Dry ice cleaning process of PTC heater PCBA and dry ice cleaning device thereof

Abstract

The application belongs to the technical field of electronic device manufacturing, and discloses a dry ice cleaning process for PTC heater PCBA and a dry ice cleaning device thereof. The process distinguishes between the to-be-cleaned parts and the exempted parts through incoming material diversion determination; the to-be-cleaned parts are fixed by an anti-static jig and the inclination angle and / or rotation angle thereof are adjusted so that the to-be-cleaned surface and the cleaning dead angle are directed towards the spray gun; dry ice particles are sprayed with preset spraying parameters to remove the flux residue by means of low-temperature embrittlement, kinetic energy impact and sublimation expansion; then, secondary inspection is performed and the unqualified parts are subjected to secondary cleaning and wiping to further ensure the stability of the cleaning quality. The process improves the cleaning efficiency, the consistency of the cleaning quality and the coverage of the cleaning dead angle under the premise of ensuring non-destructive cleaning. The device comprises a dry ice cleaning main machine and an anti-static jig, and can improve the cleaning efficiency, the consistency of the cleaning quality and the coverage of the cleaning dead angle under the premise of ensuring non-destructive cleaning, and reduce environmental pollution and comprehensive cost.

Description

Technical Field

[0001] This invention relates to the field of electronic device manufacturing technology, and in particular to a dry ice cleaning process and apparatus for PTC heater PCBA. Background Technology

[0002] The PTC (Positive Temperature Coefficient) heater is a core component of the electric vehicle's thermal management system, primarily used for battery pack heating, cabin heating, and motor coolant preheating. The PTC heater's control circuit board (PCBA) integrates a power drive module, temperature sampling circuit, communication interface circuit, and multiple protection circuits. Its reliability directly affects the safety and comfort of the entire vehicle's thermal management system. After soldering processes such as wave soldering, flux residue often remains on the solder surfaces of the PTC heater PCBA. If not thoroughly cleaned, this residue can cause decreased insulation performance, leakage short circuits, creepage, and even thermal runaway. Therefore, a high level of cleanliness is required.

[0003] Current PCBA cleaning methods mainly include chemical solvent cleaning, ultrasonic cleaning, and manual wiping. Chemical solvent cleaning requires the use of isopropyl alcohol (IPA), hydrocarbon cleaners, or water-based cleaners. White residues may remain after cleaning, affecting the adhesion of subsequent conformal coatings, and some solvents pose a risk of corrosion to the substrate and component packaging materials. Ultrasonic cleaning is difficult to effectively penetrate the tiny spaces such as the bottom of BGA (Ball Grid Array) and the gaps between QFP (Quad Flat Package) pins, and high-frequency vibrations may cause displacement or detachment of micro-surface components. Manual wiping is inefficient, inconsistent, and prone to causing scratches on the PCB surface or mechanical damage to components due to uneven pressure. When cleaning PTC heater PCBAs, these methods generally suffer from low cleaning efficiency, unstable cleaning quality, risk of damage to precision components, and difficulty in covering cleaning dead zones such as the bottom of the heat dissipation structure and gaps.

[0004] Dry ice cleaning technology utilizes solid carbon dioxide particles propelled at high speed by compressed air to the surface being cleaned. Contaminants are removed through low-temperature embrittlement, kinetic impact, and sublimation expansion. It offers advantages such as no chemical solvents, no wastewater discharge, and minimal damage to the substrate and metal solder joints. However, existing dry ice cleaning equipment is mostly general-purpose industrial equipment, lacking specialized fixtures and controllable process parameters for PTC heater PCBAs. This can easily lead to incomplete cleaning or damage to precision components.

[0005] Therefore, there is an urgent need for a dry ice cleaning process and device suitable for PTC heater PCBA, in order to improve cleaning efficiency and quality while ensuring non-destructive cleaning and covering cleaning dead corners such as the bottom of the heat dissipation structure and gaps. Summary of the Invention

[0006] The purpose of this invention is to provide a dry ice cleaning process and apparatus for PTC heater PCBA, which can efficiently and non-destructively remove flux residues on PTC heater PCBA after the soldering process by means of incoming material diversion, anti-static fixture angle adjustment and dry ice spray parameter control, and cover cleaning dead corners such as the bottom of the heat dissipation structure and gaps, thereby improving the consistency of cleaning quality.

