HDI circuit board, and using mechanical drilling to open the second through hole at the fourth preset position of the HDI circuit board; performing copper plating on the second blind hole and the second through hole to make the metal layers in the HDI circuit board interconnected, comprises: forming a thin metal layer on the hole wall of the second blind hole and the second through hole respectively; performing electroplating on the second blind hole, and performing vacuum resin plugging on the second through hole to fill the second blind hole and the second through hole; wherein, the depression formed by the filled second blind hole and the top surface of the HDI circuit board is less than 25μm.

[0013] Wherein, before the first surface and the second surface are etched simultaneously by using different etching liquid spray pressures so as to form circuits on the first surface and the second surface, the method includes: performing LDI dry film masking on the surfaces of the second blind hole and the second through hole, micro-etching the metal layer on the top surface of the HDI circuit board, and flattening the metal layer at the openings of the second blind hole and the second through hole; providing a mask layer on the top surface of the HDI circuit board, micro-etching the antenna area on the top surface of the HDI circuit board to form the first surface; wherein the thickness of the metal layer in the antenna area on the top surface of the HDI circuit board after micro-etching is 22 to 28 μm; making outer layer patterns on the first surface and the second surface, and providing etch-resistant disks at the corners of the outer layer patterns; wherein the radius of the etch-resistant disks is 2.5 mil.

[0014] Wherein, after the first surface and the second surface are etched simultaneously by using different etching liquid spray pressures so as to form circuits on the first surface and the second surface, the method includes: performing subsequent processes on the HDI circuit board.

[0015] In order to solve the above technical problems, another technical solution adopted by the present invention is to provide an HDI circuit board, which is prepared by using any one of the above HDI circuit board manufacturing methods.

[0016] In order to solve the above technical problem, another technical solution adopted by the present invention is to provide a millimeter wave radar sensor, including the above HDI circuit board.

[0017] The beneficial effects of the present invention are as follows: Different from the prior art, the manufacturing method of the circuit board of the present application includes: laminating at least two layers of first circuit substrates to form an inner circuit board; laminating the inner circuit board and a second circuit substrate to form an HDI circuit board; wherein the metal layer thickness of the first surface of the HDI circuit board is greater than the metal layer thickness of the second surface; using different etching liquid spray pressures, etching the first surface and the second surface at the same time, so as to form a circuit on the first surface and the second surface; wherein the different etching liquid spray pressures are set according to the metal layer thickness of the first surface and the second surface respectively. By laminating at least two layers of first circuit substrates to form an inner circuit board, and then laminating the inner circuit board and a second circuit substrate, the formed HDI circuit board can meet the antenna requirements of the millimeter wave radar. In addition, by using different etching liquid spray pressures, etching the first surface and the second surface with different metal layer thicknesses at the same time, it is possible to complete the circuit production of two sides with different metal layer thicknesses in one etching, so that the cost is reduced, and technical support can be provided for providing low-cost and small-size antennas for millimeter wave radars. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0019] Figure 1 This is a schematic flow chart of a first embodiment of a method for manufacturing an HDI circuit board of the present application;

[0020] Figure 2 This is a flow chart of a second embodiment of the method for manufacturing an HDI circuit board of the present application;

[0021] Figure 3 yes Figure 2 A schematic flow chart of an implementation method of step S202;

[0022] Figure 4 yes Figure 2 A schematic diagram of a flow chart of an implementation method of step S205;

[0023] Figure 5 This is a schematic structural diagram of an embodiment of an HDI circuit board of the present application;

[0024] Figure 6 It is a schematic diagram of the top view structure of the metal base and the groove;

[0025] Figure 7 This is a schematic diagram of the definition of EA value. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] See also Figure 1 , Figure 1 This is a flow chart of a first embodiment of a method for manufacturing an HDI circuit board of the present application. The method for manufacturing a circuit board in this embodiment includes the following steps:

[0028] S101: laminating at least two layers of first circuit substrates to form an inner circuit board.

[0029] It is understandable that the first circuit substrate can be a commonly used copper-clad laminate, specifically a double-sided copper-clad laminate, which includes a dielectric layer and a metal layer located on opposite sides of the dielectric layer. The number of layers of the first circuit substrate can be set according to the complexity of the wiring, which can provide the possibility of upgrading the version for a more complex circuit photo-drawing design under the condition of adding 0 cost to the HDI (High Density Interconnector) circuit board. In this step, several layers of the first circuit substrate are stacked and then pressed together to form an inner circuit board.

