Apparatus and method for atmosphere control of plasma

Abstract

The present application discloses a device and method for atmosphere control by plasma for removing residues in an at least partially closed chamber. A reactive gas is formed from a gas mixture, the reactive gas comprising an inert gas and / or a reducing gas; the reactive gas is delivered into a plasma generation system, the generated plasma is introduced into the at least partially closed chamber; the plasma diffuses and reacts with the residues in the chamber until the concentration of the residues is reduced to below a preset value. The technical solution of the present application is particularly suitable for situations where the atmosphere needs to be quickly switched and quickly reduced to an extremely low oxygen content.

Description

Technical Field

[0001] This invention relates to apparatus and methods for controlling the atmosphere in a chamber. More particularly, it relates to an apparatus and method for removing residual oxygen from a chamber to control the atmosphere. Specifically, it relates to an apparatus and method for controlling the atmosphere using plasma. Background Technology

[0002] Many processes, such as reflow soldering, require an atmosphere with extremely low oxygen levels. This typically involves purging with an inert gas for protection, placing the packaged component in an environment with reduced oxygen and moisture content. This environment can be a vacuum, a nitrogen-filled chamber, or a room. In some processes that are highly sensitive to residual oxygen (ROL) concentrations, ROL needs to be controlled below 5 ppm. Residual oxygen concentration is generally reduced through gas exchange with an inert gas (such as pure nitrogen). As the residual oxygen concentration decreases, the efficiency of this inert gas exchange decreases further. Although the exchange efficiency can be significantly improved in some vacuum furnaces, vacuum furnaces are very expensive. Some vacuum furnaces can cost up to five times more than atmospheric pressure furnaces.

[0003] US Patent No. 9539672B2 discloses a portable device for monitoring and controlling the oxygen level in a reflow oven atmosphere. The device includes a nitrogen injection flow control unit, a data acquisition and analysis unit, etc. A reflow oven is a heating device used to solder electronic components onto printed circuit boards using surface mount technology (SMT). There may be some waste or insufficiency of nitrogen in the reflow oven atmosphere. This insufficiency results in a high oxygen level in the soldering environment / spotlight, which can lead to soldering defects such as open circuits, solder balls, short circuits, etc. This portable device is used to control the oxygen concentration in the reflow oven environment to below 3000 ppm. During monitoring, if the device detects excessive oxygen in the reflow oven environment, such as an oxygen level higher than a previously predetermined level by the user, the device automatically injects more nitrogen into the reflow oven until the predetermined level is reached.

[0004] Chinese patent CN101268411B discloses a method for manufacturing an electronic device. The roughness and material of the inner surface of the heating equipment significantly affect the content of impurities such as oxygen and moisture in the heating atmosphere. Controlling the residual oxygen content in the heating atmosphere is effective in improving the transparency of thermosetting resins. The atmosphere is replaced with an inert gas, and the residual oxygen concentration in the atmosphere is controlled to below 10 ppm. When the residual oxygen concentration is above 10 ppm, the oxidative deterioration of the thermosetting resin begins, resulting in decreased transparency. Summary of the Invention

[0005] The general objective of this disclosure is to expose the space and atmosphere in a chamber to plasma treatment, thereby removing residual oxygen and achieving atmosphere control.

[0006] The first aspect of this application provides a method for plasma atmosphere control to remove residues from at least a partially enclosed chamber, the method comprising:

[0007] A reactive gas is formed from a gas mixture, said reactive gas comprising an inert gas and / or a reducing gas;

[0008] The reactive gas is delivered to the plasma generating system, and the generated plasma is introduced into a chamber that is at least partially enclosed.

[0009] The plasma diffuses and reacts with the residue in the chamber until the residue concentration drops below a preset value.

[0010] Furthermore, the reactive gas includes inert gas and reducing gas.

[0011] Furthermore, the residue includes residual oxygen.

[0012] Furthermore, the preset value is 500 ppm, preferably 200 ppm, more preferably 100 ppm, even more preferably 50 ppm, most preferably 10 ppm, or even 5 ppm.

[0013] Furthermore, the inert gas in the reactive gas includes nitrogen, helium, and / or argon.

[0014] Furthermore, the reducing gas in the reactive gas includes hydrogen and / or methane, preferably hydrogen.

