A selective tin stripping process for PCB

Abstract

This invention relates to the field of PCB board processing technology, and more specifically, to a selective tin stripping process for PCB boards, including pretreatment cleaning, dry film lamination, exposure and development, tin stripping, and film removal. An antioxidant pre-protection step is added between the pretreatment cleaning and dry film lamination steps. Specifically, an antioxidant protective layer is applied to the surface of the PCB board after pretreatment cleaning. This antioxidant protective layer is formed by an antioxidant. Before laminating the dry film, the antioxidant protective layer is desorbed by preheating, restoring the PCB board surface to an active state suitable for dry film lamination. The preheating desorption step and the dry film lamination step are sequential steps and share the same heat system. The preheating desorption temperature is lower than the dry film lamination temperature. This selective tin stripping process for PCB boards improves production scheduling flexibility by applying an antioxidant protective layer to the PCB board surface and performing preheating desorption before laminating the dry film.

Description

Technical Field

[0001] This invention relates to the field of PCB board processing technology, and in particular to a selective desoldering process for PCB boards. Background Technology

[0002] Selective tin stripping of PCBs is a process that precisely removes the tin layer from specific areas of the board while retaining the tin layer in the remaining areas to meet the functional requirements of subsequent mixed surface treatments or circuit fabrication. It typically includes the following steps: pretreatment cleaning, application of acid-resistant and corrosion-resistant dry film, exposure and development, selective tin stripping, and film removal.

[0003] Pre-treatment cleaning typically includes steps such as acidic degreasing, abrasion, and micro-etching. Its purpose is to remove oxides, oil, and fingerprints from the board surface and create a microscopic rough structure on the copper surface to enhance the adhesion between the dry film and the copper. After pre-treatment cleaning, the copper surface is in a highly activated, fresh state. If it is exposed to air for too long before film application, a very thin oxide layer can easily form on the copper surface. Although this oxide layer is invisible to the naked eye, it reduces the adhesion between the dry film and the copper surface, leading to problems such as bubbles, dry film peeling, or insufficient adhesion after film application. This, in turn, can cause quality defects such as seepage and side etching during subsequent selective tin stripping, resulting in an increased defect rate. To mitigate this risk, current production processes must strictly limit the waiting time between the pre-treatment cleaning step and film application, or perform the dry film application step immediately after pre-treatment cleaning. However, this significantly reduces the flexibility of production scheduling. Summary of the Invention

[0004] To address the problems existing in the prior art, this application provides a selective desoldering process for PCB boards.

[0005] The selective desoldering process for PCB boards provided by this invention adopts the following technical solution: A selective tin stripping process for PCB boards includes pretreatment cleaning, dry film lamination, exposure and development, tin stripping, and film removal. In the dry film lamination step, the PCB board is fed into a dry film laminator, which applies the dry film to the PCB board surface in a single pass using heat pressing. The process is characterized by adding an antioxidant pre-protection step between the pretreatment cleaning and the dry film lamination, including: An antioxidant protective layer is applied to the surface of the PCB board after pretreatment cleaning. The antioxidant protective layer is formed by an antioxidant. Before applying the dry film, the antioxidant protective layer is desorbed by preheating, so that the PCB board surface is restored to an active state suitable for applying the dry film. The preheating desorption step and the dry film application step are sequential steps and share the same heat system. The temperature of the preheating desorption is lower than the temperature of the dry film application.

[0006] Preferably, the antioxidant is a water-soluble imidazole hydrochloride.

[0007] Preferably, the preheating desorption is carried out in a closed cavity. A conveying device and a preheating device are arranged in the closed cavity. The conveying device conveys the PCB board to be preheated through the preheating device. The preheating device includes two parallel front hot pressing rollers arranged vertically. The heat of the two front hot pressing rollers is respectively used to preheat the upper and lower surfaces of the PCB board.

[0008] Preferably, the temperature of the preheating desorption increases with the increase of the interval time between applying the antioxidant protection layer and laminating the dry film on the surface of the PCB board, and decreases with the decrease of the interval time between applying the antioxidant protection layer and laminating the dry film on the surface of the PCB board.

[0009] Preferably, the conveying device conveys the PCB board to be preheated through the two front hot pressing rollers at a constant power. Heat expansion sleeves are sleeved on both of the front hot pressing rollers, and the front hot pressing rollers always use the heat expansion sleeves to abut against the PCB board.