[0030] S102: Laminating the inner circuit board and a second circuit substrate to form an HDI circuit board; wherein the thickness of the metal layer on the first surface of the HDI circuit board is greater than the thickness of the metal layer on the second surface.

[0031] After forming the inner circuit board, a second circuit substrate is stacked on the inner circuit board, and then the inner circuit board and the second circuit substrate are integrally formed into an HDI circuit board by lamination. The second circuit substrate can also be a double-sided copper-clad laminate, and the formed HDI circuit board includes n circuit layers, n is greater than or equal to 6, which are circuit layer L1, circuit layer L2, circuit layer L3, circuit layer L4...circuit layer Ln-1, circuit layer Ln in sequence. The HDI circuit board has a first surface and a second surface relative to each other, and the copper thickness of the first surface is the thickness of the single-sided copper layer of the second circuit substrate away from the inner circuit board, that is, the circuit layer L1, and the copper thickness of the second surface is the thickness of the single-sided copper layer of the first circuit substrate, that is, the circuit layer Ln; it can be understood that a high-power circuit area needs to be formed on the circuit layer L1, so the thickness of the circuit layer L1 is greater than the thickness of the circuit layer Ln, that is, the copper thickness of the first surface is greater than the copper thickness of the second surface.

[0032] S103: using different etching liquid spray pressures to simultaneously etch the first surface and the second surface so as to form circuits on the first surface and the second surface; wherein the different etching liquid spray pressures are set according to the metal layer thickness of the first surface and the second surface, respectively.

[0033] Since the copper thickness of the circuit layer L1 and the circuit layer Ln are inconsistent, the conventional method cannot complete the circuit production of the circuit layer L1 and the circuit layer Ln by one-time etching, and the use of two single-sided etching methods will increase a lot of costs. Therefore, different etching liquid spray pressures can be set according to the copper thickness of the first surface and the second surface, and the first surface and the second surface are etched simultaneously using different etching liquid spray pressures, so that circuits can be formed on the first surface and the second surface.

[0034] In this embodiment, at least two layers of first circuit substrates are laminated to form an inner circuit board, and then the inner circuit board and a second circuit substrate are laminated. The formed HDI circuit board can meet the antenna requirements of the millimeter wave radar. In addition, different etching liquids are sprayed and the first surface and the second surface with different metal layer thicknesses are etched at the same time. It is possible to complete the circuit production on two sides with different metal layer thicknesses in one etching, so that the cost is reduced, and technical support can be provided for providing low-cost and small-size antennas for millimeter wave radars.

[0035] See also Figure 2 , Figure 2 This is a flow chart of a second embodiment of the method for manufacturing an HDI circuit board of the present application. The method for manufacturing a circuit board in this embodiment includes the following steps:

[0036] S201: pre-processing each of the first circuit substrate and the second circuit substrate through inner layer pre-processing, inner layer exposure, and inner layer etching processes to form a circuit on a surface of each of the first circuit substrate and the second circuit substrate.

[0037] Before manufacturing an HDI circuit board using at least two layers of first circuit substrates and one layer of second circuit substrate, it is first necessary to form each layer of the first circuit substrate and the second circuit substrate, and to form the circuit structure of each circuit layer of the HDI circuit board. Specifically, at least two first circuit substrates and one second circuit substrate are provided, and each first circuit substrate and the second circuit substrate are pre-processed through inner layer pre-processing, inner layer exposure, and inner layer etching processes to form circuits on the surface of each first circuit substrate and the second circuit substrate.

[0038] S202: Laminating at least two layers of first circuit substrates to form an inner circuit board.

[0039] In this implementation scenario, step S202 provided in this embodiment is substantially similar to step S101 in the first embodiment of the method for manufacturing an HDI circuit board provided in this application.

[0040] Specifically, please combine Figure 3 , Figure 3 yes Figure 2 The flowchart of step S202 of an implementation method is shown in FIG. 1 , wherein step S202 includes:

[0041] S2021: stacking at least one first insulating layer between two adjacent layers of the first circuit substrate.

[0042] S2022: Pressing all the first circuit substrates after stacking the first insulating layer to form the inner circuit board.

[0043] Specifically, a first insulating layer is provided between two adjacent first circuit substrates, and the first insulating layer may be a prepreg, and then all the first circuit substrates and the first insulating layer are pressed together so that the two adjacent first circuit substrates are bonded together through the first insulating layer, thereby forming an inner circuit board. In the above process, the first circuit substrates to be combined need to be arranged in order and pressed together after accurate positioning; the positioning method may be riveting positioning or pin positioning to avoid misalignment between multiple first circuit substrates. The pressing process needs to be carried out at a certain temperature and pressure, and the specific temperature and pressure range can be determined according to the properties of the dielectric layer in the first circuit substrate and the material of the first insulating layer.

