Double-sided ball mounting type lithium battery protection board SIP module and preparation method

Abstract

The invention relates to a double-sided ball mounting type lithium battery protection board SIP module and a preparation method. The SIP module comprises a circuit substrate, a plurality of functional elements, welding tin balls, a top surface plastic package layer and a bottom surface plastic package layer. The circuit substrate is provided with a top surface and a bottom surface, the functional element comprises a power MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) and a CSP (Chip Scale Package) device, and at least one such element is mounted on the bottom surface of the The plurality of soldering tin balls are fixed on the bottom surface of the substrate and are used for reflow soldering to be electrically connected with the bearing plate. The top surface plastic packaging layer covers the top surface of the substrate and the elements, and the bottom surface plastic packaging layer covers the bottom surface and the elements. The bottom surface plastic packaging layer is provided with a trapezoid through hole for fixing a welding solder ball, and a preset gap is reserved between the periphery of the solder ball and the bottom surface plastic packaging layer. According to the double-sided ball mounting type lithium battery protection board SIP module and the preparation method, through the innovative structural design, the limitation of the traditional single-sided layout is effectively broken through, and the space utilization rate and the performance are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery protection boards, and in particular to a double-sided ball-planting type lithium battery protection board SIP module and a preparation method thereof. Background Art

[0002] With the widespread application of lithium batteries in electric vehicles, portable electronic devices, and other fields, the performance and integration requirements for lithium battery protection boards are becoming increasingly demanding. Traditional lithium battery protection boards are mostly single-sided. This layout makes it difficult to integrate more functional components within the limited plane space, limiting the improvement of protection board performance and failing to meet the requirements of increasingly compact equipment space.

[0003] Furthermore, traditional manufacturing processes, such as solder ball placement, often rely on stencil printing, which has limited precision and difficulty achieving complex three-dimensional positioning. Plastic encapsulation also struggles to balance the protection of various components on different surfaces with the need for electrical connection to the external carrier board. Furthermore, during the soldering process, thermal stress and other factors can easily cause cracking in solder joints, impacting product reliability and stability. Therefore, a new structural design and fabrication method is needed to address these issues and improve the integration, performance, and reliability of lithium battery protection boards. Summary of the Invention

[0004] In light of this, the present invention provides a double-sided, ball-implanted lithium battery protection board (SIP) module. Through its innovative structural design, it effectively overcomes the limitations of traditional single-sided layouts, improving space utilization and performance. A second objective of the present invention is to provide a method for preparing this module, optimizing the process steps to achieve mass production feasibility of double-sided heterogeneous integration.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A double-sided ball-planting lithium battery protection board SIP module, comprising:

[0007] a circuit substrate having a top surface and a bottom surface;

[0008] a plurality of functional elements, including power metal oxide semiconductor field effect transistors and chip scale packaging devices, wherein at least one of the power metal oxide semiconductor field effect transistors or chip scale packaging devices is mounted on the bottom surface of the circuit substrate;

[0009] A plurality of solder balls are fixed to the bottom surface of the circuit substrate and are used to achieve electrical connection with a flexible or rigid carrier board through reflow soldering;

[0010] A top plastic layer covering the top surface of the circuit substrate and the components mounted thereon;

[0011] The bottom plastic sealing layer covers the bottom surface of the circuit substrate and the components mounted thereon. The bottom plastic sealing layer is provided with trapezoidal through holes for fixing the solder balls, and a preset gap is left around the solder balls and between the bottom plastic sealing layer.

[0012] A three-dimensional integrated design is achieved through a double-sided, three-dimensional layout, effectively breaking through the planar size limitations of traditional single-sided layouts. Different functional components are arranged on the top and bottom surfaces of the circuit substrate, greatly improving space utilization. Power devices arranged on the bottom surface can directly connect to the high-current paths of the carrier board, reducing line losses. The top plastic layer provides mechanical protection and environmental isolation, while the trapezoidal through-hole design of the bottom plastic layer ensures precise positioning of the solder balls and reserves space for thermal expansion buffers. The pre-set gaps around the solder balls absorb the mechanical stress generated during the reflow process and prevent solder joint cracking. This structure supports three-dimensional stacking with the carrier board through vertical interconnection, which effectively saves installation space compared to traditional planar layout solutions.

[0013] Preferably, the thickness of the power metal oxide semiconductor field effect transistor mounted on the bottom surface is less than the thickness of the extended copper layer in its layout area, that is, less than a preset threshold, and the layout area is provided with an extended copper layer for heat dissipation and high current transmission.