[0007] To achieve this objective, the present invention adopts the following technical solution: A dry ice cleaning process for PTC heater PCBAs, used for cleaning PTC heater PCBAs after soldering processes, includes the following steps: S1. Inspect the soldering surface of the PCBA and determine whether the PCBA is a component to be cleaned or a component that does not require cleaning according to the preset residue judgment criteria. The residue judgment criteria include whether there are black oxides and / or flux residues on the surface of the PCBA. S2. Fix the part to be cleaned to the antistatic fixture, and adjust the tilt angle of the antistatic fixture relative to the horizontal plane and / or the rotation angle around the vertical axis so that the surface of the part to be cleaned is exposed to the spray path of the spray gun. S3. The spray gun sprays dry ice particles onto the surface to be cleaned with preset cleaning parameters, and the spray gun moves along the surface to be cleaned for cleaning. The cleaning parameters include spray pressure, ice output, spray distance and single-point spray time. S4. Check the cleaned PCBA surface for any of the following: black oxides, flux residue, and water droplets. If any are present, the PCBA is deemed unqualified and requires secondary cleaning or wiping. If none are present, the PCBA is deemed qualified.

[0008] Preferably, in step S1, the conditions for determining the presence of flux residue are that the thickness of flux residue on the solder pad is greater than 0.05 mm and / or the total area of ​​flux residue outside the solder pad is greater than 5 mm. 2 .

[0009] Preferably, in step S2, the tilt angle of the antistatic fixture is in the range of 0°-45°, and the rotation angle of the antistatic fixture around the vertical axis is in the range of 0°-360°.

[0010] Preferably, in step S3, the spray pressure ranges from 0.1 to 0.8 MPa, the ice output ranges from 0.1 to 0.6 kg / min, the spray distance ranges from 90 to 150 mm, the single-point spray time ranges from 2 to 3 seconds / point, and the spray gun's moving speed is 25 to 47.5 mm / s.

[0011] Preferably, in step S3, the cleaning is carried out inside the noise-reducing outer cover, and at the same time, the negative pressure dust removal system is turned on to perform negative pressure dust removal at the cleaning station inside the noise-reducing outer cover.

[0012] Preferably, in step S3, the cleaning parameters of the spray gun are selected according to the PCBA model, and the cleaning is automatically stopped and an alarm is triggered when the cleaning is abnormal.

[0013] Preferably, after step S4, the method further includes: S5. Perform ion contamination test, surface insulation resistance test and solder joint pull test on the PCBA to verify the cleaning cleanliness and whether the PCBA has cleaning damage. The pass standard for the ion contamination test is that the residual ion content is not greater than 1.56 μg NaCl eq / cm. 2 The pass standard for the surface insulation resistance test is that the surface insulation resistance is not less than 1×10⁻⁶. 8 Ω, the pass standard for the weld joint tensile test is that the weld joint tensile force change rate is not greater than 1%.

[0014] A dry ice cleaning apparatus for a PTC heater PCBA, used to implement the dry ice cleaning process for the PTC heater PCBA as described above, the dry ice cleaning apparatus comprising: Dry ice cleaning unit, including a movable spray gun for providing dry ice spray with preset cleaning parameters; An anti-static fixture is used to fix a PCBA in an anti-static manner and can adjust the tilt angle of the PCBA relative to the horizontal plane and the rotation angle about the vertical axis.

[0015] Preferably, the antistatic fixture includes a fixed base, an angle adjustment bracket, and a rotating platform. The angle adjustment bracket is connected to the fixed base and is used to adjust the tilt angle of the fixed base relative to the horizontal plane. The angle adjustment bracket is disposed on the rotating platform, and the rotating platform enables the angle adjustment bracket and the fixed base to rotate together around a vertical axis.

[0016] Preferably, the dry ice cleaning device further includes: Noise-reducing enclosures are used to isolate the cleaning station from the outside environment and reduce operating noise. The negative pressure dust removal system is connected to the interior of the noise reduction cover and is used to create negative pressure at the cleaning station and filter the exhaust gas.

[0017] The beneficial effects of this invention are: This invention provides a dry ice cleaning process for PTC heater PCBAs, used for cleaning PTC heater PCBAs after soldering. Through incoming material inspection and sorting, PCBAs are divided into cleanable and non-cleanable components based on preset residue judgment standards, thus avoiding over-cleaning of non-cleanable components and under-cleaning of cleanable components, ensuring consistency in batch cleaning. By fixing the cleanable components to an anti-static fixture and adjusting its tilt and / or rotation angle so that the cleanable surface faces the spray gun, both the anti-static fixture avoids electrostatic damage during the cleaning process, and the attitude adjustment ensures that the bottom of the BGA, QFP pin gaps, through-hole solder joints, and the bottom and gaps of the heat dissipation structure of the PCBA are sequentially exposed to the spray path of the spray gun. This process overcomes the shortcomings of conventional cleaning methods that struggle to cover cleaning dead zones. By spraying dry ice particles onto the surface to be cleaned using a spray gun at preset spray pressure, ice output, spray distance, and single-point spray time, the triple action of low-temperature embrittlement, kinetic energy impact, and sublimation expansion of the dry ice particles causes flux residue to peel off from the PCBA surface and be carried away by the airflow. Because the hardness of the dry ice particles is lower than that of the PCB substrate and metal solder joints, and the single-point action time is short, efficient cleaning is achieved without causing mechanical or thermal damage to the substrate, solder joints, or precision components. After cleaning, the PCBA is inspected for black oxides, flux residue, and water droplets, and defective parts are cleaned or wiped again, further ensuring the stability of cleaning quality. This process improves cleaning efficiency, consistency of cleaning quality, and coverage of cleaning dead zones while ensuring non-destructive cleaning.