[0044] S203: Making a first blind hole and a first through hole at a preset position of the inner circuit board.

[0045] Specifically, laser drilling can be used to open a first blind hole at a first preset position of the first circuit substrate located at the bottom layer of the inner circuit board. Since the first blind hole only connects the circuit layer Ln-1 and the circuit layer Ln and is relatively thin, the first blind hole is formed by releasing energy to the first circuit substrate located at the bottom layer of the inner circuit board, which can effectively avoid structural defects such as excessive blind hole depth and burrs caused by mechanical drilling, which not only ensures product quality but also shortens the process flow. Mechanical drilling can be used to open a first through hole at a second preset position of the inner circuit board. Since the first through hole is used to connect the circuit layer L3 to the circuit layer Ln and is relatively thick, mechanical drilling can be used to ensure the aperture size while meeting the hole making thickness.

[0046] S204: performing copper electroplating on the first blind hole and the first through hole to interconnect the metal layers in the inner circuit board.

[0047] Through copper plating, the circuit layers can be connected. The ground wire GND can be connected by laser blind holes and mechanical through holes. Specifically, a thin copper layer is formed on the hole walls of the first blind hole and the first through hole respectively by copper plating; then the first blind hole is electroplated to fill the first blind hole, wherein the depression formed between the filled first blind hole and the bottom surface of the inner circuit board is less than 25μm; in addition, the first through hole is plugged with vacuum resin to fill the first through hole. In addition, the number of blind holes can be set according to the needs of the actual production process, and the apertures of each blind hole can be the same or different. In addition to connecting the circuit layers, multiple blind holes can also be used as a metal base for heat conduction to enhance the heat dissipation performance of the circuit board.

[0048] S205: Laminating the inner circuit board and a second circuit substrate to form an HDI circuit board; wherein the thickness of the metal layer on the first surface of the HDI circuit board is greater than the thickness of the metal layer on the second surface.

[0049] Specifically, please combine Figure 4 , Figure 4 yes Figure 2 The schematic diagram of the process of step S205 of an implementation method, step S205 comprises:

[0050] S2051: stacking at least one second insulating layer between the inner circuit board and the second circuit substrate.

[0051] S2052: Laminating the inner circuit board and the second circuit substrate after stacking the second insulating layer to form an HDI circuit board.

[0052] Specifically, a second insulating layer is arranged between the inner circuit board and the second circuit substrate, that is, the second insulating layer is arranged on the circuit layer L3, and the second insulating layer may be a prepreg, and then the inner circuit board, the second insulating layer and the second circuit substrate are pressed together so that the inner circuit board and the second circuit substrate are bonded together through the second insulating layer, thus forming an HDI circuit board. The pressing process needs to be carried out at a certain temperature and pressure, and the specific temperature and pressure range can be determined according to the properties of the materials of the first circuit substrate, the dielectric layer in the second circuit substrate, and the first insulating layer and the second insulating layer.

[0053] Among them, the materials of the first insulating layer and the second insulating layer can be the same or different. When the same material is used, the pressing temperature and pressure can be better controlled within an appropriate range. When different materials are used, for example, some can use polytetrafluoroethylene sheets, and others can use ordinary sheets FR4. Since polytetrafluoroethylene sheets can transmit signals transmitted on circuit boards at high frequencies and high speeds, they are particularly suitable for products such as radars and 5G communication equipment that have high requirements for signal transmission rates and transmission frequencies. Therefore, high-frequency materials with better dielectric constants (Dk values) (such as Rogers' RO3003G2) are selected for mixed pressing with ordinary sheets FR4. The wiring density of each layer of the circuit board can be increased, and the thickness of the insulating dielectric material can be reduced.

[0054] It is understandable that before laminating the inner circuit board and the second circuit substrate to form the HDI circuit board, a metal base needs to be configured. For example, a copper metal base with a high thermal conductivity can be used to dissipate heat by adopting a highly efficient embedded metal base. The design of the high heat dissipation solution provides a basis for the subsequent HDI circuit board upgrade to integrate more functional modules. Therefore, in one embodiment, before step S2021, the above method includes: milling grooves at corresponding positions of each layer of the first circuit substrate, the first insulating layer and the second insulating layer, so that the formed inner circuit board has a groove for accommodating the metal base. At this time, step S2051 specifically includes: superimposing at least one layer of the second insulating layer on the top layer of the inner circuit board; placing the metal base in the groove, and superimposing the second circuit substrate on the second insulating layer; wherein the transverse cross-section of the metal base is a first rectangle, the corner of the first rectangle is a right angle, the transverse cross-section of the groove is a second rectangle, the corner of the second rectangle is an oblique angle, and the right angle is opposite to the oblique angle.