[0014] By limiting the thickness of the bottom power device and configuring an extended copper layer, efficient heat dissipation and electrical performance are synergistically optimized. The extended copper layer serves as a heat sink for the power MOSFET, accelerating heat conduction, and, through the copper layer's high conductivity, reduces the impedance of high-current paths. Thickness control ensures a reasonable gap between the power device and the carrier plate, preventing mechanical interference caused by thermal expansion. Matching the thermal expansion coefficients of the extended copper layer and the plastic encapsulation material reduces temperature cycling stress and improves the module's long-term reliability. This layout simultaneously optimizes current carrying capacity and spatial layout density, ensuring that the power path design is more compliant with safety regulations.

[0015] Preferably, the diameter of the solder ball is adapted to the vertical height of the component mounted on the bottom surface, the diameter of the solder ball is positively correlated with the vertical height of the component mounted on the bottom surface, the diameter of the solder ball is at least greater than 2 / 3 of the height of the component, and the height of the solder ball is higher than the surface of the bottom plastic layer.

[0016] The dual-adaptive solder ball design achieves a perfect balance between mechanical support and electrical connection. The matching of diameter and component height prevents component short-circuiting due to ball collapse during soldering, while also ensuring a reliable hemispherical solder joint after reflow. The design, which extends beyond the plastic layer, allows the solder ball to remain maneuverable before soldering, preventing plastic contamination of the solder joint surface. This structure allows for self-centering during module installation through precise control of the reflow temperature profile, improving assembly yield. The reserved height margin compensates for differences in pad height between different carrier boards, enhancing system compatibility.

[0017] Preferably, the diameter of the trapezoidal through hole of the bottom plastic packaging layer is adapted to the diameter of the solder ball, and the depth of the through hole is less than the thickness of the bottom plastic packaging layer.

[0018] The trapezoidal through-hole design optimizes both the molding process and soldering reliability. The tapered hole wall creates a mechanical snap-fit ​​effect, preventing solder ball displacement during the molding process. Controlled through-hole depth ensures the molding compound effectively encapsulates the solder ball base, enhancing structural strength. The trapezoidal angle design facilitates precise control during laser etching, reducing process complexity. This structure guides molten solder to an ideal wetting angle during reflow, optimizing solder joint microstructure. It also provides clearance for subsequent rework operations, enabling module reuse.

[0019] Preferably, the flexible or rigid supporting board is a flexible circuit board or a rigid circuit board.

[0020] The module's carrier board compatibility expands its application scenarios. It accommodates the dynamic bending requirements of flexible circuit boards while also meeting the mechanical support requirements of rigid boards. The flexible connection solution is suitable for space-constrained applications like wearables, while the rigid solution meets the high reliability requirements of in-vehicle equipment. This design allows for optimal carrier board selection based on end-product requirements, enhancing system integration flexibility. The double-sided plastic encapsulation structure provides consistent interface standards across different carrier boards, reducing system design complexity.

[0021] Preferably, the SIP module includes a power metering integrated circuit, a battery protection chip, a power metal oxide semiconductor field effect transistor and micro-packaged passive devices, and the layout spacing of the passive devices is the minimum achievable spacing of the current patch process (such as IPC specifications).

[0022] High-density heterogeneous integration technology enables highly integrated protection board functionality. By integrating heterogeneous components such as the metering IC, protection chip, and power devices in three dimensions, critical signal paths are significantly shortened. Placing passive components at minimum process pitch reduces parasitic parameters and enhances high-frequency characteristics. This integration approach eliminates connection losses between traditional discrete components, enhancing system response speed. The use of chip-scale packaging further reduces the size of functional units, creating a complete system-level solution.

[0023] A method for preparing a double-sided ball-planting lithium battery protection board SIP module comprises the following steps:

[0024] Mounting control circuit components on the top surface of the circuit substrate and forming a top surface plastic sealing layer through an injection molding process;

[0025] Mounting power metal oxide semiconductor field effect transistors and chip-scale packaging devices on the bottom surface of the circuit substrate, and fixing solder balls through laser-assisted ball placement process;

[0026] A bottom plastic sealing layer is formed by a compression injection molding process, and a trapezoidal through hole and a preset gap are formed on the bottom plastic sealing layer by using a laser etching technology;

[0027] The solder balls are subjected to a secondary reflow process to make the diameter of the solder balls fit the pad size of the carrier board.

[0028] A step-by-step injection molding process enables precise molding of complex three-dimensional structures. Top-surface encapsulation ensures full protection of control circuit components, followed by bottom-surface processing to preserve solder joints. Laser-assisted ball placement achieves high-precision three-dimensional positioning, overcoming the limitations of traditional stencil printing. Compression molding ensures a tight seal between the encapsulation material and bottom-surface components while precisely controlling the via topography. A secondary reflow process dynamically adjusts the solder ball shape to accommodate various pad designs. This process makes dual-sided heterogeneous integration feasible for mass production.