[0010] Preferably, a plurality of the heat expansion sleeves of the front hot pressing roller are arranged at intervals along the axial direction.

[0011] Preferably, two groups of the front hot pressing rollers are arranged before and after along the conveying direction of the PCB board. Among the two groups of front hot pressing rollers, the heat expansion sleeves of the two front hot pressing rollers located at the same height and distributed before and after are arranged in a staggered manner.

[0012] Preferably, the dry film laminating machine includes two parallel rear hot pressing rollers arranged vertically. Two static eliminator rollers are arranged in the closed cavity. The static eliminator rollers are made of metal rollers and grounded. The two static eliminator rollers respectively roll on the two surfaces of the PCB board under the action of elastic force.

[0013] Preferably, the dry film laminating machine adjusts the target distance between the two rear hot pressing rollers in real time according to the distance between the two static eliminator rollers. The target distance D 目标 =k˙D 测量 , where D 测量 is the measured distance between the two static eliminator rollers, k is the preheating coefficient, and the value range is 0 < k < 1. And the preheating coefficient k is inversely proportional to the preheating temperature.

[0014] Preferably, in the step of antioxidant pre-protection, the closed cavity is a drying chamber. The PCB board performs thermal desorption of the antioxidant protection layer through the ambient heat of the drying chamber. The heat expansion sleeve continuously covers the roller surface of the front hot pressing roller along the axial direction.

[0015] The beneficial effects of this invention are as follows: 1. Compared with the prior art, the present invention can form an antioxidant protective layer on the PCB board surface by adding an antioxidant pre-protection step, thereby avoiding the formation of an oxide layer on the PCB board before the dry film is applied, which would reduce the adhesion between the dry film and the board surface and cause problems such as bubbles, dry film peeling or insufficient adhesion after the film is applied. This reduces the defect rate. At the same time, it is no longer necessary to strictly limit the waiting time from the pretreatment cleaning step to the film application during the production process, which effectively improves the flexibility of production scheduling. 2. By connecting the preheating and desorption steps with the dry film lamination steps, the same heat system can be used, eliminating the need for additional independent heating equipment. This reduces equipment occupancy and maintenance costs, fully utilizes the heat source of the dry film laminator, avoids energy waste caused by repeated heating, and significantly improves process integration and energy utilization efficiency. 3. Since the preheating and desorption temperature is lower than the dry film lamination temperature, a gradient heating process is formed, which avoids the PCB board surface from experiencing a sudden temperature rise, making the board surface temperature more uniform and the hot pressing effect more consistent, effectively improving the dry film lamination quality, and ultimately achieving a complementary effect between the two steps. Attached Figure Description

[0016] Figure 1 This is a flowchart of the selective desoldering process for the PCB board in Example 1; Figure 2 This is a flowchart of the antioxidant pre-protection step in Example 1; Figure 3 This is a simplified schematic diagram of the structure inside the sealed cavity in Example 1; Figure 4 This is a simplified schematic diagram of the front hot press roller in Example 1; Figure 5 It is D in Example 1 目标 The calculation formula.

[0017] Explanation of reference numerals in the attached diagram: 1. PCB board; 2. Front hot press roller; 21. Thermal expansion sleeve; 3. Conveyor wheel; 4. Antistatic roller. Detailed Implementation

[0018] The following will combine Figures 1-5 The present invention will be further illustrated by the embodiments.

[0019] Example 1 This embodiment discloses a selective desoldering process for PCB boards.

[0020] Reference Figure 1 and Figure 2 The selective desoldering process for PCB boards includes the following steps: S1: Pre-treatment cleaning steps, specifically including: S11: Use an acidic cleaner, such as a sulfuric acid-based cleaner, at a concentration of 3%-5%, spray or soak at 40-50℃, then emulsify and disperse the oil stains with surfactants, and finally peel off the contaminants under the physical impact of high-pressure spraying, so as to remove oil stains, fingerprints and organic contaminants from the surface of PCB board 1. S12: Use a grinding brush or sandblasting to create grinding marks on the surface of PCB board 1, increase the surface roughness of PCB board 1, and improve the adhesion of subsequent dry film. After treatment, the residual brush debris needs to be washed away by high pressure water. S13: Using chemical micro-etching methods such as sodium persulfate and sulfuric acid, the surface of PCB board 1 is further roughened to enhance the adhesion between the dry film and the board surface.

