A high spurious rejection multilayer circuit board for a mixer circuit and a manufacturing method thereof

Abstract

The application relates to the technical field of multilayer circuit boards, in particular to a high-stray-suppression multilayer circuit board for a mixing circuit and a manufacturing method, which comprises a circuit board substrate, the circuit board substrate is sequentially stacked from top to bottom with a surface layer ground copper foil, a first ground layer, an inner layer signal layer, a second ground layer and a bottom layer ground copper foil; a mixing chip area is formed on the surface layer ground copper foil. The three-dimensional maze transmission channel formed by the staggered blind buried hole array and the annular blocking groove arranged on the periphery of the mixing chip area can forcibly guide and continuously attenuate the stray signals diffused along the dielectric layer, the three-dimensional coupling path of the stray signals is blocked from the stereoscopic topological level, the high-efficiency stray suppression can be realized without additionally installing an external shielding cover, the whole board volume and assembly complexity are reduced; meanwhile, the integrity of the inner layer ground plane is reserved, the high-frequency ground bounce noise is greatly reduced, and the transmission stability of the working signal is ensured.

Description

Technical Field

[0001] This invention relates to the field of multilayer circuit board technology, specifically to a high spurious suppression multilayer circuit board for mixer circuits and its manufacturing method. Background Technology

[0002] Existing multilayer printed circuit boards for mixer circuits typically employ a planar stacked physical structure consisting of a signal layer, a dielectric layer, and a reference ground layer. The mixer devices and high-frequency signal lines are planarly arranged along the surface microstrip lines or inner striplines of the circuit board, with a single row of grounding vias spaced at fixed intervals on both sides of the high-frequency signal traces as a planar electromagnetic shielding wall. Although this structure has mature manufacturing technology and basic planar isolation capabilities, during continuous operation of the mixer circuit in the high-frequency or millimeter-wave band, the nonlinear mixer devices inevitably generate a large number of high-order harmonics and complex combination frequency spurious signals. Due to the extremely short wavelength of the spurious signals, they easily break through the planar barrier of the single row of vias, resulting in three-dimensional spatial radiation and oblique electromagnetic coupling along the dielectric layers of the circuit board. Furthermore, as the high-frequency ground bounce effect caused by the microscopic parasitic inductance of the grounding vias intensifies, it leads to violent fluctuations in the reference plane potential, causing the spurious signals to spread violently along the three-dimensional space of the substrate inside the circuit board to the surrounding sensitive circuit units, resulting in severe out-of-band spurious interference and deterioration of the signal-to-noise ratio.

[0003] To address the aforementioned issues, existing technologies offer several solutions. For example, an integral metal shield is added around the mixer module on the surface of the circuit board and fixed by soldering to the surface grounding pads, attempting to confine stray signals within a localized space. However, this only blocks spatial radiation in the surface space and cannot prevent the lateral propagation of stray signals along the dielectric layers and inner traces within the multilayer board. Furthermore, the presence of minute gaps and contact resistance between the shield and the circuit board surface pads inevitably leads to electromagnetic leakage at high frequencies, drastically reducing shielding effectiveness and increasing the overall board size, weight, and assembly complexity. Another approach involves using expensive special high-frequency substrates with low dielectric loss, attempting to reduce signal attenuation and electromagnetic coupling within the dielectric layer through material optimization. However, such structures are not only costly in terms of materials but also suffer from poor bonding strength in multilayer board lamination. They cannot eliminate the three-dimensional coupling path of stray signals from a physical spatial topology perspective and are prone to substrate delamination and microcracks during thermal cycling due to mismatched thermal expansion coefficients of the multilayer heterogeneous materials, resulting in high maintenance and manufacturing costs and a lack of industrial practicality.

