CT detector structure

Abstract

The invention provides a CT (Computed Tomography) detector structure which comprises a photodiode, a readout integrated circuit and a flexible thin film, wherein the photodiodes are arranged in an array mode, electrode structures arranged in an array mode are arranged on the bottom faces of the photodiodes, and the electrode structures are welded to the flexible thin film through the adapter plate and used for converting optical signals into electric signals; the number of the reading integrated circuit is at least one, and the reading integrated circuit is welded to the flexible film and used for processing electric signals output by the photodiode. According to the invention, the glass adapter plate is used as an adapter to realize the connection of the photodiode and the flexible film, the stress impact on a welding spot is reduced in the welding process of the photodiode and the flexible film, and the warping condition of the photodiode is improved to a great extent; when the photodiode is connected with the flexible film through the glass adapter plate, due to the fact that the glass adapter plate has a certain thickness, the cracking risk caused by the fact that the photodiode is too thin is reduced, the overall yield is improved, meanwhile, the technology is simplified, and reworking feasibility is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of medical equipment, and in particular relates to a CT detector structure. Background Art

[0002] As a core innovation direction in the field of medical imaging, the four-sided splicing technology of computed tomography (CT) detectors has a direct impact on the imaging quality, manufacturing cost and reliability of the system due to its structural design. "Four-sided splicing" means that in the detector splicing process, the four sides of the detector module are used for splicing to form a complete detector array. This splicing method can achieve seamless connection, reduce the impact of splicing gaps on imaging quality, and achieve large-area, high-resolution imaging capabilities. The current mainstream four-sided detector solution still faces multiple technical bottlenecks in packaging technology, thermal management and signal integrity, and a breakthrough solution is urgently needed.

[0003] In the existing technology, the packaging solution based on through silicon via (TSV) achieves high-density integration between modules through vertical interconnection, effectively reduces the gap width of the detection array and improves the fill factor, but this technology has significant defects. The TSV process requires the preparation of micro-holes with an aspect ratio greater than 10:1 on the silicon substrate and the completion of metal filling. Its manufacturing yield is limited by the volatility of silicon wafer thinning, through-hole etching and electroplating processes, resulting in high production costs. In addition, although the four-sided docking of the TSV module can reduce the dead zone, the inherent brittleness of the silicon substrate is prone to cause micro-cracks during mechanical splicing, further restricting the feasibility of large-scale production.

[0004] Another typical rigid-flex PCB solution, although it achieves the flexibility of multi-module three-dimensional wiring through a rigid-flexible composite substrate, it exposes two problems in actual application: first, the fluctuation of the dielectric layer thickness of the flexible section will lead to signal transmission impedance mismatch, especially in GHz-level high-speed signal transmission, which will generate reflection noise and seriously affect the imaging signal-to-noise ratio; second, the stress concentration phenomenon at the rigid-flex interface will easily cause fatigue fracture of copper wires under thermal cycling conditions, resulting in long-term reliability degradation. More importantly, this solution needs to be manufactured using a multi-stage HDI process, and its inter-layer alignment accuracy is required to reach ±5μm, which causes the cost of a single board to increase by more than 3 times compared with the traditional FR4 substrate.

[0005] In terms of circuit layout architecture, the traditional design flips the read-out integrated circuit (ROIC) onto the bottom of the printed circuit board (PCB). Although this can reduce the complexity of external routing, the limited wiring space may cause the signal transmission path to be too long or too narrow, increase signal interference and transmission loss, and may affect production efficiency and reliability. In addition, the ROIC will generate a lot of heat during operation, which may cause the chip performance to degrade or even be damaged, and the heat dissipation risk is high.

[0006] In addition, in the CT four-sided detector solution, the use of connectors is crucial to achieving electrical connection and signal transmission between modules. Through its high performance and flexible design, it can ensure stable connection and signal transmission between detector modules. However, in high-channel count systems such as CT detectors, the cost of high-speed connectors accounts for a high proportion.