[0021] S2: Antioxidant pre-protection steps, specifically including: S21: Apply an antioxidant protective layer to the surface of the PCB board 1 after pretreatment cleaning. The antioxidant protective layer is formed by an antioxidant. S22: Before applying the dry film, the antioxidant protective layer is desorbed by preheating, so that the surface of the PCB board 1 is restored to an active state suitable for applying the dry film. The preheating desorption step and the dry film application step are consecutive steps and share the same heat system, that is, they share the same heat source generating device and heat energy transmission network, rather than each having its own independent heating system. The temperature of the preheating desorption is lower than the temperature of applying the dry film.

[0022] S3: Applying dry film, specifically including: PCB board 1 is fed into a dry film laminating machine. The dry film is then applied to the upper and lower surfaces of PCB board 1 by a hot press roller. After lamination, the dry film adheres tightly to the surface of PCB board 1 without bubbles or wrinkles.

[0023] S4: Exposure and development, specifically including: S41: Based on the CAM design data, create two films, one for the upper and one for the lower surfaces of PCB 1. The areas requiring desoldering have been drawn on the films. S42: Exposure is performed. The dry film under the light-transmitting area of ​​the film absorbs UV light and undergoes cross-linking polymerization, thereby curing. The dry film under the opaque area of ​​the film is not exposed to light and remains in its initial state. S43: Use an alkaline solution such as a 1% sodium carbonate (Na2CO3) aqueous solution, with the temperature controlled at 28-32℃, and spray the solution under high pressure to impact the surface of PCB board 1, dissolving the uncured dry film and developing the area to be desoldered.

[0024] S5: AOI inspection, or Automated Optical Inspection, specifically includes: S51: The image is fed back to the device for processing through the principle of optical reflection. It is compared with the set logical judgment principle or data graphics to find the location of the defect. S52: Secondary manual inspection to reduce misjudgment.

[0025] S6: Solder removal, specifically including: Immerse or spray PCB board 1 with a desoldering solution, such as a nitric acid-based desoldering solution, to rapidly etch only the exposed tin layer, peeling the tin off the surface of PCB board 1 and forming desoldering solution, while the tin layer in the dry film-covered area is completely preserved.

[0026] S7: Overflow water wash, specifically including: High-pressure overflow water washing quickly neutralizes and washes away residual solder stripping solution on the board surface, preventing chemical residue from causing over-etching or penetrating and attacking the edges of the dry film, while avoiding cross-contamination of subsequent processes.

[0027] S8: Film removal, specifically including: The remaining dry film on the board surface is dissolved by using an alkaline stripping solution, which re-exposes the previously protected tin layer, thus achieving the final effect of selectively retaining the tin layer in certain areas and removing the tin layer in the rest of the board.

[0028] S9: Drying and quality inspection, specifically including: First, the board surface is thoroughly dried using a dryer. Then, visual inspection or electrical testing is used to confirm that there is no residual solder, oxidation, or side etching on the copper surface in the desoldering area, and that the solder layer in the protected area is intact and has not peeled off, ensuring that the circuit pattern meets the design requirements.

[0029] Compared to existing technologies, the selective desoldering process for PCB boards in this embodiment, by adding an anti-oxidation pre-protection step, can form an anti-oxidation protective layer on the surface of the PCB board 1. This avoids the formation of an oxide layer on the PCB board 1 before the dry film is applied, which would reduce the adhesion between the dry film and the board surface, leading to problems such as bubbles, dry film peeling, or insufficient adhesion after film application. This reduces the defect rate. At the same time, it eliminates the need to strictly limit the waiting time from the pretreatment cleaning step to the film application during the production process, effectively improving the flexibility of production scheduling. In addition, by connecting the preheating and desorption steps with the dry film lamination steps, the same heat system can be used, eliminating the need for additional independent heating equipment. This reduces equipment occupancy and maintenance costs, fully utilizes the heat source of the dry film laminator, avoids energy waste caused by repeated heating, and significantly improves process integration and energy efficiency. On the other hand, since the preheating and desorption temperature is lower than the dry film lamination temperature, a gradient heating process is formed, preventing the PCB board 1 from experiencing a sudden temperature rise. This results in a more uniform board surface temperature, a more consistent hot pressing effect, and effectively improves the dry film lamination quality. Ultimately, the two steps complement each other.