[0055] Specifically, there is a gap between the inner wall of the groove and the metal base, and the gap can be filled with adhesive to fix the metal base; the four right angles of the metal base correspond to the four oblique angles of the groove, and through the coordination of the oblique angles and the right angles, the vertical distance from the corner of the metal base to the corner of the groove is smaller than the vertical distance from the outer wall of the metal base to the inner wall of the groove, so that the displacement of the metal base in the groove can be reduced, which can not only facilitate manual insertion, but also improve the problem of the metal base being greatly offset in one direction and lacking glue during the pressing process.

[0056] S206: Making a second blind hole and a second through hole at a preset position of the HDI circuit board.

[0057] Specifically, laser drilling can be used to open a second blind hole at a third preset position of the second circuit substrate located on the top layer of the HDI circuit board. Since the second blind hole only connects the circuit layer L1 and the circuit layer L2 and is relatively thin, the second blind hole is formed by releasing energy to the second circuit substrate located on the top layer of the HDI circuit board, which can effectively avoid structural defects such as excessive blind hole depth and burrs caused by mechanical drilling, which not only ensures product quality but also shortens the process flow. Mechanical drilling can be used to open a second through hole at a fourth preset position of the HDI circuit board. Since the second through hole is used to connect the circuit layer L1 to the circuit layer Ln and is relatively thick, mechanical drilling can be used to ensure the aperture size while meeting the hole making thickness.

[0058] S207: performing copper electroplating on the second blind hole and the second through hole to interconnect the metal layers in the HDI circuit board.

[0059] The various circuit layers can be connected by copper plating. Specifically, thin copper layers are formed on the hole walls of the second blind hole and the second through hole respectively by copper plating; then the second blind hole is electroplated to fill the second blind hole, wherein the depression formed between the filled second blind hole and the top surface of the HDI circuit board is less than 25μm; in addition, the second through hole is plugged with vacuum resin to fill the second through hole.

[0060] S208: performing LDI dry film masking on the surfaces of the second blind hole and the second through hole, micro-etching the metal layer on the top surface of the HDI circuit board, and flattening the metal layer at the openings of the second blind hole and the second through hole.

[0061] Specifically, LDI dry film is used to mask the surfaces of the second blind hole and the second through hole on the circuit layer L1, and then the outer surface of the circuit layer L1 is processed by a micro-etching process, and the copper layer at the openings of the second blind hole and the second through hole is flattened after the dry film is removed. At this time, the thickness of the circuit layer L1 can be used as the line copper thickness of the high-power area.

[0062] S209: Setting a mask layer on the top surface of the HDI circuit board, and micro-etching the antenna region on the top surface of the HDI circuit board to form the first surface; wherein the thickness of the metal layer in the antenna region on the top surface of the HDI circuit board after micro-etching is 22 to 28 μm.

[0063] S210: making outer patterns on the first surface and the second surface, and setting corrosion-resistant plates at the corners of the outer patterns; wherein the radius of the corrosion-resistant plates is 2.5 mil.

[0064] After the thickness of the circuit layer L1 is made to be the line copper thickness of the high-power area, a mask layer is set on the circuit layer L1, and then the antenna area of ​​the top surface of the HDI circuit board (i.e., the circuit layer L1) is micro-etched. At this time, the copper thickness of the antenna area of ​​the circuit layer L1 after micro-etching needs to be controlled to be 22±3μm, thus forming the first surface of the HDI circuit board. Then, after removing the mask layer, the outer layer graphics can be made on the first surface and the second surface. It is understandable that it is difficult to achieve the requirement that the outer layer graphics have a right angle at the angle between adjacent edges after etching, that is, the EA value is ≤10um, when processing HDI circuit boards using conventional process flows, where the EA value refers to the distance from the vertex of the ellipse at the angle between two adjacent edges of the outer layer graphics after actual processing to the intersection of the two theoretical adjacent edges, such as Figure 7 As shown, this distance is the EA value, and the usual design standard is that the EA value is ≤10um. In the present application, by setting a corrosion-resistant disk with a radius of 2.5 mil at the corner of the outer pattern, the EA value can be effectively controlled to be ≤10um.