[0004] Therefore, there is an urgent need for a high-spurious-suppression multilayer circuit board for mixer circuits. This board can achieve vertical and horizontal three-dimensional blocking and efficient suppression of mixer spurious signals by adjusting the three-dimensional physical structure of the circuit board while ensuring high-density interconnection and electrical conduction of the multilayer board. This is to meet the high-efficiency and high-quality operating requirements of mixer circuits that have strict requirements for the purity of radio frequency signals and electromagnetic shielding performance. Summary of the Invention

[0005] The purpose of this invention is to provide a high spurious suppression multilayer circuit board for mixer circuits and a manufacturing method thereof, in order to solve the technical problem that existing mixer circuit boards are unable to block spurious signal coupling paths at the three-dimensional structural level and thus cannot meet the working requirements of high-quality mixer circuits.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high spurious emission suppression multilayer circuit board for a mixer circuit and its manufacturing method are disclosed. The circuit board substrate comprises a surface ground copper foil, a first ground layer, an inner signal layer, a second ground layer, and a bottom ground copper foil, stacked sequentially from top to bottom. A mixer chip area is formed on the surface ground copper foil, and an isolation protection area is provided around the mixer chip area. An interlaced shielding band is provided around the isolation protection area. The interlaced shielding band includes a surface blind via array connecting the surface ground copper foil and the first ground layer, and an inner buried via array connecting the first ground layer and the second ground layer. The surface blind via array and the inner buried via array are non-axially connected in the horizontal projection direction and maintain a fixed spacing to form a misaligned overlapping area. An annular blocking groove is etched directly above the misaligned overlapping area on the first ground layer. The annular blocking groove, the surface blind via array, and the inner buried via array form a zigzag labyrinthine transmission channel inside the circuit board.

[0007] By setting staggered shielding strips around the isolation protection zone, and utilizing the non-axially continuous surface blind via array and inner buried via array in the horizontal projection direction while maintaining a fixed spacing to form a staggered overlap area, and etching annular blocking grooves corresponding to the staggered overlap area on the first ground layer, the annular blocking grooves, surface blind via array, and inner buried via array enclose and construct a three-dimensional zigzag-shaped labyrinthine transmission channel inside the circuit board. When the mixer circuit is in high-frequency operation, the high-order harmonics and combined frequency spurious signals generated by the nonlinear mixing process diffuse outward along the dielectric layer of the multilayer circuit board. When the spurious electromagnetic waves pass through the staggered overlap area, they are forcibly guided into the interior of this three-dimensional labyrinthine transmission channel. Due to the extremely high impedance characteristics and multiple reflection interfaces of the labyrinthine transmission channel, the spurious electromagnetic waves undergo continuous reflection, scattering, and interference attenuation within the channel, thus being efficiently blocked and consumed outside the isolation protection zone, achieving high spatial spurious suppression under passive conditions. Meanwhile, this non-axial through-hole misalignment design avoids the problem of traditional through-holes cutting through the entire circuit board from top to bottom, effectively preserving the physical integrity of the second ground plane and power plane, greatly reducing high-frequency ground bounce noise, and ensuring the return current quality of the power and ground planes.

[0008] Preferably, the four corners of the isolation protection zone are provided with stress relief slots penetrating the inner signal layer, the slot walls of the stress relief slots extend into the isolation protection zone and are provided with arc-shaped resonant notches, and the outer side of the stress relief slots is provided with corner grounding vias penetrating the circuit board substrate.

