A low-stress vacuum filling process integrating thin film capacitor

Abstract

The application discloses a thin-film capacitor integrated low-stress vacuum filling process, and relates to the technical field of thin-film capacitor manufacturing processes.The specific steps of the process are as follows: first, the capacitor is positioned in a closed cavity positioning tool and sealed, then, hierarchical pumping is performed to discharge residual gas in the core, then, glue is injected under vacuum and mechanical oscillation is simultaneously applied to promote glue filling, then, segmented temperature rising and holding are performed to make the glue fully crosslink and solidify, then, slow cooling is performed to reduce internal stress, finally, the finished product is taken out after pressure relief and opening of the cabin; by integrating vacuum pumping, glue injection, oscillation and temperature control in a single closed cavity, the application realizes dust-free closed loop in the whole process, avoids transportation pollution and air wrapping, and improves batch consistency and production capacity; segmented temperature rising and slow cooling match the glue reaction period, reduce internal stress, and prevent film layer damage; fast replacement of damping tools and multi-grade glue injection ports adapt to different specifications and viscosities, meet flexible production, and improve the finished product quality and long-term stability of the equipment.

Description

Technical Field

[0001] This invention relates to the field of thin-film capacitor manufacturing technology, specifically to an integrated low-stress vacuum potting process for thin-film capacitors. Background Technology

[0002] Film capacitors are indispensable passive components in power electronic systems, widely used in core equipment such as new energy vehicle electronic control systems, photovoltaic power conversion devices, industrial frequency converters, and rail transit converter modules. During long-term operation, capacitors need to withstand complex conditions such as alternating voltage, high and low temperature cycles, and humidity and dust. The potting process is a core manufacturing step that determines the long-term reliability of capacitors. The potting compound fills all the gaps between the capacitor winding core and the metal shell, forming a complete protective layer, simultaneously achieving multiple functions such as electrical insulation, heat conduction, moisture isolation, and mechanical buffering. The quality of potting directly determines the capacitor's capacitance stability, dielectric loss, withstand voltage threshold, and overall service life. In current large-scale production, film capacitor potting is generally completed using specialized vacuum potting equipment. The industry is continuously pursuing integrated processing solutions with low defects, low internal stress, and flexible adaptation to multiple product specifications to meet the market production demands of simultaneous production of multiple categories and small to medium batches. Traditional segmented potting processing solutions are no longer sufficient to meet the current quality control and capacity improvement requirements of high-end power electronic components.

[0003] Traditional potting systems employ a modular layout, with adhesive preparation, vacuum degassing, filling, and curing performed in separate equipment. Workpieces require multiple manual transfers between processes, introducing dust and impurities during material handling. Furthermore, the depressurization and repressurization process within the cavity allows air to re-enter the adhesive, causing bubble defects in the finished product. Vacuum degassing, using only a single vacuum pump with constant negative pressure, cannot match the physical laws governing the stratified gas release within the multi-layered wound structure of the thin film. Trace amounts of gas adsorbed in deep crevices are difficult to expel completely, continuously reducing the capacitor's insulation and withstand voltage performance. During the filling stage, the lack of synchronized vibration means the adhesive slowly permeates the core gaps under its own weight, preventing tiny bubbles from quickly rising and precipitating. This necessitates an additional static degassing process, lengthening the entire production line. The curing stage uses only a single constant-temperature baking mode, resulting in asynchronous cross-linking and volume shrinkage of the adhesive. This creates a significant temperature difference between the inner and outer layers, leading to concentrated internal stress after curing. This can easily tear the film dielectric layer and peel off the metal vapor deposition layer, causing capacitance decay and increased leakage. Meanwhile, the tooling structure is fixed and cannot be quickly disassembled or assembled. When changing capacitors with different shapes, it is necessary to disassemble and adjust the equipment over a large area, which cannot be adapted to flexible mixed-line production. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a low-stress vacuum potting process for integrated thin-film capacitors. The process employs a quickly replaceable six-degree-of-freedom positioning fixture and a fluororubber sealing structure to achieve high-precision gas sealing. A two-stage pump group is connected in series for graded gas extraction to ensure sufficient exhaust of gas from the capacitor core. During the glue injection process, an electromagnetic vibrator applies mechanical vibration synchronized with the glue injection to assist in glue filling. Subsequently, gradient temperature-controlled curing is achieved through segmented heating and controlled slow cooling, effectively reducing the internal shrinkage stress generated during the glue cross-linking and cooling stages.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: an integrated low-stress vacuum potting process for thin-film capacitors, the specific steps of which are as follows: S100, workpiece clamping and sealing; the thin film capacitor to be processed is placed into the positioning fixture inside the sealed cavity to fix its position, and the cavity door is closed to form an airtight sealed space inside the cavity. S200, staged extraction and degassing; staged extraction is performed inside the sealed cavity to gradually reduce the internal air pressure and complete the removal of gas trapped inside the thin-film capacitor core. S300, synchronous potting oscillation; maintain the vacuum environment inside the sealed cavity, inject potting compound into the inside of the film capacitor shell, and apply mechanical oscillation to the film capacitor simultaneously during the potting process; S400, gradient temperature control curing; maintain the closed state of the sealed cavity, perform segmented heating and heat preservation treatment on the internal environment of the cavity, and perform linear cooling operation after the cross-linking reaction of the potting colloid is completed, so that the potting colloid is uniformly cured and formed. S500, depressurize and cool the material; introduce external gas into the sealed cavity to release the internal vacuum, open the cavity door and take out the potted and cured film capacitor.

