Low-thermal shrinkage polymer adhesive film for laser drilling and preparation method thereof

Abstract

This invention belongs to the field of polymer materials, specifically relating to a low-heat-shrinkage polymeric film for laser drilling and its preparation method. The film comprises modified polyphenylene ether resin, vinyl-containing benzoxazine resin, a specific cationic initiator, a toughening agent, and inorganic modified fillers: gadolinium lanthanum zirconate core-shell nanocrystals and lithium aluminum borosilicate nanowires. The preparation method includes: first, surface-treating the two inorganic fillers with a silane coupling agent and then dispersing them in a solvent to obtain a slurry; then, mixing this slurry with the modified polyphenylene ether resin, vinyl-containing benzoxazine resin, cationic initiator, and toughening agent to form a homogeneous adhesive; finally, coating the adhesive onto a carrier film and drying and curing it at three temperature stages from low to high to obtain the finished film. The film prepared by this method exhibits extremely low heat shrinkage during laser drilling, effectively controlling resin protrusion or indentation defects on the hole wall, and significantly improving the quality and reliability of micropore processing.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a low-heat-shrinkable polymer film for laser drilling and its preparation method. Background Technology

[0002] In the manufacturing processes of high-density interconnect printed circuit boards and advanced packaging, laser drilling technology has become a core process for forming micro-blind vias to achieve interlayer electrical interconnection. This technology utilizes a high-energy laser beam to precisely ablate dielectric materials, offering significant advantages such as high efficiency, good hole quality, and suitability for micro-hole processing. As electronic products continue to evolve towards higher frequencies, higher speeds, and thinner, smaller designs, the requirements for circuit board linewidth, line spacing, and micro-hole diameter are becoming increasingly stringent, making the precision and reliability of laser drilling processes crucial. Against this backdrop, ensuring the integrity of the hole walls after laser processing and avoiding any defects that could affect electrical performance or mechanical reliability is a key step in improving overall product yield and performance.

[0003] However, laser drilling technology faces a long-standing technical bottleneck: the problem of adhesive shrinkage at the hole wall. This problem stems from the significant difference in thermophysical properties between the copper foil and the polymer dielectric film that make up the laminate. Copper foil has excellent thermal conductivity, enabling it to quickly dissipate the instantaneous heat generated by the laser; while polymer films typically have low thermal conductivity and a high coefficient of thermal expansion. When a high-energy-density laser pulse acts on the material surface, the local area of ​​the film undergoes a rapid heating, thermal degradation, and even vaporization process. Due to the asynchronous thermal responses of the adhesive and the copper foil, complex thermal stresses are generated at the hole wall interface. This stress causes uneven shrinkage of the film material, manifested as the resin around the hole wall concave inward or bulge outward relative to the copper ring after drilling, a phenomenon collectively referred to in the industry as "adhesive shrinkage." Severe shrinkage defects can directly damage the smoothness and continuity of the hole walls, which not only makes subsequent chemical copper plating and electroplating processes difficult, but also easily leads to uneven metal plating, voids or cracks. Furthermore, it can degrade the integrity of signal transmission and become a potential failure point under long-term thermal cycling or mechanical stress, seriously restricting the reliability of high-end electronic products.

[0004] To address the shrinkage problem, existing technological improvements mainly focus on two directions: first, optimizing laser process parameters, such as using ultraviolet lasers, adjusting pulse energy and frequency, and optimizing beam paths, aiming to reduce heat input and control the heat-affected zone; second, improving the substrate, such as using copper foil with lower micro-roughness to enhance physical adhesion to the resin. While these methods have achieved some success, they are essentially external process adjustments or interface modifications, failing to fundamentally change the sensitivity of the polymer dielectric layer to laser thermal shock. The thermal decomposition and shrinkage behavior of polymer films under laser irradiation is determined by their inherent thermophysical and chemical properties. Therefore, developing a novel polymer film material with inherently low thermal shrinkage characteristics, capable of actively adapting to and resisting the severe thermal shock during laser processing, is an inevitable path to fundamentally solve the shrinkage defect in hole walls and overcome the limitations of current laser drilling technology. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a low-heat-shrinkage polymer film for laser drilling and its preparation method.

[0006] In a first aspect, the present invention provides a method for preparing a low-heat-shrinkage polymeric film for laser drilling, comprising the following steps:

[0007] S1. By weight, 0.5-3 parts of γ-aminopropyltriethoxysilane are dissolved in ethanol, and then added to a mixed powder of 5-15 parts of gadolinium lanthanum zirconate core-shell nanocrystals and 5-15 parts of lithium aluminum borosilicate nanowires, wherein the gadolinium lanthanum zirconate core-shell nanocrystals have gadolinium lanthanum zirconate as the core and yttrium-doped silicon dioxide as the shell; a surface-treated composite filler is obtained, and the surface-treated composite filler is added to a stirring tank of toluene / butanone mixed solvent and ultrasonically dispersed to obtain a filler slurry;

[0008] S2. In a reaction vessel, add 80-120 parts of modified polyphenylene ether resin and toluene / butanone solvent, and stir in a water bath at 58-62℃; add filler slurry, and simultaneously add 15-30 parts of vinyl-containing benzoxazine resin, 0.1-5 parts of diaryliodonium salt and 3-12 parts of toughening agent, and stir at 58-62℃ under nitrogen protection to obtain a glue solution; coat the glue solution onto a polyethylene terephthalate film that has undergone demolding treatment to obtain a coated wet film, and pass the coated wet film through three drying tunnels in sequence: the first tunnel at 68-72℃; the second tunnel at 98-102℃; and the third tunnel at 128-132℃.

