A processing method for step-by-step pressing and overflow glue control of a rigid-flex printed circuit board

Abstract

This application relates to the field of printed circuit board manufacturing technology and discloses a step-by-step lamination and adhesive overflow control method for rigid-flex boards. The method includes: laminating a polyimide cover film onto the core inner layer; after rapid lamination, printing twice in the flexible board area and performing stepped heating and baking to form an anti-overflow blue adhesive layer; introducing an add-on material, performing plasma treatment and two-stage hot-melt false lamination followed by the first stage of lamination; extracting measured shrinkage offset data after lamination to correct the alignment parameters for subsequent laminations; performing laser blind via removal, dry plasma treatment, and wet adhesive removal after lamination; repeating the add-on, data correction, lamination, and adhesive removal steps sequentially to complete multi-level lamination; wherein the intensity of the dry plasma treatment for subsequent laminations increases progressively, while the parameters for wet adhesive removal remain constant; finally, laser capping and plasma cleaning complete the process. This method solves the problems of poor interlayer alignment accuracy, adhesive overflow into the flexible board area, and residual adhesive on the walls of blind vias in the multi-level lamination process of rigid-flex boards.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, specifically to a step-by-step lamination and adhesive overflow control method for rigid-flex boards. Background Technology

[0002] Rigid-flex printed circuit boards (PCBs) are widely used in high-density 3D assembly due to their combination of the support of rigid boards and the flexibility of flexible boards. However, traditional one-time co-lamination processes face significant challenges in manufacturing multi-layered, high-order (e.g., eight layers or more) rigid-flex PCBs. Because of the significant difference in thermal expansion coefficients between the flexible polyimide material and the rigid epoxy resin substrate, repeated high-temperature and high-pressure lamination causes nonlinear and unpredictable dimensional expansion and contraction, leading to a severe decrease in interlayer alignment accuracy. Relying solely on theoretically designed coordinates for alignment is highly susceptible to the cumulative deformation tolerances layer by layer, resulting in blind vias deviating from the target pads and rendering the product unusable.

[0003] Furthermore, to ensure complete filling of the fine inner layer circuitry, the prepreg (PP) used in lamination must possess good flowability at high temperatures. However, under pressure, this flowability inevitably leads to lateral resin overflow (excess resin) into the unsupported open areas of the flexible circuit board. The overflowing resin not only contaminates the gold finger functional areas of the flexible circuit board, but the rigid residue formed after curing also restricts the board's bending performance. Existing technologies typically employ low-flow PP or adhesive barrier films to mitigate excess resin, but this often comes at the cost of sacrificing the filling capability of inner layer blind vias, leaving stubborn residual resin and drilling contaminants on the via walls and bottoms, posing a potential threat to the reliability of subsequent via metallization interconnects.

[0004] Therefore, this invention proposes a step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a step-by-step lamination and overflow control processing method for rigid-flex PCBs. This method solves the problems of difficulty in controlling interlayer alignment shrinkage offset caused by the difference in expansion coefficients of different materials during the multilayer lamination process of existing rigid-flex PCBs, as well as the problems of resin overflow into the flexible board uncovering area under high temperature and high pressure, resulting in damage to the flexible board and residual adhesive in blind hole metallization.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a step-by-step lamination and adhesive overflow control method for rigid-flex PVC boards, comprising the following steps: S1: The core inner layer is laminated with a polyimide cover film, and then subjected to rapid pressing, surface plasma treatment and coating baking in sequence. S2: Print the first layer of anti-overflow blue glue in the flexible board area, and perform the first ultraviolet exposure and baking of the first blue glue; overprint the second layer of anti-overflow blue glue on the surface of the first layer of anti-overflow blue glue, and perform the second ultraviolet exposure and baking of the second blue glue; S3: Introduce the outermost layer material and perform plasma treatment, align the outermost layer material with the core inner layer, and sequentially perform the first stage of hot melt false bonding and the second stage of hot melt false bonding. S4: Perform the first stage of lamination and extract the first shrinkage offset data; S5: Perform the first laser blind hole processing, the first dry plasma treatment, the first wet desmearing treatment and the first hole metallization; S6: Introduce a second material layer, and sequentially perform the first stage hot melt false bonding, the second stage hot melt false bonding and the second stage lamination according to the first shrinkage offset data, and extract the second shrinkage offset data; perform the second laser blind hole processing, the second dry plasma treatment, the second wet adhesive removal treatment and the second hole metallization; S7: Introduce outer layer material, and perform the first stage hot melt false bonding, the second stage hot melt false bonding and the third stage lamination in sequence according to the second shrinkage offset data; perform the third laser blind hole processing, the third dry plasma treatment, the third wet adhesive removal treatment, the third hole metallization and circuit etching. S8: The cover is removed using laser equipment to remove waste materials, the first layer of anti-overflow blue adhesive and the second layer of anti-overflow blue adhesive, and then plasma treatment and solder resist processing are performed after the cover is removed.

[0007] By adopting the above technical solution, the original lamination process is broken down into a progressive assembly, combined with multi-layer blue adhesive overprinting and interlayer data compensation. To address the issue of resin overflowing into the flexible board area during high-temperature lamination, two layers of blue adhesive are pre-printed in the flexible board area and cured in stages, forming a flow-blocking zone at the interface between the rigid and flexible boards to intercept the molten resin. The bottom layer of blue adhesive adheres tightly to the cover film to fill microscopic gaps, while the top layer of overprinted blue adhesive provides a pressure-bearing buffer space. During layer stacking, a two-stage hot-melt false bonding method is used instead of direct high-temperature lamination. In the first stage, air trapped between layers is expelled under low pressure, and initial positioning is completed; subsequently, the temperature and pressure are increased to enter the second stage, causing localized micro-melting cross-linking of the interface resin to fix the internal structure. To address dimensional shrinkage anomalies caused by multiple laminations, the actual shrinkage offset data is extracted after each lamination, guiding the alignment compensation of the next layer, thereby eliminating the cumulative deformation tolerance caused by multi-layer stacking. Meanwhile, the blind hole processing is broken down into different pressing stages and performed separately, avoiding the problems of excessive taper and residual adhesive at the bottom of the hole that are easily caused by one-time deep control blind hole forming.

[0008] Preferably, in step S2, both the first layer of anti-overflow blue adhesive and the second layer of anti-overflow blue adhesive are made from raw materials comprising the following parts by weight: Carboxyl-terminated butadiene-acrylonitrile rubber modified bisphenol A type epoxy resin 35.0-50.0 parts; trimethylolpropane triacrylate 5.0-10.0 parts; triethylene glycol diacrylate 5.0-10.0 parts; 1-hydroxycyclohexylphenyl ketone 1.0-3.0 parts; dicyandiamide 1.5-4.5 parts; 2-ethyl-4-methylimidazolium 0.5-1.5 parts; hydrophobic fumed silica 1.5-2.5 parts; modified talc 28.0-33.5 parts; polydimethylsiloxane 1.0-2.5 parts; phthalocyanine blue 1.0-2.0 parts.

[0009] Carboxyl-terminated nitrile butadiene rubber modified bisphenol A type epoxy resin is a prepolymer containing butadiene-acrylonitrile rubber segments, formed by the ring-opening esterification reaction of bisphenol A type epoxy resin and carboxyl-terminated liquid nitrile butadiene rubber. The mass fraction of acrylonitrile in the carboxyl-terminated liquid nitrile butadiene rubber is 18%–26%, and the weight-average molecular weight is 3000–5000. The epoxy equivalent of the carboxyl-terminated nitrile butadiene rubber modified bisphenol A type epoxy resin is 200–350 g / eq.

[0010] The wet film thickness of both the first and second layers of anti-overflow blue adhesive is 15–25 μm. The wavelength of the light source for both the first and second UV exposures is 365 nm, and the radiation energy is 500–1000 mJ / cm². 2 The first blue gum is baked at 75–90℃ for 15–30 minutes. The second blue gum is baked at 140–160℃ for 45–60 minutes. The baking temperature of the second blue gum is higher than that of the first blue gum.

[0011] By adopting the above technical solution, the blue adhesive with the specific ratio described above improves its flow-blocking effect through a dual photothermal curing reaction. During the reaction, the terminal carboxyl groups undergo a ring-opening esterification reaction with the epoxy groups of the epoxy resin under the action of a catalyst, and the reaction formula is as follows: R-COOH + R'-CH(O)CH2→ R-COO-CH2-CH(OH)-R'; This reaction integrates flexible rubber segments into the resin backbone, allowing the colloid to absorb longitudinal pressure under stress. The epoxy equivalent is controlled at 200-350 g / eq to maintain a moderate crosslinking density, ensuring complete film peeling during subsequent capping operations. After printing, UV irradiation initiates the addition polymerization of acrylate double bonds, causing the wet film to rapidly lose fluidity and crosslink into a primary network framework. The subsequent baking process addresses latent epoxy groups: the first blue adhesive is baked at a low temperature, retaining slight surface tack to facilitate overprinting of the second layer; the second blue adhesive is baked at 140-160°C, promoting covalent crosslinking of unreacted groups at the interface of the two layers, forming a flow-blocking layer with overall compressive strength. The hydrophobic fumed silica and modified talc in the formulation provide thixotropy for printing and reduce volume shrinkage during the heating phase, respectively.