[0006] Furthermore, the positioning fixture is set above the worktable inside the sealed cavity, and adopts a detachable structure. It is rigidly locked to the worktable of the cavity by quick clamps. The surface of the fixture is provided with six-degree-of-freedom limiting grooves for translation in the X, Y, and Z directions and rotation around three axes. The assembly gap between the limiting grooves and the capacitor shell on one side is in the range of 0.1mm to 0.3mm. A silicone rubber or polyurethane damping pad with a thickness of 3mm to 8mm and a Shore hardness of A50 to A70 is bonded to the bottom of the fixture. The pad completely fits the bottom surface of the fixture and the worktable surface. A fluororubber O-ring is installed at the fitting position of the cavity door. The temperature resistance range of the sealing ring is -40℃ to 200℃. The overall airtight seal of the cavity is formed by extrusion deformation.

[0007] Furthermore, the positioning fixture can be replaced and disassembled according to the shape and specifications of the film capacitor. The limiting groove is divided into a rectangular groove suitable for square shells and a circular groove suitable for cylindrical shells. The overall disassembly and assembly of the fixture takes ≤5 minutes. After the fixture is replaced, it can be used simply by re-locking it with clamps. The replacement of the fixture does not require any modification to the main structure of the sealed cavity. The replaced positioning fixture can stably constrain film capacitors of different shapes and sizes.

[0008] Furthermore, the staged evacuation process employs a two-stage pump set connected in series to regulate the chamber pressure. The two pump sets are connected to the chamber via a DN32 stainless steel pipeline. The first-stage actuator is a rotary vane vacuum pump, which first evacuates the chamber pressure to the range of -0.08MPa to -0.06MPa and maintains this pressure for 3 to 8 minutes, at a pumping speed of 8 L / s. The second-stage actuator is a Roots vacuum pump, which, after coordinated operation, evacuates the chamber pressure to below -0.095MPa and maintains this pressure for 3 to 8 minutes, at a pumping speed of 30 L / s. The chamber assembly range is 1×10⁻⁶. 5 Pa to 1×10 -1 The Pa capacitive thin-film vacuum sensor collects the air pressure value and controls the start and stop of the pump group in real time, so that the fluctuation range of the vacuum degree of the cavity is controlled within ±0.002MPa throughout the process.

[0009] Furthermore, the colloid delivery is driven by a gear metering pump with a flow metering accuracy of ±1%. The dispensing execution end is a lifting dispensing nozzle driven by a servo motor and ball screw, with a lifting stroke of 0-200mm and a positioning accuracy of ±0.5mm. After the dispensing nozzle descends to the bottom of the capacitor housing, it rises uniformly at a speed of 0.5-2mm / s. The colloid delivery flow rate is constantly set to 5g / min-20g / min. A pressure stabilizing valve is connected in series in the colloid delivery pipeline to lock the pipeline pressure fluctuation within ±0.02MPa. The dispensing nozzle outlet diameter is divided into three specifications according to the colloid viscosity: 1-2mm diameter for colloids with viscosity of 1000-3000mPa·s, 2-3mm diameter for colloids with viscosity of 3000-6000mPa·s, and 3-5mm diameter for colloids with viscosity of 6000-10000mPa·s.

[0010] Furthermore, the mechanical vibration is output by an electromagnetic vibrator embedded in the bottom of the workbench. The bottom of the workbench includes an electromagnetic vibrator and an eccentric wheel amplitude adjustment mechanism. The vibration force is transmitted vertically upward to the capacitor housing through a locking and fixed positioning fixture. The vibration frequency ranges from 5Hz to 30Hz, the amplitude ranges from 0.1mm to 0.3mm, and the vibrator outputs an excitation force ranging from 0N to 500N. The damping pad at the bottom of the fixture absorbs the high-frequency resonance generated by the vibration, preventing the vibration energy from being transmitted to the sealed cavity housing and causing structural resonance. The vibration start and stop times are completely synchronized with the glue injection start and stop times, and the vibration duration fully covers the entire glue injection process.

[0011] Furthermore, the gradient temperature-controlled curing step involves the installation of electric heating components in sections on the sidewalls and bottom of the cavity, with a heating rate ranging from 0.5℃ / min to 2.0℃ / min. After heating, three constant temperature zones are set: the first zone is 60℃ to 80℃, the second zone is 80℃ to 100℃, and the third zone is 100℃ to 120℃. The holding time for each zone is matched according to the potting compound material. A PT100 platinum resistance temperature sensor is installed inside the cavity, with a single-point temperature measurement accuracy of ±0.1℃. Temperature control adopts PID closed-loop regulation, where PID is a proportional-integral-derivative closed-loop temperature control regulation algorithm. The overall temperature fluctuation range of the cavity is ±1℃, and the cavity is maintained in a vacuum-sealed state throughout the heating process.

