A method for preparing a high-performance cold-peelable conductive copper film

Abstract

The application discloses a preparation method of a high-performance conductive copper film which can be cold-stripped. The conductive copper film is prepared from a glass-powder-free copper paste. Micro and nano copper powders, an organic carrier of mixed acrylic resin and diethylene glycol butyl ether acetate, an antioxidant and a leveling agent are rapidly stirred to form a copper paste precursor. The gap of the feeding port and the discharging port is reduced in stages, and the copper paste is rolled for several times to obtain a uniform copper paste. Then, the copper paste is sintered at high temperature by using an aluminum oxide substrate and by passing nitrogen gas to form a copper film. The copper film is cold-stripped and transferred to an arbitrary flexible substrate by using a pressure-sensitive adhesive tape. The cold-stripped copper film is fixed on the substrate by using acrylic resin, and the copper film is isolated from oxidation by using a double-layered polydimethylsiloxane film to form a low-square-resistance flexible copper film. The application realizes reliable integration of the high-conductivity flexible copper film on an arbitrary flexible substrate by optimizing the material formula and innovating the process, and solves the problems of oxidation inhibition and mechanical durability.

Description

Technical Field

[0001] This invention relates to the field of electronic paste technology, and in particular to a method for preparing a high-performance conductive copper film that can be cold-peeled. Background Technology

[0002] The manufacturing of flexible electronic devices currently faces two major challenges: First, the choice of substrate materials is limited: traditional flexible substrates (such as PET and PI) are prone to thermal deformation during high-temperature processes, leading to printed circuit failure; while rigid substrates, although able to withstand high-temperature sintering, cannot be directly used in flexible applications. Second, there are bottlenecks in conductive film transfer technology: existing transfer methods generally suffer from the following defects: Wet transfer printing relies on chemical etching and stripping, which can easily damage the conductive layer and makes it difficult to achieve large-area, high-precision patterning (e.g., line width <50μm). Heat release transfer printing: requires precise control of the temperature gradient, and the process is complex and energy-intensive. Laser-assisted transfer printing: The equipment is expensive and difficult to apply on a large scale; Dynamically controlled transfer printing: requires strict control of interfacial adhesion and has a low yield rate.

[0003] The aforementioned problems make it difficult for existing transfer printing processes to balance conductivity, mechanical flexibility, and manufacturing costs, necessitating the development of an efficient and low-cost alternative. Summary of the Invention

[0004] To address the aforementioned shortcomings, this invention proposes a method for preparing a high-performance conductive copper film that can be cold-peeled. Through material formulation optimization and process innovation, it achieves reliable integration of a highly conductive flexible copper film on any flexible substrate, while simultaneously solving the problems of oxidation inhibition and mechanical durability.

[0005] This invention provides the following technical solution: a method for preparing a cold-peelable high-performance conductive copper film, wherein the conductive copper film is prepared from a glass-free copper paste, and the components of the glass-free copper paste, by mass percentage, include 40-61 wt% micron-sized copper powder, 25-30 wt% nano-sized copper powder, 10-20 wt% acrylic resin, 3-8 wt% diethylene glycol butyl ether acetate, 0.5-1 wt% antioxidant, and 0.5-1 wt% leveling agent. The copper film preparation includes the following steps: S1: Micron-sized and nano-sized copper powders are mixed using a planetary mixer to form a uniform dry powder mixture of micron-sized and nano-sized powders; S2: Add acrylic resin and diethylene glycol butyl ether acetate to a beaker in a mass ratio and heat in a constant temperature water bath while stirring until completely dissolved. Then cool to room temperature to prepare the organic carrier. S3: Place the mixed dry powder, organic carrier, antioxidant and leveling agent in a mixer and stir rapidly to form a copper paste precursor; S4: A three-roll mill is used to reduce the gap between the feed inlet and the outlet of the copper paste precursor in stages and roll it several times at the same speed to obtain a uniform printing copper paste. The printing copper paste is then sintered at high temperature using an alumina substrate and nitrogen gas to form a copper film, thereby achieving the densification of copper particles and the formation of a conductive network. S5: The copper film is cold-peeled and transferred to any flexible substrate using pressure-sensitive adhesive tape. The cold-peeled copper film is fixed on the substrate using acrylic resin. At the same time, a double layer of polydimethylsiloxane with a thickness of 90-110μm is used as an encapsulation film to isolate and oxidize the copper film, so as to form a low sheet resistance flexible copper film with a sheet resistance of 6.3-12.5mΩ / □.

