Microwave coaxial interposer
By designing a microwave coaxial interposer, the reliability and loss issues of board-to-board connections in existing technologies are solved, providing a low-loss, reproducible connection solution suitable for active antennas and amplifier modules with high-frequency signal density.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- THALES SA
- Filing Date
- 2024-09-05
- Publication Date
- 2026-04-21
AI Technical Summary
Existing technologies struggle to achieve efficient and reliable board-to-board connections in electrical interconnects across the DC to microwave frequency range, especially in active antennas and amplifier modules. Conventional solutions such as silver-filled flexible conductive epoxy adhesives, soldering, sintering, and coaxial connectors suffer from problems such as high losses, non-removability, high cost, and large size.
Employing a microwave coaxial interposer, including a printed circuit board, cylindrical diffuser contacts, and copper grounding vias, heterogeneous components are connected via a conductive epoxy adhesive layer, providing flexible, low-loss RF connections that can adapt to the thermomechanical requirements of different materials.
It achieves low-loss, reproducible board-to-board connections, adapts to substrates with different dielectric constants, avoids delamination and asymmetry, and is suitable for active antenna applications with high-frequency signal density.
Smart Images
Figure CN121909565A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a microwave coaxial interposer. Background Technology
[0002] This invention is intended for electrical interconnects operating in a frequency range from direct current (DC) to microwave frequencies (40 GHz and above). It is applicable to all types of board-to-board or board-to-wire electrical connections (such as amplifiers, filters, combiners, radiating elements, circulators, isolators, etc.). It is particularly useful for amplification, transposition, or active antenna functions where constraints on signal density and integration are considerable, and the interrelationships between functions require managing different spread factors.
[0003] To develop clamp interconnect amplifiers based on modular principles, it is necessary to be able to ground the modules while maintaining their removability. Without this, the desired performance characteristics cannot be achieved.
[0004] Several solutions have been tested: - Use braided O-rings; - Use adhesive bonding (silver-filled epoxy adhesive). - Use a gasket made of pyrolytic graphite sheets (PGS); and - Use a conductive seal of type Getelec GT1000.
[0005] These solutions are ineffective due to RF contact quality and associated losses. Clamped interconnects are not feasible in this situation.
[0006] It is also necessary to be able to transmit RF signals from one board to another (boards stacked on top of each other in the driver module). Spacing constraints are imposed by the DC board to board connectors, and it is difficult to find off-the-shelf solutions that perfectly meet the same spacing requirements under size constraints.
[0007] Finally, in the context of active antennas operating in the Ka band (31 GHz), it is necessary to connect a board or printed circuit board integrating one or more components of a beamforming integrated circuit (BFIC) to metallic radiating elements whose varying extents do not allow for conventional soldering. This assembly is referred to as a BFIC board.
[0008] The main solutions to the above problems are conventional solutions, the inventions of which have fallen into the public domain. These solutions either use flexible materials (silver-filled epoxy adhesives or soft solder) or use the coaxial connector principle (SMP, which stands for "Sub Miniature Push-on"), equipped with so-called spring tumblers.
[0009] Solutions based on silver-filled flexible conductive epoxy adhesives cannot be used because the losses are too high, and when the RF power exceeds one watt, the adhesive heats up and evaporates. Furthermore, in the case of active antennas, it is impossible to accurately measure the required amount of adhesive (as in the case of viscous solutions). This process is not feasible on an industrial scale. Pre-molded silver-filled conductive epoxy adhesives or "pre-molded glues" (e.g., Canalfilm or Canalstick 5025E or equivalents) would then be required; however, this is not feasible for RF contacts with a diameter of approximately 0.5 mm in the Ka band. The adhesive degrades on very small surfaces and has a tendency to crack over time.
[0010] Soldering solutions are also ineffective in industrial production workflows because components are routed on a single surface on BFIC boards, leading to circuit bending: the contact quality with radiating elements becomes uncontrollable. This necessitates increasing fatigue associated with differential thermal expansion stresses. These components are non-removable.
[0011] Sintering solutions cannot be used because the remelted profile of components mounted on BFIC boards or RF modules is incompatible with the temperatures used in the sintering process.
[0012] Coaxial connection solutions using SMP springs are too bulky, too expensive, and result in excessive wear.
[0013] Contact pressure solutions or "clamping" solutions are not feasible in certain scenarios (especially on active antenna interposers or amplifier module RF grounding contacts). Summary of the Invention
[0014] One object of the present invention is to alleviate the above-mentioned problems.
