Antenna substrate of millimeter wave radar chip and design method

Abstract

The invention provides an antenna substrate of a millimeter wave radar chip and a design method, the antenna substrate comprises a first substrate layer, a second substrate layer, a third substrate layer and a fourth substrate layer which are sequentially arranged from top to bottom, and the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer are interconnected through blind holes or buried holes; the first substrate layer is electrically connected with the millimeter wave radar chip, and the first substrate layer is provided with an antenna feeder comprising four signal transmitting paths and four signal receiving paths; the second substrate layer and the third substrate layer are respectively used as a grounding layer and a power supply layer and are used for grounding reference and power supply; the fourth substrate layer is connected with an external PCB, transmission line routing corresponding to the four signal transmitting paths and the four signal receiving paths sequentially penetrates through the first substrate layer, the second substrate layer and the third substrate layer through blind holes or buried holes and is connected with the fourth substrate layer, and transmission path loss of the four signal transmitting and receiving paths can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of millimeter wave radar chips, and in particular to an antenna substrate and a design method for a millimeter wave radar chip. Background Art

[0002] Millimeter-wave radar chips are widely used in autonomous driving, intelligent transportation systems (ITS), drones, 5G communications and other fields. As these applications have increasing requirements for signal quality and transmission efficiency, the design of the antenna substrate becomes critical. The antenna substrate not only needs to ensure efficient signal transmission, but also has good electromagnetic compatibility (EMC) and anti-interference capabilities to cope with complex electromagnetic environments.

[0003] However, the traditional antenna substrate design usually adopts a single-layer or multi-layer PCB structure. However, in the high frequency band of 77GHz, the dielectric constant of the traditional PCB material is high, which leads to increased loss in the signal transmission path, affecting the integrity and transmission distance of the signal. In addition, the signal lines in the multi-layer PCB are easily affected by external electromagnetic interference, especially when the transmit (TX) and receive (RX) signals coexist. The crosstalk problem is particularly prominent, further reducing the performance of the system. Therefore, there is an urgent need for an antenna substrate design that can effectively solve these problems to meet the strict requirements of high-frequency millimeter-wave radar chips for signal quality and transmission efficiency. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide an antenna substrate and a design method for a millimeter-wave radar chip, which can effectively reduce the loss in the signal transmission path and the influence of external electromagnetic interference, and can effectively improve the signal transmission quality and system reliability.

[0005] In a first aspect, an embodiment of the present invention provides an antenna substrate of a millimeter-wave radar chip, the antenna substrate comprising: a first substrate layer, a second substrate layer, a third substrate layer and a fourth substrate layer arranged in sequence from top to bottom, the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer are interconnected by blind holes or buried holes; the first substrate layer is electrically connected to the millimeter-wave radar chip, and an antenna feeder including four transmit signal paths and four receive signal paths is arranged on the first substrate layer; the second substrate layer and the third substrate layer are respectively used as a ground layer and a power layer for ground reference and power supply; the fourth substrate layer is connected to an external PCB board, and the transmission line routing corresponding to the four transmit signal paths and the four receive signal paths passes through the first substrate layer, the second substrate layer and the third substrate layer in sequence through the blind holes or the buried holes, and is connected to the fourth substrate layer.

[0006] In some embodiments, in the area where the second substrate layer or the third substrate layer is located below the pad of the millimeter-wave radar chip, the substrate material is partially or completely removed to form a hollow area to reduce the parasitic capacitance between the millimeter-wave radar chip and the antenna substrate.

[0007] In some embodiments, a plurality of exhaust holes are arranged on the copper sheets of the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer, the diameter of the exhaust holes is 0.2 mm to 0.5 mm, and the spacing between the plurality of exhaust holes is set according to the copper sheet area and the number of substrate layers.

[0008] In some embodiments, the second substrate layer and the third substrate layer are provided with a grounding shielding structure around the transmission line routing of the four transmitting signal paths and the four receiving signal paths and the blind holes, and the grounding shielding structure includes an annular grounding strip, and a plurality of grounding vias are arranged on the outer side of the annular grounding strip; a solder ball array is provided on the fourth substrate layer, and the solder ball array is used to connect to an external PCB board, and the grounding shielding structure is provided around the solder ball array.

[0009] In some embodiments, the millimeter-wave radar chip is a 77GHz millimeter-wave four-transmit and four-receive chip, and the transmission line routings of the four transmission signal paths and the transmission line routings of the four receiving signal paths are symmetrically arranged on the antenna substrate.

[0010] Among them, it can be understood that in order to ensure efficient transmission of four transmit (TX) and four receive (RX) signal paths and reduce crosstalk and electromagnetic interference between signals, the transmission line routing on the antenna substrate is symmetrically set. Specifically: the four transmit signal paths and the four receive signal paths are arranged in pairs on the antenna substrate. For example, TX1 and TX2 are a pair, and TX3 and TX4 are another pair; RX1 and RX2 are a pair, and RX3 and RX4 are another pair. The two pairs of transmit signal paths and the two pairs of receive signal paths are symmetrically distributed on the substrate to ensure that their electrical characteristics are the same.

