High-consistency lumped parameter isolator based on LTCF process

Abstract

The invention discloses a high-consistency lumped parameter isolator based on an LTCF process, and belongs to the technical field of microwave devices. Comprising an upper shell (1), a strontium constant magnet (2), an LTCF ferrite substrate (8), a PCB (9) and a lower shell (7) which are sequentially connected from top to bottom, the LTCF ferrite substrate (8) comprises a ferrite base material (8-1), one face of the ferrite base material (8-1) is provided with three square bonding pads A (8-2), the other face of the ferrite base material (8-1) is completely provided with a metal layer (8-3) in a fired mode, and the metal layer (8-3) is arranged on the lower shell (7). The three square bonding pads A (8-2) are communicated with the metal layer on the other side through the metal layers (8-3) on the side surfaces; or the ferrite base material (8-1) is communicated with the bonding pad A (8-2) in a metalized via hole mode; on the premise that performance indexes are not changed, higher production consistency can be achieved, the S parameter CPK can reach 1.3 or above, and the production efficiency can be improved by 50% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave devices, and particularly to a highly consistent lumped parameter isolator based on the LTCF process. Background Art

[0002] A lumped parameter isolator is a microwave passive device with unidirectional conduction and reverse isolation functions, which is widely used in microwave electronic systems and can effectively improve the working efficiency, stability and reliability of the system. The lumped parameter isolator circuit mainly consists of two parts: a ferrite ring module and a matching capacitor load. The consistency of the ferrite ring module determines the consistency of the device performance. Usually, the implementation method of the ferrite ring module is that three soft-state center conductors forming 120° with each other wrap the ferrite substrate, and the center conductor arms in the vertical direction are isolated by polyimide films. In the actual production and assembly process, due to factors such as the size tolerance of the ferrite, the forming accuracy of the equipment, and the sensitivity of the ring module, it is very difficult to guarantee the consistency of the ferrite ring module, thus resulting in lumped parameters. Therefore, how to ensure the consistency of the ferrite ring module has always been one of the key tasks in the research of microwave ferrite devices.

[0003] The structure of the current mainstream 5mm lumped parameter device is as Figure 1 shown, and it mainly consists of seven parts: an upper housing 1, a strontium permanent magnet 2, a ferrite ring module 3, a capacitor 4, a load 5, a plastic package 6, and a lower housing 7. The components are connected by soldering; among them, the ferrite ring module 3 consists of three parts: a center conductor 3-1, a ferrite substrate 3-2, and a polyimide film 3-3, as Figure 2 shown.

[0004] The fabrication of the ferrite ring module 3 is achieved through mechanical actions. The specific steps are as follows: Place the ferrite substrate 3-2 at the center of the center conductor 3-1, and the three soft-state arms of the center conductor 3-1 wrap the ferrite substrate 3-2 respectively. Each center conductor arm is isolated by a polyimide film 3-3. After the wrapping action is completed, use a tooling to level the three rectangular pads of the ferrite ring module 3 to keep them in a plane.

[0005] The ferrite ring module 3 fabricated by mechanical actions has at least the following problems for a long time due to factors such as the size tolerance of the ferrite, the forming accuracy of the equipment, and the sensitivity of the ring module: 1. The state of the equipment mechanism is unstable and the forming consistency is poor. The forming process of the ferrite ring module 3 requires the use of a mechanical structure. In the actual production process, differences inevitably exist in the repeated installation process of the mechanical structure, resulting in inconsistent states of the ferrite ring modules 3 in different batches; 2. The poor consistency of the ferrite ring module status leads to obvious changes in device performance. Multiple factors such as the forming angle of the arm of the center conductor and the height of the ferrite ring module 3 will affect the device performance, and the sensitivity is relatively high, resulting in difficulty in maintaining the performance consistency of different devices. 3. The efficiency of using the mechanically formed ferrite ring module 3 is low, which is not conducive to mass production.