[0065] S211: using different etching liquid spray pressures to simultaneously etch the first surface and the second surface so as to form circuits on the first surface and the second surface; wherein the different etching liquid spray pressures are set according to the metal layer thickness of the first surface and the second surface, respectively.

[0066] Since the copper thickness of the circuit layer L1 and the circuit layer Ln are inconsistent, the conventional method cannot complete the circuit production of the circuit layer L1 and the circuit layer Ln by one-time etching, and the use of two single-sided etching methods will increase a lot of costs. Therefore, different etching liquid spray pressures can be set according to the copper thickness of the first surface and the second surface, and the first surface and the second surface are etched simultaneously using different etching liquid spray pressures, so that circuits can be formed on the first surface and the second surface.

[0067] S212: performing subsequent processes on the HDI circuit board.

[0068] After completing the circuit production of circuit layer L1 and circuit layer Ln, the solder mask, exposure, development, characterization, and post-curing are carried out. At this point, the HDI circuit board is basically completed. Finally, the Route, Clean, O / S, Hole test, AVI, OSP, FQA and other processes are completed to obtain the finished circuit board.

[0069] The manufacturing method of the above-mentioned HDI circuit board can complete the production of a composite copper RF HDI circuit board. The manufactured circuit board has the functions of high circuit precision, small RF frequency deviation, high-efficiency heat dissipation, high integration, etc., and can be used to manufacture millimeter-wave radar sensors for assembly in mid-to-high-end automobiles in the market.

[0070] The present application also provides an HDI circuit board, which is manufactured using the manufacturing method provided in the above embodiment. Figure 5 , Figure 5 The structural diagram of an embodiment of the HDI circuit board of the present application. The HDI circuit board 50 includes an inner circuit board 501 and a second circuit substrate 502, wherein the inner circuit board 501 includes at least two first circuit substrates 5011 stacked, and the second circuit substrate 502 is arranged on the inner circuit board 501, and the first circuit substrate 5011 and the second circuit substrate 502 each include a dielectric layer and two metal layers located on opposite sides of the dielectric layer; wherein the metal layer on the side of the second circuit substrate 502 away from the inner circuit board 501 is the first surface 503 of the HDI circuit board 50, and the metal layer on the side of the inner circuit board 501 away from the second circuit substrate 502 is the second surface 504 of the HDI circuit board 50, the metal layer thickness of the first surface 503 of the HDI circuit board 50 is greater than the metal layer thickness of the second surface 504, and the circuits formed on the first surface 503 and the second surface 504 are obtained by using different etching liquids to spray and etch the first surface 503 and the second surface 504 at the same time.

[0071] Specifically, the first circuit substrate 5011 and the second circuit substrate 502 can adopt commonly used copper clad laminates, specifically double-sided copper clad laminates, which include a dielectric layer and metal layers located on opposite sides of the dielectric layer. The number of layers of the first circuit substrate 5011 can be set according to the complexity of the wiring, which can provide the possibility of upgrading the version to a more complex circuit photo-drawing design under the condition of adding 0 cost to the HDI circuit board 50 in the future. By stacking several layers of the first circuit substrate 5011, and then forming the inner circuit board 501 as a whole by pressing, after the inner circuit board 501 is formed, a second circuit substrate 502 is superimposed on the inner circuit board 501, and then the inner circuit board 501 and the second circuit substrate 502 are formed as a whole by pressing to form the HDI circuit board 50. The formed HDI circuit board 50 includes n circuit layers, n is greater than or equal to 6, which are circuit layer L1, circuit layer L2, circuit layer L3, circuit layer L4...circuit layer Ln-1, circuit layer Ln in sequence. The HDI circuit board 50 has a first surface 503 and a second surface 504 relative to each other. The copper thickness of the first surface 503 is the thickness of the single-sided copper layer of the second circuit substrate 502 away from the side of the inner circuit board 501, that is, the circuit layer L1, and the copper thickness of the second surface 504 is the thickness of the single-sided copper layer of the first circuit substrate 5011, that is, the circuit layer Ln; it can be understood that a high-power line area needs to be formed on the circuit layer L1, therefore, the thickness of the circuit layer L1 is greater than the thickness of the circuit layer Ln, that is, the copper thickness of the first surface 503 is greater than the copper thickness of the second surface 504. Since the copper thickness of the circuit layer L1 and the circuit layer Ln are inconsistent, the conventional method cannot complete the circuit production of the circuit layer L1 and the circuit layer Ln through a one-time etching, and the use of two single-sided etching methods will increase a lot of costs. Therefore, different etching liquid spray pressures can be set according to the copper thickness of the first surface 503 and the second surface 504. Different etching liquid spray pressures are used to etch the first surface 503 and the second surface 504 at the same time, so that circuits can be formed on the first surface 503 and the second surface 504.

