EMI filter for image intensifier and assembly method thereof

Abstract

The present invention belongs to the technical field of image intensifiers, and specifically provides an EMI filter for image intensifiers and an assembly method thereof, wherein the EMI filter is a two-stage combined filter structure, integrates capacitors, inductors and magnetic beads, and uses a flexible printed circuit board to design a layout separately, and then the designed flexible printed circuit board is stacked and welded on a high-voltage power supply PCB, the front pad is reinforced, the back side is insulated, and the high-voltage power supply PCB is bent together and placed in a metal housing, and silicone rubber is used for potting to complete the overall shaping, and finally the shielding wire is welded to the metal housing at 360 degrees. The reasonable placement of the EMI filter is achieved, and the problem that the small image intensifier cannot directly use the EMI filter or the placement position and layout design are not ideal is solved. At the same time, it can be reliably assembled on the image intensifier, effectively improving the electromagnetic compatibility performance of the image intensifier, and ensuring that the image intensifier can meet the requirements of the electromagnetic compatibility test.

Description

Technical Field

[0001] The invention belongs to the technical field of image intensifiers, and in particular relates to an EMI filter used for an image intensifier and an assembly method thereof. Background Art

[0002] Image intensifier is a vacuum electronic imaging device that can enhance the image of extremely weak light reflected by the target object through cathode photoelectric conversion, microchannel plate electron multiplication and phosphor screen electro-optical conversion. It is mainly composed of a vacuum image tube and a high-voltage power supply. The high-voltage power supply converts low-voltage DC into high voltage to supply power to the image tube, and samples the phosphor screen current to automatically adjust the amplitude and pulse width of the power supply voltage to ensure that the brightness of the image tube can remain stable under weak and strong light conditions, realizing automatic brightness control.

[0003] The vacuum image tube is usually a T-shaped cylindrical structure, the high-voltage power supply is a ring-shaped shell structure, and the vacuum image tube and the high-voltage power supply are potted together. Due to the ring-shaped shell structure of the high-voltage power supply, the existing high-voltage power supply can only use a long flexible PCB as a carrier. At the same time, due to the high density of component integration on the PCB and the long size of the PCB, it needs to be bent in many places or even folded back and forth before it can be put into the shell. Therefore, it is currently difficult to directly place an EMI filter on the high-voltage power supply PCB of a small image intensifier such as 16mm or 18mm, or it is difficult to design the EMI filter layout to a reasonable position and layout it into an ideal shape, resulting in unsatisfactory filtering effect.

[0004] EMI filtering is one of the main means to achieve electromagnetic compatibility. If there is a lack of EMI filters, the interference generated by the high-voltage power supply itself and the external interference can easily be conducted and coupled through the line or space stray capacitance, causing the image intensifier to exceed the radiation emission standard when conducting the RE102 test according to GJB151B-2013; when conducting the RS103 test, the external electric field interference affects the automatic brightness control circuit inside the power supply, causing the fluorescent screen to display sensitive phenomena such as highlighting, flickering, and extinction, seriously affecting observation and use.

[0005] In addition, electromagnetic compatibility tests have also found that even with an external EMI filter, the image intensifier will still be sensitive within a specific frequency range. Only by designing a suitable EMI filter circuit structure and component selection can the image intensifier pass the RE102 and RS103 tests. Summary of the invention

[0006] The present invention designs an EMI filter for an image intensifier and an assembly method thereof. On the basis of ensuring mutual insulation and assembly reliability between the filter and the high-voltage power supply, the present invention effectively solves the problem that the EMI filter cannot be reasonably placed due to the annular shell structure of the high-voltage power supply and the layout design is not ideal; at the same time, the electromagnetic compatibility performance of the image intensifier is effectively improved to ensure that the image intensifier can meet the electromagnetic compatibility test requirements.

[0007] The present invention provides an EMI filter for an image intensifier. The EMI filter is a two-stage combined filtering structure, and is specifically composed of a low-frequency ceramic capacitor C1, a high-frequency ceramic capacitor C2, a high-frequency common-mode inductor L1, a high-frequency magnetic bead L2, a high-frequency magnetic bead L3 and a low-frequency ceramic capacitor C3, which are arranged on the front of a flexible printed circuit board. One end of the low-frequency ceramic capacitor C1 is connected to an input positive and a No. 1 pin of the high-frequency common-mode inductor L1, and the other end of the low-frequency ceramic capacitor C1 is connected to an input ground and a No. 4 pin of the high-frequency common-mode inductor L1; the No. 2 pin of the high-frequency common-mode inductor L1 is connected to one end of the high-frequency ceramic capacitor C2 and one end of the high-frequency magnetic bead L2, and the other end of the high-frequency magnetic bead L2 is connected to an output positive and one end of the low-frequency ceramic capacitor C3; the No. 3 pin of the high-frequency common-mode inductor L1 is connected to the other end of the high-frequency ceramic capacitor C2 and one end of the high-frequency magnetic bead L3, and the other end of the high-frequency magnetic bead L3 is connected to the output ground and the other end of the low-frequency ceramic capacitor C3.

