Functional board assembly method

Abstract

The application discloses a functional board assembly method, characterized in that the method comprises the following steps: adding an anti-deformation tool on the functional board; dividing the board surface of the functional board into a non-top layer and a four-side closed mounting surface, a non-top layer and at least one non-closed mounting surface, and a top layer mounting surface; adopting corresponding solder paste application methods for different mounting surfaces, and applying the solder paste in a low-to-high order; pasting devices on pads of each mounting surface in a low-to-high order; and reflow soldering the functional board and the devices together to complete the assembly. The application has the beneficial effects that: for uneven functional board surfaces, the mounting surfaces are classified, different solder paste application methods are adopted for different mounting surfaces, and the solder paste is applied from low to high, so that the solder paste at a high position is prevented from dropping and polluting pads at a low position; devices are pasted from low to high, and finally, reflow soldering is uniformly performed, so that one-time assembly of non-continuous planar multifunctional boards is realized.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) manufacturing technology, and more particularly to a method for assembling functional boards. Background Technology

[0002] With the rapid development of the low-altitude economy, the problem of unauthorized and reckless flights by "low, slow, and small" aircraft, represented by drones, has become increasingly prominent, posing a severe challenge to the safety supervision of low-altitude airspace. Although detection systems, such as tethered balloon-borne radar, are suitable for detecting such targets, existing systems generally suffer from high costs and complex structures.

[0003] To reduce system costs and achieve miniaturization and lightweight design, existing technologies have attempted to adopt a functional board design that integrates microwave and digital board functions. However, in the actual engineering implementation of this solution, the following assembly challenges exist: there is a height difference between the mounting surfaces of microwave devices and digital devices, making it impossible to unify them onto the same horizontal plane, resulting in a discontinuous structural feature on the functional board surface. Due to conventional surface mount technology ( SMT )Require PCB The surface is a continuous flat plane, and the soldering surfaces of all components to be mounted must be at the same height. Therefore, the non-coplanar structure of this functional board cannot be directly implemented using conventional methods. SMT The process involves assembly.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by this invention is to solve the problem that conventional mounting technology cannot be used to assemble the devices because the mounting surfaces of microwave devices and digital devices are not on the same horizontal plane.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] This invention claims a method for assembling a functional board, characterized by comprising the following steps: Anti-deformation fixtures are added to the functional boards; The functional panel surface is divided into a non-top layer and four-sided closed mounting surface, a non-top layer and at least one unclosed mounting surface, and a top layer mounting surface; Appropriate solder paste application methods should be used for different mounting surfaces, and the solder paste should be applied in order from low to high. Components are mounted on the pads of each mounting surface in ascending order of height. The functional boards and components are reflow soldered together to complete the assembly.

[0008] For uneven functional board surfaces, the mounting surfaces are classified, and different solder paste application methods are used for different mounting surfaces. Solder paste is applied from low to high to avoid solder paste dripping from high places and contaminating the pads on low places. In addition, components are mounted from low to high, and finally uniform reflow soldering is performed to achieve one-time assembly of non-continuous planar multifunctional boards.

[0009] Preferably, the non-top layer and four-sided enclosed mounting surface is a recessed square groove structure with a groove depth ≤3mm, and the square groove is enclosed on all four sides; The mounting surface, which is not the top layer and has at least one open side, is a recessed groove structure; The top mounting surface is the mounting surface located on the top layer of the functional board.

[0010] Preferably, the appropriate solder paste application method for different mounting surfaces includes the following steps: When the mounting surface is not the top layer and is closed on all four sides, the solder paste is applied by spraying, and the amount of solder paste sprayed is determined by volume ratio. When the mounting surface is not the top layer and at least one side is not closed, solder paste is applied by inkjet printing or by applying solder paste using a first printed stencil. When the top mounting surface is used, solder paste is applied using a second printed stencil.