[0006] As an improvement, both the micron-sized and nano-sized copper powder particles conform to a normal distribution. The D50 particle size of the micron-sized copper powder is 0.5-1.5 μm, and the D50 particle size of the nano-sized copper powder is 130-170 nm.

[0007] As an improvement, the stirring speed in step S1 is 1800-2200 rpm and the stirring time is 10-20 min.

[0008] As an improvement, the water bath heating temperature in step S2 is 60-70℃, and the stirring speed is 250-350r / min.

[0009] As an improvement, the stirring speed in step S3 is 1000-3000 rpm and the stirring time is 30-90 s.

[0010] As an improvement, the rolling process in step S4 specifically includes the following steps: S4.1: Under the conditions of feed inlet gap of 150-180 μm, discharge outlet gap of 75-90 μm and rotation speed of 100-150 r / min, the intermediate roll is rolled 3-8 times; S4.2: Adjust the feed inlet gap to 100-130μm, the discharge outlet gap to 50-65μm, and roll at the same speed 3-8 times; S4.3: Adjust the feed inlet gap to 50-80μm, the discharge outlet gap to 25-40μm, and roll at the same speed of 100-150 for 6-14 times to obtain the desired printing copper paste.

[0011] As an improvement, the antioxidant in step S4 is a benzotriazole compound.

[0012] As an improvement, the leveling agent in step S4 is a polyether-modified siloxane.

[0013] As an improvement, the preparation of the low sheet resistance copper film in step S4 specifically includes the following steps: S4.4: Copper paste is screen-printed onto an alumina substrate to form a preset circuit pattern, with a printing thickness of 10-20μm; S4.5: Place the printed alumina substrate in an oven and preheat at 80-100℃ for 5-15 minutes to remove the solvent and pre-cure the paste; S4.6: Transfer the sample to a tube furnace, introduce nitrogen gas at a flow rate of 450-550 sccm, heat to 600-700℃ at a rate of 8-12℃ / min, and hold for 20-40 minutes to achieve densification of copper particles and formation of a conductive network.

[0014] As an improvement, after sintering in step S5, the copper film is naturally cooled to room temperature to form a copper film. The copper film and the substrate are only in physical contact and naturally separate after cooling. The peeling force is ≤0.1 N / cm to achieve non-destructive cold peeling, obtain a flexible copper film, and then use pressure-sensitive adhesive tape to achieve cold peeling and transfer of the copper film to any flexible substrate.

[0015] Compared with the prior art, the advantages of the present invention are as follows: Traditional copper paste relies on glass powder for substrate bonding, but this solution abandons the glass powder binder and adopts a glass powder-free formulation, namely an acrylic resin + organic solvent system. Micron-sized copper powder is used as the main conductive phase, while nano-sized copper powder fills the pores, increasing the internal conductive pathways of the film and reducing the sheet resistance. Acrylic resin is used as the organic carrier resin, and the interaction forces within the resin form a cross-linked network structure in the paste, giving it printability. Antioxidants and leveling agents prevent agglomeration between copper particles and reduce the surface tension of the paste, extending its storage time and reducing printing defects. This invention, through a three-in-one technological innovation of "formulation-process-encapsulation," enables the copper film and alumina substrate to form only a weak physical bond. Upon cooling after sintering, the peel force between the copper film and the alumina substrate is ≤0.1 N / cm, allowing them to separate naturally. The mechanical peel success rate is >99%, thus achieving non-destructive cold peel transfer to any flexible substrate such as PET / PI / TPU, avoiding the damage and cost caused by laser or chemical etching. Nitrogen gas with a flow rate of 450-550 sccm is introduced during the high-temperature sintering stage at 600-700℃ to effectively inhibit the oxidation of copper particles and ensure the integrity of the conductive network. This results in an initial sheet resistance of the copper film as low as 6.3 mΩ / □. Combined with a 90-110μm thick polydimethylsiloxane film double-layer encapsulation of the copper film, environmental oxidation is isolated. Under environmental conditions of 85℃ / 85%RH, the sheet resistance of the encapsulated copper film only increases to 12.5 mΩ / □ after 5 days, while the sheet resistance of the unencapsulated copper film soars to 38.1 Ω / □ after 5 days, with a significant risk of failure. Furthermore, after 1000 bends, the radius of curvature of the transferred copper film is 1.5 cm, and the sheet resistance remains stable at ≤20 mΩ / □, meeting the dynamic usage requirements of wearable devices. Meanwhile, by directly utilizing the high-temperature resistance of the alumina substrate, there is no need for laser sintering equipment. Combined with the three-roll mill staged rolling process, the feed port gap is gradually compressed from 150-180 μm to 50-80 μm, and the discharge port gap is gradually compressed from 75-90 μm to 25-40 μm. Each stage is repeatedly rolled to ensure the uniformity of the slurry and significantly reduce equipment investment. Attached Figure Description