[0008] The input positive lead and the input ground lead are shielded wires with wave-proof sleeves, the shielded wires form a shielding layer, the end of the shielding layer is connected to the No. 4 pin of the high-frequency common-mode inductor L1, and the front end of the shielding layer is suspended.

[0009] The present invention also provides an EMI filter assembly method, including layout design and stacking assembly;

[0010] The layout design includes the following steps:

[0011] S1. Arrange the low-frequency ceramic capacitor C1, high-frequency common-mode inductor L1, high-frequency ceramic capacitor C2, high-frequency magnetic bead L2, high-frequency magnetic bead L3 and low-frequency ceramic capacitor C3 that have been electrically connected on the front side of the flexible printed circuit board in sequence from input to output;

[0012] S2. A single-sided input positive pad A and a single-sided input ground pad B are set at the front input end of the flexible printed circuit board, and long strip welding rods are designed on both sides of the front output end of the flexible printed circuit board. A front and back output positive pad D with a via and a front and back output ground pad C are set at the end of the welding rod;

[0013] S3. Copper shielding is performed on the reverse side of the flexible printed circuit board, with the pad distance between the input side and the output side of the high-frequency common mode inductor L1 as the spacing;

[0014] The stacking assembly includes the following steps:

[0015] S4. Place the back of the flexible printed circuit board, align the output positive pad D with the pad E on the high-voltage power supply PCB, and solder it to fix it. Then, bend it 90° to the upper right along the folding line a; bend it 90° to the right along the folding line b to form a step, and flip it to the front of the flexible printed circuit board.

[0016] S5, bend 90° to the lower left along folding line c, bend 90° to the upper right along folding line d to form a step, align the output ground pad C with the pad F on the high-voltage power supply PCB, and weld and fix it;

[0017] S6. Place the flexible printed circuit board flat against the high-voltage power supply PCB, with the back side close to the components on the high-voltage power supply PCB. After soldering the shielding wire to the input positive pad A and the input ground pad B, bend it together with the high-voltage power supply PCB and put it into the metal casing. Use silicone rubber potting to complete the overall shaping. Finally, solder the shielding wire to the metal casing 360°.

[0018] The flexible printed circuit board is a laminated structure of a front protective film, a substrate, and a back protective film; wherein the substrate is a laminated structure of rolled copper, polyimide, and rolled copper; the front protective film and the back protective film are both laminated structures of polyimide and epoxy resin glue; the front protective film has a solder mask window according to the layout design, and the back protective film only has windows corresponding to the output positive pad D and the output ground pad C.

[0019] Compared with the prior art, the present invention has the following beneficial effects: on the basis of ensuring mutual insulation and assembly reliability between the EMI filter and the high-voltage power supply, the present invention effectively solves the problem that the EMI filter cannot be reasonably placed due to the ring shell structure of the high-voltage power supply and the layout design is not ideal; the EMI filter is designed separately by using a flexible printed circuit board, and a two-stage combined filtering structure is used to filter and absorb interference to the maximum extent; filtering components are selected according to the frequency band of image intensifier radiation exceeding the standard and the sensitive frequency band to electric field interference, and chip filter capacitors, common mode inductors and high-frequency magnetic beads are integrated on the flexible printed circuit board, and then the designed flexible printed circuit board is stacked and welded on the high-voltage power supply PCB, the front pad is reinforced, the back side is insulated, and then it is bent together with the high-voltage power supply PCB and placed in a metal shell, and silicone rubber is used for potting to complete the overall shaping. The above assembly method realizes the reasonable placement of the EMI filter and solves the problem of its layout design being not ideal; the input line of the EMI filter adopts an electromagnetic shielding line and is grounded in a specific way, and can be reliably assembled on the image intensifier, effectively improving the electromagnetic compatibility performance of the image intensifier, and ensuring that the image intensifier can meet the electromagnetic compatibility test requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the circuit principle of the EMI filter in the present invention;

[0021] Figure 2 A schematic diagram of the layout design of the EMI filter in the present invention;

[0022] Figure 3 The schematic diagram of the laminated assembly structure design of the flexible printed circuit board FPC in the present invention;

[0023] Figure 4 The figure is a schematic diagram of the back side insulation and front side pad reinforcement design of the flexible printed circuit board FPC in the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited in any way. Any changes or improvements made based on the teachings of the present invention belong to the protection scope of the present invention.