[0009] In this invention, the overall preparation and curing mechanism of the low-thermal-shrinkage polymer film for laser drilling is a concentrated embodiment of the principles of interface engineering, cationic ring-opening polymerization, and synergistic reinforcement of multiphase composite materials. In the initial stage of adhesive formulation, the hydrolytic group at one end of the silane coupling agent molecule undergoes a condensation reaction with the hydroxyl groups on the surfaces of two inorganic nanofillers, forming a strong chemical bond. Simultaneously, the organic functional group at the other end aims to be compatible with the subsequent resin matrix, thereby constructing a strong and tough covalent bond interface bridge between the inorganic filler and the organic resin. This is crucial for effective stress transfer and prevention of interfacial delamination. The core curing and crosslinking reaction of the film is completed by a vinyl-containing benzoxazine resin under the action of a cationic initiator. The diaryliodonium salt initiator decomposes under heating conditions, generating cationic active species with strong Lewis acidity. These cations attack the oxygen atoms on the benzoxazine ring, initiating ring-opening polymerization of the oxazine ring. The Mannich bridge structure and phenolic hydroxyl groups generated after ring opening can not only continue to initiate the ring opening of other oxazine rings, causing the molecular chain to grow continuously, but also react with possible active sites on the modified polyphenylene ether resin segments, ultimately forming an interpenetrating network three-dimensional cross-linked structure with benzoxazine resin as the cross-linking node and polyphenylene ether resin as the backbone. This structure is dense and stable, giving the film high heat resistance. Throughout the process, surface-treated core-shell nanocrystals and one-dimensional nanowires are uniformly dispersed in the above resin network. At the moment of laser processing, the core-shell structure of the nanocrystals dissipates energy through the deformation of the shell and the propagation of microcracks, protecting the resin matrix; while the nanowires directly constrain the thermal deformation of the resin network through their own thermal behavior. The addition of toughening agents further enhances the composite material's resistance to laser shock and thermal stress by inducing mechanisms such as crazes and shear bands. Finally, through a three-step stepped heating process, the solvent is gradually and gently removed, allowing the resin system to be fully prepolymerized and cured, forming a high-performance composite film that integrates low thermal shrinkage, high heat resistance, and toughness.

[0010] According to a preferred embodiment of the present invention, in step S1, the ultrasonic dispersion time is 1-2 hours.

[0011] According to a preferred embodiment of the present invention, in step S2, the stirring time is 2-4 hours; the toughening agent is Qishi toughening agent.

[0012] According to a preferred embodiment of the present invention, the method for preparing the gadolinium lanthanum zirconate core-shell nanocrystals includes:

[0013] A1. Dissolve gadolinium nitrate, lanthanum nitrate and zirconium oxychloride in deionized water, and add dropwise to an ethanol solution containing PEG-PPO-PEG under stirring to obtain a precursor sol; transfer the precursor sol to a hydrothermal reactor, react at 195-205℃, centrifuge and wash to obtain nanocrystalline nuclei;

[0014] A2. The nanocrystal nuclei were redispersed in a mixed solution of ethanol and ammonia. Under ultrasonic dispersion, an ethanol solution of tetraethyl orthosilicate and yttrium nitrate was added dropwise. The reaction was continued at 28-32℃ to obtain the product. The product was centrifuged, washed with ethanol, and dried under vacuum at 78-82℃.

[0015] In this invention, the preparation of gadolinium lanthanum zirconate core-shell nanocrystals follows a stepwise construction mechanism combining hydrothermal synthesis and surface sol-gel modification. In the first stage, gadolinium nitrate, lanthanum nitrate, and zirconium oxychloride undergo hydrolysis in a mixed solvent of water and ethanol, interacting with a block copolymer template. Through the guiding effect of their hydrophilic and hydrophobic segments, precursor micelles of mixed metal hydroxides or basic salts are initially formed. In a closed, high-temperature, and high-pressure hydrothermal environment, these precursors undergo a vigorous dissolution and recrystallization process, with ions rearranging and overcoming the nucleation energy barrier, ultimately growing directionally into well-crystallized gadolinium lanthanum zirconate nanocrystals. Their crystal structure effectively accommodates and stabilizes gadolinium and lanthanum ions. In the second stage, the formed nanocrystals serve as seeds, dispersed in an alkaline ammonia solution. Their surface-active hydroxyl sites initiate the synergistic hydrolysis and condensation of tetraethyl orthosilicate and yttrium nitrate precursors. The silanol groups generated from the hydrolysis of tetraethyl orthosilicate and the yttrium ion hydrolysis products from yttrium nitrate undergo a co-condensation reaction on the surface of the nanocrystal nucleus. Through chemical bonding and physical adsorption, they are deposited layer by layer to form an amorphous silica shell doped with yttrium ions. This shell not only physically isolates the nanocrystal nucleus, preventing its aggregation in the polymer matrix, but more importantly, the incorporation of yttrium ions optimizes the thermal expansion behavior and interfacial energy of the shell, making it an effective stress buffer and thermal barrier layer under laser thermal shock, laying the structural foundation for the realization of the core function.