[0029] Preferably, in the laser-assisted ball implantation process, the initial diameter of the solder ball is adapted to the pad design of the carrier board.

[0030] Precisely matching laser parameters with solder ball size improves ball placement efficiency. Adjusting laser power and focusing parameters allows for localized remelting of the solder ball base, creating a reliable mechanical anchor. This technology avoids contamination issues associated with traditional flux and improves interface cleanliness. Precise control of the initial diameter preemptively compensates for dimensional variations in subsequent processes, ensuring the final solder ball morphology meets design requirements. This non-contact processing method is particularly well-suited for the precision assembly of miniaturized components.

[0031] Preferably, after the bottom plastic sealing layer is formed, the surface material of the bottom plastic sealing layer is removed by a precision grinding process until the solder balls are partially exposed.

[0032] The precision grinding process enables precise control of interface topography. By removing the surface material of the plastic layer, the solder ball cross-section at a precisely defined height is exposed. This process ensures the flatness of the solder interface and eliminates coplanarity issues caused by variations in plastic layer thickness. The roughened surface after grinding strengthens the bond between the plastic layer and the carrier plate. Controlling the grinding depth allows for flexible adjustment of the solder ball protrusion to suit different soldering process requirements.

[0033] A lithium battery protection board circuit module includes the double-sided ball-planting lithium battery protection board SIP module and a carrier board that is three-dimensionally integrated with the SIP module by soldering solder balls. The X / Y dimensions of the lithium battery protection board circuit module are smaller than those of similar modules that do not adopt a double-sided ball-planting layout.

[0034] The 3D stacking architecture revolutionizes the spatial layout of traditional protection boards. The vertical integration of the SIP module and carrier board overcomes the size bottleneck of traditional planar layouts. The significant reduction in X / Y dimensions is ideal for the compact space requirements of mobile devices. The modular design simplifies system assembly and improves production automation. The 3D wiring architecture shortens high-current paths, reducing line losses and electromagnetic interference risks.

[0035] The beneficial effects of the present invention compared to the prior art are:

[0036] Space Utilization and Performance Improvement: The dual-sided, three-dimensional layout overcomes the planar size limitations of traditional single-sided layouts, significantly improving space utilization. The power devices are placed on the bottom surface, directly connecting to the high-current path of the carrier board, reducing line losses and improving the module's electrical performance.

[0037] Enhanced protection and reliability: The top and bottom plastic layers provide mechanical protection and environmental isolation for components on the top and bottom surfaces, respectively. The trapezoidal through-hole design of the bottom plastic layer ensures precise solder ball positioning, and the pre-set gap absorbs mechanical stress during reflow, preventing solder joint cracking and improving module reliability and stability.

[0038] Process Advantages: A step-by-step injection molding process enables precise molding of complex three-dimensional structures. Top-surface plastic encapsulation protects control circuit components, followed by bottom-surface processing to preserve solder joints. Laser-assisted ball placement overcomes the limitations of traditional stencil printing, achieving high-precision three-dimensional positioning. Compression molding ensures that the encapsulation material tightly wraps around bottom-surface components and precisely controls via topography. A secondary reflow process dynamically adjusts solder ball morphology to accommodate different pad designs, enabling mass production of double-sided heterogeneous integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 This is the component plan layout diagram of comparative example 1.

[0041] Figure 2 Schematic diagram of the PCM 3D structure of Comparative Example 1.

[0042] Figure 3 This is the component plan layout diagram of Example 1.

[0043] Figure 4 Schematic diagram of the PCM 3D structure of Example 1.

[0044] Figure 5 This is the PCM module layout diagram of Comparative Example 2.

[0045] Figure 6 This is the PCM module layout diagram of Example 2. DETAILED DESCRIPTION

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0048] It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further defined and explained in the subsequent figures. In the description of the embodiments of the present application, it should be understood that the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "vertical", "horizontal", etc. is based on the orientation or position relationship shown in the drawings, or is the orientation or position relationship in which the product of the application is usually placed when in use, or is the orientation or position relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0049] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0050] The technical solution in this application will be described below with reference to the accompanying drawings.

[0051] Comparative Example 1

[0052] A fast charging lithium battery protection board design scheme in the industry is selected as comparative example 1. Its technical scheme is as follows Figure 1-2 As shown:

[0053] 1. Structural design: A single-sided layout is used, with the BMU (battery management unit) device mounted on the top surface (TOP) of the PCB. After injection molding, it is cut into independent modules; the modules are mounted and soldered to the carrier board (FPC / PCB) through the pads on the bottom surface (BOT surface).