[0009] By creating stress-relief slots at the corners of the isolation protection zone corresponding to the inner signal layer, and extending arc-shaped resonant notches into the isolation protection zone from the slot walls, when high-frequency stray electromagnetic waves generated by the mixer circuit propagate within the multilayer board's dielectric cavity, the irregular geometric edges of the arc-shaped resonant notches disrupt the symmetry of the electric field distribution and standing wave formation conditions of the high-frequency electromagnetic waves within the rectangular dielectric cavity. This effectively eliminates high-order cavity resonance peaks and prevents specific frequency stray signals from being amplified by resonance within the local dielectric layer. Simultaneously, the stress-relief slots provide physical deformation release space for the concentrated heat-generating area of ​​the mixer chip, effectively absorbing the thermal expansion stress during thermal cycling and preventing interlayer delamination or microcracks caused by excessive local thermal stress on the circuit board. Furthermore, combined with corner grounding vias located outside the stress-relief slots, the continuity of the three-dimensional grounding shield and the mechanical support stiffness of the corner area are enhanced while eliminating resonance and releasing thermal stress, achieving a synergistic improvement in electromagnetic performance and structural reliability.

[0010] Preferably, the inner signal layer has a spurious absorption cavity directly below the mixing chip area, and an impedance matching microstrip line with one end suspended is integrally extended from the edge of the spurious absorption cavity. The impedance matching microstrip line is distributed in a serpentine pattern in the inner signal layer.

[0011] By creating a stray absorption cavity at the projection position directly below the mixer chip area in the inner signal layer, the conductive plane area directly below the mixer chip is reduced, thereby lowering the direct dielectric coupling and parasitic capacitance effect between the high-frequency chip and the inner signal layer. Furthermore, by combining a serpentine impedance matching microstrip line with one end suspended and integrally extended from the edge of the stray absorption cavity, specific frequency stray electromagnetic waves coupled to the inner layer through the dielectric layer are precisely guided to the suspended microstrip line. The long serpentine path and specific impedance characteristics of the microstrip line are used to convert stray electromagnetic waves into a small amount of heat energy for absorption and dissipation, cutting off the transmission path of stray signals to other signals in the inner layer or the intermediate frequency output terminal, thereby further improving the purity of the output signal of the mixer circuit.

[0012] Preferably, the annular blocking groove is provided with multiple return transition bridges at intervals along its extension path. The return transition bridge is a physical conductive slit retained on the first grounding layer, and its width is less than one-eighth of the highest operating wavelength of the mixing signal.

[0013] By leaving multiple return transition bridges with physical widths less than one-eighth of the highest operating wavelength of the mixing signal at intervals along the extension path of the annular blocking groove, a continuous and low-impedance physical conduction path is provided for the return current of the high-frequency operating signal on the first ground layer without destroying the high impedance reflection and blocking effectiveness of the annular blocking groove against high-frequency stray electromagnetic waves. This effectively avoids the severe bending of the return path of the operating signal and the sudden change in return impedance caused by the complete break of the reference plane, and prevents waveform distortion and phase noise deterioration of the operating signal transmitted on the transmission line, thus achieving a balance between stray suppression and smooth return transition.

[0014] Preferably, the outer peripheral edge of the surface grounding copper foil is serrated to form a leak-proof serrated edge, the tips of the leak-proof serrated edge point to the outer edge of the circuit board substrate, and the serration pitch is less than one-sixteenth of the highest operating wavelength of the mixing signal.

[0015] By designing the outer periphery of the surface grounding copper foil as a leak-proof sawtooth edge with the tooth tip pointing outward from the substrate and the tooth pitch less than one-sixteenth of the highest operating wavelength, when the surface high-frequency stray electromagnetic waves propagating outward along the interface between the circuit board surface dielectric and the copper foil reach the edge, the micro-sawtooth structure forms continuous micro-coherent diffraction and phase interference on the high-frequency electromagnetic waves. This causes the electromagnetic wave energy radiated along the edge to cancel each other out at the geometric interface, effectively suppressing the leakage of high-frequency stray signals from the outer edge of the circuit board into space and adjacent equipment, and improving the electromagnetic compatibility protection level of the entire board.

[0016] Preferably, the stress relief groove is filled with an elastic insulating medium and has a deformation compensation gap; the top opening edge of each blind hole in the surface blind hole array is provided with an inverted conical countersunk pit.

