High-frequency high-suppression low-pass filter and preparation method thereof

Abstract

The invention discloses a low-pass filter and a preparation method thereof, and the low-pass filter comprises a porcelain body, a first inductor, a second inductor, a third inductor, a fourth inductor, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, and a fifth capacitor. A first inductor, a second inductor, a third inductor and a fourth inductor which are electrically connected in sequence are arranged in the left side of the porcelain body to form a series inductor middle layer, and a first capacitor, a third capacitor and a fifth capacitor are arranged above the inductor middle layer and electrically connected with the series inductor middle layer. The second capacitor and the fourth capacitor are arranged below the inductor middle layer and electrically connected with the series inductor middle layer, the capacitor and the inductor on the left side form a first filter circuit, the second filter circuit symmetrical to the first filter circuit is arranged on the right side of the porcelain body and electrically connected with the first filter circuit, and the first capacitor is connected to the input pin. The output end of the second filter circuit is connected to the output pin, and the input pin and the output pin are arranged on the upper surface of the porcelain body. The two filters are cascaded, so that high suppression can be realized.

Description

Technical Field

[0001] The invention relates to a high-frequency high-inhibition low-pass filter and a preparation method thereof, belonging to the technical field of LTCC low-temperature co-fired ceramic filters. Background Art

[0002] A low-pass filter is an electronic filter device that allows signals below the cutoff frequency to pass, but does not allow signals above the cutoff frequency to pass. Conventional low-pass filter electrical assembly processes use reflow soldering processes, which can cause contamination and the entire board to be over-reflowed during reflow soldering. Assembly is achieved by bringing out surface electrodes and bonding them together.

[0003] In addition, it is difficult to achieve high suppression with conventional filters, and debugging is very difficult using high-order filters. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a high-frequency high-suppression low-pass filter and a preparation method thereof, which can meet the requirements of high suppression and bonding process without the need for reflow soldering.

[0005] The technical solution adopted by the present invention is: a high-frequency high-suppression low-pass filter, including a porcelain body, a first inductor, a second inductor, a third inductor, a fourth inductor, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and a fifth capacitor. The first inductor, the second inductor, the third inductor and the fourth inductor are arranged in sequence through silver electrodes on the left side of the porcelain body to form a series inductor. The first capacitor, the third capacitor and the fifth capacitor are arranged below the inductor layer to form a grounding capacitor with the ground. The second capacitor and the fourth capacitor are arranged above the inductor middle layer and are connected in parallel with the second inductor and the third inductor. The capacitors and inductors on the left side form a first filter circuit. A second filter circuit symmetrical to the first filter circuit is arranged on the right side of the porcelain body and is electrically connected to the first filter circuit. The first inductor is connected to the input pin. The second filter circuit is connected to the output pin after mirroring. The input pin and the output pin are arranged on the upper surface of the porcelain body, and the low-pass filter is connected to the circuit board through a gold wire mesh cable. Furthermore, the first capacitor, the third capacitor and the fifth capacitor include three first upper electrode plates and a common lower electrode plate arranged in gaps, the common lower electrode plate is connected to the common ground plane on the bottom of the porcelain body through a silver electrode column, and the second capacitor and the fourth capacitor both include a second upper electrode plate and a first lower electrode plate.

[0006] Furthermore, the common lower electrode plate is connected to four test ground terminals through a plurality of inner electrodes, and the four test ground terminals are arranged on the top surface of the porcelain body and are located at two on each side of each input pin and output pin.

[0007] Furthermore, the second inductor and the third inductor are arranged in a front-to-back staggered manner in the ceramic body.

