Method for realizing general microstrip printed board with extremely low cavity ratio

Abstract

The present application relates to a kind of general microstrip printed board extremely low cavity ratio implementation method, comprising the following steps: take out conductive silver paste and then stir, conductive silver paste is coated in radio frequency cavity bottom, then conductive silver paste is flattened;Microstrip printed board is placed in radio frequency cavity;Again, fluorosilicone rubber flexible press block and aluminum alloy rigid press block are sequentially loaded into radio frequency cavity;Using screw and nut, lower pressing clamp, upper pressing clamp and radio frequency cavity are pressed, so that the double-layer press block structure of fluorosilicone rubber flexible press block and aluminum alloy rigid press block extrudes microstrip printed board, the close adhesion of microstrip printed board and radio frequency cavity is realized;The fixed radio frequency shell and double-layer press block structure are placed in oven, and the baking time in oven is at least extended by more than 1 times than the specified curing baking time of conductive silver paste.The above technical scheme can effectively solve the technical problem of high cavity ratio when microstrip printed board is bonded with radio frequency shell.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency microwave device technology, and specifically relates to a method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board. Background Technology

[0002] Microstrip circuits are widely used in radio frequency (RF) and microwave device components due to their simple manufacturing process, convenient assembly, and adjustable specifications, giving them a dominant position among various microwave circuits. However, when transmitting RF / microwave signals using microstrip circuits, a housing is required as a carrier. The back of the microstrip circuit board, serving as the signal reference ground, needs to be in close contact with the housing. The quality of this contact directly affects the transmission quality of the RF / microwave signal, especially in the Ka-band, where the porosity of the contact between the microstrip circuit board and the housing has a significant impact on signal transmission performance.

[0003] Currently, there are two main bonding methods between microstrip printed circuit boards and housings in microwave devices and components: soldering and conductive silver paste bonding. The microstrip line ground plane needs to be in full contact with the RF housing. If the microstrip line is poorly grounded or has voids, the transmitted signal will generate higher-order modes, causing a decrease in signal quality and affecting the overall performance of the microwave component. The quality of the microstrip line grounding is particularly noticeable at high frequencies.

[0004] Soldering the microstrip line to the RF housing improves the reliability of the soldering between the microstrip printed circuit board and the RF housing. However, soldering has poor reworkability for the printed circuit board. Typically, soldering the microstrip line to the RF housing requires a high-temperature hot plate, and the microstrip line clamping block must be a high-temperature resistant block. This bonding method first requires a solderability underlayer treatment for the RF housing. Secondly, once the soldering is completed, the reworkability of the microstrip printed circuit board and the RF housing is poor. In addition, this soldering bonding method is only suitable for lower operating frequencies. At Ka-band or higher frequencies, the void ratio of the solder will greatly affect the signal transmission quality.

[0005] When using conductive silver paste to bond the microstrip printed circuit board to the RF housing, the silver paste overflows into the resin during the bonding process, causing some contamination to the signal lines of the microstrip printed circuit board. Furthermore, when conventional metal blocks are used to bond microstrip lines at high temperatures, the void ratio requires high flatness of both the block and the RF housing. Thus, it is also difficult to control the void ratio when using conductive silver paste to bond microstrip lines, especially at high frequencies, particularly above the Ka band. Controlling the void ratio becomes even more difficult, making it impossible to guarantee high-quality transmission of Ka band signals from the microstrip lines.

[0006] In summary, the main disadvantages of the existing technology are: (1) Soldering of microstrip printed circuit boards is generally not suitable for Ka band and above, the void ratio is poorly controlled, and the signal transmission quality is poor; (2) When conventional microstrip line silver paste is bonded, resin will be generated, which will cause pollution to the signal line and affect the signal transmission; (3) The hard pad when bonding microstrip lines to RF housings cannot avoid the problem of high void ratio caused by poor flatness of the pad and RF housing. Summary of the Invention

[0007] To address the problems in existing technologies, this invention proposes a method for achieving extremely low void ratios in general-purpose microstrip printed circuit boards (PCBs). This method effectively solves the void ratio problem during the assembly process of microstrip PCBs and housings, providing technical assurance for the high-quality use of microstrip PCBs in microwave components.