[0072] In this embodiment, at least two layers of first circuit substrates 5011 are laminated to form an inner circuit board 501, and then the inner circuit board 501 and a second circuit substrate 502 are laminated. The formed HDI circuit board 50 can meet the antenna requirements of the millimeter wave radar. In addition, different etching liquids are sprayed and the first surface 503 and the second surface 504 with different metal layer thicknesses are etched at the same time. It is possible to complete the circuit production on two sides with different metal layer thicknesses in one etching, so that the cost is reduced, and technical support can be provided for providing low-cost and small-size antennas for millimeter wave radars.

[0073] Furthermore, the HDI circuit board 50 includes a first blind hole 505 and a first through hole 506. The first blind hole 505 is used to electrically connect the two metal layers of the first circuit substrate 5011 located at the bottom layer of the inner circuit board 501, and the first through hole 506 is used to electrically connect the metal layers of all the first circuit substrates 5011. The first blind hole 505 is a laser hole, and the first through hole 506 is a mechanical hole. Specifically, the first blind hole 505 can be opened at a first preset position of the first circuit substrate 5011 located at the bottom layer of the inner circuit board 501 by laser drilling. Since the first blind hole 505 only connects the circuit layer Ln-1 and the circuit layer Ln, the thickness is relatively thin. The first blind hole 505 is formed by releasing energy to the first circuit substrate 5011 located at the bottom layer of the inner circuit board 501, which can effectively avoid structural defects such as excessive blind hole depth and burrs caused by mechanical drilling, which not only ensures product quality but also shortens the process flow. A first through hole 506 can be opened at a second preset position of the inner circuit board 501 by mechanical drilling. Since the first through hole 506 is used to connect the circuit layer L3 to the circuit layer Ln and has a relatively large thickness, mechanical drilling can be used to ensure the hole size while meeting the hole thickness.

[0074] Furthermore, at least one first insulating layer 5012 is stacked between two adjacent first circuit substrates 5011, and at least one second insulating layer 507 is stacked between the inner circuit board 501 and the second circuit substrate 502. Specifically, the first insulating layer 5012 is disposed between two adjacent first circuit substrates 5011, and the first insulating layer 5012 may be a prepreg, and then all the first circuit substrates 5011 and the first insulating layer 5012 are pressed together so that the two adjacent first circuit substrates 5011 are bonded together through the first insulating layer 5012, thereby forming the inner circuit board 501. Similarly, a second insulating layer 507 is arranged between the inner circuit board 501 and the second circuit substrate 502, that is, the second insulating layer 507 is arranged on the circuit layer L3, and the second insulating layer 507 can be a semi-cured sheet. Then, the inner circuit board 501, the second insulating layer 507 and the second circuit substrate 502 are pressed together so that the inner circuit board 501 and the second circuit substrate 502 are bonded together through the second insulating layer 507, thereby forming an HDI circuit board 50.

[0075] It is understandable that the materials of the first insulating layer 5012 and the second insulating layer 507 are the same or different. The pressing process needs to be performed at a certain temperature and pressure, and the specific temperature and pressure range can be determined according to the properties of the materials of the first circuit substrate 5011, the dielectric layer in the second circuit substrate 502, and the first insulating layer 5012 and the second insulating layer 507.

[0076] Please combine Figure 6In one embodiment, the inner circuit board 501 is provided with a groove 5013, and a metal base 5014 is provided in the groove 5013; wherein, the transverse cross-section of the metal base 5014 is a first rectangle, the corner of the first rectangle is a right angle, and the transverse cross-section of the groove 5013 is a second rectangle, the corner of the second rectangle is an oblique angle, and the positions of the right angle and the oblique angle are opposite. Specifically, there is a gap between the inner wall of the groove 5013 and the metal base 5014, and the gap can be filled with adhesive to fix the metal base 5014; the four right angles of the metal base 5014 correspond to the four oblique angles of the groove 5013, and through the coordination of the oblique angles and the right angles, the vertical distance from the corner of the metal base 5014 to the corner of the groove 5013 is smaller than the vertical distance from the outer wall of the metal base 5014 to the inner wall of the groove 5013, so that the displacement of the metal base 5014 in the groove 5013 can be reduced, which can facilitate manual insertion and improve the problem of the metal base 5014 being greatly offset in one direction and lacking glue during the pressing process.