[0011] The three mounting surfaces employ corresponding solder paste application methods. For non-top-layer mounting surfaces with four closed sides, inkjet printing is used. The inkjet head can extend into narrow blind slots, directly spraying solder paste onto the pads without being limited by the confined space or requiring contact with the mounting surface. For non-top-layer mounting surfaces with at least one open side, inkjet printing or a first stencil is used. The L-shaped or N-shaped special pattern of the first stencil allows it to extend from the slot opening, resulting in high printing efficiency. The top-layer mounting surface uses conventional second stencil printing to complete the entire board's solder paste application in one pass, offering the fastest speed. This approach allows for flexible combinations of processes based on the structural characteristics of the mounting surfaces, ensuring both welding quality and production efficiency.

[0012] Preferably, the amount of solder paste printed is determined by volume ratio, wherein the amount of solder paste printed on the grounding pad of microwave device is 120% to 150% of the pad volume ratio, the amount of solder paste printed on the pin pads around the microwave device is 150% to 200% of the pad volume ratio, and the amount of solder paste printed on resistor-capacitor devices is 120% to 150% of the pad volume ratio.

[0013] Optimal printing volume is set according to the characteristics of different components and pads, ensuring solder penetration and solder climb height while avoiding solder paste waste and process defects, thus achieving the best balance between quality and cost.

[0014] Preferably, the first printed stencil is L-shaped or n-shaped.

[0015] Preferably, during the assembly process, the functional board and components are reflow soldered together. For solder paste with a melting point of 183°C, the soldering temperature of the functional board with anti-deformation tooling is set to 260°C to 275°C.

[0016] Considering that when the anti-deformation fixture is placed under the functional board 1, the actual temperature of the board surface will be significantly reduced due to the heat absorption of the fixture, a temperature compensation scheme is proposed: the reflow oven temperature is increased from the conventional 220℃ to 260-275℃ to ensure that the actual temperature of the board surface can still meet the requirements for solder paste melting when welding with the fixture, thus resolving the contradiction between the heat absorption of the fixture and the welding temperature.

[0017] Preferably, the process also includes the following steps: baking the functional plate and the anti-deformation fixture, with the baking temperature set to 120°C. C Baking time t , t Satisfying the formula: t =60 d +30, of which d The thickness of the functional board is expressed in units of 1. mm.

[0018] Preferably, the following steps are also included: cleaning the mounting surface of the function board.

[0019] Preferably, the method further includes the following steps: after the functional board is welded, it is allowed to cool naturally to room temperature, and the anti-deformation fixture is removed.

[0020] Preferably, in order from low to high, the components are mounted on the pads of each mounting surface as follows: for horizontal surfaces with at least two reference points, the components are mounted by machine; for horizontal surfaces without two reference points, a pad with a diameter of 1 mm or a side length of 1 mm is used as a reference point for machine mounting; for horizontal surfaces without any reference points or pads that can be used as reference points, the components are mounted manually.

[0021] The advantages of this invention are that it not only meets the requirements of miniaturization and lightweighting of the multifunctional board 1, but also solves the problem that the assembly surfaces of the multifunctional board 1 are not on the same plane and contain a large number of semi-enclosed independent blind slots, making it difficult to assemble in batches, while improving assembly reliability. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the functional board assembly method in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of the functional board in Embodiment 1 of the present invention; Figure 3 This is in Embodiment 1 of the present invention QFN Relationship between the volume ratio of grounding pad printing on microwave-like devices and the solder penetration rate; Figure 4This is in Embodiment 1 of the present invention QFN Relationship between solder paste spraying volume ratio and solder creep height for microwave-like devices around their pins; Figure 5 This is a simulation diagram of the assembly and welding of the anti-deformation tooling functional plate in Comparative Example 5 of this invention; 1. Functional panel; 10. Non-top layer and four-sided enclosed mounting surface; 11. Non-top layer and at least one unenclosed mounting surface; 110. Groove; 12. Top layer mounting surface. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 See Figure 1 This embodiment requires a method for assembling a protective functional board, used for the process assembly of a functional board 1 with a discontinuous surface. Specifically, it includes the following steps: S 1. Clean the mounting surfaces of each functional panel using alcohol wiping or plasma cleaning methods.