[0012] Preferably, in steps S3, S6, and S7, the temperature of the first stage hot-melt stencil is 80–100°C, the pressure is 0.5–1.0 MPa, and the time is 3–5 s; the temperature of the second stage hot-melt stencil is 120–140°C, the pressure is 1.5–2.5 MPa, and the time is 8–12 s. The pressure of the second stage hot-melt stencil is greater than the pressure of the first stage hot-melt stencil.

[0013] In step S3, a nitrogen-oxygen mixture with a volume ratio of 3:1 to 5:1 is introduced for plasma treatment. The working pressure is 20 to 40 Pa, the radio frequency power is 1.5 to 2.0 kW, and the treatment time is 3 to 5 minutes. After plasma treatment, the outermost layer material and the inner core layer are placed in an environment with a relative humidity of 20% to 28%. If the placement time is longer than 1 hour, a plasma refresh treatment step is added before the first stage of thermal fusion bonding. The parameters for the plasma refresh treatment step are: a nitrogen-oxygen mixture with a volume ratio of 5:1 is introduced, the working pressure is 40 Pa, the radio frequency power is 1.2 kW, and the treatment time is 1.5 minutes.

[0014] By adopting the above technical solution, the combination of plasma surface activation treatment and two-stage pressure increment parameters improves the bonding state of the material interface. Nitrogen-oxygen mixed plasma bombardment of the material surface can break the macromolecular backbone and introduce polar groups, increasing the initial interlayer adhesion. Considering that prolonged placement of the board during actual processing can lead to passivation due to the adsorption of moisture by the activated groups, an additional plasma refresh treatment is added. This process uses low-power secondary bombardment to peel off the hydration layer, restoring the material surface activity. During the initial bonding stage, the two-stage parameter settings are tailored to the rheological characteristics of the resin: at 80–100°C, the resin softens but does not possess macroscopic fluidity, allowing for stable extrusion of interlayer gas under low pressure; when the temperature rises to 120–140°C and enters the molten state, the applied high pressure forces the interfacial resin chains to undergo molecular-level entanglement, achieving a strong interlayer bond.

[0015] Preferably, the method for extracting the first shrinkage offset data in step S4 is as follows: The measured coordinates of the target are detected using X-ray equipment, and the coordinate difference between the measured and designed coordinates is extracted to generate the first shrinkage offset data. The parameters for the first stage of lamination are: venting at a temperature of 100–130℃ and a pressure of 1.0–1.5 MPa, with a heating rate controlled at 1.5–2.5℃ / min; heating to 165–180℃ and maintaining curing at a pressure of 3.0–4.5 MPa for 60–90 min. After extracting the first shrinkage offset data, a first step of milling away the edge waste is added; after extracting the second shrinkage offset data, a second step of milling away the edge waste is added.

[0016] By adopting the above technical solution, dynamic compensation for interlayer alignment is achieved through feedback calculation based on measured coordinate differences. After lamination, stress release of the glass fiber cloth inside the prepreg and resin crosslinking inevitably cause dimensional deformation. Using X-ray equipment to detect the measured coordinates of the target and comparing them with the design drawings, the resulting offset data directly guides the alignment compensation of subsequent equipment, preventing tolerance transmission caused by multilayer stacking. Immediately after obtaining shrinkage data, the edge waste is removed, destroying the rigid constraint band formed by edge glue curing and promoting the natural release of residual stress inside the board. This treatment method makes the expansion and contraction of the board dimensions more uniform, thus physically ensuring the overall alignment accuracy after multilayer lamination.

[0017] Preferably, in steps S5, S6, and S7, the first, second, and third dry plasma treatments all introduce a mixture of carbon tetrafluoride and oxygen in a volume ratio of 1:5 to 1:9, and the gas pressure is 30 to 50 Pa. The radio frequency power of the first dry plasma treatment is 2.5 to 3.0 kW, and the time is 10 to 15 min; the radio frequency power of the second dry plasma treatment is 2.8 to 3.5 kW, and the time is 15 to 20 min; the radio frequency power of the third dry plasma treatment is 2.8 to 4.0 kW, and the time is 20 to 25 min. The radio frequency power of the second dry plasma treatment is greater than that of the first dry plasma treatment, or the time of the second dry plasma treatment is greater than that of the first dry plasma treatment; the radio frequency power of the third dry plasma treatment is greater than that of the second dry plasma treatment, or the time of the third dry plasma treatment is greater than that of the second dry plasma treatment.

[0018] The first, second, and third wet degumming treatments each consist of the following steps, sequentially: immersion in a bulking solution composed of 50–80 g / L diethylene glycol butyl ether and 10–20 g / L sodium hydroxide at 65–75°C for 3–5 minutes; immersion in an oxidizing solution composed of 45–65 g / L potassium permanganate and 35–55 g / L sodium hydroxide at 75–85°C for 5–8 minutes; and immersion in a neutralizing solution composed of 2%–5% sulfuric acid and 1%–3% hydrogen peroxide at 40–50°C for 3–5 minutes. The concentrations of the bulking solution, oxidizing solution, neutralizing solution, treatment temperature, and treatment time are all identical.

[0019] The above-mentioned technical solution, employing progressively increasing dry plasma parameters, primarily addresses the issue of accumulated heat from multilayer lamination. During the step-by-step drilling process, although each laser blast only penetrates the newly added dielectric layer, the exposed target pads and surrounding residual adhesive at the bottom of the hole have undergone multiple high-temperature laminations. The more laminations, the higher the cross-linking degree of the underlying resin, making the residual adhesive increasingly stubborn. Therefore, by progressively increasing the RF power or extending the dry processing time, high-energy plasma is used to effectively degrade these highly cross-linked residual adhesives at the bottom of the hole. After the dry processing resolves the stubborn residual adhesive at the bottom, wet descaling does not require increasing the chemical concentration or time; only a standard concentration of potassium permanganate alkaline solution is needed to remove the microscopic loose layer on the hole wall, avoiding excessive etching of the newly lamination, less cross-linked resin by high-concentration chemicals. This combination of dynamic dry adjustment and constant wet parameters eliminates the need for repeated adjustments to the chemical bath, ensuring the stability of the metallization bonding force of each hole layer.

[0020] This invention provides a step-by-step lamination and adhesive overflow control method for rigid-flex PVC boards. It offers the following advantages: 1. By pre-printing two layers of anti-overflow blue adhesive in the flexible board area and employing a stepped curing process combining UV curing and two-stage thermal baking, a physical flow-blocking structure is formed at the interface of the rigid-flex PCB. This structure effectively intercepts the flow of molten resin into the flexible board area during high-temperature and high-pressure lamination, preventing adhesive overflow from contaminating and damaging the flexible board area. Simultaneously, it ensures the cleanliness of the hole bottom during subsequent blind via machining, providing a reliable foundation for hole metallization.

[0021] 2. This invention breaks down the traditional one-time lamination process into multi-step lamination, and after each lamination, the expansion and contraction data of the board are measured using X-ray equipment. This data is used to compensate for and calibrate the alignment parameters of the next layer of material, achieving dynamic elimination of accumulated deformation tolerances during the lamination process. Combined with the milling of edge waste to release internal stress, the final interlayer alignment accuracy of the multilayer rigid-flex board is improved.

[0022] 3. To address the adhesive removal requirements of blind vias at different levels in the step-by-step lamination process, this invention sets progressively increasing dry plasma treatment parameters. This is because the pads on the bottom layer undergo more thermal lamination processes, resulting in a higher degree of cross-linking and curing of residual resin on their surface, making it more difficult to remove. By progressively increasing the plasma treatment intensity, these stubborn adhesive residues can be effectively removed while maintaining constant wet adhesive removal parameters. This avoids excessive attack of chemical solutions on the walls of the newly added dielectric layer vias, ensuring the reliability of metallization for each layer of blind vias.

