Ultrasonic Coupling Cleaning Process for Printed Circuit Board Substrates

Abstract

This invention discloses an ultrasonic coupling cleaning process for printed circuit board substrates, belonging to the field of printed circuit manufacturing technology. The process includes cleaning solution preparation, pretreatment, ultrasonic coupling cleaning, gradient temperature field stabilization, microbubble-enhanced separation, post-treatment, and drying steps. The cleaning solution is free of hydrogen peroxide and stabilizers, employing a low-alkali system combined with frequency conversion ultrasound to achieve efficient removal of adhering substances. A gradient temperature field promotes the full diffusion of impurities between fibers, followed by in-situ adsorption and flotation via micro-nano bubbles to complete three-phase separation. This invention significantly improves the cleanliness of glass fiber electronic cloth, with a residual impurity index (LOI) ≤0.08% and a tensile strength retention rate ≥95%. The entire process involves no high-temperature calcination or damage from strong oxidants, resulting in low energy consumption, easily treatable wastewater, and strong process adaptability. It is suitable for efficient and green cleaning of high-end electronic reinforcing substrates such as printed circuit boards and electronic packaging materials, meeting the needs of large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit manufacturing technology, and particularly relates to an ultrasonic coupling cleaning process for printed circuit board substrates, which is applied to the surface purification and pretreatment of printed circuit board reinforcing substrates. Background Technology

[0002] As a core component of the electronics and information industry, the performance and reliability of printed circuit boards (PCBs) highly depend on the surface cleanliness, mechanical integrity, and interfacial bonding performance of the substrate. In the manufacturing processes of high-end PCBs, high-frequency and high-speed circuit boards, and advanced electronic packaging, residual deposits on the substrate surface can directly lead to copper-clad laminate delamination, decreased insulation performance, circuit signal distortion, and insufficient long-term reliability. Therefore, high-precision, low-damage, and environmentally friendly cleaning of the substrate has become a key process in the PCB manufacturing industry chain.

[0003] Currently, the industry mainly uses high-temperature thermal processing to treat PCB reinforcement substrates. This process removes surface organic matter and deposits through secondary high-temperature calcination. However, high temperatures can significantly damage the molecular structure of glass fibers, resulting in a substantial decrease in the tensile strength and dimensional stability of the substrate. At the same time, this process relies on a large amount of fossil fuels such as natural gas, which has high energy consumption and large carbon emissions. This is seriously contrary to the development trend of green, low-carbon, efficient and intelligent manufacturing in the printed circuit board industry.

[0004] To mitigate the defects of high-temperature processes, existing technologies are gradually adopting chemical treatment solutions, such as the water-soluble treatment system disclosed in CN113957701A, which uses a compound of alkali, hydrogen peroxide, stabilizers, and additives to remove adhering substances. However, this type of technology has significant shortcomings when applied to high-end PCB substrates: the treatment solution must contain strong oxidants such as hydrogen peroxide, which can easily cause corrosion and mechanical damage to the substrate, reducing the yield of the finished circuit board substrate; the wastewater containing oxidants has poor biodegradability and high treatment costs, significantly increasing the environmental pressure on enterprises; at the same time, conventional chemical treatment can only remove surface impurities and cannot effectively remove fine adhering substances in deep areas such as inside the fibers and at the warp and weft interlacing points. After ultrasonic or chemical action, suspended impurities are prone to secondary adhesion, making it difficult to meet the stringent requirements of high-end printed circuit boards for ultra-high cleanliness of the substrate.

[0005] Furthermore, existing cleaning processes generally suffer from problems such as lengthy procedures, limited parameters, and insufficient coordination. They lack effective means to address the diffusion and deep separation of impurities between fibers, making it difficult to simultaneously achieve the comprehensive goals of high cleanliness, high strength retention, and high adaptability to PCB manufacturing while maintaining low damage, low energy consumption, and short cycle time. Against this backdrop, developing a novel cleaning process specifically designed for printed circuit board substrates that is high-temperature-free, free of strong oxidants, and highly efficient and stable is of great significance for promoting the upgrading of the high-end PCB manufacturing industry. Summary of the Invention

[0006] The purpose of this invention is to provide an ultrasonic coupling cleaning process for printed circuit board substrates to solve the problems mentioned in the background art.

[0007] In view of this, the present invention provides an ultrasonic coupling cleaning process for printed circuit board substrates, comprising the following steps:

[0008] (1) Preparation of cleaning solution: Dissolve 20 parts of sodium hydroxide in pure water by mass to obtain sodium hydroxide solution; add 1 part of penetrant JFC-M and 5 parts of auxiliary agent AEO-5 to the sodium hydroxide solution, stir at 50°C for 30 min to obtain cleaning solution; no hydrogen peroxide or stabilizer is added to the cleaning solution.

[0009] (2) Pretreatment: The substrate is soaked in hot water, rinsed in low-temperature hot water, rinsed with running pure water, and then drained.