[0006] In the prior art, for example, in Chinese Patent Application CN113555655A, its induction structure is still the structure where the center conductor wraps the ferrite substrate, so it still has the above problems of inconsistent forming state and poor performance consistency. Another example is Chinese Patent Application CN115986359A. The essence of its ferrite circuit is to use processes such as thick film technology, magnetron sputtering, and low-temperature sintering to implement the induction structure in CN113555655A or the ferrite ring module of the above-mentioned existing lumped parameter devices. That is, CN115986359A integrates the center conductor circuit above the ferrite using the above processes, and its PCB printed circuit board only plays a role in structural support and carrying components. The design principles and the structural positions of the components of CN115986359A and CN113555655A are completely the same, only the process implementation is different.

[0007] That is to say, the structures reported in the prior art are essentially all traditional ferrite ring module structures and also have similar problems. Summary of the Invention

[0008] One of the purposes of the present invention is to provide a high-consistency lumped parameter isolator based on the LTCF process to solve the above problems.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A high-consistency lumped parameter isolator based on the LTCF process includes an upper housing, a strontium permanent magnet, an LTCF ferrite substrate, a PCB circuit board, and a lower housing that are connected in sequence from top to bottom.

[0010] As a preferred technical solution, the upper housing, the strontium permanent magnet, the LTCF ferrite substrate, the PCB circuit board, and the lower housing are sequentially connected by soldering with solder paste.

[0011] As a preferred technical solution, the LTCF ferrite substrate includes a ferrite base material. On one side of the ferrite base material, there are three square pads A, and the other side is entirely fired with a metal layer. The three square pads A are connected to the metal layer on the other side through the metal layer on the side; or the ferrite base material and the pad A are connected through metallized vias.

[0012] As a preferred technical solution, the PCB circuit board is composed of three layers of PCB boards in total. The first layer prints a mesh circuit, the second layer realizes isolation from the ground plane, and the third layer is provided with slots for welding the lower housing. The three layers of PCB boards are connected by metallized vias; pads B for welding with the LTCF ferrite substrate are reserved on the upper surface of the PCB circuit board.

[0013] Structurally, compared with the prior art such as the aforementioned CN113555655A and CN115986359A, the structure of the prior art is that the central conductor circuit wraps the ferrite, while the structure of the present application is that the central conductor circuit is printed on the mesh-structured PCB circuit board, and only one layer of LTCF ferrite substrate is used, and the LTCF process can be adopted, and the implementation difficulty is much lower than the induction structure in CN115986359A. In addition, the structure of the present invention is, from bottom to top, a PCB printed board (including the central conductor circuit), an LTCF ferrite substrate; while the structures of CN113555655A and CN115986359A are, from bottom to top, a PCB printed board (not including the central conductor circuit), a ferrite, and a central conductor circuit, and the structural differences are obvious.

[0014] The present invention uses a PCB circuit board with a mesh circuit structure to print the central conductor circuit on the PCB circuit board, avoiding the operation of the central conductor wrapping the ferrite in the prior art, and reducing the high braiding forming difficulty caused by the small size during the wrapping process and the consistency problem caused by the limited mechanical movement accuracy.

[0015] Compared with the prior art, the advantages of the present invention are as follows: (1) Compared with the existing conventional 5mm lumped parameter devices, the 5mm highly consistent lumped parameter isolator based on the LTCF process of the present invention can achieve higher production consistency on the premise of unchanged performance indicators, and the S parameter CPK can reach more than 1.3; (2) The production efficiency of the 5mm highly consistent lumped parameter isolator based on the LTCF process of the present invention can be increased by more than 50% on the basis of the existing 5mm lumped parameter devices; (3) The present invention avoids the secondary processing of parts in the existing 5mm lumped parameter device solution (that is, using mechanical movement to realize the forming of the ferrite toroidal module), significantly reducing the production difficulty; the present invention uses the common SMT reflow soldering process for mounting, which is conducive to mass production. Description of the Drawings

[0016] Figure 1 Schematic diagram of the structure of the lumped parameter device in the prior art; Figure 2 is Figure 1 Schematic diagram of the ferrite toroidal module in Figure 3 Device structure diagram of an embodiment of the present invention; Figure 4 is Figure 3 Structure diagram of the LTCF ferrite substrate in Figure 5 is Figure 3 Structure diagram of the PCB circuit board in Figure 6 Device simulation curve of an embodiment of the present invention; Figure 7 is the simulation curve of a 5mm lumped parameter device in the prior art.