[0016] According to a preferred embodiment of the present invention, in step A1, the reaction time at 195-205°C is 24-30 h.

[0017] According to a preferred embodiment of the present invention, in step A2, the reaction is carried out at 28-32°C for 6-8 hours.

[0018] According to a preferred embodiment of the present invention, the method for preparing the lithium borosilicate aluminum nanowires includes:

[0019] B1. Tetraethyl silicate, aluminum isopropoxide, triethyl borate and lithium nitrate are added to a mixed solvent consisting of anhydrous ethanol, deionized water and nitric acid, and the mixture is stirred in a water bath at 58-62°C to obtain a sol.

[0020] B2. Add polyvinylpyrrolidone to the sol and continue stirring to obtain a precursor spinning solution. Load the precursor spinning solution into an electrospinning device for spinning to obtain nascent fibers. Heat the nascent fibers in air to 698-702℃ and keep them warm.

[0021] In this invention, the preparation mechanism of lithium aluminum borosilicate nanowires is based on the one-dimensional structure controllable growth principle combining sol-gel chemistry and electrospinning technology. Tetraethyl silicate, aluminum isopropoxide, triethyl borate, and lithium nitrate are mixed together under acidic catalytic conditions. The precursor molecules simultaneously undergo hydrolysis to generate corresponding silanol, aluminumol, boronol, and lithium ions. Subsequently, these active hydroxyl groups undergo intricate condensation reactions to form an inorganic polymer network mainly composed of silicon-oxygen-silicon bonds, silicon-oxygen-aluminum bonds, and boron-oxygen-silicon bonds. Lithium ions are embedded in the network interstices to balance the charge and regulate the network connectivity, ultimately yielding a uniform, stable lithium aluminum borosilicate sol with a certain degree of viscoelasticity. The addition of high molecular weight polyvinylpyrrolidone to this sol allows its long-chain molecules to intertwine with the inorganic sol network through intermolecular forces such as hydrogen bonds, greatly increasing the system's viscosity and spinnability. During electrospinning, under the influence of a high-voltage electrostatic field, the composite precursor droplets are stretched into charged jets. During flight, the solvent rapidly evaporates, the jets continuously refine and solidify, and finally, composite fibers containing inorganic components encapsulated by a polymer template are collected. Finally, through programmed temperature calcination, the polyvinylpyrrolidone template is completely decomposed and removed. The remaining inorganic network further condenses, densifies, and rearranges at high temperatures, crystallizing into one-dimensional lithium aluminum borosilicate nanowires with specific low or negative thermal expansion characteristics. These nanowires can physically intertwine within the resin matrix, directly counteracting the thermal motion of polymer chain segments with their unique thermal deformation behavior, thus achieving active control of the overall thermal expansion coefficient of the material at the molecular scale.

[0022] According to a preferred embodiment of the present invention, in step B1, the stirring reaction time in a water bath at 58-62°C is 48-50 hours.

[0023] According to a preferred embodiment of the present invention, in step B2, the time for holding the temperature at 698-702°C is 2-4 hours.

[0024] The present invention also provides a low heat shrinkage polymer film for laser drilling prepared according to the preparation method of the low heat shrinkage polymer film for laser drilling.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The most significant effect of this invention lies in the extremely low thermal shrinkage rate and excellent thermal stability of the adhesive film, which effectively suppresses the colloidal defects of the hole wall during laser drilling from the material source. By introducing uniquely designed gadolinium lanthanum zirconate core-shell nanocrystals and lithium aluminum borosilicate nanowires as composite fillers, and synergizing with the main matrix composed of modified polyphenylene ether resin and vinyl-containing benzoxazine resin, the overall thermal expansion coefficient of the adhesive film is significantly reduced. When subjected to the instantaneous high temperature impact of laser, the core-shell nanocrystal structure can effectively dissipate and buffer thermal stress, while the nanowires with special thermal expansion behavior can physically compensate for the shrinkage tendency of the matrix resin, thereby doubly suppressing the uneven deformation of the colloid. After laser processing, the degree of protrusion or indentation of the pore wall resin of the adhesive film prepared by this method can be strictly controlled within an extremely low μm range, which is significantly better than traditional adhesive film materials, providing a key material basis for achieving high-precision and high-reliability micropore interconnection.

[0027] (2) The technical effects of this invention benefit from its precise material design and preparation process, ensuring the full utilization of the functions of each component and the long-term stability of the system. The two inorganic modified compounds are not simply physical blends; their preparation method ensures the integrity of the nanocrystalline core-shell structure, the uniformity of the nanowire morphology, and its inherent functionality. Surface treatment with a silane coupling agent significantly enhances the interfacial bonding force between the inorganic filler and the organic polymer matrix, avoiding the risk of performance degradation or delamination due to weak interfaces. Simultaneously, the selection of vinyl-containing benzoxazine resin and a matching cationic initiator constitutes a highly efficient and stable curing system, enabling the film to fully cure in the subsequent stepped heating process, forming a dense, highly cross-linked three-dimensional network structure. This strong polymer network, combined with uniformly dispersed functional fillers, not only ensures low thermal shrinkage but also endows the film with higher glass transition temperature, modulus, and chemical resistance.