[0030] The antioxidant is a water-soluble imidazole hydrochloride, which is applied to the copper surface in aqueous solution. It forms a dense antioxidant protective film by coordinating nitrogen atoms with copper atoms, effectively isolating oxygen and moisture, and exhibiting excellent antioxidant properties. Furthermore, when heated to the range of 70 to 100°C, the coordinating bond adsorption structure between the antioxidant and the copper surface breaks, and the antioxidant film desorbs from the copper surface. Based on this, the preheating temperature can be set to 80-90°C, and the temperature for applying the dry film can be set to 100-120°C, thus creating a gradient heating effect. In other embodiments, other imidazole derivatives and alkylimidazoline antioxidants can also be selected. Alkylimidazoline is a hydrogenated derivative of imidazole, and its film-forming mechanism is consistent with that of imidazole.

[0031] Reference Figure 3 The PCB board 1 is preheated and desorbed in a sealed cavity, and an exhaust device or negative pressure device is installed in the sealed cavity to collect the volatile gases generated by the preheating and desorption. The volatile gases are treated by an activated carbon adsorption device before being discharged into the atmosphere.

[0032] Reference Figure 3 and Figure 4 A conveying device and a preheating device are arranged within a sealed cavity. The conveying device transports the PCB board 1 to be preheated through the preheating device. The conveying device includes two sets of horizontally arranged conveyor rollers, one on each side of the conveying path of the PCB board 1. Each set of conveyor rollers includes multiple conveyor rollers 3 spaced apart along the conveying direction. The two sets of conveyor rollers 3 contact the PCB board 1 from the left and right sides respectively, and drive the PCB board 1 forward through the synchronous rotation of the conveyor rollers 3. At least one set of conveyor rollers is equipped with a lateral adjustment mechanism to accommodate PCB boards 1 of different widths. The preheating device includes two parallel and vertically arranged front hot press rollers 2. The heat from the two front hot press rollers 2 is used to preheat the upper and lower surfaces of the PCB board 1, causing the anti-oxidation protective layer on the upper and lower surfaces of the PCB board 1 to gradually desorb as it passes through the two front hot press rollers 2, facilitating the application of dry film.

[0033] The preheating desorption temperature increases with the increase of the interval between applying the antioxidant protective layer and applying the dry film on the PCB board 1, and decreases with the decrease of the interval between applying the antioxidant protective layer and applying the dry film on the PCB board 1. The purpose is that as the placement time is extended, the bonding strength between the antioxidant protective film and the copper surface will increase, and the desorption difficulty will increase accordingly. Therefore, a higher preheating desorption temperature is required. Conversely, if the placement time is short, the bonding strength between the antioxidant protective film and the copper surface will be low, and the desorption difficulty will not be high. Therefore, a lower preheating desorption temperature can be adopted to ensure that the surface of the PCB board 1 is restored to a more uniform active state before applying the dry film.

[0034] Reference Figure 3 and Figure 4The conveying device transports the PCB board 1 to be preheated through two front hot press rollers 2 at a constant power. Both front hot press rollers 2 are fitted with thermal expansion sleeves 21, such as silicone rubber sleeves, which always contact the PCB board 1. Based on this, as the temperature decreases, the thermal expansion sleeves 21 contract, reducing the resistance of the two hot press rollers to the PCB board 1, thus shortening the preheating time while lowering the preheating temperature. Conversely, as the temperature increases, the thermal expansion sleeves 21 expand, increasing the resistance of the two hot press rollers to the PCB board 1, thus extending the preheating time while raising the preheating temperature. Based on this scheme, by adjusting only the preheating temperature, the preheating temperature and time can be increased or decreased synchronously, reducing the minimum preheating effect and increasing the maximum preheating effect, thereby effectively increasing the adjustable range of preheating and avoiding the overly narrow controllable range when only the temperature is adjusted.