[0011] It can be understood that the transmission line length, width, shape and distance from the surrounding copper foil of each transmit signal path and receive signal path are consistent. This symmetrical design can simplify the simulation and manufacturing process, reduce the differences between different signal paths, and ensure the same performance of each channel; and through symmetrical layout, the distance between the transmit (TX) and receive (RX) signal paths is kept consistent, reducing the possibility of mutual interference and reducing the complexity of simulation, because the symmetrical structure means that the electrical characteristics of each signal path are similar, reducing the simulation and design time, and simulation tools (such as HFSS) can more easily handle symmetrical structures to ensure consistent performance of all paths.

[0012] In addition, in order to further reduce the interference between the transmit (TX) and receive (RX) signal paths, the transmit and receive signal paths are usually kept at a larger distance or isolated by a ground shield. The specific distance can be optimized based on simulation results to ensure that the isolation is greater than 40dB.

[0013] In some embodiments, the first substrate layer and the second substrate layer are interconnected by blind holes, the hole disk of the blind holes is 120um, and the hole diameter is 70um; the second substrate layer and the third substrate layer are interconnected by buried holes, the hole disk of the buried holes is 150um, and the hole diameter is 80um, which are double-sided laser holes; the third substrate layer and the fourth substrate layer are interconnected by blind holes, the hole disk of the blind holes is 120um, and the hole diameter is 70um.

[0014] In some embodiments, the core layer thickness of the second substrate layer is 80um, the prepreg layer thickness between the first substrate layer and the second substrate layer is 25um, the prepreg layer thickness between the second substrate layer and the third substrate layer is 25um, and the prepreg layer thickness between the third substrate layer and the fourth substrate layer is 25um.

[0015] In some embodiments, the core layer material of one or more of the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer is CCL-HL972LF, and the prepreg layer material is GHPL-970LF. At 80GHz, the dielectric constant of the CCL-HL972LF is 3.3, and the dielectric constant of the GHPL-970LF is 3.1.

[0016] In a second aspect, an embodiment of the present invention provides a design method for an antenna substrate, which is used for the antenna substrate of a millimeter-wave radar chip as described in any one of the first aspects, and the design method includes: establishing a three-dimensional model of the millimeter-wave radar chip and an external PCB board in a simulation tool; using the simulation tool to simulate the initial design of the antenna substrate, evaluating whether the four-way transmitting and four-way receiving signal paths meet the design conditions of insertion loss less than 1dB and isolation greater than 40dB, and confirming whether the boundary conditions of the simulation meet the current application scenario; if the design conditions of insertion loss less than 1dB and isolation greater than 40dB are not met, or the boundary conditions of the simulation do not meet the current application scenario, optimizing and adjusting the design parameters of the antenna substrate to achieve the design of the above-mentioned antenna substrate.

[0017] In some embodiments, the optimization and adjustment of the design parameters of the antenna substrate includes at least one of the following: adjusting the feed line routing and the spacing between it and the copper foil; adjusting the number and position of ground vias; adjusting the layer thickness of the core and prepreg; checking the isolation between the transmitting path and the receiving path to adjust the isolation structure.

[0018] The antenna substrate and design method of the millimeter-wave radar chip provided by the embodiments of the present invention have at least the following beneficial effects: the antenna substrate comprises a first substrate layer, a second substrate layer, a third substrate layer and a fourth substrate layer arranged in sequence from top to bottom, and the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer are interconnected by blind holes or buried holes; the first substrate layer is electrically connected to the millimeter-wave radar chip, and an antenna feeder including four transmission signal paths and four reception signal paths is arranged on the first substrate layer; the second substrate layer and the third substrate layer are respectively used as a ground layer and a power supply layer for ground reference and power supply; the fourth substrate layer is connected to an external PCB board, and the four transmission signal paths are connected to the external PCB board. The transmission line routing corresponding to the signal path and the four receiving signal paths passes through the first substrate layer, the second substrate layer and the third substrate layer in sequence through blind holes or buried holes, and is connected to the fourth substrate layer; it can be understood that the present application interconnects the layers through blind holes or buried holes, and uses the second substrate layer as the ground layer and the third substrate layer as the power layer to provide a stable ground reference and power supply, reduce the impact of power supply noise on the signal, and the fourth substrate layer is connected to the external PCB board through a solder ball array, which can effectively reduce the transmission path loss of the transmission line routing of the four transmitting and receiving signal paths, and reduce the impact of external electromagnetic interference, thereby effectively improving the signal transmission quality and system reliability.

[0019] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0021] The present invention is further described below in conjunction with the accompanying drawings and embodiments;

[0022] Figure 1 is a schematic diagram of the antenna structure and chip connection provided by an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of the antenna feeder portion of the first substrate layer provided by an embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of a second substrate layer antenna feeder provided by an embodiment of the present invention;

[0025] Figure 4 is a schematic diagram of a third substrate layer antenna feeder provided by an embodiment of the present invention;

[0026] Figure 5 It is a partial schematic diagram of the antenna feed line of the fourth substrate layer provided in an embodiment of the present invention.