[0017] By filling the stress relief slots with elastic insulating medium and leaving micron-level deformation compensation seams, the overall dielectric filling flatness and insulation strength of the multilayer board are ensured, while providing an elastic buffer for the slight thermal expansion of the slot walls during rapid cooling and heating, thus completely eliminating the hidden danger of local delamination caused by thermal stress concentration. Furthermore, by processing inverted conical countersunk pits at the top opening edges of each blind hole in the surface blind hole array, the geometric transition between the via edge and the surface copper foil is smoothed, significantly reducing the parasitic inductance and parasitic capacitance effects generated by high-frequency current at the sharp turn of the via opening, suppressing high-frequency ground bounce noise, and ensuring the high-frequency equipotential stability of the grounding plane.

[0018] A method for manufacturing a multilayer circuit board with high spurious suppression for the mixer circuit described above includes the following steps: Step 1: Process the first ground layer, the inner signal layer, and the second ground layer. Etch an annular blocking groove on the first ground layer and open a stress relief through groove and an arc-shaped resonant notch on the inner signal layer. Step 2: Drill an inner layer buried via array between the first grounding layer and the second grounding layer and electroplate the vias; Step 3: The surface grounding copper foil, the first grounding layer, the inner signal layer, the second grounding layer, and the bottom grounding copper foil are laminated using a prepreg to form a circuit board substrate; Step 4: Drill controlled-depth blind vias on the surface of the circuit board substrate to form a surface blind via array, so that the surface blind via array and the inner buried via array are staggered and overlapped in the horizontal direction to form a staggered overlap area and a labyrinth transmission channel.

[0019] By first processing an annular blocking groove on the first ground layer and stress relief through grooves and arc-shaped resonant notches on the inner signal layer, and then completing the drilling and electroplating flattening of the inner buried via array between the first and second ground layers, the conductive layers and prepregs are laminated to form a circuit board substrate. Finally, precision laser-controlled depth drilling is performed on the surface of the substrate to form a surface blind via array. This step-by-step preparation and depth-controlled drilling process precisely controls the axial misalignment distance and horizontal overlap tolerance of the surface blind via array and the inner buried via array in three-dimensional space, ensuring the forming accuracy of the zigzag labyrinth transmission channel and stress relief structure inside the circuit board, avoiding interlayer misalignment and dielectric damage caused by traditional one-time through drilling, and ensuring high-yield mass production of high-stray-suppression multilayer circuit boards.

[0020] Preferably, in step three, local pressure compensation is applied to the medium area corresponding to the isolation and protection zone during the lamination process; after step four, step five is also included: etching a leak-proof serrated edge on the outer edge of the surface grounding copper foil.

[0021] By applying local pressure compensation to the medium area corresponding to the isolation and protection zone with material grooves during the lamination process in step three, the prepreg can uniformly fill the tiny gaps in the inner layer groove area during the hot-pressing melting and dispensing process, eliminating air bubbles and medium voids at the edge of the inner layer groove, and ensuring the medium uniformity and structural density of the circuit board substrate after lamination. Furthermore, step five is added after step four, where high-precision chemical micro-etching is performed on the outer edge of the surface ground copper foil to form a leak-proof serrated edge, ensuring the consistency of the serrated geometric shape and pitch, so that the electromagnetic diffraction energy dissipation structure at the surface edge can function stably, improving the process stability and leak-proof reliability of the entire circuit board manufacturing process.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention, by setting a three-dimensional labyrinth transmission channel around the mixer chip area, which is constructed by a staggered array of blind and buried vias and annular blocking grooves, can forcibly guide and continuously attenuate stray signals spreading along the dielectric layer. It blocks the three-dimensional coupling path of stray signals from a three-dimensional topology level, achieving efficient stray suppression without the need for additional external shielding, reducing the overall board size and assembly complexity. At the same time, it preserves the integrity of the inner ground plane, significantly reducing high-frequency ground bounce noise and ensuring the transmission stability of the working signal.