[0015] Furthermore, the volume fraction of the reducing gas in the reactive gas ranges from 0.1% to 4%, preferably from 1% to 3%.

[0016] Taking nitrogen as the inert gas and hydrogen as the reducing gas as an example, a plasma gun is configured to generate a plasma of hydrogen and nitrogen. Hydrogen ions and some free radicals rapidly react with residual oxygen, quickly reducing the amount of residual oxygen in the device.

[0017] For example, reactive gases are supplied by a cylinder supply system. The cylinders store inert and reducing gases, and the high-pressure gas can be reduced to the required operating pressure via a pressure reducing valve and delivered to the point of use via pipeline.

[0018] A second aspect of this application provides an apparatus for plasma atmosphere control, the apparatus comprising:

[0019] A chamber that is at least partially enclosed, the chamber including a top, side walls and a bottom wall, which together define the internal volume of the chamber;

[0020] A plasma generating system generates plasma and introduces it into the at least partially enclosed chamber, whereby the plasma diffuses and reacts with residues in the chamber until the residue concentration decreases to a preset value.

[0021] Furthermore, the plasma generation system includes a plasma spray gun, the nozzle of which is engaged with the top of the chamber.

[0022] Furthermore, the device also includes fans, which are symmetrically distributed at the top of the chamber.

[0023] Compared with the prior art, the technical solution provided in this application has the following advantages:

[0024] 1. The technical solution of this application solves the problem of low efficiency in conventional inert gas replacement, such as the need to reduce the residual oxygen concentration to below 1000 ppm for a long time. Therefore, the technical solution of this application is particularly suitable for situations where the atmosphere needs to be switched quickly and the oxygen content needs to be reduced to extremely low levels rapidly.

[0025] 2. The technical solution of this application can be operated at room temperature and pressure, saving equipment costs.

[0026] 3. The technical solution of this application is particularly suitable for applications that require adjustment of local atmosphere distribution, such as improving the balance of oxygen and nitrogen diffusion in reflow soldering, or in the process of other packaging components. Attached Figure Description

[0027] The advantages and spirit of this application can be further understood through the following detailed description of the invention and accompanying drawings.

[0028] Figure 1 This is a time curve showing the change in residual oxygen concentration in the chambers of Embodiment 1 and Comparative Example 1 of this application.

[0029] Figure 2 This is a schematic diagram of the chamber in Embodiment 1 and Comparative Example 1 of this application.

[0030] In the diagram: 100 represents the chamber, 101 represents the top of the chamber, 102 represents the side wall, 103 represents the bottom wall, 104 represents the fan, and 105 represents the nozzle of the plasma spray gun. Detailed Implementation

[0031] The specific embodiments of this application are described in detail below with reference to the accompanying drawings. However, this application should be understood as not being limited to the embodiments described below, and the technical concept of this application can be implemented in combination with other known technologies or other technologies with the same function as those known technologies.

[0032] In the following description of specific embodiments, in order to clearly illustrate the structure and working method, a number of directional terms will be used for description. However, terms such as "front", "rear", "left", "right", "outer", "inner", "outward", "inward", "axial", and "radial" should be understood as convenient terms and not as limiting terms.

[0033] In the following description of specific embodiments, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the purpose of simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application. Furthermore, when the first structure is described as being positioned "above" or "below" the second structure, this should be understood to mean that the first structure is positioned further away from or closer to the horizontal plane.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and do not refer to a limitation on time sequence, quantity, or importance. They should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated, but are merely used to distinguish one technical feature from another in this technical solution. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified. Similarly, qualifiers such as "a" appearing herein do not refer to a limitation on quantity, but describe technical features not mentioned above. Likewise, unless a noun is modified by a specific quantifier, it should be considered herein to include both singular and plural forms; the technical solution may include either a singular or plural number of that technical feature. Similarly, modifiers such as "approximately" or "approximately" appearing before numerals generally include the number itself, and their specific meaning should be understood in conjunction with the context.

[0035] It should be understood that in this application, "at least one (item)" means one or more, and "more than one" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0036] The terms “unit,” “item,” “object,” and “module” described in this specification refer to a unit for performing at least one function and operation, and can be implemented by hardware components or software components and combinations thereof.

[0037] The terms "high pressure" and "medium pressure" mean that high pressure is higher than medium pressure, so the difference between the two may be relatively small.