[0028] (3) The adhesive film prepared by this invention exhibits excellent comprehensive performance and wide process adaptability, and has important practical value. In addition to overcoming the major problem of adhesive shrinkage, the adhesive film also maintains excellent dielectric properties suitable for high-frequency and high-speed circuit applications, such as low dielectric constant and dielectric loss. It has good bonding strength with copper foil, ensuring the structural integrity of the multilayer board after lamination. From a process perspective, the preparation method has a clear process and controllable parameters. Except for special fillers, the raw materials used are all commercially available, which is convenient for large-scale production. The finished adhesive film is suitable for existing roll-to-roll coating, lamination and laser drilling production lines without the need to modify existing equipment. It provides a plug-and-play material solution for quality upgrades in the fields of high-end printed circuit boards and advanced packaging, and is of great significance for promoting the development of electronic components towards smaller, denser and more reliable directions. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing a low-heat-shrinkable polymer film for laser drilling, the steps of which include:

[0032] Preparation of gadolinium lanthanum zirconate core-shell nanocrystals: Step 1, preparation of nanocrystal nuclei. Accurately weigh 3.26 g of gadolinium nitrate hexahydrate, 3.25 g of lanthanum nitrate hexahydrate, and 6.44 g of zirconium oxychloride octahydrate, and dissolve them together in 50 mL of deionized water. Stir at 500 rpm using a magnetic stirrer until completely dissolved, forming a clear mixed salt solution A. In a separate 500 mL three-necked flask, add 200 mL of anhydrous ethanol and 2.00 g of PEG-PPO-PEG (average molecular weight ~5800), and stir in a 40 °C water bath until completely dissolved. While continuously stirring, slowly add solution A dropwise at a rate of 1 drop per second to the ethanol solution of the block copolymer using a constant pressure dropping funnel. After the addition is complete, continue stirring for 2 hours to obtain a homogeneous milky white precursor sol. Transfer this sol entirely to a 300 mL polytetrafluoroethylene-lined high-pressure hydrothermal reactor, seal it, and place it in a forced-air drying oven. The drying oven temperature was set to 200℃, and the reaction time was set to 26 h. After the reaction was completed, the reaction vessel was allowed to cool naturally to room temperature, and the white precipitate at the bottom of the vessel was collected. The precipitate, along with deionized water, was poured into a 50 mL centrifuge tube and centrifuged at 8000 rpm for 5 min. The supernatant was discarded, and the mixture was washed three times each with deionized water and anhydrous ethanol, centrifuged under the same conditions after each wash. The precipitate obtained from the last centrifugation was placed in a petri dish and preliminarily dried in an oven at 80℃ for 2 h to obtain the gadolinium lanthanum zirconate nanocrystal precursor.

[0033] The second step involves preparing the core-shell structure. All the nanocrystalline precursors obtained above were redispersed in a mixed solution containing 150 mL of anhydrous ethanol and 10 mL of a 25% (w / w) ammonia solution. The container was ultrasonically dispersed for 30 min in an ultrasonic cleaner (500 W, 40 kHz) to form a homogeneous suspension B. 12.50 g of tetraethyl orthosilicate and 1.13 g of yttrium nitrate hexahydrate were weighed and dissolved together in 50 mL of anhydrous ethanol, denoted as solution C. Under continuous ultrasonic dispersion and mechanical stirring (300 rpm), solution C was slowly injected into suspension B at a rate of 2 mL / min using a syringe pump. After the addition was complete, the mixture was transferred to a 30°C constant temperature water bath and stirred continuously for 7 h. After the reaction was complete, the product was collected by centrifugation at 8000 rpm for 5 min and washed three times with anhydrous ethanol. The resulting white solid was placed in a vacuum drying oven and dried at 80°C and -0.1 MPa for 12 hours. After grinding, gadolinium zirconate core-shell nanocrystals were obtained, denoted as GLZ-CS, for later use.

[0034] Preparation of lithium aluminum borosilicate nanowires: Step 1, preparation of the sol. In a dry 500mL round-bottom flask, 100mL of anhydrous ethanol, 20mL of deionized water, and 1.0mL of concentrated nitric acid (65% by mass) were added sequentially and mixed thoroughly. While stirring, 30.00g of tetraethyl silicate, 4.50g of aluminum isopropoxide, 3.00g of triethyl borate, and 1.20g of lithium nitrate were added sequentially. The flask was placed in a constant temperature water bath at 60℃, connected to a reflux condenser, and the reaction was continuously stirred at 400rpm for 49h. After the reaction was completed, a clear, homogeneous, and transparent sol D with a certain viscosity was obtained.

