A composite circuit board for achieving vacuum sealing and a vacuum low-light imaging device

Abstract

The present invention relates to a composite circuit board for achieving vacuum sealing and a vacuum low-light imaging device. The composite circuit board includes a ceramic substrate layer, a polyimide layer, and an FR4 substrate layer. The ceramic substrate is located on the inner layer on the vacuum side, and the polyimide layer is located between the ceramic substrate layer and the FR4 substrate layer. Vias for realizing electrical connection between the ceramic substrate layer and the FR4 substrate layer are provided in the ceramic substrate layer, the polyimide layer, and the FR4 substrate layer. The vias are realized by blind buried vias and filled with copper paste. The vacuum low-light imaging device includes an input window, a tube shell, and a base. The base includes an image sensor located in the vacuum cavity and the composite circuit board for achieving vacuum sealing of the present invention. The ceramic substrate layer is used for soldering the image sensor. There are pins at the lower end of the base equivalent to the number of pins of the image sensor. The present invention solves the problems of high temperature resistance and sealing in vacuum sealing and can be used to achieve vacuum sealing of low-light imaging devices.

Description

Technical Field

[0001] The present invention belongs to the field of vacuum imaging devices, and particularly relates to a composite circuit board for achieving vacuum sealing and a vacuum low-light imaging device. Background Art

[0002] For vacuum imaging devices, most of the currently adopted processes are to first weld the tube shell and the output window, then place them in a vacuum exhaust table for high-temperature baking to remove gas, and then perform indium sealing with the input window.

[0003] With the development of imaging digitization, a vacuum imaging device that seals an image sensor in a vacuum cavity to replace the output window has emerged. However, since traditional vacuum sealing technology requires baking to remove gas by heating at a high temperature above 410°C for several hours, and the image sensor belongs to electronic components and cannot withstand high temperatures for a long time, it is necessary to improve the sealing process to achieve vacuum sealing.

[0004] In addition, this vacuum imaging device usually uses a ceramic adapter board as the base, and the image sensor usually requires hundreds of pins to be welded to it for data communication. This structure is likely to cause air leakage in the entire vacuum device.

[0005] Traditional PCBs are mainly used to carry electronic components and cannot be used as vacuum-sealed parts either. There are mainly the following reasons:

[0006] The mainstream PCB material is FR4, which is a mixed board of resin and glass fiber. Although it has excellent processing performance and good manufacturing capabilities, there are small voids in the board, and gas will penetrate into the vacuum cavity through these holes.

[0007] FR4 is mainly an organic material and is likely to volatilize organic gases in a high-temperature environment, polluting the vacuum cavity.

[0008] The bending strength of FR4 board is relatively weak compared to inorganic materials such as metals and ceramics, and cracks may occur if it is used as a vacuum-sealed part. Summary of the Invention

[0009] The problem to be solved by the present invention is how to overcome the deficiencies that traditional plates cannot be used for vacuum sealing and traditional vacuum sealing technologies cannot overcome the damage caused by high-temperature degassing. A composite circuit board for vacuum sealing is provided. The composite circuit board includes a ceramic substrate layer, a polyimide layer, and an FR4 substrate layer. The inner layer on the vacuum side uses a ceramic substrate, taking into account both bending strength and airtightness. At the same time, the ceramic substrate is an inorganic material and will not release organic gases at high temperatures; the polyimide layer is used in the filling layer. Polyimide has excellent bending strength and sealing performance, has very little outgassing in extremely high vacuum, and has good thermal stability at high and low temperatures; the outermost layer uses an FR4 substrate layer. The FR4 substrate layer has a certain bending strength, and at the same time, due to its good manufacturing processability, components can be mounted on its back surface.

[0010] The general objective of the present invention is to provide a composite circuit board for vacuum sealing and a vacuum low-light imaging device, aiming to solve the problems that in the existing vacuum sealing process, the image sensor cannot withstand high temperatures, the ceramic adapter plate is prone to air leakage as the base, and traditional PCBs cannot be used for vacuum sealing.

[0011] Specifically, one objective of the present invention is to provide a composite circuit board for vacuum sealing, which can solve the disadvantages of traditional plates that cannot be used as vacuum components, and at the same time can solve the deficiencies of traditional vacuum components that cannot carry image sensors and cannot be used as circuit boards.