[0038] The terms "high temperature" and "low temperature" mean that high temperature is higher than low temperature, so the difference between the two may be relatively small.

[0039] Plasma, the fourth state of matter, is an electrically neutral ionized gas. Any gas can be transformed into plasma by applying sufficient energy to it, generating a large amount of charged matter—electrons and ions. Plasma possesses some properties of gases, but differs from ordinary gases. Plasma responds to both electric and magnetic fields, and these properties are due to the charged matter present in the plasma state.

[0040] A plasma generating system equipped with a plasma nozzle, suitable for performing the methods described in this specification, is, for example, a plasma spray gun sold by Plasmatreat GmbH. For example... Plasma spray guns are used to generate and apply low-temperature plasma to the product or chamber being processed. The plasma is generated by a discharge between the stator and rotor inside the plasma spray gun. The generated plasma is then delivered outside the plasma spray gun through a nozzle.

[0041] Depending on the initiation voltage, power input, initiation method, and electric field configuration, in some embodiments, the plasma power is less than or equal to about 6500 W, further less than or equal to about 1000 W, and further from about 200 W to about 600 W. The plasma frequency can be any suitable frequency. In some embodiments, the plasma has a frequency in the range of about 200 kHz to 30 MHz. In some embodiments, the plasma frequency is less than or equal to about 20 MHz, less than or equal to about 10 MHz, less than or equal to about 5 MHz, less than or equal to about 1000 kHz, or less than or equal to about 500 kHz. In some embodiments, the plasma frequency is greater than or equal to about 210 kHz, greater than or equal to about 250 kHz, greater than or equal to about 600 kHz, greater than or equal to about 750 MHz, greater than or equal to about 1200 kHz, greater than or equal to about 2 MHz, greater than or equal to about 4 MHz, greater than or equal to about 7 MHz, greater than or equal to about 12 MHz, greater than or equal to about 15 MHz, or greater than or equal to about 25 MHz. In one or more embodiments, the plasma has a frequency of about 13.56 MHz, or about 350 kHz, or about 400 kHz, or about 27 MHz, or about 40 MHz, or about 60 MHz.

[0042] The chambers used in this specification can be at least partially enclosed chambers. Contaminants in such chambers include one or more of the following: oxygen, nitrogen, carbon, or halogens (e.g., fluorine, chlorine, bromine, or iodine). In some embodiments, the contaminant is oxygen. "At least partially enclosed" means completely or partially enclosed. The degree of sealing of the chamber is not strictly limited in this application; it can be an open chamber with an opening or a chamber that is closed except for the nozzle inlet.

[0043] Although the invention is described with reference to the chamber shown in the accompanying drawings, the invention can be implemented in other types of chambers. Furthermore, the chamber does not need to be dedicated; it can be combined with other chambers, and multiple operations can be performed in the same or different chambers.

[0044] The apparatus and method of this application are used to rapidly consume residual oxygen in the atmosphere.

[0045] From an economic cost perspective, the first step may optionally involve purging with an inert gas to control the residual oxygen concentration in the atmosphere below a preset value. The type of inert gas is not particularly limited, and may include nitrogen, helium, neon, argon, krypton, or xenon. The preset residual oxygen concentration in the atmosphere is preferably 500 ppm, more preferably 200 ppm, more preferably 100 ppm, and most preferably 50 ppm or even 10 ppm or less than 5 ppm. This preset residual oxygen concentration can be adjusted by those skilled in the art based on the chamber's operating conditions, process requirements, and economic budget.

[0046] Extremely low residual oxygen concentration refers to less than 100 ppm, preferably less than 50 ppm or even less than 10 ppm, more preferably less than 5 ppm or less than 1 ppm.

[0047] Once the residual oxygen concentration in the chamber has decreased to a reasonable range, the second step is to further remove the residual oxygen to below a preset value using plasma containing a reducing gas added to an inert gas. The volume fraction of the reducing gas ranges from 0.1% to 4%, preferably from 1% to 3%. The type of reducing gas used in this invention is not particularly limited, as long as it can undergo an oxidation reaction with the residual oxygen. Common reducing gases include carbon monoxide, methane, ammonia, or hydrogen. However, from the perspective of achieving a good reduction effect and high gas purity, hydrogen is preferred.

[0048] Unless otherwise clearly indicated, each aspect or embodiment defined herein may be combined with any other aspect or embodiment. In particular, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous.

