CFG antenna plate and SIP tube shell stack assembly process method

Abstract

This invention discloses a stacking assembly process for CFG antenna boards and SIP shells, relating to the fields of microelectronic packaging and satellite communication technology. Addressing the problems of excessive void rates in solder balls after CFG antenna board ball placement and the inability of fully automated placement machines to accurately mount SIP shells in existing technologies, this invention employs a combined process of "pre-treatment venting – sealing gas channels – non-vacuum soldering – dedicated fixture positioning," specifically as follows: Heating the board on a flat heating stage vents the gas inside and removes solder to form a sealing layer; non-vacuum ball placement is performed with the vacuum function turned off, controlling the void rate to ≤25%; a load-bearing fixture with positioning reference points and an adaptive clamping structure is designed to achieve precise positioning and mounting of the SIP shells. This invention solves the problem of excessive voids caused by the "ballooning" effect, increasing the first-pass yield to over 95%, meeting the long-term reliability requirements of satellite radiation-resistant environments, and is suitable for the stacking assembly of aerospace-grade active phased array antenna modules.

Description

Technical Field

[0001] This invention relates to the fields of microelectronic packaging and satellite communication technology, and more specifically to a process for stacking and assembling CFG antenna boards and SIP housings. Background Technology

[0002] With the rapid development of satellite communication technology, active phased array antenna systems are evolving towards miniaturization, lightweighting, and high integration. In surface-mount planar active phased array antenna systems, the mainstream technology route is to integrate RF active chips and electronic components into a SIP package using System-in-Package (SIP) technology, and then achieve vertical integration of the antenna array layer, low-frequency power supply control layer, and beamforming network layer through multilayer mixed-signal printed circuit board (MS / DSC) technology.

[0003] In this three-dimensional stacked architecture, the CFG (Copper Clad Laminate) antenna board, as the top-level antenna array, needs to achieve high-density interconnection with the SIP (Single In-Pack) housing below. The CFG antenna board typically uses high-frequency copper clad laminate materials (such as Rogers RO4000 and RO3000 series), which have excellent dielectric properties and low-loss characteristics, making them suitable for high-frequency applications such as 5G communication, radar, and satellite systems. The SIP housing integrates core functional modules such as T / R components and beamforming networks. The two are electrically connected and mechanically fixed through a solder ball array to form a complete antenna module.

[0004] However, this stacking assembly process faces many technical challenges: First, there is a serious problem with excessive void ratio in the solder balls. After SAC305 (Sn-3.0Ag-0.5Cu) solder balls are implanted into the CFG antenna board, gas enters the solder balls during reflow soldering, creating a "ballooning" effect. This causes the solder balls to expand abnormally, with a void area ratio as high as 50% to 80%, far exceeding the aerospace standard requirement of less than 25%. When reworking solder balls with excessive void ratios, even if a 350℃ hot air gun is used to melt the solder balls and restore them to their normal shape, the solder balls will still bulge again after heating is stopped, exhibiting a cycle of "expansion-cracking-expansion-cracking again." This problem occurs in more than 88.5% of cases. This phenomenon seriously restricts welding quality and product reliability.

[0005] Second, the issue of gas overflow mechanism within the printed circuit board (PCB). Because the antenna board's front and back pads are connected by vias or blind vias, and these vias and blind vias have a hole-in-pad structure, they are sealed with copper plating after resin plugging. The plugging material (resin) cannot completely fuse with the PCB substrate (high-frequency copper-clad laminate), leaving microscopic gaps with residual air. During soldering, the gas inside the board expands due to heat and overflows from the PCB into the solder balls during the vacuuming process. Since the solder ball surface has solidified, the gas cannot escape, leading to a sharp increase in void ratio. Studies show a clear positive correlation between higher vacuum levels in the furnace cavity and larger voids in the solder balls.