[0012] Furthermore, the cooling operation is initiated after all the segmented heating and heat preservation processes are completed. The cooling structure consists of a combination of an air-cooled radiator and a water-cooled coil. The cooling medium is compressed air or circulating cooling water. The circulating cooling water flow rate is constant at 8L / min, and the compressed air purging pressure is set to 0.3MPa. The overall cooling rate is locked in the range of 0.5℃ / min to 1.0℃ / min until the internal temperature of the cavity drops to 60℃ and the cooling output stops. During the cooling stage, temperature data is continuously uploaded to dynamically adjust the supply flow rate of the cooling medium, so as to gradually reduce the internal ambient temperature of the cavity and avoid inconsistent volume shrinkage rates of the potting compound caused by excessively rapid cooling. This minimizes the internal shrinkage stress generated by the curing of the compound. The cavity door is not opened during the entire cooling process to avoid damaging the sealing environment.

[0013] Furthermore, in the depressurization and cooling discharge step, after the internal temperature of the cavity drops to the range of 40℃ to 60℃, dust-removing, dehumidifying, and dry air is introduced to release the internal vacuum. The air inlet valve is gradually adjusted to open. After the internal pressure of the cavity is consistent with the external atmospheric pressure, the hatch is opened, the quick clamps are released, and the finished capacitor is taken out. When switching product specifications, only the positioning tooling is disassembled and assembled. The cavity pipeline, air pump group, and temperature control components do not need to be disassembled and adjusted.

[0014] Compared with existing technologies, this integrated low-stress vacuum potting process for thin-film capacitors has the following advantages: I. This invention integrates the entire process of vacuuming, adhesive injection, vibration degassing, and temperature-controlled curing into a single sealed cavity and a unified main control system. It abandons the traditional multi-equipment, segmented transfer and processing mode, eliminating the need for manual intervention throughout the process, thus increasing overall processing capacity. Simultaneously, the unified closed-loop control logic stably manages the core indicators of each process, effectively reducing performance differences between batches and ensuring consistent output. From clamping to cooling and unloading, the product remains in a closed, dust-free environment, eliminating the problems of impurity contamination and secondary air entrainment caused by cross-equipment transfer. Simultaneously, the synergistic effect of staged vacuuming and bottom-synchronized vibration releases gas trapped in the deep crevices of the capacitor core in layers, accelerating the precipitation and dissipation of bubbles within the adhesive. This eliminates the need for a separate static degassing process, reducing overall processing time. The integrated layout also reduces energy consumption from operating multiple independent devices and lowers the need for manual supervision.

[0015] II. This invention utilizes a segmented heating and cooling integrated temperature control system with linear slow cooling to match the complete reaction cycle of the potting compound's cross-linking shrinkage. This system smoothly regulates the temperature variation throughout the curing process, mitigating the difference in shrinkage rates between the inner and outer layers of the compound, reducing internal stress during curing, and preventing defects such as delamination and damage to the internal film layers and metal plating of the thin-film capacitor. This extends the stable service life of the components. The accompanying six-degree-of-freedom damping positioning fixture, which can be quickly disassembled, adapts to capacitor shells of different shapes and sizes. Combined with a multi-position adaptable dispensing structure, it is compatible with various viscosities of potting compounds, allowing for rapid switching between production types and adapting to flexible production needs. The damping structure at the bottom of the fixture isolates vibration from transmission to the cavity shell, avoiding equipment resonance losses. The various functional components work together to create a synergistic effect, comprehensively improving the quality of the thin-film capacitor potting product and the long-term operational stability of the equipment.

[0016] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0018] Figure 1 This is a framework diagram of an integrated low-stress vacuum potting process for thin-film capacitors. Figure 2 This is a flowchart of a low-stress vacuum potting process for integrated thin-film capacitors. Detailed Implementation

[0019] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0020] Example 1: In some optional embodiments, this embodiment processes a square aluminum-shell thin-film capacitor for a new energy vehicle electronic control system, using a matching 3000 mPa·s epoxy resin potting compound. The entire process employs a low-stress vacuum potting process for integrated thin-film capacitors, completed using integrated vacuum potting equipment. For example... Figure 1 As shown.

[0021] Specifically, in step S100, the workpiece is clamped and sealed. A rectangular six-degree-of-freedom locating groove positioning fixture with a square shell measuring 60mm×40mm×35mm is selected. The fixture is made of SUS304 stainless steel, and a 5mm thick silicone rubber damping pad with a Shore hardness of A60 is attached to the bottom of the fixture. The capacitor shell is embedded into the locating groove, with a single-sided assembly gap of 0.2mm between the shell and the locating groove. A quick clamp is used to rigidly lock the fixture onto the surface of the cavity worktable. The cavity door is closed, and a fluororubber O-ring is installed at the door contact point to complete the seal. The sealing ring has a temperature resistance range of -40℃ to 200℃. After compression deformation, the cavity forms a complete airtight sealed space. The complete disassembly and replacement of this fixture takes 4 minutes and requires no modification to the cavity piping, pump set, or temperature control main structure.