[0077] Furthermore, the HDI circuit board 50 includes a second blind hole 508 and a second through hole 509. The second blind hole 508 is used to electrically connect the two metal layers of the second circuit substrate 502, and the second through hole 509 is used to electrically connect the metal layers of all the first circuit substrates 5011 and the two metal layers of the second circuit substrate 502. The second blind hole 508 is a laser hole, and the second through hole 509 is a mechanical hole. Specifically, the second blind hole 508 can be opened at the third preset position of the second circuit substrate 502 located at the top layer of the HDI circuit board 50 by laser drilling. Since the second blind hole 508 only connects the circuit layer L1 and the circuit layer L2, the thickness is relatively thin. The second blind hole 508 is formed by releasing energy to the second circuit substrate 502 located at the top layer of the HDI circuit board 50, which can effectively avoid structural defects such as excessive blind hole depth and burrs caused by mechanical drilling, which not only ensures product quality but also shortens the process flow. A second through hole 509 can be opened at the fourth preset position of the HDI circuit board 50 by mechanical drilling. Since the second through hole 509 is used to connect the circuit layer L1 to the circuit layer Ln and has a relatively large thickness, the mechanical drilling method can ensure the hole size while meeting the hole thickness.

[0078] Furthermore, the first surface 503 of the HDI circuit board 50 is provided with a high-power area S1 and an antenna area S2 . The metal layer thickness of the high-power area S1 is greater than that of the antenna area S2 . The metal layer thickness of the antenna area S2 is 22 to 28 μm.

[0079] Furthermore, an outer layer pattern (not shown) is formed on the first surface 503 and the second surface 504, and the EA value at the corner of the outer layer pattern is ≤10μm. It is understandable that it is difficult to achieve the requirement that the angle between adjacent edges of the outer layer pattern after etching is a right angle, that is, the EA value is ≤10um, when processing the HDI circuit board 50 using conventional process flow, wherein the EA value refers to the distance from the vertex of the ellipse at the angle between two adjacent edges of the outer layer pattern after actual processing to the intersection of the two adjacent edges in theory, such as Figure 7 As shown, this distance is the EA value, and the usual design standard is that the EA value is ≤10um. In the present application, by setting a corrosion-resistant disk with a radius of 2.5 mil at the corner of the outer pattern, the EA value can be effectively controlled to be ≤10um.

[0080] The present application also provides an electronic device having any of the above-mentioned HDI circuit boards 50. The electronic device may be a millimeter wave radar sensor, a smart home, various transportation vehicles and aircraft that require all-weather, all-day, and strong environmental adaptability, or various electronic products that require low-cost, small-size toys, etc. that require IoT sensing space.

[0081] It should be noted that, in the present application, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0082] The above description is only an implementation method of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent principle transformation made using the contents of the description and drawings of the present application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for manufacturing an HDI circuit board, characterized in that: The method for manufacturing the circuit board comprises: At least two layers of first circuit substrates are laminated to form an inner circuit board; including: stacking at least one first insulating layer between two adjacent layers of the first circuit substrates; pressing all the first circuit substrates after the first insulating layer is stacked to form the inner circuit board; before stacking at least one first insulating layer between two adjacent layers of the first circuit substrates, the method includes: milling grooves at corresponding positions of each layer of the first circuit substrate, the first insulating layer and the second insulating layer, so that the formed inner circuit board has a groove for accommodating the metal base; The inner circuit board and a second circuit substrate are laminated to form an HDI circuit board; wherein the thickness of the metal layer on the first surface of the HDI circuit board is greater than the thickness of the metal layer on the second surface; comprising: stacking at least one second insulating layer between the inner circuit board and the second circuit substrate; pressing the inner circuit board and the second circuit substrate after stacking the second insulating layer to form the HDI circuit board; the stacking of at least one second insulating layer between the inner circuit board and the second circuit substrate comprises: stacking at least one second insulating layer on the top layer of the inner circuit board; placing the metal base in the groove, and stacking the second circuit substrate on the second insulating layer; wherein the transverse cross-section of the metal base is a first rectangle, the corner of the first rectangle is a right angle, the transverse cross-section of the groove is a second rectangle, the corner of the second rectangle is an oblique angle, and the right angle is opposite to the oblique angle; Using different etching liquid spray pressures to etch the first surface and the second surface at the same time, so as to form circuits on the first surface and the second surface; wherein the different etching liquid spray pressures are set according to the thickness of the metal layer on the first surface and the second surface respectively; Before the first surface and the second surface are etched simultaneously by using different etching solutions to form circuits on the first surface and the second surface, the method includes: setting a mask layer on the top surface of the HDI circuit board, micro-etching the antenna area on the top surface of the HDI circuit board to form the first surface; wherein the thickness of the metal layer in the antenna area on the top surface of the HDI circuit board after micro-etching is 22 to 28 μm.