[0025] S 2. Due to the uneven thickness of the functional board 1, it is very easy to deform during the reflow soldering process, which affects the quality of the solder joints. Anti-deformation fixtures are added to the functional board 1. Anti-deformation fixtures are special devices used to prevent the workpiece from changing shape during manufacturing or processing. This is existing technology and is installed by screws or clamps.

[0026] S 3. Place Functional Board 1 and the anti-deformation fixture together in an oven for baking, setting the baking temperature to 120°C. C Baking time t , t Satisfying the formula: t =60 d +30, of which d The maximum thickness of functional board 1, in units of mm In practical applications, the specific time can be slightly adjusted based on the complexity of function board 1 and the style of the anti-deformation tooling, generally ranging from 2 to 4 seconds. h .

[0027] See Figure 2 , S4. After baking, according to the style of functional panel 1, the mounting surface of functional panel 1 is divided into a non-top layer mounting surface 10 with four closed sides, a non-top layer mounting surface 11 with at least one open side, and a top layer mounting surface 12. Among them, The non-top-level and four-sided enclosed mounting surface 10 is a recessed square groove structure with a groove depth ≤3. mm Furthermore, the square groove is enclosed on all four sides.

[0028] The mounting surface 11, which is not the top layer and has at least one unclosed side, is a recessed groove structure 110.

[0029] The top mounting surface 12 is a flat mounting surface located on the top layer of the functional panel 1.

[0030] S 5. Apply appropriate solder paste methods to different mounting surfaces, and apply the solder paste in ascending order from low to high pressure. Specifically, this includes: S 50. When the mounting surface 10 is not the top layer and is closed on all four sides, solder paste is applied by spraying. The amount of solder paste sprayed is determined by volume ratio, specifically as follows: QFN For microwave-type devices, a differentiated compensation scheme is adopted for solder paste printing amount: 120% of the ground pad volume ratio and 150% of the peripheral pin pad volume ratio; for other resistor-capacitor devices, the solder paste printing amount is 120% of the pad volume ratio.

[0031] S 51. When the mounting surface 11 is not the top layer and at least one side is not closed, solder paste is applied by inkjet printing or by applying solder paste using a first printed stencil; specifically, the first printed stencil is set as follows: L shape or n The shape extends to the end of the stencil, allowing it to reach into the mounting surface from the slot 110. This facilitates the application of solder paste and, after application, makes it easy to remove the first printed stencil.

[0032] S 52. When the top mounting surface 12 is used, solder paste is applied using a second printed stencil, the thickness of which is 0.12 mm. mm ~0.15 mm .

[0033] It is worth mentioning that for sizes smaller than 0.3 mm For tiny solder pads, solder paste cannot be printed using a second printing stencil to avoid insufficient solder application; inkjet printing is the only option.

[0034] S 6. After the solder paste is applied, mount the components on the pads of each mounting surface in ascending order of mounting surface.

[0035] S 60. For horizontal surfaces with at least two reference points, machine mounting of components shall be used.

[0036] S 61. Since there are no conditions to establish a plane with two reference points, a plane with a diameter of 1 is used. mm Or the side length is approximately 1. mm The pads serve as reference points to facilitate the printing of solder paste and machine mounting of components.

[0037] S 62. For horizontal planes that have neither a reference point nor an approximate pad to serve as a reference point, components should be mounted manually.

[0038] S 7. Check the assembly orientation of components on each mounting surface to ensure that no components are missing or incorrectly installed.

[0039] S 8. Functional board 1 and components are reflow soldered together to complete assembly. (For a melting point of 183°C) C The solder paste, with the functional board 1 featuring anti-deformation fixture, has a soldering temperature set to 260°C. C .