[0022] For example, in step S200, the gas is evacuated and degassed in stages. A two-stage series pump group is started. The first-stage rotary vane vacuum pump operates at a speed of 8 L / s, evacuating the chamber pressure to -0.07 MPa and maintaining this pressure for 5 minutes. Simultaneously, the second-stage Roots vacuum pump is started at a speed of 30 L / s, evacuating the chamber pressure to -0.098 MPa and maintaining this pressure for 5 minutes. The internal capacitive thin-film vacuum sensor has a range covering 1×10⁻⁶. 5 Pa ~ 1×10 -1 The system collects the gas pressure value inside the cavity in real time throughout the process and transmits it to the main control system. The start and stop of the pump group are controlled by the main control system in a closed loop. The vacuum fluctuation range is stably controlled within ±0.002MPa throughout the process.

[0023] Understandably, step S300 involves synchronous glue injection and vibration to maintain a vacuum-sealed environment within the cavity. A gear metering pump is activated to drive the glue delivery, with a flow rate accuracy of ±1% and a constant glue delivery flow rate of 12g / min. A pressure regulating valve is connected in series in the glue delivery pipeline, locking the pipeline pressure fluctuation within ±0.02MPa. Given the glue viscosity of 3000mPa·s, a 3mm diameter glue nozzle is selected. A servo motor and ball screw drive the glue nozzle to descend to the bottom of the capacitor housing, then it rises at a uniform speed of 1mm / s to complete the glue injection operation. An electromagnetic vibrator embedded in the bottom of the worktable starts synchronously, equipped with an eccentric wheel amplitude adjustment mechanism. The vibration frequency is 20Hz, the amplitude is 0.2mm, and the vibrator outputs a vibration force of 300N. The vibration start and stop times are completely synchronized with the glue injection start and stop times. The damping pad at the bottom of the fixture absorbs the high-frequency resonance generated by the vibration, preventing vibration energy from being transmitted to the cavity housing and causing structural resonance.

[0024] In the relevant technology, step S400, gradient temperature-controlled curing, is performed. Electric heating components are arranged in sections on the sidewalls and bottom of the cavity. The heating rate is set to 1℃ / min. After heating, three-stage constant temperature holding treatment is performed: the first stage is held at 70℃ for 60 minutes, the second stage at 90℃ for 60 minutes, and the third stage at 110℃ for 120 minutes. The holding time matching rules are: the total holding time for epoxy resin potting compound is ≥240 minutes, the total holding time for polyurethane potting compound is ≥180 minutes, and the holding time for high-filler, high-viscosity potting compound is extended by 50%–100% for each stage. A PT100 platinum resistance temperature sensor is installed inside the cavity, with a single-point temperature measurement accuracy of ±0.1℃. The temperature control system adopts PID closed-loop regulation, and the overall temperature fluctuation range of the cavity is stabilized within ±1℃. The cavity is maintained in a vacuum-sealed state throughout the heating process. After all three insulation processes are completed, the cooling operation is initiated. The cooling structure simultaneously utilizes air-cooled radiators and water-cooled coils, with a constant circulating cooling water flow rate of 8L / min and compressed air purging pressure of 0.3MPa. The overall cooling rate is locked at 0.5℃ / min, and cooling continues until the internal temperature of the cavity drops to 60℃ before stopping the cooling output. Throughout the cooling process, the cavity door is not opened to disrupt the sealed environment, thus gradually reducing the internal temperature of the cavity, controlling the difference in colloid shrinkage rate, and reducing the internal shrinkage stress during curing.

[0025] Specifically, after performing step S500, depressurizing and cooling the material, and after the internal temperature of the cavity drops to the 55°C range, the opening of the air inlet valve is gradually adjusted to introduce dust-removing, dehumidifying, and dry air into the cavity to release the internal vacuum. After the internal pressure of the cavity is completely consistent with the external atmospheric pressure, the hatch is opened, the quick clamps are released, and the finished automotive thin-film capacitor that has been potted and cured is taken out.

[0026] In this embodiment, the measured residual bubble rate of the finished product is less than 0.05%, the curing stress is 1.8MPa, the stable output of 1200 finished products per shift, the batch capacitance deviation is controlled within ±0.8%, the capacitance change rate of the finished product after 1000h high temperature and high humidity aging test is less than 1%, and the insulation resistance is greater than 10GΩ, which meets the standards for automotive-grade film capacitors.

[0027] Example 2: In some optional embodiments, this embodiment processes a cylindrical aluminum-cased thin-film capacitor for a photovoltaic inverter, using a polyurethane potting compound with a viscosity of 1500 mPa·s. All the process steps defined in this invention are fully implemented, and integrated vacuum potting equipment is used to complete the integrated processing. Figure 2 As shown.

[0028] Specifically, in step S100, the workpiece is clamped and sealed. A circular six-degree-of-freedom limiting groove positioning fixture with a cylindrical shell of 50mm diameter and 80mm height is selected. The fixture is made of SUS304 stainless steel, and a 3mm thick polyurethane damping pad with a Shore hardness of A50 is attached to the bottom of the fixture. The capacitor shell is embedded into the limiting groove, with a single-sided assembly gap of 0.1mm between the shell and the limiting groove. A quick clamp is used to rigidly lock the fixture onto the surface of the cavity worktable. The cavity door is closed, and a fluororubber O-ring is installed at the door contact point to complete the seal. The sealing ring has a temperature resistance range of -40℃ to 200℃. After compression deformation, the cavity forms a complete airtight sealed space. The complete disassembly and replacement of this fixture takes 3 minutes and does not require modification of the cavity piping, pump set, or temperature control main structure.