[0008] The objective of this invention and the technical problem it solves are achieved by the following technical solution. A method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board, according to this invention, includes the following steps:

[0009] After removing the conductive silver paste, stir it. Then, coat the conductive silver paste onto the bottom of the RF cavity of the RF housing, and then spread the conductive silver paste coated on the bottom of the RF cavity.

[0010] Place the microstrip printed circuit board flat inside the radio frequency cavity;

[0011] Next, the circuit templates protruding from the lower surfaces of the fluorosilicone rubber flexible block and the aluminum alloy rigid block are sequentially installed into the radio frequency cavity;

[0012] The lower clamping clamp is placed below the RF housing, and the upper clamping clamp is placed above the aluminum alloy rigid pressure block. Screws and nuts are used to lock the lower and upper clamping clamps together, thereby causing the double-layer pressure block structure composed of the fluorosilicone rubber flexible pressure block and the aluminum alloy rigid pressure block to squeeze the microstrip printed circuit board, so as to achieve full contact between the microstrip printed circuit board and the RF cavity.

[0013] The fixed RF housing and double-layer pressing structure are placed in an oven, and the baking time in the oven is extended by at least twice the specified curing time of the conductive silver paste. After baking, the conductive silver paste is cured to achieve a tight bond between the microstrip printed circuit board and the RF housing.

[0014] Furthermore, the shape of the fluorosilicone rubber flexible clamping block and the shape of the microstrip printed circuit board are both controlled with negative tolerances to ensure that the fluorosilicone rubber flexible clamping block can be easily placed into the radio frequency cavity; the outer dimensions of the aluminum alloy clamping block are consistent with those of the fluorosilicone rubber flexible clamping block.

[0015] Furthermore, the thickness of the fluorosilicone rubber is 1mm, and the protrusion height of the circuit template on the aluminum alloy rigid block is 2.5mm. The protrusion height of the circuit template is 0.4mm to 0.5mm higher than the depth of the wiring groove of the RF cavity.

[0016] Furthermore, when H20E silver paste is used as the conductive silver paste, the specified curing conditions for H20E silver paste are: baking at 120℃ for 15 minutes; therefore, the actual baking time for the conductive silver paste is 30 minutes or 45 minutes.

[0017] Furthermore, the rigid aluminum alloy pressing block is made of 6061 aluminum alloy.

[0018] Furthermore, corresponding screw holes are provided on both the RF housing and the aluminum alloy rigid pressure block. The screw holes are distributed around the RF housing and the center of the aluminum alloy rigid pressure block. After the screw passes through the corresponding screw hole, it is locked with the nut so that the double-layer pressure block structure applies a uniform pressing force to the microstrip printed circuit board in the direction of the RF housing.

[0019] Furthermore, a concave steel sheet is used to flatten the conductive silver paste at the bottom of the RF cavity. The front end of the concave steel sheet has a groove, and protrusions are symmetrically distributed on both sides of the groove. The groove is used to avoid the conductive silver paste on the bottom of the RF cavity, and the bottom of the groove can flatten the conductive silver paste to ensure that the amount of silver paste at the bottom of the RF cavity is uniform. The protrusions can scrape off the conductive silver paste near the side wall of the RF cavity to prevent the conductive silver paste at the root of the side wall from overflowing onto the microstrip printed circuit board when it is laminated.

[0020] Furthermore, the overall width of the concave steel sheet is 2.3mm, the groove depth is 0.12mm, the groove width is 1.725mm, the protrusion width is 0.12mm, and the rounded corners of both sides of the front end of the concave steel sheet are 0.05mm.

[0021] Furthermore, the oven temperature is first raised to the specified temperature for curing the conductive silver paste before the product is placed in the oven.