[0006] Third, there is the issue of SIP housing positioning and mounting accuracy. The SIP housing dimensions (12mm × 10mm × 3.05mm) are smaller than the CFG antenna board (12.5mm × 12.5mm × 2.45mm), and the pads are close to the housing edge (usually less than 0.5mm from the edge). Since fully automated pick-and-place machines require the device to be held at the edge for transport, SIP housings that are too small and have pads close to the edge cannot be directly held by the standard track. When using a carrier board for mounting, the housing slides on the carrier board during transport on the pick-and-place machine track, making precise positioning impossible. This results in a machine mounting offset exceeding ±0.1mm, and a first-pass yield rate of less than 60%.

[0007] In existing technologies, vacuum reflow soldering equipment is typically used to reduce void ratios in BGA / CSP ball-mounting processes, generally controlling the void ratio to 5%~15%. However, for substrates with special internal structures (resin-filled vias + copper plating) such as CFG antenna boards, vacuuming can actually exacerbate void formation. Furthermore, existing SIP shell mounting methods mostly use general-purpose clamps or adhesive films for fixation, which cannot solve the mounting challenges of small sizes and high positioning accuracy requirements.

[0008] Therefore, there is an urgent need for a highly reliable and automated process for stacking and assembling CFG antenna boards and SIP housings to solve the key technical problems of high solder ball void rate, difficult mounting and positioning, and low yield, so as to meet the stringent requirements of aerospace satellite applications. Summary of the Invention

[0009] The purpose of this invention is to solve the technical problems of large solder ball voids, large mounting offsets, and low yield caused by existing assembly processes. This invention provides a stacking assembly process for CFG antenna boards and SIP housings.

[0010] To achieve the above objectives, the present invention specifically adopts the following technical solution: This invention provides a method for stacking and assembling a CFG antenna board and a SIP housing, comprising the following steps: S1. CFG antenna board pretreatment: After baking the CFG antenna board according to preset conditions, solder paste is printed on the pads of the CFG antenna board; the printed CFG antenna board is heated, and after the solder melts, the heating continues to allow the gas in the vias and blind holes inside the CFG antenna board to be discharged; then the CFG antenna board is naturally cooled, and the solder on the pads is removed, so that the solder forms a sealing layer at the gas channel outlet to block the gas backflow channel; S2, CFG antenna board ball planting: The pre-treated CFG antenna board is placed on the carrier plate and sent into the hot air vacuum reflow soldering equipment. During the soldering process, the vacuum function is turned off, and SAC305 solder balls are planted on the CFG antenna board pads using a non-vacuum reflow soldering process. After the solder balls are cured, a pre-balled antenna board is formed. S3, SIP housing positioning and mounting: Provides SIP housing support fixture. The positioning groove of the support fixture adopts a double-sided positioning + double-sided adaptive clamping structure. By attaching adjustable thickness antistatic tape, the dimensional tolerance of the SIP housing is compensated, so as to achieve accurate positioning and reliable clamping of the SIP housing on the fully automatic pick and place machine. The mounting accuracy is controlled within ±0.05mm. The fully automatic pick and place machine identifies the positioning reference point and mounts the pre-planted ball antenna board onto the SIP housing to form a stacked assembly. S4. Stacking and Welding: The tooling carrying the stacked components is placed on a hot air vacuum reflow soldering carrier and reflow soldering is performed to complete the stacking and welding, forming a stacked assembly of CFG antenna board and SIP tube shell. S5. Reliability verification: Perform X-ray inspection on the stacked assembly to ensure that the void rate of the solder balls is ≤25% and that the solder joints are free of cracks and misalignment.

[0011] In one embodiment, the specific method of CFG antenna board preprocessing in step S1 is as follows: After baking the CFG antenna board under preset conditions, SAC305 solder paste is printed on the pads of the CFG antenna board using a 0.06mm thick stencil with an opening ratio of 1:1. The printed CFG antenna board is then placed on a flat heating table at a temperature of 245℃. After the solder melts, heating continues for 3 minutes to allow the gas in the vias and blind holes inside the CFG antenna board to be fully expelled. The CFG antenna board is then removed from the heating table and allowed to cool naturally. Solder absorbers are used to remove the solder from the pads, forming a sealed layer at the gas channel outlet to block the gas backflow channel.