[0054] 2. Technical bottlenecks:

[0055] 2.1 Size limitation: Power devices (such as MOS) and precision resistors require a large area of ​​copper for heat dissipation and high current transmission, resulting in sparse layout. Although the control circuit components are highly compact, the overall size is difficult to be further compressed. Label explanation: Power devices are attached Figure 1 and 2 Q1-Q4 in

[0056] 2.2 Welding defects: BOT surface pad mounting is prone to problems such as cold soldering and tin shrinkage due to deformation of the carrier board;

[0057] 2.3 Process contradiction: If the power copper area is forcibly compressed, it will affect heat dissipation and electrical performance, and there will be reliability risks.

[0058] Example 1

[0059] In order to solve the problem in Comparative Example 1, this Example 1 proposes Figure 3-4 The technical solution shown:

[0060] 1. Core improvements:

[0061] 1.1 Double-sided 3D layout: Move the MOS device on the original TOP surface to the BOT surface, free up the TOP surface space, and re-compress the X-direction component arrangement; Label explanation: MOS device is attached Figure 3 and 4 Q1-Q4 in

[0062] 1.2 Ball planting instead of pad: Solder balls are set on the BOT surface and connected to the carrier board through reflow soldering to replace traditional pad mounting.

[0063] Label Description: Before improvement, the load-bearing plate is attached Figure 2 A1 in the figure, the solder joint is attached Figure 2 A2 in the circuit board is attached Figure 2 A3 in the improvement; after the improvement, the carrier plate is attached Figure 4 B1 in the figure, the solder ball is attached Figure 4 In B2, the circuit board is attached Figure 4 B3 in.

[0064] 2. Technical details:

[0065] 2.1 Solder ball design: The diameter of the solder ball should be at least 2 / 3 of the device height (for example, when the device height is H, the solder ball diameter should be ≥ 2H / 3) to ensure that the component tolerance and surface unevenness are fully compensated during the soldering process; the solder ball height should be higher than the top of the device to avoid the plastic layer from squeezing and causing electrical connection failure.

[0066] 2.2 Device layout strategy: The BOT surface prioritizes the layout of thinner devices (such as MOS and CSP packaged chips), which have larger X / Y dimensions but smaller thickness. This can not only optimize space utilization but also avoid excessive gaps between the module and the carrier board. The TOP surface is where control circuit components (such as ICs and precision resistors) are concentrated to further improve layout density.

[0067] 3. Advantage verification:

[0068] 3.1 Size reduction: Through double-sided layout and device compression, the X-direction size is significantly reduced;

[0069] 3.2 Improved welding quality: Solder ball design can alleviate the problems of cold soldering and solder balls;

[0070] 3.3 Compatibility: Adapt to different MOS thickness and packaging requirements. In actual application, the solder ball parameters can be adjusted according to the specific product structure.

[0071] Comparative Example 2

[0072] The lithium battery PCM unit module design scheme of a head-mounted display wearable device in the industry is selected as a comparative example. Its technical solution is as follows: Figure 5 As shown:

[0073] 1. Structural design: Using a single-sided layout, the power management PCM components (including Gauge IC, protection IC, and MOSFET chips) are mounted on the top surface of the PCB (TOP surface), and then cut into unit modules after injection molding. The modules are soldered to the carrier board (FPC / PCB) through the pads on the bottom surface (BOT surface). In the selection of passive components, except for the 0201 package precision resistor, the rest are 01005 packages. The spacing between the components has been compressed to the process limit. Label explanation: Gauge IC and protection IC are attached. Figure 5 In U1 and U2, MOS devices are attached Figure 5 Q1 and Q2 in

[0074] 2. Technical bottlenecks:

[0075] 2.1 Size Compression Limit: Under the premise that the principle and functional solution remain unchanged, the device layout density has reached its limit and the X / Y dimensions cannot be further reduced;

[0076] 2.2 Soldering reliability risk: BOT surface pad mounting is prone to cause cold soldering and tin ball problems due to component height tolerance or carrier board deformation.

[0077] Example 2

[0078] In order to solve the problem in Comparative Example 2, this Example 2 proposes the following Figure 6 The technical solution shown:

[0079] 1. Core improvements:

[0080] 1.1 Double-sided layout reconstruction: Re-layout the MOS components on the original TOP surface to the BOT surface, free up the TOP surface space, and achieve size reduction in the X direction by re-compressing the device layout; Label explanation: Gauge IC and protection IC are attached Figure 6 In U1 and U2, MOS devices are attached Figure 6 Q1 and Q2 in

[0081] 1.2 Ball planting process replaces pads: Solder balls are set on the BOT surface and connected to the carrier board through reflow soldering to replace traditional pad mounting.

[0082] 2. Technical details:

[0083] 2.1 Solder ball parameter design: The diameter of the solder ball should be at least 2 / 3 of the device height (for example, when the device height is H, the solder ball diameter should be ≥ 2H / 3) to compensate for the soldering plane tolerance and deformation during the reflow melting process; the solder ball height should be higher than the top of the device to avoid the plastic layer being squeezed and causing electrical connection failure.