[0017] In the figure: 1. Upper shell; 2. Strontium permanent magnet; 3. Ferrite ring module; 3-1. Central conductor; 3-2. Ferrite substrate; 3-3. Polyimide film; 4. Capacitor; 5. Load; 6. Plastic package shell; 7. Lower shell; 8. LTCF ferrite substrate; 8-1. Ferrite base material; 8-2. Pad A; 8-3. Metal layer; 9. PCB circuit board; 9-1. Mesh circuit; 9-2. Slot; 9-3. Pad B. Detailed implementation manners

[0018] The present invention will be further described below in conjunction with embodiments.

[0019] It should be noted that the LTCF ferrite substrate and PCB printed board of the present invention are prepared by methods well known in the art. In the following embodiments, the ferrite material of the LTCF ferrite substrate uses 10G21 garnet ferrite with a size of 3×3×0.15mm (saturation magnetization intensity of 1000 Gauss, dielectric constant of 13.5), and the PCB printed board uses Rogers 4350B (dielectric constant of 3.66, loss tangent of 0.004), with thicknesses of 0.25 / 0.127 / 0.25 / 0.2mm from top to bottom in sequence, and the circuit trace design schematic diagram is as shown in the attached drawings. Through the above material parameter settings, those of ordinary skill in the art can implement and realize the present invention.

[0020] Embodiment 1: Refer to Figure 3 , a highly consistent lumped parameter isolator based on the LTCF process, which is composed of seven parts: an upper shell 1, a strontium permanent magnet 2, an LTCF ferrite substrate 8, a capacitor 4, a load 5, a PCB circuit board 9, and a lower shell 7, and the components are connected by solder paste welding.

[0021] Taking the common 2110 - 2170 MHz frequency band as an example in this embodiment, through the solution described in this embodiment, a 2110 - 2170 MHz isolator with a size of 5mm×5mm is simulated and designed. The simulation result curve is as Figure 6As shown, the return loss and isolation are greater than 20 dB, and the insertion loss is less than 0.4 dB. As Figure 7 shown, compared with the existing 5 mm lumped parameter devices, the simulation indexes of this embodiment have no obvious difference.

[0022] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high consistency lumped parameter isolator based on LTCF process, characterized in that: It comprises an upper shell (1), a strontium permanent magnet (2), an LTCF ferrite substrate (8), a PCB circuit board (9), and a lower shell (7) which are connected in sequence from top to bottom.

2. The high consistency lumped parameter isolator based on LTCF process according to claim 1, characterized in that: The upper housing (1), the strontium permanent magnet (2), the LTCF ferrite substrate (8), the PCB circuit board (9) and the lower housing (7) are connected in sequence by soldering with solder paste.

3. The high consistency lumped parameter isolator based on LTCF process according to claim 1, characterized in that: The LTCF ferrite substrate (8) comprises a ferrite base material (8-1), one side of the ferrite base material (8-1) is provided with three square pads A (8-2), and the other side is completely fired with a metal layer (8-3), the three square pads A (8-2) are connected to the metal layer on the other side through the metal layer (8-3) on the side; or the ferrite base material (8-1) and the pads A (8-2) are connected by means of metallized vias.

4. The high consistency lumped parameter isolator based on LTCF process according to claim 1, characterized in that: The PCB circuit board (9) is composed of three layers of PCB boards in total, the first layer is a printed mesh circuit (9-1), the second layer is isolated from the ground plane, and the third layer is provided with slots (9-2) for welding the lower shell (7), and the three layers of PCB boards are connected through metallized vias; the upper surface of the PCB circuit board (9) is reserved for a pad B (9-3) for welding to the LTCF ferrite substrate (8).

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