A method for removing trace metal element contaminants between lines of a flexible circuit board

Abstract

This invention discloses a method for removing trace metallic element contaminants between lines on a flexible circuit board, belonging to the field of semiconductor manufacturing technology. The method includes: placing the flexible circuit board in a processing chamber of a plasma device and evacuating it to a vacuum level of 1×10⁻⁶. ‑6 Below Torr; a reaction gas containing O2, CF4, and Ar is introduced, and the chamber pressure is controlled at 200~250 mTorr. Radio frequency energy is applied to generate plasma, and the reaction temperature is controlled between room temperature and 60°C. F· free radicals in the plasma penetrate to the bottom of the inter-line trenches and react with metal element contaminants to form metal fluorides. Under chamber pressure, these fluorides desorb into a gaseous state and diffuse into the chamber. The gaseous metal fluorides are then removed to complete the cleaning process. This invention achieves effective penetration of F· free radicals into high aspect ratio trenches and low-damage cleaning of the circuitry through the synergistic combination of a low-pressure environment and a low CF4 flow rate. The metal removal rate can reach 99%, and the product damage rate can be controlled below 2%, making it suitable for the large-scale production of various FPCs.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board manufacturing, and more specifically to a method for removing trace metal element contaminants between lines of a flexible circuit board. Background Technology

[0002] As integrated circuit manufacturing technology continues to evolve towards finer scales, device feature sizes are shrinking, with linewidths and spacings reaching the order of tens of micrometers. In such high aspect ratio line structures, even minute amounts of contaminants, especially mobile metal ions, can have a catastrophic impact on the electrical performance and long-term reliability of the devices.

[0003] Traditional wet cleaning processes, which involve immersion in chemical reagents and brushing, struggle to reach the bottom of trenches with high aspect ratios, failing to effectively remove trace amounts of metallic contaminants and easily causing chemical residues and circuit corrosion. Conventional plasma cleaning technologies primarily target organic contaminants, carbides, and oxide layers, exhibiting low efficiency in removing elemental metals and prone to over-etching damage to circuits, thus failing to meet the cleaning requirements of advanced process FPCs.

[0004] Therefore, there is an urgent need for a cleaning process that can target trace metal elements between FPC lines while achieving both high metal removal rate and low line damage rate. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method for removing trace metal element contaminants between lines on flexible circuit boards. This method can efficiently remove trace metal contaminants from trenches between lines with high aspect ratios, while minimizing damage to the circuitry and improving the yield and reliability of FPC products.

[0006] To achieve the above objectives, this invention proposes a method for removing trace metal element contaminants between lines on a flexible circuit board, comprising the following steps: S1. Place the flexible circuit board to be processed in the processing chamber of the plasma equipment, and evacuate the chamber until the pressure is below 1×10⁻⁶. -6 Torr; S2. A reaction gas containing O2, CF4, and Ar is introduced into the chamber, and the chamber pressure is controlled at 200~250 mTorr. Radio frequency energy is applied to generate plasma, and the reaction temperature is controlled between room temperature and 60°C. Under the chamber pressure, the F· free radicals in the plasma penetrate to the bottom of the inter-line trenches of the flexible circuit board and react chemically with the residual metal element contaminants in the inter-line trenches to generate metal fluorides. Under the chamber pressure, the metal fluorides desorb from the reaction site into a gaseous state and diffuse along the inter-line trenches into the chamber under the concentration difference between the bottom of the inter-line trenches and the chamber. S3. Remove the gaseous metal fluoride from the chamber to complete the cleaning.

[0007] According to the present invention, a method for removing trace metallic element contaminants between lines in a flexible circuit board significantly increases the mean free path of F· free radicals by controlling the chamber pressure within a low-pressure range of 200~250 mTorr, enabling them to effectively penetrate to the bottom of the high aspect ratio trenches between lines and fully react with the residual metallic element contaminants in the trenches. By controlling the reaction temperature within a low-temperature range of room temperature to 60°C, thermal damage to the FPC flexible substrate and fine circuitry is avoided. The method further involves first evacuating the chamber to a vacuum level of 1×10⁻⁶ m / s. -6 By introducing reaction gas below the Torr level, interference from impurities such as air and moisture within the chamber is eliminated, ensuring the reactivity of F· free radicals. The generated metal fluoride is directly desorbed into a gaseous state under low pressure in the chamber and diffuses into the main space of the chamber on its own driven by the concentration difference between the bottom of the trench and the chamber. The directional transport of the product can be completed without additional operations, and finally, cleaning is completed by extraction. The entire process is simple and highly synergistic, achieving efficient and non-destructive removal of trace metal element contaminants between lines.