[0015] According to one aspect of the invention, a microwave coaxial interposer layer intended for arrangement between two heterogeneous elements is provided, comprising: - Printed circuit boards; - At least one cylindrical diffusion contact, said at least one cylindrical diffusion contact being inserted into a hole in a board, said board forming a gasket and insulating guide for said diffusion contact, one end of said diffusion contact extending to a portion of said printed circuit board and contacting said printed circuit board, and the other end of said diffusion contact extending out of said hole; - An RF track in the printed circuit board, one end of which extends into the bottom of the hole in the board and opposite the diffusion contact, and is configured to contact the diffusion contact; and the other end of the RF track extends to the outer surface of the printed circuit board, located outside the interposer layer; and - At least one cylindrical copper grounding via, the at least one cylindrical copper grounding via being coaxially arranged in the board around the diffusion contact, extending to one side of the board and also extending to the other side of the board, and configured to be electrically connected through the outer surface of the printed circuit board located outside the interposer layer.
[0016] In printed circuits, a via is a metallized hole that allows electrical connections to be established between two or more layers.
[0017] In one embodiment, the printed circuit board is a single-layer printed circuit board.
[0018] In this variant, the printed circuit board is a multilayer printed circuit board.
[0019] According to one embodiment, the interlayer includes a conductive epoxy adhesive layer disposed between the board and the printed circuit board.
[0020] In one embodiment, the interposer includes an RF track in the printed circuit board, one end of which extends opposite a cylindrical via, and the other end of which extends to the outer surface of the printed circuit board outside the interposer.
[0021] For example, the plate is made of metallized PTFE (which represents polytetrafluoroethylene), or ceramic or glass / PTFE composite material, or a low-loss RF laminate substrate.
[0022] According to one embodiment, the board comprises at least one layer of a printed circuit board.
[0023] According to one embodiment, a cylindrical grounding via extends to the outer surface of the printed circuit board located outside the interposer layer.
[0024] According to another aspect of the invention, an active antenna is also provided, comprising: - At least one radiating element; - A printed circuit board with at least one BFIC component; - An intermediary layer as described in any of the preceding claims is disposed between the radiating element and the printed circuit board; - A conductive epoxy resin adhesive layer between the plate of the radiating element and the intermediate layer; and - Solder balls between the BFIC component and the outer surface of the printed circuit board (BGA package). Attached Figure Description
[0025] The invention will be better understood by studying several embodiments described by way of entirely non-limiting examples and illustrated in the accompanying drawings, in which: Figure 1 A microwave coaxial interposer layer according to one aspect of the invention is schematically shown; and Figure 2 Another microwave coaxial interposer layer according to one aspect of the invention is schematically shown.
[0026] In all the accompanying drawings, elements with the same reference numerals are similar. Detailed Implementation
[0027] This invention is based on the use of diffusion contacts originally intended for the production of flexible board-to-board contacts. Such diffusion contacts consist of interlaced metal wires, for example, made of a gold-plated alloy of copper and beryllium.
[0028] When this interlaced structure is properly compressed (typically at a compression ratio of 30%), it provides sufficient resilience and excellent contact quality. This contact can be customized to have diameters ranging from 0.25 mm to 7 mm, and lengths greater than 1 mm, up to a maximum of 7 mm.
[0029] Therefore, the present invention is a component that implements this type of contact in an RF module or active antenna (or any other type of heterostructure or combination thereof designed to be stacked with RF contacts that may be up to 40 GHz).
[0030] Figure 1 A microwave coaxial interposer layer, intended to be arranged between two heterogeneous elements according to one aspect of the invention, is schematically shown.
[0031] The microwave coaxial interposer intended to be disposed between two heterogeneous components includes a printed circuit board 1 and at least one cylindrical diffusion contact 2 inserted into a hole 3 in a plate 4. The plate 4 forms a gasket and insulating guide for the diffusion contact 2. One end 2a of the diffusion contact 2 extends to and contacts a portion 1a of the printed circuit board, and the other end 2b of the diffusion contact extends out of the hole 3.
[0032] The microwave coaxial interposer also includes an RF track 5 in the printed circuit board 1, one end 5a of which extends to the bottom of the hole 3 in the board 4 and is opposite to the diffusion contact 2 and is configured to contact the diffusion contact 2, and the other end 5b of which extends to the outer surface of the printed circuit board 1 outside the interposer.