[0040] S 9. After the functional board 1 is welded, allow it to cool naturally to room temperature and remove the anti-deformation fixture.

[0041] step S In 50, the selection logic for the grounding pad volume ratio is as follows: FN The grounding pad of microwave-like devices is located at the bottom of the device and has a large area, mainly serving the functions of heat dissipation and grounding. During reflow soldering, insufficient solder paste will lead to an increased solder void rate, affecting heat dissipation and grounding reliability; excessive solder paste can easily cause solder paste short circuits. To determine the optimal solder paste application rate, experiments were conducted using solder pastes with different volume ratios, with solder penetration rate used as the evaluation index.

[0042] Based on experimental verification, the above solder paste spraying amount parameters are derived from the following experimental data, as shown in Table 1: Table 1 shows... QFN Relationship between the volume ratio of grounding pad printing on microwave devices and the penetration rate

[0043] Based on the experimental data in Table 1, please refer to... Figure 3 Fit a mathematical model, when QFN When the volume ratio of the grounding pad printing for microwave-like devices is in the range of 120% to 150%, the solder penetration rate is... P wetting Satisfy the following formula: P wetting =0.5×V ratio +15 ,in, Vratio for QFN The volume ratio of grounding pad printing for microwave devices, expressed as a percentage. This stage, along with... QFN As the volume ratio of the grounding pad printing on microwave-like devices increases, the solder penetration increases linearly, and the slope... k =0.5, that is, QFN For microwave-like devices, a 1% increase in the volume ratio of the grounding pad printing leads to a stable 0.5% increase in solder penetration. When the volume ratio is in the range of 150-200%, P wetting ≈0.08× V _ ratio +78, at this stage the penetration rate does not increase significantly, slope k =0.08 indicates that after exceeding 150%, the marginal cost of increasing the amount of solder paste to improve the penetration rate is extremely high, and it is easy to cause short circuit risk in soldering.

[0044] When the volume ratio is in the range of 150%–200%, P wetting Satisfy the following formula: P wetting ≈0.08 V ratio +78. During this stage, as the volume ratio of printed solder paste increases, the increase in solder penetration is not significant, and the first slope coefficient... k =1=0.08, which means that after exceeding 150%, the marginal cost of increasing the amount of solder paste to improve the penetration rate is extremely high, and it is easy to cause short circuit risk in the soldering.

[0045] The selection logic for the volume ratio of the four-sided lead pads is as follows: Microwave devices have small lead spacing and narrow leads on all four sides; insufficient solder paste will lead to insufficient solder climb height and a risk of cold solder joints; excessive solder paste can easily cause bridging short circuits. To determine the optimal print volume, experiments were conducted using solder pastes with different volume ratios, with the side solder climb height used as the evaluation index. The experimental results are shown in Table 2: Table 2 is... QFN Relationship between solder paste volume ratio and solder creep height around the leads of microwave-like devices

[0046] Based on the experimental data in Table 2, please refer to... Figure 4 Define normalized solder crawling height h (v） and QFN Volume ratio of solder paste sprayed on the four sides of microwave-like device leads v The functional relationship is: when QFN When the solder paste spraying range for the four perimeter leads of microwave-like devices is 150-200%, h (v) ≈1.4v -180, second slope coefficient k2 = 1.4: This indicates QFN For microwave-like devices, a 1% increase in the solder paste spraying volume ratio around the pins results in an average increase of 1.4% in the solder climb height. This is primarily attributed to the strong capillary driving force generated by the narrow gap between the microwave pins. In practical applications, although... QFN Achieving a 200% volume ratio of solder paste spraying on the four-sided leads of microwave-like devices QFN The solder ramp height on the device side is 100%, but in the industry, a 50% side solder ramp height is generally considered sufficient. Only in certain high-reliability applications is a 100% solder ramp height required; that is, under normal circumstances... QFN For microwave-like devices, the solder paste volume of the pins around the perimeter should be 170%.