[0023] 4. A two-stage hot-melt pre-lamination process is employed to pre-treat the laminated structure before formal lamination. The first stage, low-pressure venting, ensures no air residue remains between layers, while the second stage, heating and pressurizing, causes the prepreg to undergo initial melting and bonding, firmly fixing each layer of material together. This method effectively prevents interlayer slippage that may occur during the press process, reduces the risk of defects such as delamination and board bursting caused by air inclusions, and improves product yield. Attached Figure Description

[0024] Figure 1 The diagram shows the thermal analysis and rheological properties of the anti-overflow blue adhesive at different processing stages in Test Example 1 of the present invention; wherein, (a) is the differential scanning calorimetry curve of each state sample under programmed temperature rise conditions, and (b) is the energy storage modulus evolution trend curve of the first and second shaped state samples in Example 1 within the temperature range covering the subsequent pressing process. Figure 2 The figure shows the test results of the basic reliability and conductivity of the finished substrate in Test Example 2 of the present invention; where (a) is the scatter distribution of the delamination area ratio data of each embodiment sample after the 288℃ thermal shock test, and (b) is the scatter distribution of the initial on-resistance measurement value of the blind via chain pattern corresponding to each embodiment sample. Figure 3 This is a graph showing the test data of the lateral overflow distance in the soft-hard transition zone for each group in Test Example 3 of the present invention; Figure 4 The following is a comparison chart of the interface bonding reliability and cascade alignment accuracy test under different process conditions in Test Example 4 of the present invention; where (a) is the measurement data of the peel strength at 90° and the proportion of blistering area after high temperature and high humidity aging for each test group, and (b) is the distribution of the average interlayer offset and the maximum offset of blind holes for each test group after cascaded pressing. Figure 5This is a comparison chart of the weight loss rate and the change rate of conduction resistance of the flexible circuit board material of each test object in Test Example 5 of the present invention; wherein, (a) is the distribution of the percentage of mass loss of the polyimide flexible circuit board sample before and after the corresponding descaling process in each test group, and (b) is the evolution trend of the change rate of the DC resistance of the blind hole chain relative to the initial resistance value of each test group under the high and low temperature thermal shock environment from -55℃ to 125℃ after the completion of hole metallization. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Inorganic reagents and small molecule reagents not specifically mentioned are all commercially available analytical grade or higher grade products. Resins, rubbers, fillers and additives not specifically mentioned are all commercially available industrial grade or electronic material grade products.

[0027] The carboxyl-terminated nitrile butadiene rubber modified bisphenol A type epoxy resin is formed by a ring-opening esterification reaction between bisphenol A type epoxy resin (CAS No. 25068-38-6) and carboxyl-terminated liquid nitrile butadiene rubber (CAS No. 68891-46-3), resulting in a rubber-modified epoxy prepolymer. This modified resin contains bisphenol A type epoxy resin segments and butadiene-acrylonitrile rubber segments, with the butadiene-acrylonitrile rubber segments introduced into the epoxy resin system as flexible and toughening reinforcing segments. The acrylonitrile mass fraction of the carboxyl-terminated liquid nitrile butadiene rubber used is 18% to 26%, and the weight-average molecular weight of the carboxyl-terminated liquid nitrile butadiene rubber used is 3000 to 5000. The epoxy equivalent of this carboxyl-terminated nitrile butadiene rubber modified bisphenol A type epoxy resin is 200 to 350 g / eq.

[0028] Hydrophobic fumed silica (CAS No. 68909-20-6) is fumed silica with a surface hydrophobic modification treatment using hexamethyldisilazane. Its primary particles have an average particle size of 7 to 20 nm and a specific surface area of ​​150 to 300 m². 2 / g. Polydimethylsiloxane (CAS No. 63148-62-9) is preferably a trimethylsiloxy-terminated linear polydimethylsiloxane, whose main chain is composed of linearly linked dimethylsiloxane repeating units, with a weight-average molecular weight of 3000 to 7000 and a kinematic viscosity of 50 to 100 cSt at 25°C. Modified talc is a commercially available talc filler surface-treated with a coupling agent, preferably talc surface-treated with a silane coupling agent or a titanate coupling agent, with a D50 particle size of 2 to 10 μm and a moisture content of not more than 0.5%. Before use, it can be baked at 105°C until its quality is stable before being added to the blue glue system.

[0029] Other common raw materials include trimethylolpropane triacrylate (CAS No. 15625-89-5), triethylene glycol diacrylate (CAS No. 1680-21-3), 1-hydroxycyclohexylphenyl ketone (CAS No. 947-19-3), dicyandiamide (CAS No. 461-58-5), 2-ethyl-4-methylimidazolium (CAS No. 931-36-2), phthalocyanine blue (CAS No. 147-14-8), diethylene glycol butyl ether (CAS No. 112-34-5), potassium permanganate (CAS No. 7722-64-7), sodium hydroxide (CAS No. 1310-73-2), concentrated sulfuric acid (CAS No. 7664-93-9), and hydrogen peroxide (CAS No. 7722-84-1).

[0030] Preparation Example 1: This preparation example provides a method for preparing anti-overflow blue adhesive, including the following steps: 42.5 kg of carboxyl-terminated butadiene-acrylonitrile rubber modified bisphenol A epoxy resin, 7.5 kg of trimethylolpropane triacrylate, and 7.5 kg of triethylene glycol diacrylate were added to a planetary stirred tank and stirred for 40 minutes at 45°C and 200 rpm to obtain a resin base. The jacket cooling system of the stirred tank was turned on to cool the resin base to 20°C. Then, 1.5 kg of 1-hydroxycyclohexylphenyl ketone, 3.0 kg of dicyandiamide, 1.0 kg of 2-ethyl-4-methylimidazolium, 2.0 kg of hydrophobic fumed silica, 32.5 kg of modified talc, 1.5 kg of polydimethylsiloxane, and 1.0 kg of phthalocyanine blue were added sequentially and dispersed and stirred for 30 minutes at 300 rpm to obtain a preliminary slurry. The preliminary slurry was transferred to a three-roll mill, the roller gap was adjusted to 20 μm, and it was continuously milled 4 times. The fineness of the slurry was measured to be 8 μm using a scraper fineness meter. The ground slurry was placed in a vacuum degassing machine and degassed for 20 minutes under an absolute pressure of 2000Pa. The discharged material was an anti-overflow blue glue.

[0031] Preparation Example 2: This preparation example provides a method for preparing anti-overflow blue adhesive, including the following steps: 35.0 kg of carboxyl-terminated butadiene-acrylonitrile rubber modified bisphenol A epoxy resin, 10.0 kg of trimethylolpropane triacrylate, and 10.0 kg of triethylene glycol diacrylate were added to a planetary mixer and stirred at 50°C and 150 rpm for 45 minutes to obtain a resin base. The resin base was cooled to 25°C, and 3.0 kg of 1-hydroxycyclohexylphenyl ketone, 4.5 kg of dicyandiamide, 1.5 kg of 2-ethyl-4-methylimidazolium, 2.5 kg of hydrophobic fumed silica, 29.5 kg of modified talc, 2.0 kg of polydimethylsiloxane, and 2.0 kg of phthalocyanine blue were added sequentially. The mixture was dispersed and stirred at 400 rpm for 40 minutes to obtain a preliminary slurry. The preliminary slurry was transferred to a three-roll mill, the roller gap was adjusted to 25 μm, and the milling was performed three times consecutively. The fineness of the slurry was measured to be 10 μm using a scraper fineness meter. The ground slurry was placed in a vacuum degassing machine and degassed for 30 minutes under an absolute pressure of 1500Pa. The discharged material was an anti-overflow blue glue.

[0032] Preparation Example 3: This preparation example provides a method for preparing anti-overflow blue adhesive, including the following steps: 50.0 kg of carboxyl-terminated butadiene-acrylonitrile rubber modified bisphenol A epoxy resin, 5.0 kg of trimethylolpropane triacrylate, and 5.0 kg of triethylene glycol diacrylate were added to a planetary mixer and stirred for 30 minutes at 40°C and 250 rpm to obtain a resin base. The resin base was cooled to 22°C, and 1.0 kg of 1-hydroxycyclohexylphenyl ketone, 1.5 kg of dicyandiamide, 0.5 kg of 2-ethyl-4-methylimidazolium, 1.5 kg of hydrophobic fumed silica, 33.5 kg of modified talc, 1.0 kg of polydimethylsiloxane, and 1.0 kg of phthalocyanine blue were added sequentially. The mixture was dispersed and stirred for 25 minutes at 250 rpm to obtain a preliminary slurry. The preliminary slurry was transferred to a three-roll mill, the roller gap was adjusted to 15 μm, and the milling was performed continuously for 5 passes. The fineness of the slurry was measured to be 5 μm using a scraper fineness meter. The ground slurry was placed in a vacuum degassing machine and degassed for 15 minutes under an absolute pressure of 3000Pa, and the discharged material was an anti-overflow blue glue.

[0033] Preparation Example 4: This preparation example provides a method for preparing anti-overflow blue adhesive, including the following steps: 46.0 kg of carboxyl-terminated butadiene-acrylonitrile rubber modified bisphenol A epoxy resin, 8.0 kg of trimethylolpropane triacrylate, and 7.0 kg of triethylene glycol diacrylate were added to a planetary mixer and stirred at 42°C and 220 rpm for 35 minutes to obtain a resin base. The resin base was cooled to 18°C, and 2.0 kg of 1-hydroxycyclohexylphenyl ketone, 2.5 kg of dicyandiamide, 1.0 kg of 2-ethyl-4-methylimidazolium, 2.0 kg of hydrophobic fumed silica, 28.0 kg of modified talc, 2.5 kg of polydimethylsiloxane, and 1.0 kg of phthalocyanine blue were added sequentially. The mixture was dispersed and stirred at 350 rpm for 35 minutes to obtain a preliminary slurry. The preliminary slurry was transferred to a three-roll mill, the roller gap was adjusted to 18 μm, and the milling was performed four times. The fineness of the slurry was measured to be 7 μm using a scraper fineness meter. The ground slurry was placed in a vacuum degassing machine and degassed for 25 minutes under an absolute pressure of 2500Pa. The discharged material was an anti-overflow blue glue.