[0033] The microwave coaxial interposer also includes a cylindrical copper grounding via 6, which is arranged coaxially around the diffusion contact 2 in the board 4, extends to one side of the board 4 and also extends to the other side of the board 4, and is configured to be electrically connected through the outer surface of the printed circuit board 1 located outside the interposer.
[0034] Figure 1 The microwave coaxial interposer is shown between two elements, in this example, an active antenna radiating element 7 and a board 1 provided with BFIC components 8 in BGA (BGA stands for "Ball Grid Array", i.e., provided with solder balls 9) format.
[0035] exist Figure 1 In the example, printed circuit board 1 is a multilayer printed circuit board, but it can alternatively be a single-layer circuit board.
[0036] For example, the microwave coaxial interlayer includes a conductive epoxy resin adhesive layer 10 disposed between the board 4 and the printed circuit board 1.
[0037] The epoxy resin adhesive used is filled with silver and is preferably in the form of a preform, thereby ensuring the thickness of the adhesive (compared to a tack formulation).
[0038] exist Figure 1 In the example, the interposer layer as described in any of the preceding claims includes at least one RF track 11 in the printed circuit board 1, one end 11a of which extends opposite to the cylindrical via 6, and the other end 11b of which extends to the outer surface of the printed circuit board 1 located outside the interposer layer and intended for connecting to RF ground.
[0039] Board 4 can be made of metallized PTFE or a glass / ceramic / PTFE composite RF laminate substrate, thus enabling operation with a low relative permittivity typically less than 3, and its geometry is compatible with the manufacturing tolerances of the diffused contacts for high frequencies of approximately 40 GHz and above. For frequencies below the Ku band (12 GHz), other substrates with higher relative permittivity can be used.
[0040] This embodiment allows for the adaptation of completely different materials without inducing thermomechanical stress, because the silver-filled epoxy adhesive is flexible and thermally conductive. This avoids the use of stacks of layers of different thicknesses for the printed circuit board 1, which could lead to asymmetry in the delamination of the printed circuit board 1.
[0041] When beamforming integrated circuits (BFICs) are used, the substrate typically employed is a ceramic / glass / PTFE composite RF laminate substrate with a relative permittivity of approximately 3.48 at a substrate thickness of 10 mils (0.254 mm). This is because the BFIC's coverage area is designed to operate with a standard impedance of 50 ohms in a ball grid array (BGA) format. The diameter of the spheres, the spacing between the spheres, and the interface between the spheres and the integrated circuit board or printed circuit board (PCB) are considered in the component design. Therefore, this wiring constraint is imposed by the component and its package.
[0042] On the other side of the interposer, the radiating elements impose dimensional constraints. When these constraints differ from those imposed by the BFIC components, it is impossible to obtain a symmetrical multilayer printed circuit board. However, symmetry is crucial for avoiding buckling and delamination effects. Therefore, there is no alternative but to use an interposer with adhesive bonding. Prepreg could be used, but adhesive bonding must occur after die bonding of the BFIC circuitry, making the use of prepreg impossible.
[0043] Therefore, low-temperature adhesive bonding via preforms is necessary. Furthermore, the use of a ceramic / glass / PTFE composite RF laminate substrate allows for the creation of grounding vias around the diffuser contacts. This allows for limitations on the number and spacing of the diffuser contacts (which will then also be used for grounding). However, as mentioned above, a vertical grounding connection is then required. A silver-filled epoxy adhesive allows for the interconnection of grounding components. Without this adhesive layer, grounding paths could frequently be interrupted due to the natural buckling of the BFIC board (since all components are soldered to a single surface) or the interlayer.
[0044] It is crucial to ensure the required compression ratio for good contact quality. As a general rule, a 30% compression ratio is recommended for the diffuser stud 2. To absorb excess compression, a hole is formed at a 30° angle at the end of the exposed area of the hole, with a thickness of 0.15 mm. An isolation device is required between the contact area and the grounding area to ensure no short circuits.
[0045] Given the density of the signals to be processed, this new component is specifically designed for applications with active antennas.
[0046] exist Figure 2 In the example, board 4 consists of at least one layer of printed circuit board 1. In other words, the printed circuit board also acts as board 4 to form gaskets and insulating guides for diffusion contacts 2.
[0047] A cylindrical grounding via 6 extends to the outer surface of the printed circuit board 1, which is located outside the interposer layer.
