Microwave packaging circuit and packaging method

Abstract

The present invention provides a microwave packaging circuit and packaging method. The microwave packaging circuit comprises a microwave circuit, a shell cavity, a shell cover, a first protective layer and a second protective layer; the bottom of the microwave circuit is fixed to the shell cavity, the first protective layer is coated on the surface of the microstrip line in the microwave circuit, and the second protective layer is filled between the surface of the first protective layer and the shell cover; the dielectric loss tangent of the first protective layer is less than the dielectric loss tangent of the second protective layer. The present invention can provide anti-overload impact protection for the microwave circuit while ensuring the performance of the microwave circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit protection, and in particular to a microwave packaging circuit and a packaging method. Background Art

[0002] The transceiver front end is an important component of the missile-borne data link. Under high overload impact (axial impact of 12000g, duration 3-5ms), the internal circuit unit cannot meet normal operation in terms of vibration, impact, strength and stiffness. The general protection method is to use potting glue to fill it so that the electronic components and the structure are fully integrated to solve the problem of uneven structural force.

[0003] However, the potting compound has no effect on the control circuit and the lower-frequency RF circuit, but has a significant attenuation effect on the higher-frequency microwave circuit. The higher the frequency, the greater the attenuation. This is especially evident in the X-band, where the output power of the transmitting power amplifier unit and the noise coefficient of the receiving unit deteriorate, seriously affecting system operation. Summary of the invention

[0004] The embodiments of the present invention provide a microwave packaging circuit and a packaging method to solve the problem that potting glue has a significant attenuation effect on high-frequency microwave circuits.

[0005] In a first aspect, an embodiment of the present invention provides a microwave packaging circuit, including a microwave circuit, a housing cavity, a housing cover, a first protective layer and a second protective layer;

[0006] The bottom of the microwave circuit is fixed to the shell cavity, the first protective layer is coated on the surface of the microstrip line in the microwave circuit, and the second protective layer is filled between the surface of the first protective layer and the shell cover;

[0007] The dielectric loss tangent of the first protective layer is smaller than the dielectric loss tangent of the second protective layer.

[0008] In a possible implementation manner, the dielectric constant of the first protective layer is smaller than the dielectric constant of the second protective layer.

[0009] In a possible implementation, the first protective layer is an acetal drying adhesive layer; the thickness of the first protective layer is 10 to 20 μm.

[0010] In a possible implementation, the second protective layer is a potting glue layer.

[0011] In a possible implementation manner, the second protective layer is a polyurethane layer.

[0012] In a possible implementation manner, the first protective layer is coated on the surface of the microwave circuit.

[0013] In one possible implementation, the microwave circuit is a missile-borne transceiver front end.

[0014] In a possible implementation, the microwave circuit operates in the X-band.

[0015] In a second aspect, an embodiment of the present invention provides a packaging method for a microwave packaging circuit, comprising:

[0016] A first protective layer is coated on the surface of a microstrip line in a microwave circuit; wherein the bottom of the microwave circuit is fixed to the housing cavity;

[0017] Filling a second protective layer above each component of the microwave circuit and the first protective layer; wherein the dielectric loss tangent of the first protective layer is smaller than the dielectric loss tangent of the second protective layer;

[0018] The second protective layer is covered with a housing cover to obtain a microwave packaging circuit.

[0019] An embodiment of the present invention provides a microwave packaging circuit and a packaging method. Before a second protective layer is filled into the shell cavity of the microwave circuit, a first protective layer is first coated on the surface of the microwave circuit. Since the first protective layer has a lower loss tangent value and a lower dielectric constant than the second protective layer, coating the first protective layer on the surface can reduce the loss deterioration of the microstrip line in the microwave circuit, and indirectly reduce the insertion loss of each device in the circuit, thereby reducing the output power of the transmitting power amplifier unit and the noise coefficient deterioration of the receiving unit, and providing the microwave circuit with anti-overload impact protection while ensuring the performance of the microwave circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0021] Figure 1 is a schematic structural diagram of a microwave circuit provided by an embodiment of the present invention;

[0022] Figure 2 is a schematic structural diagram of an existing microwave packaging circuit provided by an embodiment of the present invention;

[0023] Figure 3 is a schematic structural diagram of a microwave packaging circuit provided by an embodiment of the present invention;