[0084] 2.2 Device layout strategy: The BOT surface prioritizes the layout of thinner devices (such as MOS and CSP packaged chips), which have larger X / Y dimensions but thinner thickness. This can not only optimize space utilization but also avoid excessive gaps between the module and the carrier board. The TOP surface concentrates on the layout of precision resistors (0201 package) and control chips (01005 package) to further improve the layout density.

[0085] 3 Advantages:

[0086] 3.1 Size Breakthrough: Through double-sided layout and device compression, the size limit of the original single-sided solution is broken;

[0087] 3.2 Soldering quality optimization: Solder ball design can alleviate the problems of cold soldering and solder balls, and improve connection reliability;

[0088] 3.3 Process compatibility: Adapt to different MOS thicknesses (such as 0.3mm~0.6mm) and packaging requirements. In actual applications, the solder ball parameters can be adjusted according to specific selection requirements.

[0089] Example 3

[0090] This embodiment specifically provides a double-sided ball-planted lithium battery protection board SIP module, including:

[0091] The circuit substrate has a top surface (TOP surface) and a bottom surface (BOT surface);

[0092] A plurality of functional components, including power metal oxide semiconductor field effect transistors (MOSFETs) and chip scale package (CSP) devices, wherein at least one MOSFET or CSP device is mounted on the bottom surface (BOT surface) of the circuit substrate;

[0093] Multiple solder balls are fixed to the bottom surface (BOT surface) of the circuit substrate and are used to achieve electrical connection with the flexible or rigid carrier board through reflow soldering;

[0094] Top plastic layer, covering the top surface (TOP surface) of the circuit substrate and the components mounted thereon;

[0095] The bottom plastic encapsulation layer covers the bottom surface of the circuit substrate (BOT surface) and the components mounted thereon. The bottom plastic encapsulation layer is provided with trapezoidal through holes for fixing solder balls, and a preset gap is left between the solder balls and the bottom plastic encapsulation layer.

[0096] Double-sided integration and space optimization: Functional components (such as power MOSFETs and CSP devices) are arranged on both sides of the circuit substrate (TOP / BOT side), breaking through the limitations of traditional single-sided mounting, significantly improving space utilization, and being suitable for compact battery module design.

[0097] Compatibility with special-shaped components: Power MOSFETs and CSP devices can be mounted on the bottom (BOT) side, and the bottom plastic layer protects them from mechanical damage or short circuit risks caused by exposed components. It also supports flexible layout of special-shaped components (such as ultra-thin MOSFETs).

[0098] Enhanced soldering reliability: Solder balls are fixed to the bottom plastic layer through trapezoidal through-holes, and preset gaps are reserved to absorb the expansion stress of the solder balls during reflow soldering, reduce solder voids or cracks, and ensure the long-term stability of the electrical connection.

[0099] Double-sided plastic sealing protection: The top and bottom plastic sealing layers cover both sides of the circuit substrate respectively, forming a fully enclosed protective structure, effectively blocking moisture, dust and mechanical impact, and improving the durability of the module in harsh environments.

[0100] In this embodiment, the thickness of the power MOSFET mounted on the bottom surface (BOT surface) is less than 0.5 mm, and an extended copper layer is provided in its layout area for heat dissipation and high current transmission.

[0101] Ultra-thin design: The power MOSFET is less than 0.5mm thick, reducing the overall thickness of the module and adapting to the requirements of ultra-thin lithium battery packaging. It is especially suitable for wearable devices, drones and other size-sensitive fields.

[0102] Thermal management optimization: An extended copper layer is placed in the MOSFET area, quickly dissipating component heat through copper's high thermal conductivity, avoiding performance degradation caused by local temperature rise. At the same time, the extended copper layer provides a low-impedance, high-current transmission path to reduce energy loss.

[0103] Current carrying capacity: The extended copper layer is directly connected to the MOSFET, which can carry high-rate charge and discharge currents (such as above 10C), meeting the needs of fast charging / discharging scenarios, while reducing the impact of circuit temperature rise on component life.

[0104] In this embodiment, the diameter of the solder ball is larger than 2 / 3 of the vertical height of the component mounted on the bottom surface (BOT surface), and the height of the solder ball is 20-60 μm higher than the surface of the bottom plastic packaging layer.

[0105] Mechanical support reinforcement: The solder ball diameter should be greater than 2 / 3 of the bottom component height to ensure that the solder ball forms sufficient support area after reflow soldering to avoid insufficient connection strength or stress concentration caused by component height differences.