[0018] This invention also provides a dry ice cleaning device for PTC heater PCBAs, used to implement the above-mentioned cleaning process. The device provides dry ice spray with adjustable parameters such as spray pressure, ice output, spray distance, and single-point spray time through a dry ice cleaning host, so that the cleaning process parameters can be flexibly adjusted according to the PCBA model and degree of contamination. This ensures the cleaning effect while avoiding insufficient cleaning or component damage caused by fixed parameters. The PCBA is fixed in place by an anti-static fixture, and its tilt and rotation angles are adjusted to prevent electrostatic damage during the cleaning process. This also ensures that the surface of the PCBA to be cleaned, as well as the bottom and gaps of the heat dissipation structure, face the spray gun, facilitating all-round cleaning. Attached Figure Description

[0019] Figure 1 This is a partial flowchart of the dry ice cleaning process for the PTC heater PCBA in an embodiment of the present invention. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0021] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" 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 based on the specific circumstances.

[0022] 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.

[0023] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, 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 the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0024] like Figure 1 As shown, this invention discloses a dry ice cleaning process for PTC heater PCBAs, used for cleaning PTC heater PCBAs after soldering processes, including the following steps: S1. Inspect the PCBA soldering surface and determine whether the PCBA is a component to be cleaned or a component that does not require cleaning according to the preset residue judgment criteria. The residue judgment criteria include whether there are black oxides and / or flux residues on the PCBA surface. S2. Fix the part to be cleaned to the anti-static fixture, and adjust the tilt angle of the anti-static fixture relative to the horizontal plane and / or the rotation angle around the vertical axis so that the surface of the part to be cleaned is exposed to the spray path of the spray gun. S3. Spray dry ice particles onto the surface to be cleaned with the spray gun according to the preset cleaning parameters, and move the spray gun along the surface to be cleaned for cleaning. The cleaning parameters include spray pressure, ice output, spray distance and single-point spray time. S4. Check the cleaned PCBA surface for any of the following: black oxides, flux residue, and water droplets. If any are present, the PCBA is deemed unqualified and requires secondary cleaning or wiping. If none are present, the PCBA is deemed qualified.

[0025] It is understood that the following embodiments all use the cleaning requirements of PCBA after wave soldering as an example. Of course, other soldering processes can also be used in other embodiments. This is only for illustrative purposes and should not be construed as a limitation on the soldering process. Specifically, in step S1, incoming materials are sorted by a preset residue judgment standard, which can avoid over-cleaning of non-cleanable parts and under-cleaning of parts to be cleaned, ensuring the consistency of batch cleaning. In step S1, the appearance of the TOP and BOT sides of the PCBA is inspected by the operator visually or with the help of tools. The BOT side is the wave soldering surface and is the main distribution surface of flux residue. It is necessary to focus on inspecting the bottom of BGA, the gap between QFP pins, and the area around the solder pads of plug-in components. The TOP side is the component side and needs to be checked for flux splashes or oxides. Through a comprehensive inspection of the TOP and BOT sides, omissions are avoided. Before step S1, there is also a production preparation stage, in which the operator wears an anti-static wrist strap (grounding resistance 0.75-1.5MΩ) and anti-static gloves (surface resistance 10). 6 -10 9Ω), and confirm that the compressed air pressure is ≥0.6MPa and the dry ice storage is ≥3kg to avoid electrostatic damage during the inspection process and interruption of the subsequent cleaning process. The compressed air is used to blow dry ice particles from the dry ice cleaning host to achieve dry ice spraying from the spray gun. In step S2, an anti-static fixture is used to fix the part to be cleaned, which can prevent static electricity from damaging the PCBA during the cleaning process. At the same time, by adjusting the tilt angle and / or the rotation angle around the vertical axis of the anti-static fixture, the cleaning dead corners of the part to be cleaned, such as the bottom of BGA (Ball Grid Array), the pin gap of QFP (Quad Flat Package), the solder joints of the plug-in, the bottom of the heat dissipation structure and the gaps, can be facing and exposed to the spray gun nozzle, overcoming the defect of general cleaning methods that are difficult to cover cleaning dead corners. In step S3, the triple action of low-temperature embrittlement, kinetic impact, and sublimation expansion of dry ice particles causes flux residue to peel off from the PCBA surface and be carried away by the airflow. Because the hardness of dry ice particles is lower than that of the PCB substrate and metal solder joints, and the single-point action time is short, efficient cleaning is achieved without causing mechanical or thermal damage to the substrate, solder joints, or precision components. In step S4, black oxides, flux residue, and water droplets are inspected. If any one of these is present, the component is deemed defective and undergoes secondary cleaning or wiping to further ensure cleaning quality. It should be noted that the criteria for judging black oxides and / or flux residue are the same as the preset residue judgment criteria in step S1; if water droplets are present, a secondary wiping is performed.