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 A comparison chart of packaged and unpackaged sheet resistance under dual 85 conditions; Figure 2 The graph shows the results of the bending cycle stability test. Detailed Implementation

[0017] Example like Figures 1 to 2As shown, a method for preparing a cold-peelable high-performance conductive copper film is described. The conductive copper film is prepared from a glass-free copper paste. The glass-free copper paste comprises, by mass percentage, 55 wt% micron-sized copper powder, 28 wt% nano-sized copper powder, 14 wt% acrylic resin, 5 wt% diethylene glycol butyl ether acetate, 0.8 wt% benzotriazole compounds, and 0.7 wt% polyether-modified siloxane. The particle sizes of both the micron-sized and nano-sized copper powders conform to a normal distribution. The D50 particle size of the micron-sized copper powder is 1 μm, and the D50 particle size of the nano-sized copper powder is 150 nm. The copper film preparation includes the following steps: S1: Dry mix micron-sized and nano-sized copper powders at 2000 rpm for 15 minutes using a planetary mixer to form a uniform dry powder mixture of micron-sized and nano-sized powders; S2: Acrylic resin and diethylene glycol butyl ether acetate are placed in a beaker at a mass ratio and heated in a constant temperature water bath at 65°C while stirring at 300 r / min until completely dissolved. Then, the mixture is cooled to room temperature to prepare the organic carrier. S3: Place the mixed dry powder, organic carrier, benzotriazole compound and polyether modified siloxane in a mixer and stir rapidly at 2000 rpm for 60 seconds to form a uniform copper paste precursor; S4.1: Five passes of intermediate roll rolling with a feed inlet gap of 160μm, a discharge outlet gap of 80μm, and a rotation speed of 120 r / min; S4.2: Adjust the feed inlet gap to 120μm, the discharge outlet gap to 60μm, and roll at the same speed 5 times; S4.3: Adjust the feed inlet gap to 60μm, the discharge outlet gap to 30μm, and roll at the same speed 10 times to obtain the desired printing copper paste; S4.4: Copper paste is screen-printed onto an alumina substrate using a 300-mesh screen to form a preset circuit pattern, with a printing thickness of 15 μm; S4.5: Place the printed alumina substrate in an oven and preheat at 90°C for 10 minutes to remove the solvent and pre-cure the paste; S4.6: Transfer the sample to a tube furnace, introduce nitrogen gas at a flow rate of 500 sccm, heat to 650℃ at a rate of 10℃ / min, and hold for 3 minutes to achieve densification of copper particles and formation of a conductive network.