[0008] A method for preparing a high-frequency high-rejection low-pass filter, the method comprising the following steps: S1. Ingredients: Select a material with a dielectric constant of 5.1, and ball-mill the powder into a particle size of 0.3-0.5 μm; S2, tape casting: the ingredients after ball milling are prepared into slurry, and the raw porcelain tapes of different thicknesses are obtained by tape casting technology; S3, cutting: cutting the raw porcelain tape into 6-inch-long raw porcelain tapes of various thicknesses; S4, drilling: according to the prepared drilling pattern, use a laser drilling machine to drill holes on the raw porcelain belt that needs to be drilled; S5. Printing: The printing method is screen printing. The design graphics are prepared on the film. After exposure, the inductance and capacitance of the product are transferred to the 400-mesh steel screen covered with photosensitive adhesive to form a printing jig; by controlling the thickness of the photosensitive adhesive coating: 32μm~55μm; printing GAP value: 0.5mm~3mm; printing scraper pressure: 0.05MPa~0.20MPa; scraper step speed 0.01m / s~0.10m / s; each layer of the design model containing the inductor or capacitor pattern is printed on the raw porcelain tape of the corresponding thickness, the printed inductor line width error is within 2μm, the inductor thickness is 12-15μm, the printed capacitor length and width error is within 5μm, and the capacitor thickness is 8-10μm; S6, lamination: lamination of each printed raw ceramic tape according to the design sequence using a fully automatic alignment lamination machine; S7, isostatic pressing: the laminated membrane is subjected to final isostatic pressing; the maximum isostatic pressing temperature is 70℃~75℃; the holding time is 600s~900s; the holding pressure is 5100psi~8300psi, forming a Bar block; S8, cutting: divide the Bar block into independent product units with a size of 6.95mm*3.24mm and an error of ±0.1mm; S9, debinding: Debinding the split products for 36 hours according to the debinding curve with a dielectric constant of 5.1; S10, sintering: the debinding products are sintered in a tunnel furnace; the tunnel furnace belt speed is 45mm / min, there are 12 sintering temperature zones, the sintering temperature is 875℃, and the holding time is 50min~60min; S11, chamfering: chamfering the sintered product; S12, Silver Dipping: Use a fully automatic terminal electrode silver dipping machine to coat the external terminal electrodes of the chamfered products; S13, Silver Burning: Silver burning process is performed on the silver-coated products; silver burning is performed using a tunnel furnace; there are 6 sintering temperature zones, sintering temperature: 715°C, and holding time: 20min~25min; S14, electroplating: After silver firing, the product is electroplated with nickel, tin and lead to obtain the final product.

[0009] The beneficial effects of the present invention are as follows: compared with the prior art, the cascaded first filter circuit and the second filter circuit of the present invention can achieve high frequency and high suppression, reduce the difficulty of debugging, and are connected to the product circuit board by a gold wire mesh connection method to reduce pollution. The capacitor structure is arranged with a compact structure, and the pole capacitor on the upper side is far away from the ground terminal to avoid parasitic interference from the ground terminal and improve the stability of the filter. Through simulation data, the two cascaded seventh-order low-pass filters of the present invention can meet the design requirements of a passband frequency of DC-13.48GHz, a stopband of 14GHz, and a loss greater than 20dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the three-dimensional structure of a low-pass filter; Figure 2 This is a schematic diagram of the three-dimensional structure of the low-pass filter from another perspective; Figure 3 It is a schematic diagram of the forward-looking structure of the low-pass filter; Figure 4 It is a schematic diagram of the left-view structure of the low-pass filter; Figure 5 It is a schematic diagram of the structure of a low-pass filter viewed from above; Figure 6 It is a schematic diagram of the simulation structure of the low-pass filter forward-looking circuit; Figure 7 It is the insertion loss and rejection curve of the low-pass filter. DETAILED DESCRIPTION

[0011] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0012] Example 1: Figure 1-7A low-pass filter comprises a ceramic body 1, a first inductor 2, a second inductor 3, a third inductor 4, a fourth inductor 5, a first capacitor 6, a second capacitor 7, a third capacitor 8, a fourth capacitor 9 and a fifth capacitor 10. The first inductor 2, the second inductor 3, the third inductor 4 and the fourth inductor 5 are arranged in sequence and electrically connected to form a series inductor middle layer on the left side of the ceramic body 1. The first capacitor 6, the third capacitor 8 and the fifth capacitor 10 are arranged above the inductor middle layer and electrically connected to the series inductor middle layer. The second capacitor 7 and the fourth capacitor 9 are arranged below the inductor middle layer and electrically connected to the series inductor middle layer. The capacitors and inductors on the left side form a first filter circuit. A second filter circuit symmetrical to the first filter circuit is arranged on the right side of the ceramic body 1 and is electrically connected to the first filter circuit. The first capacitor 2 is connected to an input pin 15, and the output end of the second filter circuit is connected to an output pin 16. The input pin 15 and the output pin 16 are arranged on the upper surface of the ceramic body 1 and are respectively connected to the input end of the first filter and the output end of the second filter through an input inner electrode 17 and an output inner electrode 18. The low-pass filter is connected to a circuit board through a gold wire mesh line.

[0013] Usually, the input and output terminals of a product are led out from the side. The present invention introduces the input and output terminals from the top surface, and welding can be achieved through micro-assembly. Structurally, the input and output are led to the surface of the product by designing long through holes, thereby achieving lead-out, meeting the welding process requirements of gold wire bonding.