[0024] Figure 4 is a loss comparison diagram of microstrip lines covered with different protection layers provided by an embodiment of the present invention;

[0025] Figure 5 is a flow chart of an implementation method of a packaging method for a microwave packaging circuit provided by an embodiment of the present invention;

[0026] Figure 6 is a flow chart of an implementation method of a packaging method for a microwave packaging circuit provided by another embodiment of the present invention;

[0027] Figure 7 It is a block diagram of the microwave circuit transceiver channel principle provided by an embodiment of the present invention;

[0028] Figure 8 It is a schematic diagram of the structure after integrated protection of the transmitting and receiving channels according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0031] First, the terms involved in the present invention are explained:

[0032] Microwave circuit: usually refers to a circuit with a working frequency band wavelength between 10m and 1cm (i.e., a frequency between 30MHz and 30GHz). It can be classified into active circuits and passive circuits, where active circuits include: power amplifiers, low-noise amplifiers, frequency sources, oscillators, etc.; passive circuits include power dividers, couplers, filters, isolators, etc.

[0033] X-band: refers to the frequency band ranging from 8-12GHz.

[0034] High overload shock: High overload means "very excessive", "very excessive", which means that the overload has reached a very high level. The acceleration under overload state usually reaches more than 1,000 g, and the acceleration under high overload state reaches more than 10,000 g or even higher.

[0035] Microassembly technology: On a high-density substrate, surface mounting and interconnection processes are used to assemble integrated circuit chips, chip components and various micro components that constitute electronic circuits, and package them in the same housing to form high-density, high-speed, and high-reliability advanced microelectronic components.

[0036] Potting glue: Liquid polyurethane compound is poured into the housing containing electronic components and circuits by mechanical or manual methods, and solidified under certain conditions to become a high-performance polymer insulating material. The polyurethane compound used in this process is potting glue.

[0037] Figure 1 Schematic diagram of the structure of the microwave circuit provided by the embodiment of the present invention. Figure 1 As shown in the figure, before the overload protection packaging, the microwave circuit is placed in the metal shell cavity, and the medium is air. At this time, the microwave circuit has good working performance, but does not have the ability to resist overload impact. The various parts are described as follows:

[0038] Metal cavity——metal cavity, aluminum profile.

[0039] Printed circuit board ground copper layer - the ground copper layer at the bottom of the printed circuit board.

[0040] Printed circuit board dielectric layer - printed circuit board dielectric layer, polytetrafluoroethylene glass fiber cloth clad copper foil board.

[0041] Printed circuit board signal layer - the signal layer on the top of the printed circuit board, including microwave circuit routing: microstrip lines, microstrip power dividers, microstrip couplers, etc.

[0042] Components - active and passive packaged devices mounted on the signal layer of the printed circuit board, such as: LTCC filters, GaN power tubes, microwave monolithic amplifiers, isolators, cavity filters in the transmitting circuit; low-noise amplifiers in the receiving circuit; step-down DC / DC, diodes, transistors in the power control circuit; and surface-mount resistors, capacitors, inductors, etc.

[0043] Air cavity - the air-covered portion of the metal cavity from the top of the printed circuit board to the metal cavity cover.

[0044] Metal cavity cover - the metal cover of the metal cavity where the printed circuit board is located.

[0045] The printed circuit board grounding copper layer, printed circuit board dielectric layer, printed circuit board signal layer and components constitute a microwave circuit.

[0046] After the packaged components are mounted on the printed circuit board, they are fixed on the inner wall of the metal cavity by screws or sintering. To ensure that the components can withstand high overload impact, the general method is to fill the air cavity from the top of the printed circuit board to the metal cavity cover with potting glue. The structure after filling is as follows Figure 2 As shown. Potting glue includes: silicone rubber, epoxy resin potting glue, polyurethane potting glue. These three potting glues have a great influence on the transmission quality of microwave circuits, which is manifested as the higher the frequency, the greater the transmission loss. In order to ensure weight reduction, polyurethane glue is usually used for potting glue.

[0047] Through the potting experiment, it was found that the performance of the X-band microwave circuit changed after the potting glue was filled and cured, which was manifested in that the output power of the transmitting circuit dropped by 1.2dB, the passband flatness fluctuated greatly, and the flatness deteriorated from 0.8dB to 0.6dB; the noise coefficient of the receiving circuit deteriorated by 1.1dB. That is, the potting glue had a great impact on the transmission quality of the X-band microwave circuit, making the 50-ohm impedance line discontinuous and unable to meet tactical requirements.