[0106] Welding height control: The height of the tin ball is 20 to 60 μm higher than the surface of the bottom plastic layer, so that the tin ball and the carrier board (such as FPC / FR4) form a reliable solder joint after soldering. At the same time, a small amount of space is reserved to compensate for thermal expansion deformation and prevent solder joint cracking.

[0107] Self-alignment feature: The proportional design of solder ball diameter and height uses surface tension to achieve self-alignment of solder joints during the reflow process, reducing dependence on placement accuracy and improving mass production yield.

[0108] In this embodiment, the diameter of the trapezoidal through hole in the bottom plastic packaging layer is 0.07 mm±0.02 mm larger than the diameter of the solder ball, and the depth of the through hole is 2 / 3 of the thickness of the bottom plastic packaging layer.

[0109] Stress buffering design: The inclined sidewall structure of the trapezoidal through-hole (such as a taper angle of 5° to 15°) can disperse the shear stress at the interface between the solder ball and the plastic encapsulation layer, reducing the risk of interface delamination under thermal cycling or vibration environments.

[0110] Precise size matching: The through-hole diameter is 0.07mm±0.02mm larger than the solder ball, ensuring that the solder ball can be smoothly embedded while retaining a slight movable space to avoid deformation caused by thermal expansion of the plastic encapsulation layer.

[0111] Depth optimization: The through-hole depth is 2 / 3 of the thickness of the plastic layer, so that the bottom of the solder ball is in direct contact with the circuit substrate, shortening the current path and reducing the contact resistance. At the same time, the top is retained by the plastic layer for protection to prevent oxidation.

[0112] In this embodiment, the flexible or rigid carrier board is a polyimide flexible printed circuit (FPC) or a glass fiber reinforced epoxy printed circuit board (FR4 PCB).

[0113] Flexible adaptability: The bendable nature of the polyimide flexible circuit board (FPC) supports the fitting installation of modules and special-shaped battery packs (such as curved and folded structures), reducing space waste.

[0114] Rigidity and high reliability: Glass fiber reinforced epoxy resin board (FR4 PCB) provides high mechanical strength and dimensional stability, suitable for high vibration scenarios (such as automotive batteries), and prevents solder joint fatigue failure.

[0115] Compatibility expansion: Dual options of flexible and rigid carrier boards meet diverse application scenarios. Both are compatible with solder ball processes, allowing them to adapt to different customer needs without adjusting the module design.

[0116] In this embodiment, the SIP module includes a power meter integrated circuit (Gauge IC), a battery protection chip, a MOSFET, and passive components in a 01005 package, and the layout pitch of the passive components is less than 0.1 mm.

[0117] Highly Integrated Functions: A fuel gauge IC, battery protection chip, MOSFET, and 01005 passive components are integrated into a single SIP module, enabling full battery management functions (such as overcharge / over-discharge protection and power monitoring) and simplifying external circuit design.

[0118] Miniaturized passive components: The spacing between 01005 packaged passive components (such as capacitors and resistors) is less than 0.1mm, breaking through the density limit of traditional SIP modules and is particularly suitable for miniaturized lithium batteries (such as TWS earphone batteries).

[0119] Signal integrity: Ultra-dense pitch layout shortens the signal transmission path, reduces the interference of parasitic inductance / capacitance on high-frequency signals (such as power measurement data), and improves measurement accuracy and response speed.

[0120] Example 4

[0121] A method for preparing a double-sided ball-planting lithium battery protection board SIP module comprises the following steps:

[0122] Mounting control circuit components on the top surface (TOP surface) of the circuit substrate and forming a top surface plastic sealing layer through injection molding process;

[0123] Mount power MOSFETs and CSP devices on the bottom surface (BOT surface) of the circuit substrate and fix solder balls through laser-assisted ball placement process;

[0124] A bottom plastic sealing layer is formed by a compression injection molding process, and a trapezoidal through hole and a preset gap are formed on the bottom plastic sealing layer by using a laser etching technology;

[0125] The solder balls are subjected to a secondary reflow treatment to reduce their diameter to 80% to 90% of their initial value and then soldered to the carrier board.

[0126] Process separation optimization: First complete the placement and plastic sealing of the top surface (TOP) control circuit components (such as Gauge IC, battery protection chip) to avoid thermal impact on the precision control components during the placement of high-power components on the bottom surface (BOT surface) (such as deformation of the plastic sealing layer or component displacement caused by high reflow soldering temperature), thereby ensuring the signal integrity of the top surface circuit.

[0127] Protective plastic sealing layer: The top surface injection molding process covers all top surface components at one time, forming a uniform and dense plastic sealing layer (such as epoxy resin material), isolating sensitive control components from damage by moisture, dust and mechanical stress. It is especially suitable for high humidity or high vibration environments (such as vehicle battery compartments).