[0026] In some embodiments, dry ice particles with a temperature as low as -78.5°C, when sprayed onto the PCBA surface, rapidly freeze and embrittle flux residues, increasing their hardness by more than three times. At this point, the adhesion between the flux residues and the PCB substrate and component leads is significantly reduced, forming microcracks. Subsequently, driven by compressed air, the dry ice particles impact the embrittled flux layer at speeds of, for example, 200-400 m / s, producing a mechanical peeling effect. It is understood that the dry ice particles sublimate directly from a solid to a gaseous state upon impact with the area to be cleaned on the PCBA surface, with a latent heat of phase change of approximately 573 kJ / kg and a volume expansion of nearly 800 times. This creates a "micro-explosion" effect at the impact point, blowing the embrittled flux particles away from the PCBA surface. Furthermore, the dry ice particles completely evaporate as CO2 gas, leaving no residue on the PCBA surface. Because the hardness of the dry ice particles is lower than that of the PCB substrate and metal solder joints, and the single-point impact time is short, it does not cause mechanical or thermal damage to the PCBA.

[0027] In some embodiments, in step S1, the condition for determining the presence of flux residue is that the thickness of the flux residue on the solder pad is greater than 0.05 mm and / or the total area of ​​flux residue outside the solder pad is greater than 5 mm².2 Understandably, this criterion quantifies incoming material inspection and avoids subjective judgment discrepancies. Through thickness and area thresholds, it accurately distinguishes between parts requiring cleaning and parts that do not require cleaning. A flux residue thickness greater than 0.05mm indicates significant residue, and a flux residue area greater than 5mm... 2 This indicates a large residual area, requiring cleaning in any of the above situations. In some optional embodiments, the inspection tool can be a magnifying glass or a microscope to assist in quick and accurate judgment. For example, when judging the thickness and area of ​​flux residue, the thickness can be determined using cross-sectional metallography. Specifically, a sample of the residue on the surface to be cleaned is embedded in resin, ground, and sectioned. The cross-sectional thickness is then measured directly under a microscope, suitable for solder slag and large particle-like protrusions. Alternatively, a super depth-of-field microscope can be used, which is also a commonly used thickness measurement method in the field; specific details are not elaborated here. The area of ​​the residue can be determined using a high-magnification magnifying glass. Specifically, the surface to be cleaned is observed and photographed under a high-magnification magnifying glass, and the residue area is selected using image processing software. The area is then directly read out using the image processing software.

[0028] In some specific embodiments, in step S2, the tilt angle of the antistatic fixture ranges from 0° to 45°, and the rotation angle of the antistatic fixture around its vertical axis ranges from 0° to 360°, meaning it can rotate horizontally by 360°. It can be understood that the tilt angle range of 0° to 45° allows a suitable spray angle to be formed between the PCBA's surface to be cleaned and the spray gun, facilitating the dry ice particles to reach the bottom and gaps of the heat dissipation structure; the horizontal rotation of 360° allows each side of the PCBA to face the spray gun sequentially, achieving all-around cleaning.

[0029] In some embodiments, in step S3, the spray pressure ranges from 0.1 to 0.8 MPa, the ice output ranges from 0.1 to 0.6 kg / min, the spray distance ranges from 90 to 150 mm, the single-point spray time ranges from 2 to 3 seconds per point, and the spray gun's moving speed is 25 to 47.5 mm / s. It is understood that these parameters work together to ensure both cleaning effectiveness and component safety. It is important to note that too low a spray pressure will result in incomplete cleaning, while too high a pressure may damage components. The ice output controls the dry ice consumption and cleaning intensity. Too short a spray distance results in high impact force, while too long a distance leads to poor results. The single-point spray time controls the dwell time of the spray gun at a single point, and the spray gun's moving speed controls the cleaning cycle. In some specific embodiments, the spray pressure is preferably 0.3-0.5 MPa, the ice output rate is preferably 6.5-7.5 rpm, the spray distance is preferably 100-120 mm, the single-point spray time is preferably 2.5 seconds / point, and the spray gun moving speed is preferably 35-40 mm / s.