[0048] There are two protection schemes for microwave circuits: Scheme 1: directly potting the RF circuit and accepting the influence of parameter deterioration; Scheme 2: using micro-assembly technology for secondary packaging, and potting the lower frequency control cavity with potting glue. That is, microwave (or RF) packaging components are not used in the microwave link, but microwave (or RF) bare chips are used to realize micro-assembly modules.

[0049] Among the above solutions, Solution 1: directly encapsulating the RF circuit will sacrifice too much RF performance and is not conducive to the realization of tactical indicators.

[0050] Solution 2: The micro-assembly module uses micro-assembly technology, which is an advanced electrical interconnection technology that interconnects bare integrated circuit chips, thin / thick film hybrid circuits, and micro-sized surface mount components at a high density. It requires dedicated micro-assembly process equipment and has more complex process requirements. In the field of high overload, the micro-assembly module does not require potting inside. When interconnecting with other modules, coaxial interconnection is used and secondary potting is required. The physical layout has certain limitations.

[0051] Compared with micro-assembly modules, the realization of microwave circuits composed of microwave packaging components is relatively simple, and the degree of dependence on the process is greatly reduced. If the influence of potting glue on microwave signals is solved, the application of microwave circuits composed of microwave packaging components will be greatly increased under overload shock environment, the layout of circuit units and control units will be more flexible, and the process cost will be greatly reduced.

[0052] Figure 3 The structure diagram of the microwave packaging circuit provided by the embodiment of the present invention is shown. For the convenience of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0053] like Figure 3 As shown, the microwave packaging circuit includes a microwave circuit 31, a housing cavity 32, a housing cover 33, a first protective layer 34 and a second protective layer 35;

[0054] The bottom of the microwave circuit 31 is fixed to the housing cavity 32, the first protective layer 34 is coated on the surface of the microstrip line in the microwave circuit 31, and the second protective layer 35 is filled between the surface of the first protective layer 34 and the housing cover 33;

[0055] The dielectric loss tangent of the first protective layer 34 is smaller than the dielectric loss tangent of the second protective layer 35 .

[0056] In this embodiment, the applicant found that the reason why the potting glue affects the microwave signal is that before potting, there is air above the microstrip line in the microwave circuit, which ensures the normal transmission of the microstrip line. After potting, the microstrip line is tightly bonded by the potting glue. Due to the inherent dielectric constant and loss tangent value of the potting glue, the transmission characteristics of the microstrip line of the microwave circuit are changed, causing the impedance characteristics of the microstrip line to change, thereby affecting the transmission of microwave signals, increasing the insertion loss of the transceiver device, and causing the device performance and microwave circuit characteristics to decline. In some simulation experiments, the dielectric constant of the first protective layer 34 can be no less than the dielectric constant of the second protective layer 35. It is only necessary to ensure that the dielectric loss tangent of the first protective layer 34 is less than the dielectric loss tangent of the second protective layer 35 to achieve the effect of ensuring device performance and microwave circuit characteristics.

[0057] Paper DOI: 10.1002 / mame.201000431 Through dynamic mechanical analysis (DMA), the loss tangent (tanδ) of polyurethane films with different crosslinker concentrations was measured. The data shows that the loss tangent is greatly affected by temperature, and tanδ is above 0.1. Zhao Feiming from the Institute of Aerospace Materials and Technology's paper "Research on Polyurethane Potting Materials and Processes for Aerospace Products" tested the electrical properties of two polyurethane adhesives. The dielectric loss tangent tanδ (1MHz) of the ADq552J-91B polyurethane material is 0.0221, and the dielectric constant is 3.5.

[0058] The microstrip line of the printed circuit board was simulated using the microwave simulation software ADS (the material parameters are shown in Table 1). It was found that after the air cavity was replaced with polyurethane, the insertion loss of the 40mm long standard microstrip line at 8GHz deteriorated from 0.12dB to 0.57dB (polyurethane 1). The data theoretically verified the reason for the deterioration of the microstrip line insertion loss. It should be noted that the dielectric loss tangent tanδ of the polyurethane material will further deteriorate with the increase of frequency, which will cause the insertion loss to further deteriorate with the increase of frequency, especially in the X-band, where the output power of the transmitting power amplifier unit and the noise coefficient of the receiving unit are particularly deteriorated.