[0029] For example, in step S200, the gas is evacuated and degassed in stages. A two-stage series pump group is started. The first-stage rotary vane vacuum pump operates at a speed of 8 L / s, evacuating the chamber pressure to -0.06 MPa and maintaining this pressure for 3 minutes. Simultaneously, the second-stage Roots vacuum pump is started at a speed of 30 L / s, evacuating the chamber pressure to -0.095 MPa and maintaining this pressure for 3 minutes. The internal capacitive thin-film vacuum sensor has a range covering 1×10⁻⁶. 5 Pa ~ 1×10 -1 The system collects the gas pressure value inside the cavity in real time throughout the process and transmits it to the main control system. The start and stop of the pump group are controlled by the main control system in a closed loop. The vacuum fluctuation range is stably controlled within ±0.002MPa throughout the process.

[0030] It is understandable that step S300 involves synchronous glue injection and vibration to maintain a high-vacuum sealed environment in the cavity. A gear metering pump is activated to drive the glue delivery, with a flow rate accuracy of ±1% and a constant glue delivery flow rate of 15g / min. A pressure regulating valve is connected in series in the glue delivery pipeline to lock the pipeline pressure fluctuation within ±0.02MPa. Given the glue viscosity of 1500mPa·s, a 2mm diameter glue nozzle is selected. A servo motor and ball screw drive the glue nozzle to descend to the bottom of the capacitor housing, then lift it upwards at a uniform speed of 0.5mm / s to complete the glue injection operation. An electromagnetic vibrator embedded in the bottom of the worktable starts synchronously, equipped with an eccentric wheel amplitude adjustment mechanism. The vibration frequency is 25Hz, the amplitude is 0.15mm, and the vibrator outputs a vibration force of 220N. The vibration start and stop times are completely synchronized with the glue injection start and stop times. The damping pad at the bottom of the fixture absorbs the high-frequency resonance generated by the vibration, preventing the vibration energy from being transmitted to the cavity housing and causing structural resonance.

[0031] In the relevant technology, step S400, gradient temperature-controlled curing, is performed. Electric heating components are arranged in sections on the sidewalls and bottom of the cavity. The heating rate is set to 0.8℃ / min. After heating, three stages of constant temperature holding are performed: the first stage is held at 65℃ for 60 minutes, the second stage at 85℃ for 60 minutes, and the third stage at 105℃ for 120 minutes. A PT100 platinum resistance temperature sensor is installed inside the cavity, with a single-point temperature measurement accuracy of ±0.1℃. The temperature control system uses PID closed-loop regulation, and the overall temperature fluctuation range of the cavity is stabilized within ±1℃. The cavity is maintained in a vacuum-sealed state throughout the heating process. After all three insulation processes are completed, the cooling operation is initiated. The cooling structure simultaneously utilizes air-cooled radiators and water-cooled coils, with a constant circulating cooling water flow rate of 8L / min and compressed air purging pressure of 0.3MPa. The overall cooling rate is locked at 0.8℃ / min, and cooling continues until the internal temperature of the cavity drops to 50℃ before stopping the cooling output. Throughout the cooling process, the cavity door is not opened to disrupt the sealed environment, thus gradually reducing the internal temperature of the cavity, controlling the difference in colloid shrinkage rate, and reducing the internal shrinkage stress during curing.

[0032] Specifically, after performing step S500, depressurizing and cooling the material, and the internal temperature of the cavity drops to the 50°C range, the opening of the air inlet valve is gradually adjusted to introduce dust-removing, dehumidifying, and dry air into the cavity to release the internal vacuum. After the internal pressure of the cavity is completely consistent with the external atmospheric pressure, the hatch is opened, the quick clamps are released, and the finished photovoltaic thin-film capacitor that has been potted and cured is taken out.

[0033] In this embodiment, the measured bubble residue rate of the finished product is less than 0.08%, the curing stress is 1.5MPa, the stable output of 1350 finished products per shift, and the finished products do not delamination or cracking after 2000 temperature cycles from -40℃ to 85℃, and the equivalent series resistance change rate is less than 5%.

[0034] Example 3: In some optional embodiments, the object of processing in this embodiment is a square aluminum shell film capacitor for industrial high-power frequency converters, which is equipped with a high-filling epoxy resin potting colloid with a viscosity of 8000mPa・s. All the process steps defined in this invention are fully adopted, and integrated vacuum potting equipment is used to complete the integrated processing.