[0012] In one embodiment, the specific method for positioning and mounting the SIP housing in step S3 is as follows: The support fixture is provided with a positioning reference point, and the positioning groove of the support fixture is positioned with two adjacent sides of a right angle of the SIP housing as positioning sides. 1-3 layers of antistatic tape are pasted on the other two sides of the positioning groove to adapt to the dimensional tolerance of the SIP housing. The SIP housing with solder paste is placed into the positioning groove according to the marked direction, ensuring that the exposed height of the upper surface of the SIP housing is 0~0.1mm. A fully automatic chip mounter is used to identify the positioning reference point and mount the pre-planted ball antenna board onto the SIP housing to form a stacked assembly.

[0013] In one embodiment, in step S1, the opening diameter of the screen-printed stencil is 0.36 mm, the alloy composition of the SAC305 solder paste is Sn-3.0Ag-0.5Cu, and the metal content in the SAC305 solder paste is 88%~90%.

[0014] In one embodiment, in step S1, the baking conditions are: temperature 125°C, time 4 hours, or temperature 150°C, time 2 hours; the temperature control accuracy of the flat heating table is ±5°C, and the flatness of the heating surface is ≤0.05mm.

[0015] In one embodiment, in step S1, the desoldering strip is a copper braided desoldering strip with a width of 2-3 mm. When used, it is applied with flux and the solder is removed by gently pressing the surface of the pad at an angle of 30°-45° and dragging it in a single direction.

[0016] In one embodiment, in step S2, after the antenna board is completed with the solder ball, the appearance of the solder ball is checked with a 20x microscope and no abnormality or enlargement is found. Then, an X-ray inspection device is used to check that the voids inside the solder ball do not exceed 25%.

[0017] In one embodiment, in step S3, the SIP tube shell bearing fixture is made of aluminum alloy or stainless steel, the positioning edge of the positioning groove is machined with an accuracy of ±0.02mm, and the surface roughness Ra≤1.6μm.

[0018] In one embodiment, in step S3, the antistatic tape is made of polyimide substrate with a thickness of 0.05~0.1mm / layer and a surface resistance of 10^6~10^9Ω.

[0019] In one embodiment, in step S3, the mounting process uses a visual alignment system to identify positioning reference points. The positioning reference points are circular metallized marks or cross marks with a diameter of 0.5~1mm, and the relative positional accuracy between them and the positioning groove of the SIP tube shell is ≤±0.03mm.

[0020] Working Principle: The pretreatment, soldering method, and automatic placement fixture of the CFG antenna board in this assembly process differ from current methods. The difference lies in the fact that this assembly process first applies solder paste to the pads of the CFG antenna board and heats it with a flatbed heating table to expel air from the CFG antenna board. After the solder paste melts and cools, it is cleaned off with desoldering tape. The remaining solder on the pads seals the ventilation channels of blind holes and vias. During reflow soldering, the vacuum function is turned off to prevent residual gas in blind holes and vias from overflowing into the solder balls, reducing the void size inside the solder balls. When the CFG antenna board is stacked with the SIP housing, a SIP housing fixing fixture is used to solve the problem of housing misalignment during the movement of the fully automatic placement machine. These methods effectively solve the problems of large voids in the solder balls on the CFG antenna board and the difficulty in positioning the CFG antenna board and SIP housing during stacking, ensuring smooth assembly of the antenna assembly.