[0035] The second step is electrospinning and heat treatment. Add 4.00 g of polyvinylpyrrolidone (PVP, average molecular weight ~1,300,000) to the above sol D, and continue stirring in a 60°C water bath for 6 hours until the PVP is completely dissolved, obtaining a viscous, homogeneous precursor spinning solution. Load this spinning solution into a 10 mL plastic syringe and attach a 21G (0.51 mm inner diameter) flat-tipped stainless steel needle. Fix the syringe to the feed pump of the electrospinning machine, setting the feed rate to 0.5 mL / h. Use a metal plate covered with aluminum foil as a receiver, with a distance of 15 cm between it and the needle tip. Apply an 18 kV DC high voltage between the needle and the receiver. Spinning is carried out at room temperature and relative humidity below 40% for approximately 6 hours, collecting a layer of white nascent fiber membrane on the aluminum foil. Peel this fiber membrane off the aluminum foil, place it in an alumina crucible, and then place it in a box-type muffle furnace for heat treatment. Under air atmosphere, the temperature was increased from room temperature to 700℃ at a heating rate of 2℃ / min, and then calcined at 700℃ for 3 hours. After calcination, the furnace was allowed to cool naturally to room temperature, resulting in a white, fluffy aggregate of lithium aluminum borosilicate nanowires. After gentle grinding, well-dispersed nanowire powder was obtained, designated LABS-NW, for later use.

[0036] Preparation of a low-heat-shrinkage polymeric film for laser drilling: Step 1, preparation of filler slurry. Accurately weigh 10.00 g of the prepared GLZ-CS and LABS-NW, and mix them uniformly in a mortar. Weigh 1.00 g of γ-aminopropyltriethoxysilane and dissolve it in 20 mL of anhydrous ethanol to prepare a silane solution. Under stirring in a high-speed shear disperser (10000 rpm), slowly add the silane solution dropwise to the mixed inorganic filler. After the addition is complete, continue dispersion for 30 min to complete the filler surface modification. Transfer the surface-treated composite filler to a 500 mL glass mixing jar and add 200 g of a mixed solvent prepared from toluene and butanone in a 1:1 mass ratio. Seal the mixing jar and place it in an ultrasonic cell disruptor. Under ice-water bath cooling, ultrasonically disperse at 500 W for 1.5 h, pausing for 2 min every 10 min to prevent overheating, finally obtaining a uniform and stable filler slurry E.

[0037] The second step is to prepare the adhesive solution. In a 1L four-necked flask equipped with a mechanical stirrer, thermometer, condenser, and nitrogen inlet, add 100.00g of brominated end-group modified polyphenylene ether resin (intrinsic viscosity ~0.40 dL / g) and 300g of the aforementioned toluene / butanone mixed solvent. Place the flask in a 60°C constant-temperature water bath and stir at 200 rpm until the resin is completely dissolved, resulting in a clear, viscous resin solution. Under continuous stirring and nitrogen protection, slowly pour all of the filler slurry E prepared in the first step into the resin solution. Subsequently, add 20.00g of vinyl-containing benzoxazine resin, 1.00g of diaryliodonium hexafluorophosphate, and 6.00g of core-shell structured acrylate rubber particle toughening agent sequentially. After the addition is complete, increase the stirring speed to 1200 rpm and react vigorously at 60°C under a continuous nitrogen flow for 3 hours. After the reaction is complete, stop heating and let the adhesive solution stand for 1 hour to remove bubbles, resulting in a uniform, stable, and coatable adhesive solution F.

[0038] The third step is film formation and curing. Using a precision doctor blade coater, adhesive F is applied to a 125μm thick polyethylene terephthalate release film treated with a silicone release agent, controlling the wet film thickness to 500μm. The coated wet film is immediately fed into a three-zone continuous hot air drying tunnel oven for segmented curing. The first temperature zone is set at 70℃, and the conveyor belt speed is adjusted to allow the wet film to remain in this zone for 5 minutes to gently remove most of the solvent. The second temperature zone is set at 100℃ for 5 minutes to allow the resin system to undergo initial prepolymerization. The third temperature zone is set at 130℃ for 3 minutes to bring the film to a B-stage semi-cured state, exhibiting suitable adhesion and strength. The film is then wound up from the exit, yielding a finished low-heat-shrinkage polymer film with a thickness of approximately 50±3μm and a smooth, uniform surface.

[0039] Example 2

[0040] The difference between this embodiment and Example 1 lies in the preparation of gadolinium lanthanum zirconate core-shell nanocrystals: First, 1.63 g of gadolinium nitrate hexahydrate, 1.62 g of lanthanum nitrate hexahydrate, and 3.22 g of zirconium oxychloride octahydrate were weighed and dissolved in 30 mL of deionized water to obtain solution A. Solution A was added dropwise to 100 mL of anhydrous ethanol containing 1.00 g of block copolymer, and the mixture was stirred to form a sol. This sol was placed in a hydrothermal reactor at 200 °C and reacted for 24 h. The reaction product was centrifuged, washed with water, and washed with alcohol to obtain the crystal nucleus precursor. Second, the crystal nucleus precursor was dispersed in a mixture of 100 mL of ethanol and 7 mL of ammonia. Solution C, consisting of 6.25 g of tetraethyl orthosilicate and 0.56 g of yttrium nitrate hexahydrate dissolved in 25 mL of ethanol, was added dropwise to the above suspension, and the mixture was continuously stirred at 28 °C for 6 h. The product was centrifuged, washed with alcohol, and then dried under vacuum at 80°C for 12 hours to obtain GLZ-CS.