[0034] This invention is applicable to multi-layer symmetrical rigid-flex boards, especially to eight-layer rigid-flex boards with a 1+1+1+2+1+1+1 structure. In the following embodiments, L1 to L8 represent the first to eighth conductive pattern layers and the corresponding substrate layers of the eight-layer multilayer rigid-flex board from top to bottom, respectively, while L4 and L5 represent the core inner layers.

[0035] Example 1: This example provides a step-by-step lamination and adhesive overflow control method for rigid-flex PVC boards, including the following steps: S1: The copper-clad layers L4 and L5 were subjected to browning micro-etching, and a 18μm thick polyimide cover film was laminated onto the surface. The laminated substrate was placed in a high-pressure press, with the temperature set at 160℃ and the pressure at 4.0MPa, and held for 120s. A 1:1 O2 and Ar mixed gas was introduced for plasma treatment, with the RF power set at 2.0kW and the treatment time at 3min. After treatment, the substrate was baked in an oven at 155℃ for 50min.

[0036] S2: The anti-overflow blue adhesive obtained in Example 1 was printed in the flexible circuit board area, and the wet film thickness was controlled to be 20 μm. A 365 nm ultraviolet light source with 800 mJ / cm² was used. 2 Expose the material to ultraviolet radiation energy, then bake it in an oven at 85°C for 20 minutes. A second layer of anti-overflow blue adhesive, obtained in Preparation Example 1, is then overprinted in situ onto the first layer of blue adhesive, controlling the thickness of the single-layer wet film to be 20 μm. The film is then again exposed to ultraviolet light at a wavelength of 365 nm and an intensity of 800 mJ / cm². 2 Expose it to radiation energy, and then bake it in an oven at 150°C for 50 minutes.

[0037] S3: Introduce L3 and L6 layers. Introduce a 4:1 N2 / O2 mixture to the bonding surface for plasma treatment. Set the working pressure to 30 Pa, the RF power to 1.8 kW, and the treatment time to 4 min. After plasma treatment, place the layers in an environment with 25% relative humidity for 2 h. Align the L3 and L6 layers with the core layer and send them into a hot melt machine. The first stage is set at 90℃ and 0.8 MPa, maintaining contact for 4 s; the second stage involves raising the temperature to 130℃ and applying a pressure of 2.0 MPa, maintaining contact for 10 s.

[0038] S4: The material is fed into a vacuum laminator for the first stage of lamination. Exhaust is applied at 115℃ and 1.2MPa, with a heating rate of 2.0℃ / min; then the temperature is increased to 170℃ and held at 3.8MPa for 75 minutes, followed by cooling to 55℃ before removal from the furnace. The actual coordinates of the reference target are detected using an X-ray target machine, and the XY axis shrinkage offset data is extracted. The difference between the measured target coordinates and the designed target coordinates in the X and Y directions is used as a compensation amount. This data is then used to correct the CCD alignment parameters for the next layer of hot-melt false bonding process; subsequently, the residual adhesive area of ​​the frame is milled off.

[0039] S5: Perform laser blind via processing. A CF4 / O2 mixture (volume ratio 1:7) is introduced for plasma treatment at a pressure of 40 Pa, an RF power of 2.8 kW, and a processing time of 12 minutes. Subsequently, the substrate is sequentially immersed in a swelling solution composed of 65 g / L diethylene glycol butyl ether and 15 g / L sodium hydroxide at 70°C for 4 minutes, then immersed in an oxidation solution composed of 55 g / L potassium permanganate and 45 g / L sodium hydroxide at 80°C for 6 minutes, and finally immersed in a neutralization solution composed of 3% sulfuric acid and 2% hydrogen peroxide at 45°C for 4 minutes. Finally, chemical copper plating and via filling are performed.

[0040] S6: Introduce L2 and L7 layer materials, and use the shrinkage offset data extracted in step S4 to perform the two-stage hot-melt false bonding described in step S3. Perform the second-stage lamination using the same parameters as in step S4. After exiting the furnace, extract new shrinkage offset data using an X-ray target machine, and use this data for subsequent CCD alignment parameter correction; then mill off the residual adhesive area of ​​the second-stage frame. After laser blind hole processing, introduce a CF4 and O2 mixed gas with the same volume ratio as in step S5, adjust the RF power to 3.2kW, and set the processing time to 18min. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, perform electroplating for conductivity.

[0041] S7: Introduce the outer layer materials L1 and L8, and use the shrinkage offset data extracted in step S6 to correct the CCD alignment parameters before performing hot-melt false bonding. Perform the third-stage lamination using the same parameters as in step S4; after exiting the furnace, use an X-ray target machine to confirm the final interlayer alignment and mill off the residual adhesive area of ​​the third-stage frame. Then perform laser blind via processing, adjusting the RF power to 3.8kW and setting the processing time to 22min. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, complete the electroplating for conduction and the etching of the outer layer circuitry.

[0042] S8: A dual-wavelength UV / green laser device is used to laser-remove the cover area of ​​the flexible circuit board, removing the waste material and residual anti-overflow blue adhesive layer covering the cover area. Pure O2 gas is introduced, and plasma treatment is performed for 4 minutes at an RF power of 1.8kW and a working pressure of 25Pa. Solder resist processing is then performed.

[0043] Example 2: This example provides a step-by-step lamination and adhesive overflow control method for rigid-flex PVC boards, including the following steps: Step S1: Perform browning micro-etching on the copper-clad layers L4 and L5, and then laminate a 12.5 μm thick polyimide cover film onto the surface. Place the laminated substrate in a high-pressure press, set the temperature to 150℃, the pressure to 3.0 MPa, and hold the pressure for 90 seconds. Introduce a 1:1 O2 and Ar mixed gas for plasma treatment, set the RF power to 1.5 kW, and the treatment time to 2 minutes. After treatment, bake in a 150℃ oven for 45 minutes.

[0044] S2: The anti-overflow blue adhesive obtained in Example 2 was printed in the flexible circuit board area, and the wet film thickness was controlled to be 15 μm. A 365 nm ultraviolet light source with 500 mJ / cm² was used. 2 Expose the material to ultraviolet radiation energy, then bake it in an oven at 75°C for 15 minutes. A second layer of anti-overflow blue adhesive, obtained in Preparation Example 2, is then overprinted on the first layer of blue adhesive in situ, controlling the thickness of the single-layer wet film to be 15 μm. The film is then again exposed to ultraviolet light at a wavelength of 365 nm and a concentration of 500 mJ / cm². 2 The sample was exposed to radiation energy and then baked in an oven at 140°C for 45 minutes.

[0045] S3: Introduce L3 and L6 layers. Introduce a 3:1 N2 / O2 mixture to the bonding surface for plasma treatment. Set the working pressure to 20 Pa, the RF power to 1.5 kW, and the treatment time to 3 min. After plasma treatment, place the layers in an environment with 20% relative humidity for 1 h. Align the L3 and L6 layers with the core layer and send them into a hot melt machine. The first stage is set at 80℃ and 0.5 MPa, maintaining contact for 3 s; the second stage involves raising the temperature to 120℃ and applying a pressure of 1.5 MPa, maintaining contact for 8 s.

[0046] S4: The material is fed into a vacuum laminator for the first stage of lamination. Exhaust is applied at 100℃ and 1.0MPa, with a heating rate of 1.5℃ / min; then the temperature is increased to 165℃ and held at 3.0MPa for 60 minutes, followed by cooling to 50℃ before removal from the furnace. The actual coordinates of the reference target are detected using an X-ray target machine, and the XY axis shrinkage offset data is extracted. The difference between the measured target coordinates and the designed target coordinates in the X and Y directions is used as a compensation amount. This data is then used to correct the CCD alignment parameters for the next layer of hot-melt false bonding process; subsequently, the residual adhesive area of ​​the frame is milled off.

[0047] S5: Perform laser blind via processing. A plasma treatment is performed using a 1:5 volume ratio of CF4 and O2 gas, with a pressure of 30 Pa, an RF power of 2.5 kW, and a treatment time of 10 min. Subsequently, the substrate is sequentially immersed in a swelling solution composed of 50 g / L diethylene glycol butyl ether and 10 g / L sodium hydroxide at 65°C for 3 min, then immersed in an oxidation solution composed of 45 g / L potassium permanganate and 35 g / L sodium hydroxide at 75°C for 5 min, and finally immersed in a neutralization solution composed of 2% sulfuric acid and 1% hydrogen peroxide at 40°C for 3 min. Finally, chemical copper plating and via filling are performed.