[0022] Furthermore, the stirring time for the conductive silver paste shall not be less than 30 minutes.

[0023] By employing the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0024] 1. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board proposed in this invention mainly adopts a double-layer pressing structure. That is, a flexible fluorosilicone rubber pressing block and a rigid aluminum alloy pressing block are used to press the microstrip printed circuit board together. At the same time, the rigid aluminum alloy pressing block is locked with screws to ensure uniform and tight bonding between the microstrip printed circuit board and the RF housing after pressing. This solves the problem of high void ratio when the microstrip printed circuit board is bonded to the RF housing. Moreover, this invention can achieve high-quality transmission of Ka-band and higher frequency signals from microstrip printed circuit boards.

[0025] 2. The microstrip printed circuit board and the RF housing are bonded together using conductive silver paste. The silver paste is cured at its own curing temperature, but the curing time needs to be more than twice as long as the specified curing time of the silver paste to reduce the amount of resin overflow in the silver paste. In addition, the fluorosilicone rubber flexible clamping block uses fluorosilicone rubber with similar polarity to the resin material and can be well integrated, thereby solving the problem of resin contamination of microstrip circuit signal lines when the microstrip printed circuit board is bonded to the conductive silver paste.

[0026] 3. This invention solves the assembly consistency problem of bonding microstrip printed circuit boards and RF housings, and improves the consistency of mass production of microstrip circuits.

[0027] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0028] Figure 1 This is an exploded view of the method for achieving extremely low void ratio in a universal microstrip printed circuit board according to the present invention before the assembly of various components.

[0029] Figure 2 This is a schematic diagram of the concave steel sheet used in this invention.

[0030] Figure 3 This is a cross-sectional schematic diagram of the upper and lower clamping fixtures in this invention after they are locked together by screws. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0032] like Figures 1 to 3As shown, a method for achieving an extremely low void ratio in a general-purpose microstrip printed circuit board includes a lower clamping fixture 8, an RF housing 7, a microstrip printed circuit board 5, a fluorosilicone rubber flexible pressure block 4, an aluminum alloy pressure block 3, and an upper clamping fixture 2 arranged sequentially from bottom to top. The upper surface of the RF housing 7 is provided with an RF cavity 71 for accommodating the microstrip printed circuit board. The microstrip printed circuit board 5 is an integral microstrip circuit, and the routing form of the microstrip circuit is consistent with the routing groove opening form of the RF cavity. The method for achieving extremely low void ratio in this invention specifically includes the following steps: After taking out conductive silver paste, it is stirred for at least 30 minutes. After stirring, the conductive silver paste is quickly coated onto the bottom of the RF cavity. Then, a concave steel sheet 10 is used to flatten the conductive silver paste coated onto the bottom of the RF cavity. Next, the microstrip printed circuit board 5 is placed flat in the wiring groove of the RF cavity 71. Then, the circuit template 31, protruding from the lower surface of the fluorosilicone rubber flexible pressure block 4 and the aluminum alloy rigid pressure block 3, is sequentially inserted into the wiring groove of the RF cavity. The lower clamping clamp 8 is placed below the RF housing 7, and the upper clamping clamp 2 is placed above the aluminum alloy rigid pressure block 3. Screws 1 and nuts 9 are used to lock and press the lower and upper clamping clamps together, thereby causing the double-layer pressure block structure composed of the fluorosilicone rubber flexible pressure block 4 and the aluminum alloy rigid pressure block 3 to compress the microstrip printed circuit board 5, achieving full contact and cooperation between the microstrip printed circuit board 5 and the RF cavity 71. Figure 3 As shown. Then, the fixed RF housing and double-layer press structure are placed in an oven; the oven temperature should be raised to the specified curing temperature of the conductive silver paste before placing the product in the oven to reduce resin overflow during the drying process; the baking time in the oven should be at least twice the specified curing time of the conductive silver paste. For example, when H20E silver paste is used, the specified curing conditions for H20E silver paste are: 120℃ baking time for 15 minutes; therefore, the actual baking time of the conductive silver paste in this invention is 30 minutes or 45 minutes. After baking, the conductive silver paste is cured to achieve a tight bond between the microstrip printed circuit board and the RF housing, thereby reducing the void ratio between the microstrip printed circuit board and the RF housing.