[0021] The beneficial effects of this invention are as follows: 1. Completely eliminates the "ballooning" effect in solder balls, reducing the void ratio to within aerospace standards: This invention utilizes a pre-treatment venting process in step S1, heating the CFG antenna board at 245°C for 3 minutes before the actual solder ball placement. This allows the gas in the vias and blind holes within the board to be fully expelled while the solder is molten. More importantly, after removing the solder, the molten solder forms a microscopic sealing layer at the gas channel outlet, effectively blocking the gas backflow channel. Combined with the non-vacuum soldering process in step S2, which disables the vacuum function, residual gas inside the board is prevented from overflowing into the solder balls under negative pressure, fundamentally resolving the technical paradox that "vacuuming increases voids." X-ray inspection shows that the solder ball void rate is consistently controlled below 25%, meeting the requirements of aerospace standards such as GJB 548B-2020, and solving the problem of excessive voids occurring in more than 88.5% of existing technologies.

[0022] 2. Achieve fully automated precision mounting of SIP housings, increasing the first-pass yield rate to over 95%. The SIP housing support fixture designed in this invention adopts a "double-sided positioning + double-sided adaptive clamping" structure. The two adjacent right-angled sides of the SIP housing serve as precise positioning edges, while 1-3 layers of anti-static tape are applied to the other two sides to compensate for dimensional tolerances. This design ensures precise positioning of the SIP housing within the fixture groove (positioning accuracy ±0.02mm) and achieves adaptive clamping through the elastic deformation of the anti-static tape, preventing slippage during transportation. The fixture is equipped with positioning reference points, enabling the fully automatic placement machine to accurately identify and align the components. Placement offset is controlled within ±0.05mm, increasing the first-pass yield from 60% in existing technologies to over 95%, significantly improving production efficiency.

[0023] 3. Strong process compatibility and wide range of applications: The process method of this invention can also be adapted to the stacking and assembly requirements of different shapes, thicknesses, and solder ball specifications (such as SAC305, SAC105, SAC0307, ​​etc.) by adjusting process parameters such as the tooling groove size, stencil opening parameters, and heating table temperature. The process method is compatible with existing SMT production lines, requires no special equipment purchase, and can be implemented only by making special tooling and stencils, thus having good engineering application value.

[0024] 4. Overall costs are significantly reduced: By eliminating rework processes (existing technologies have a rework rate exceeding 85%), increasing the first-pass yield (from 60% to 95%), and reducing scrap losses, this invention reduces the assembly cost of a single antenna module by more than 40%. Simultaneously, due to improved solder joint reliability, the on-orbit failure rate is expected to decrease from 3% to below 0.1%, significantly reducing the satellite's total lifecycle maintenance costs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a flowchart of a process for stacking and assembling a CFG antenna board with a SIP tube shell.

[0027] Figure 2 This is a structural schematic diagram of the load-bearing tooling.

[0028] Figure 3 This is a structural diagram of the assembly of the SIP casing and the load-bearing tooling. Detailed Implementation

[0029] To make the technical problems, technical solutions, and technical effects of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0031] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0033] Example 1 like Figures 1 to 3 As shown, this embodiment provides a method for stacking and assembling a CFG antenna board and a SIP housing, including the following steps: S1. CFG Antenna Board Pretreatment: After baking the CFG antenna board according to preset conditions, use a 0.06mm thick stencil with an opening ratio of 1:1 to print SAC305 solder paste on the pads of the CFG antenna board. Place the printed CFG antenna board on a flat heating table at a temperature of 245℃. After the solder melts, continue heating for 3 minutes to fully expel the gas from the vias and blind holes inside the CFG antenna board. Then, remove the CFG antenna board from the heating table and allow it to cool naturally. Use desoldering tape to remove the solder from the pads, so that the solder forms a closed layer at the gas channel outlet, blocking the gas backflow channel. S2, CFG antenna board ball planting: The pre-treated CFG antenna board is placed on a carrier plate and sent into a hot air vacuum reflow soldering machine. During the soldering process, the vacuum function is turned off, and SAC305 solder balls are planted on the CFG antenna board pads using a non-vacuum reflow soldering process. After the solder balls solidify, a pre-balled antenna board is formed. After the antenna board is completed, the appearance of the solder balls is checked with a 20x microscope and no abnormalities or enlargement are found. Then, X-ray inspection equipment is used to check that the voids in the solder balls do not exceed 25%.