[0007] Therefore, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art.

[0008] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0009] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a CT detector structure for solving the problems of low yield and high cost caused by complex processes in the prior art, as well as the problems of difficult rework and maintenance in the existing design.

[0010] To achieve the above-mentioned and other related objects, the present invention provides a CT detector structure, which includes a photodiode, a readout integrated circuit and a flexible film;

[0011] The photodiodes are arranged in an array, and an array-arranged electrode structure is provided on the bottom surface of the photodiodes. The electrode structure is welded to the flexible film through an adapter plate to convert optical signals into electrical signals.

[0012] At least one readout integrated circuit is provided, and the readout integrated circuit is welded on the flexible film and is used for processing the electrical signal output by the photodiode.

[0013] Preferably, the adapter plate has a top surface and a bottom surface arranged opposite to each other, the top surface of the adapter plate is provided with array-arranged welding points, each welding point is arranged one-to-one corresponding to the electrode structure, and the electrode structure is welded to the top surface of the adapter plate through a welding packaging process.

[0014] Preferably, the adapter plate is a glass adapter plate.

[0015] Preferably, the adapter plate has a thickness of 500 μm to 1000 μm.

[0016] Preferably, the bottom surface of the adapter plate is provided with solder pads, and the solder pads are spaced apart on both sides of the bottom surface of the adapter plate and are arranged linearly.

[0017] Preferably, the edge of the flexible film is provided with gold fingers arranged in finger shapes, and the pads on the bottom surface of the adapter board are connected to the gold fingers by using ACF thermal compression bonding technology.

[0018] Preferably, the readout integrated circuit is soldered onto the flexible film by a flip-chip process.

[0019] Preferably, the flexible film is made of polyimide material.

[0020] As described above, the CT detector structure of the present invention has the following beneficial effects:

[0021] The CT detector in the present invention has a simpler structure and a simpler process. The photodiode and the readout integrated circuit are integrated on a flexible film, allowing multiple functions to be integrated into a single flexible film, reducing the gap between modules and improving the fill factor of the detector. Based on the mechanical adaptability of the flexible film, the CT detector structure can achieve seamless splicing when the four sides are butted together, so that the modules have a certain degree of flexibility when splicing, eliminating the physical dead zone of traditional rigid splicing and avoiding the risk of splicing misalignment.

[0022] The present invention utilizes a glass transfer plate as a transfer to achieve the connection between the upper photodiode and the lower flexible film. Since the thermal expansion coefficients of the glass transfer plate and the photodiode are close, the stress impact on the soldering point can be reduced during the welding process of the two, thereby greatly improving the warping of the photodiode. When the photodiode is connected to the flexible film through the glass transfer plate, since the glass transfer plate has a certain thickness, the risk of cracking caused by the photodiode being too thin can be reduced when the ACF hot pressing bonding technology is used for connection, thereby improving the overall yield, while also simplifying the process and improving the feasibility of rework. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram showing the structure of the photodiodes arranged in an array in a specific embodiment of the present invention.

[0024] Figure 2 It is a schematic diagram showing the structure of the top surface of the glass transfer plate in a specific embodiment of the present invention.

[0025] Figure 3 It is a schematic structural diagram of the bottom surface of the glass transfer plate in a specific embodiment of the present invention.

[0026] Figure 4 It is a schematic diagram showing the structure of a flexible film in a specific embodiment of the present invention.

[0027] Figure 5 It is a schematic diagram of the structure of the CT detector after packaging in a specific embodiment of the present invention.

[0028] Component number description

[0029] 10 Flexible film

[0030] 101 Gold Finger

[0031] 20 Photodiode

[0032] 201 Electrode structure

[0033] 30 Adapter Plate

[0034] 301 solder joints

[0035] 302 pad

[0036] 40 Readout IC DETAILED DESCRIPTION

[0037] The following embodiments of the present application are described in conjunction with the drawings in the embodiments of the present application. People familiar with this technology can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. For example, when describing the embodiments of the present application in detail, for ease of explanation, the cross-sectional view representing the device structure will not be partially enlarged according to the general proportion, and the schematic diagram is only an example, which should not limit the scope of protection of the present application. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual production.