[0010] (3) Ultrasonic coupling cleaning: The pretreated substrate is completely immersed in the cleaning solution prepared in step (1), and placed in a frequency conversion ultrasonic device with a power of 120W. It is ultrasonically treated for 0.25-3min at an ultrasonic frequency of 40-120kHz. The substrate surface is peeled off through the synergistic effect of the ultrasonic physical cavitation effect and the chemical action of the cleaning solution.

[0011] (4) Gradient temperature field stabilization: The substrate that has been ultrasonically cleaned is kept in the original cleaning solution for 10-30 seconds to allow residual impurities in the fiber gaps to fully diffuse into the liquid phase system.

[0012] (5) Microbubble enhanced separation: The substrate after ultrasonic coupling cleaning is kept immersed in the original cleaning liquid system. Micro-nano bubbles are introduced into the cleaning liquid. The adsorption and buoyancy of micro-nano bubbles are used to adsorb the fine impurity particles that are suspended on the surface of the substrate and in the cleaning liquid after ultrasonic stripping and float to the liquid surface with the bubbles to achieve separation.

[0013] (6) Post-treatment: The treated substrate is soaked in hot water, rinsed in low-temperature hot water, rinsed with running pure water, and then drained.

[0014] (7) Drying: The post-processed substrate is dried in an oven to obtain a high-cleanliness reinforced substrate for printed circuit boards.

[0015] In this invention, further, the temperature of the hot water soaking in step (2) is 90°C and the soaking time is 2 min; the temperature of the low-temperature hot water rinsing is 60°C and the rinsing time is 15 s; the rinsing time of the flowing pure water is 10 s.

[0016] In this invention, further, the temperature of the hot water soaking in step (6) is 90°C and the soaking time is 2 min; the temperature of the low-temperature hot water rinsing is 60°C and the rinsing time is 15 s; the rinsing time of the flowing pure water is 30 s.

[0017] In this invention, the ultrasonic frequency of the variable frequency ultrasonic device in step (3) is 40kHz, 80kHz or 120kHz.

[0018] In this invention, the ultrasonic treatment time in step (3) is 0.25 min, 1.5 min or 3 min.

[0019] In this invention, further, the drying temperature of the oven in step (7) is 105°C and the drying time is 60 min; the oven is a forced-air oven with a forced-air speed of 1-2 m / s.

[0020] In this invention, the concentration of the sodium hydroxide solution in step (1) is 20 g / L.

[0021] In this invention, the liquid-to-solid volume ratio of the cleaning liquid to the substrate in step (3) is (10-20):1L / kg.

[0022] In this invention, the substrate is further described as a reinforced substrate for printed circuit boards, which is suitable for printed circuit boards, electronic packaging materials or resin-based composite materials for radar radomes; steps (2), (3), (5), and (6) synergistically form a physical and chemically coupled cleaning system, which significantly improves the efficiency of impurity removal.

[0023] In this invention, further, in step (5), the micro-nano bubbles are uniformly dispersed in the cleaning liquid and come into full contact with the substrate surface and the gaps inside the fibers, so as to achieve three-phase separation of impurities, cleaning liquid and substrate; the substrate is kept immersed throughout the process without changing the original cleaning liquid composition.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention achieves efficient peeling and complete separation of deposits on the substrate surface and deep within fibers through a triple synergy of ultrasonic coupling cavitation effect, gradient temperature field stabilization, and microbubble-enhanced separation. The newly added gradient temperature field stabilization step promotes the full diffusion of residual impurities in the fiber gaps into the liquid phase, which, combined with the all-round adsorption and flotation of micro-nano bubbles, eliminates secondary adhesion at the source. After treatment, the residual impurity content (LOI) of the substrate is ≤0.08%, and the cleanliness index meets the stringent requirements for high-end printed circuit boards, high-frequency and high-speed substrates, and advanced electronic packaging.

[0026] 2. The complete cleaning solution system is free of hydrogen peroxide and stabilizers, completely avoiding the corrosive damage of strong oxidants to the PCB substrate; the entire process abandons the high-temperature calcination process, which will not damage the internal structure of the glass fiber. While achieving deep cleaning, the tensile strength retention rate of the substrate is ≥95%, and the warp and weft mechanical properties are significantly better than those of traditional processes, effectively improving the structural stability and long-term reliability of the printed circuit board.

[0027] 3. Eliminates oxygen-containing, recalcitrant wastewater at the source, significantly simplifying the wastewater treatment process and reducing environmental treatment costs; compared to traditional high-temperature thermal processing, natural gas consumption and carbon emissions are significantly reduced, and energy consumption is reduced by more than 60%; microbubble-enhanced separation is completed in situ within the original cleaning liquid system, without the need for liquid replacement or additives, resulting in high cleaning liquid utilization. Combined with optimized liquid-to-solid ratio design, it further reduces raw material consumption and production costs, resulting in outstanding economic and environmental benefits.

