Rigid-flex board glue-blocking uncovering film and preparation method thereof

Abstract

The invention relates to the technical field of adhesive-resistant uncovering films, and provides an adhesive-resistant uncovering film for a rigid-flex board and a preparation method thereof.The adhesive-resistant uncovering film comprises a PET carrier film, a PI high-temperature adhesive layer and a pure PI film, the PET carrier film is coated with the PI high-temperature adhesive layer, the pure PI film is compounded on the PI high-temperature adhesive layer, the pure PI film is subjected to laser depth-controlled cutting to form a local covering structure, only a pad area of the flexible board is protected, and the thickness of the pad area of the flexible board is reduced. The PI high-temperature adhesive layer covers the whole soft board area, and the cutting depth is 70-80% of the thickness of the adhesive layer. Through the composite structure design, the pure PI film (non-adhesive layer) is in direct contact with the bonding pad area (only covering the bonding pad), the contact between the adhesive layer and the bonding pad is avoided, the physical contact between the adhesive layer and the bonding pad is thoroughly blocked, and the adhesive residue risk is eliminated from the source.

Description

Technical Field

[0001] The present invention relates to the technical field of resistive opening films, and specifically, to a resistive opening film for rigid-flex printed circuit boards and a preparation method thereof. Background Art

[0002] As a core component of high-end electronic devices, rigid-flex printed circuit boards (Rigid-Flex PCBs) are widely used in the fields of aerospace, medical equipment, and consumer electronics. Solder pads are often designed in the bending area of rigid-flex printed circuit boards to achieve electrical connection. However, this area is vulnerable to the influence of residual glue layers and dust pollution during processes such as lamination and cover opening, resulting in problems such as pad oxidation and poor soldering. Therefore, the protection process for the bending area has become a key technical difficulty in the manufacturing of rigid-flex printed circuit boards. Currently, the industry generally adopts the PI high-temperature film opening process, which can be divided into two categories according to the film sticking direction: First, the positive sticking method (the glue surface is attached to the flexible board) Process flow: directly attach the glue-containing surface of the PI high-temperature film to the surface of the bending area of the flexible board (FPC), cure it through high-temperature baking after lamination, and finally remove the PI film to complete the cover opening. This process has certain technical defects. Among them, the surface roughness (Ra≥0.8μm) of the flexible board pads increases significantly after brownification treatment, and the PI glue layer easily penetrates into the micro-pores. After lamination, residual glue traces (residual rate≥15%) are left, resulting in a decrease in the solderability of the pads. Moreover, the residual glue is prone to carbonization during subsequent reflow soldering, causing problems such as solder joint voids or short circuits. Second, the reverse sticking method (the glue surface is attached to the PP layer) Process flow: attach the glue-containing surface of the PI high-temperature film to the polypropylene (PP) layer to isolate the bending area of the flexible board from the glue layer. This process also has technical defects. Among them, during the lamination process, the PP layer generates micron-sized dust (particle size 5-20μm) when heated. The dust invades the bending area through the film layer gaps and adheres to the surface of the pads (pollution rate≥10%), resulting in electrical performance failure. The difference in the thermal expansion coefficients of the PP layer and the flexible board leads to lamination offset (tolerance ±0.1mm), and the protective film coverage is incomplete.

[0003] In view of this, the present invention proposes a resistive opening film for rigid-flex printed circuit boards and a preparation method thereof. Summary of the Invention

[0004] The present invention proposes a resistive opening film for rigid-flex printed circuit boards and a preparation method thereof, which solves the problems of residual glue after lamination and dust pollution existing in the prior art.

[0005] The technical solution of the present invention is as follows: a soft-hard combination board adhesive blocking and opening film, comprising a PET carrier film, a PI high-temperature adhesive layer coated on the PET carrier film, and a pure PI film compounded on the PI high-temperature adhesive layer. The pure PI film forms a local covering structure by laser controlled depth cutting, which only protects the soft board pad area. The PI high-temperature adhesive layer covers the entire soft board area, and the cutting depth is 70-80% of the adhesive layer thickness.

[0006] Preferably, four symmetrical edges of the PET carrier film are provided with PIN holes, and the four PIN holes are all full-layer cut-through structures with a hole diameter tolerance of ±0.05 mm.

[0007] The present invention also provides a method for preparing a soft-hard combination board adhesive blocking and cover opening film, comprising the following steps: S1: A dry film laminator is used to laminate the PET carrier film, PI high-temperature adhesive layer and pure PI film to form a composite film with an integrated structure; S2: Use a laser cutting machine to perform layered depth-controlled cutting on the composite film in S1. The cutting parameters are: wavelength 355nm, power 5-8W, cutting speed 500-800mm / s. After the cutting is completed, the waste material is peeled off to form a glue-blocking and cover-lifting film. S3: The cover film in S2 is attached to the soft board area by PIN positioning, and the PET carrier film (101) is removed after pressing by a fast pressing machine to form a protective structure.