[0059] Table 1

[0060]

[0061] In view of the above facts, the present invention conducts a relatively detailed study on the influence of polyurethane foam encapsulation and curing on microwave signals, and innovatively proposes a protection method for microwave packaging circuits, which significantly improves the transmission quality of X-band microwave circuits.

[0062] Specifically, according to the above-mentioned laminated structure of the printed circuit board, the present invention improves the laminated structure of the printed circuit board by adding a medium between the microstrip circuit and the polyurethane adhesive layer, thereby improving the attenuation effect of the polyurethane layer on the microstrip circuit. Figure 4 The four curves in the middle are, from top to bottom, the curve of the change of the loss of the microstrip line in the air medium with the frequency, the curve of the change of the loss of the microstrip line after coating the sample medium and then covering the polyurethane glue 1 with the frequency, the curve of the change of the loss of the microstrip line after covering the polyurethane glue 1 with the frequency, and the curve of the change of the loss of the microstrip line after covering the polyurethane glue 2 with the frequency. Figure 4 It can be seen that after the material changes from polyurethane 1 to polyurethane 2, the loss tangent changes from 0.021 to 0.05, and the loss of the 40mm long standard microstrip line at 8GHz deteriorates to 1.37dB. After a sample medium is covered between the microstrip line and polyurethane glue 1, the loss deterioration of the standard microstrip line (40mm long) at 8GHz is optimized from 0.57dB to 0.228dB, proving the feasibility of the theory.

[0063] Based on the above theoretical and experimental comparison, it is found that coating a certain thickness of dielectric on the microwave circuit, and the loss tangent and / or dielectric constant of the dielectric is lower than the protective layer of the potting glue, and then performing polyurethane potting, can greatly improve the attenuation effect of the X-band signal and retain the potting glue's anti-overload impact protection effect on the microwave circuit. Through temperature experimental comparison, the performance indicators of the microwave circuit are basically not deteriorated under this packaging method.

[0064] In the embodiment of the present invention, before the second protective layer is filled into the shell cavity of the microwave circuit, the first protective layer is first coated on the surface of the microwave circuit. Since the first protective layer has a lower loss tangent value and a lower dielectric constant than the second protective layer, coating the first protective layer on the surface can reduce the loss deterioration of the microstrip line in the microwave circuit, and indirectly reduce the insertion loss of each device in the circuit, thereby reducing the output power of the transmitting power amplifier unit and the noise coefficient deterioration of the receiving unit, thereby providing the microwave circuit with anti-overload impact protection and ensuring the performance of the microwave circuit.

[0065] In a possible implementation, the dielectric constant of the first protective layer 34 is smaller than the dielectric constant of the second protective layer 35 .

[0066] In this embodiment, it can be seen from the above content that the dielectric constant of the microstrip line medium also has a great influence on the impedance characteristics of the microstrip line. When the loss tangent and dielectric constant of the first protective layer 34 are both smaller than those of the second protective layer 35, the composed microwave packaging circuit can have better performance.

[0067] In a possible implementation, the first protective layer 34 is an acetal baking adhesive layer; the thickness of the first protective layer 34 is 10-20 μm.

[0068] In this embodiment, after a large number of experimental comparisons, it is found that after a layer of acetal drying glue of a certain thickness is first coated on the top of the printed circuit board microstrip circuit, and then potting is performed, the theoretical effect of the above embodiment can be achieved. That is, when the first protective layer 34 is an acetal drying glue layer, the attenuation effect of the signal when the microwave circuit works in the X-band can be greatly improved.

[0069] Through the comparative test of coating 1 to 4 layers of acetal drying glue and then filling with foam glue, it is found that the influence on the microstrip line is the smallest when 1 to 2 layers of acetal drying glue are coated and then filled with foam glue, but it will be affected by the thickness of the acetal drying glue. After analysis, the influence on the microstrip line is the smallest when the thickness of acetal drying glue is 10~20μm.

[0070] In a possible implementation, the second protective layer 35 is a potting glue layer.

[0071] In this embodiment, the second protective layer 35 is used to provide the microwave circuit with an overload shock resistance function, and therefore a potting glue is required.