[0048] S6: Introduce L2 and L7 layer materials, and use the shrinkage offset data extracted in step S4 to perform the two-stage hot-melt false bonding described in step S3. Perform the second-stage lamination using the same parameters as in step S4. After exiting the furnace, extract new shrinkage offset data using an X-ray target machine, and use this data for subsequent CCD alignment parameter correction; then mill off the residual adhesive area of ​​the second-stage frame. After laser blind hole processing, introduce a CF4 and O2 mixed gas with the same volume ratio as in step S5, adjust the RF power to 3.0kW, and set the processing time to 15min. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, perform electroplating for conductivity.

[0049] S7: Introduce the outer layer materials L1 and L8, and use the shrinkage offset data extracted in step S6 to correct the CCD alignment parameters before performing hot-melt false bonding. Perform the third-stage lamination using the same parameters as in step S4; after exiting the furnace, use an X-ray target machine to confirm the final interlayer alignment and mill off the residual adhesive area of ​​the third-stage frame. Then perform laser blind via processing, adjusting the RF power to 3.5kW and setting the processing time to 20min. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, complete the electroplating for conduction and the etching of the outer layer circuitry.

[0050] S8: A dual-wavelength UV / green laser device is used to laser-remove the cover area of ​​the flexible circuit board, removing the waste material and residual anti-overflow blue adhesive layer covering the cover area. Pure O2 gas is introduced, and plasma treatment is performed for 3 minutes at an RF power of 1.5kW and a working pressure of 20Pa. Solder resist processing is then performed.

[0051] Example 3: This example provides a step-by-step lamination and adhesive overflow control method for rigid-flex PVC boards, including the following steps: S1: The copper-clad layers L4 and L5 were subjected to browning micro-etching, and a 25μm thick polyimide cover film was laminated onto the surface. The laminated substrate was placed in a high-pressure press, with the temperature set at 175℃ and the pressure at 5.5MPa, and held at that pressure for 150s. A 1:1 volume ratio O2 and Ar mixed gas was introduced for plasma treatment, with the RF power set at 2.5kW and the treatment time at 4min. After treatment, the substrate was baked in an oven at 160℃ for 60min.

[0052] S2: The anti-overflow blue adhesive obtained in Example 3 was printed in the flexible circuit board area, and the wet film thickness was controlled to be 25 μm. A 365 nm ultraviolet light source with 1000 mJ / cm² was used. 2 Expose the material to ultraviolet radiation energy, then bake it in an oven at 90°C for 30 minutes. A second layer of anti-overflow blue adhesive, obtained in Preparation Example 3, is then overprinted on the first layer of blue adhesive in situ, controlling the single-layer wet film thickness to be 25 μm. The film is then again exposed to ultraviolet light at a wavelength of 365 nm and an intensity of 1000 mJ / cm². 2 The sample was exposed to radiation energy and then baked in an oven at 160°C for 60 minutes.

[0053] S3: Introduce L3 and L6 layers. Introduce a 5:1 N2 / O2 mixture to the bonding surface for plasma treatment. Set the working pressure to 40 Pa, the RF power to 2.0 kW, and the treatment time to 5 min. After plasma treatment, place the layers in an environment with 28% relative humidity for 6 h. Introduce a 5:1 N2 / O2 mixture at a working pressure of 40 Pa and an RF power of 1.2 kW for 1.5 min of plasma treatment. Align the L3 and L6 layers with the core layer and send them into a hot melt machine. In the first stage, set the temperature to 100℃ and the pressure to 1.0 MPa, maintaining contact for 5 s. In the second stage, raise the temperature to 140℃ and apply a pressure of 2.5 MPa, maintaining contact for 12 s.

[0054] S4: The material is fed into a vacuum laminator for the first stage of lamination. Exhaust is applied at 130℃ and 1.5MPa, with a heating rate of 2.5℃ / min; then the temperature is increased to 180℃ and held at 4.5MPa for 90 minutes, followed by cooling to 60℃ before removal from the oven. The actual coordinates of the reference target are detected using an X-ray target machine, and the XY axis shrinkage offset data is extracted. The difference between the measured target coordinates and the designed target coordinates in the X and Y directions is used as a compensation amount. This data is then used to correct the CCD alignment parameters for the next layer of hot-melt false bonding process; subsequently, the residual adhesive area of ​​the frame is milled off.

[0055] S5: Perform laser blind via processing. A plasma treatment is performed using a 1:9 volume ratio of CF4 and O2 gas, with a pressure of 50 Pa, an RF power of 3.0 kW, and a treatment time of 15 min. Subsequently, the substrate is sequentially immersed in a swelling solution composed of 80 g / L diethylene glycol butyl ether and 20 g / L sodium hydroxide at 75°C for 5 min, then immersed in an oxidation solution composed of 65 g / L potassium permanganate and 55 g / L sodium hydroxide at 85°C for 8 min, and finally immersed in a neutralization solution composed of 5% sulfuric acid and 3% hydrogen peroxide at 50°C for 5 min. Finally, chemical copper plating and via filling are performed.

[0056] S6: Introduce L2 and L7 layer materials, and use the shrinkage offset data extracted in step S4 to perform the two-stage hot-melt false bonding described in step S3. Perform the second-stage lamination using the same parameters as in step S4. After exiting the furnace, extract new shrinkage offset data using an X-ray target machine, and use this data for subsequent CCD alignment parameter correction; then mill off the residual adhesive area of ​​the second-stage frame. After laser blind hole processing, introduce a CF4 and O2 mixed gas with the same volume ratio as in step S5, adjust the RF power to 3.5kW, and set the processing time to 20min. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, perform electroplating for conductivity.

[0057] S7: Introduce the outer layer materials L1 and L8, and correct the CCD alignment parameters using the shrinkage offset data extracted in step S6 before performing hot-melt false bonding. Perform the third-stage lamination using the same parameters as in step S4; after baking, confirm the final interlayer alignment using an X-ray target machine, and mill off the residual adhesive area of ​​the third-stage frame. Then, perform laser blind via processing, adjusting the RF power to 4.0kW and setting the processing time to 25 minutes. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, complete the electroplating for conduction and the etching of the outer layer circuitry.

[0058] S8: A dual-wavelength UV / green laser device is used to laser-remove the cover area of ​​the flexible circuit board, removing the waste material and residual anti-overflow blue adhesive layer covering the cover area. Pure O2 gas is introduced, and plasma treatment is performed for 5 minutes at an RF power of 2.0kW and a working pressure of 30Pa. Solder resist processing is then performed.

[0059] Example 4: This example provides a step-by-step lamination and adhesive overflow control method for rigid-flex PVC boards, including the following steps: Steps S1 to S4 are performed using the same process parameters as in Example 1, except that the anti-overflow blue adhesive in step S2 is replaced with the anti-overflow blue adhesive obtained in Preparation Example 4.

[0060] S5: Perform laser blind via processing. A CF4 / O2 mixed gas (volume ratio 1:7) is introduced for plasma treatment at a pressure of 40 Pa, an RF power of 2.8 kW, and a treatment time of 10 min. The substrate is then sequentially immersed in the swelling solution, oxidation solution, and neutralization solution described in Example 1, using the same temperature and time parameters as in Example 1. Finally, chemical copper plating and via filling are performed.

[0061] S6: Introduce L2 and L7 layer materials, and use the previous stage shrinkage offset data to perform two-stage hot-melt false bonding and second-stage lamination. After exiting the furnace, extract new shrinkage offset data using an X-ray target machine, and use this data for subsequent CCD alignment parameter correction; then mill away the residual adhesive area of ​​the second-stage frame. After laser blind hole processing, introduce a CF4 and O2 mixed gas with the same volume ratio as in step S5, maintain the RF power at 2.8kW, and adjust the processing time to 16min. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, perform electroplating for conductivity.

[0062] S7: Introduce L1 and L8 outer layer materials, and use the previous stage shrinkage offset data to perform hot-melt false bonding and third-stage lamination. After baking, use an X-ray target machine to confirm the final interlayer alignment and mill off the residual adhesive area of ​​the third-stage border. Then, perform laser blind via processing, introducing a CF4 and O2 mixed gas with the same volume ratio as in step S5, maintaining the RF power at 2.8kW, and adjusting the processing time to 24min. After plasma treatment, immerse the substrate sequentially in the same expansion solution, oxidation solution, and neutralization solution with the same composition, concentration, temperature, and processing time as in step S5. Finally, complete the electroplating for conduction and outer layer etching.

[0063] S8: Processing is performed using the same laser capping and plasma treatment process parameters as in Example 1, followed by solder resist processing.

[0064] Comparative Example 1: Compared to Example 1, the difference lies in the blue adhesive printing and baking operation in step S2. The multi-stage printing and step-by-step baking process is eliminated, and step S2 is replaced by: a single printing of the anti-overflow blue adhesive obtained in Example 1 in the flexible circuit board area, controlling the wet film thickness to 40 μm, which is the same as the total wet film thickness after two blue adhesive printings in Example 1. A 365 nm ultraviolet light source with 1600 mJ / cm² is used. 2 The sample was subjected to a single exposure using radiant energy, and then baked in an oven at 150°C for 70 minutes. All other steps and parameters were the same as in Example 1.