[0049] Specific embodiments of this application are described in detail below with reference to the accompanying drawings. Embodiments are present throughout multiple views of the drawings. The same reference numerals in the embodiments generally denote the same or corresponding elements. Therefore, the description of the embodiments is incorporated herein by reference, and descriptions of common subject matter across embodiments are generally not repeated herein.

[0050] Some embodiments of methods for removing residual oxygen from a chamber are provided. However, the methods disclosed herein, or other methods shown and / or described herein, may be shown and / or described as a series of actions or events. It should be understood that the order in which these actions or events are shown should not be interpreted in a limiting sense. For example, some actions may be performed in a different order and / or simultaneously with the actions or events shown and / or described herein. Furthermore, not all shown actions are required to implement one or more aspects or embodiments of this disclosure, and one or more actions of this disclosure may be performed as one or more separate actions and / or stages.

[0051] A plasma generation system, acting as a plasma initiation device, typically includes a high-voltage power supply, electrodes, and a trigger. The high-voltage power supply provides the necessary electrical energy. The electrodes are used to generate an electric arc or plasma. The trigger is used to control the start and stop of the arc. Taking a plasma nozzle as an example, its design depends on the specific application requirements. A plasma nozzle typically consists of an inlet, a mixing chamber, and an outlet. The inlet of the plasma nozzle is used to introduce the gas mixture. The mixing chamber of the plasma nozzle is used to mix the gas mixture with the energy required for plasma excitation. The plasma generated in the plasma nozzle is released through the nozzle outlet.

[0052] As illustrated in this article, the chamber is kept at normal temperature and pressure. The instrument used to detect the oxygen concentration within the chamber is not particularly limited. Oxygen analyzers well-known to those skilled in the art can detect residual oxygen concentration, such as fuel cell-based trace oxygen analyzers.

[0053] The initial atmosphere is defined as one where the residual oxygen concentration in the chamber exceeds a certain range, specifically 200,000 ppm. The goal is to reduce the residual oxygen concentration in the atmosphere to 50 ppm.

[0054] The following Example 1 uses the above-described scheme of this application for plasma de-oxygenation. The following Comparative Example 1 uses a conventional nitrogen replacement method. Figure 2 The dynamic curves of both are shown.

[0055] Example 1:

[0056] A glove box with a volume of 810L is used as the chamber.

[0057] Figure 1 A schematic diagram of a plasma processing chamber is shown according to some embodiments. The chamber 100 generally includes a top 101, side walls 102, and a bottom wall 103, collectively defining the internal volume of the plasma processing chamber. At least one plasma gun nozzle 105 is engaged with the top 101 of the chamber, allowing reactive gas exiting the nozzle 105 to be introduced into the chamber 100. The plasma gun nozzles 105 are symmetrically distributed within the chamber 100. Typically, chambers 100 with a volume of 1000 L or less are configured with one or two plasma guns.

[0058] A reactive gas containing inert and reducing gases can be supplied to the plasma torch. The reactive gas can be supplied from a storage tank containing one or more raw materials. The reactive gas is exposed to a plasma source to generate plasma, including free radicals, ions, and other reactive substances of the reactive gas. The reactive gas is introduced into the chamber 100 through nozzle 105 of the plasma torch to consume residual oxygen in the chamber 100. Free radicals, ions, and other reactive substances can circulate within the chamber 100 by the rotation of fan 104. The circulating plasma is uniformly distributed around the chamber 100 at a sufficient speed to effectively react with residual oxygen and minimize the formation of dead zones. The configuration of fan 104 is adjusted according to the internal conditions of the chamber 100. Exemplarily, fans 104 are symmetrically distributed at the top of the chamber 100.

[0059] The initial oxygen concentration [O2]0 in the initial atmosphere is 200,000 ppm. The desired final residual oxygen concentration [O2] is 50 ppm. Assume the plasma combustion rate constant k is 0.00289 s^-1, where d[O2] / dt = -k×[O2].

[0060] A mixture of hydrogen and nitrogen was used as the reactive gas. The total flow rate of the reactive gas, F, was 30 L / min. The proportion of hydrogen in the reactive gas was 4%. Depending on the power of the plasma torch, the conversion rate of the reactive gas to plasma was assumed to be 30%. That is, it is assumed that 30% of the mixture was converted into plasma capable of reacting with residual oxygen. It is known to those skilled in the art that although the plasma deoxygenation process generates a very small amount of water vapor, many efficient and inexpensive methods are known to remove this water vapor.