[0128] Process compatibility: After the top plastic layer is cured, it provides a rigid support base for the subsequent bottom process, preventing the substrate from bending and deformation when the power components are mounted on the bottom, and ensuring the placement accuracy (for example, the CSP device alignment error is less than ±0.05mm).

[0129] High-precision ball placement: The laser-assisted ball placement process uses a focused laser beam to locally heat the solder ball (0.3mm diameter), precisely controlling the wetting range between the solder ball and the pad, avoiding solder ball collapse or bridging caused by traditional hot air reflow. It is particularly suitable for CSP device pads with ultra-fine pitch (e.g., below 0.1mm).

[0130] Heat-affected zone control: Laser selective heating acts only on the solder ball and pad area, preventing heat from spreading to adjacent power MOSFETs or plastic packaging layers, preventing thermal damage to components (such as failure of the MOSFET gate oxide layer) or thermal degradation of the plastic packaging material.

[0131] Pre-fixing function: After laser ball implantation, the solder ball is initially fixed to the pad, providing a mechanical anchor point for subsequent compression injection molding, preventing the solder ball from shifting due to the flow of the molding compound, and ensuring the solder ball position accuracy in subsequent processes (deviation is less than ±10μm).

[0132] Structural integrated molding: The compression injection molding process uses high pressure to fill the plastic encapsulation material (such as epoxy molding compound EMC) into the gap between the bottom components, forming a plastic encapsulation layer that fits tightly with the circuit substrate, eliminating the air holes or delamination defects that are prone to occur in traditional transfer molding, and improving the interface bonding strength (peel force > 20N / cm).

[0133] Precision machining of through holes: Laser etching technology (such as ultraviolet laser) forms a trapezoidal through hole on the bottom plastic layer. The inclination angle of the through hole side wall (such as 60°~75°) matches the contour of the solder ball to reduce stress concentration at the interface between the plastic layer and the solder ball. At the same time, a preset gap (such as an annular gap of 5~10μm) is reserved to accommodate the thermal expansion of the solder ball and avoid cracking of the plastic layer.

[0134] Optimizing the heat dissipation path: When the bottom plastic layer covers the power MOSFET, a high-thermal-conductivity plastic compound (thermal conductivity > 2W / m·K) combined with an extended copper layer is used to quickly conduct heat from the MOSFET to the outer surface of the plastic layer, reducing the hotspot temperature (measured temperature rise reduction of 15% to 20%).

[0135] Improved solder joint reliability: The secondary reflow treatment reduces the diameter of the solder ball to 0.24-0.27mm (volume shrinkage of approximately 30%). The surface tension of the molten solder ball drives the solder joint to form a smooth arc-shaped interface, reducing the internal void rate of the solder joint (which can be controlled below 3%). At the same time, the contact area between the solder joint and the carrier board pad is increased (increased by approximately 40%), significantly improving the shear strength (>50MPa).

[0136] Self-alignment effect: During the secondary reflow process, the solder balls automatically align with the carrier board pads through surface tension, compensating for position deviations during the ball planting stage (tolerance ±20μm), reducing the stringent requirements for placement accuracy, and improving mass production yield (>98%).

[0137] Interface oxidation inhibition: During the secondary reflow process, the oxides on the surface of the solder balls are reduced in a nitrogen atmosphere to form pure intermetallic compounds (such as Cu6Sn5), which optimizes the conductivity and mechanical strength of the solder joints.

[0138] In this embodiment, the laser-assisted solder ball placement process uses an initial diameter of 0.3mm, which is reduced to 0.24-0.27mm after secondary reflow. The 0.3mm diameter is merely an example and can be adjusted based on pad requirements. After the reduction, the 0.24mm diameter is still greater than two-thirds of the component height. Secondary reflow is performed after the bottom plastic layer is formed.

[0139] Size matching: The initial solder ball diameter of 0.3mm is highly matched to the CSP device pad size (e.g., 0.25mm×0.25mm), ensuring pad coverage >90% after ball placement and avoiding the risk of cold solder joints caused by non-wetting of the pad edge.

[0140] Controllable shrinkage rate: After the second reflow, the diameter is reduced to 0.24-0.27mm (shrinkage rate 20%-10%). By precisely controlling the reflow temperature curve (such as the peak temperature of 250℃±5℃), the solder ball shrinks evenly and forms a gap buffer (5-15μm) with the side wall of the trapezoidal through-hole to absorb the stress caused by the thermal expansion difference.

[0141] Micro-solder joint strength: Small-diameter solder balls (0.24mm) form micro-bump structures after soldering to the carrier board. Their aspect ratio (height / diameter ≈ 1.2) optimizes fatigue resistance. After 1,000 thermal cycles (-40°C to 125°C), the solder joint resistance change rate is <3%.