[0030] The key process parameter ranges and preferred values ​​are shown in Table 1 below: Table 1: As shown in Table 1, the setting range for ice-discharging air pressure (i.e., spray pressure) is 0.1-0.8 MPa, with a preferred value of 0.3-0.5 MPa; the setting range for ice discharge rate is 5.5-8.0 rpm, with a preferred value of 6.5-7.5 rpm; the setting range for spray distance is 90-150 mm, with a preferred value of 100-120 mm; the setting range for spray time is 2-3 seconds / point, with a preferred value of 2.5 seconds / point; and the setting range for motor movement speed (i.e., spray gun movement speed, the movement of the spray gun) is... The setting range for the motor-driven dry ice is 50-95% of the motor's rated moving speed, with a preferred value of 70-80%. In this embodiment, the rated moving speed of the motor in Table 1 is 50 mm / s. 50-95% of the rated moving speed corresponds to a spray gun moving speed of 25-47.5 mm / s, and 70-80% of the rated moving speed corresponds to a spray gun moving speed of 35-40 mm / s. The dry ice is a standard block of 140 mm × 125 mm × 250 mm, weighing approximately 5 kg per block.

[0031] It is understandable that the ice output is measured in "revolutions per minute" because the ice dispensing mechanism of the dry ice cleaning unit controls the supply rate of dry ice particles by adjusting the rotation speed of the regulating valve. The faster the regulating valve rotates, the more dry ice particles are delivered to the spray gun per unit time, and the greater the dry ice mass flow rate. This measurement method is a conventional parameter expression method for dry ice cleaning equipment in this field. In a specific embodiment, an ice output of 5.5-8.0 revolutions per minute corresponds to a dry ice mass flow rate of approximately 0.1-0.6 kg / min, and preferably, an ice output of 6.5-7.5 revolutions per minute corresponds to a dry ice mass flow rate of approximately 0.3-0.5 kg / min.

[0032] In some embodiments, in step S3, the cleaning is carried out inside a noise-reducing enclosure, and simultaneously, a negative pressure dust removal system is activated to remove dust from the cleaning station within the noise-reducing enclosure. It is understood that the noise-reducing enclosure isolates the cleaning station from the outside environment and reduces operating noise, improving the working environment for operators; the negative pressure dust removal system creates negative pressure at the cleaning station, promptly removing CO2 gas and stripped flux particles generated during the cleaning process, preventing the spread of pollutants and meeting cleanroom emission requirements.

[0033] In some embodiments, in step S3, the cleaning parameters of the spray gun are selected according to the PCBA model. If a cleaning malfunction occurs, the cleaning process automatically stops and an alarm is triggered. It is understood that selecting corresponding cleaning parameters based on different PCBA models enables automation of the cleaning process and ensures parameter consistency, reducing the impact of human error on cleaning quality. Automatic shutdown and alarm activation in case of equipment malfunction ensures the safety of both the equipment and the PCBA. In some optional embodiments, production data such as cleaning quantity and cleaning time can also be recorded for quality traceability.

[0034] In some specific embodiments, after step S4, the method further includes: S5. Perform ion contamination testing, surface insulation resistance testing, and solder joint pull-out testing on the PCBA to verify the cleanliness of the cleaning and whether there is any cleaning damage to the PCBA. The passing standard for the ion contamination test is that the residual ion content is no more than 1.56 μg NaCl eq / cm 2 The pass standard for surface insulation resistance testing is a surface insulation resistance of not less than 1×10⁻⁶. 8 Ω, the pass standard for the weld joint tensile test is that the change rate of weld joint tensile force is not greater than 1%.

[0035] Understandably, in order to objectively evaluate the cleanliness and non-destructive nature of the cleaning process, the ion residue was measured using the ROSE method, 1.56 μg NaCl eq / cm. 2 This is the industry standard. The surface insulation resistance is not less than 1×10⁻⁶. 8 Ω ensures insulation performance under high-voltage conditions. A change rate of no more than 1% in the tensile strength of the solder joint indicates that the cleaning process did not damage the solder joint.

[0036] In some embodiments, after step S5, the method further includes: S6. Arrange the inspected and qualified parts neatly in the storage box in a uniform direction, with alternating layers, and affix labels. The labels should include at least one of the following: model number, batch number, cleaning date, and operator information, to prepare for the next process, i.e., ICT testing or conformal coating. Anti-static blister boxes can be used for the storage box to avoid electrostatic damage to the PCBAs. Alternating layers mean that multiple layers can be placed in the storage box, each with a placement board. PCBAs placed across these placement boards are staggered to avoid one-to-one stacking and mechanical compression damage. For example, each layer of the board can hold 8 PCBAs, arranged in two rows and four columns. The first row from left to right has placement positions 1, 2, 3, and 4, and the second row from left to right has placement positions 5, 6, 7, and 8. When placing the first layer, the PCBAs are placed in placement positions 1, 3, 5, and 7. When placing the second layer, they are placed in placement positions 2, 4, 6, and 8, and so on. Alternatively, when placing the first layer, the PCBAs are placed in placement positions 1, 2, 3, and 4. When placing the second layer, they are placed in placement positions 5, 6, 7, and 8, and so on. PCBAs in adjacent layers are placed crosswise to avoid mechanical compression damage.