[0014] In order to save space and increase the grounding effect, the first capacitor 6, the third capacitor 8 and the fifth capacitor 10 include three first upper electrode plates and a common lower electrode plate arranged in gaps. The common lower electrode plate is connected to the common grounding surface 12 on the bottom surface of the porcelain body 1 through a short terminal 11. The second capacitor 7 and the fourth capacitor 9 both include a second upper electrode plate and a first lower electrode plate. This structure can improve the grounding effect.

[0015] The circuit of the low-pass filter includes a first filter circuit and a second filter circuit connected in series. The first filter circuit includes an input terminal, a first inductor 2, a second inductor 3, a third inductor 4 and a fourth inductor 5 which are electrically connected in sequence. One end of the first capacitor 6, the third capacitor 8 and the fifth capacitor 10 are electrically connected between the first inductor 2 and the second inductor 3, between the second inductor 3 and the third inductor 4 and between the third inductor 4 and the fourth inductor 5, respectively, and the other end is grounded. One end of the second capacitor 7 and the fourth capacitor 9 are both electrically connected between the second inductor 3 and the third inductor 4, and the other end is electrically connected between the first inductor 2 and the second inductor 3 and between the second inductor 2 and the third inductor 3, respectively. The second filter circuit is symmetrical in structure with the first filter circuit and is connected to the output terminal. To facilitate testing, the common lower electrode plate is connected to four test ground terminals 14 through multiple internal electrodes 13. The four test ground terminals 14 are arranged on the top surface of the porcelain body 1 and are located on both sides of each input pin 15 and output pin 16, two each. The ground terminals are led to the upper side of the porcelain body to facilitate wiring during testing and improve test efficiency.

[0016] In order to achieve adjustable inductance, the second inductor 3 and the third inductor 4 are arranged front to back in the ceramic body 1 in an alternating manner. The alternating arrangement can free up more space for adjusting the inductance. Because the inductance of the inductor is related to the length, the larger the space, the more convenient it is to adjust.

[0017] Embodiment: A method for preparing a low-pass filter, the method comprising the following steps: S1. Ingredients: The dielectric constant of the product material is 5.1, and the powder is ball-milled to a set particle size (0.3-0.5μm); S2, tape casting: the ingredients after ball milling are prepared into slurry, and the tape casting technology is used to obtain high-precision green porcelain tapes of different thicknesses (the key film thickness is 45μm); S3, cutting: cutting the raw porcelain tape into raw porcelain tapes of various thicknesses of a set size (usually 6 inches long); S4, drilling: according to the prepared drilling pattern, use a laser drilling machine to drill holes on the raw porcelain belt that needs to be drilled; S5. Printing: The printing method is screen printing. The designed three-dimensional graphics are prepared on the film. After exposure, the inductance and capacitance of the product are transferred to the 400-mesh steel screen covered with photosensitive adhesive to form a printing jig; by controlling the thickness of the photosensitive adhesive coating: 32μm~55μm; printing GAP value: 0.5mm~3mm; printing scraper pressure: 0.05MPa~0.20MPa; scraper step speed 0.01m / s~0.10m / s; each layer of the design model containing the inductor or capacitor pattern is printed on the raw porcelain tape of the corresponding thickness, the printed inductor line width error is within 2μm, the inductor thickness is 12-15μm, the printed capacitor length and width error is within 5μm, and the capacitor thickness is 8-10μm; S6, stacking: stack the printed raw ceramic tapes according to the design sequence using special equipment (such as a fully automatic alignment stacking machine); S7, isostatic pressing: the laminated membrane is subjected to final isostatic pressing; the maximum isostatic pressing temperature is 70℃~75℃; the holding time is 600s~900s; the holding pressure is 5100psi~8300psi, forming a Bar block; S8, cutting: divide the Bar block into 6.95mm*3.24mm, with an error of ±0.1mm and independent product units; S9, debinding: Debinding the split products for 36 hours according to the debinding curve with a dielectric constant of 5.1; S10, sintering: the debinding products are sintered in a tunnel furnace; the tunnel furnace belt speed is 45mm / min, there are 12 sintering temperature zones, the sintering temperature is 875℃, and the holding time is 50min~60min; S11, chamfering: chamfering the sintered product; S12, Silver Dipping: Use a fully automatic terminal electrode silver dipping machine to coat the external terminal electrodes of the chamfered products; S13, silver burning: silver burning process is carried out on the silver-coated products; silver burning is carried out using a tunnel furnace; there are 6 sintering temperature zones, sintering temperature: 715℃, and holding time: 20min~25min; S14, electroplating: The silver-sintered product is electroplated into the final product.