[0027] Reference numerals:

[0028] 100, antenna substrate; 110, first substrate layer; 111, transmission signal path; 112, reception signal path; 120, second substrate layer; 130, third substrate layer; 140, fourth substrate layer; 200, millimeter wave radar chip. DETAILED DESCRIPTION

[0029] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0030] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, "above", "below", "within", etc. are understood to include the number itself, "any one" means one or more, "at least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. If there is a description of the first and the second, it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0031] It should be noted that the terms such as setting, installing, and connecting in the embodiments of the present invention should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the embodiments of the present invention in combination with the specific content of the technical solution. For example, the term "connection" can be a mechanical connection, an electrical connection, or mutual communication; it can be directly connected or indirectly connected through an intermediate medium.

[0032] It should be noted that the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Millimeter-wave radar chips are widely used in fields such as autonomous driving, intelligent transportation systems (ITS), drones, and 5G communications. As the requirements for signal quality and transmission efficiency of these applications continue to increase, the design of antenna substrates becomes crucial. Antenna substrates not only need to ensure efficient signal transmission, but also have good electromagnetic compatibility (EMC) and anti-interference capabilities to cope with complex electromagnetic environments. However, traditional antenna substrate designs usually use single-layer or multi-layer PCB structures. However, in high-frequency bands such as 77GHz, the dielectric constant of traditional PCB materials is high, resulting in increased losses on the signal transmission path, affecting signal integrity and transmission distance. In addition, signal lines in multi-layer PCBs are easily affected by external electromagnetic interference, especially when transmit (TX) and receive (RX) signals coexist. The crosstalk problem is particularly prominent, further reducing the performance of the system. Therefore, there is an urgent need for an antenna substrate design that can effectively solve these problems to meet the strict requirements of high-frequency millimeter-wave radar chips for signal quality and transmission efficiency.

[0034] Based on this, the purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide an antenna substrate and design method for a millimeter-wave radar chip, which can effectively reduce the loss in the signal transmission path and the influence of external electromagnetic interference, and can effectively improve the signal transmission quality and system reliability.

[0035] The embodiments of the present invention are further described below in conjunction with the accompanying drawings.

[0036] refer to Figures 1 to 5 , Figure 1 is a schematic diagram of the antenna structure and chip connection provided by an embodiment of the present invention; Figure 2 is a schematic diagram of the antenna feeder portion of the first substrate layer provided by an embodiment of the present invention; Figure 3 is a schematic diagram of a second substrate layer antenna feeder provided by an embodiment of the present invention; Figure 4 is a schematic diagram of a third substrate layer antenna feeder provided by an embodiment of the present invention; Figure 5 It is a partial schematic diagram of the antenna feed line of the fourth substrate layer provided in an embodiment of the present invention.

[0037] In a first aspect, an embodiment of the present invention provides an antenna substrate of a millimeter-wave radar chip, the antenna substrate comprising: a first substrate layer, a second substrate layer, a third substrate layer and a fourth substrate layer arranged in sequence from top to bottom, the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer are interconnected through blind holes or buried holes; the first substrate layer is electrically connected to the millimeter-wave radar chip, and an antenna feeder including four transmit signal paths and four receive signal paths is arranged on the first substrate layer; the second substrate layer and the third substrate layer are respectively used as a ground layer and a power layer for ground reference and power supply; the fourth substrate layer is connected to an external PCB board, and the transmission line routing corresponding to the four transmit signal paths and the four receive signal paths passes through the first substrate layer, the second substrate layer and the third substrate layer in sequence through blind holes or buried holes, and is connected to the fourth substrate layer.

[0038] Among them, the first substrate layer is electrically connected to the millimeter-wave radar chip, and is provided with an antenna feeder including four transmission signal paths and four receiving signal paths. It is responsible for the interconnection between the millimeter-wave radar chip and the substrate of the FC and the design of the 77GHz antenna feeder to ensure efficient transmission of signals at high frequencies; the second substrate layer is a ground layer, which provides a stable ground reference, absorbs current and reduces electromagnetic interference, ensures low impedance of the signal return path, improves signal integrity, and performs a hollowing design under the pad of the millimeter-wave radar chip to reduce parasitic capacitance and optimize impedance matching; the third substrate layer is used as a power layer to ensure the voltage stability of the chip when working at high frequencies. It is connected to the ground layer through multiple vias to form a complete power distribution network (PDN), reduce the impact of power noise on the ground line, and perform a hollowing design under the pad to reduce parasitic capacitance and optimize impedance matching; the fourth substrate layer is provided with a solder ball array, which is used to realize the connection between the substrate and the external PCB circuit to ensure that the signal can be smoothly transmitted to the external system. A ground shielding structure is arranged around the solder ball array to reduce electromagnetic interference and crosstalk between signals, and ensure the stability and reliability of signal transmission.