[0038] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. It should be understood that when component A is fixedly connected to component C through component B, changes in the relative position relationship caused by the deformation of component A, component B and component C itself are allowed. "Rotational connection" means that they are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that they are connected to each other and can slide relative to each other after the connection. Among them, the two components are obtained by an integrated structure through an integrated molding process, which means that in the process of forming one of the two components, the component is connected to the other component, and there is no need to connect the two components together through reprocessing (such as bonding, welding, snap connection, screw connection).

[0039] The directional terms mentioned in the embodiments of the present application, such as "upper", "lower", "side", "top", "bottom", etc., are only references to the directions of the drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0040] The term "plurality" means at least two. The term "above" includes the number itself. The term "and / or" is a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", etc. are used only for descriptive purposes and cannot be understood as suggesting or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more of the features.

[0041] Please refer to Figures 1 to 5 , the present invention provides a CT detector structure, the CT detector structure includes a photodiode 20, a readout integrated circuit 40 and a flexible film 10;

[0042] The photodiodes 20 are arranged in an array, and the bottom surface of the photodiodes 20 is provided with an array-arranged electrode structure 201, which is welded to the flexible film 10 through an adapter plate 30, and is used to convert optical signals into electrical signals;

[0043] At least one readout integrated circuit 40 is provided. The readout integrated circuit 40 is welded on the flexible film 10 and is used to process the electrical signal output by the photodiode 20 .

[0044] Specifically, the present invention is a novel CT detector structure designed using COF (chip on film) technology. COF is a packaging technology that directly mounts a chip on a flexible film 1010. In the present invention, the photodiode 2020 and the readout integrated circuit 4030 are specifically integrated on the flexible film 1010; the flexible film 1010 is used to connect the photodiode 2020 and the readout integrated circuit 4030 in the detector, which not only provides electrical connection but also plays a role of mechanical support; the COF solution allows multiple functions to be integrated into a single flexible film 1010, with high integration. In a specific embodiment of the present invention, an adapter plate 30 is welded to the bottom surface of the photodiode 20, and is welded to the flexible film 10 through the adapter plate 30. The design structure is simpler, the process is more simplified, and the yield and rework feasibility are improved; at the same time, based on the mechanical adaptability of the flexible film 10, seamless splicing is achieved when the four sides of the CT detector are butt-jointed.

[0045] As an example, the adapter plate 30 has a top surface and a bottom surface that are relatively set. The top surface of the adapter plate 30 is provided with array-arranged welding points 301. Each welding point 301 is arranged one-to-one corresponding to the electrode structure 201. The electrode structure 201 is welded to the top surface of the adapter plate 30 through a welding packaging process.

[0046] As an example, the adapter plate 30 is an adapter plate 30 made of glass.

[0047] For details, see Figure 1 is a schematic structural diagram of the bottom surface of the photodiode 20, Figure 1 The photodiode 20 in the embodiment is a 15×7 array, that is, the arrangement of the electrode structure 201; see Figure 2 Schematic diagram of the structure of the top surface of the glass transfer plate 30. The top surface of the glass transfer plate 30 is adjacent to the bottom surface of the photodiode 20 and welded together. The top surface of the glass transfer plate 30 is also provided with welding points 301 arranged in a 15×7 array. Each welding point 301 is arranged one-to-one with the electrode structure 201, and then they are welded together through a welding packaging process. In a specific embodiment of the present invention, the photodiode 20 and the glass transfer plate 30 are welded together by a welding packaging process, which can effectively protect the stability and reliability of the motor structure and provide a good electrical connection. Appropriate welding parameters need to be set during the welding process. There is no excessive restriction here, and it can meet the actual needs.