[0033] In this embodiment, both the shape of the fluorosilicone rubber flexible clamping block 4 and the shape of the microstrip printed circuit board 5 are controlled with negative tolerances to ensure that the fluorosilicone rubber flexible clamping block can be easily placed into the radio frequency cavity. For example, when the length of the fluorosilicone rubber flexible clamping block is 6mm, the typical processing error is 6mm ± 0.2mm. Therefore, using negative tolerances means controlling the processing accuracy to 6mm - 0.2mm. The dimensions of the aluminum alloy clamping block are the same as those of the fluorosilicone rubber flexible clamping block.

[0034] Preferably, the flexible fluorosilicone rubber clamping block is a fluorosilicone rubber pad with a thickness of 1mm; the circuit template protrusion height on the rigid aluminum alloy clamping block is 2.5mm, which is 0.4mm to 0.5mm higher than the depth of the wiring groove in the RF cavity. Both the upper and lower clamping fixtures are made of synthetic stone, and the rigid aluminum alloy clamping block is made of 6061 aluminum alloy.

[0035] Furthermore, both the RF housing 7 and the aluminum alloy rigid pressure block 3 have corresponding screw holes, distributed around the perimeter and center of both. The screws pass through the corresponding screw holes and are locked with the nuts 10. After the screws are locked, the double-layer pressure block structure experiences uniform force, allowing it to apply a uniform pressing force towards the bottom of the RF housing to the microstrip printed circuit board. This improves the bonding reliability between the microstrip printed circuit board and the RF housing, solves the assembly consistency problem of bonding the microstrip printed circuit board and the RF housing, and improves the consistency of mass production of microstrip circuits. Combined with… Figure 3 As shown, the lower clamping fixture is also provided with a guide pin 6, which is used to guide the upper clamping fixture to quickly and accurately engage with the lower clamping fixture.

[0036] like Figure 2 As shown, a groove 101 is formed in the middle of one end of the concave steel sheet 10, and protrusions 102 are symmetrically distributed on both sides of the groove. The groove is used to avoid the conductive silver paste on the bottom of the RF cavity, and the bottom of the groove can flatten the conductive silver paste to ensure that the amount of silver paste at the bottom of the RF cavity is uniform. The protrusions can scrape off the conductive silver paste near the side wall of the RF cavity to prevent the conductive silver paste at the root of the side wall from overflowing onto the microstrip printed circuit board during the lamination of the microstrip printed circuit board. As a preferred embodiment, the overall width of the concave steel sheet is 2.3 mm, the groove depth is 0.12 mm, the groove width is 1.725 mm, and the groove width is generally preferably 0.75 times the overall width of the concave steel sheet. The width of the protrusions is 0.12 mm, and the rounded corners of the front two sides of the concave steel sheet are both 0.05 mm. However, the present invention does not limit the size of the concave steel sheet and can be adapted to the width, depth, and other parameters of the wiring groove of the RF cavity.

[0037] In this invention, the use of a flexible fluorosilicone rubber pad effectively prevents resin contamination of the microstrip circuit from overflowing during the high-temperature baking and curing of the conductive silver paste. Specifically, the conductive silver paste is applied to the bottom surface of the RF cavity, and the microstrip printed circuit board is attached to the conductive silver paste. Due to the flexibility of the fluorosilicone rubber pad, it can make full contact with the microstrip printed circuit board, preventing the silver paste from being squeezed from the edges onto the microstrip lines when the microstrip printed circuit board is pressed against the RF housing. At the same time, because the polarity of fluorosilicone rubber and resin is similar, the resin and fluorosilicone rubber can fuse well during baking, preventing overflow onto the gold layer of the microstrip lines; and after baking, when the fluorosilicone rubber pad and the rigid aluminum alloy pad need to be removed from the RF housing, the resin fused with the fluorosilicone rubber pad can also be removed along with it.