[0008] Optionally, the aspect ratio of the inter-line groove is greater than 10:1.

[0009] Optionally, the metallic element contaminant is palladium.

[0010] Optionally, the power of the radio frequency energy is 1000~3000 W, and the frequency of the radio frequency energy is 13.56 MHz.

[0011] Optionally, the flow rate of O2 is 1000~3000 sccm, the flow rate of CF4 is 100~1500 sccm, and the flow rate of Ar is 100~1500 sccm.

[0012] Furthermore, the flow rate of CF4 is 100~200 sccm, the flow rate of O2 is 3000 sccm, the flow rate of Ar is 800 sccm, and the power of the radio frequency energy is 3000 W.

[0013] Optionally, in step S3, a vacuum pump system is used to extract the gaseous metal fluoride in the chamber to the exhaust gas treatment system for harmless treatment.

[0014] Optionally, the method further includes step S4, which involves introducing O2-based plasma into the chamber to clean the inner wall of the chamber and remove deposited polymers or byproducts.

[0015] Optionally, in step S2, the chamber pressure is controlled to be 220 mTorr.

[0016] Optionally, in step S1, the flexible circuit board is conveyed to the processing chamber by winding.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] Figure 1 This is the transmission structure of the FPC product according to an embodiment of the present invention; Figure 2 A partial view of the FPC product after ENEPIG process, showing the appearance of the product without palladium metal contaminant removal. Figure 3 This is a magnified view of a portion of an FPC product that has undergone ENEPIG processing without palladium metal contaminant removal. Figure 4 This is a partial view of the FPC product of Embodiment 1 of the present invention after being processed by the ENEPIG process; Figure 5 This is a magnified view of the FPC product of Embodiment 1 of the present invention after being processed by the ENEPIG process. Detailed Implementation

[0019] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0020] This application is based on the inventor's considerations regarding the following: In the prior art, the removal of trace metal element contaminants between FPC lines mainly relies on wet cleaning or conventional plasma cleaning. Wet cleaning, which uses chemical reagent immersion and brushing, is difficult to penetrate to the bottom of the trenches with high aspect ratios (>10:1), and cannot effectively remove residual trace metal element contaminants such as copper, cobalt, tungsten, and titanium in the trenches. It also easily causes problems such as chemical reagent residues and circuit corrosion, leading to reliability issues such as device leakage and short circuits. Although conventional plasma cleaning technology can achieve dry treatment, it mainly targets organic contaminants, carbides, and oxide layers, and has low removal efficiency for elemental metals. Under high power conditions, it is easy to cause over-etching damage to the circuit, and under low power conditions, it is difficult to generate enough active free radicals to penetrate to the bottom of the trench, thus failing to meet the requirements of high metal removal rate and low circuit damage rate.

[0021] To address these issues, this application proposes a plasma cleaning method that solves the problems of traditional cleaning processes, such as the inability to reach the bottom of trenches with high aspect ratios, the inability to selectively remove metallic element contaminants, the tendency to cause over-etching damage to the lines, and the difficulty in balancing removal rate and damage rate. At the same time, it is compatible with existing FPC roll-to-roll mass production processes, achieving the cleaning requirements for trace metallic element contaminants between lines with high removal rate, low damage rate, and high efficiency.

[0022] Specifically, this application proposes a method for removing trace metal element contaminants between lines of a flexible circuit board, comprising the following steps: S1. Place the flexible circuit board to be processed in the processing chamber of the plasma equipment, and evacuate the chamber until the pressure is below 1×10⁻⁶. -6 Torr; S2. A reaction gas containing O2, CF4, and Ar is introduced into the chamber, and the chamber pressure is controlled at 200~250 mTorr. Radio frequency energy is applied to generate plasma, and the reaction temperature is controlled between room temperature and 60°C. Under the chamber pressure, the F· free radicals in the plasma penetrate to the bottom of the inter-line trenches of the flexible circuit board and react chemically with the residual metal element contaminants in the inter-line trenches to generate metal fluorides. Under the chamber pressure, the metal fluorides desorb from the reaction site into a gaseous state and diffuse along the inter-line trenches into the chamber under the concentration difference between the bottom of the inter-line trenches and the chamber. S3. Remove the gaseous metal fluoride from the chamber to complete the cleaning.