[0041] Preparation of lithium borosilicate aluminum nanowires: First, 25.00 g tetraethyl silicate, 3.00 g aluminum isopropoxide, 2.50 g triethyl borate, and 0.80 g lithium nitrate were added to a solvent consisting of 80 mL ethanol, 15 mL water, and 0.8 mL nitric acid. The mixture was stirred in a water bath at 58 °C for 48 h to obtain sol D. Second, 3.00 g polyvinylpyrrolidone was added to sol D and stirred to dissolve, obtaining a spinning solution. Electrospinning was performed (voltage 18 kV, distance 15 cm, feed rate 0.4 mL / h). The collected nascent fibers were placed in a muffle furnace and heated to 698 °C at a rate of 1.5 °C / min, held for 2 h, and cooled to obtain LABS-NW.

[0042] Film Preparation: 5.00g of GLZ-CS and 5.00g of LABS-NW were mixed and surface-treated with 10mL of ethanol solution containing 0.50g of γ-aminopropyltriethoxysilane. The treated filler was dispersed in 150g of toluene / butanone (1:1) solvent and sonicated for 1h to obtain slurry E. 80.00g of modified polyphenylene ether resin and 200g of mixed solvent were added to a reactor and dissolved at 58℃. Slurry E, 15.00g of vinylbenzoxazine resin, 0.50g of diaryliodonium salt, and 3.00g of acrylate toughening agent were added, and the mixture was stirred at 1000rpm for 2h at 58℃ under nitrogen protection to obtain adhesive solution F. After coating, the wet film was cured sequentially through three drying tunnels at 68℃ / 5min, 98℃ / 5min, and 128℃ / 3min to obtain the film.

[0043] Example 3

[0044] The difference between this embodiment and Example 1 lies in the preparation of gadolinium lanthanum zirconate core-shell nanocrystals: First, 4.89 g of gadolinium nitrate hexahydrate, 4.87 g of lanthanum nitrate hexahydrate, and 9.66 g of zirconium oxychloride octahydrate were weighed and dissolved in 70 mL of deionized water to obtain solution A. Solution A was added dropwise to 300 mL of anhydrous ethanol solution containing 3.00 g of block copolymer, and the mixture was stirred to form a sol. This sol was placed in a hydrothermal reactor at 205 °C and reacted for 30 h. The reaction product was centrifuged, washed with water, and washed with alcohol to obtain the crystal nucleus precursor. Second, the crystal nucleus precursor was dispersed in a mixture of 200 mL of ethanol and 13 mL of ammonia. Solution C, consisting of 18.75 g of tetraethyl orthosilicate and 1.70 g of yttrium nitrate hexahydrate dissolved in 75 mL of ethanol, was added dropwise to the above suspension, and the mixture was continuously stirred at 32 °C for 8 h. The product was centrifuged, washed with alcohol, and then dried under vacuum at 80°C for 12 hours to obtain GLZ-CS.

[0045] Preparation of lithium borosilicate aluminum nanowires: First, 35.00 g of tetraethyl silicate, 6.00 g of aluminum isopropoxide, 4.00 g of triethyl borate, and 1.50 g of lithium nitrate were added to a solvent consisting of 120 mL of ethanol, 25 mL of water, and 1.2 mL of nitric acid. The mixture was stirred in a water bath at 62 °C for 50 h to obtain sol D. Second, 5.00 g of polyvinylpyrrolidone was added to sol D and stirred to dissolve, obtaining a spinning solution. Electrospinning was performed (voltage 18 kV, distance 15 cm, feed rate 0.6 mL / h). The collected nascent fibers were placed in a muffle furnace and heated to 702 °C at a rate of 2.5 °C / min, held at this temperature for 4 h, and then cooled to obtain LABS-NW.

[0046] Film Preparation: 15.00g of GLZ-CS and 15.00g of LABS-NW were mixed and surface-treated with a 30mL ethanol solution of 3.00g of γ-aminopropyltriethoxysilane. The treated filler was dispersed in 300g of toluene / butanone (1:1) solvent and sonicated for 2h to obtain slurry E. 120.00g of modified polyphenylene ether resin and 400g of mixed solvent were added to a reactor and dissolved at 62℃. Slurry E, 30.00g of vinylbenzoxazine resin, 2.00g of diaryliodonium salt, and 10.00g of acrylate toughening agent were added, and the mixture was stirred at 1500rpm for 4h at 62℃ under nitrogen protection to obtain adhesive solution F. After coating, the wet film was cured sequentially through three drying tunnels at 72℃ / 5min, 102℃ / 5min, and 132℃ / 3min to obtain the film.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that the film formulation of this comparative example completely excludes gadolinium lanthanum zirconate core-shell nanocrystals, lithium aluminum borosilicate nanowires, and toughening agents. The preparation steps are as follows: 100.00 g of modified polyphenylene ether resin and 300 g of toluene / butanone mixed solvent were directly added to a reactor and stirred at 60°C to dissolve. Subsequently, only 20.00 g of vinyl-containing benzoxazine resin and 1.00 g of diaryliodonium salt were added. The mixture was stirred for 3 hours at the same temperature, under nitrogen protection, and at 1200 rpm to obtain the adhesive solution. This adhesive solution was then used to prepare a comparative film through the same coating and drying / curing processes as Example 1 (70°C / 5 min, 100°C / 5 min, 130°C / 3 min).