[0038] The above description is merely a preferred embodiment of the present invention, and all aspects not detailed herein are existing technologies. Any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board, characterized in that, Includes the following steps: After removing the conductive silver paste, stir it. Then, apply the conductive silver paste to the bottom of the RF cavity on the RF housing. Finally, spread the conductive silver paste applied to the bottom of the RF cavity. Place the microstrip printed circuit board flat inside the radio frequency cavity; Next, the circuit templates protruding from the lower surfaces of the fluorosilicone rubber flexible block and the aluminum alloy rigid block are sequentially installed into the radio frequency cavity; The lower clamping clamp is placed below the RF housing, and the upper clamping clamp is placed above the aluminum alloy rigid pressure block. Screws and nuts are used to lock the lower and upper clamping clamps together, thereby causing the double-layer pressure block structure composed of the fluorosilicone rubber flexible pressure block and the aluminum alloy rigid pressure block to squeeze the microstrip printed circuit board, so as to achieve full contact between the microstrip printed circuit board and the RF cavity. The fixed RF housing and double-layer pressing structure are placed in an oven, and the baking time in the oven is extended by at least twice the specified curing time of the conductive silver paste. After baking, the conductive silver paste is cured to achieve a tight bond between the microstrip printed circuit board and the RF housing.

2. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: Both the shape of the fluorosilicone rubber flexible clamping block and the shape of the microstrip printed circuit board are processed with negative tolerances to ensure that the fluorosilicone rubber flexible clamping block can be easily placed into the radio frequency cavity; the outer dimensions of the aluminum alloy clamping block are consistent with those of the fluorosilicone rubber flexible clamping block.

3. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: The thickness of the fluorosilicone rubber flexible pressure block is 1mm, and the height of the circuit template protrusion on the aluminum alloy rigid pressure block is 2.5mm. The height of the circuit template protrusion is 0.4mm to 0.5mm higher than the depth of the wiring groove of the RF cavity.

4. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: When H20E silver paste is used as the conductive silver paste, the specified curing conditions for H20E silver paste are: baking at 120℃ for 15 minutes; therefore, the actual baking time for the conductive silver paste is 30 minutes or 45 minutes.

5. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: The rigid aluminum alloy pressure block is made of 6061 aluminum alloy.

6. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: Both the RF housing and the aluminum alloy rigid pressure block have corresponding screw holes. The screw holes are distributed around the RF housing and the center of the aluminum alloy rigid pressure block. After the screw passes through the corresponding screw hole, it is locked with the nut so that the double-layer pressure block structure applies a uniform pressing force to the microstrip printed circuit board in the direction of the RF housing.

7. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: A concave steel sheet is used to flatten the conductive silver paste at the bottom of the radio frequency cavity. The front end of the concave steel sheet has a groove, and the two sides of the groove have symmetrically distributed protrusions. The groove is used to avoid the conductive silver paste at the bottom of the radio frequency cavity, and the bottom of the groove can flatten the conductive silver paste to ensure that the amount of silver paste at the bottom of the radio frequency cavity is uniform. The protrusion can scrape off the conductive silver paste near the side wall of the RF cavity to prevent the conductive silver paste at the root of the side wall from overflowing onto the microstrip printed circuit board during the lamination process.

8. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 7, characterized in that: The concave steel sheet has an overall width of 2.3mm, a groove depth of 0.12mm, a groove width of 1.725mm, a protrusion width of 0.12mm, and rounded corners of both front edges of the concave steel sheet of 0.05mm.

9. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: First, raise the oven temperature to the specified temperature for curing the conductive silver paste, and then place the product into the oven.

10. The method for achieving extremely low void ratio in a general-purpose microstrip printed circuit board according to claim 1, characterized in that: The stirring time for conductive silver paste shall not be less than 30 minutes.

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