[0034] S3. SIP Housing Positioning and Mounting: The support fixture is equipped with positioning reference points. The positioning groove of the support fixture uses two adjacent sides of a right angle of the SIP housing as positioning edges. 1-3 layers of anti-static tape are pasted on the other two sides of the positioning groove to accommodate the dimensional tolerances of the SIP housing. The SIP housing with solder paste is placed into the positioning groove according to the marked direction, ensuring that the exposed height of the upper surface of the SIP housing is 0~0.1mm. A fully automatic chip mounter is used to identify the positioning reference points and mount the pre-planted ball antenna board onto the SIP housing to form a stacked assembly.

[0035] S4. Stacking and Welding: The tooling carrying the stacked components is placed on a hot air vacuum reflow soldering carrier and reflow soldering is performed to complete the stacking and welding, forming a stacked assembly of CFG antenna board and SIP tube shell. S5. Reliability verification: Perform X-ray inspection on the stacked assembly to ensure that the void rate of the solder balls is ≤25% and that the solder joints are free of cracks and misalignment.

[0036] In step S1, the opening diameter of the screen-printed stencil is 0.36mm, the alloy composition of the SAC305 solder paste is Sn-3.0Ag-0.5Cu, and the metal content in the SAC305 solder paste is 88%~90%.

[0037] Baking conditions are: temperature 125℃, time 4 hours, or temperature 150℃, time 2 hours; the temperature control accuracy of the flat heating plate is ±5℃, and the flatness of the heating surface is ≤0.05mm.

[0038] The desoldering wick is a copper braided desoldering wick with a width of 2-3mm. When using it, apply flux and gently press the surface of the pad at a 30°-45° angle, then drag it in one direction to remove the solder.

[0039] In step S3, the SIP tube shell bearing fixture is made of aluminum alloy or stainless steel, the positioning edge of the positioning groove is machined with an accuracy of ±0.02mm, and the surface roughness Ra≤1.6μm.

[0040] The antistatic tape is made of polyimide substrate with a thickness of 0.05~0.1mm / layer and a surface resistance of 10^6~10^9Ω.

[0041] The mounting process uses a visual alignment system to identify positioning reference points. The positioning reference points are circular metallized marks or cross marks with a diameter of 0.5~1mm. The relative positional accuracy between the reference points and the positioning groove of the SIP tube shell is ≤±0.03mm.

Claims

1. A method for stacking and assembling a CFG antenna board and a SIP tube shell, characterized in that, Includes the following steps: S1. CFG antenna board pretreatment: After baking the CFG antenna board according to preset conditions, solder paste is printed on the pads of the CFG antenna board. The printed CFG antenna board is heated, and the heating continues after the solder melts, so that the gas in the through holes and blind holes inside the CFG antenna board can be discharged. The CFG antenna board is then allowed to cool naturally, and the solder on the pads is removed, so that the solder forms a sealing layer at the gas channel outlet, blocking the gas backflow channel. S2, CFG antenna board ball planting: The pre-treated CFG antenna board is placed on the carrier plate and sent into the hot air vacuum reflow soldering equipment. During the soldering process, the vacuum function is turned off, and SAC305 solder balls are planted on the CFG antenna board pads using a non-vacuum reflow soldering process. After the solder balls are cured, a pre-balled antenna board is formed. S3, SIP housing positioning and mounting: Provides SIP housing support fixture. The positioning groove of the support fixture adopts a double-sided positioning + double-sided adaptive clamping structure. By attaching adjustable thickness antistatic tape, the dimensional tolerance of the SIP housing is compensated, so as to achieve accurate positioning and reliable clamping of the SIP housing on the fully automatic pick and place machine. The mounting accuracy is controlled within ±0.05mm. The fully automatic pick and place machine identifies the positioning reference point and mounts the pre-planted ball antenna board onto the SIP housing to form a stacked assembly. S4. Stacking and Welding: The tooling carrying the stacked components is placed on a hot air vacuum reflow soldering carrier and reflow soldering is performed to complete the stacking and welding, forming a stacked assembly of CFG antenna board and SIP tube shell. S5. Reliability verification: Perform X-ray inspection on the stacked assembly to ensure that the void rate of the solder balls is ≤25% and that the solder joints are free of cracks and misalignment.

2. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 1, characterized in that, In step S1, the specific method for CFG antenna board preprocessing is as follows: After baking the CFG antenna board under preset conditions, SAC305 solder paste is printed on the pads of the CFG antenna board using a 0.06mm thick stencil with an opening ratio of 1:

1. The printed CFG antenna board is then placed on a flat heating table at a temperature of 245℃. After the solder melts, heating continues for 3 minutes to allow the gas in the vias and blind holes inside the CFG antenna board to be fully expelled. The CFG antenna board is then removed from the heating table and allowed to cool naturally. Solder absorbers are used to remove the solder from the pads, forming a sealed layer at the gas channel outlet to block the gas backflow channel.

3. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 1, characterized in that, In step S3, the specific method for positioning and mounting the SIP housing is as follows: The support fixture is provided with a positioning reference point. The positioning groove of the support fixture uses two adjacent sides of a right angle of the SIP housing as positioning edges. 1-3 layers of antistatic tape are pasted on the other two sides of the positioning groove to accommodate the dimensional tolerances of the SIP housing. The SIP housing with solder paste is placed into the positioning groove according to the marked direction, ensuring that the exposed height of the upper surface of the SIP housing is 0~0.1mm. The positioning reference point is identified by a fully automatic chip mounter, and the pre-planted ball antenna board is mounted onto the SIP housing to form a stacked assembly.

4. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 2, characterized in that, In step S1, the opening diameter of the screen-printed stencil is 0.36mm, the alloy composition of the SAC305 solder paste is Sn-3.0Ag-0.5Cu, and the metal content in the SAC305 solder paste is 88%~90%.

5. The method for stacking and assembling a CFG antenna board and a SIP tube shell according to claim 2, characterized in that, In step S1, the baking conditions are: temperature 125℃, time 4 hours, or temperature 150℃, time 2 hours; the temperature control accuracy of the flat heating plate is ±5℃, and the flatness of the heating surface is ≤0.05mm.

6. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 2, characterized in that, In step S1, the desoldering wick is a copper braided desoldering wick with a width of 2-3mm. When using it, it is used with flux, and the surface of the pad is lightly pressed at an angle of 30°-45° and dragged in one direction to remove the solder.

7. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 3, characterized in that, In step S2, after the antenna board is filled with solder balls, the appearance of the solder balls is checked with a 20x microscope and no abnormalities or enlargement are found. Then, an X-ray inspection device is used to check that the voids inside the solder balls do not exceed 25%.

8. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 3, characterized in that, In step S3, the SIP tube shell bearing fixture is made of aluminum alloy or stainless steel, the positioning edge of the positioning groove is machined with an accuracy of ±0.02mm, and the surface roughness Ra≤1.6μm.

9. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 3, characterized in that, In step S3, the antistatic tape is made of polyimide substrate with a thickness of 0.05~0.1mm / layer and a surface resistance of 10^6~10^9Ω.

10. The method for stacking and assembling a CFG antenna board and a SIP housing according to claim 3, characterized in that, In step S3, the mounting process uses a visual alignment system to identify the positioning reference point. The positioning reference point is a circular metallized mark or a cross mark with a diameter of 0.5~1mm, and the relative positional accuracy with the positioning groove of the SIP tube shell is ≤±0.03mm.

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