[0035] Specifically, in step S100, the workpiece is clamped and sealed. A rectangular six-degree-of-freedom locating groove positioning fixture suitable for a large 100mm×60mm×50mm square shell is selected. The fixture is made of SUS304 stainless steel, and an 8mm thick silicone rubber damping pad with a Shore hardness of A70 is attached to the bottom of the fixture. The capacitor shell is embedded into the locating groove, with a single-sided assembly gap of 0.3mm between the shell and the locating groove. A quick clamp is used to rigidly lock the fixture onto the surface of the cavity worktable. The cavity door is closed, and a fluororubber O-ring is installed at the door contact point to complete the seal. The sealing ring has a temperature resistance range of -40℃ to 200℃. After compression deformation, the cavity forms a complete airtight sealed space. The complete disassembly and replacement of this fixture takes 5 minutes and does not require modification of the cavity piping, pump group, or temperature control main structure. If the disassembly and replacement of the fixture takes more than 5 minutes, the six-degree-of-freedom positioning accuracy of the locating groove needs to be recalibrated to ensure that the assembly gap is stable within the range of 0.1mm to 0.3mm.

[0036] For example, in step S200, the gas is evacuated and degassed in stages. A two-stage series pump group is started. The first-stage rotary vane vacuum pump operates at a speed of 8 L / s, evacuating the chamber pressure to -0.08 MPa and maintaining this pressure for 8 minutes. Simultaneously, the second-stage Roots vacuum pump is started at a speed of 30 L / s, evacuating the chamber pressure to -0.098 MPa and maintaining this pressure for 8 minutes. The internal capacitive thin-film vacuum sensor has a range covering 1×10⁻⁶. 5 Pa ~ 1×10 -1 The system collects the gas pressure value inside the cavity in real time throughout the process and transmits it to the main control system. The start and stop of the pump group are controlled by the main control system in a closed loop. The vacuum fluctuation range is stably controlled within ±0.002MPa throughout the process.

[0037] Understandably, step S300 involves synchronous glue injection and vibration to maintain a high-vacuum sealed environment within the cavity. A gear metering pump is activated to drive the glue delivery, with a flow rate accuracy of ±1% and a constant glue delivery flow rate of 8g / min. A pressure regulating valve is connected in series in the glue delivery pipeline, locking the pipeline pressure fluctuation within ±0.02MPa. Given the glue viscosity of 8000mPa·s, a 5mm diameter glue nozzle is selected. A servo motor and ball screw drive the glue nozzle to descend to the bottom of the capacitor housing, then it rises at a uniform speed of 2mm / s to complete the glue injection operation. An electromagnetic vibrator embedded in the bottom of the worktable starts synchronously, equipped with an eccentric wheel amplitude adjustment mechanism. The vibration frequency is 15Hz, the amplitude is 0.25mm, and the vibrator outputs a vibration force of 450N. The vibration start and stop times are completely synchronized with the glue injection start and stop times. The damping pad at the bottom of the fixture absorbs the high-frequency resonance generated by the vibration, preventing vibration energy from being transmitted to the cavity housing and causing structural resonance.

[0038] In the relevant technology, step S400, gradient temperature-controlled curing, is performed. Electric heating components are arranged in sections on the sidewalls and bottom of the cavity. The heating rate is set to 0.5℃ / min. After heating, three stages of constant temperature holding are performed: the first stage is held at 60℃ for 120 minutes, the second stage at 80℃ for 120 minutes, and the third stage at 100℃ for 180 minutes. A PT100 platinum resistance temperature sensor is installed inside the cavity, with a single-point temperature measurement accuracy of ±0.1℃. The temperature control system uses PID closed-loop regulation, and the overall temperature fluctuation range of the cavity is stabilized within ±1℃. The cavity is maintained in a vacuum-sealed state throughout the heating process. After all three insulation processes are completed, the cooling operation is initiated. The cooling structure simultaneously uses air-cooled radiators and water-cooled coils, with a constant circulating cooling water flow rate of 8L / min and compressed air purging pressure of 0.3MPa. The overall cooling rate is locked at 0.5℃ / min, and cooling continues until the internal temperature of the cavity drops to 40℃ before stopping the cooling output. The cavity door is not opened during the entire cooling process to avoid disrupting the sealed environment, thus gradually reducing the internal temperature of the cavity, controlling the difference in colloid shrinkage rate, and reducing the internal shrinkage stress during curing.

[0039] Specifically, after performing step S500, depressurizing and cooling the material, and after the internal temperature of the cavity drops to the 40°C range, the opening of the air inlet valve is gradually adjusted to introduce dust-removing, dehumidifying, and dry air into the cavity to release the internal vacuum. After the internal pressure of the cavity is completely consistent with the external atmospheric pressure, the hatch is opened, the quick clamps are released, and the finished industrial inverter film capacitor that has been potted and cured is taken out.

[0040] In this embodiment, the measured residual bubble rate of the finished product is less than 0.06%, the curing stress is 1.9 MPa, and the single-shift output is stable at 800 finished products, which can stably meet the needs of large-scale potting production of high-viscosity filler colloids.

[0041] Comparative Example 1: The synchronous oscillation process is cancelled, and the remaining process parameters remain the same as in Example 1.

[0042] In some optional implementations, the processing objects, colloid types, tooling specifications, air extraction parameters, temperature control parameters, and dispensing parameters of this comparative example are all the same as those in Example 1. Only step S300 and the operation related to synchronous mechanical vibration are removed. The electromagnetic vibrator is not started during the entire dispensing process, and the execution flow of the remaining processes remains unchanged.