[0037] In some optional embodiments, to verify the adaptability of the process of the present invention to different flux types, the same PCBA model was selected, and cleaning tests were conducted on three common fluxes under the same conditions of spray gun distance, spray time, motor moving speed, and dry ice specifications. The results are shown in Table 2 below: Table 2: As shown in Table 2, for rosin-based (R-type) flux, the residue before cleaning was a pale yellow, viscous residue. After cleaning with air pressure of 0.4 MPa and ice discharge rate of 7.0 rpm (0.4 kg / min), the flux was completely removed, and the ion residue was 0.38 μg / cm³. 2 (μg / cm in this table) 2 All refer to μg NaCl eq / cm 2 For no-clean (RMA) flux, a trace amount of transparent residue remained before cleaning. After cleaning with parameters of 0.3 MPa air pressure and 6.0 rpm (0.2 kg / min) ice discharge, it was completely removed, with an ion residue of 0.25 μg / cm³. 2 For water-soluble (WS type) flux, white crystalline residue remained before cleaning. After cleaning with parameters of 0.5 MPa air pressure and 7.5 rpm (0.5 kg / min) ice discharge, it was completely removed, with a residual ion concentration of 0.45 μg / cm³. 2 The results show that the cleaning process of this invention has a good cleaning effect on various fluxes, and the residual ion content is far lower than the industry standard requirements.

[0038] In some optional embodiments, continuous production verification was conducted in the wave soldering workshop: two shifts, 8 hours per shift, with an average daily output of approximately 800 PCBAs, for 30 consecutive days, totaling approximately 24,000 PCBAs cleaned. The verification results are shown in Table 3 below: Table 3: As shown in Table 3, during the continuous production verification period, the actual daily output reached 800 units, exceeding the target of 700 units; the actual cleaning yield was 99.7%, exceeding the target of 99%; the actual cleaning time per unit was 2 minutes and 15 seconds, lower than the target of 3 minutes; the actual cost of consumables per unit was 0.32 yuan, lower than the target of 0.4 yuan; the actual equipment failure rate was 0.8%, lower than the target of 2%; the actual noise level was 63 dB, lower than the target of 70 dB; and the actual operator satisfaction rate was 92%, higher than the target of 80%. The continuous production verification demonstrates that the device and process described in this invention operate stably and reliably, meeting the needs of large-scale industrial production.

[0039] In some optional embodiments, 100 PTC heater PCBAs from the same batch were selected and compared using traditional chemical cleaning (isopropanol wiping) and the dry ice cleaning method of the present invention. The results are shown in Table 4 below: Table 4: As shown in Table 4, compared with traditional isopropanol wiping chemical cleaning, the dry ice cleaning of this invention reduces the single-piece cleaning time from 12 minutes to 2.5 minutes, an improvement of 79%; the flux residue rate decreases from 6.5% to 0.08%, a reduction of 99%; the PCBA yield increases from 94.2% to 99.8%, an improvement of 5.6%; the cost of consumables per piece decreases from 0.85 yuan to 0.32 yuan, a reduction of 62%; wastewater generation decreases from 2.5L / piece to 0, a reduction of 100%; VOCs (volatile organic compounds) emissions decrease from 15g / piece to 0, a reduction of 100%; the number of operators decreases from 3 people / shift to 1 person / shift, a reduction of 67%; and the floor space required decreases from 15m² to 100%. 2 Reduced to 8m 2 The efficiency was reduced by 47%. Comparative results show that the present invention is significantly superior to traditional chemical cleaning processes in terms of cleaning efficiency, cleaning quality, environmental performance, and cost control.

[0040] This invention also discloses a dry ice cleaning apparatus for a PTC heater PCBA, used to implement the dry ice cleaning process of the PTC heater PCBA in any of the above embodiments, comprising: Dry ice cleaning unit, including spray gun, for providing dry ice spray with adjustable parameters such as spray pressure, ice output, spray distance and single-point spray time; Antistatic fixtures are used to fix PCBAs in an antistatic manner and can adjust the tilt and rotation angles of the PCBAs.

[0041] Understandably, the dry ice cleaning unit provides adjustable dry ice spray parameters, allowing cleaning process parameters to be flexibly adjusted according to the PCBA model and degree of contamination, avoiding insufficient cleaning or component damage due to fixed parameters. Anti-static fixtures are used to fix the PCBA in place and adjust its posture for easy all-around cleaning. A negative pressure dust removal system removes CO2 gas and flux particles, while a noise-reducing enclosure reduces noise. An intelligent control system stores and retrieves process parameter formulas for automated control. The dry ice cleaning unit, negative pressure dust removal system, and noise-reducing enclosure are all existing equipment in the field, and their specific structures and working principles will not be elaborated further. The fixed base, angle adjustment bracket, and rotating platform of the anti-static fixture can all be implemented using conventional anti-static materials and transmission structures in the field.