[0065] Comparative Example 2: Compared to Example 3, the difference lies in the plasma treatment operation in step S3. The short-term plasma refresh treatment after the flow timeout is cancelled. Specifically, it is replaced by: introducing a N2 and O2 mixed gas with a volume ratio of 5:1 into the pressing surface for plasma treatment, setting the working pressure to 40 Pa, the radio frequency power to 2.0 kW, and the treatment time to 5 min. After plasma treatment, it is placed in an environment with a relative humidity of 28% for 6 h. After placement, the L3 and L6 layers are directly aligned with the core layer and sent to the hot melt machine for subsequent hot melt operation. The remaining steps and parameters are the same as in Example 3.

[0066] Comparative Example 3: Compared to Example 1, the difference lies in the blind hole desizing parameters in steps S6 and S7. The step of increasing the dry plasma parameters with each lamination stage is eliminated; instead, the treatment time of the wet plasma solution is extended. Specifically, the dry plasma treatment parameters in steps S6 and S7 are fixed at the same pressure (40 Pa), radio frequency power (2.8 kW), and treatment time (12 min) as in step S5. Simultaneously, the treatment times for immersion in the swelling solution, oxidation solution, and neutralization solution in step S6 are extended to 7 min, 9 min, and 7 min, respectively; and the treatment times for immersion in the swelling solution, oxidation solution, and neutralization solution in step S7 are further extended to 10 min, 12 min, and 10 min, respectively. The swelling solution, oxidation solution, and neutralization solution used are the same as in Example 1. All other steps and parameters are the same as in Example 1.

[0067] Comparative Example 4: Compared to Example 1, the difference lies in the hot-melt sham application operation in step S3. The two-stage separation design of the first hot-melt pre-positioning and the second hot-melt shaping is eliminated. The hot-melt process in step S3 is replaced by: aligning layers L3 and L6 with the core layer and feeding them into the hot-melt machine, setting the temperature to 130°C and the pressure to 2.0 MPa, holding for 14 seconds in a single stage. This single-stage holding time is consistent with the total holding time of the two-stage hot-melt sham application in Example 1. All other steps and parameters are the same as in Example 1.

[0068] Comparative Example 5: Compared to Example 3, the difference lies in the coordinate positioning and data retrieval operations in steps S4, S6, and S7. The feedforward mechanism of extracting the shrinkage offset data of the previous stage for subsequent cascaded pressing compensation has been eliminated. Specifically, in steps S6 and S7, when introducing materials for hot-melt false bonding and lamination, fixed theoretical coordinate parameters set in the design drawings are used for CCD visual positioning and alignment, without importing measured expansion and contraction data or correcting parameters. The remaining steps and process parameters are the same as in Example 3.

[0069] Test Example 1: Test objective: To verify whether the curing degree, modulus change in hot pressing temperature zone, and anti-flow state of the anti-overflow blue adhesive after the first shaping treatment and the second final shaping treatment meet the requirements of step-by-step pressing.

[0070] The experimental steps are as follows: 1. Extract the original anti-overflow adhesive that has not undergone exposure and baking as the benchmark test sample. Samples were simultaneously taken from the processing operation of Example 1 to obtain a first-stage blue adhesive sample that underwent only a single exposure and baking at 85°C, and a second-stage blue adhesive sample that underwent overprinting and a second exposure and baking at 150°C. After obtaining the samples, they were placed in glass containers with desiccant to cool to room temperature before testing.

[0071] 2. Differential scanning calorimetry (DSC) was used for testing. The reference sample, the first-stage blue adhesive sample, and the second-stage blue adhesive sample were weighed and sealed in standard aluminum crucibles. Under dynamic high-purity nitrogen protection, a heating program was set to heat from 30.0℃ to 250.0℃ at a heating rate of 10.0℃ / min. The heat flow curves were recorded, and the residual reaction exothermic peak area was integrated to obtain the residual reaction exothermic enthalpy for each sample. The relative degree of curing at the corresponding stage was calculated based on the exothermic enthalpy of the reference sample.

[0072] 3. The rheological properties of the samples at each stage were tested using a rotational rheometer. The pre-acquired samples were pressed into circular specimens with a diameter of 25.0 mm and a thickness of 1.5 mm. The circular specimens were placed between the parallel plate clamps of the rheometer, and the test oscillation frequency was set to 1.0 Hz with an initial strain amplitude of 0.1%. A dynamic temperature scan was performed on the samples from 50.0℃ to 200.0℃, and the storage modulus data of the samples at the two critical hot-pressing temperatures of 130.0℃ and 170.0℃ were extracted.

[0073] The experimental results are shown in Table 1: Table 1: Thermal analysis and rheological test data of blue adhesive at different processing stages according to Figure 1 According to the data in Table 1, after the first stage of exposure and baking, the residual exothermic enthalpy of the anti-overflow blue adhesive in Example 1 was 152.17 J / g, corresponding to a relative degree of curing of 36.02%. The storage modulus of the material at 130°C in this stage was 0.47 MPa. This low degree of crosslinking and modulus state allows the bottom blue adhesive to have fluidity and permeability in the early stage, enabling it to form interfacial wetting and physical bonding with the surface of the bottom cover film under low-temperature hot-melt operation.

[0074] After overprinting the second layer of blue adhesive and completing the overall high-temperature baking at 150℃, the relative curing degree of the blue adhesive system increased to 94.71%, reaching a near-complete cross-linking state. At this point, the storage modulus at 170℃ increased to 21.35 MPa. Because the bottom layer of blue adhesive had already established a bond with the substrate during the initial treatment, the subsequent high-temperature treatment resulted in a continuous, well-defined layer with a high degree of curing between the bottom and surface layers. During the subsequent lamination process at 170℃, the resin substrate melted under pressure, generating lateral extrusion stress. The cross-linked, high-modulus anti-overflow layer could restrict the lateral flow of resin due to its own rigidity, while the initial adhesion at the bottom helped reduce the risk of overall displacement of the anti-overflow adhesive layer under lateral shear. This step-by-step processing mechanism achieved good adhesion between the anti-overflow layer and the substrate while also giving the processing system good adhesive flow boundary stability.

[0075] Test Example 2: Test objective: To test the basic reliability and electrical conductivity of the rigid-flex board prepared according to the embodiments of the present invention.

[0076] The experimental steps are as follows: 1. From the finished products processed in Examples 1 to 4, 20 panels were randomly selected as thermal shock resistance test samples, and 5 panels were randomly selected as electrical connectivity test samples. The test samples were placed in an oven at 125°C and baked for 2 hours.

[0077] 2. Immerse each of the baked thermal shock test samples into a tin bath at 288°C for 10 seconds each time, and then cool them at room temperature for 60 seconds. Repeat the immersion and cooling process three times for each panel sample.

[0078] 3. The bonding interface of the test sample is scanned using an ultrasonic scanning detection device. The area of ​​the delamination or void defect is calculated using the acoustic signal, and its proportion of the total scanned area of ​​the sample is calculated. The average delamination area ratio of the samples in each embodiment is recorded.

[0079] 4. At room temperature, use a four-wire probe tester to measure the DC resistance at both ends of the blind via chains in the daisy-chain test pattern on the electrical connectivity test sample. Record the resistance of each test via chain and calculate the average value.

[0080] The experimental results are shown in Table 2: Table 2: Test data on the basic reliability and conductivity of rigid-flex PCBs prepared in different embodiments according to Figure 2 According to the data in Table 2, after thermal shock at 288°C, the average delamination area ratio of Examples 1 to 4 ranged from 0.14% to 0.23%. The localized anti-overflow coating and plasma treatment processes introduced during the manufacturing process did not cause significant interface separation under high-temperature shock. The anti-overflow blue adhesive maintained the stability of the interface area between the cover film and the bonding resin during the step-by-step lamination process, and multiple dry plasma treatments did not cause deterioration of the material surface thermal stability. Furthermore, the initial on-resistance of the blind via chains in each example was concentrated between 238.19 mΩ and 245.82 mΩ. The cross-linking degree of the inner layer resin in the multilayer board increased during cascade lamination, which placed demands on the blind via descaling process. The current on-resistance data indicates that the dry-wet combined descaling parameters are beneficial in reducing the impact of residual adhesive in blind vias on metallization bonding, enabling the subsequent chemical copper plating layer to form a metallization bond with the inner layer conductive pattern. Based on the results of thermal shock resistance and electrical resistance tests, the substrate prepared using the method in this embodiment maintains the mechanical connection of the bonding interface in the soft-hard transition zone and the electrical conductivity of the blind vias between layers.

[0081] Test Example 3: Test objective: To test the effects of the blue glue dual-state shaping process and the two-stage hot melt false bonding process on the lateral extrusion flow of the adhesive in the soft-hard transition zone.

[0082] The experimental steps are as follows: 1. The rigid-soft bonded boards after lamination in Example 1, Comparative Example 1 and Comparative Example 4 were selected as test objects, and 10 boards were randomly selected from each group for measurement.