[0023] Compared with the prior art, the present invention has the following beneficial effects: First, high removal efficiency; by controlling the chamber pressure within a low-pressure range of 200-250 mTorr, the mean free path of F· radicals is significantly increased, enabling them to effectively penetrate to the bottom of the inter-line trenches with an aspect ratio greater than 10:1. This allows them to fully react with residual copper, cobalt, tungsten, titanium, and other metallic contaminants within the trenches, achieving a metal removal rate of over 99%. This solves the problem of traditional cleaning processes being unable to reach the bottom of the trenches. In other words, under the set low pressure, the highly reactive free radicals generated in the plasma zone are effectively transported and evenly distributed onto the FPC surface through diffusion and flow, further penetrating to the bottom of the high aspect ratio inter-line trenches. These free radicals preferentially adsorb onto the surface of residual metal atoms (such as Cu and Co) within the trenches, undergoing a chemical reaction.

[0024] Second, low-damage characteristics; by controlling the CF4 flow rate in the low range of 100~200 sccm, the over-etching damage to the FPC circuit is significantly reduced, and the product damage rate can be controlled below 2%, which solves the contradiction between metal removal rate and circuit damage rate in the existing technology.

[0025] Third, it has good process compatibility; it adopts a roll-to-roll continuous processing mode, which can be adapted to existing FPC mass production lines without changing the existing production line layout, and has high processing efficiency without affecting the production cycle.

[0026] Fourth, it is environmentally friendly and pollution-free; the dry process does not require chemical reagents and does not generate waste liquid discharge, avoiding the chemical waste liquid treatment problem of wet cleaning, and meeting the requirements of green manufacturing.

[0027] Optionally, the aspect ratio of the inter-line trench is greater than 10:1. Under this aspect ratio, traditional wet cleaning and conventional plasma cleaning have difficulty reaching the bottom of the trench, while the present invention uses low-pressure control to allow F· free radicals to have sufficient mean free path to penetrate to the depth of the trench.

[0028] Optionally, the metallic element contaminants include at least one of copper, cobalt, tungsten, and titanium. Therefore, the method of this application can handle a variety of key metallic element contaminants commonly found in FPC manufacturing. These metallic elements tend to remain in the inter-line trenches during FPC processes (such as after chemical mechanical polishing and electroplating), leading to reliability issues such as leakage and short circuits. This method can specifically convert them into volatile fluorides and remove them, making it widely applicable.

[0029] Optionally, the power of the radio frequency energy is 1000~3000 W, and the frequency of the radio frequency energy is 13.56 MHz.

[0030] Optionally, the flow rate of O2 is 1000~3000 sccm, the flow rate of CF4 is 100~1500 sccm, and the flow rate of Ar is 100~1500 sccm.

[0031] Furthermore, the flow rate of CF4 is 100-200 sccm, the flow rate of O2 is 3000 sccm, the flow rate of Ar is 800 sccm, and the power of the radio frequency energy is 3000 W. Orthogonal experiments show that plasma power is the decisive factor affecting the metal removal rate; higher power results in a higher metal removal rate. Simultaneously, power has no significant impact on the product damage rate. Therefore, a high power within the range of 1000-3000 W can be selected to achieve the best removal effect. O2 flow rate is the second most important factor affecting the metal removal rate; increasing the O2 flow rate helps improve the removal rate. As a source of F· radicals, controlling CF4 within a low flow rate range of 100-200 sccm effectively suppresses over-etching damage to the circuit. Under these parameter conditions, the metal removal rate can reach 99%, and the product damage rate is only 2%. Optionally, in step S3, a vacuum pump system is used to extract the gaseous metallic fluoride from the chamber to a tail gas treatment system for harmless treatment. The continuous operation of the vacuum pump system maintains a low-pressure environment within the chamber while simultaneously extracting the gaseous metallic fluoride generated during the reaction, promoting the forward chemical reaction and improving cleaning efficiency. The tail gas treatment system performs harmless treatment such as combustion or washing on the extracted fluorine-containing gas, avoiding direct emission of fluorine-containing gas and thus improving the environmental friendliness of the process.