[0042] For example, the dry ice cleaning unit uses the HQ-21 handheld noise-reducing dry ice cleaning machine, which is suitable for AC220V (50-60Hz), has dimensions of L750mm×W700mm×H1500mm, weighs 80kg, and has a main motor power of 0.25kW; the air supply flow rate is 0.5-4.0m³ / h. 3 The dry ice spray rate is 0.1-0.6 kg / min, with an air supply pressure of 0.1-0.8 MPa (adjustable parameters). It is suitable for dry ice sizes of 140mm×125mm×250mm (approximately 5 kg / block), and has a hopper capacity of 5-10 kg. It is equipped with a 3-meter inner diameter 1 / 2-inch low-temperature dry ice conveying pipe, a 5-meter high-pressure air pipe (1 / 2-inch external thread connector & C-type quick-connect connector), and multiple replaceable nozzle assemblies. The main unit has an independent exhaust system that effectively removes small and large dust particles, which naturally fall into the mesh funnel for effective recycling. The accompanying cover ensures quiet operation.

[0043] In some embodiments, the antistatic fixture includes a fixed base, an angle adjustment bracket, and a rotating platform. The angle adjustment bracket is fixedly connected to the fixed base and is used to adjust the tilt angle of the fixed base. The angle adjustment bracket is disposed on the rotating platform, which enables the angle adjustment bracket and the fixed base to rotate together around a vertical axis. The surface resistance of the fixed base is 10 Ω. 6 -10 9The system features an Ω-shaped, locating groove that matches the PCBA's shape, with a groove depth ranging from 2-3mm. The angle adjustment bracket can be tilted within a 0°-45° range, and the rotating platform supports 360° rotation around the vertical direction. Essentially, the fixed base supports the PCBA, and the locating groove prevents PCBA displacement. The angle adjustment bracket adjusts the tilt angle, ensuring the bottom of the heat dissipation structure and any gaps face the spray gun. The rotating platform drives the angle adjustment bracket and fixed base to rotate vertically, ensuring the areas of the PCBA to be cleaned face the spray gun sequentially. The surface resistance of the fixed base ensures anti-static performance.

[0044] In some embodiments, the dry ice cleaning device for the PTC heater PCBA further includes a noise-reducing enclosure and a negative pressure dust removal system. The noise-reducing enclosure isolates the cleaning station from the outside environment and reduces operating noise; the negative pressure dust removal system is connected to the interior of the noise-reducing enclosure and is used to create negative pressure at the cleaning station and filter the exhaust gas. Optionally, the dry ice cleaning device for the PTC heater PCBA also includes a control system, which includes a controller and a control panel electrically connected to the controller. This control system stores and recalls cleaning parameters for different PCBA models and controls the operation of the dry ice cleaning host and the negative pressure dust removal system. Exemplarily, the controller can be a PLC (Programmable Logic Controller).

[0045] In some specific embodiments, the negative pressure dust removal system includes a dust collection hood, a centrifugal fan, and a filter unit. The dust collection hood is located inside a noise-reducing outer casing and above the cleaning station. The outer contour of the dust collection hood is conical, with a through hole at the top and an opening at the bottom. The air intake of the centrifugal fan is connected to the through hole of the dust collection hood via a pipe to achieve dust collection. The filter unit is located on the pipe between the air intake and the dust collection hood and is used to filter the gas drawn in and discharged by the centrifugal fan. For example, the air volume of the centrifugal fan is 1200 m³ / h. 3 The noise reduction cover has a negative pressure of -2000Pa and a double-layer structure. It features an observation window and a silicone-sealed glove opening, reducing operating noise to below 75dB. The dust hood is made of transparent acrylic with an opening size of 600mm × 400mm. It collects CO2 gas and flux particles, while the centrifugal fan creates negative pressure. The filter unit filters the gas discharged from the centrifugal fan to remove particulate matter and trace amounts of organic gases. The noise reduction cover has a double-layer structure: an outer layer of cold-rolled steel plate and an inner layer of sound-absorbing cotton. Optionally, the outer layer can be 1.5mm cold-rolled steel plate, and the inner layer can be 50mm thick sound-absorbing cotton with a density of 32kg / m³. 3The sound-absorbing cotton has a sound absorption coefficient ≥0.85@1000Hz (the sound absorption coefficient at 1000Hz is not less than 0.85). The noise-reducing cover also features a double-layered tempered glass laminated observation window and two glove holes. Optionally, the double-layered tempered glass laminated observation window is 10mm thick with a light transmittance ≥85%, and the two glove holes are two 160mm diameter silicone-sealed glove holes, capable of reducing equipment operating noise from 85-100dB to below 75dB. In some optional embodiments, the filtration unit can be a HEPA filter (filtration efficiency ≥99.97%@0.3μm particles, with a filtration efficiency of not less than 99.97% for particles with a diameter of 0.3 micrometers), an activated carbon adsorption layer, or a combination thereof. Both the HEPA filter and the activated carbon adsorption layer are conventional commercially available components in the art and will not be described in detail here. In one specific embodiment, the filtration unit includes a HEPA filter and an activated carbon adsorption layer. The HEPA filter is used to filter particulate matter, and the activated carbon adsorption layer is used to adsorb trace amounts of organic gases to prevent the spread of odors.