[0012] Another objective of the present invention is to provide a vacuum low-light imaging device including a composite circuit board for vacuum sealing.

[0013] To solve the above technical problems and achieve the objectives of the present invention, the technical solution of the present invention is as follows:

[0014] A composite circuit board for vacuum sealing includes a ceramic substrate layer, at least one polyimide layer, and at least one FR4 substrate layer arranged in sequence. The inner layer on the vacuum side uses a ceramic substrate layer, taking into account both bending strength and airtightness. At the same time, the ceramic substrate is an inorganic material and will not release organic gases at high temperatures; the polyimide layer is used in the filling layer. Polyimide has excellent bending strength and sealing performance, has very little outgassing in extremely high vacuum, and has good thermal stability at high and low temperatures; the outermost layer uses FR4. FR4 has a certain bending strength, and at the same time, due to its good manufacturing processability, components can be mounted on its back surface. The polyimide layer is located between the ceramic substrate layer and the FR4 substrate layer. When there are multiple FR4 substrate layers, the polyimide layer is used as the filling between the FR4 substrate layers to ensure that there is no air leakage between layers. Communication between the ceramic substrate layer and the FR4 substrate layer or between two FR4 substrate layers is achieved through vias. The vias are realized through blind buried vias, and all blind buried vias are filled with copper paste.

[0015] A vacuum low-light imaging device, comprising a vacuum low-light imaging device with an input window, a tube shell, and a base seat arranged in sequence, and the base seat is located at the lowermost end. The base seat includes an image sensor located in a vacuum cavity, a ceramic substrate layer for welding the image sensor, two polyimide layers, and two FR4 substrate layers. The polyimide layers are located between the ceramic substrate layer and the FR4 substrate layers and between the two FR4 substrate layers. The polyimide layers are used as fillers to ensure that there is no air leakage between layers. The ceramic substrate layer communicates with the FR4 substrate layer and between the two FR4 substrate layers through vias, and the vias are filled with copper paste. There are pins at the lower end of the base seat, which are equivalent to the number of pins of the image sensor, for transmitting image data.

[0016] To prevent air leakage, the data communication between the layers of the ceramic substrate layer and the FR4 substrate layer of the present invention is realized through blind buried vias, and all blind buried vias are filled with copper paste.

[0017] Compared with the prior art, the beneficial effects of the present invention include:

[0018] The composite circuit board of the present invention uses a multi-layer composite structure to form a PCB. The inner layer on the vacuum side uses a ceramic substrate layer, which takes into account the bending strength and airtightness. At the same time, the ceramic substrate belongs to inorganic materials and will not release organic gases at high temperatures. The polyimide layer is used in the filling layer. Polyimide has excellent bending strength and sealing performance, has very little outgassing in extremely high vacuum, and has good thermal stability at high and low temperatures. FR4 is used in the outermost layer. FR4 has a certain bending strength, and at the same time, because of its good manufacturing processability, components can be carried on its back. Polyimide layers are used as fillers between multiple layers to ensure that there is no air leakage between layers. The ceramic substrate layer communicates with the FR4 substrate layer through vias, and the vias are realized through blind buried vias, and all blind buried vias are filled with copper paste. The present invention solves the problems in the existing vacuum sealing process that the image sensor cannot withstand high temperatures, the ceramic adapter plate is prone to air leakage as the base seat, and the traditional PCB cannot be used for vacuum sealing, and can be used to realize the vacuum sealing of low-light imaging devices. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of the vacuum low-light imaging device of the present invention.

[0020] Figure 2 It is a schematic partial structural diagram of the base seat.

[0021] Figure 3 It is a schematic overall structural diagram of the base seat.

[0022] Figure 4 It is a schematic structural diagram of the polyimide layer.

[0023] Figure 5It is a schematic diagram of the FR4 substrate layer structure.

[0024] Among them, Figure 1 the reference numerals in

[0025] are: 1: input window; 2: input window sealing material; 3: flange; 4: package body; 5: image sensor; 6: pad; 7: ceramic substrate layer; 8, 10: polyimide layer; 9, 11: FR4 substrate layer; 12: device pin; 13: via; 14: pad on the FR4 substrate layer; 15: base.