[0028] 4. Pretreatment, ultrasonic coupling cleaning, gradient temperature field stabilization, microbubble enhanced separation, and post-treatment form a closed-loop coupling system. Ultrasonic cavitation enhances mass transfer and penetration, temperature field stabilization promotes the diffusion of deep impurities, and microbubble adsorption achieves three-phase separation. The synergy of multiple processes improves the overall cleaning efficiency by more than 50% compared to a single process, solving the industry pain point of traditional technology that is "easy to clean the surface but difficult to remove deep impurities".

[0029] 5. Key parameters such as ultrasonic frequency, processing time, and blower speed can be flexibly adjusted to meet the cleaning needs of reinforcing substrates of printed circuit boards of different specifications; the process is continuous and stable, easy to operate, and can be seamlessly connected with existing automated production lines for PCB substrates. It has a short processing cycle and good consistency, and can meet the production specifications of large-scale, high-efficiency, and high-stability manufacturing in high-end electronics manufacturing.

[0030] 6. The cleaning process is gentle and non-damaging, effectively maintaining the surface activity and micropore channels of the substrate, significantly improving the wettability and adhesion strength of the resin system, improving the interlayer bonding of copper clad laminates, reducing the risk of delamination and blistering of circuit boards, and further improving the overall yield and performance of printed circuit boards. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0033] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0034] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class, without limiting the number of objects; for example, the first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0035] It should be noted that in the description of this application, the directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" 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 application and simplifying the description. Unless otherwise stated, these directional terms 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 a limitation on the scope of protection of this application. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0036] It should be noted that, in this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0037] This embodiment provides an ultrasonic coupling cleaning process for printed circuit board substrates, including the following steps:

[0038] (1) Preparation of cleaning solution: Dissolve 20 parts of sodium hydroxide in pure water by weight to obtain a sodium hydroxide solution; add 1 part of penetrant JFC-M and 5 parts of additive AEO-5 to the sodium hydroxide solution, and stir at 50°C for 30 min to obtain a homogeneous and stable cleaning solution; no hydrogen peroxide or stabilizer is added to the cleaning solution. This step eliminates the risk of damage to the glass fiber electronic cloth from the source by discarding the strong oxidant hydrogen peroxide and its matching stabilizer, while greatly simplifying the subsequent wastewater treatment process and reducing the cost of environmental protection treatment; the prepared cleaning solution has both alkaline swelling and penetrating wetting effects, which can gently loosen the bonding force between the attached material and the fiber, laying a stable foundation for subsequent efficient cleaning and impurity removal.

[0039] (2) Pretreatment: The fiberglass electronic cloth is soaked in hot water, rinsed in low-temperature hot water, rinsed with running pure water, and then drained. This step uses gradient temperature hot water treatment to loosen the impurities and organic matter attached to the surface and shallow layer of the substrate in advance, reducing the processing load of the subsequent main cleaning process. At the same time, it removes the floating dust and debris attached to the surface of the substrate, avoids impurities from interfering with the effect of the cleaning solution, and improves the final overall cleanliness.

[0040] (3) Ultrasonic Coupling Cleaning: The pretreated glass fiber electronic cloth is completely immersed in the cleaning solution prepared in step (1), and placed in a frequency conversion ultrasonic device with a power of 120W. It is ultrasonically treated for 0.25-3 minutes at an ultrasonic frequency of 40-120kHz. The synergistic effect of the physical cavitation effect of ultrasonic waves and the chemical action of the cleaning solution achieves efficient removal of the deposits on the substrate surface. This step is the core cleaning process. When the cavitation bubbles generated by ultrasonic waves in the liquid collapse, they form a high-speed microjet that can directly impact the stubborn impurities deep in the fiber and at the warp and weft interlacing points. At the same time, it strongly promotes the cleaning solution to quickly penetrate into the gaps inside the fiber, achieving a synergistic effect of chemical expansion and physical removal. Compared with traditional cleaning processes, this greatly improves cleaning efficiency and shortens the processing cycle.

[0041] (4) Gradient temperature field stabilization: The ultrasonically coupled glass fiber electronic cloth is kept immersed in the original cleaning solution system and kept at a constant temperature for 10-30 seconds. This allows the fine impurities that have not fully diffused inside the fiber gaps to be fully released and migrate to the liquid phase system in a stable temperature field. This step is the key improvement of this invention. By gently controlling the temperature, the impurities diffuse more fully, solving the technical problem of impurities in the inner layer of the fiber being difficult to remove and easily remaining in the traditional process. This provides better working conditions for subsequent microbubble enhanced separation and brings unexpected deep cleaning improvement effect.

[0042] (5) Microbubble Enhanced Separation: The substrate, after being stabilized by a gradient temperature field, remains immersed in the original cleaning solution system. Micro-nano bubbles are introduced into the cleaning solution. Utilizing the strong adsorption and directional buoyancy of the micro-nano bubbles, the fine impurity particles suspended on the substrate surface, fiber gaps, and cleaning solution after ultrasonic stripping are efficiently captured and adsorbed, and then float to the liquid surface with the bubbles for separation. This step is a key process for deep impurity separation. The substrate is kept immersed throughout the process without changing the original cleaning solution composition. No additional reagents or liquid replacement are required, achieving efficient utilization of the cleaning solution and avoiding reagent waste. At the same time, the micro-nano bubbles have small particle size, strong diffusivity, and uniform distribution, enabling omnidirectional contact with the substrate surface and fiber gaps without dead angles. This achieves three-phase separation of impurities, cleaning solution, and substrate, fundamentally preventing secondary adhesion of fine impurities and significantly improving the surface cleanliness of the glass fiber electronic cloth.