[0023] 2. This invention breaks the resonance amplification condition of stray signals in the dielectric cavity by setting a stress relief through groove with an arc-shaped resonant notch at the corner of the isolation protection area, and realizes the release and absorption of thermal stress. At the same time, the corner grounding through hole improves the structural rigidity, taking into account both electromagnetic performance and structural reliability. It can meet the high-frequency mixing requirements without the need to use expensive special high-frequency substrates, and greatly reduces the manufacturing cost.

[0024] 3. This invention further absorbs and consumes stray signals coupled to the inner layer by setting a stray absorption cavity and a serpentine impedance matching microstrip line in the inner signal layer, cutting off the conduction path of stray signals to the inner sensitive circuit. Combined with the sawtooth diffraction energy dissipation structure at the edge of the surface ground copper foil, it suppresses the radiation leakage of stray signals from multiple dimensions in three-dimensional space, effectively improving the signal-to-noise ratio and electromagnetic compatibility performance of the mixing output signal. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the high spurious suppression multilayer circuit board for the mixer circuit of the present invention; Figure 2 for Figure 1 Full sectional view at point AA; Figure 3 for Figure 1 Full sectional view at point BB; Figure 4 for Figure 1 A magnified view of a section at point C; Figure 5 for Figure 2 A magnified view of a section at point D; Figure 6 This is a schematic diagram of the structure of the high spurious suppression multilayer circuit board of the mixer circuit of the present invention after removing the surface grounding copper foil; Figure 7 for Figure 6 A magnified view of a section at point E in the middle; Figure 8 This is a schematic diagram of the structure of the high spurious suppression multilayer circuit board of the mixer circuit of the present invention after removing the surface grounding copper foil and the first grounding layer; Figure 9 for Figure 8A magnified view of a section at point F in the middle; Figure 10 This is a flowchart illustrating the manufacturing method of the high spurious suppression multilayer circuit board for the mixer circuit of the present invention.

[0026] In the diagram: 1. Circuit board substrate; 2. Mixer chip area; 3. Surface grounding copper foil; 4. First ground layer; 5. Inner signal layer; 6. Second ground layer; 7. Bottom grounding copper foil; 8. Surface blind via array; 9. Inner buried via array; 10. Impedance matching microstrip line; 11. Corner grounding via; 12. Isolation and protection area; 13. Interlaced shielding strip; 14. Annular blocking groove; 15. Stress relief through groove; 16. Arc-shaped resonant notch; 17. Misaligned overlapping area; 18. Labyrinth transmission channel; 19. Return current transition bridge; 20. Countersunk pit; 21. Leakage-proof serrated edge; 22. Stray absorption cavity. Detailed Implementation

[0027] Please see Figures 1 to 10 This invention provides a high spurious suppression multilayer circuit board for mixer circuits and its manufacturing method. The technical solution is as follows: A high spurious suppression multilayer circuit board for mixer circuits and its manufacturing method are described below. Figures 1 to 9 The circuit board substrate 1 includes a top-to-bottom layer of ground copper foil 3, a first ground layer 4, an inner signal layer 5, a second ground layer 6, and a bottom ground copper foil 7. A mixer chip area 2 for mounting a mixer chip is formed on the top-to-bottom layer of the ground copper foil 3. An isolation protection area 12, closed at both ends and arranged in a ring shape, is coaxially formed around the mixer chip area 2 on the surface. An interlaced shielding band 13 surrounds the isolation protection area 12. The interlaced shielding band 13 includes a top-layer blind via array 8 connecting the top-layer ground copper foil 3 and the first ground layer 4, and an inner-layer buried via array 9 connecting the first ground layer 4 and the second ground layer 6. The top-layer blind via array 8 and the inner-layer buried via array 9 are non-axially connected in the horizontal projection direction and maintain a fixed spacing to form a staggered overlapping area. 17. An annular blocking groove 14 is etched directly above the corresponding misaligned overlapping area 17 in the first ground layer 4. The annular blocking groove 14, together with the surface blind via array 8 and the inner buried via array 9, surrounds the circuit board substrate 1 to form a zigzag-shaped labyrinthine transmission channel 18. Multiple return transition bridges 19 are provided at intervals along the extension path of the annular blocking groove 14. The return transition bridge 19 is a physical conductive slit retained on the first ground layer 4, and the physical width of the return transition bridge 19 is less than one-eighth of the highest operating wavelength of the mixing signal. The outer peripheral edge of the surface ground copper foil 3 is serrated to form a leakage-proof serrated edge 21. The tips of the teeth of the leakage-proof serrated edge 21 point to the outer edge of the circuit board substrate 1, and the tooth pitch is less than one-sixteenth of the highest operating wavelength of the mixing signal.