[0035] Reference Figure 3 and Figure 4 Multiple thermal expansion sleeves 21 of the front hot press roller 2 are spaced apart along the axial direction to reduce the impact of the thermal expansion sleeves 21 on the heat dissipation effect of the front hot press roller 2. That is, the heat of the front hot press roller 2 can be better dissipated from the gap between adjacent thermal expansion sleeves 21, thereby increasing the adjustment range while ensuring effective heat dissipation of the hot press roller. Furthermore, there are two sets of front hot press rollers 2. Each set consists of two front hot press rollers 2 arranged in parallel, and the two sets of front hot press rollers 2 are distributed back and forth along the conveying direction of the PCB board 1. In the two sets of front hot press rollers 2, the multiple thermal expansion sleeves 21 of the two front hot press rollers 2 located at the same height and distributed back and forth are staggered. This ensures that when the PCB board 1 passes through the two sets of front hot press rollers 2 in sequence, the same position on its board surface will pass through the thermal expansion sleeves 21 and the gap between the thermal expansion sleeves 21 respectively. This results in multiple positions on the board surface of the PCB board 1 being heated evenly, improving the consistency of thermal desorption of the anti-oxidation protective layer.

[0036] Reference Figure 3 In the anti-oxidation pre-protection step, two anti-static rollers 4 are arranged in the sealed cavity. In this embodiment, the anti-static rollers 4 are located in front of the front hot press roller 2. The anti-static rollers 4 are metal rollers and grounded. The two anti-static rollers 4 roll on the two surfaces of the PCB board 1 under the action of elasticity. The anti-static rollers are used to eliminate the static electricity accumulated in the PCB board 1 during storage and transportation, so as to avoid the static electricity from having an adverse effect on the subsequent preheating desorption and dry film lamination.

[0037] Reference Figure 3, in the step of laminating the dry film, the dry film laminating machine includes two parallel and vertically arranged post-heating rollers. Further, the dry film laminating machine adjusts the distance between the two post-heating rollers in real time according to the distance between the two static eliminator rollers 4. Specifically, the two static eliminator rollers 4 respectively abut against the upper and lower surfaces of the PCB board 1 under the action of elastic force and roll synchronously with the conveyance of the PCB board 1. When the thickness of the PCB board 1 changes, the distance between the two static eliminator rollers 4 correspondingly changes. The dry film laminating machine is provided with a displacement sensor for detecting the change in the distance between the two static eliminator rollers 4 in real time and transmitting the detection signal to the control system. The control system calculates the target distance that the two post-heating rollers need to be adjusted according to the received distance change signal according to a preset control algorithm, and drives the servo adjustment mechanism to synchronously adjust the relative positions of the two post-heating rollers, so that the distance when the post-heating rollers laminate the dry film matches the measured thickness of the PCB board 1 by the static eliminator rollers 4. Thus, the post-heating rollers can adaptively adjust the pressing gap according to the actual thickness of the PCB board 1, ensuring that the dry film is uniformly pressured on both sides of the PCB board 1 and avoiding bonding defects or pressing damage caused by board thickness fluctuations.

[0038] Refer to Figure 3 and Figure 5 , the control algorithm of the post-heating roller is D 目标 =k˙D 测量 , where D 目标 is the target distance between the two post-heating rollers when laminating the dry film, D 测量 is the measured distance between the two static eliminator rollers 4, k is the preheating coefficient, and the value range is 0 < k < 1. And the preheating coefficient k is inversely proportional to the preheating temperature. The dry film laminating machine can read the preheating temperature value set in the antioxidant pre-protection step, that is: the higher the preheating temperature - the greater the desorption effect of the antioxidant protective layer - the more the thickness of the PCB board 1 is reduced - the smaller the coefficient k - the smaller the target distance, the lower the preheating temperature - the smaller the desorption effect of the antioxidant protective layer - the less the thickness of the PCB board 1 is reduced - the larger the coefficient k - the larger the target distance, finally making the target distance between the two post-heating rollers more reasonable when laminating the dry film. Further, in this embodiment, when the preheating temperature is 80°C, k = 0.98, and when the preheating temperature is 90°C, k = 0.95, with linear interpolation for intermediate temperatures, making the k value linearly vary between 0.98 and 0.95.

[0039] Example 2 This embodiment also discloses a selective tin removal process for PCB boards.