[0083] 2. Fix the plate to be tested on the test platform of the industrial 2D coordinate measuring machine. Use the boundary line between the rigid plate area and the flexible plate area as the measurement reference line, and select measurement points along the reference line in the transition zone between the rigid and flexible areas.

[0084] 3. On the baseline of each individual board, set a measuring point at 5.0mm intervals. Use a measuring instrument to measure the horizontal projection distance of the edge of the pressed resin extending into the flexible board area at each point.

[0085] 4. Record the data of each measurement point on the test board, extract the maximum glue overflow distance of a single board, calculate the average glue overflow distance of the test points, and calculate the standard deviation of each group of sample data.

[0086] The experimental results are shown in Table 3: Table 3: Test data on lateral overflow distance in the soft-hard transition zone under different process conditions according to Figure 3According to the data in Table 3, the average overflow distance of Example 1 was 82.7 μm, and the maximum overflow distance was 118.4 μm. The average overflow distance of Comparative Example 1 was 251.4 μm, and the average overflow distance of Comparative Example 4 was 198.2 μm. Comparative Example 1 used a single coating and baking process, and the cross-linking state inside the anti-overflow layer was consistent. Anti-overflow layers with uniform modulus are difficult to simultaneously meet the mechanical requirements of interfacial bonding and resistance to transverse shear during the lamination process. Under the vertical pressure of hot pressing, the prepreg resin melts and generates transverse extrusion stress. Single-layer anti-overflow adhesive is prone to deformation or displacement under shear force. The maximum overflow distance of 326.8 μm and the standard deviation of 48.6 μm in the test data reflect the performance of this state in terms of flow resistance. The anti-overflow layer of Example 1 was processed in stages to form a modulus difference distribution. The lower modulus of the bottom layer maintains physical bonding with the surface of the cover film, while the high modulus of the top layer provides structural stiffness to block resin flow. The combination of interface anchoring and structural stiffness limited the extrusion of resin into the soft plate region. Comparative Example 4 applied a direct pressure of 2.0 MPa during the hot-melt stage. The resin viscosity was low in the initial stage of hot-melt, and the direct intervention of high pressure promoted the diffusion of low-viscosity resin outwards. Example 1 employed a segmented pressure loading method, maintaining low-pressure contact during the pre-positioning stage when the resin viscosity was low, and then applying high pressure for shaping after the resin viscosity increased with temperature. The loading path based on the resin rheological properties reduced the lateral displacement of the fluid in the low-viscosity region. The combination of the blue glue treatment process and the segmented pressure loading method controlled the lateral flow dimensions of the resin in the soft-hard transition zone.

[0087] Test Example 4: Test objective: To test the impact of plasma timeout refresh processing on the bonding reliability of the lamination interface, and to test the effect of X-ray inspection data on interlayer offset control by thermal fusion false bonding alignment compensation.

[0088] The experimental steps are as follows: 1. Extract the rigid-soft bonded boards that have completed the lamination process from Example 3, Comparative Example 2 (which was left unused for an extended period and did not undergo surface refresh treatment), and Comparative Example 5 (which did not introduce cascaded detection compensation). Cut peel test strips of standard width along the interface between the cover film and the lamination layer, and prepare aging test templates of specified dimensions and full-board samples for accuracy testing.

[0089] 2. Use a universal tensile testing machine to clamp one end of the peel test strip and apply a 90° vertical stretch at a constant rate. Measure the average tensile force when the interface breaks and separates to calculate the peel strength.

[0090] 3. Place the aging test sample in a high-pressure accelerated aging test chamber and treat it continuously for 24 hours at 121℃, 100% relative humidity, and 2 atm ambient pressure. Remove the sample, observe the surface morphology, measure the total blistering area, and calculate its percentage of the sample's test area.

[0091] 4. Use X-ray inspection equipment to perform a transmissive scan of the entire board sample. Measure the actual interlayer offset distance between the internal targets after cascade lamination, as well as the deviation distance of the blind via center relative to the inner layer target pad center. Record the average interlayer offset and the maximum blind via offset of each test board, and statistically analyze the proportion of measured values ​​exceeding the process tolerance range.

[0092] The experimental results are shown in Table 4: Table 4: Test data on interface bonding and alignment accuracy under different process conditions according to Figure 4 According to the data in Table 4, the 90° peel strength of the cover film and the bonding layer interface in Example 3 was 1.24 N / mm, and the blistering area after high-temperature and high-humidity aging treatment accounted for 0.38%. Comparative Example 2 underwent the same resting time but without plasma refresh treatment; its peel strength decreased to 0.68 N / mm, and the blistering area after aging increased to 2.53%. Plasma treatment can improve the activation state and wettability of the surface to be laminated. The surface activation state after plasma treatment decays with prolonged resting time, leading to a decrease in the chemical activity of the material surface. In Example 3, plasma refresh treatment before laminating the plates re-energized the surface activity of the cover film, maintaining a high level of interfacial bonding force and reducing the probability of environmental moisture intruding into the laminating interface and causing localized blistering.

[0093] Multilayer boards undergo nonlinear dimensional expansion and contraction during repeated heating, melting, and cooling curing processes. Comparative Example 5, using fixed theoretical coordinates for positioning, measured an average interlayer offset of 46.5 μm, with a maximum blind via offset reaching 82.6 μm. This indicates that the deformation error of a single layer accumulates layer by layer during multi-stage lamination. Example 3 uses actual coordinate data from X-ray inspection after the previous stage of lamination to correct the positioning parameters of the current stage's hot-melt dummy bonding. Coordinate feedforward compensation based on measured expansion and contraction data controls the average interlayer offset to 18.7 μm, and reduces the maximum blind via offset to 31.4 μm. This measured coordinate adjustment mechanism reduces the cumulative alignment deviation caused by nonlinear material deformation, maintaining the interlayer alignment accuracy of the cascaded lamination process.

[0094] Test Example 5: Test objective: To test the impact of a hierarchical dry-wet adhesive removal process on the reliability of blind via metallization and the quality loss of flexible circuit board materials.

[0095] The experimental steps are as follows: 1. Extract polyimide flexible board material samples from Examples 1, 2, and Comparative Example 3, which uses fixed dry plasma parameters and extends the wet desmearing time. Simultaneously, extract blind hole chain test plates that have completed the electroplating metallization process.

[0096] 2. Take samples with an area of ​​50.0 mm × 50.0 mm from each group of polyimide flexible sheet materials. Soak the samples in deionized water and ultrasonically clean for 5 minutes, then transfer them to a 105℃ drying oven and bake until a constant weight is achieved. Before and after the desizing process, measure the sample mass using an analytical balance with an accuracy of 0.01%. Calculate the ratio of the mass difference before and after processing to the initial mass to obtain the weight loss rate of the flexible sheet material.

[0097] 3. Place the blind hole chain test plates of each group in the test chamber of the thermal shock test chamber for high and low temperature thermal shock cycling. Set the lower limit of the cycling temperature to -55℃ and the upper limit to 125℃. The single residence time of the sample in the high and low temperature ranges is 15 minutes, and the temperature transition recovery time is set to less than 10 seconds.

[0098] 4. Before the start of the thermal shock cycle, and after 200, 500, and 1000 cycles, measure the DC resistance of the blind via chain on the test board using a four-wire microresistance meter at room temperature. Record the resistance values ​​at each stage and calculate the rate of change of resistance relative to the initial resistance at each cycle node.

[0099] The experimental results are shown in Table 5: Table 5: Weight loss rate and resistivity change rate of flexible circuit board material for each test object at different cycle numbers Reference Figure 5 After multiple laminations, the removal of resin drilling residue at the bottom and walls of blind holes in multilayer boards becomes more difficult. According to the data in Table 5, Comparative Example 3, which uses fixed dry plasma parameters but extends the wet desmearing time, achieved a material weight loss rate of 6.42%. This result indicates that simply extending the wet treatment time increases the degree to which the flexible board material is affected by the chemical solution, leading to increased material quality loss. Examples 1 and 2, employing a process that adjusts the dry plasma treatment intensity according to the lamination stage and ensures that the wet desmearing amount does not increase synchronously with the number of laminations, achieved material weight loss rates of 1.18% and 1.25%, respectively. This result demonstrates that the layered dry-wet co-processing desmearing process of this invention can maintain the quality stability of the flexible board material while reducing the wet treatment load.

[0100] After 1000 high and low temperature thermal shock cycles, the resistance change rate of the blind via chain in Comparative Example 3 increased to 11.59%, higher than 3.27% in Example 1 and 3.14% in Example 2. This result indicates that while extending the wet desmearing time can enhance the desmearing effect, it increases the risk of over-processing in the flexible circuit board material and via wall areas, and adversely affects the thermal shock reliability of subsequent metallized interconnects. Examples 1 and 2, by increasing the intensity of the dry plasma treatment after subsequent lamination while maintaining a consistent wet desmearing amount with the number of lamination cycles, ensured that the blind via chain maintained a low resistance change rate after thermal shock. This demonstrates that the hierarchical dry-wet co-processing desmearing process is beneficial for balancing blind via conductivity reliability and flexible circuit board material protection.