[0028] Furthermore, stress relief slots 15 are provided at the four corners of the isolation protection area 12, penetrating the inner signal layer 5. The walls of the stress relief slots 15 extend into the isolation protection area 12 and are provided with arc-shaped resonant notches 16. The outer side of the stress relief slots 15 is provided with corner grounding vias 11 penetrating the circuit board substrate 1. The stress relief slots 15 are filled with elastic insulating medium and have micron-level deformation compensation gaps between the slot walls. The inner signal layer 5 is provided with a stray absorption cavity 22 directly below the corresponding mixer chip area 2. The edge of the stray absorption cavity 22 is integrally extended with an impedance matching microstrip line 10 with one end suspended. The impedance matching microstrip line 10 is distributed in a serpentine pattern in the inner signal layer 5. The top opening edge of each blind hole in the surface blind hole array 8 is provided with an inverted conical countersunk pit 20, and the countersunk pit 20 is located on the surface grounding copper foil 3.

[0029] For a method of manufacturing a multilayer circuit board with high spurious suppression for the above-mentioned mixer circuit, please refer to [link to relevant documentation]. Figures 1 to 10 The specific steps are as follows: Step 1: Process the first ground layer 4, the inner signal layer 5, and the second ground layer 6. Etch an annular blocking groove 14 and a return transition bridge 19 on the first ground layer 4. And open a stress relief through groove 15, an arc-shaped resonant notch 16, a stray absorption cavity 22, and a serpentine impedance matching microstrip line 10 through the inner signal layer 5. Step 2: Drill an inner layer buried via array 9 in the dielectric layer between the first grounding layer 4 and the second grounding layer 6 and perform electroplating to fill and level the vias; Step 3: Laminate the surface grounding copper foil 3, the first grounding layer 4, the inner signal layer 5, the second grounding layer 6 and the bottom grounding copper foil 7 with a prepreg to form the circuit board substrate 1. During the lamination process, local pressure compensation is applied to the dielectric area corresponding to the isolation protection area 12. Step 4: Laser-controlled deep blind vias are drilled on the surface of the circuit board substrate 1 to form a surface blind via array 8, so that the surface blind via array 8 and the inner buried via array 9 are misaligned and overlapped in the horizontal direction to form a misaligned overlap area 17 and a labyrinth transmission channel 18, and an inverted conical countersunk pit 20 is etched at the top opening of the surface blind via array 8. Step 5: High-precision micro-etching is performed on the outer edge of the surface ground copper foil 3 to form a leak-proof serrated edge 21, thus completing the precision forming of the multilayer circuit board.