[0046] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A dry ice cleaning process for PTC heater PCBAs, used for cleaning PTC heater PCBAs after soldering processes, characterized in that, Includes the following steps: S1. Inspect the soldering surface of the PCBA and determine whether the PCBA is a component to be cleaned or a component that does not require cleaning according to the preset residue judgment criteria. The residue judgment criteria include whether there are black oxides and / or flux residues on the surface of the PCBA. S2. Fix the part to be cleaned to the antistatic fixture, and adjust the tilt angle of the antistatic fixture relative to the horizontal plane and / or the rotation angle around the vertical axis so that the surface of the part to be cleaned is exposed to the spray path of the spray gun. S3. The spray gun sprays dry ice particles onto the surface to be cleaned with preset cleaning parameters, and the spray gun moves along the surface to be cleaned for cleaning. The cleaning parameters include spray pressure, ice output, spray distance and single-point spray time. S4. Check the cleaned PCBA surface for any of the following: black oxides, flux residue, and water droplets. If any are present, the PCBA is deemed unqualified and requires secondary cleaning or wiping. If none are present, the PCBA is deemed qualified.

2. The dry ice cleaning process for PTC heater PCBA according to claim 1, characterized in that, In step S1, the conditions for determining the presence of flux residue are that the thickness of flux residue on the solder pad is greater than 0.05 mm and / or the total area of ​​flux residue outside the solder pad is greater than 5 mm. 2 .

3. The dry ice cleaning process for PTC heater PCBA according to claim 1, characterized in that, In step S2, the tilt angle of the antistatic fixture is in the range of 0°-45°, and the rotation angle of the antistatic fixture around the vertical axis is in the range of 0°-360°.

4. The dry ice cleaning process for PTC heater PCBA according to claim 1, characterized in that, In step S3, the spray pressure ranges from 0.1 to 0.8 MPa, the ice output ranges from 0.1 to 0.6 kg / min, the spray distance ranges from 90 to 150 mm, the single-point spray time ranges from 2 to 3 seconds / point, and the spray gun moving speed is 25 to 47.5 mm / s.

5. The dry ice cleaning process for PTC heater PCBA according to claim 1, characterized in that, In step S3, the cleaning is carried out inside the noise-reducing outer cover, and at the same time, the negative pressure dust removal system is turned on to remove dust from the cleaning station inside the noise-reducing outer cover.

6. The dry ice cleaning process for PTC heater PCBA according to claim 1, characterized in that, In step S3, the cleaning parameters of the spray gun are selected according to the PCBA model, and the cleaning is automatically stopped and an alarm is triggered when the cleaning is abnormal.

7. The dry ice cleaning process for PTC heater PCBA according to claim 1, characterized in that, Following step S4, the method further includes: S5. Perform ion contamination test, surface insulation resistance test and solder joint pull test on the PCBA to verify the cleaning cleanliness and whether the PCBA has cleaning damage. The pass standard for the ion contamination test is that the residual ion content is not greater than 1.56 μg NaCl eq / cm. 2 The pass standard for the surface insulation resistance test is that the surface insulation resistance is not less than 1×10⁻⁶. 8 Ω, the pass standard for the weld joint tensile test is that the weld joint tensile force change rate is not greater than 1%.

8. A dry ice cleaning apparatus for a PTC heater PCBA, used to implement the dry ice cleaning process for the PTC heater PCBA as described in any one of claims 1-7, characterized in that, The dry ice cleaning device includes: Dry ice cleaning unit, including a movable spray gun for providing dry ice spray with preset cleaning parameters; An anti-static fixture is used to fix a PCBA in an anti-static manner and can adjust the tilt angle of the PCBA relative to the horizontal plane and the rotation angle about the vertical axis.

9. The dry ice cleaning device for PTC heater PCBA according to claim 8, characterized in that, The antistatic fixture includes a fixed base, an angle adjustment bracket, and a rotating platform. The angle adjustment bracket is connected to the fixed base and is used to adjust the tilt angle of the fixed base relative to the horizontal plane. The angle adjustment bracket is disposed on the rotating platform, and the rotating platform enables the angle adjustment bracket and the fixed base to rotate together around a vertical axis.

10. The dry ice cleaning device for PTC heater PCBA according to claim 8, characterized in that, The dry ice cleaning device also includes: Noise-reducing enclosures are used to isolate the cleaning station from the outside environment and reduce operating noise. The negative pressure dust removal system is connected to the interior of the noise reduction cover and is used to create negative pressure at the cleaning station and filter the exhaust gas.

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