[0048] Figure 1 and Figure 2 The present invention’s intermediary layer is shown in an active antenna, wherein solder balls 9 are provided between at least one radiating element 7 and BFIC board 8, between BFIC board 8 and the outer surface of printed circuit board 1, and a conductive epoxy resin adhesive layer 12 is provided between radiating element 7 and intermediary layer board 4.
[0049] Figure 2 The intermediary layer in the middle is similar to Figure 1The intermediate layer in this solution is simplified. Specifically, in this case, board 4 consists of at least one layer of printed circuit board 1, thus printed circuit board 1 directly acts as a spacer and integrated guide for the diffusion contact 2. Within the hole 3, the diffusion contact 2 abuts against the surface of one of the inner layers. The advantages of this solution are that it eliminates the need for adhesive bonding 10, reduces costs, eliminates the need for an additional board 4, and shortens the RF path length (resulting in less loss). However, the wiring constraints applied to printed circuit board 11 must remain the same.
[0050] Given the density of the signals to be processed, this type of interposer component is new and is specifically designed for applications with active antennas.
[0051] The present invention has the following advantages, specifically for active antennas or for bonding heterogeneous elements or boards by adhesive bonding: - Non-statically indeterminate (flexible) RF connections can manage high differential expansion coefficients (the concept of heterogeneity). This solution makes it particularly possible to connect printed circuit boards to mechanical components (additive manufacturing or metal 3D printing) while meeting both RF and thermomechanical requirements; - Low-loss and reproducible (industrial) connections, provided that adhesive bonding is used with conductive adhesive preforms. - Very dense, inexpensive, and easy-to-use connections; - This allows for RF confinement between two substrates with different relative permittivity without creating asymmetric or delamination connections within the substrates; and - Ultra-short connection if the contacts are integrated into the narrow hole (depending on the constraints on either side of the printed circuit board).
Claims
1. A microwave coaxial interposer layer to be disposed between two heterogeneous components, the microwave coaxial interposer layer comprising: Printed circuit board (1); At least one cylindrical diffusion contact (2) comprising interlaced metal wires, the at least one cylindrical diffusion contact (2) being inserted into a hole (3) in a plate (4), the plate (4) forming a gasket and insulating guide for the diffusion contact (2), one end (2a) of the diffusion contact (2) extending to a portion (1a) of the printed circuit board and contacting the portion (1a) of the printed circuit board, and the other end (2b) of the diffusion contact extending out of the hole (3); The RF track (5) in the printed circuit board (1) has one end (5a) extending to the bottom of the hole (3) in the board (4) and opposite to the diffusion contact (2), and is configured to contact the diffusion contact (2), and the other end (5b) of the RF track extends to the outer surface of the printed circuit board (1) outside the interposer layer. as well as At least one cylindrical copper grounding via (6) is arranged coaxially around the diffusion contact (2) in the plate (4), extends to one side of the plate (4) and also extends to the other side of the plate (4), and is configured to be electrically connected through the outer surface of the printed circuit board (1) located outside the interposer layer.
2. The intermediary layer according to claim 1, wherein, The printed circuit board (1) is a single-layer printed circuit board.
3. The intermediary layer according to claim 1, wherein, The printed circuit board (1) is a multilayer printed circuit board.
4. The intermediary layer according to any one of the preceding claims includes a conductive epoxy resin adhesive layer (10) disposed between the plate (4) and the printed circuit board (1).
5. An interposer according to any one of the preceding claims, comprising at least one RF track (11) in the printed circuit board (1), one end (11a) of the RF track extending opposite the cylindrical via (6), and the other end (11b) of the RF track extending to the outer surface of the printed circuit board (1) outside the interposer.
6. The intermediary layer according to any one of the preceding claims, wherein, The plate (4) is made of metallized polytetrafluoroethylene or ceramic / glass / polytetrafluoroethylene composite RF laminate substrate.
7. The intermediary layer according to claim 3, wherein, The board (4) consists of at least one layer of the printed circuit board (1).
8. The intermediary layer according to claim 7, wherein, The cylindrical grounding via (6) extends to the outer surface of the printed circuit board (1) located outside the interposer layer.
9. An active antenna, comprising: At least one radiating element (7) ； The printed circuit board (1) according to claim 1 is provided with at least one BFIC component (8). The intermediate layer according to any one of the preceding claims is disposed between the radiating element (7) and the printed circuit board (1); A conductive epoxy resin adhesive layer (12) is placed between the radiating element (7) and the plate (4) of the intermediate layer. as well as Solder ball (9) is located between the BFIC component (8) and the outer surface of the printed circuit board (1).