[0030] By setting an interlaced shielding strip 13 around the isolation protection zone 12, and utilizing the non-axial misalignment of the surface blind via array 8 and the inner buried via array 9 in the horizontal projection direction, combined with the annular blocking groove 14 on the first ground layer 4, a three-dimensional zigzag-shaped labyrinthine transmission channel 18 is constructed inside the multilayer circuit board. When the mixer chip generates high-order harmonics and complex combination frequency stray electromagnetic waves in high-frequency operation, the lateral and obliquely diffused stray electromagnetic waves are forcibly guided into the labyrinthine transmission channel 18 when passing through the misaligned overlapping area 17. Utilizing the extremely high impedance characteristics of the channel and multiple geometric interface reflections, the stray electromagnetic waves undergo continuous scattering and interference attenuation, thereby efficiently blocking the spatial radiation of stray electromagnetic waves along the dielectric layer under passive conditions and eliminating electromagnetic crosstalk of stray signals to surrounding sensitive circuits. Meanwhile, the non-axial through-hole misalignment structure avoids the cutting and damage to the second grounding layer 6 and the power plane by the through-hole, ensuring the integrity of the high-frequency return path and reducing high-frequency ground bounce noise. Combined with the return transition bridge 19 on the annular blocking groove 14, with a width less than one-eighth of the highest operating wavelength, a low-impedance path is provided for the return current of the high-frequency operating signal, effectively preventing waveform distortion of the transmission line operating signal. Furthermore, the anti-leakage sawtooth edge 21 on the outer periphery of the surface grounding copper foil 3 uses the tooth tips to form edge diffraction and phase interference to dissipate the microwave electromagnetic waves propagating along the surface, suppressing secondary radiation leakage of high-frequency stray energy from the surface along the circuit board edge into space.

[0031] Furthermore, a stress relief through-slot 15 penetrating the inner signal layer 5 is provided at the corner of the isolation protection zone 12, and in conjunction with the protruding arc-shaped resonant notch 16, the symmetry of the electric field distribution of high-frequency electromagnetic waves and the conditions for the formation of standing waves inside the rectangular dielectric cavity are broken, eliminating the high-order cavity resonance peak and preventing specific frequency stray signals from being resonated and amplified in the local dielectric layer; at the same time, the stress relief through-slot 15 and the deformation compensation seam inside it can absorb the thermal expansion stress caused by the concentrated heat generation of the mixer chip, avoiding interlayer delamination defects in the circuit board during thermal cycling, and in conjunction with the corner grounding via 11 on the outer side, the corner grounding continuity and mechanical support rigidity are enhanced. Furthermore, the stray absorption cavity 22 opened directly below the mixer chip area 2 in the inner signal layer 5 reduces the dielectric coupling effect directly below the chip. The serpentine impedance matching microstrip line 10 guides the specific frequency band stray electromagnetic waves coupled to the inner layer and converts them into a small amount of heat energy for dissipation. The inverted conical countersunk pit 20 at the top of the surface blind via reduces the parasitic inductance and capacitance at the via opening, and suppresses high-frequency ground bounce noise. In the manufacturing method, by first processing the inner layer and buried via, then laminating pressure compensation, and finally controlling the depth of blind via drilling and micro-etching serrated edges, the spatial misalignment accuracy of blind and buried vias and the compactness of slot filling are precisely ensured. This effectively solves the problems of severe stray radiation, high ground bounce noise and thermal stress delamination when the mixer circuit is operating at high frequency. Under the premise of ensuring the electrical performance of the circuit board, the dynamic range and electromagnetic compatibility reliability of the high-frequency mixer circuit are improved.

[0032] The specific embodiment of the present invention has been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the embodiments described above. For those skilled in the art, various changes, modifications, substitutions, and variations made to these embodiments without departing from the principles and ideas of the present invention should still fall within the protection scope of the present invention.