2. The method for manufacturing an HDI circuit board according to claim 1, wherein: Before laminating at least two layers of first circuit substrates to form an inner circuit board, the method includes: Each of the first circuit substrate and the second circuit substrate is pre-processed through inner layer pre-processing, inner layer exposure, and inner layer etching processes to form a circuit on the surface of each of the first circuit substrate and the second circuit substrate.

3. The method for manufacturing an HDI circuit board according to claim 1, wherein: After laminating at least two layers of first circuit substrates to form an inner circuit board, the method includes: Making a first blind hole and a first through hole at a preset position of the inner circuit board; Copper electroplating is performed on the first blind hole and the first through hole to interconnect the metal layers in the inner circuit board.

4. The method for manufacturing an HDI circuit board according to claim 3, wherein: The method of making a first blind hole and a first through hole at a preset position of the inner circuit board includes: A first blind hole is formed at a first preset position of the first circuit substrate located at the bottom layer of the inner circuit board by laser drilling, and a first through hole is formed at a second preset position of the inner circuit board by mechanical drilling; The copper plating is performed on the first blind hole and the first through hole to interconnect the metal layers in the inner circuit board, including: forming thin metal layers on the hole walls of the first blind hole and the first through hole respectively; The first blind hole is electroplated, and the first through hole is vacuum-filled with resin to fill the first blind hole and the first through hole; wherein the depression formed between the filled first blind hole and the bottom surface of the inner circuit board is less than 25 μm.

5. The method for manufacturing an HDI circuit board according to claim 1, wherein: The first insulating layer and the second insulating layer may be made of the same or different materials.

6. The method for manufacturing an HDI circuit board according to claim 1, wherein: After laminating the inner circuit board and a second circuit substrate to form a HDI circuit board, the method includes: Making a second blind hole and a second through hole at a preset position of the HDI circuit board; The second blind hole and the second through hole are subjected to copper electroplating to interconnect the metal layers in the HDI circuit board.

7. The method for manufacturing an HDI circuit board according to claim 6, wherein: The method of making a second blind hole and a second through hole at a preset position of the HDI circuit board includes: Using laser drilling to open a second blind hole at a third preset position of the second circuit substrate located on the top layer of the HDI circuit board, and using mechanical drilling to open a second through hole at a fourth preset position of the HDI circuit board; The copper plating is performed on the second blind hole and the second through hole to interconnect the metal layers in the HDI circuit board, including: forming thin metal layers on the hole walls of the second blind hole and the second through hole respectively; The second blind hole is electroplated, and the second through hole is vacuum-filled with resin to fill the second blind hole and the second through hole; wherein the depression formed between the filled second blind hole and the top surface of the HDI circuit board is less than 25 μm.

8. The method for manufacturing an HDI circuit board according to claim 7, wherein: Before the first surface and the second surface are etched simultaneously by using different etching liquid spray pressures so as to form circuits on the first surface and the second surface, the method includes: Performing LDI dry film masking on the surfaces of the second blind hole and the second through hole, micro-etching the metal layer on the top surface of the HDI circuit board, and flattening the metal layer at the openings of the second blind hole and the second through hole; An outer layer pattern is made on the first surface and the second surface, and a corrosion-resistant disk is arranged at the corner of the outer layer pattern; wherein the radius of the corrosion-resistant disk is 2.5 mil.

9. The method for manufacturing an HDI circuit board according to claim 1, wherein: After the first surface and the second surface are etched simultaneously by using different etching liquid spray pressures so as to form circuits on the first surface and the second surface, the method includes: The HDI circuit board is manufactured through subsequent processes.

10. An HDI circuit board, characterized in that: The HDI circuit board is manufactured by the manufacturing method of any one of claims 1 to 9.

11. A millimeter wave radar sensor, characterized in that: Including the HDI circuit board as claimed in claim 10.

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