[0072] In a possible implementation, the second protective layer 35 is a polyurethane layer.

[0073] In this embodiment, the potting glue includes: silicone rubber, epoxy resin potting glue, and polyurethane potting glue. These three potting glues have a great influence on the transmission quality of the microwave circuit, which is manifested in that the higher the frequency, the greater the transmission loss. In order to ensure weight reduction, the potting glue is usually selected from polyurethane glue.

[0074] In a possible implementation, the first protective layer 34 is coated on the surface of the microwave circuit 31 .

[0075] In this embodiment, the first protective layer 34 mainly acts on the surface of the microstrip line in the microwave circuit 31, but has no adverse effect on other parts of the microwave circuit 31. In order to ensure that the first protective layer 34 evenly covers the surface of the microstrip line and simplify the coating process, the first protective layer 34 can be directly coated on the surface of the microwave circuit 31.

[0076] In a possible implementation, the microwave circuit 31 is a missile-borne transceiver front end.

[0077] In this embodiment, the missile-borne transceiver front end is susceptible to high overload shock during operation, and the microwave circuit is required to have good transmission quality and working performance. Therefore, for the microwave circuit 31 used as the missile-borne transceiver front end, the microwave packaging circuit provided by the present invention can be encapsulated to provide overload shock protection for the microwave circuit 31 while ensuring the performance of the microwave circuit 31.

[0078] In a possible implementation, the microwave circuit 31 operates in the X-band.

[0079] In this embodiment, the potting glue has almost no effect on the control circuit and the radio frequency circuit with a lower frequency, but has a significant attenuation effect on the microwave circuit with a higher frequency. The higher the frequency, the greater the attenuation. In particular, the output power of the transmitting power amplifier unit and the noise coefficient of the receiving unit deteriorate significantly in the X-band, which seriously affects the operation of the system. Therefore, for the microwave circuit 31 working in the X-band, the encapsulation is the microwave encapsulation circuit provided by the present invention, which can improve the influence of the existing potting method on the transmission quality of the X-band microwave circuit 31.

[0080] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0081] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0082] See also Figure 5 , which shows a flowchart of the implementation of the packaging method of the microwave packaging circuit provided by the embodiment of the present invention, and is described in detail as follows:

[0083] Step 501, coating a first protective layer on the surface of a microstrip line in a microwave circuit; wherein the bottom of the microwave circuit is fixed to the housing cavity.

[0084] Step 502, filling a second protective layer on top of each component of the microwave circuit and the first protective layer; wherein the dielectric loss tangent of the first protective layer is smaller than the dielectric loss tangent of the second protective layer.

[0085] Step 503, covering the second protective layer with a housing cover to obtain a microwave packaging circuit.

[0086] In a possible implementation manner, the dielectric constant of the first protective layer is smaller than the dielectric constant of the second protective layer.

[0087] In a possible implementation, the first protective layer is an acetal drying adhesive layer; the first protective layer is coated on the surface of the microstrip line in the microwave circuit, including:

[0088] Anhydrous ethanol and acetal drying glue mixed in a preset ratio are coated on the surface of the microwave circuit, and high-temperature curing is performed, and the process is repeated 1 to 3 times.

[0089] Based on the above structural embodiment, it can be known that applying 1 to 2 layers of acetal drying glue and then pouring foam glue has the least impact on the microstrip line, but will be affected by the thickness of the acetal drying glue.

[0090] In view of the difference in coating thickness, the present invention determines a uniform coating process of acetal drying glue through a comparative test of coating thickness. The specific operation method is as follows:

[0091] a) Acetal drying glue should use the original barrel of glue liquid (without solvent volatilization, low viscosity, to avoid bubble generation).

[0092] b) Dilution of acetal drying glue: Mix anhydrous ethanol (alcohol content: 99.9%) and acetal drying glue in a ratio of (2-3):1. Use a fine brush to stir slowly during mixing to avoid bubbles. If bubbles are generated after stirring, the mixture should be left to stand for 1 minute and wait for the bubbles to disappear safely.

[0093] c) Coating range: All RF circuit surfaces to be coated.