[0048] In addition, the thermal expansion coefficient of the photodiode 20 is about 10 -6 / ℃, the thermal expansion coefficient of common glass materials, such as borosilicate glass, is about 3×10 -6 / ℃, while some special glasses, such as high alumina-silicon glass, may have a lower thermal expansion coefficient, close to 3.2×10 -6 / ℃, but the thermal expansion coefficient of the glass transfer plate 30 and the thermal expansion coefficient of the photodiode 20 are at the same order of magnitude, and the thermal expansion coefficients of the two are relatively close. Using the glass transfer plate 30 as the transfer plate 30 between the photodiode 20 and the flexible film 10 can effectively reduce the stress and failure caused by thermal expansion mismatch, and can reduce the stress impact on the welding point 301 during the welding process, which greatly improves the situation where the photodiode 20 is prone to warping.

[0049] As an example, the thickness of the adapter plate 30 is 500 μm to 1000 μm.

[0050] Specifically, the thickness of the adapter plate 30 may include values ​​within any range such as 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm, etc.; after the adapter plate 30 is added to the electrode structure 201 of the photodiode 20, since the adapter plate 30 has a certain thickness, when the electrode structure 201 is welded to the flexible film 10 through the adapter plate 30, the risk of the photodiode 20 being cracked due to being too thin is greatly reduced, thereby improving the overall yield.

[0051] As an example, the bottom surface of the adapter board 30 is provided with solder pads 302 , and the solder pads 302 are arranged at intervals on both sides of the bottom surface of the adapter board 30 and are arranged linearly.

[0052] As an example, the edge of the flexible film 10 is provided with gold fingers 101 arranged in finger shapes, and the pads 302 on the bottom surface of the adapter board 30 are connected to the gold fingers 101 using ACF thermal compression bonding technology.

[0053] For details, see Figure 3 FIG. 3 is a schematic diagram of the bottom structure of the adapter board 30. The pads 302 are arranged in two rows. The two rows of pads 302 are arranged at intervals on both sides of the bottom surface of the adapter board 30 and are arranged linearly. Figure 4 FIG. 1 is a schematic diagram of the structure of the flexible film 10. The gold finger 101 of the flexible film 10 is a conductive part connecting the flexible film 10 and the external circuit. The gold finger 101 is connected to the pad 302 on the bottom surface of the adapter board 30 to achieve conduction between the two. The arrangement of the gold finger 101 matches the structural arrangement of the pad 302, and the ACF hot pressing bonding technology is used for connection; see FIG. Figure 5 This is a schematic diagram of the structure after the CT detector structure is packaged.

[0054] ACF hot-press bonding uses ACF glue as welding material, and connects the pad 302 on the bottom surface of the adapter board 30 with the gold finger 101 on the flexible film 10 by applying pressure and heat. This process can achieve high-precision alignment and high-reliability electrical connection. The specific steps include: first, aligning the pad 302 on the bottom surface of the adapter board 30 with the gold finger 101 one by one, placing the ACF glue (anisotropic conductive film) in the connection area, and aligning the position of the pad 302; then, pre-pressing the ACF glue with appropriate temperature, time and pressure, but no actual electrical connection is formed at this time; then, applying higher temperature and pressure through hot-pressing welding equipment, during this process, the conductive particles of the ACF glue will form a conductive path to achieve electrical connection between the adapter board 30 and the gold finger 101; after hot pressing, cooling and solidification.

[0055] As an example, the readout integrated circuit 40 is bonded to the flexible film 10 by a flip chip bonding process.

[0056] Specifically, the readout integrated circuit 40 is used to digitally process the electrical signal output by the photodiode 20. In a specific embodiment of the present invention, the readout integrated circuit 40 is also integrated with a preamplifier, which amplifies weak electrical signals to provide signal strength and quality to reduce interference and loss during signal transmission.