[0032] Optionally, the process also includes step S4, introducing O2-based plasma into the chamber to clean the inner wall of the chamber and remove deposited polymers or byproducts. During plasma cleaning, fluoropolymers or other byproducts may deposit on the inner wall of the chamber, and long-term accumulation can affect process stability and repeatability. Regularly cleaning the inner wall of the chamber with O2-based plasma can effectively remove these deposits, maintain chamber cleanliness, ensure batch-to-batch process consistency, and extend equipment maintenance cycles.

[0033] Optionally, in step S2, the chamber pressure is controlled at 220 mTorr. At this pressure, the mean free path of F· radicals is optimally matched with the trench depth, ensuring that the radicals fully penetrate to the bottom of the trench while maintaining a sufficient radical concentration to guarantee reaction efficiency.

[0034] Optionally, in step S1, the flexible circuit board is conveyed to the processing chamber by winding. FPC is a flexible strip material, and the roll-to-roll (RTR) winding method enables continuous and automated production, eliminating the need for manual placement of each piece, significantly improving production efficiency and capacity, while reducing the risk of contamination from human operation, and facilitating integration with upstream and downstream processes of FPC mass production lines.

[0035] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0036] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0037] Example 1 This embodiment provides a method for removing trace metal element contaminants between lines in flexible printed circuit boards (FPCs). The method is used to treat FPC products with inter-line trenches of 60-80 μm copper thickness and 40-50 μm line spacing, removing residual palladium metal contaminants within the trenches. Since the exposed PI layer of some products may adsorb trace amounts of palladium, the specific steps are as follows: S1. Connect the FPC that has undergone chemical mechanical polishing to the guide belt via a connector, place it at the unwinding point, and pull the guide belt to the take-up reel and fix it by winding; (e.g.) Figure 1 As shown, the FPC is conveyed to the processing chamber of the plasma device by winding; the processing chamber is sealed, and a turbomolecular pump is started to evacuate the chamber, reducing the chamber pressure to 8 × 10⁻⁶. -7 Torr, keep for 30 minutes to eliminate interference from air, moisture and impurities in the chamber.

[0038] S2. The flow rate of the reaction gas is precisely controlled by the flow controller of the plasma equipment and introduced into the processing chamber. The reaction gas composition is: O2 flow rate 3000 sccm, Ar flow rate 800 sccm, and CF4 flow rate 100 sccm. The chamber pressure is stabilized at 220 mTorr, and 3000 W of 13.56 MHz radio frequency energy is applied. The reaction temperature is controlled at 45℃, and the reaction time is 3 min. Under the above chamber pressure, the radio frequency energy dissociates the reaction gas to generate a high concentration of F· free radicals. F· free radicals have a large mean free path under low pressure. They diffuse and flow to the bottom of the inter-line trenches of the FPC, where they react chemically with the palladium contaminants remaining in the trenches to form metal fluorides. The metal fluorides desorb from the reaction site into a gaseous state under the chamber pressure and diffuse along the inter-line trenches into the main space of the chamber driven by the concentration difference between the bottom of the inter-line trenches and the chamber. The plasma fluorination reaction described above is an auxiliary process; before the fluorination reaction, the metal contaminants need to be oxidized to form metal oxides. Subsequently, a high-energy gas cloud (Ar plasma) physically bombards the substrate surface: producing a very small amount of etching on the PI surface layer; physical sputtering also breaks the PI molecular chains, slowly removing the PI material and exposing the internal metal covered by the PI thin layer; the exposed metal is then carried away by subsequent ion bombardment, achieving complete removal.

[0039] S3. A turbomolecular pump with a pumping speed of 1500 L / s is used to continuously extract the gaseous metal fluoride in the chamber to the combustion exhaust gas treatment system for harmless treatment.

[0040] S4. Turn off the RF power, stop the plasma, and shut off the reactive gas flow. Introduce high-purity N2 to restore the chamber to atmospheric pressure, and then transfer the cleaned FPC out of the chamber. Subsequently, introduce O2 plasma at a flow rate of 2000 sccm to clean the inner wall of the chamber for 10 minutes to remove deposited polymers or byproducts.