[0047] Example 2 The difference between this embodiment and Embodiment 1 lies in two aspects: Difference 1: In the steps S In the 50, the ground pad volume ratio is 135%, the peripheral lead pad volume ratio is 170%, and the solder paste printing amount for other resistor-capacitor devices is 135% of the pad volume ratio; Difference 2: In the steps S In 8, for a melting point of 183°C C The solder paste, with the functional board 1 featuring anti-deformation fixture, has a soldering temperature set to 267°C. C .

[0048] Example 3 The difference between this embodiment and Embodiment 1 lies in two aspects: Difference 1: In the steps S In 50, the volume ratio of the ground pad is 150%, the volume ratio of the pads around the perimeter is 200%, and the amount of solder paste printed for other resistors and capacitors is 150% of the pad volume ratio.

[0049] Difference 2: In the steps S In 8, for a melting point of 183°C C The solder paste, with the functional board 1 featuring anti-deformation fixture, has a soldering temperature set to 275°C. C .

[0050] In fact, when there is no anti-deformation tooling, the reflow oven temperature is set to 220℃, which can make the actual temperature of the board surface reach more than 210℃, meeting the melting requirement of solder paste with a melting point of 183℃.

[0051] See Figure 5When an anti-deformation fixture is placed under functional board 1, the actual temperature of the board surface decreases significantly due to the heat absorption of the fixture. Simulation results show that when the fixture thickness is 3mm, the actual temperature of the board surface is approximately 210℃; when the fixture thickness is 5mm, the actual temperature of the board surface is approximately 180℃. If the conventional furnace temperature of 220℃ is still used, the actual temperature of the board surface will be lower than the melting point of the solder paste, resulting in the solder paste not being able to melt completely.

[0052] Therefore, in order to fully melt the SnPb solder paste with a melting point of 183℃, the actual furnace temperature setting needs to be increased by about 40℃ from the conventional 220℃.

[0053] Based on the simulation results, the furnace temperature was set to 260℃, and thermocouples were placed at different locations on functional board 1 for furnace temperature testing. The actual temperature of functional board 1 was approximately 210℃. Considering that the furnace temperature test used a bare board without adding components or solder, and the actual heat demand during soldering is greater, a furnace temperature of 260-275℃ is more suitable.

[0054] The advantages of this invention are as follows: First, for uneven functional board 1 surfaces, this invention classifies the mounting surfaces and applies differentiated solder paste application methods to different mounting surfaces, applying solder paste from low to high to avoid solder paste dripping from high surfaces and contaminating low surface pads; furthermore, it combines this with component mounting from low to high and finally unified reflow soldering, achieving one-time assembly of the discontinuous planar multifunctional board 1. This method not only meets the requirements of miniaturization and lightweighting of the multifunctional board 1, but also solves the problem of multifunctional board 1 having non-plane assembly surfaces and containing a large number of semi-enclosed independent blind slots, making batch assembly difficult, while improving assembly reliability.

[0055] Secondly, the anti-deformation fixture can fix and support the multi-functional plate 1 with uneven thickness, effectively preventing warping and deformation during the reflow welding process and ensuring the quality of the weld.

[0056] Then, the three mounting surfaces are treated with corresponding solder paste application methods. The non-top-layer, four-sided closed mounting surface 10 is treated with inkjet printing. The inkjet head can extend into the narrow blind slot and spray directly onto the solder pads, without being limited by the confined space and without needing to contact the mounting surface. The non-top-layer, at least one-sided open mounting surface 11 is treated with inkjet printing or a first stencil. The L-shaped or N-shaped special pattern of the first stencil can be utilized, extending from the slot 110, resulting in high printing efficiency. The top-layer mounting surface 12 uses conventional second stencil printing to complete the solder paste application of the entire board in one pass, achieving the fastest speed. Based on the structural characteristics of the mounting surface, it allows for flexible combinations of various processes, ensuring both welding quality and production efficiency.