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 1 is that the film formulation in this comparative example only contains gadolinium lanthanum zirconate core-shell nanocrystals and does not contain lithium aluminum borosilicate nanowires. The preparation steps are as follows: 10.00 g of GLZ-CS was surface-treated with a 20 mL ethanol solution of 1.00 g of γ-aminopropyltriethoxysilane. The treated filler was dispersed in 200 g of mixed solvent and sonicated for 1.5 h to obtain a slurry. 100.00 g of modified polyphenylene ether resin and 300 g of solvent were added to a reaction vessel and dissolved at 60 °C. This slurry, 20.00 g of vinylbenzoxazine resin, 1.00 g of diaryliodonium salt, and 6.00 g of toughening agent were added, and the mixture was stirred under the same conditions (60 °C, N2, 1200 rpm, 3 h) to obtain a gel solution. A comparative film was prepared using the same coating and drying process as in Example 1.

[0051] Comparative Example 3

[0052] The difference between this comparative example and Example 1 is that the key process temperature for film curing was changed. The types and amounts of raw materials used in the film preparation were exactly the same as in Example 1, but in the final three-stage drying and curing process, the curing temperature of the third temperature zone was adjusted to 110°C, while the temperatures of the first and second temperature zones (70°C and 100°C) and the residence time in each zone (5 min) remained unchanged, ultimately yielding the comparative film.

[0053] In accordance with national and industry standard testing specifications, all performance tests were conducted in a standard laboratory environment with a temperature of 23±2℃ and a relative humidity of 50±5%. The film samples used for testing were prepared according to the methods described in Examples 1-3 and Comparative Examples 1-3, and were used after curing for 24 hours.

[0054] Heat shrinkage rate test: Square specimens measuring 100.0 mm × 100.0 mm were cut from each sample and placed on a clean glass plate. Measurement points were marked at the four corners and center of the specimen using a precision image measuring instrument. The specimens were then placed in a preheated 250°C drying oven and statically heated for 5 minutes to simulate the localized thermal shock process of laser drilling. After removing the specimens and cooling to room temperature, the distance between each marked point was measured again. The longitudinal and transverse dimensional changes were calculated, and the arithmetic mean of the five points was taken as the heat shrinkage rate of the sample. The calculation formula is: [(initial length - length after heating) / initial length] × 100%.

[0055] Laser drilling morphology testing: Each adhesive film was laminated with an 18μm thick low-profile copper foil in a vacuum press at 210℃ and 3.0MPa for 90 minutes to create a laminate test sample. A row of 100μm diameter blind holes was machined on the test sample using a UV laser drilling machine (wavelength 355nm) under fixed parameters (single pulse energy 0.8mJ, pulse frequency 30kHz, spot overlap rate 85%). The hole wall morphology was observed using a field emission scanning electron microscope at 5000x magnification. Using the accompanying measurement software, 20 holes were randomly selected, and the maximum protrusion height and maximum indentation depth of the resin wall relative to the copper ring were measured. The average values ​​were calculated as "hole wall adhesive protrusion amount" and "hole wall adhesive indentation amount".

[0056] Thermomechanical property testing: Using a thermomechanical analyzer and referring to standard methods, a strip of film about 10 mm long was taken and heated from 30°C to 300°C at a heating rate of 5°C / min under a nitrogen atmosphere. The dimensional changes before and after the glass transition temperature range were measured. The average linear thermal expansion coefficient in the temperature range of 50-150°C and the glass transition temperature obtained by the tangent method were calculated respectively.

[0057] Peel strength test: According to relevant standards, after the adhesive film and copper foil are pressed together, they are cut into strips 25mm wide. A universal testing machine is used to perform a 90° peel test at a peel speed of 50mm / min. The stable average peel force is recorded and the peel strength is calculated.

[0058] The performance test data above are shown in Table 1.

[0059] Table 1 Performance Test Results

[0060]

[0061] The test results in Table 1 above clearly show that the technical solutions of the present invention represented by Examples 1 to 3, compared with Comparative Examples 1 to 3, effectively solve the core technical problem of severe deformation of the hole wall caused by thermal shrinkage of polymer film in laser drilling.

[0062] The deformation of the pore wall colloid in all embodiments (protrusion between +8.5 and +10.1 μm, and indentation between -6.2 and -7.8 μm) was strictly controlled within the target value of 15 μm, while the deformation of Comparative Example 1 (protrusion +35.6 μm, indentation -28.4 μm) far exceeded this standard. This directly proves that the present invention can reduce the deformation of the pore wall by about 70% to 80%, fundamentally ensuring the geometric integrity of the pore wall.

[0063] Comparative Example 1, as a base resin control, exhibits a high thermal shrinkage rate of 0.85% and a coefficient of thermal expansion of 52 ppm / ℃, which contrasts sharply with the 0.12% and 18 ppm / ℃ of Example 1. This conclusively demonstrates that the material itself is completely unable to withstand laser thermal shock without the introduction of the two specific inorganic modifying compounds of the present invention.

