Accelerated plasma device for cleaning PCB (Printed Circuit Board)

Abstract

The invention discloses an accelerated plasma device for cleaning a PCB (Printed Circuit Board). The accelerated plasma device comprises a Boost PFC (Power Factor Correction) circuit, a full-bridge inverter circuit, a high-frequency transformer and a cyclotron, during working, the commercial power AC 200V is rectified and boosted to DC 380V through the Boost PFC circuit; the full-bridge inverter circuit inverts the current into high-frequency alternating current; the high-frequency transformer is boosted to 10KV to generate plasma containing positive ions, electrons and neutral particles. Then, a magnetic field is introduced, positive ions and electrons are made to move along different tracks through Lorentz force, and effective separation is achieved. The separated positive ions enter a cyclotron and are continuously accelerated under the action of an alternating electric field and a uniform magnetic field, the movement radius is gradually increased, and finally high energy is obtained. And the accelerated positive ions and the previously separated electrons are recombined and jointly act on the oxide layer on the surface of the circuit board. The method is suitable for application scenes requiring high-precision, high-efficiency and low-damage PCB surface treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plasma cleaning, in particular to an accelerated plasma device for cleaning PCB. BACKGROUND

[0002] As a non-contact and non-pollution precision cleaning method, plasma cleaning technology has shown significant advantages in the field of electronic manufacturing, especially in the removal of surface oxide layer and organic contaminants of printed circuit board (PCB). Atmospheric pressure plasma has become a research and application hotspot in this field due to its characteristics of not requiring a vacuum environment and easy operation.

[0003] However, there are still some key performance bottlenecks in existing atmospheric pressure plasma cleaning technology. First, in terms of cleaning efficiency, the average kinetic energy of ions generated by conventional plasma sources (such as dielectric barrier discharge and corona discharge) is generally low (usually less than 30 eV), which limits the physical bombardment capability of the plasma on the micron-scale oxide layer on the surface of the circuit board, resulting in insufficient cleaning depth and difficulty in completely removing stubborn contaminants.

[0004] Secondly, in terms of cleaning quality, the spatial distribution of active particles (such as ions and free radicals) in the plasma jet is often uneven, and the ion energy dispersion is large, which easily leads to regional differences in the cleaning effect on the surface of the circuit board, affecting the reliability of subsequent precision welding or coating processes.

[0005] More importantly, in terms of process safety, the continuous bombardment of high-energy ions on the substrate can cause the accumulation of positive charges on the surface, which in turn can cause unavoidable electrochemical corrosion (i.e., "plasma damage"), forming an inherent contradiction that "the more thorough the cleaning, the higher the risk of electrochemical damage to the substrate", which seriously restricts the application of this technology in high-end precision circuit board cleaning.

[0006] In addition, in terms of system energy efficiency and compatibility, the power supply system of existing plasma cleaning equipment mostly uses conventional AC-DC-AC conversion topology, and the poor PFC performance of the front-stage power factor correction (PFC) can inject harmonics into the power grid, while the efficiency, frequency stability and matching degree of the plasma load of the rear-stage inverter and high-voltage generation circuit also need to be optimized, which affects the overall system energy efficiency and long-term operation reliability.

[0007] Therefore, there is an urgent need in the industry for a new type of plasma cleaning technology and device that can simultaneously achieve deep, uniform and non-damaging cleaning, and has high system energy efficiency and stable operation, to break through the current technical bottlenecks. SUMMARY

[0008] In view of the deficiencies of the prior art, such as insufficient cleaning depth caused by low ion kinetic energy (usually less than 30eV), poor cleaning uniformity caused by uneven spatial distribution of active particles, and defects such as charge accumulation and electrochemical corrosion of the substrate caused by high-energy ion bombardment, an innovative solution is proposed.

[0009] To achieve the above-mentioned purpose, the application provides an accelerating plasma device for cleaning PCB, comprising: a power factor correction circuit, an inverter circuit, a high-frequency voltage boosting circuit and a cyclotron.

[0010] The power factor correction circuit is connected to the input end of the alternating current power supply, and the output end is connected to the input end of the inverter circuit, which is used to rectify and boost the alternating current power supply to a stable direct current.

[0011] The input end of the inverter circuit is connected to the output end of the power factor correction circuit, and the output end is connected to the input end of the high-frequency voltage boosting circuit, which is used to invert the direct current into high-frequency alternating current.

[0012] The input end of the high-frequency voltage boosting circuit is connected to the output end of the inverter circuit, and the output end is connected to the cyclotron, which is used to boost the high-frequency alternating current to high voltage.