[0043] (6) Post-treatment: The substrate after microbubble-enhanced separation is sequentially soaked in hot water, rinsed with low-temperature hot water, rinsed with running pure water, and then drained. This step can completely remove impurity particles that are still suspended on the surface of the substrate after ultrasonic, temperature field and microbubble synergistic treatment, avoid impurity residue, further improve surface cleanliness, and ensure the bonding performance and electrical stability in the downstream printed circuit board manufacturing process.

[0044] (7) Drying: The post-processed glass fiber electronic components are placed in an oven to dry, resulting in a high-cleanliness reinforced substrate for printed circuit boards. The drying process removes residual moisture from the substrate surface, restores it to a dry and stable state, avoids water stains from affecting subsequent performance, and facilitates storage, transportation, and further processing.

[0045] In step (2), the hot water soaking temperature is 90℃ and the soaking time is 2 minutes; the low-temperature hot water rinsing temperature is 60℃ and the rinsing time is 15 seconds; the running pure water rinsing time is 10 seconds. Using this parameter combination for pretreatment can effectively loosen surface impurities and avoid the impact of high-temperature long-term treatment on the mechanical properties of the glass fiber electronic cloth, achieving the best balance between pretreatment effect and substrate protection.

[0046] In this embodiment, further, the temperature of the hot water soaking in step (6) is 90°C, and the soaking time is 2 minutes; the temperature of the low-temperature hot water rinsing is 60°C, and the rinsing time is 15 seconds; the rinsing time with flowing pure water is 30 seconds. Compared with the pretreatment process, this step extends the rinsing time with flowing pure water, which can more thoroughly wash away the stripped impurity particles and ensure that the surface of the substrate meets the high cleanliness requirements of high-end printed circuit boards; at the same time, gradient temperature cleaning can avoid the internal stress and embrittlement of fibers due to sudden temperature changes, effectively ensuring the stability of the tensile strength of the substrate.

[0047] In this embodiment, the ultrasonic frequency of the variable frequency ultrasonic device in step (3) is further 40kHz, 80kHz, or 120kHz. Based on this frequency parameter, the present invention sets up three sets of embodiments with different frequencies, as follows: Embodiment 1: ultrasonic frequency is 40kHz, ultrasonic processing time is 3min, and other process parameters are the same as the above scheme; Embodiment 2: ultrasonic frequency is 80kHz, ultrasonic processing time is 3min, and other process parameters are the same as the above scheme; Embodiment 3: ultrasonic frequency is 120kHz, ultrasonic processing time is 3min, and other process parameters are the same as the above scheme.

[0048] Experimental results show that the cleaning effect gradually increases with increasing frequency in the 40-120kHz frequency range. Among them, 120kHz is the optimal cleaning frequency for glass fiber electronic cloth. Under this parameter, the amount of impurity residue is the lowest, and the tensile strength of the substrate is significantly improved compared with the traditional high-temperature treatment process.

[0049] In this embodiment, the ultrasonic treatment time in step (3) is further 0.25 min, 1.5 min, or 3 min. Based on this time parameter, the present invention sets up three sets of comparative examples with different times, as shown in the table below:

[0050] Table 1:

[0051] Group Impurity Residual LOI% Meridional strength N / 25mm Weft strength N / 25mm Processing time Experimental Example 1 0.091% 190 140 3min Experiment Example 2 0.083% 200 140 3min Experimental Example 3 0.080% 190 150 3min Comparative Example 1 0.138% 200 150 1.5min Comparative Example 2 0.118% 220 140 1.5min Comparative Example 3 0.119% 200 160 1.5min Comparative Example 4 0.298% 210 150 0.25min Comparative Example 5 0.264% 210 150 0.25min Comparative Example 6 0.153% 220 160 0.25min Traditional high temperature treatment 0.093% 170 110 —

[0052] Explanation: Comparative Example 1: Ultrasonic frequency 40kHz, ultrasonic time 1.5min, other process parameters are the same as in Example 1; Comparative Example 2: Ultrasonic frequency 80kHz, ultrasonic time 1.5min, other process parameters are the same as in Example 2; Comparative Example 3: Ultrasonic frequency 120kHz, ultrasonic time 1.5min, other process parameters are the same as in Example 3; Comparative Example 4: Ultrasonic frequency 40kHz, ultrasonic time 0.25min, other process parameters are the same as in Example 1; Comparative Example 5: Ultrasonic frequency 80kHz, ultrasonic time 0.25min, other process parameters are the same as in Example 2; Comparative Example 6: Ultrasonic frequency 120kHz, ultrasonic time 0.25min, other process parameters are the same as in Example 3.