[0039] It can be understood that among the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer arranged in sequence from top to bottom: the first substrate layer (M1 layer) is the top layer, which is responsible for the electrical connection with the millimeter-wave radar chip. The M1 layer is provided with an antenna feeder including four transmit signal paths (TX1, TX2, TX3, TX4) and four receive signal paths (RX1, RX2, RX3, RX4). The design of the antenna feeder is optimized to ensure efficient transmission in the 77GHz frequency band and reduce losses and reflections; the second substrate layer (M2 layer) is used as a ground layer to provide a stable ground reference, absorb current and reduce electrical Magnetic interference, the existence of the M2 layer ensures the low impedance of the signal return path and improves the signal integrity; the third substrate layer (M3 layer) is used as the power layer to provide stable power supply and ensure the voltage stability of the chip when working at high frequency. The M3 layer is connected to the ground layer of the M2 layer through multiple vias to form a complete power distribution network (PDN) to reduce the impact of power noise on the ground line; the fourth substrate layer (M4 layer) is used as the bottom layer, which is mainly used for solder ball array arrangement to realize the connection between the substrate and the external PCB circuit. The solder ball array on the M4 layer is aligned with the PAD on the external PCB board to ensure that the signal can be smoothly transmitted to the external system.

[0040] In some embodiments, the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer are interconnected through blind holes or buried holes. The blind holes are used to connect the top layer (M1 layer) and the middle layer (M2 layer), and the middle layer (M3 layer) and the bottom layer (M4 layer), while the buried holes are used to connect the middle layer (M2 layer) and the M3 layer. The design of the blind holes and buried holes ensures low-loss transmission of the signal path and provides good mechanical stability. The transmission line routing corresponding to the four transmitting signal paths and the four receiving signal paths passes through the first substrate layer, the second substrate layer and the third substrate layer in turn through the blind holes or buried holes, and is finally connected to the fourth substrate layer. This design ensures that the signal can be efficiently transmitted to the external PCB board, while reducing the loss and reflection on the signal path.

[0041] In some embodiments, in an area where the second substrate layer or the third substrate layer is located below the pad of the millimeter-wave radar chip, the substrate material is partially or completely removed to form a hollow area to reduce the parasitic capacitance between the millimeter-wave radar chip and the antenna substrate.

[0042] It can be understood that in the second substrate layer or the third substrate layer below the flip chip pad (diepad), the substrate material is partially or completely removed to form a hollow area, which helps to reduce the parasitic capacitance between the chip and the substrate, optimize impedance matching, and ensure efficient transmission of signals at high frequencies. The hollow design reduces losses and reflections in high-frequency signal transmission, especially in high-frequency applications such as 77GHz, where any tiny parasitic capacitance will affect the signal quality, thereby effectively improving the high-frequency performance of the system.

[0043] In some embodiments, a plurality of exhaust holes are arranged on the copper foil of the first substrate layer, the second substrate layer, the third substrate layer, and the fourth substrate layer, and the diameter of the exhaust holes is 0.2 mm to 0.5 mm, and the spacing between the plurality of exhaust holes is set according to the copper foil area and the number of substrate layers; it can be understood that a plurality of exhaust holes are arranged on the large copper foil of each layer to ensure that the gas can be discharged smoothly during the lamination process of the multilayer board to prevent the delamination problem caused by gas residue. The diameter of the exhaust hole is usually 0.2 mm to 0.5 mm, and the spacing between the plurality of exhaust holes is optimized according to the copper foil area and the number of substrate layers to ensure that the gas can be discharged evenly and avoid local bubble accumulation; the design of the exhaust hole not only avoids delamination failure, but also improves the mechanical strength and reliability of the substrate, ensuring that the substrate will not have delamination or warping problems under high temperature or high pressure environment.

[0044] In some embodiments, the second substrate layer and the third substrate layer are provided with a grounding shielding structure around the transmission line routing of the four-way transmitting signal path and the four-way receiving signal path and the blind hole, and the grounding shielding structure includes an annular grounding strip, and a plurality of grounding vias are arranged on the outside of the annular grounding strip; a solder ball array is provided on the fourth substrate layer, and the solder ball array is used to connect to the external PCB board, and a grounding shielding structure is provided around the solder ball array; wherein, it can be understood that a grounding shielding structure is provided around the transmission line routing of the four-way transmitting (TX) and four-way receiving (RX) signal paths and the blind hole, including an annular grounding strip and a grounding via array, the annular grounding strip forms a closed grounding ring around each signal line, and the width is 0.2mm to 0.5mm to reduce external electromagnetic interference, and the grounding via array is arranged on the outside of the annular grounding strip, with a spacing of 1mm to 2mm, and the annular grounding strip is connected to the ground layer of the second substrate layer to form a three-dimensional shielding structure, thereby further enhancing the shielding effect.