[0061] Therefore, the hydrogen flow rate F_H2 = 0.04 × 30 L / min = 1.2 L / min.

[0062] The hydrogen plasma flow rate F_H2(plasma) = 0.3 × 1.2 L / min = 0.36 L / min.

[0063] The effective rate constant for the reaction between the plasma and residual oxygen, taking into account the dilution effect, is as follows:

[0064] K (effective) =k+F / V=0.00289+(30 / 60) / 810≈3.51×10^-3 s^-1

[0065] After the plasma is introduced into the chamber, nitrogen replacement and hydrogen plasma deoxygenation reactions occur simultaneously within the chamber.

[0066] The equation for the change in oxygen concentration consumed by hydrogen plasma over time is: O2=[O2]0 e^(-K (effective) ×t)

[0067] The equation for the change in oxygen concentration consumed by nitrogen replacement is: O2=[O2]0 e^(-F / V×t).

[0068] like Figure 2 As shown in the dotted-line diagram, when the nitrogen replacement and hydrogen plasma deoxygenation reactions are carried out simultaneously, it takes 39.64 minutes for the residual oxygen concentration to decrease from 200,000 ppm to 50 ppm.

[0069] Comparative Example 1:

[0070] The same chamber configuration as in Example 1 is used. Nitrogen gas is introduced into the chamber to replace residual oxygen and remove it from the chamber. This process produces a controlled atmosphere acceptable to many processes. Maintaining a certain purging rate allows the residual oxygen concentration to continue to decrease. Some commercial furnaces of Carbolite Gero employ this principle.

[0071] from Figure 2 As shown in the solid line graph, reducing the residual oxygen concentration to 50 ppm requires 240.02 minutes using only nitrogen purging. In contrast, plasma deoxidation takes only 39.64 minutes. This application's solution solves the problem of low efficiency when using only inert gas purging, making it particularly suitable for situations requiring rapid removal of residual oxygen from the atmosphere, and even more so for applications requiring extremely low residual oxygen concentrations.

[0072] The embodiments described in this specification are merely preferred embodiments of this application. These embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of this application. Any technical solutions that can be obtained by those skilled in the art based on the concept of this application through logical analysis, reasoning, or limited experimentation should be within the scope of this application.

Claims

1. A method for plasma atmosphere control for removing residues from at least a partially enclosed chamber, characterized in that, The method includes: A reactive gas is formed from a gas mixture, said reactive gas comprising an inert gas and / or a reducing gas; The reactive gas is delivered to the plasma generating system, and the generated plasma is introduced into the at least partially enclosed chamber; The plasma diffuses and reacts with the residue in the chamber until the residue concentration drops below a preset value.

2. The method according to claim 1, characterized in that, The reactive gases include inert gases and reducing gases.

3. The method according to claim 1 or 2, characterized in that, The residue includes residual oxygen.

4. The method according to claim 3, characterized in that, The preset value is 200 ppm, preferably 100 ppm, more preferably 50 ppm, and most preferably 10 ppm.

5. The method according to claim 1 or 2, characterized in that, The inert gases in the reactive gases include nitrogen, helium, and / or argon.

6. The method according to claim 1 or 2, characterized in that, The reducing gas in the reactive gas includes hydrogen and / or methane, preferably hydrogen.

7. The method according to claim 6, characterized in that, The volume fraction of the reducing gas in the reactive gas ranges from 0.1% to 4%, preferably from 1% to 3%.

8. An apparatus for plasma atmosphere control, characterized in that, The device includes: A chamber that is at least partially enclosed, the chamber including a top, side walls and a bottom wall, which together define the internal volume of the chamber; A plasma generating system generates plasma and introduces it into the at least partially enclosed chamber, whereby the plasma diffuses and reacts with residues in the chamber until the residue concentration decreases to a preset value.

9. The apparatus according to claim 8, characterized in that, The plasma generation system includes a plasma spray gun, the nozzle of which is engaged with the top of the chamber.

10. The apparatus according to claim 8, characterized in that, The device also includes fans, which are symmetrically distributed at the top of the chamber.

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