[0057] In flip-chip soldering, the active surface of the readout integrated circuit 40 faces downward and is aligned with the pad 302 on the flexible film 10 for soldering. The active surface of the readout integrated circuit 40 is made with bumps. After the bumps are aligned with the pad 302 on the flexible film 10, they are placed in a reflow soldering furnace. The bumps are melted by heating and form solder joints 301 with the pad 302 of the flexible film 10. The temperature and time during the soldering process are not specifically limited in the specific embodiments of the present invention.

[0058] As an example, the flexible film 10 is made of polyimide material.

[0059] Specifically, the flexible film 10 made of polyimide has good mechanical flexibility and electrical insulation performance.

[0060] Of course, in a specific embodiment of the present invention, the CT detector structure also includes a thermal management structure (not shown in the figure) for heat dissipation, and the thermal management structure includes a thermal via (not shown in the figure) and a thermally conductive gasket (not shown in the figure) for conducting and dissipating heat.

[0061] In summary, the CT detector structure in the present invention is simpler and the process is more simplified. The photodiode and the readout integrated circuit are integrated on the flexible film, allowing multiple functions to be integrated into a single flexible film, reducing the gap between modules and improving the fill factor of the detector; based on the mechanical adaptability of the flexible film, the CT detector structure can achieve seamless splicing when the four sides are butted, so that the module has a certain flexibility when splicing, eliminating the physical dead zone of traditional rigid splicing, and avoiding the risk of splicing misalignment. The present invention uses a glass adapter plate as a transfer to achieve the connection between the upper photodiode and the lower flexible film. Since the thermal expansion coefficients of the glass adapter plate and the photodiode are close, the stress impact on the solder joint can be reduced during the welding process of the two, thereby greatly improving the warping of the photodiode; when the photodiode is connected to the flexible film through the glass adapter plate, since the glass adapter plate has a certain thickness, the risk of cracking caused by the photodiode being too thin can be reduced when connected by ACF hot pressing bonding technology, thereby improving the overall yield, while also simplifying the process and improving the feasibility of rework. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0062] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the present application, which should be included in the protection scope of the present application; in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. The structural member materials, sizes, shapes, etc. mentioned in the embodiments of the present application are all schematic descriptions and do not constitute strict or absolute limitations. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A CT detector structure, characterized in that: The CT detector structure includes a photodiode, a readout integrated circuit and a flexible film; The photodiodes are arranged in an array, and an array-arranged electrode structure is provided on the bottom surface of the photodiodes. The electrode structure is welded to the flexible film through an adapter plate to convert optical signals into electrical signals. At least one readout integrated circuit is provided, and the readout integrated circuit is welded on the flexible film and is used for processing the electrical signal output by the photodiode.

2. The CT detector structure according to claim 1, characterized in that: The adapter plate has a top surface and a bottom surface that are arranged opposite to each other. The top surface of the adapter plate is provided with welding points arranged in an array. Each welding point is arranged in a one-to-one correspondence with the electrode structure. The electrode structure is welded to the top surface of the adapter plate through a welding packaging process.

3. The CT detector structure according to claim 1, characterized in that: The adapter plate is a glass adapter plate.

4. The CT detector structure according to claim 1, characterized in that: The adapter plate has a thickness of 500 μm to 1000 μm.

5. The CT detector structure according to claim 2, characterized in that: The bottom surface of the adapter plate is provided with soldering pads, and the soldering pads are arranged at intervals on both sides of the bottom surface of the adapter plate and are arranged linearly.

6. The CT detector structure according to claim 5, characterized in that: The edge of the flexible film is provided with gold fingers arranged in finger shapes, and the solder pads on the bottom surface of the adapter board are connected to the gold fingers by adopting ACF hot pressing bonding technology.

7. The CT detector structure according to claim 1, characterized in that: The readout integrated circuit is welded on the flexible film through a flip-chip welding process.

8. The CT detector structure according to claim 1, characterized in that: The flexible film is made of polyimide material.

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