[0008] Preferably, in S1, the operating parameters of the dry film laminator are: temperature 50-80°C, pressure 0.4-0.6MPa.

[0009] Preferably, in S2, the cutting depth of the laser cutting machine satisfies that the pure PI film does not cut through the PI high temperature adhesive layer, the PI high temperature adhesive layer does not cut through the PET carrier film, and the PIN hole position is fully cut through.

[0010] Preferably, in S2, when cutting the pure PI film, the depth is controlled at 80-90% of the total thickness of the pure PI film to avoid cutting through the PI high temperature adhesive layer; when cutting the PI high temperature adhesive layer, the depth is controlled at 70-80% of the thickness of the PI high temperature adhesive layer to avoid cutting through the PET carrier film (103).

[0011] Preferably, in S3, the working parameters of the rapid press are: temperature 80-100°C, pressure 0.5-1.0 MPa, and time 10-20s.

[0012] The working principle and beneficial effects of the present invention are: 1. Through the composite structure design of PET carrier film, PI high-temperature adhesive layer and pure PI film, the pure PI film (non-adhesive layer) directly contacts the pad area (only covers the pad), avoiding the contact between the adhesive layer and the pad, completely blocking the physical contact between the adhesive layer and the pad, and eliminating the risk of residual adhesive from the root; 2. The PI high-temperature adhesive layer covers the entire flexible board area to form a sealed protection structure. After the pure PI films are laminated, the external environment is isolated, preventing PP dust from entering the pad area and ensuring the cleanliness of the pad surface. 3. By using pin positioning (hole diameter tolerance ±0.05 mm) and an integrated composite film structure, the alignment accuracy is improved, the covering deviation caused by the difference in material expansion is reduced, and the fitting accuracy of the protection structure is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0014] Figure 1 FIG. is a schematic structural diagram of a resist-opening film for a rigid-flex printed circuit board according to the present invention; Figure 2 TABLE FOR EXPERIMENTAL TEST EXAMPLE 1 OF THE PRESENT INVENTION; Figure 3 TABLE FOR EXPERIMENTAL TEST EXAMPLE 2 OF THE PRESENT INVENTION; Figure 4 TABLE FOR EXPERIMENTAL TEST EXAMPLE 3 OF THE PRESENT INVENTION; Figure 5 TABLE FOR EXPERIMENTAL TEST EXAMPLE 4 OF THE PRESENT INVENTION.

[0015] In the figure: 101, PET carrier film; 102, PI high-temperature adhesive layer; 103, pure PI film; 104, PIN hole. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Embodiment

[0017] As Figure 1 , this embodiment provides a resist-opening film for a rigid-flex printed circuit board, including a PET carrier film 101, a PI high-temperature adhesive layer 102 coated on the PET carrier film 101, and a pure PI film 103 laminated on the PI high-temperature adhesive layer 102. The pure PI film 103 forms a partial coverage structure through laser-controlled depth cutting and only protects the flexible board pad area. The PI high-temperature adhesive layer 102 covers the entire flexible board area and the cutting depth is 70-80% of the adhesive layer thickness. The thickness of the PI high-temperature adhesive layer 102 is 20 μm, the thickness of the pure PI film 103 is 12 μm, and PIN holes 104 are provided at four symmetric edges of the PET carrier film 101. The four PIN holes 104 are all full-layer cut-through structures with a hole diameter tolerance of ±0.05 mm.

[0018] Through the composite structure design of the PET carrier film 101, the PI high-temperature adhesive layer 102 and the pure PI film 103, the pure PI film 103 (non-adhesive layer) directly contacts the pad area (only covers the pads), avoiding the contact between the adhesive layer and the pads, completely blocking the physical contact between the adhesive layer and the pads, and eliminating the risk of residual adhesive residue from the source; The PI high-temperature adhesive layer 102 covers the entire flexible board area to form a sealed protection structure. After the pure PI film 103 is compounded with the pure PI film 103, it isolates the external environment, blocks the PP dust from entering the pad area, and ensures the cleanliness of the pad surface. Embodiment