[0041] Testing revealed that the FPC product in this embodiment, manufactured using the ENEPIG process (which employs an immersion nickel-palladium-gold process, where residual metal between lines will result in gold plating), confirmed the presence of residual palladium metal between lines. Figure 4 and Figure 5 As shown, with Figure 2 and Figure 3 A comparison of FPC products without palladium metal contaminant removal after ENEPIG processing shows that the FPC product in this embodiment exhibits no gold infiltration after ENEPIG processing, indicating that the palladium metal contaminant has been removed. Figure 2 and Figure 3Gold infiltration was observed in the FPC product. In this embodiment, the removal rate of palladium contaminants between lines was 99% (removal rate is calculated using the pass rate, the number of samples without gold infiltration / the total number of samples, confirmed by 100% visual inspection and open / short circuit testing), and the product damage rate was 2% (PI damage, partial circuit damage; judged by 100% visual inspection).

[0042] Example 2 The difference between this embodiment and Embodiment 1 lies in the reactant gas parameters and radio frequency power in S2. In this embodiment, the reactant gas components are: O2 flow rate 1000 sccm, Ar flow rate 800 sccm, CF4 flow rate 800 sccm, and radio frequency power 2000W. The remaining steps are the same as in Embodiment 1.

[0043] Tests showed that the removal rate of inter-line metal element contaminants in this embodiment was 85%, and the product damage rate was 6%.

[0044] Example 3 The difference between this embodiment and Embodiment 1 lies in the reaction gas parameters in S2. In this embodiment, the reaction gas components are: O2 flow rate 2000 sccm, Ar flow rate 100 sccm, CF4 flow rate 800 sccm, and RF power 3000 W. The remaining steps are the same as in Embodiment 1.

[0045] Tests showed that the removal rate of inter-line metal element contaminants in this embodiment was 92%, and the product damage rate was 7%.

[0046] Example 4 The difference between this embodiment and Embodiment 1 lies in the reactant gas parameters and radio frequency power in S2. In this embodiment, the reactant gas components are: O2 flow rate 2000 sccm, Ar flow rate 1500 sccm, CF4 flow rate 100 sccm, and radio frequency power 2000W. The remaining steps are the same as in Embodiment 1.

[0047] Tests showed that the removal rate of inter-line metallic contaminants in this embodiment was 87%, and the product damage rate was 2%. Both this embodiment and Embodiment 1 used a low CF4 flow rate (100 sccm), and the product damage rate was controlled at a low level of 2%, further verifying the key role of low CF4 flow rate in suppressing line damage.

[0048] Example 5 The difference between this embodiment and Embodiment 1 lies in the reactant gas parameters and radio frequency power in S2. In this embodiment, the reactant gas components are: O2 flow rate 1000 sccm, Ar flow rate 1500 sccm, CF4 flow rate 1500 sccm, and radio frequency power 3000W. The remaining steps are the same as in Embodiment 1.

[0049] Tests showed that the removal rate of inter-line metallic contaminants in this embodiment was 87%, and the product damage rate was 11%. Compared with Embodiment 1, the CF4 flow rate increased from 100 sccm to 1500 sccm, and the product damage rate increased from 2% to 11%, indicating that the CF4 flow rate is a key factor affecting the product damage rate, and reducing the CF4 flow rate can significantly reduce line damage.

[0050] Example 6 The difference between this embodiment and Embodiment 1 lies in the reactant gas parameters and radio frequency power in S2. In this embodiment, the reactant gas components are: O2 flow rate 3000 sccm, Ar flow rate 100 sccm, CF4 flow rate 1500 sccm, and radio frequency power 2000W. The remaining steps are the same as in Embodiment 1.

[0051] Tests showed that the removal rate of inter-line metallic contaminants in this embodiment was 90%, and the product damage rate was 12%. Compared with Example 1, the CF4 flow rate increased from 100 sccm to 1500 sccm, and the product damage rate increased from 2% to 12%, further verifying the decisive influence of CF4 flow rate on the product damage rate.

[0052] Comparative Example 1 The difference between this comparative example and Example 1 lies in the reactant gas parameters and radio frequency power in S2. In this comparative example, the reactant gas components are: O2 flow rate 1000 sccm, Ar flow rate 100 sccm, CF4 flow rate 100 sccm, and radio frequency power 1000W. The remaining steps are the same as in Example 1.

[0053] Testing revealed that the removal rate of inter-line metallic contaminants in this comparative example was only 55%, with a product damage rate of 1%. Compared to Example 1, this comparative example reduced the O2 flow rate from 3000 sccm to 1000 sccm and the RF power from 3000 W to 1000 W. Although the damage rate was low, the removal rate was far from meeting production requirements, indicating that high O2 flow rate and high RF power are necessary conditions for achieving a high removal rate.