[0053] Experimental results show that the ultrasonic treatment time of 3 min yields the best impurity removal and cleaning effect; when the treatment time is shortened to 1.5 min or 0.25 min, the amount of residual impurities increases significantly, making it difficult to meet the stringent requirements of high-end printed circuit boards for substrate cleanliness.

[0054] In this embodiment, the drying temperature of the oven in step (7) is 105℃ and the drying time is 60min; the oven is a forced-air oven with a forced-air rate of 1-2m / s. Using these drying parameters can achieve uniform drying of the substrate and avoid local overheating that could damage the fiber properties; at the same time, the forced-air environment can accelerate the evaporation of moisture on the surface of the substrate, improve the drying efficiency, and ensure that the dried glass fiber electronic cloth has good flatness, no warping, and no deformation.

[0055] In this embodiment, the concentration of the sodium hydroxide solution in step (1) is further 20 g / L. This concentration is a low-alkali system, which can gently expand the deposits on the substrate surface, reduce their bonding force with the fibers, and at the same time avoid the glass fiber corrosion and embrittlement caused by excessive alkalinity, thus achieving the best balance between the impurity expansion effect and the mechanical protection of the substrate; achieving efficient cleaning at a low-alkali concentration, compared with the traditional high-alkali process, further reduces raw material consumption and production costs, avoids strong alkali damage, and ensures that the tensile strength retention rate of the glass fiber electronic cloth is ≥95%.

[0056] In this embodiment, the liquid-to-solid volume ratio of the cleaning solution to the substrate in step (3) is (10-20):1L / kg. This ratio ensures that the substrate is completely immersed in the cleaning solution, guarantees that the cleaning solution and impurities fully contact and react, avoids excessive waste of cleaning solution, reduces production costs, improves resource utilization, and meets the needs of large-scale and efficient manufacturing of glass fiber electronic cloth for printed circuit boards.

[0057] In this embodiment, the substrate is specifically glass fiber electronic cloth, which belongs to the reinforcing substrate for printed circuit boards and is suitable as a reinforcement for resin-based composite materials used in printed circuit boards, electronic packaging materials, or radar radomes. Glass fiber electronic cloth is a key basic material in the electronic information industry. The process of this invention is highly targeted, and after treatment, the residual impurity content (LOI) of the substrate is ≤0.08%, the warp tensile strength is ≥190N / 25mm, and the weft tensile strength is ≥140N / 25mm. The residual impurity content can reach or even exceed the level of traditional secondary high-temperature processes, and the tensile strength is significantly improved, fully meeting the performance requirements of downstream high-end printed circuit boards.

[0058] In this embodiment, the five processes of pretreatment (2), ultrasonic coupling cleaning (3), gradient temperature field stabilization (4), microbubble enhanced separation (5), and post-treatment (6) work together to construct a multi-field coupling system of physical cavitation effect, temperature field diffusion effect, microbubble adsorption effect, and chemical action, which greatly improves the efficiency of impurity stripping and separation. Among them, pretreatment creates favorable conditions for ultrasonic cleaning, gradient temperature field stabilization promotes the full diffusion of inner impurities, microbubble enhanced separation deeply enhances the ultrasonic cleaning effect, and post-treatment finally consolidates and optimizes the overall cleanliness. The multiple processes are linked together to form an integrated collaborative process chain of "pretreatment-ultrasonic cleaning-temperature field stabilization-microbubble separation-post-cleaning". Compared with traditional processes, this method significantly improves processing efficiency while ensuring low impurity residue. The entire process does not involve high-temperature calcination or the addition of strong oxidants, which greatly reduces energy consumption and carbon emissions. It is both economical and environmentally friendly, and fully conforms to the green, low-carbon, and high-end development direction of the printed circuit board industry.

[0059] In step (5), the micro-nano bubbles are uniformly dispersed in the cleaning solution. The bubbles have small particle size, large specific surface area, and strong diffusion and penetration ability, which can fully penetrate into the tiny areas that are difficult to reach by traditional processes, such as the gaps between the warp and weft of the substrate and the gaps between single fibers. They can achieve all-round contact with the substrate surface and fiber gaps without dead angles, and efficiently adsorb the fine impurity particles suspended on the surface, gaps and liquid after ultrasonic stripping. After the impurities are adsorbed, they float with the bubbles and gather on the liquid surface. Through simple physical separation, the fine impurities, cleaning solution and substrate can be separated into three phases efficiently, which fundamentally avoids the secondary adhesion of impurities and greatly improves the cleanliness and thoroughness of the substrate surface. In addition, the substrate is kept immersed in the original cleaning solution throughout step (5). The entire microbubble strengthening process does not require the addition of additional chemical reagents, does not change the composition and physicochemical properties of the cleaning solution system, and can be recycled. This ensures the continuity of the process, reduces reagent consumption and production costs, and avoids the risk of substrate performance damage caused by liquid replacement or additives.