[0045] In addition, the grounding shielding structure not only reduces electromagnetic interference, but also effectively reduces crosstalk between different signal paths, ensuring signal purity and transmission quality. Especially in the case of high-density interconnection, the grounding shielding structure can significantly reduce mutual interference between signals, ensuring the independence and stability of each signal path; further, a grounding shielding structure is also arranged around the solder ball array of the fourth substrate layer to reduce electromagnetic interference and crosstalk between signals, ensuring that the signal can be efficiently transmitted to the external PCB board, the center position of the solder ball array is aligned with the PAD on the PCB board, and the grounding shielding structure ensures the stability and reliability of signal transmission.

[0046] In some embodiments, the first substrate layer and the second substrate layer are interconnected by blind holes, the hole disk of the blind hole is 120um, and the aperture is 70um; the second substrate layer and the third substrate layer are interconnected by buried holes, the hole disk of the buried hole is 150um, and the aperture is 80um, which is a double-sided laser hole; the third substrate layer and the fourth substrate layer are interconnected by blind holes, the hole disk of the blind hole is 120um, and the aperture is 70um.

[0047] Among them, the blind hole between the first substrate layer (M1 layer) and the second substrate layer (M2 layer) has a hole plate diameter of 120um and an aperture of 70um, which is used to connect the signal path on the first substrate layer with the second substrate layer. Since the blind hole only extends from the top layer to the middle layer and does not penetrate the entire substrate, it reduces unnecessary signal path length and reduces the influence of parasitic inductance and capacitance. This design helps to maintain efficient signal transmission, especially in high-frequency applications, reducing signal loss and reflection.

[0048] The buried via between the second substrate layer (M2 layer) and the third substrate layer (M3 layer) has a hole plate diameter of 150um and an aperture of 80um. It is a double-sided laser via. The buried via is completely located between the internal layers and does not contact the surface layer, further reducing the length of the signal path and parasitic effects. The double-sided laser via technology ensures high precision of the hole and good electrical connection, which is suitable for high-frequency signal transmission. The buried via design can effectively reduce the loss on the signal path and ensure efficient transmission of signals between different layers.

[0049] The blind hole between the third substrate layer (M3 layer) and the fourth substrate layer (M4 layer) has a hole plate diameter of 120um and an aperture of 70um, which is used to connect the signal path on the third substrate layer to the fourth substrate layer. Through the blind hole design, the signal can be transmitted from the inner layer to the bottom layer, ensuring that the signal can smoothly reach the BGA / CSP solder ball array and finally connect to the external PCB board. The design of the blind hole also reduces the length of the signal path and the parasitic effect, ensuring efficient transmission of the signal.

[0050] In some embodiments, the core layer thickness of the second substrate layer is 80um, the prepreg layer thickness between the first substrate layer and the second substrate layer is 25um, the prepreg layer thickness between the second substrate layer and the third substrate layer is 25um, and the prepreg layer thickness between the third substrate layer and the fourth substrate layer is 25um.

[0051] It can be understood that, in the above-mentioned embodiment, the thickness of each layer and the material selection of the antenna substrate are optimized to ensure the high efficiency of signal transmission and the reliability of the system, as follows:

[0052] Corresponding to the second substrate layer, the second substrate layer serves as a ground layer to provide a stable ground reference. The thickness of the core layer is 80um. After simulation optimization, it can maintain good signal integrity in the 77GHz frequency band while reducing the influence of parasitic capacitance and inductance. The thickness selection of the core layer also takes into account the requirements of mechanical strength and thermal management to ensure the stability and reliability of the substrate in high temperature environments.

[0053] The prepreg layer corresponds to the prepreg layer between the first substrate layer and the second substrate layer, and is used to bond the first substrate layer and the second substrate layer and control the distance between adjacent layers; by adjusting the thickness of the prepreg layer to 25um, the characteristic impedance matching of the signal transmission path can be optimized, the influence of parasitic capacitance and inductance can be reduced, and the efficient transmission of the signal at high frequency can be ensured; in addition, the thickness of 25um provides sufficient mechanical strength to prevent the multilayer board from delamination failure during the lamination process.

[0054] Corresponding to the prepreg layer between the second substrate layer and the third substrate layer, the prepreg layer is used to bond the second substrate layer and the third substrate layer and control the distance between adjacent layers; by adjusting the thickness of the prepreg layer to 25um, the characteristic impedance matching of the signal transmission path can be further optimized, reducing the influence of parasitic capacitance and inductance, and ensuring efficient transmission of the signal from the ground layer to the power layer; in addition, the thickness of 25um also ensures a good electromagnetic shielding effect and reduces mutual interference between different layers.

[0055] The prepreg layer between the third substrate layer and the fourth substrate layer is used to bond the third substrate layer and the fourth substrate layer and control the distance between adjacent layers. By adjusting the thickness of the prepreg layer to 25um, the characteristic impedance matching when the signal is transmitted from the inner layer to the bottom layer can be optimized, reducing signal loss and reflection while maintaining a good electromagnetic shielding effect. In addition, the thickness of 25um ensures that the signal can be efficiently transmitted to the BGA / CSP solder ball array and finally connected to the external PCB board.