[0025] like Figure 1 As shown, the present invention provides an EMI filter for an image intensifier, the EMI filter is composed of a low-frequency ceramic capacitor C1, a high-frequency ceramic capacitor C2, a high-frequency common-mode inductor L1, a high-frequency magnetic bead L2, a high-frequency magnetic bead L3 and a low-frequency ceramic capacitor C3 arranged on the front side of a flexible printed circuit board; one end of the low-frequency ceramic capacitor C1 is connected to the input positive and pin No. 1 of the high-frequency common-mode inductor L1, and the other end of the low-frequency ceramic capacitor C1 is connected to the input ground and pin No. 4 of the high-frequency common-mode inductor L1; pin No. 2 of the high-frequency common-mode inductor L1 is connected to one end of the high-frequency ceramic capacitor C2 and one end of the high-frequency magnetic bead L2, and the other end of the high-frequency magnetic bead L2 is connected to the output positive and one end of the low-frequency ceramic capacitor C3; pin No. 3 of the high-frequency common-mode inductor L1 is connected to the other end of the high-frequency ceramic capacitor C2 and one end of the high-frequency magnetic bead L3, and the other end of the high-frequency magnetic bead L3 is connected to the output ground and the other end of the low-frequency ceramic capacitor C3.

[0026] The input positive lead and the input ground lead are shielded wires with wave-proof sleeves, the shielded wires form a shielding layer, the end of the shielding layer is connected to the No. 4 pin of the high-frequency common-mode inductor L1, and the front end of the shielding layer is suspended.

[0027] like Figure 2-3 As shown, the present invention also provides an EMI filter assembly method, including layout design and stacking assembly;

[0028] The layout design includes the following steps:

[0029] S1. Arrange the low-frequency ceramic capacitor C1, high-frequency common-mode inductor L1, high-frequency ceramic capacitor C2, high-frequency magnetic bead L2, high-frequency magnetic bead L3 and low-frequency ceramic capacitor C3 that have been electrically connected on the front side of the flexible printed circuit board in sequence from input to output;

[0030] S2. A single-sided input positive pad A and a single-sided input ground pad B are set at the front input end of the flexible printed circuit board, and long strip welding rods are designed on both sides of the front output end of the flexible printed circuit board. A front and back output positive pad D with a via and a front and back output ground pad C are set at the end of the welding rod;

[0031] S3. Copper shielding is performed on the reverse side of the flexible printed circuit board, with the pad distance between the input side and the output side of the high-frequency common mode inductor L1 as the spacing;

[0032] The stacking assembly includes the following steps:

[0033] S4. Place the back of the flexible printed circuit board, align the output positive pad D with the pad E on the high-voltage power supply PCB, and solder it to fix it. Then, bend it 90° to the upper right along the folding line a; bend it 90° to the right along the folding line b to form a step, and flip it to the front of the flexible printed circuit board.

[0034] S5, bend 90° to the lower left along folding line c, bend 90° to the upper right along folding line d to form a step, align the output ground pad C with the pad F on the high-voltage power supply PCB, and weld and fix it;

[0035] S6. Place the flexible printed circuit board flat against the high-voltage power supply PCB, with the back side close to the components on the high-voltage power supply PCB. After soldering the shielding wire to the input positive pad A and the input ground pad B, bend it together with the high-voltage power supply PCB and put it into the metal casing. Use silicone rubber potting to complete the overall shaping. Finally, solder the shielding wire to the metal casing 360°.

[0036] like Figure 4 As shown, the flexible printed circuit board is a laminated structure of a front protective film, a substrate, and a back protective film; wherein the substrate is a laminated structure of rolled copper, polyimide, and rolled copper; the front protective film and the back protective film are both laminated structures of polyimide and epoxy resin glue; the front protective film has a solder mask window according to the layout design, and the back protective film has windows only corresponding to the positions of the output positive pad D and the output ground pad C. Example

[0037] Figure 1 This is the schematic diagram of the circuit principle of the EMI filter. The design and selection parameters of each component are as follows.

[0038] The low-frequency ceramic capacitor C1 uses a chip-type 0603 ceramic dielectric capacitor with a capacity of several uF, which is placed at the front end of the input to reduce the input impedance and avoid input voltage resonance when connected to a linear stable impedance network (LSIN) to cause power supply abnormality.