[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for step-by-step lamination and adhesive overflow control of rigid-flex PVC boards, characterized in that, Includes the following steps: S1: The core inner layer is laminated with a polyimide cover film, and then subjected to rapid pressing, surface plasma treatment and coating baking in sequence. S2: Print the first layer of anti-overflow blue glue in the flexible board area, and perform the first ultraviolet exposure and baking of the first blue glue; overprint the second layer of anti-overflow blue glue on the surface of the first layer of anti-overflow blue glue, and perform the second ultraviolet exposure and baking of the second blue glue; S3: Introduce the outermost layer material and perform plasma treatment, align the outermost layer material with the core inner layer, and sequentially perform the first stage of hot melt false bonding and the second stage of hot melt false bonding. S4: Perform the first stage of lamination and extract the first shrinkage offset data; S5: Perform the first laser blind hole processing, the first dry plasma treatment, the first wet desmearing treatment and the first hole metallization; S6: Introduce a second material layer, and sequentially perform the first stage hot melt false bonding, the second stage hot melt false bonding and the second stage lamination according to the first shrinkage offset data, and extract the second shrinkage offset data; perform the second laser blind hole processing, the second dry plasma treatment, the second wet adhesive removal treatment and the second hole metallization; S7: Introduce outer layer material, and perform the first stage hot melt false bonding, the second stage hot melt false bonding and the third stage lamination in sequence according to the second shrinkage offset data; perform the third laser blind hole processing, the third dry plasma treatment, the third wet adhesive removal treatment, the third hole metallization and circuit etching. S8: The cover is removed using laser equipment to remove waste materials, the first layer of anti-overflow blue adhesive and the second layer of anti-overflow blue adhesive, and then plasma treatment and solder resist processing are performed after the cover is removed.

2. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, In step S2, both the first layer of anti-overflow blue adhesive and the second layer of anti-overflow blue adhesive are made from raw materials comprising the following parts by weight: 35.0–50.0 parts of carboxyl-terminated butadiene-acrylonitrile rubber modified bisphenol A type epoxy resin; 5.0 to 10.0 parts of trimethylolpropane triacrylate; 5.0 to 10.0 parts of triethylene glycol diacrylate; 1.0 to 3.0 parts of 1-hydroxycyclohexylphenyl ketone; Dicyandiamide 1.5–4.5 parts; 0.5 to 1.5 parts of 2-ethyl-4-methylimidazole; 1.5–2.5 parts of hydrophobic fumed silica; 28.0–33.5 parts of modified talc; 1.0 to 2.5 parts of polydimethylsiloxane; Phthalocyanine blue 1.0-2.0 parts.

3. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 2, characterized in that, The carboxyl-terminated nitrile rubber modified bisphenol A type epoxy resin is a prepolymer containing butadiene-acrylonitrile rubber segments formed by the ring-opening esterification reaction of bisphenol A type epoxy resin and carboxyl-terminated liquid nitrile rubber; the mass fraction of acrylonitrile in the carboxyl-terminated liquid nitrile rubber is 18% to 26%, and the weight average molecular weight is 3000 to 5000; the epoxy equivalent of the carboxyl-terminated nitrile rubber modified bisphenol A type epoxy resin is 200 to 350 g / eq. The hydrophobic fumed silica is fumed silica with a surface hydrophobic modification treatment using hexamethyldisilazane, and the average particle size of the primary particles of the hydrophobic fumed silica is 7-20 nm. The modified talc powder is talc powder surface-treated with silane coupling agent or titanate coupling agent, and the D50 particle size of the modified talc powder is 2-10 μm.

4. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, The processing parameters for step S2 are: The baking temperature of the second blue glue is higher than that of the first blue glue. The wet film thickness of both the first layer of anti-overflow blue adhesive and the second layer of anti-overflow blue adhesive is 15-25 μm. The wavelength of the light source for both the first and second ultraviolet exposures was 365 nm, and the radiation energy was 500–1000 mJ / cm². 2 ; The baking temperature of the first blue glue is 75-90℃, and the baking time of the first blue glue is 15-30 minutes; The second blue glue is baked at a temperature of 140–160°C for 45–60 minutes.

5. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, In steps S3, S6, and S7, the parameters for the first-stage heat-melt false bonding and the second-stage heat-melt false bonding are as follows: The pressure of the second-stage hot melt false bonding is greater than the pressure of the first-stage hot melt false bonding; The temperature of the first stage of hot melt false bonding is 80-100℃, the pressure of the first stage of hot melt false bonding is 0.5-1.0MPa, and the time of the first stage of hot melt false bonding is 3-5s; The temperature of the second-stage hot-melt stencil is 120-140℃, the pressure of the second-stage hot-melt stencil is 1.5-2.5MPa, and the time of the second-stage hot-melt stencil is 8-12s.

6. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, The parameters for the plasma treatment in step S3 are as follows: A nitrogen-oxygen mixture with a volume ratio of 3:1 to 5:1 is introduced, the working pressure is 20 to 40 Pa, the radio frequency power is 1.5 to 2.0 kW, and the processing time is 3 to 5 min. After plasma treatment, the outermost layer material and the inner core layer are placed in an environment with a relative humidity of 20% to 28%. When the placement time is greater than 1 hour, a plasma refresh treatment step is added before the first stage of hot melt false bonding. The parameters of the plasma refresh treatment step are: a nitrogen and oxygen mixture with a volume ratio of 5:1 is introduced, the working pressure is 40 Pa, the radio frequency power is 1.2 kW, and the processing time is 1.5 min.

7. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, The data processing and lamination parameters for steps S4 and S6 are as follows: The method for extracting the first shrinkage offset data in step S4 is as follows: the measured coordinates of the target are detected by X-ray equipment, and the coordinate difference between the measured coordinates of the target and the design coordinates is extracted to generate the first shrinkage offset data; The parameters for the first stage of lamination in step S4 are as follows: exhaust at a temperature of 100-130℃ and a pressure of 1.0-1.5MPa, with the heating rate controlled at 1.5-2.5℃ / min; heating to 165-180℃ and maintaining curing at a pressure of 3.0-4.5MPa for 60-90min. After extracting the first shrinkage offset data in step S4, a first milling step to remove border waste is added; after extracting the second shrinkage offset data in step S6, a second milling step to remove border waste is added.

8. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, In steps S5, S6, and S7, the parameters for the first dry plasma treatment, the second dry plasma treatment, and the third dry plasma treatment are as follows: The radio frequency power of the second dry plasma treatment is greater than that of the first dry plasma treatment, or the time of the second dry plasma treatment is greater than that of the first dry plasma treatment. The radio frequency power of the third dry plasma treatment is greater than that of the second dry plasma treatment, or the time of the third dry plasma treatment is greater than that of the second dry plasma treatment. The first dry plasma treatment, the second dry plasma treatment, and the third dry plasma treatment all introduce a mixture of carbon tetrafluoride and oxygen in a volume ratio of 1:5 to 1:9, and the gas pressure is 30 to 50 Pa. The radio frequency power of the first dry plasma treatment is 2.5–3.0 kW, and the time is 10–15 min; The second dry plasma treatment has a radio frequency power of 2.8–3.5 kW and a duration of 15–20 min; The radio frequency power of the third dry plasma treatment is 2.8–4.0 kW, and the time is 20–25 min.

9. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, In steps S5, S6, and S7, the first wet adhesive removal process, the second wet adhesive removal process, and the third wet adhesive removal process each sequentially include: Immerse in a swelling solution composed of 50–80 g / L diethylene glycol butyl ether and 10–20 g / L sodium hydroxide, and treat at 65–75 °C for 3–5 min. Immerse in an oxidizing solution composed of 45–65 g / L potassium permanganate and 35–55 g / L sodium hydroxide, and treat at 75–85 °C for 5–8 min. Immerse in a neutralization solution consisting of 2%–5% sulfuric acid and 1%–3% hydrogen peroxide by mass, and treat at 40–50°C for 3–5 minutes. In the first wet degumming treatment, the second wet degumming treatment, and the third wet degumming treatment, the concentrations of the bulking liquid, the oxidizing liquid, and the neutralizing liquid are all exactly the same, the treatment temperature is exactly the same, and the treatment time is exactly the same.

10. The step-by-step lamination and adhesive overflow control processing method for rigid-flex PVC boards according to claim 1, characterized in that, The parameters for steps S1 and S8 are: In step S1, the rapid pressing treatment is carried out at a temperature of 150–175°C, a pressure of 3.0–5.5 MPa, and a time of 90–150 s; the surface plasma treatment involves introducing a mixture of oxygen and argon gas, with a radio frequency power of 1.5–2.5 kW and a time of 2–4 min; the coating baking is carried out at a temperature of 150–160°C and a time of 45–60 min. In step S8, after the lid is removed, pure oxygen is introduced into the plasma treatment, the radio frequency power is 1.5 to 2.0 kW, the working pressure is 20 to 30 Pa, and the time is 3 to 5 min.

Images