[0057] Then, for the characteristics of different components and pads, the optimal printing amount was set respectively. While ensuring the solder penetration rate and solder climb height, solder paste waste and process defects were avoided, achieving the best balance between quality and cost.

[0058] Finally, considering that when the anti-deformation fixture is placed under the functional board 1, the actual temperature of the board surface will be significantly reduced due to the heat absorption of the fixture, a temperature compensation scheme is proposed: the reflow oven temperature is increased from the conventional 220℃ to 260-275℃ to ensure that the actual temperature of the board surface can still meet the requirements for solder paste melting when welding with the fixture, thus resolving the contradiction between the heat absorption of the fixture and the welding temperature.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for assembling a functional board, characterized in that, Includes the following steps: Anti-deformation fixtures are added to the functional boards; The functional panel surface is divided into a non-top layer and four-sided closed mounting surface, a non-top layer and at least one unclosed mounting surface, and a top layer mounting surface; Appropriate solder paste application methods should be used for different mounting surfaces, and the solder paste should be applied in order from low to high. Components are mounted on the pads of each mounting surface in ascending order of height. The functional boards and components are reflow soldered together to complete the assembly.

2. The functional board assembly method according to claim 1, characterized in that, The non-top-level and four-sided enclosed mounting surface is a recessed square groove structure with a groove depth ≤3. mm Furthermore, the square groove is enclosed on all four sides; The mounting surface, which is not the top layer and has at least one open side, is a recessed groove structure; The top mounting surface is the mounting surface located on the top layer of the functional board.

3. The functional board assembly method according to claim 1, characterized in that, The appropriate solder paste application method for different mounting surfaces includes the following steps: When the mounting surface is not the top layer and is closed on all four sides, the solder paste is applied by spraying, and the amount of solder paste sprayed is determined by volume ratio. When the mounting surface is not the top layer and at least one side is not closed, solder paste is applied by inkjet printing or by applying solder paste using a first printed stencil. When the top mounting surface is used, solder paste is applied using a second printed stencil.

4. The functional board assembly method according to claim 3, characterized in that, The amount of solder paste printed is determined by volume ratio. Specifically, the amount of solder paste printed on the grounding pad of microwave devices is 120% to 150% of the pad volume ratio, the amount of solder paste printed on the pads of the four pins of microwave devices is 150% to 200% of the pad volume ratio, and the amount of solder paste printed on the pads of resistor-capacitor devices is 120% to 150% of the pad volume ratio.

5. The functional board assembly method according to claim 3, characterized in that, The first printing steel mesh is L Type or n type.

6. The functional board assembly method according to claim 1, characterized in that, The functional board and components are being reflow soldered together for assembly, for a melting point of 183°C. C The solder paste, with a functional board featuring anti-deformation fixtures, has a soldering temperature set to 260°C. C ~275° C。 7. The functional board assembly method according to claim 1, characterized in that, It also includes the following steps: Baking function plate and anti-deformation fixture, baking temperature set to 120°C C Baking time t , t Satisfying the formula: t =60 d +30, of which d The thickness of the functional board is expressed in units of 1. mm .

8. The functional board assembly method according to claim 1, characterized in that, It also includes the following steps: Clean the mounting surface of the function board.

9. The functional board assembly method according to claim 1, characterized in that, It also includes the following steps: After the functional boards are welded, allow them to cool naturally to room temperature and remove the anti-deformation fixture.

10. The functional board assembly method according to claim 1, characterized in that, Components are mounted on the pads of each mounting surface in ascending order of height: For horizontal surfaces with at least two reference points, machine mounting is used for components; for horizontal surfaces without two reference points, pads with a diameter of 1 mm or a side length of 1 mm are used as reference points for machine mounting; for horizontal surfaces without reference points or pads that can be used as reference points, components are mounted manually.

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