[0013] The cyclotron is connected to the output end of the high-frequency voltage boosting circuit, which is used to generate plasma with the high voltage and to screen and accelerate the charged particles in the plasma multiple times.

[0014] As an improved scheme of the application, the power factor correction circuit is a Boost PFC circuit based on voltage and current double-loop PI control, which is configured to convert 220V alternating current power supply into 380V direct current.

[0015] As an improved scheme of the application, the inverter circuit is a full-bridge inverter circuit, which is configured to invert 380V direct current into 10KHz sine alternating current.

[0016] As an improved scheme of the application, the high-frequency voltage boosting circuit is a high-frequency transformer, which is configured to boost 10KHz alternating current to 10KV high voltage.

[0017] As an improved scheme of the application, the cyclotron comprises a pair of D-shaped boxes placed in a uniform magnetic field and a high-frequency alternating electrode arranged in the gap therebetween, the uniform magnetic field is used for screening charged particles, and the high-frequency alternating electrode is used for multiple acceleration of positive ions in cooperation with the uniform magnetic field.

[0018] As an improved scheme of the present application, the device is configured to make the kinetic energy of the positive ions after the cyclotron acceleration exceed 100eV by adjusting the magnetic field intensity and the acceleration voltage.

[0019] As an improved scheme of the present application, the cyclotron accelerator is further configured to make the high-energy positive ions after the acceleration and the electron flow filtered by the magnetic field meet at the output port, form a high-energy plasma beam of electric neutrality and direct to the cleaning surface of the circuit board.

[0020] The present application has the advantages that compared with the prior art, the acceleration plasma device for cleaning the PCB provided by the present application comprises a power factor correction circuit, an inverter circuit, a high-frequency voltage boosting circuit and a cyclotron accelerator. In the working process, the front-stage circuit converts the commercial power into high-frequency high-voltage power efficiently and stably to supply the cyclotron accelerator. The cyclotron accelerator first filters the initial plasma by using the uniform magnetic field to separate the positive ions from the electrons; then, the positive ions are accelerated back and forth in the D-shaped box gap under the synergistic action of the alternating electric field and the magnetic field, and the kinetic energy is accumulated and increased; finally, the high-energy positive ions are mixed with the controlled electron flow and shot out to act on the surface of the circuit board. The innovation of the system is that the cyclotron acceleration principle is introduced into the industrial plasma cleaning field for the first time, the ion kinetic energy is actively accelerated to more than 100eV, the magnetic field filtering and charge neutralization mechanism are combined, and the three technical difficulties of the conventional technology, i.e., the shallow cleaning depth, the poor uniformity and the easy electrochemical damage to the substrate, are solved, so that the efficient, uniform and non-damaging deep cleaning of the oxide layer and the pollutants of the circuit board is realized. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a Boost PFC circuit simulation topology graph of an embodiment of the present application;

[0022] Figure 2 It is an input voltage and current waveform graph of the Boost PFC circuit of an embodiment of the present application;

[0023] Figure 3 It is an output voltage waveform graph of the Boost PFC circuit of an embodiment of the present application;

[0024] Figure 4 It is a full-bridge inverter circuit simulation topology graph of an embodiment of the present application;

[0025] Figure 5 It is an output voltage and current waveform graph of the full-bridge inverter circuit of an embodiment of the present application;

[0026] Figure 6 It is a Boost PFC and full-bridge inverter circuit cascade simulation topology graph of an embodiment of the present application;

[0027] Figure 7A flow chart of the working process of the accelerated plasma device for cleaning PCBs in the present application;

[0028] Figure 8 A structural schematic diagram of the accelerated plasma device for cleaning PCBs in the present application.

[0029] The main element symbols are explained as follows:

[0030] 1, uniform magnetic field; 2, first high-frequency alternating electrode; 3, second high-frequency alternating electrode; 4, D-shaped box; 5, insulating isolation block; 6, beam extraction magnetic field DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with the accompanying drawings.

[0032] In the following description, the example details are given in order to provide a more in-depth understanding of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. It should be understood that the described specific embodiments are only used to explain the present application, and are not used to limit the present application.

[0033] It should be understood that when the terms "comprising" and / or "including" are used in the specification, it means that the features, integers, steps, operations, elements, or components described in the specification exist, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

[0034] As shown in Figure 1 , Figure 4 and Figure 6 The accelerated plasma device for cleaning PCBs provided by the present application is composed of four functional modules connected in sequence: power factor correction circuit, inverter circuit, high-frequency voltage boosting circuit and cyclotron.