[0019] This embodiment provides a resist glue opening film for a rigid-flex board, including a PET carrier film 101, a PI high-temperature adhesive layer 102 coated on the PET carrier film 101, and a pure PI film 103 compounded on the PI high-temperature adhesive layer 102. The pure PI film 103 forms a partial coverage structure through laser controlled-depth cutting and only protects the flexible board pad area. The PI high-temperature adhesive layer 102 covers the entire flexible board area and the cutting depth is 70 - 80% of the adhesive layer thickness. The thickness of the PI high-temperature adhesive layer 102 is 25μm, the thickness of the pure PI film 103 is 20μm, and PIN holes 104 are provided at four symmetric edges of the PET carrier film 101. The four PIN holes 104 are all full-layer through-cut structures, and the aperture tolerance is ±0.05mm. Embodiment

[0020] This embodiment provides a resist glue opening film for a rigid-flex board, including a PET carrier film 101, a PI high-temperature adhesive layer 102 coated on the PET carrier film 101, and a pure PI film 103 compounded on the PI high-temperature adhesive layer 102. The pure PI film 103 forms a partial coverage structure through laser controlled-depth cutting and only protects the flexible board pad area. The PI high-temperature adhesive layer 102 covers the entire flexible board area and the cutting depth is 70 - 80% of the adhesive layer thickness. The thickness of the PI high-temperature adhesive layer 102 is 30μm, the thickness of the pure PI film 103 is 25μm, and PIN holes 104 are provided at four symmetric edges of the PET carrier film 101. The four PIN holes 104 are all full-layer through-cut structures, and the aperture tolerance is ±0.05mm. Embodiment

[0021] This embodiment provides a preparation method for a resist glue opening film for a rigid-flex board, including the following steps: S1: Use a dry film laminator (temperature 50°C, pressure 0.4MPa) to compound the PET carrier film 101, the PI high-temperature adhesive layer 102 and the pure PI film 103 to form a composite film with an integrated structure; S2: Use a laser cutting machine to perform layer-by-layer depth-controlled cutting on the composite film in S1. The cutting parameters are: wavelength 355 nm, power 5 W, cutting speed 500 mm / s. When cutting the pure PI film 103, the depth is controlled at 80% of the total thickness of the pure PI film 103 to avoid cutting through the PI high-temperature adhesive layer 102. When cutting the PI high-temperature adhesive layer 102, the depth is controlled at 80% of the thickness of the PI high-temperature adhesive layer 102 to avoid cutting through the PET carrier film 103. The PIN hole 104 position is cut through completely. After cutting, strip the waste to form a resistive adhesive cover film; S3: Attach the cover film in S2 to the flexible board area through PIN positioning. After pressing with a quick press (temperature 80 °C, pressure 0.5 MPa, time 20 s), tear off the PET carrier film 101 to form a protective structure. Example

[0022] This example provides a method for preparing a resistive adhesive opening film for a rigid-flex printed circuit board, including the following steps: S1: Use a dry film laminating machine (temperature 50 °C, pressure 0.4 MPa) to laminate the PET carrier film 101, PI high-temperature adhesive layer 102, and pure PI film 103 to form a composite film with an integrated structure; S2: Use a laser cutting machine to perform layer-by-layer depth-controlled cutting on the composite film in S1. The cutting parameters are: wavelength 355 nm, power 6.5 W, cutting speed 500 mm / s. When cutting the pure PI film 103, the depth is controlled at 80% of the total thickness of the pure PI film 103 to avoid cutting through the PI high-temperature adhesive layer 102. When cutting the PI high-temperature adhesive layer 102, the depth is controlled at 80% of the thickness of the PI high-temperature adhesive layer 102 to avoid cutting through the PET carrier film 103. The PIN hole 104 position is cut through completely. After cutting, strip the waste to form a resistive adhesive cover film; S3: Attach the cover film in S2 to the flexible board area through PIN positioning. After pressing with a quick press (temperature 80 °C, pressure 0.5 MPa, time 20 s), tear off the PET carrier film 101 to form a protective structure. Example

[0023] This example provides a method for preparing a resistive adhesive opening film for a rigid-flex printed circuit board, including the following steps: S1: Use a dry film laminating machine (temperature 50 °C, pressure 0.4 MPa) to laminate the PET carrier film 101, PI high-temperature adhesive layer 102, and pure PI film 103 to form a composite film with an integrated structure; S2: Use a laser cutting machine to perform layered depth-controlled cutting on the composite film in S1. The cutting parameters are: wavelength 355 nm, power 8 W, cutting speed 500 mm / s. When cutting the pure PI film 103, the depth is controlled at 80% of the total thickness of the pure PI film 103 to avoid cutting through the PI high-temperature adhesive layer 102. When cutting the PI high-temperature adhesive layer 102, the depth is controlled at 80% of the thickness of the PI high-temperature adhesive layer 102 to avoid cutting through the PET carrier film 103. The PIN hole 104 position is cut through completely. After cutting, strip the waste to form a resistive glue cover film; S3: Attach the cover film in S2 to the flexible board area by PIN positioning, and use a quick press (temperature 80 °C, pressure 0.5 MPa, time 20 s) to press and then tear off the PET carrier film 101 to form a protective structure. Example