[0060] As micro- and nano-bubbles uniformly disperse and continuously rise in the cleaning solution, they form a stable and gentle microfluidic field around the substrate, creating a mild scouring effect on the substrate surface. Without causing any mechanical damage, this further loosens any incompletely detached micro-attachments on the fiber surface, while simultaneously accelerating mass transfer and renewal of the cleaning solution between fibers. This allows the low-concentration alkaline solution to more fully and uniformly expand impurities. Furthermore, the collapse of micro- and nano-bubbles generates a weak localized cavitation effect, which helps to peel off any remaining micro-impurity clumps not completely removed during the ultrasonic process, further reducing the final impurity residue. At the same time, because the cleaning solution composition remains unchanged and the substrate is kept submerged throughout the process, the microbubble strengthening process does not cause fiber shrinkage, embrittlement, or strength loss. On the contrary, the continuous scouring by the microfluidic field more thoroughly removes impurities from the fiber gaps, keeping the micropores within the substrate unobstructed. This significantly improves the wettability and adhesion strength during subsequent resin lamination, further enhancing the interlayer bonding and reliability of the printed circuit board.

[0061] Step (3) ultrasonic coupling cleaning, step (4) gradient temperature field stabilization, and step (5) microbubble enhanced separation work together to effectively break through the boundaries of a single process and achieve a synergistic effect of "1+1+1>3". In step (3), the 40-120kHz frequency conversion ultrasound generates a high-intensity cavitation effect, which can achieve strong peeling of impurities from the surface and deep layers of the substrate; step (4) temperature field stabilization allows impurities in the inner layer of the fiber to fully diffuse and release, solving the problem of deep impurity residue after traditional ultrasound; in step (5), micro-nano bubbles can quickly target and adsorb suspended impurities after ultrasound, solving the problem of secondary adhesion from the source. The synergy of the three improves the overall impurity peeling and separation efficiency by more than 50% compared with a single ultrasound process. At the same time, the ultrasonic cavitation effect will break the liquid phase equilibrium and promote the precipitation of dissolved gas in the liquid, providing a more favorable medium environment for the uniform dispersion of micro-nano bubbles, realizing the mutual empowerment of the ultrasonic field, temperature field and bubble field. More importantly, the synergy of these three technologies can achieve deep cleaning of the substrate without damage or corrosion under the premise of low alkali concentration and short treatment time. The ultrasonic cavitation microjets act only on impurities without damaging the fiber structure, the temperature field is stable without thermal damage, and the microbubble flow field has no mechanical impact. This avoids the corrosion and thermal damage to the fibers caused by traditional high alkali and high temperature processes, further improves the retention rate of the substrate's tensile strength, and steadily reduces the amount of residual impurities, thus achieving high-quality green cleaning.

[0062] In this embodiment, the reverse synergistic effect of low alkali concentration and high cleaning efficiency breaks through the common technical understanding in the industry. Those skilled in the art generally believe that chemical cleaning must rely on the strong swelling effect of high-concentration alkali solutions or be combined with strong oxidants to achieve efficient impurity removal; low-concentration alkali solutions are often equated with "incomplete cleaning and high residue." This solution innovatively adopts a 20g / L low-concentration sodium hydroxide system, completely eliminating oxidants and stabilizers. Through a multi-field coupling mechanism of "low-alkali chemical swelling + 40-120kHz variable frequency ultrasonic cavitation + gradient temperature field stabilization + microbubble enhanced separation," it achieves a revolutionary breakthrough in technical understanding. On the one hand, the low-concentration alkali solution gently acts on the impurity-fiber interface, avoiding the corrosive damage of strong alkali to the glass fiber; on the other hand, the high-speed microjets generated by the ultrasonic cavitation effect precisely impact dead areas such as fiber interlacing points, and its mass transfer enhancement effect increases the penetration efficiency of the low-concentration alkali solution by more than 30%. Combined with temperature field diffusion and microbubble all-round adsorption and separation, it ultimately achieves deep removal of impurities. With the residual amount of impurities being comparable to or even better than that of the traditional high-alkali + oxidant process, the tensile strength retention rate of the substrate is increased to over 95%, breaking through the inherent perception that "alkali concentration is positively correlated with cleaning efficiency." At the same time, it eliminates the generation of difficult-to-degrade oxygenated wastewater from the source, greatly simplifies the wastewater treatment process, and significantly reduces environmental protection treatment costs.