[0094] d) Use a fine brush to apply the mixed acetal drying glue evenly at a 45° angle to the board surface. The brushing marks should overlap. Be careful not to repeatedly apply to the same area to avoid bubbles. The brushing action should be done slowly to fully infiltrate the acetal drying glue and the printed board and components. After brushing, let it dry naturally for 2 hours and cure at 75℃ for 2 hours.

[0095] e) Apply a second coat as in step c) and then cure.

[0096] After following the above steps, the thickness of the acetal drying glue applied once is 5-10μm, and the thickness of the acetal drying glue applied twice is 10-20μm. The influence of the 50Ω microstrip line is shown as follows. The standing wave changes slightly, and the insertion loss changes slightly, which is acceptable for the change of RF circuit performance.

[0097] In a possible implementation manner, the second protective layer is a potting glue layer.

[0098] In a possible implementation manner, the second protective layer is a polyurethane layer.

[0099] In a possible implementation manner, the first protective layer is coated on the surface of the microwave circuit.

[0100] In one possible implementation, the microwave circuit is a missile-borne transceiver front end.

[0101] In a possible implementation, the microwave circuit operates in the X-band.

[0102] In the embodiment of the present invention, before the second protective layer is filled into the shell cavity of the microwave circuit, the first protective layer is first coated on the surface of the microwave circuit. Since the first protective layer has a lower loss tangent value and a lower dielectric constant than the second protective layer, coating the first protective layer on the surface can reduce the loss deterioration of the microstrip line in the microwave circuit, and indirectly reduce the insertion loss of each device in the circuit, thereby reducing the output power of the transmitting power amplifier unit and the noise coefficient deterioration of the receiving unit, thereby providing the microwave circuit with anti-overload impact protection and ensuring the performance of the microwave circuit.

[0103] In a specific embodiment, Figure 6 As shown, the packaging process operation method for the microwave packaging circuit is as follows:

[0104] Step 1: Structure and PCB assembly pre-processing

[0105] 1) Use an air gun to clean the dust, impurities and other excess materials in the transceiver cavity;

[0106] 2) Use a non-woven cloth dipped in sewage ethanol to repeatedly scrub the surface of the printed circuit board assembly, and go through the processes of primary scrubbing, self-inspection, secondary scrubbing, self-inspection, etc. until the surface of the printed circuit board is clean and tidy;

[0107] 3) Oven drying: Use a high-temperature hot air oven at 60℃±5℃ for 20min~30min.

[0108] Step 2: Acetal drying glue coating

[0109] 1) Use acetal drying glue (glue that has not undergone solvent evaporation) when coating.

[0110] 2) Mix anhydrous ethanol (alcohol content: 99.9%) and acetal drying glue in a ratio of (2-3):1, and stir in an "8" shape with a glass stirring rod for at least 3 minutes. The stirring speed should be slowed down to avoid bubbles. If bubbles are generated after stirring, the mixture should be left to stand for 3 minutes and wait for the bubbles to disappear.

[0111] 3) Use a fine brush to dip in an appropriate amount of diluted acetal drying glue (the glue should not drip on the brush), and brush it evenly at a 45° angle to the surface of the board. The brushing marks should overlap (be careful not to brush repeatedly in the same area to avoid bubbles). The brushing action should be done slowly to ensure that the PF glue, printed circuit board and components are fully infiltrated.

[0112] 4) After painting, allow to dry naturally for 2 hours and then cure at 80℃±5℃ for 2 hours.

[0113] 5) Follow steps 3) and 4) in step 2 for secondary coating and curing.

[0114] Step 3: Coating Inspection

[0115] 1) Use a 5x to 10x magnifying glass to check if the acetal drying adhesive coating has any defects such as orange peel, bubbles, pinholes, cracks, etc.

[0116] 2) Use a 5x to 10x magnifying glass to check that the coating has completely covered the printed circuit board surface and all component surfaces, and there is no missing coating.

[0117] 3) Use a 5x to 10x magnifying glass to check if there are any extraneous objects on the front end of the transmitter and receiver and on the surface of the printed circuit board.

[0118] Step 4: Pretreatment before potting

[0119] 1) Apply a release agent on the inner surface of the potting box cover;

[0120] 2) Use a torque screwdriver to fasten the potting box cover to the box body at the front end of the transceiver using cross recessed countersunk screws.