[0039] The high-frequency ceramic capacitor C2 uses a chip-type 0402 RF ceramic dielectric capacitor with a high quality factor (Q value) of tens of pF, and is particularly required to have a lower impedance between 100MHz and 1GHz, mainly to provide a low-impedance filtering path for the differential mode current caused by the unequal impedance of the positive and negative lines to the ground when the common-mode interference of the external RS103 electric field is coupled and transmitted.

[0040] The high-frequency common-mode inductor L1 uses a chip-type 0805 common-mode inductor, which presents high impedance and filters the external high-frequency common-mode interference and the interference generated by the power supply itself. In particular, it is required that its impedance reaches hundreds to thousands of ohms in the frequency band of 100MHz~1GHz, and it has a magnetic shielding structure and the ability to pass hundreds of mA of direct current.

[0041] The high-frequency magnetic beads L2 and L3 are both chip-type 0603 high-frequency magnetic beads, which are mainly used to absorb the previous differential mode conduction interference and the high-frequency common mode interference coupled by the external environment. In particular, the impedance is required to reach tens to hundreds of ohms in the frequency band of 100MHz~1GHz, and have the ability to pass hundreds of mA DC current.

[0042] The low-frequency ceramic capacitor C3 uses a chip-type 0603 ceramic dielectric capacitor with a capacity of several uF, mainly to reduce the low-frequency ripple current generated when the DC / DC inside the power supply works, and to suppress differential mode conduction and emission.

[0043] The low-frequency ceramic capacitor C1, the high-frequency ceramic capacitor C2 and the high-frequency common-mode inductor L1 form a front-stage filtering structure, and the high-frequency magnetic beads L2, the high-frequency magnetic beads L3 and the low-frequency ceramic capacitor C3 form a post-stage filtering structure to form a two-stage filtering structure; small chip components are selected, and it is required that within the sensitive frequency band of the image intensifier, the inductive components have a higher impedance and the capacitive components have a lower impedance to achieve EMI filtering.

[0044] Figure 2 Design schematic for the layout design of EMI filter.

[0045] The electrically connected low-frequency ceramic capacitor C1, high-frequency common-mode inductor L1, high-frequency ceramic capacitor C2, high-frequency magnetic bead L2, high-frequency magnetic bead L3 and low-frequency ceramic capacitor C3 are arranged on the front side of the flexible printed circuit board in sequence from input to output; the above components are close to each other to minimize the current loop area to reduce electromagnetic induction and radiation emission.

[0046] A single-sided input positive pad A and a single-sided input ground pad B are set at the front input end of the flexible printed circuit board, and long strip welding rods are designed on both sides of the front output end of the flexible printed circuit board. Front and back output positive pads D and front and back output ground pads C with vias are set at the ends of the welding rods; the entire welding rod is copper-plated to facilitate bending and shaping. In order to reduce mechanical stress, the area where the welding rod and the flexible printed circuit board are connected is rounded to avoid tearing when pulled.

[0047] No components are placed on the back of the flexible printed circuit board. A large area of ​​copper is used as a shield. The pad distance between the input and output sides of the common-mode inductor L1 is used as an interval to minimize high-frequency coupling and achieve the design of the lowest impedance return path for high-frequency current.

[0048] Figure 3It is a schematic diagram of the laminated assembly structure design of the flexible printed circuit board FPC in the present invention.

[0049] The first step is as follows Figure 3 As shown in (a), first place the back of the flexible printed circuit board, align the output positive pad D with the pad E on the high-voltage power supply PCB, and then bend it 90° to the upper right along the folding line a; bend it 90° to the right along the folding line b to form a step, and turn it over to the front of the flexible printed circuit board to obtain the attached Figure 3 (b) Structure.

[0050] In the second step, bend 90° to the lower left along the folding line c, and bend 90° to the upper right along the folding line d to form a step, and align the output ground pad C with the pad F on the high-voltage power supply PCB and weld it to fix it.

[0051] The third step is to slightly move the welding rod left and right to adjust the folding position so that the flexible printed circuit board is flat and facing the high-voltage power supply PCB, and the back is close to the components on the high-voltage power supply PCB. After welding the shielding wire on the input positive pad A and the input ground pad B, bend it together with the power supply PCB and put it into the metal casing. Use silicone rubber potting to complete the overall shaping. Finally, weld the shielding wire to the metal casing 360°.

[0052] Figure 4 The figure is a schematic diagram of the back side insulation and front side pad reinforcement design of the flexible printed circuit board FPC in the present invention.