[0026] Figure 2 the reference numerals in

[0027] are: 7: ceramic substrate layer; 8, 10: polyimide layer; 9, 11: FR4 substrate layer; 12: device pin; 13: via; 9-1, 11-1: reserved pads on the FR4 substrate layer; 9-2, 11-2: traces on the FR4 substrate layer; 13-1: copper filling the via; 13-2: copper filling the reserved via in the polyimide layer.

[0028] Figure 3 the reference numerals in

[0029] are: 5: image sensor; 6: pad; 15: base; 15-1: pad on the base.

[0030] Figure 4 the reference numerals in

[0031] are: 8, 10: polyimide layer; 8-1, 10-1: reserved vias in the polyimide layer.

[0032] Figure 5 the reference numerals in

[0033] are: 9, 11: FR4 substrate layer; 9-1, 11-1: reserved pads on the FR4 substrate layer; 9-2, 11-2: traces on the FR4 substrate layer; 9-3, 11-3: vias on the FR4 substrate layer. Detailed implementation manner

[0034] As Figure 1 and Figure 2 shown, a composite circuit board for realizing vacuum sealing includes a ceramic substrate layer, a polyimide layer, and an FR4 substrate layer arranged in sequence; the ceramic substrate layer is located in the inner layer on the vacuum side, and the polyimide layer is filled between the ceramic substrate layer and the FR4 substrate layer; vias for realizing electrical connection between the ceramic substrate layer and the FR4 substrate layer are provided on the ceramic substrate layer, the polyimide layer, and the FR4 substrate layer, the vias are realized by blind buried vias, and all the blind buried vias are filled with copper paste.

[0035] The FR4 substrate layer can be provided with two or more layers, and the polyimide layer is filled between two FR4 substrate layers.

[0036] Each FR4 substrate layer is provided with vias for realizing mutual electrical connection.

[0037] Such as Figure 1 As shown, a vacuum low-light imaging device includes an input window, a tube shell, and a base seat arranged in sequence, and the base seat is located at the lowermost end; the base seat includes an image sensor located in a vacuum cavity and the composite circuit board for realizing vacuum sealing; the ceramic substrate layer is used for welding the image sensor; there are pins at the lower end of the base seat equivalent to the number of pins of devices such as the image sensor for transmitting image data.

[0038] The composite circuit board for realizing vacuum sealing includes two polyimide layers and two FR4 substrate layers.

[0039] The input window can be made of materials such as a panel, glass, quartz glass, a grating, etc., and its function is to provide incident electrons for the entire device.

[0040] The tube shell is composed of a tube shell body and a flange. The tube shell body is made of metal or ceramic material, and the flange is made of metal material. When manufacturing the tube shell, the flange is welded to the tube shell body. The flange has two functions. One is to place an indium ring to reliably connect the input window and the tube shell during sealing, and the other is to serve as an electrode to provide the required electric field for the normal operation of the vacuum device.

[0041] The base seat includes an image sensor, a ceramic substrate layer, two polyimide layers, and two FR4 substrate layers located in a vacuum cavity. Among them, the image sensor is generally an image sensor, and the signal collected by the image sensor is transmitted to the lower end of the base seat through blind buried vias to realize data transmission; among them, the ceramic substrate layer is generally alumina or aluminum nitride, with stable performance and will not release organic gases to damage the vacuum degree of the device. There is a ring of pads around it for welding the tube shell; between the ceramic substrate layer and the FR4 substrate layer and between the two FR4 substrate layers, the polyimide layer is used as a filling to ensure that there is no air leakage between layers. Communication between the ceramic substrate layer and the FR4 substrate layer and between the two FR4 substrate layers is through vias, and the vias are filled with copper paste. There are pins at the lower end of the base seat equivalent to the number of pins of devices such as the image sensor for transmitting image data.

[0042] When implementing the present invention, the selection and functions of its components are as follows:

[0043] Input window 1: The input window of the vacuum device. The material is a panel, glass (such as quartz glass), a grating, etc., and its function is to provide incident electrons for the entire device.

[0044] Input window sealing material 2: Indium. Before sealing, the indium ring is melted in the cathode flange and then the indium is turned, leaving an appropriate amount of indium for sealing the input window and the shell.

[0045] Flange 3: Generally made of metal materials. When manufacturing the shell, it is welded to the shell. One function is to place the indium ring, and it can reliably connect the input window and the shell during welding. In addition, it can also serve as an electrode to provide the required electric field for the normal operation of the device.

[0046] Shell body 4: Made of ceramic or metal materials, used to provide a vacuum cavity for the imaging device.