[0056] In some embodiments, the core layer material of one or more layers of the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer is CCL-HL972LF, and the prepreg layer material is GHPL-970LF. At 80GHz, the dielectric constant of CCL-HL972LF is 3.3, and the dielectric constant of GHPL-970LF is 3.1; it can be understood that in this embodiment, the core layer and prepreg layer materials of the antenna substrate can ensure its low loss and high heat resistance in high-frequency applications.

[0057] Specifically, CCL-HL972LF is a low-loss, low-coefficient of thermal expansion (CTE), and high-heat-resistant halogen-free BT environmentally friendly material with a dielectric constant of 3.3. It is suitable for high-frequency applications and can significantly reduce the loss in the signal transmission path to ensure high-quality signal transmission. In addition, CCL-HL972LF has good mechanical strength and thermal stability, so the core layer material is CCL-HL972LF, which can be used in the application scenarios of 77GHz millimeter-wave radar chips; GHPL-970LF is a low-loss, low-coefficient of thermal expansion (CTE), and high-heat-resistant halogen-free BT environmentally friendly material with a dielectric constant of 3.1. It is suitable for high-frequency applications and can further reduce the loss in the signal transmission path to ensure efficient signal transmission. In addition, GHPL-970LF has good fluidity and adhesion, so the prepreg layer material is GHPL-970LF, which can ensure good bonding of the multilayer board during the lamination process to prevent delamination failure.

[0058] In a second aspect, an embodiment of the present invention provides a design method for an antenna substrate, which is used for the antenna substrate of a millimeter-wave radar chip as described in any one of the first aspects, and the design method includes: establishing a three-dimensional model of the millimeter-wave radar chip and an external PCB board in a simulation tool; using the simulation tool to simulate the initial design of the antenna substrate, evaluating whether the four-way transmitting and four-way receiving signal paths meet the design conditions of insertion loss less than 1dB and isolation greater than 40dB, and confirming whether the boundary conditions of the simulation meet the current application scenario; if the design conditions of insertion loss less than 1dB and isolation greater than 40dB are not met, or the boundary conditions of the simulation do not meet the current application scenario, optimizing and adjusting the design parameters of the antenna substrate to achieve the design of the above-mentioned antenna substrate.

[0059] In some embodiments, optimizing and adjusting the design parameters of the antenna substrate includes at least one of the following: adjusting the feed line routing and the spacing between the feed line and the copper foil; adjusting the number and position of the ground vias; adjusting the layer thickness of the core and prepreg; and checking the isolation between the transmitting path and the receiving path to adjust the isolation structure.

[0060] It is understandable that the present application can establish a three-dimensional model of the millimeter wave radar chip and the external PCB board by using electromagnetic simulation software (such as HFSS, CST, etc.). These tools can accurately simulate the transmission behavior of high-frequency signals in multi-layer boards and evaluate their performance. The specific process may include:

[0061] According to the actual chip size, pad layout, flip chip (FC) solder ball position and other parameters, a detailed chip model is constructed to ensure that the model contains the S parameters of the four-way transmit (TX) and four-way receive (RX) ports to accurately reflect the electrical characteristics of the chip; according to the design requirements of the antenna substrate, a multi-layer structure model including the first substrate layer (M1 layer), the second substrate layer (M2 layer), the third substrate layer (M3 layer) and the fourth substrate layer (M4 layer) is constructed. Ensure that the model includes the core layer and prepreg layer thickness, material properties (such as dielectric constant, loss tangent, etc.) of each layer, as well as the location and size of blind and buried vias; according to the actual size and layout of the external PCB board, a three-dimensional model of the PCB board is constructed to ensure that the model contains the solder ball array (BGA / CSP solder ball) connected to the antenna substrate and its corresponding PAD position.

[0062] Set the excitation sources of the transmit (TX) and receive (RX) ports in the simulation tool, ensure that the frequency range of the excitation source covers the 77GHz frequency band, and set the appropriate power level according to the actual application scenario; define the boundary conditions of the simulation, including free space boundaries, absorption boundaries, etc., to ensure that the simulation results can accurately reflect the electromagnetic field distribution in the actual working environment. Pay special attention to confirm whether the boundary conditions meet the requirements of the current application scenario, such as working temperature, humidity, electromagnetic interference, etc.

[0063] Furthermore, simulation tools are used to simulate the initial design of the antenna substrate and evaluate the insertion loss of the four-way transmit (TX) and four-way receive (RX) signal paths. Insertion loss refers to the energy loss generated during the transmission of the signal from the transmitter to the receiver, usually expressed in dB. The goal is to ensure that the insertion loss is less than 1dB to ensure high-quality signal transmission. At the same time, the isolation between the transmit (TX) and receive (RX) signal paths is evaluated. Isolation refers to the ability of the transmit signal to suppress the receive signal, usually also expressed in dB. The goal is to ensure that the isolation is greater than 40dB to reduce the interference of the transmit signal on the receive signal.