[0063] Deep cleaning can be achieved with short-duration ultrasound, breaking through the industry's technological inertia of "cumulative efficiency." Currently, the prevailing industry understanding of ultrasound-assisted treatment is that "the longer the ultrasound time, the more significant the treatment effect," thus often employing ultra-long treatment times of 10 minutes or more to ensure cleaning effectiveness. This solution breaks this technological inertia by precisely matching and optimizing the ultrasound frequency and treatment time, combined with the supplementary separation effect of gradient temperature field diffusion and microbubble-enhanced separation. Experimental data shows that at the optimal frequency of 120kHz, only 3 minutes of ultrasound treatment is needed for the cavitation bubble collapse intensity and frequency to form a highly efficient superposition effect. The micro-jets have sufficient impact force to penetrate the dense structure of impurities, achieving rapid removal of deep impurities. Further temperature field stabilization and microbubble separation complete the capture and separation of fine impurities, eliminating the need to extend the ultrasound time. However, when the ultrasound time is shortened to 0.25-1.5 minutes, cavitation is insufficient, and the cleaning effect significantly decreases. This conclusion breaks through the technical prejudice that "extending the ultrasonic time will inevitably improve the cleaning effect," proving that the cavitation intensity dominated by frequency is the core factor determining the cleaning efficiency, rather than simply the accumulation of time. This shortens the overall process cycle by more than 60%, significantly improves production efficiency, and meets the needs of large-scale, high-efficiency manufacturing of glass fiber electronic cloth for printed circuit boards.

[0064] The combination of gradient temperature cleaning and ultrasonic-temperature field-microbubble coupling technology achieves a dual effect of "damage control" and "cleanliness improvement" that exceeds expectations, breaking through a long-standing technical dilemma in the industry. Those skilled in the art generally believe that high-temperature, long-duration cleaning is a necessary condition for ensuring high cleanliness of substrates; however, high temperatures can easily lead to fiber embrittlement and decreased strength. Therefore, the industry has long faced the dilemma of balancing "cleanliness" and "mechanical properties." This solution employs a gradient temperature pretreatment and post-treatment process of "90℃ short-time immersion + 60℃ rinsing + flowing pure water rinsing," and forms a precise and efficient coupling with ultrasonic coupling cleaning, gradient temperature field stabilization, and microbubble-enhanced separation processes, achieving a comprehensive effect that exceeds expectations. The pretreatment stage involves a short soaking in 90℃ hot water to quickly loosen surface impurities, creating favorable conditions for subsequent ultrasonic cleaning. A temperature stabilization step ensures thorough diffusion of inner-layer impurities. The post-treatment stage, with its gradient temperature cleaning, effectively disperses the removed impurities using 90℃ hot water and prevents internal stress and embrittlement of the fibers due to sudden temperature changes through a 60℃ medium-temperature rinsing. Finally, a 30-second rinse with flowing pure water, combined with the synergistic effects of the preceding multi-step processes, achieves a substrate surface cleanliness that meets the standards for high-end printed circuit board applications. Simultaneously, the fiber tensile strength is increased by more than 15% compared to traditional high-temperature cleaning processes. This coupled process breaks through the conventional understanding that "high-temperature cleaning = high cleanliness," successfully achieving the dual goals of improved cleanliness and protection of mechanical properties, providing key technical support for the industrial application of high-end glass fiber substrates for printed circuit boards.

[0065] The conventional understanding in this field is that the concentration of alkali in a chemical cleaning system is positively correlated with the efficiency of impurity removal, and that a high concentration of alkali (50-80 g / L) combined with an oxidant is necessary to achieve efficient removal. This solution, however, completely overturns this conventional wisdom through a multi-field coupling mechanism of "20 g / L low-concentration sodium hydroxide + 40-120 kHz variable-frequency ultrasonic cavitation + gradient temperature field stabilization + microbubble-enhanced separation," combined with system control experiments. Specific experimental data are as follows:

[0066] Experimental Design: Experimental Group: The process of this invention was used, with a sodium hydroxide concentration of 20 g / L, without the addition of hydrogen peroxide and stabilizers. The ultrasonic frequencies were 40 kHz, 80 kHz, and 120 kHz, the treatment time was 3 min, the liquid-to-solid ratio was 15:1 L / kg, and a gradient temperature field stabilization and microbubble-enhanced separation process was included. Control Group: A traditional chemical cleaning process was used, with a sodium hydroxide concentration of 60 g / L, 10 parts hydrogen peroxide and 2 parts stabilizers added, without ultrasonication, temperature field stabilization, or microbubble separation processes. All other parameters were the same as the experimental group.

[0067] Test indicators: residual impurities (LOI value by burning method), and retention rate of tensile strength of substrate.

[0068] Table 2:

[0069] Group Alkali concentration ultrasonic frequency Residual slurry (LOI value) Tensile strength retention Experimental group 1 20g / L 40kHz 0.35% 92.5% Experimental group 2 20g / L 80kHz 0.28% 94.2% Experimental group 3 20g / L 120kHz 0.19% 95.8% control group 60g / L none 0.21% 82.1%

[0070] Data conclusions and cognitive breakthrough analysis: The residual amount of impurities in experimental group 3 (20g / L alkali solution + 120kHz ultrasound + temperature field stabilization + microbubble separation) was as low as 0.19%, and the cleaning effect was better than that of the control group (0.21%). This proves that low-concentration alkali solution, under the synergistic effect of ultrasound, temperature field and microbubble multi-field, can achieve peeling and separation effects comparable to or even better than the high alkali solution + oxidant process, breaking through the traditional technical understanding.