[0040] The difference from Example 1 is that in the anti-oxidation pre-protection step, the sealed cavity is a drying chamber. That is, the PCB board 1 uses ambient heat to thermally desorb the anti-oxidation protective layer, rather than using the heat from the front hot roller 2. In this example, the thermal expansion sleeve 21 continuously wraps around the surface of the front hot roller 2 axially. This achieves the thermal expansion effect without worrying about the heat dissipation effect of the front hot roller 2, allowing for a wider range of options for the thermal expansion sleeve 21 and simplifying the installation process. The ambient temperature of the drying chamber is controlled at 80-90℃, consistent with the preheating desorption temperature in Example 1, ensuring sufficient desorption of the anti-oxidation protective layer while creating a gradient heating with the subsequent 100-120℃ dry film application.

[0041] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A selective desoldering process for a PCB board, comprising pretreatment cleaning, dry film lamination, exposure and development, desoldering, and film removal, wherein in the dry film lamination step, the PCB board (1) is fed into a dry film laminator, the dry film laminator applying dry film to the surface of the PCB board (1) by hot pressing, characterized in that, An antioxidant pre-protection step is added between the pretreatment cleaning and the application of the dry film, including: An antioxidant protective layer is applied to the surface of the PCB board (1) after pretreatment cleaning, the antioxidant protective layer being formed by an antioxidant; Before applying the dry film, the antioxidant protective layer is desorbed by preheating, so that the surface of the PCB board (1) is restored to an active state suitable for applying the dry film. The preheating desorption step and the dry film application step are consecutive steps and share the same heat system. The temperature of the preheating desorption is lower than the temperature of applying the dry film.

2. The selective desoldering process for PCB boards according to claim 1, characterized in that: The antioxidant is a water-soluble imidazole hydrochloride.

3. The selective desoldering process for PCB boards according to claim 1, characterized in that: Preheating and desorption are carried out in a sealed cavity, which is equipped with a conveying device and a preheating device. The conveying device transports the PCB board (1) to be preheated through the preheating device. The preheating device includes two parallel front heat pressure rollers (2) arranged vertically. The heat from the two front heat pressure rollers (2) is used to preheat the upper and lower surfaces of the PCB board (1).

4. The selective desoldering process for PCB boards according to claim 3, characterized in that: The preheating desorption temperature increases with the increase of the interval between the application of the antioxidant protective layer and the application of the dry film on the PCB board (1) and decreases with the decrease of the interval between the application of the antioxidant protective layer and the application of the dry film on the PCB board (1).

5. The selective desoldering process for PCB boards according to claim 4, characterized in that: The conveying device conveys the PCB board (1) to be preheated through two front heat press rollers (2) at a constant power. Both front heat press rollers (2) are fitted with thermal expansion sleeves (21). The front heat press rollers (2) always abut against the PCB board (1) using the thermal expansion sleeves (21).

6. The selective desoldering process for PCB boards according to claim 5, characterized in that: The thermal expansion sleeves (21) of the front hot press roller (2) are provided at intervals along the axial direction.

7. A selective desoldering process for PCB boards according to claim 6, characterized in that: Two sets of front hot press rollers (2) are arranged in the front and rear along the conveying direction of the PCB board (1). In the two sets of front hot press rollers (2), the multiple thermal expansion sleeves (21) of the two front hot press rollers (2) located at the same height and distributed in the front and rear are staggered.

8. A selective desoldering process for PCB boards according to claim 5, characterized in that: The dry film laminating machine includes two parallel and vertically arranged rear hot press rollers. Two antistatic rollers (4) are also arranged in the sealed cavity. The antistatic rollers (4) are metal rollers and grounded. The two antistatic rollers (4) roll on the two surfaces of the PCB board (1) under the action of elasticity.

9. A selective desoldering process for PCB boards according to claim 8, characterized in that: The dry film pasting machine adjusts the target interval of the two rear heat pressing rollers in real time according to the interval of the two static electricity removing rollers (4), and the target interval D 目标 =k˙D 测量 , wherein D 测量 is the measured interval of the two static electricity removing rollers (4), k is a preheating coefficient, the value range of which is 0<k<1, and the preheating coefficient k is inversely proportional to the preheating temperature.

10. A selective desoldering process for PCB boards according to claim 5, characterized in that: In the anti-oxidation pre-protection step, the sealed cavity is a drying chamber, and the PCB board (1) undergoes thermal desorption of the anti-oxidation protective layer through the ambient heat of the drying chamber. The thermal expansion sleeve (21) continuously covers the roller surface of the front hot pressure roller (2) along the axial direction.

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