[0064] Furthermore, check the simulation results to confirm whether the insertion loss of the four-way transmit and receive signal paths meets the design requirement of less than 1dB. If the insertion loss is too large, it means that there is a large energy loss during signal transmission, and it may be necessary to optimize the feeder routing or adjust other design parameters. At the same time, check whether the isolation between the transmit and receive signal paths meets the design requirement of greater than 40dB. If the isolation is insufficient, it means that the transmit signal has caused significant interference to the receive signal, and it may be necessary to adjust the isolation structure or increase the ground shielding.

[0065] In addition, it is also possible to confirm whether the boundary conditions of the simulation meet the requirements of the current application scenario. If the boundary conditions are incorrect, the simulation results may not match the actual situation, affecting the accuracy of the design.

[0066] In some embodiments, if the simulation results show that the insertion loss is not less than 1 dB or the isolation is not greater than 40 dB, or the simulated boundary conditions do not meet the current application scenario, it is necessary to optimize the design parameters of the antenna substrate. The specific optimization and adjustment measures include:

[0067] Adjust the feeder routing and the distance between it and the copper sheet: By adjusting the width and length of the feeder, optimize its characteristic impedance matching and reduce the loss and reflection on the signal transmission path. Especially in high-frequency applications, any slight impedance mismatch may cause signal loss or reflection, so it is necessary to accurately control the size of the feeder; by increasing or decreasing the distance between the feeder and the surrounding copper sheet, reduce the influence of parasitic capacitance and inductance, and further optimize the characteristic impedance matching of the signal transmission path. A larger spacing can reduce the coupling between the feeder and the copper sheet, reducing signal loss and crosstalk.

[0068] Adjust the number and position of ground vias: Increase the number of ground vias around the signal line to form a more effective shielding structure, reduce electromagnetic interference and crosstalk between signals. The number of ground vias can be optimized according to the density and frequency requirements of the signal line to ensure the best shielding effect. Then, by adjusting the position of the ground vias, ensure that they are evenly distributed around the signal line to form a continuous grounding ring. The grounding ring can effectively reduce external electromagnetic interference and improve the purity and transmission quality of the signal.

[0069] Adjust the thickness of the core and prepreg layers: By adjusting the thickness of the core layer, the characteristic impedance matching of the signal transmission path can be optimized and the influence of parasitic capacitance and inductance can be reduced. Especially for high-frequency applications, the thickness selection of the core layer is crucial because it directly affects the transmission efficiency and quality of the signal. By adjusting the thickness of the prepreg layer, the distance between adjacent layers can be controlled to further optimize the characteristic impedance matching of the signal transmission path. A smaller prepreg layer thickness can reduce the loss on the signal path.

[0070] Check the isolation between the transmit path and the receive path, and adjust the isolation structure: By increasing the physical spacing between the transmit (TX) and receive (RX) signal paths and reducing mutual interference between them, a larger spacing can effectively improve the isolation and ensure that the transmit signal does not have a significant impact on the receive signal. It is understandable that if the physical spacing cannot be further increased, the isolation can be improved by adjusting the isolation structure. For example, an additional ground shielding layer can be set between the transmit and receive signal paths, or their reference ground layers can be cut and isolated to reduce coupling between different signal paths. In addition, more ground vias can be added between the transmit and receive signal paths to form a more effective shielding structure.

[0071] In some embodiments, after completing the above optimization adjustments, the modified design is re-simulated using a simulation tool to verify whether the insertion loss and isolation meet the design requirements. Based on the simulation results, further fine-tuning parameters such as feeder routing, ground via positions, core and prepreg layer thicknesses are performed until the design conditions of insertion loss less than 1 dB and isolation greater than 40 dB are met.

[0072] Furthermore, after the simulation verification is passed, the design method of the antenna substrate includes: making a physical sample for testing to ensure that the actual performance is consistent with the simulation results. If the physical test results are not ideal, the design can be further optimized based on the test feedback until the expected performance indicators are achieved.

[0073] The antenna substrate and design method of the millimeter-wave radar chip provided by the embodiments of the present invention have at least the following beneficial effects: the antenna substrate comprises a first substrate layer, a second substrate layer, a third substrate layer and a fourth substrate layer arranged in sequence from top to bottom, and the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer are interconnected by blind holes or buried holes; the first substrate layer is electrically connected to the millimeter-wave radar chip, and an antenna feeder including four transmission signal paths and four reception signal paths is arranged on the first substrate layer; the second substrate layer and the third substrate layer are respectively used as a ground layer and a power supply layer for ground reference and power supply; the fourth substrate layer is connected to an external PCB board, and the four transmission signal paths are connected to the external PCB board. The transmission line routing corresponding to the signal path and the four receiving signal paths passes through the first substrate layer, the second substrate layer and the third substrate layer in sequence through blind holes or buried holes, and is connected to the fourth substrate layer; it can be understood that the present application interconnects the layers through blind holes or buried holes, and uses the second substrate layer as the ground layer and the third substrate layer as the power layer to provide a stable ground reference and power supply, reduce the impact of power supply noise on the signal, and the fourth substrate layer is connected to the external PCB board through a solder ball array, which can effectively reduce the transmission path loss of the transmission line routing of the four transmitting and receiving signal paths, and reduce the impact of external electromagnetic interference, thereby effectively improving the signal transmission quality and system reliability.