[0043] Specifically, processes S100 to S200 are operated in exactly the same manner as in Example 1. After the graded vacuuming and pressure holding are completed, the glue injection process begins. The glue injection nozzle injects glue from bottom to top at a flow rate of 12g / min and a lifting speed of 1mm / s, without any vibration assistance throughout the process. Subsequent steps such as gradient heating, segmented heat preservation, linear slow cooling, and pressure relief discharge are all performed using the parameters of Example 1.

[0044] The measured residual bubble rate of the finished product in this comparative example ranged from 0.8% to 1.5%, the curing stress ranged from 4 MPa to 6 MPa, and 900 finished products were produced per shift. The number of internal bubble defects in the finished product increased significantly, and the capacitance decay after high-temperature aging was greater than that of the finished product in Example 1.

[0045] Comparative Example 2: Gradient temperature control curing was cancelled, and single constant temperature curing was adopted. All other process parameters remained the same as in Example 1.

[0046] In some optional implementations, the processing objects, colloid types, tooling specifications, air extraction parameters, and dispensing vibration parameters of this comparative example are all the same as those in Example 1. Only the S400 temperature-controlled curing process is adjusted, and the gradient heating three-stage heat preservation linear slow cooling scheme is cancelled and replaced with a single 80°C constant temperature baking for 4 hours. The execution process of the remaining steps remains unchanged.

[0047] Specifically, the S100 to S300 processes are exactly the same as those in Example 1. After the synchronous injection and vibration are completed, the cavity is directly heated to a constant 80°C without segmented heating or multi-stage constant temperature steps. After baking, the chamber door is opened directly for natural cooling without using the air-cooling and water-cooling combined slow cooling structure. The average cooling rate of natural cooling is 3°C / min to 5°C / min, which is much higher than the controlled cooling rate of 0.5°C / min to 1°C / min of this invention.

[0048] The measured residual bubble rate of the finished product in this comparative example ranged from 0.1% to 0.3%, and the curing stress ranged from 5 MPa to 8 MPa. There was an obvious risk of stress cracking inside the finished colloid, and the delamination defect rate increased significantly after the temperature cycling test.

[0049] Comparative Example 3: The staged evacuation was cancelled, and a single-stage rotary vane pump was used for constant vacuum evacuation. All other process parameters remained the same as in Example 1.

[0050] In some optional implementations, the processing objects, colloid types, tooling specifications, dispensing vibration parameters, and temperature control parameters of this comparative example are all the same as those in Example 1. Only the S200 evacuation process is adjusted, the two-stage Roots vacuum pump is removed, and a constant vacuum of -0.095MPa is maintained solely by a single-stage rotary vane pump. There is no low-vacuum pre-evacuation and pressure holding step, and the execution flow of the remaining processes remains unchanged.

[0051] Specifically, after S100 and tooling are clamped, the single-stage rotary vane pump is started directly to draw the cavity to -0.095MPa. The vacuum degree is kept constant throughout the process without segmented pressure holding. The subsequent glue injection, vibration, curing and discharge steps are performed using the parameters of Example 1.

[0052] The measured residual bubble rate of the finished product in this comparative example ranged from 0.5% to 1.2%, and the curing stress ranged from 2.5 MPa to 3.5 MPa. The residual bubbles in the deep gaps of the capacitor core could not be completely discharged, and the breakdown failure rate of the finished product in the withstand voltage test was higher than that of the finished product in Example 1.

[0053]

[0054] The measured data in the table clearly show that the three sets of embodiments that fully implemented all the process steps of this invention consistently outperformed the three comparative sets with missing core processes in terms of both bubble residue rate and curing stress. Simultaneously, the single-shift production capacity remained in a higher range. The synchronous oscillation, staged vacuuming, and gradient temperature-controlled curing processes have a synergistic effect; the absence of any one step would lead to an increase in the defect rate and a decrease in processing capacity. This demonstrates that the complete process scheme defined in the claims of this invention has a stable and reliable actual processing effect, and that the steps work together to achieve the goal of low-bubble, low-internal-stress, and high-yield thin-film capacitor encapsulation.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A low-stress vacuum potting process for integrated thin-film capacitors, characterized in that, The specific steps of this process are as follows: S100, workpiece clamping and sealing; the thin film capacitor to be processed is placed into the positioning fixture inside the sealed cavity to fix its position, and the cavity door is closed to form an airtight sealed space inside the cavity. S200, staged extraction and degassing; staged extraction is performed inside the sealed cavity to gradually reduce the internal air pressure and complete the removal of gas trapped inside the thin-film capacitor core. S300, synchronous potting oscillation; maintain the vacuum environment inside the sealed cavity, inject potting compound into the inside of the film capacitor shell, and apply mechanical oscillation to the film capacitor simultaneously during the potting process; S400, gradient temperature control curing; maintain the sealed state of the cavity, perform segmented heating and heat preservation treatment on the internal environment of the cavity, and perform linear cooling operation after the cross-linking reaction of the potting colloid is completed. S500, depressurize and cool the material; introduce external gas into the sealed cavity to release the internal vacuum, open the cavity door and take out the potted and cured film capacitor.

2. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S100, the positioning fixture is set above the worktable inside the sealed cavity. It has a detachable structure and is rigidly locked to the worktable of the cavity by quick clamps. A six-degree-of-freedom limiting groove is opened on the surface of the fixture. The single-sided assembly gap between the limiting groove and the capacitor shell is in the range of 0.1mm to 0.3mm. A silicone rubber or polyurethane damping pad with a thickness of 3mm to 8mm is bonded to the bottom of the fixture. The pad completely fits the bottom surface of the fixture and the worktable surface. A fluororubber O-ring is installed at the fitting position of the cavity door. The temperature resistance range of the sealing ring is -40℃ to 200℃. The overall airtight seal of the cavity is formed by extrusion deformation.

3. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S100, the positioning fixture can be replaced and disassembled according to the shape and specifications of the film capacitor. The limiting groove is divided into a rectangular groove suitable for a square shell and a circular groove suitable for a cylindrical shell. The overall disassembly and assembly of the fixture takes ≤5 minutes. After the fixture is replaced, it can be used by simply re-locking it with clamps. The replacement of the fixture does not require any modification to the main structure of the sealed cavity. The replaced positioning fixture can stably constrain film capacitors of different shapes and sizes.

4. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S200, the staged evacuation process employs a two-stage pump set connected in series to regulate the cavity pressure. The two-stage pump sets are connected to the cavity via a DN32 stainless steel pipeline. The first-stage actuator is a rotary vane vacuum pump, which first evacuates the cavity pressure to the range of -0.08MPa to -0.06MPa and maintains the pressure for 3 to 8 minutes. The second-stage actuator is a Roots vacuum pump, which, after being activated in tandem, evacuates the cavity pressure to below -0.095MPa and maintains the pressure for 3 to 8 minutes. The cavity assembly range is 1×10⁻⁶. 5 Pa to 1×10 -1 The Pa capacitive thin-film vacuum sensor collects the air pressure value and controls the start and stop of the pump group in real time, so that the fluctuation range of the vacuum degree of the cavity is controlled within ±0.002MPa throughout the process.

5. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S300, the colloid delivery is driven by a gear metering pump with a flow metering accuracy of ±1%. The dispensing execution end is a lifting dispensing nozzle driven by a servo motor and ball screw, with a lifting stroke of 0-200mm and a positioning accuracy of ±0.5mm. After the dispensing nozzle descends to the bottom of the capacitor housing, it rises uniformly at a speed of 0.5-2mm / s. The colloid delivery flow rate is constantly set to 5g / min-20g / min. A pressure stabilizing valve is connected in series in the colloid delivery pipeline to lock the pipeline pressure fluctuation within ±0.02MPa. The dispensing nozzle outlet diameter is divided into three specifications according to the colloid viscosity: 1-2mm diameter for colloids with viscosity of 1000-3000mPa·s, 2-3mm diameter for colloids with viscosity of 3000-6000mPa·s, and 3-5mm diameter for colloids with viscosity of 6000-10000mPa·s.

6. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S300, the mechanical vibration is output by an electromagnetic vibrator embedded in the bottom of the workbench. The vibration force is transmitted vertically upward to the capacitor housing through the locking and fixed positioning fixture. The vibration frequency ranges from 5Hz to 30Hz, the amplitude ranges from 0.1mm to 0.3mm, and the excitation force output by the vibrator ranges from 0N to 500N. The damping pad at the bottom of the fixture absorbs the high-frequency resonance generated by the vibration. The vibration start and stop times are completely synchronized with the glue injection start and stop times, and the vibration duration completely covers the entire glue injection process.

7. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S400, the gradient temperature control curing step involves arranging electric heating components in sections on the sidewalls and bottom of the cavity, with a heating rate range of 0.5℃ / min to 2.0℃ / min. After heating, three constant temperature zones are set: the first zone is 60℃ to 80℃, the second zone is 80℃ to 100℃, and the third zone is 100℃ to 120℃. The holding time for each zone is matched according to the potting compound material. A PT100 platinum resistance temperature sensor is arranged inside the cavity, with a single-point temperature measurement accuracy of ±0.1℃. Temperature control adopts PID closed-loop regulation, and the overall temperature fluctuation range of the cavity is ±1℃. The cavity is maintained in a vacuum-sealed state throughout the heating process.

8. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S400, the cooling operation is initiated after all the segmented heating and heat preservation processes are completed. The cooling structure consists of a combination of an air-cooled radiator and a water-cooled coil. The cooling medium is compressed air or circulating cooling water. The overall cooling rate is locked in the range of 0.5℃ / min to 1.0℃ / min until the internal temperature of the cavity drops to 60℃ and the cooling output stops. During the cooling stage, temperature data is continuously uploaded to dynamically adjust the supply flow of the cooling medium and gradually reduce the internal ambient temperature of the cavity.

9. The integrated low-stress vacuum potting process for thin-film capacitors according to claim 1, characterized in that, In step S500, after the internal temperature of the cavity drops to the range of 40℃ to 60℃, the pressure relief and cooling discharge step introduces dust-removing, dehumidifying, and drying air to release the internal vacuum. The air inlet valve is gradually adjusted to open. After the internal pressure of the cavity is consistent with the external atmospheric pressure, the hatch is opened and the quick clamp is released to take out the finished capacitor.

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