[0054] Comparative Example 2 The difference between this comparative example and Example 1 lies in the reactant gas parameters and radio frequency power in S2. In this comparative example, the reactant gas components are: O2 flow rate 2000 sccm, Ar flow rate 800 sccm, CF4 flow rate 1500 sccm, and radio frequency power 1000W. The remaining steps are the same as in Example 1.

[0055] Testing showed that the removal rate of inter-line metallic contaminants in this comparative example was 70%, and the product damage rate was 9%. Compared with Example 1, this comparative example had a higher CF4 flow rate and a lower RF power, resulting in insufficient removal rate and a higher damage rate. This indicates that simply increasing the CF4 flow rate cannot effectively improve the removal rate; on the contrary, it may exacerbate line damage.

[0056] Comparative Example 3 The difference between this comparative example and Example 1 lies in the reactant gas parameters and radio frequency power in S2. In this comparative example, the reactant gas components are: O2 flow rate 3000 sccm, Ar flow rate 1500 sccm, CF4 flow rate 800 sccm, and radio frequency power 1000W. The remaining steps are the same as in Example 1.

[0057] Testing showed that the removal rate of inter-line metal contaminants in this comparative example was 72%, and the product damage rate was 7%. Compared with Example 1, the radio frequency power in this comparative example decreased from 3000 W to 1000 W, and the removal rate decreased from 99% to 72%, indicating that radio frequency power is the decisive factor affecting the metal removal rate. Under low power conditions, even increasing the O2 and CF4 flow rates cannot achieve satisfactory removal results.

[0058] In summary, according to the embodiments of the present invention, by controlling the synergistic coordination of process parameters such as chamber pressure, reaction gas composition and ratio, and radio frequency energy, F· free radicals can effectively penetrate to the bottom of the FPC line grooves under low pressure, react chemically with residual metal element contaminants to generate gaseous metal fluorides and remove them, achieving a cleaning effect with high removal rate and low damage, and has significant practical value.

[0059] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0061] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0062] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0063] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0064] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for removing trace metal element contaminants between lines of a flexible circuit board, characterized in that, Includes the following steps: S1. Place the flexible circuit board to be processed in the processing chamber of the plasma equipment, and evacuate the chamber until the pressure is below 1×10⁻⁶. -6 Torr; S2. A reaction gas containing O2, CF4, and Ar is introduced into the chamber, and the chamber pressure is controlled at 200~250 mTorr. Radio frequency energy is applied to generate plasma, and the reaction temperature is controlled between room temperature and 60°C. Under the chamber pressure, the F· free radicals in the plasma penetrate to the bottom of the inter-line trenches of the flexible circuit board and react chemically with the residual metal element contaminants in the inter-line trenches to generate metal fluorides. Under the chamber pressure, the metal fluorides desorb from the reaction site into a gaseous state and diffuse along the inter-line trenches into the chamber under the concentration difference between the bottom of the inter-line trenches and the chamber. S3. Remove the gaseous metal fluoride from the chamber to complete the cleaning.

2. The method as described in claim 1, characterized in that, The depth-to-width ratio of the inter-line groove is greater than 10:

1.

3. The method as described in claim 1, characterized in that, The metallic element contaminant is palladium.

4. The method as described in claim 1, characterized in that, The power of the radio frequency energy is 1000~3000 W, and the frequency of the radio frequency energy is 13.56 MHz.

5. The method as described in claim 1, characterized in that, The flow rate of O2 is 1000~3000 sccm, the flow rate of CF4 is 100~1500 sccm, and the flow rate of Ar is 100~1500 sccm.

6. The method as described in claim 5, characterized in that, The flow rate of CF4 is 100~200 sccm, the flow rate of O2 is 3000 sccm, the flow rate of Ar is 800 sccm, and the power of the radio frequency energy is 3000 W.

7. The method as described in claim 1, characterized in that, In step S3, a vacuum pump system is used to extract the gaseous metal fluoride in the chamber to the exhaust gas treatment system for harmless treatment.

8. The method as described in claim 1, characterized in that, It also includes S4, which introduces O2-based plasma into the chamber to clean the inner wall of the chamber to remove deposited polymers or byproducts.

9. The method as described in claim 1, characterized in that, In step S2, the chamber pressure is controlled at 220 mTorr.

10. The method as described in claim 1, characterized in that, In step S1, the flexible circuit board is conveyed to the processing chamber by winding.

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