[0053] The flexible printed circuit board is a laminated structure of a front protective film, a substrate, and a back protective film; wherein the substrate is a laminated structure of rolled copper, polyimide, and rolled copper, and has good flexibility; the front protective film and the back protective film are both laminated structures of polyimide and epoxy resin glue, and have high adhesion and insulation strength; the front protective film has solder mask windows according to the layout design, and the back protective film only has windows corresponding to the output positive pad D and the output ground pad C, and the rest are all covered with protective film to ensure insulation; the thickness of each layer of the flexible printed circuit board is designed to be tens of um, and the final overall thickness is about 0.2mm to meet the flexible bending requirements.

[0054] The layout pad size is designed to be 0.3mm larger than the actual pin pad, and the solder mask window is 0.1mm larger than the actual pin pad. In this way, the pad is reinforced by pressing the edge with a 0.2mm protective film. In addition, when designing the layout, copper is laid to press the pad to further improve reliability.

Claims

1. An EMI filter for an image intensifier, characterized in that The EMI filter is composed of a low-frequency ceramic capacitor C1, a high-frequency ceramic capacitor C2, a high-frequency common-mode inductor L1, a high-frequency magnetic bead L2, a high-frequency magnetic bead L3 and a low-frequency ceramic capacitor C3, which are arranged on the front of the flexible printed circuit board. One end of the low-frequency ceramic capacitor C1 is connected to the input positive lead and pin No. 1 of the high-frequency common-mode inductor L1, and the other end of the low-frequency ceramic capacitor C1 is connected to the input ground lead and pin No. 4 of the high-frequency common-mode inductor L1; pin No. 2 of the high-frequency common-mode inductor L1 is connected to one end of the high-frequency ceramic capacitor C2 and one end of the high-frequency magnetic bead L2, and the other end of the high-frequency magnetic bead L2 is connected to the output positive and one end of the low-frequency ceramic capacitor C3; pin No. 3 of the high-frequency common-mode inductor L1 is connected to the other end of the high-frequency ceramic capacitor C2 and one end of the high-frequency magnetic bead L3, and the other end of the high-frequency magnetic bead L3 is connected to the output ground and the other end of the low-frequency ceramic capacitor C3.

2. The EMI filter for an image intensifier according to claim 1, characterized in that: The input positive lead and the input ground lead are shielded wires with wave-proof sleeves, the shielded wires form a shielding layer, the end of the shielding layer is connected to the No. 4 pin of the high-frequency common-mode inductor L1, and the front end of the shielding layer is suspended.

3. An assembly method for implementing the EMI filter assembly according to any one of claims 1 to 2, characterized in that: Including layout design and stack-up assembly; The layout design includes the following steps: S1. Arrange the low-frequency ceramic capacitor C1, high-frequency common-mode inductor L1, high-frequency ceramic capacitor C2, high-frequency magnetic bead L2, high-frequency magnetic bead L3 and low-frequency ceramic capacitor C3 that have been electrically connected on the front side of the flexible printed circuit board in sequence from input to output; S2. A single-sided input positive pad A and a single-sided input ground pad B are set at the front input end of the flexible printed circuit board, and long strip welding rods are designed on both sides of the front output end of the flexible printed circuit board. A front and back output positive pad D with a via and a front and back output ground pad C are set at the end of the welding rod; S3. Copper shielding is performed on the reverse side of the flexible printed circuit board, with the pad distance between the input side and the output side of the high-frequency common mode inductor L1 as the spacing; The stacking assembly includes the following steps: S4. Place the back of the flexible printed circuit board, align the output positive pad D with the pad E on the high-voltage power supply PCB, and solder it to fix it. Then, bend it 90° to the upper right along the folding line a; bend it 90° to the right along the folding line b to form a step, and flip it to the front of the flexible printed circuit board. S5, bend 90° to the lower left along folding line c, bend 90° to the upper right along folding line d to form a step, align the output ground pad C with the pad F on the high-voltage power supply PCB, and weld and fix it; S6. Place the flexible printed circuit board flat against the high-voltage power supply PCB, with the back side close to the components on the high-voltage power supply PCB. After soldering the shielding wire to the input positive pad A and the input ground pad B, bend it together with the high-voltage power supply PCB and put it into the metal casing. Use silicone rubber potting to complete the overall shaping. Finally, solder the shielding wire to the metal casing 360°.

4. The assembly method according to claim 3, characterized in that The flexible printed circuit board is a laminated structure of a front protective film, a substrate, and a back protective film; wherein the substrate is a laminated structure of rolled copper, polyimide, and rolled copper; the front protective film and the back protective film are both laminated structures of polyimide and epoxy resin glue; the front protective film has a solder mask window according to the layout design, and the back protective film only has windows corresponding to the output positive pad D and the output ground pad C.

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