[0024] This example provides a method for preparing a resistive glue open cover film for a rigid-flex printed circuit board, including the following steps: S1: Use a dry film laminating machine (temperature 50 °C, pressure 0.4 MPa) to laminate the PET carrier film 101, the PI high-temperature adhesive layer 102 and the pure PI film 103 to form a composite film with an integrated structure; S2: Use a laser cutting machine to perform layered depth-controlled cutting on the composite film in S1. The cutting parameters are: wavelength 355 nm, power 5 W, cutting speed 650 mm / s. When cutting the pure PI film 103, the depth is controlled at 80% of the total thickness of the pure PI film 103 to avoid cutting through the PI high-temperature adhesive layer 102. When cutting the PI high-temperature adhesive layer 102, the depth is controlled at 80% of the thickness of the PI high-temperature adhesive layer 102 to avoid cutting through the PET carrier film 103. The PIN hole 104 position is cut through completely. After cutting, strip the waste to form a resistive glue cover film; S3: Attach the cover film in S2 to the flexible board area by PIN positioning, and use a quick press (temperature 80 °C, pressure 0.5 MPa, time 20 s) to press and then tear off the PET carrier film 101 to form a protective structure. Example

[0025] S1: Use a dry film laminating machine (temperature 50 °C, pressure 0.4 MPa) to laminate the PET carrier film 101, the PI high-temperature adhesive layer 102 and the pure PI film 103 to form a composite film with an integrated structure; S2: Use a laser cutting machine to perform layer-by-layer depth-controlled cutting on the composite film in S1. The cutting parameters are as follows: wavelength 355 nm, power 5 W, cutting speed 800 mm / s. When cutting the pure PI film 103, the depth is controlled at 80% of the total thickness of the pure PI film 103 to avoid cutting through the PI high-temperature adhesive layer 102. When cutting the PI high-temperature adhesive layer 102, the depth is controlled at 80% of the thickness of the PI high-temperature adhesive layer 102 to avoid cutting through the PET carrier film 103. The PIN hole 104 position is cut through completely. After cutting, strip the waste material to form a resistive adhesive cover film; S3: Attach the cover film in S2 to the flexible board area through PIN positioning, and use a quick press machine (temperature 80 °C, pressure 0.5 MPa, time 20 s) to press and then tear off the PET carrier film 101 to form a protective structure.

[0026] Experimental test example one: This experimental test example is used to observe the cutting depth error and the interlayer non-penetration rate of the composite film after laser cutting in Example 4, Example 5, and Example 6. Among them, the cutting depth error is measured by a laser confocal microscope. After stripping the waste material, the SEM is used to observe the integrity of the cutting interface. The specific measurement results are as Figure 2 shown; As can be seen from Figure 2 it, in Example 4, Example 5, and Example 6, the cutting depth error of the pure PI film ≤ ±5%, the error of the PI adhesive layer ≤ ±3%, and the interlayer non-penetration rate ≥ 99%. This shows that the optimal power of the laser cutting machine is 500 - 800 mm / s.

[0027] Experimental test example two: This experimental test example is used to observe the cutting depth error and the interlayer non-penetration rate of the composite film after laser cutting in Example 4, Example 7, and Example 8. Among them, the cutting depth error is measured by a laser confocal microscope. After stripping the waste material, the SEM is used to observe the integrity of the cutting interface. The specific measurement results are as Figure 3 shown; As can be seen from Figure 3 it, in Example 4, Example 5, and Example 6, the cutting depth error of the pure PI film ≤ ±5%, the error of the PI adhesive layer ≤ ±3%, and the interlayer non-penetration rate ≥ 99%. This shows that the optimal cutting speed of the laser cutting machine is 5 - 8 W.

[0028] Experimental test example three: Set control group 1, and control group 1 is the positive pasting method (PI adhesive surface pasted on the flexible board); This experimental test example is used to compare the residual adhesive rate of the composite film in Example 1 with the positive pasting method (PI adhesive surface pasted on the flexible board) of control group 1. The specific implementation steps are as follows: (1) After laminating the samples of Example 1 and Control Group 1, remove the protective film. (2) Use a laser confocal microscope to measure the surface roughness (Ra value) of the pads. (3) Observe the surface morphology of the pads by SEM and detect the residual elements in the adhesive layer by EDS. (4) Calculate the residual adhesive coverage rate (residual area / total pad area) and the residual adhesive layer thickness (SEM cross-section analysis) respectively. The calculation results are as Figure 4 shown. As Figure 4 can be seen, the residual adhesive coverage rate of Example 1 is 0.05%, and the residual thickness is 0.07 μm, while the residual adhesive coverage rate of Control Group 1 is 1.35%, and the residual thickness is 0.43 μm. Thus, it can be known that Example 1 has a better effect of suppressing residual adhesive.