[0035] Regarding the power factor correction circuit: the power factor correction circuit is used as the front end of the system to realize efficient electric energy conversion and grid harmonic suppression. Referring to Figure 1The simulation topology shown, its specific components include: including rectifier bridge, Boost inductance, switch tube, freewheeling diode, output capacitor and voltage and current double closed loop PI control module. The input end of the rectifier bridge is connected to 220V AC mains; the Boost inductance and the switch tube are connected in series and connected between the output end of the rectifier bridge and the subsequent circuit; the voltage and current double closed loop PI control module collects the output voltage and inductance current signal, the voltage outer ring compares the output voltage with the 380V reference value and outputs the current amplitude reference signal through the PI regulator, and the current inner ring generates a sinusoidal current reference according to the reference signal and the input voltage waveform, and compares it with the actual inductance current, and generates a drive signal to control the on-off of the switch tube after PI regulation and PWM modulation. The circuit is configured to make the input current waveform track the input voltage phase in real time, thereby improving the power factor to close to 1, while outputting stable 380V DC voltage. As shown in the simulation results of Figure 2 and Figure 3 , the input current and voltage are in phase and the waveform is high in sinusoidal degree, and the output voltage is stable at DC 380V.

[0036] Regarding the inverter circuit: the input end of the inverter circuit is connected to the output end of the power factor correction circuit, for converting direct current into high-frequency alternating current. Referring to Figure 4 , in one embodiment, the circuit is a full-bridge inverter circuit, characterized by including a full-bridge main circuit composed of four switch tubes and a corresponding double-loop control circuit. The double-loop control circuit includes a voltage outer ring and a current inner ring, the voltage outer ring compares the output voltage feedback with a 10KHz sinusoidal reference signal, and the current inner ring is used to improve the dynamic response speed of the system. The output of the controller is modulated by SPWM to generate four drive signals, which control the on-off timing of the four switch tubes in the full-bridge main circuit. The circuit is configured to invert 380V DC into a pure sinusoidal AC with a frequency of 10KHz. As shown in the simulation waveform of Figure 5 , the output voltage and current are sinusoidal waves with stable frequency.

[0037] Regarding the high-frequency boost circuit: the input end of the high-frequency boost circuit is connected to the output end of the inverter circuit. The circuit is usually realized by a high-frequency transformer, characterized in that the primary winding receives 10KHz medium voltage alternating current output by the inverter circuit, and through electromagnetic induction, a high-voltage alternating current of 10kV level is induced on the secondary winding. This high voltage is the energy required for the cyclotron to provide ionized gas and establish an acceleration field.

[0038] Regarding the cyclotron: this module is the core innovative component of the invention, used for screening and kinetic energy enhancement of ions in plasma. Its working principle and process are shown in Figure 7 and Figure 8 .Figure 8 As shown, its core includes a pair of D-shaped boxes placed in a uniform magnetic field, and an alternating electrode placed in the gap between the D-shaped boxes and connected to a high-frequency high-voltage power supply. After the working gas is ionized to generate plasma, in the uniform magnetic field, the positive ions and electrons are separated in trajectory by the Lorentz force. The positive ions make circular motion in the magnetic field, and each time they pass through the gap between the D-shaped boxes, they obtain acceleration in the direction-synchronous high-voltage alternating electric field, and the kinetic energy (following the formula ) and the motion radius (following the formula ) are increased successively. Through multiple cycles of acceleration, the ion kinetic energy can be accumulated to more than 100 eV. The accelerated high-energy ions and the controlled electron stream are mixed in the outlet area to form an electrically neutral high-energy plasma beam and are output.

[0039] The working process of the application is as follows:

[0040] Electric energy pretreatment and conversion: the alternating current is converted into high-quality 380V direct current through the power factor correction circuit; the direct current is converted into 10KHz sinusoidal alternating current through the inverter circuit; and then the high-frequency voltage is raised to 10kV through the high-frequency voltage raising circuit.

[0041] Plasma generation and screening: the high-voltage electricity is loaded to the cyclotron, and the working gas is ionized to generate plasma. The plasma enters the uniform magnetic field (1), and the positive ions and electrons are spatially separated due to the opposite directions of the Lorentz force.

[0042] Ion acceleration and neutralization and cleaning: the separated positive ions are repeatedly accelerated to high kinetic energy in the D-shaped box (4). The accelerated high-energy ion beam is mixed with the controlled electron stream in the outlet area to form an electrically neutral high-energy plasma beam, which finally acts on the surface of the circuit board to realize deep, uniform and charge-damage-free cleaning.

[0043] (1) In the power factor correction circuit, the parameters (proportional gain Kp and integral gain Ki) of the double closed-loop PI controller can be optimized and set according to the actual circuit component parameters to achieve the best balance between dynamic performance and stability.