[0064] While the data from Comparative Example 2 (heat shrinkage rate 0.31%, protrusion +18.7 μm) were better than Comparative Example 1, they were still significantly worse than Example 1. This reveals the limitations of a single filler function and confirms that gadolinium lanthanum zirconate core-shell nanocrystals (focusing on energy dissipation and stress buffering) and lithium aluminum borosilicate nanowires (focusing on thermal expansion compensation) must work synergistically to achieve an extremely low heat shrinkage rate of 0.12% and pore wall control at the 10 μm level; neither can be dispensed with. The results of Comparative Example 3 (heat shrinkage rate 0.40%, glass transition temperature only 176°C) show that even if the composition is correct, a curing process (the third stage temperature is reduced to 110°C) deviating from the settings of this invention (130°C) will lead to insufficient cross-linking network, causing the glass transition temperature to drop by more than 20°C and triggering a comprehensive degradation of thermal stability and deformation resistance. This, in turn, proves the necessity of complete process parameters for locking in the final performance.

[0065] In summary, this invention, through a systematic approach of using a specific ratio of composite functional fillers and a precisely matched step curing process, achieves a comprehensive effect of reducing thermal shrinkage by more than 80%, reducing hole wall deformation by more than 70%, reducing the coefficient of thermal expansion by more than 60%, and increasing the glass transition temperature by about 10°C, thus completely overcoming the shrinkage bottleneck in high-precision laser drilling.

Claims

1. A method for preparing a low-heat-shrinkage polymeric film for laser drilling, characterized in that the steps include... include: S1. By weight, 0.5-3 parts of γ-aminopropyltriethoxysilane are dissolved in ethanol, and then added to a mixed powder of 5-15 parts of gadolinium lanthanum zirconate core-shell nanocrystals and 5-15 parts of lithium aluminum borosilicate nanowires, wherein the gadolinium lanthanum zirconate core-shell nanocrystals have gadolinium lanthanum zirconate as the core and yttrium-doped silicon dioxide as the shell; a surface-treated composite filler is obtained, and the surface-treated composite filler is added to a mixing tank of a mixed solvent of toluene and butanone, and ultrasonically dispersed to obtain a filler slurry; S2. In a reaction vessel, add 80-120 parts of modified polyphenylene ether resin and a mixed solvent of toluene and methyl ethyl ketone, and stir in a water bath at 58-62℃; add filler slurry, and simultaneously add 15-30 parts of vinyl-containing benzoxazine resin, 0.1-5 parts of diaryl iodine salt and 3-12 parts of toughening agent, and stir at 58-62℃ under nitrogen protection to obtain a glue solution; coat the glue solution onto a polyethylene terephthalate film that has undergone demolding treatment to obtain a coated wet film; pass the coated wet film through three drying tunnels in sequence: the first tunnel at 68-72℃; The second section is 98-102℃; the third section is 128-132℃. The preparation method of the gadolinium lanthanum zirconate core-shell nanocrystals includes: A1. Dissolve gadolinium nitrate, lanthanum nitrate and zirconium oxychloride in deionized water, and add dropwise to an ethanol solution containing PEG-PPO-PEG under stirring to obtain a precursor sol; transfer the precursor sol to a hydrothermal reactor, react at 195-205℃, centrifuge and wash to obtain nanocrystalline nuclei; A2. The nanocrystal nuclei were redispersed in a mixed solution of ethanol and ammonia. Under ultrasonic dispersion, an ethanol solution of tetraethyl orthosilicate and yttrium nitrate was added dropwise. The reaction was continued at 28-32℃ to obtain the product. The product was centrifuged, washed with ethanol, and dried under vacuum at 78-82℃. The method for preparing the lithium borosilicate aluminum nanowires includes: B1. Tetraethyl silicate, aluminum isopropoxide, triethyl borate and lithium nitrate are added to a mixed solvent consisting of anhydrous ethanol, deionized water and nitric acid, and the mixture is stirred in a water bath at 58-62°C to obtain a sol. B2. Add polyvinylpyrrolidone to the sol and continue stirring to obtain a precursor spinning solution. Load the precursor spinning solution into an electrospinning device for spinning to obtain nascent fibers. Heat the nascent fibers in air to 698-702℃ and keep them warm. The toughening agent is a core-shell structured acrylate rubber particle toughening agent or an acrylate toughening agent.

2. The method for preparing a low-thermal shrinkage polymer adhesive film for laser drilling according to claim 1, characterized in that, In step S1, the ultrasonic dispersion time is 1-2 hours.

3. The method for preparing a low-heat-shrinkage polymeric film for laser drilling according to claim 1, characterized in that, In step S2, the stirring time is 2-4 hours under nitrogen protection at 58-62℃.

4. The method for preparing a low-heat-shrinkage polymeric film for laser drilling according to claim 1, characterized in that, In step A1, the reaction time is 24-30 h at 195-205℃.

5. The method for preparing a low-heat-shrinkage polymeric film for laser drilling according to claim 1, characterized in that, In step A2, the reaction is carried out at 28-32℃ for 6-8 hours.

6. The method for preparing a low-heat-shrinkage polymeric film for laser drilling according to claim 1, characterized in that, In step B1, the reaction is carried out in a water bath at 58-62℃ for 48-50 hours with stirring.

7. The method for preparing a low-heat-shrinkage polymeric film for laser drilling according to claim 1, characterized in that, In step B2, the temperature is raised to 698-702℃ and held for 2-4 hours.

8. A low-heat-shrinkage polymeric film for laser drilling, characterized in that, The low-heat-shrinkable polymeric film for laser drilling is prepared according to any one of claims 1-7 by the method described in the invention.

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