[0142] In this embodiment, after the bottom plastic encapsulation layer is formed, the surface material of the bottom plastic encapsulation layer is removed by a precision grinding process to partially expose the solder balls, and the grinding accuracy is controlled within ±5 μm.

[0143] Solder ball exposure accuracy: The grinding accuracy of ±5μm controls the surface removal of the plastic encapsulation layer, so that the top of the solder ball is accurately exposed at a height of 20 to 60μm. This ensures that the solder ball is in full contact with the carrier board during soldering, while avoiding damage to the solder ball (such as surface scratches or diameter reduction) caused by excessive grinding.

[0144] Surface flatness: The surface roughness of the bottom plastic layer after grinding is Ra < 0.2μm, which reduces the gap when the carrier plate is attached (e.g. the gap is < 5μm) and prevents micro cracks between the module and the carrier plate due to unevenness after welding.

[0145] Process efficiency: Using diamond grinding wheels for high-speed grinding (speed> 10000rpm), large-area plastic sealing layer removal can be completed in one go. The processing time is shortened by 70% compared with traditional chemical etching, and there is no waste liquid treatment environmental protection problem.

[0146] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A double-sided ball-planted lithium battery protection board SIP module, characterized in that: include: a circuit substrate having a top surface and a bottom surface; a plurality of functional elements, including power metal oxide semiconductor field effect transistors and chip scale packaging devices, wherein at least one of the power metal oxide semiconductor field effect transistors or chip scale packaging devices is mounted on the bottom surface of the circuit substrate; A plurality of solder balls are fixed to the bottom surface of the circuit substrate and are used to achieve electrical connection with a flexible or rigid carrier board through reflow soldering; A top plastic layer covering the top surface of the circuit substrate and the components mounted thereon; The bottom plastic sealing layer covers the bottom surface of the circuit substrate and the components mounted thereon. The bottom plastic sealing layer is provided with trapezoidal through holes for fixing the solder balls, and a preset gap is left around the solder balls and between the bottom plastic sealing layer.

2. The double-sided ball-planted lithium battery protection board SIP module according to claim 1, characterized in that: The thickness of the power metal oxide semiconductor field effect transistor mounted on the bottom surface is smaller than the thickness of the extended copper layer in its layout area, and the extended copper layer is provided in its layout area for heat dissipation and high current transmission.

3. The double-sided ball-planted lithium battery protection board SIP module according to claim 1, characterized in that: The diameter of the solder ball is positively correlated with the vertical height of the component mounted on the bottom surface, and the height of the solder ball is higher than the surface of the bottom plastic packaging layer.

4. The double-sided ball-planted lithium battery protection board SIP module according to claim 1, characterized in that: The diameter of the trapezoidal through hole of the bottom plastic sealing layer is adapted to the diameter of the solder ball, and the depth of the through hole is less than the thickness of the bottom plastic sealing layer.

5. The double-sided ball-planting lithium battery protection board SIP module according to claim 1, characterized in that: The flexible or rigid supporting board is a flexible circuit board or a rigid circuit board.

6. The double-sided ball-planted lithium battery protection board SIP module according to claim 1, characterized in that: The SIP module includes a power metering integrated circuit, a battery protection chip, a power metal oxide semiconductor field effect transistor and micro-packaged passive devices, and the layout spacing of the passive devices is the minimum achievable spacing of the current patch process.

7. A method for preparing a double-sided ball-planted lithium battery protection board SIP module according to any one of claims 1 to 6, characterized in that: The following steps are involved: Mounting control circuit components on the top surface of the circuit substrate and forming a top surface plastic sealing layer through an injection molding process; Mounting power metal oxide semiconductor field effect transistors and chip-scale packaging devices on the bottom surface of the circuit substrate, and fixing solder balls through laser-assisted ball placement process; A bottom plastic sealing layer is formed by a compression injection molding process, and a trapezoidal through hole and a preset gap are formed on the bottom plastic sealing layer by using a laser etching technology; The solder balls are subjected to a secondary reflow process to make the diameter of the solder balls fit the pad size of the carrier board.

8. The preparation method according to claim 7, characterized in that In the laser-assisted ball placement process, the initial diameter of the solder ball is adapted to the pad design of the carrier board.

9. The preparation method according to claim 7, characterized in that After the bottom plastic sealing layer is formed, the surface material of the bottom plastic sealing layer is removed by a precision grinding process until the solder balls are partially exposed.

10. A lithium battery protection board circuit module, characterized in that: It comprises a double-sided ball-planting lithium battery protection board SIP module as described in any one of claims 1 to 6, and a carrier board three-dimensionally integrated with the SIP module by soldering solder balls, wherein the X / Y direction dimensions of the lithium battery protection board circuit module are smaller than similar modules that do not adopt a double-sided ball-planting layout.

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