[0044] (2) The uniform magnetic field (1) in the cyclotron can be adjusted in the range of 0.2T to 0.8T to adapt to different ion masses (such as Ar⁺, O⁺) and different target energies (such as 50eV-200eV) for cleaning requirements.

[0045] (3) The system can integrate a closed-loop control module to monitor the load impedance or the optical emission spectrum of the plasma, and feedback adjust the output frequency of the inverter circuit or the output voltage of the high-frequency voltage raising circuit in real time to maintain the best stability of the plasma generation and acceleration process.

[0046] The advantages of the present application are:

[0047] The problem of insufficient cleaning depth is solved: by introducing a cyclotron acceleration mechanism, the kinetic energy of cleaning ions is increased from the conventional 30eV to more than 100eV, significantly enhancing the physical bombardment effect, making it possible to completely remove stubborn contaminants in deep layers.

[0048] The excellent uniformity of cleaning effect is ensured: the uniform magnetic field is used to screen and constrain the plasma components, and the output high-energy particle beam is highly consistent in space and energy distribution, thereby achieving uniform and reliable cleaning of the entire surface of the circuit board.

[0049] The risk of substrate damage is eliminated from the root: innovatively, the high-energy ion and electron are combined before the beam output, and the output is absolutely electrically neutral plasma. This fundamentally eliminates the accumulation of positive charges on the surface of the precision circuit board and the resulting electrochemical corrosion, achieving "zero damage" in the cleaning process.

[0050] The cornerstone of an efficient and green system is built: the front-end high-power factor correction technology greatly reduces the harmonic pollution to the power grid and improves the power utilization rate; the efficient design and collaborative work of various circuits provide a stable and reliable power source for the entire system, ensuring the energy efficiency and reliability of long-term operation.

[0051] The above only discloses several specific embodiments of the present application, but the present application is not limited thereto, and any changes that can be thought of by those skilled in the art shall fall within the protection scope of the present application.

Claims

1. An accelerated plasma device for cleaning PCB boards, characterized in that, include: Power factor correction module, inverter module, high-frequency boost module, and cyclotron accelerator module; A power factor correction module, the input of which is connected to AC mains power and the output of which is connected to the input of the inverter module, is used to rectify and boost the AC mains power into a stable DC power. An inverter module, the input terminal of which is connected to the output terminal of the power factor correction module, and the output terminal of which is connected to the input terminal of the high-frequency boost module, is used to invert the DC power into high-frequency AC power; A high-frequency boost module, wherein the input terminal of the high-frequency boost module is connected to the output terminal of the inverter module, and the output terminal is connected to the cyclotron module, for boosting the high-frequency AC power to high voltage; A cyclotron module, which is connected to the output of the high-frequency boost module, is used to generate plasma using the high voltage and to sift and accelerate charged particles in the plasma.

2. The accelerated plasma device for cleaning PCB boards according to claim 1, characterized in that, The power factor correction module is a Boost PFC circuit based on voltage and current dual closed-loop control, which is configured to convert 220V AC to 380V DC.

3. The accelerated plasma device for cleaning PCB boards according to claim 1, characterized in that, The inverter module is a full-bridge inverter circuit, configured to invert 380V DC power into sinusoidal AC power with a frequency of 10KHz.

4. The accelerated plasma device for cleaning PCB boards according to claim 1, characterized in that, The high-frequency boost module is a high-frequency transformer, which is configured to boost 10KHz AC power to 10KV high voltage.

5. The accelerated plasma device for cleaning PCB boards according to claim 1, characterized in that, The cyclotron module includes: A pair of D-shaped boxes placed in a uniform magnetic field; A high-frequency alternating electrode is disposed in the gap of the D-shaped box and connected to the output terminal of the high-frequency boost module; The uniform magnetic field is configured to apply a Lorentz force to the plasma in order to achieve trajectory separation of positive ions and electrons. The high-frequency alternating electrode and the uniform magnetic field work together to accelerate the positive ions entering the gap of the D-shaped box multiple times.

6. The accelerated plasma device for cleaning PCB boards according to claim 5, characterized in that, The device is configured to control the strength of the uniform magnetic field and the voltage of the high-frequency alternating electrode to make the kinetic energy of the positive ions after multiple accelerations exceed 100 eV.

7. The accelerated plasma device for cleaning PCB boards according to claim 5 or 6, characterized in that, The cyclotron module is also configured to allow the screened and accelerated positive ions to merge with the separated electron stream in the exit region, forming an electrically neutral high-energy plasma beam that is guided to the clean surface of the circuit board.

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