[0121] Step 5: Polyurethane Foam Potting

[0122] 1) Unpack the polyurethane foam components A and B and check that there is no obvious abnormality in the glue. Put the glue of components A and B into the oven for preheating at a temperature of 100℃±5℃ and a preheating time of 20min±5min;

[0123] 2) After preheating, take out the glue solution of component A and component B, stir with a stirring rod for no less than 5 minutes, and there is no obvious precipitation in the glue solution;

[0124] 3) Fill component A and component B into the A and B barrels of the glue filling machine respectively, and the filling should not exceed 75% of the volume of the barrel;

[0125] 4) Set the mixing ratio of glue A and glue B, injection speed and injection amount of the glue filling machine;

[0126] 5) After checking that the mixing ratio of the glue filling machine is correct, verify the glue filling of the first piece, and then carry out batch glue filling after passing the verification.

[0127] 6) Curing: After potting, the front end of the transmitter and receiver should be placed in a horizontal position without tilting or moving, and placed at room temperature for 30 minutes.

[0128] Step 6: Post-potting inspection

[0129] 1) Use a torque screwdriver to remove the potting box cover;

[0130] Check that the potting glue is filled fully and sufficiently.

[0131] In a specific embodiment, the above steps are used to encapsulate a certain X-band missile-borne transceiver front end, and the microwave circuit transceiver channel principle block diagram is as follows: Figure 7 As shown, the structure after packaging is completed is as follows Figure 8 shown.

[0132] The X-band missile-borne transceiver front end contains two channels, one for receiving and one for transmitting, two RF ports, and a time-division working mode. The final power amplifier and the low-noise amplifier input port are connected through a circulator. The control circuit receives external control commands to realize the down-conversion of the X-RF signal to the L-IF signal and the up-conversion of the L-IF signal to the X-RF signal. The internal 10MHz crystal oscillator provides a stable reference signal for the internal transceiver local oscillator.

[0133] When anti-overload layout is performed, the front-end unit: microwave package power transistor, low-noise amplifier, is placed in the first cavity according to the direction of stress action, and the intermediate frequency amplifier, mixer, and power supply control circuit are placed in the second cavity.

[0134] The first chamber is not limited to amplifiers, but also includes cavity filters, isolators, circulators, microstrip power dividers, RF connectors, surface-mount resistors, capacitors, inductors, etc.; the second chamber is not limited to intermediate frequency amplifiers and mixers, but also includes crystal oscillators, RF connectors, surface-mount resistors, capacitors, inductors, etc.

[0135] The metal cavity is made of 7 series aluminum profiles with a yield strength greater than 400 MPa to ensure the hardness of the structure.

[0136] The inner surface of the first chamber is partially silver-plated, and the printed circuit board where the radio frequency side components are located and the inner wall of the first chamber are sintered to improve stress impact.

[0137] The components of the first chamber are soldered to the printed circuit board through 183°C reflow soldering to form a printed circuit board assembly. The printed circuit board assembly is soldered to the first chamber at low temperature, which can effectively improve the RF grounding performance and stress resistance. The RF interface uses a semi-flexible cable, one end of which is fixed to the structure by screws with a connector, and the other end forms an open line to interconnect with the printed circuit board strip line. The outer conductor of the cable is soldered to the inner wall of the cavity, and the inner conductor of the cable is soldered to the microstrip line of the printed circuit board.

[0138] The internal circuit unit is potted with polyurethane foam glue to make the electronic components and the structure fully integrated to improve the overload resistance. Acetal drying glue is coated between the electronic components and the polyurethane foam glue to solve the attenuation effect of the potting glue on the microwave circuit. The specific potting process is as follows:

[0139] 1) Use an air gun to clean the dust, impurities and other excess materials in the cavity of the transceiver front end. Use a non-woven cloth dipped in sewage ethanol to repeatedly scrub the surface of the printed circuit board assembly, and go through the processes of primary scrubbing, self-inspection, secondary scrubbing, self-inspection, etc. until the surface of the printed circuit board is clean and tidy; place the transceiver front end in a high-temperature hot air oven and dry it at 60℃±5℃ for 20min~30min.

[0140] 2) Mix anhydrous ethanol (alcohol content: 99.9%) and acetal drying glue in a ratio of (2-3):1, and stir in an "8" shape with a glass stirring rod for at least 3 minutes. The stirring speed should be slowed down to avoid bubbles. If bubbles are generated after stirring, the mixture should be left to stand for 3 minutes and wait for the bubbles to disappear.