[0018] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A high frequency high suppression low pass filter, characterized in that: The invention comprises a ceramic body (1), a first inductor (2), a second inductor (3), a third inductor (4), a fourth inductor (5), a first capacitor (6), a second capacitor (7), a third capacitor (8), a fourth capacitor (9) and a fifth capacitor (10); the first inductor (2), the second inductor (3), the third inductor (4) and the fourth inductor (5) are arranged on the left side of the ceramic body (1) to form a series inductor middle layer; the first capacitor (6), the third capacitor (8) and the fifth capacitor (10) are arranged above the inductor middle layer to be electrically connected to the series inductor middle layer. The second capacitor (7) and the fourth capacitor (9) are arranged below the inductor middle layer and are electrically connected to the series inductor middle layer. The capacitor and the inductor on the left side form a first filter circuit. A second filter circuit symmetrical to the first filter circuit is arranged on the right side of the ceramic body (1) and is electrically connected to the first filter circuit. The first capacitor (2) is connected to the input pin (15). The output end of the second filter circuit is connected to the output pin (16). The input pin (15) and the output pin (16) are arranged on the upper surface of the ceramic body (1). The low-pass filter is connected to the circuit board through a gold wire mesh cable.

2. A low-pass filter according to claim 1, characterized in that: The first capacitor (6), the third capacitor (8) and the fifth capacitor (10) include three first upper electrode plates and a common lower electrode plate arranged at intervals, the common lower electrode plate being connected to a common ground plane (12) on the bottom surface of the porcelain body (1) via a short terminal (11), and the second capacitor (7) and the fourth capacitor (9) both include a second upper electrode plate and a first lower electrode plate.

3. A low-pass filter according to claim 1, characterized in that: The common lower electrode plate is connected to four test ground terminals (14) through a plurality of inner electrodes (13). The four test ground terminals (14) are arranged on the top surface of the porcelain body (1) and are located two on each side of each input pin (15) and output pin (16).

4. A low-pass filter according to claim 1, characterized in that: The second inductor (3) and the third inductor (4) are arranged in a front-to-back staggered manner inside the porcelain body (1).

5. The method for preparing a low-pass filter according to claim 1, characterized in that: The method comprises the following steps: S1. Ingredients: Select a material with a dielectric constant of 5.1, and ball-mill the powder into a particle size of 0.3-0.5 μm; S2, tape casting: the ingredients after ball milling are prepared into slurry, and the raw porcelain tapes of different thicknesses are obtained by tape casting technology; S3, cutting: cutting the raw porcelain tape into 6-inch-long raw porcelain tapes of various thicknesses; S4, drilling: according to the prepared drilling pattern, use a laser drilling machine to drill holes on the raw porcelain belt that needs to be drilled; S5. Printing: The printing method is screen printing. The three-dimensional graphics of the low-pass filter design are prepared on the film. After exposure, the inductance and capacitance of the product are transferred to the 400-mesh steel screen covered with photosensitive adhesive to form a printing jig; by controlling the thickness of the photosensitive adhesive coating: 32μm~55μm; printing GAP value: 0.5mm~3mm; printing scraper pressure: 0.05MPa~0.20MPa; scraper step speed 0.01m / s~0.10m / s; each layer of the design model containing the inductor or capacitor pattern is printed on the raw porcelain tape of the corresponding thickness, the printed inductor line width error is within 2μm, the inductor thickness is 12-15μm, the printed capacitor length and width error is within 5μm, and the capacitor thickness is 8-10μm; S6, lamination: lamination of each printed raw ceramic tape according to the design sequence using a fully automatic alignment lamination machine; S7, isostatic pressing: the laminated membrane is subjected to final pressing by isostatic pressing; the maximum isostatic pressing temperature is 70℃~75℃; the holding time is 600s~900s; the holding pressure is 5100psi~8300psi, forming a Bar block; S8, cutting: divide the Bar block into 6.95mm*3.24mm, with an error of ±0.1mm and independent product units; S9, debinding: Debinding the split products for 36 hours according to the debinding curve with a dielectric constant of 5.1; S10, sintering: the debinding product is sintered in a tunnel furnace; the tunnel furnace belt speed is 45mm / min, there are 12 sintering temperature zones, the sintering temperature is 875℃, and the holding time is 50min~60min; S11, chamfering: chamfering the sintered product; S12, Silver Dipping: Use a fully automatic terminal electrode silver dipping machine to coat the external terminal electrodes of the chamfered products; S13, silver burning: silver burning process is performed on the silver-coated product; silver burning is performed using a tunnel furnace; there are 6 sintering temperature zones, sintering temperature: 715°C, and holding time: 20min to 25min; S14, electroplating: After silver firing, the product is electroplated with nickel, tin and lead to obtain the final product.

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