[0074] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. An antenna substrate for a millimeter wave radar chip, characterized in that: The antenna substrate comprises: a first substrate layer, a second substrate layer, a third substrate layer and a fourth substrate layer arranged in sequence from top to bottom, wherein the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer are interconnected through blind holes or buried holes; The first substrate layer is electrically connected to the millimeter wave radar chip, and an antenna feeder including four transmission signal paths and four reception signal paths is provided on the first substrate layer; The second substrate layer and the third substrate layer are used as a ground layer and a power layer respectively, for ground reference and power supply; The fourth substrate layer is connected to an external PCB board, and the transmission line routing corresponding to the four transmitting signal paths and the four receiving signal paths passes through the first substrate layer, the second substrate layer and the third substrate layer in sequence through the blind holes or the buried holes, and is connected to the fourth substrate layer.

2. The antenna substrate of the millimeter wave radar chip according to claim 1, characterized in that: In the area where the second substrate layer or the third substrate layer is located below the pad of the millimeter-wave radar chip, the substrate material is partially or completely removed to form a hollow area to reduce the parasitic capacitance between the millimeter-wave radar chip and the antenna substrate.

3. The antenna substrate of the millimeter wave radar chip according to claim 1, characterized in that: A plurality of exhaust holes are arranged on the copper sheets of the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer. The diameter of the exhaust holes is 0.2 mm to 0.5 mm. The spacing between the plurality of exhaust holes is set according to the copper sheet area and the number of substrate layers.

4. The antenna substrate of the millimeter wave radar chip according to claim 1, characterized in that: The second substrate layer and the third substrate layer are provided with a grounding shielding structure around the transmission line routing of the four transmitting signal paths and the four receiving signal paths and the blind holes, and the grounding shielding structure includes an annular grounding belt, and a plurality of grounding vias are arranged on the outer side of the annular grounding belt; a solder ball array is provided on the fourth substrate layer, and the solder ball array is used to connect to an external PCB board, and the grounding shielding structure is provided around the solder ball array.

5. The antenna substrate of the millimeter wave radar chip according to claim 1, characterized in that: The millimeter-wave radar chip is a 77GHz millimeter-wave four-transmit and four-receive chip, and the transmission line routings of the four transmission signal paths and the transmission line routings of the four receiving signal paths are symmetrically arranged on the antenna substrate.

6. The antenna substrate of the millimeter wave radar chip according to claim 1, characterized in that: The first substrate layer and the second substrate layer are interconnected by blind holes, the hole disk of the blind hole is 120um, and the hole diameter is 70um; the second substrate layer and the third substrate layer are interconnected by buried holes, the hole disk of the buried hole is 150um, and the hole diameter is 80um, which is a double-sided laser hole; the third substrate layer and the fourth substrate layer are interconnected by blind holes, the hole disk of the blind hole is 120um, and the hole diameter is 70um.

7. The antenna substrate of the millimeter wave radar chip according to claim 1, characterized in that: The core layer thickness of the second substrate layer is 80um, the prepreg layer thickness between the first substrate layer and the second substrate layer is 25um, the prepreg layer thickness between the second substrate layer and the third substrate layer is 25um, and the prepreg layer thickness between the third substrate layer and the fourth substrate layer is 25um.

8. The antenna substrate of the millimeter wave radar chip according to claim 1, characterized in that: The core layer material of one or more of the first substrate layer, the second substrate layer, the third substrate layer and the fourth substrate layer is CCL-HL972LF, and the prepreg layer material is GHPL-970LF. At 80GHz, the dielectric constant of the CCL-HL972LF is 3.3, and the dielectric constant of the GHPL-970LF is 3.

1.

9. A method for designing an antenna substrate, characterized in that: The design method is used for an antenna substrate of a millimeter-wave radar chip according to any one of claims 1 to 8, and the design method comprises: In the simulation tool, a three-dimensional model of the millimeter-wave radar chip and the external PCB board is established; Use simulation tools to simulate the initial design of the antenna substrate to evaluate whether the four-way transmit and four-way receive signal paths meet the design conditions of insertion loss less than 1dB and isolation greater than 40dB, and confirm whether the simulated boundary conditions meet the current application scenario; When the design conditions of insertion loss less than 1 dB and isolation greater than 40 dB are not met, or the simulated boundary conditions do not conform to the current application scenario, the design parameters of the antenna substrate are optimized and adjusted to achieve the design of the above antenna substrate.

10. The antenna substrate of the millimeter wave radar chip according to claim 9, characterized in that: The optimizing and adjusting the design parameters of the antenna substrate comprises at least one of the following: Adjust the feeder routing and the distance between it and the copper sheet; Adjust the number and location of ground vias; Adjust the layer thickness of core and prepreg; Check the isolation between the transmit path and the receive path to adjust the isolation structure.

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