[0047] Image sensor 5: Realize digital imaging.

[0048] Base pad 6: The image sensor is welded above the base through the pad.

[0049] Ceramic substrate layer 7: Generally made of alumina or aluminum nitride, with stable performance and will not release organic gases to damage the vacuum degree of the device. There is a ring of pads around it for welding the shell.

[0050] Polyimide layers 8, 10: Fillers between layers to prevent air leakage from the base.

[0051] FR4 substrate layers 9, 11: For multi-layer board trace communication.

[0052] Device pin 12: Used for data transmission.

[0053] Via 13: Used for data transmission. To prevent air leakage, it is filled with copper paste.

[0054] Pad on the FR4 substrate layer 14: Its position corresponds to the via in the upper layer to achieve communication.

[0055] Base 15: Replace the output window of the vacuum imaging device.

[0056] Base pad 15-1: Used for sealing with the shell.

[0057] Polyimide layers 8, 10: Fillers between layers to prevent air leakage from the base.

[0058] Reserved vias 8-1, 10-1 in the polyimide layer: Filled with copper paste to facilitate data transmission between layers.

[0059] Reserved pads 9-1, 11-1 on the FR4 substrate layer: Their positions correspond one by one to the vias in the upper layer, used to connect with the copper filled in the vias of the upper ceramic substrate or FR4 substrate layer, prevent air leakage from the base while transmitting data.

[0060] Traces 9-2, 11-2 on the FR4 substrate layer: Blind buried via interlayer signal transmission.

[0061] FR4 substrate layer vias 9-3, 11-3: Filled with copper to communicate with the upper and lower layers for data transmission and prevent air leakage at the base.

[0062] Before sealing the vacuum low-light imaging device of the present invention, corresponding image sensors are first welded on the multi-layer laminated base, and then it is placed in a vacuum chamber of an exhaust table. The input window and the tube shell are placed in another vacuum chamber of the same exhaust table. The two vacuum chambers of this exhaust table are in the same vacuum environment, but the temperatures do not affect each other. When the input window and the tube shell are sealed and the temperature drops below 100 °C, the base is transferred into this chamber, and the solder is heated and melted to complete the vacuum sealing.

[0063] The preparation process of the composite circuit board of the present invention is as follows:

[0064] 1) Prepare the ceramic substrate layer, polyimide layer and FR4 substrate layer respectively according to the drawings, including the traces and vias of each layer;

[0065] 2) Place the pins in the fixture, place the bottom FR4 substrate layer, inject copper paste into the vias to fill the vias and fix the pins;

[0066] 3) Place the lower polyimide layer and the upper FR4 substrate layer at the corresponding positions, perform lamination, and inject copper paste again at the via positions of this layer to fill the vias;

[0067] 4) Place the upper polyimide layer at the corresponding position, place the ceramic substrate layer and perform lamination again, and inject copper paste again at the via positions to fill the vias.

Claims

1. A vacuum low-light imaging device, characterized in that: the vacuum low-light imaging device includes an input window, a tube shell and a base seat arranged in sequence, and the base seat is located at the lowermost end; the base seat includes an image sensor and a composite circuit board located in a vacuum cavity; the composite circuit board is used to achieve vacuum sealing, and the composite circuit board includes a ceramic substrate layer, a polyimide layer and an FR4 substrate layer arranged in sequence; the ceramic substrate layer is located on the inner layer on the vacuum side, and the polyimide layer is filled between the ceramic substrate layer and the FR4 substrate layer; the ceramic substrate layer, the polyimide layer and the FR4 substrate layer are all provided with vias for realizing electrical connection between the ceramic substrate layer and the FR4 substrate layer, the vias are realized by blind buried vias, and all blind buried vias are filled with copper paste; the ceramic substrate layer is used for soldering the image sensor; the lower end of the base seat has pins equivalent to the number of pins of the image sensor for transmitting image data; the composite circuit board is used to ensure that no organic gas is released during high-temperature degassing for vacuum sealing.

2. The vacuum low-light imaging device according to claim 1, characterized in that: there are more than two layers of FR4 substrate layers, and the polyimide layer is filled between the two layers of FR4 substrate layers.

3. The vacuum low-light imaging device according to claim 2, characterized in that: each layer of FR4 substrate layer is provided with vias for realizing mutual electrical connection.

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