[0141] 3) Use a fine brush to dip an appropriate amount of diluted acetal drying glue (the glue should not drip on the brush), and apply it evenly at a 45° angle to the board surface. The brushing marks should overlap and the brushing action should be done slowly so that the acetal drying glue and the printed board and components are fully infiltrated. After brushing, let it dry naturally for 2 hours and cure at 80℃±5℃ for 2 hours. Complete the second brushing according to the above requirements.

[0142] 4) Use a 5x to 10x magnifying glass to check if the acetal baking adhesive coating has defects such as orange peel, bubbles, pinholes, cracks, etc.; check that the coating layer has completely covered the surface of the printed circuit board and all component surfaces without any missing coating; check if there are other excess materials on the front end of the transmitter and receiver and the surface of the printed circuit board.

[0143] 5) Apply a release agent to the inner surface of the potting box cover. Use a torque screwdriver to fasten the potting box cover to the box body at the front end of the transmitter and receiver using cross recessed countersunk screws.

[0144] 6) Unpack the polyurethane foam A and B components and check that there is no obvious abnormality in the glue. Put the A and B component glue into the oven for preheating, the preheating temperature is 100℃±5℃, and the preheating time is 20min±5min. After preheating, take out the A and B component glue, stir with a stirring rod for no less than 5min, and there is no obvious precipitation in the glue.

[0145] 7) Fill component A and component B glue into the A and B barrels of the glue filling machine respectively, and the filling should not exceed 75% of the volume of the barrel.

[0146] 8) Set the mixing ratio of glue A and glue B, injection speed and injection amount of the glue filling machine; after checking that the mixing ratio of the glue filling machine is correct, verify the glue filling of the first piece, and perform batch glue filling after the verification is qualified.

[0147] 9) Curing: After potting, the front end of the transmitter and receiver should be placed in a horizontal state and should not be tilted or moved. It should be placed at room temperature for 30 minutes.

[0148] 10) Use a torque screwdriver to remove the potting box cover and check that the potting glue is fully filled.

[0149] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0150] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0151] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A microwave packaging circuit, characterized in that: It includes a microwave circuit, a shell cavity, a shell cover, a first protective layer and a second protective layer; the first protective layer is an acetal drying adhesive layer; The bottom of the microwave circuit is fixed to the housing cavity, the first protective layer is coated on the surface of the microstrip line in the microwave circuit, and the second protective layer is filled between the surface of the first protective layer and the housing cover; The dielectric loss tangent of the first protective layer is smaller than the dielectric loss tangent of the second protective layer.

2. The microwave packaging circuit according to claim 1, characterized in that: The dielectric constant of the first protection layer is smaller than the dielectric constant of the second protection layer.

3. The microwave packaging circuit according to claim 1, characterized in that: The thickness of the first protective layer is 10-20 μm.

4. The microwave packaging circuit according to claim 1, characterized in that: The second protective layer is a potting glue layer.

5. The microwave packaging circuit according to claim 4, characterized in that: The second protective layer is a polyurethane layer.

6. The microwave packaging circuit according to claim 1, characterized in that: The first protective layer is coated on the surface of the microwave circuit.

7. The microwave packaging circuit according to claim 1, characterized in that: The microwave circuit is a missile-borne transceiver front end.

8. The microwave packaging circuit according to claim 1, characterized in that: The microwave circuit operates in the X-band.

9. A packaging method for a microwave packaging circuit, characterized in that: include: A first protective layer is coated on the surface of a microstrip line in a microwave circuit; wherein the bottom of the microwave circuit is fixed to the housing cavity, and the first protective layer is an acetal drying adhesive layer; Filling a second protective layer above the microwave circuit components and the first protective layer; wherein the dielectric loss tangent of the first protective layer is smaller than the dielectric loss tangent of the second protective layer; The second protective layer is covered with a housing cover to obtain a microwave packaging circuit.

10. The packaging method of a microwave packaging circuit according to claim 9, characterized in that: The method of coating a first protective layer on the surface of a microstrip line in a microwave circuit comprises: Anhydrous ethanol and acetal drying glue mixed in a preset ratio are coated on the surface of the microwave circuit, and high-temperature curing is performed, and the process is repeated 1 to 3 times.

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