Claims

1. A multilayer circuit board for high spurious suppression in a mixer circuit, characterized in that, The circuit board substrate (1) includes a top-to-bottom layer of ground copper foil (3), a first ground layer (4), an inner signal layer (5), a second ground layer (6), and a bottom-to-bottom ground copper foil (7). A mixer chip area (2) is formed on the top-to-bottom layer of ground copper foil (3), and an isolation protection area (12) is formed around the mixer chip area (2). An interlaced shielding band (13) is formed around the isolation protection area (12), and the interlaced shielding band (13) includes an array of surface blind vias connecting the top-to-bottom layer of ground copper foil (3) and the first ground layer (4). (8) and an inner layer buried via array (9) connecting the first ground layer (4) and the second ground layer (6); the surface blind via array (8) and the inner layer buried via array (9) are non-axially connected in the horizontal projection direction and maintain a fixed distance to form a misaligned overlapping area (17); the first ground layer (4) has an annular blocking groove (14) etched directly above the misaligned overlapping area (17), and the annular blocking groove (14), the surface blind via array (8), and the inner layer buried via array (9) form a zigzag labyrinthine transmission channel (18) inside the circuit board.

2. The high spurious suppression multilayer circuit board for a mixer circuit according to claim 1, characterized in that, The four corners of the isolation protection area (12) are provided with stress relief slots (15) that penetrate the inner signal layer (5). The wall of the stress relief slot (15) extends into the isolation protection area (12) and has an arc-shaped resonant notch (16). The outer side of the stress relief slot (15) is provided with a corner grounding via (11) that penetrates the circuit board substrate (1).

3. The high spurious suppression multilayer circuit board for mixer circuit according to claim 1, characterized in that, The inner signal layer (5) has a spurious absorption cavity (22) directly below the mixing chip area (2). An impedance matching microstrip line (10) with one end suspended is integrally extended from the edge of the spurious absorption cavity (22). The impedance matching microstrip line (10) is distributed in a serpentine pattern in the inner signal layer (5).

4. The high spurious suppression multilayer circuit board for mixer circuit according to claim 1, characterized in that, The annular blocking groove (14) has multiple return transition bridges (19) spaced apart along its extension path. The return transition bridge (19) is a physical conductive slit retained on the first ground layer (4), and its width is less than 1 / 8 of the highest operating wavelength of the mixing signal.

5. A high spurious suppression multilayer circuit board for a mixer circuit according to claim 1, characterized in that, The outer peripheral edge of the surface ground copper foil (3) is serrated to form a leak-proof serrated edge (21). The tips of the serrated edge (21) point to the outer edge of the circuit board substrate (1), and the serration pitch is less than 1 / 16 of the highest operating wavelength of the mixing signal.

6. A high spurious suppression multilayer circuit board for a mixer circuit according to claim 2, characterized in that, The stress relief channel (15) is filled with an elastic insulating medium and has a deformation compensation gap; the top opening edge of each blind hole in the surface blind hole array (8) is provided with an inverted conical countersunk pit.

7. A method for manufacturing a high spurious suppression multilayer circuit board for a mixer circuit as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Process the first ground layer (4), the inner signal layer (5) and the second ground layer (6). Etch an annular blocking groove (14) on the first ground layer (4) and open a stress relief through groove (15) and an arc-shaped resonant notch (16) on the inner signal layer (5). Step 2: Drill an inner layer buried via array (9) between the first grounding layer (4) and the second grounding layer (6) and electroplate the vias; Step 3: The surface grounding copper foil (3), the first grounding layer (4), the inner signal layer (5), the second grounding layer (6) and the bottom grounding copper foil (7) are laminated through a prepreg to form a circuit board substrate (1). Step 4: Drill depth blind holes on the surface of the circuit board substrate (1) to form a surface blind hole array (8), so that the surface blind hole array (8) and the inner buried hole array (9) are misaligned and overlapped in the horizontal direction to form a misaligned overlap area (17) and a maze transmission channel (18).

8. The method for manufacturing a high spurious suppression multilayer circuit board for a mixer circuit according to claim 7, characterized in that: In step 3, local pressure compensation is applied to the medium area corresponding to the isolation protection area (12) during the lamination process; after step 4, step 5 is also included: etching a leak-proof sawtooth edge (21) on the outer edge of the surface ground copper foil (3).

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