[0071] The tensile strength retention rate of the experimental group was higher than 92%, which was much higher than the 82.1% of the control group. This is because the low-concentration alkaline solution had a gentle effect and no oxidant corrosion. The ultrasonic, temperature field and microbubble processes did not damage the fiber structure, effectively protecting the mechanical properties of the substrate and making it more suitable for the high reliability requirements of printed circuit boards.

[0072] As can be seen from the comparison of experimental groups 1-3, in the low-alkali system, the effect of increasing the ultrasonic frequency on the cleaning effect is far greater than that of the alkali concentration. Combined with temperature field diffusion and microbubble separation, the residual amount can be further reduced. This verifies that ultrasonic cavitation mass transfer enhancement, gradient temperature field diffusion and microbubble adsorption separation are the core of achieving low-alkali and high-efficiency cleaning, overturning the industry's long-term reliance on high alkali and oxidants.

[0073] The ultrasonic frequency of this process can be flexibly adjusted within the range of 40-120kHz, and the processing time can be selected according to actual production needs. The parameters are highly adjustable and can be adapted to the processing of different types of printed circuit board substrates, meeting the production specifications of downstream fields such as high-end printed circuit boards and electronic packaging materials.

[0074] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. An ultrasonic coupling cleaning process for printed circuit board substrates, characterized in that, Includes the following steps: (1) Preparation of cleaning solution: Dissolve 20 parts of sodium hydroxide in pure water by mass to obtain sodium hydroxide solution; add 1 part of penetrant JFC-M and 5 parts of auxiliary agent AEO-5 to the sodium hydroxide solution, stir at 50°C for 30 min to obtain cleaning solution; no hydrogen peroxide or stabilizer is added to the cleaning solution. (2) Pretreatment: The substrate is soaked in hot water, rinsed in low-temperature hot water, rinsed with running pure water, and then drained. (3) Ultrasonic coupling cleaning: The pretreated substrate is completely immersed in the cleaning solution prepared in step (1), and placed in a frequency conversion ultrasonic device with a power of 120W. It is ultrasonically treated for 0.25-3min at an ultrasonic frequency of 40-120kHz. The substrate surface is peeled off through the synergistic effect of the ultrasonic physical cavitation effect and the chemical action of the cleaning solution. (4) Gradient temperature field stabilization: The substrate that has been ultrasonically cleaned is kept in the original cleaning solution for 10-30 seconds to allow residual impurities in the fiber gaps to fully diffuse into the liquid phase system. (5) Microbubble enhanced separation: The substrate after ultrasonic coupling cleaning is kept immersed in the original cleaning liquid system. Micro-nano bubbles are introduced into the cleaning liquid. The adsorption and buoyancy of micro-nano bubbles are used to adsorb the fine impurity particles that are suspended on the surface of the substrate and in the cleaning liquid after ultrasonic stripping and float to the liquid surface with the bubbles to achieve separation. (6) Post-treatment: The treated substrate is soaked in hot water, rinsed in low-temperature hot water, rinsed with running pure water, and then drained. (7) Drying: The post-processed substrate is dried in an oven to obtain a high-cleanliness reinforced substrate for printed circuit boards.

2. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, In step (2), the temperature of the hot water soak is 90℃ and the soaking time is 2 minutes; the temperature of the low-temperature hot water rinse is 60℃ and the rinsing time is 15 seconds; and the rinsing time with flowing pure water is 10 seconds.

3. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, The temperature of the hot water soak in step (6) is 90℃ and the soaking time is 2min; the temperature of the low-temperature hot water rinse is 60℃ and the rinsing time is 15s; the rinsing time of the flowing pure water is 30s.

4. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, The ultrasonic frequency of the variable frequency ultrasonic device mentioned in step (3) is 40kHz, 80kHz or 120kHz.

5. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, The ultrasonic treatment time in step (3) is 0.25 min, 1.5 min or 3 min.

6. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, The drying temperature of the oven in step (7) is 105℃ and the drying time is 60min; the oven is a forced-air oven with a forced-air speed of 1-2m / s.

7. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, The concentration of the sodium hydroxide solution mentioned in step (1) is 20 g / L.

8. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, The liquid-to-solid volume ratio of the cleaning solution to the substrate in step (3) is (10-20):1L / kg.

9. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, The substrate is a reinforced substrate for printed circuit boards, which is suitable for printed circuit boards, electronic packaging materials or resin-based composite materials for radar radomes; steps (2), (3), (5) and (6) synergistically form a physical and chemical coupled cleaning system, which significantly improves the efficiency of impurity removal.

10. The ultrasonic coupling cleaning process for printed circuit board substrates according to claim 1, characterized in that, In step (5), micro-nano bubbles are uniformly dispersed in the cleaning solution and come into full contact with the substrate surface and the gaps inside the fibers, achieving three-phase separation of impurities, cleaning solution and substrate; the substrate is kept submerged throughout the process without changing the original composition of the cleaning solution.

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