[0029] Experimental Test Example 4: Set up Control Group 2, and Control Group 2 uses the reverse lamination method (PI adhesive surface laminates the PP layer). This experimental test example is used to compare the dust protection ability of the composite film of Example 1 and the reverse lamination method (PI adhesive surface laminates the PP layer) of Control Group 2. The specific implementation steps are as follows: (1) After laminating the samples of Example 1 and Control Group 2, remove the protective film. (2) Use a particle counter to count the number and particle size distribution of dust on the pad surface. (3) Observe the dust adhesion situation by SEM. (4) Calculate the dust pollution rate (number of contaminated pads / total number of pads) and the dust adhesion density (number of particles per unit area) respectively. The calculation results are Figure 5 shown. As Figure 5 can be seen, the dust pollution rate of Example 1 is 1.12%, and the adhesion density is 2 particles / mm², while the dust pollution rate of Control Group 2 is 12.4%, and the adhesion density is 14 particles / mm². Thus, it can be known that Example 1 has a better dust protection ability.

[0030] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A resist glue opening film for a rigid-flex board, characterized in that, It includes a PET carrier film (101); a PI high-temperature adhesive layer (102) coated on the PET carrier film (101); a pure PI film (103) laminated on the PI high-temperature adhesive layer (102); the pure PI film (103) forms a partial covering structure through laser controlled-depth cutting, only protecting the flexible board pad area; the PI high-temperature adhesive layer (102) covers the entire flexible board area, and the cutting depth is 70 - 80% of the adhesive layer thickness.

2. The resist glue opening film for a rigid-flex printed circuit board according to claim 1, wherein PIN holes (104) are provided at four symmetric edges of the PET carrier film (101), and the four PIN holes (104) are all full-layer cut-through structures with a hole diameter tolerance of ±0.05 mm.

3. A resist glue opening film for a rigid-flex printed circuit board according to claim 1, characterized in that, The thickness of the PI high-temperature adhesive layer (102) is 20 - 30 μm, and the thickness of the pure PI film (103) is 12 - 25 μm.

4. A method for preparing a resist opening film for a rigid-flex printed circuit board according to claim 3, characterized in that, It includes the following steps: S1: Use a dry film laminating machine to laminate the PET carrier film (101), the PI high-temperature adhesive layer (102) and the pure PI film (103) to form a composite film with an integrated structure; S2: Use a laser cutting machine to perform layered controlled-depth cutting on the composite film in S1, and the cutting parameters are: wavelength 355 nm, power 5 - 8 W, cutting speed 500 - 800 mm / s. After cutting, strip the waste to form a resist adhesive cover film; S3: Attach the cover film in S2 to the flexible board area through PIN positioning, and use a fast press to laminate and then tear off the PET carrier film (101) to form a protection structure.

5. The preparation method of a resist-opening film for a rigid-flex printed circuit board according to claim 4, characterized in that, In S1, the working parameters of the dry film laminating machine are: temperature 50 - 80°C, pressure 0.4 - 0.6 MPa.

6. The preparation method of a resist opening film for a rigid-flex printed circuit board according to claim 5, characterized in that, In S2, the cutting depth of the laser cutting machine satisfies that the pure PI film (103) is not cut through the PI high-temperature adhesive layer (102), the PI high-temperature adhesive layer (102) is not cut through the PET carrier film (101), and the PIN hole (104) position is fully cut through.

7. The preparation method of a resist-opening film for a rigid-flex printed circuit board according to claim 6, wherein, In S2, when cutting the pure PI film (103), the depth is controlled within 80 - 90% of the total thickness of the pure PI film (103) to avoid cutting through the PI high-temperature adhesive layer (102). When cutting the PI high-temperature adhesive layer (102), the depth is controlled within 70 - 80% of the thickness of the PI high-temperature adhesive layer (102) to avoid cutting through the PET carrier film (103).

8. A resist glue opening film for a rigid-flexible printed circuit board and its preparation method according to claim 4, characterized in that, In S3, the working parameters of the fast press are: temperature 80 - 100°C, pressure 0.5 - 1.0 MPa, time 10 - 20 s.

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