[0018] S5.1: After sintering, the copper film is naturally cooled to room temperature to form a copper film. The copper film and the substrate are only in physical contact. After cooling, they are naturally separated with a peeling force of ≤0.1 N / cm to achieve non-destructive cold peeling and obtain a flexible copper film. The copper film is then cold peeled and transferred to any flexible substrate through pressure-sensitive adhesive tape. S5.2: The cold-peeled copper film is fixed on the substrate using acrylic resin, while a double layer of 100μm thick polydimethylsiloxane is used as an encapsulation film to isolate the copper film from oxidation, so as to form a low sheet resistance flexible copper film with an initial sheet resistance of 6.3mΩ / □.

[0019] Comparative Example The copper paste containing glass powder comprises, by mass percentage, 10 wt% glass powder with a softening point of 550℃, 50 wt% micron-sized copper powder, 25 wt% nano-sized copper powder, 12 wt% ethyl cellulose, 5 wt% terpineol, 0.8 wt% phosphate ester compounds, and 0.7 wt% fluorocarbon compounds. The copper film preparation includes the following steps: S1: Micron-sized and nano-sized copper powder and glass powder are dry-mixed for 15 minutes at 2000 rpm using a planetary mixer to form a uniform dry powder mixture of glass powder, micron-sized and nano-sized powder. S2: Ethyl cellulose and terpineol are placed in a beaker in a mass ratio and heated in a constant temperature water bath at 65°C while stirring at 300r / min until they are completely dissolved. Then, the mixture is cooled to room temperature to prepare the organic carrier. S3: Place the mixed dry powder, organic carrier, phosphate ester compound and fluorocarbon compound in a mixer and stir rapidly at 2000 rpm for 60 seconds to form a uniform copper paste precursor; S4.1: Five passes of intermediate roll rolling with a feed inlet gap of 160μm, a discharge outlet gap of 80μm, and a rotation speed of 120 r / min; S4.2: Adjust the feed inlet gap to 120μm, the discharge outlet gap to 60μm, and roll at the same speed 5 times; S4.3: Adjust the feed inlet gap to 60μm, the discharge outlet gap to 30μm, and roll at the same speed 10 times to obtain the desired printing copper paste; S4.4: Copper paste is screen-printed onto an alumina ceramic hard substrate using a 300-mesh screen to form a preset circuit pattern, with a printing thickness of 15 μm; S4.5: Place the printed alumina ceramic hard substrate in an oven and preheat it at 90°C for 10 minutes to remove the solvent and pre-cure the paste; S4.6: Transfer the sample to a tube furnace, introduce nitrogen gas at a flow rate of 500 sccm, heat to 650℃ at a rate of 10℃ / min, and hold for 3 minutes to achieve densification of copper particles and formation of a conductive network.

[0020] S5.1: After sintering, the copper film is naturally cooled to room temperature to form a strong bond between the copper film and the substrate. Its peel force is ≥5 N / cm, which makes cold peeling impossible and also limits the substrate. If printed on a PI flexible substrate, sintering at 650℃ will cause the PI to carbonize and decompose, and the glass powder has no adhesion to the PI.

[0021] Table 1. Detailed Sheet Resistance Data for Packaged and Unpackaged Units under Dual 85 Conditions Table 2 Comparison of core differences between the embodiments As shown in Tables 1 and 2, under dual 85 conditions, the initial sheet resistance of the packaged and unpackaged copper films was similar. Within 6 hours, the sheet resistance of the unpackaged copper film increased by 172 times, accelerating oxidation failure. The sheet resistance of the packaged copper film increased only from 6.3 mΩ / □ to 12.50 mΩ / □ after 5 days, while the sheet resistance of the unpackaged copper film increased from 6.1 to 38100 after 5 days, an increase of 620,000 times. The dual-layer PDMS packaging made the sheet resistance increase of the copper film under high temperature and high humidity environment controllable (only increased to 12.5 mΩ / □ after 120 hours), meeting the long-term stability requirements. The increase after 5 days was small, while the unpackaged copper film completely failed, with a sheet resistance >38 kΩ / □, confirming the rapid oxidation problem of the copper film in the exposed environment.

[0022] The glass-powder-free formula allows the copper film to bond to the alumina substrate solely through physical adsorption, with a peel force ≤0.1 N / cm (far lower than ≥5 N / cm for glass-powder-containing films), achieving "natural separation upon cooling." Pressure-sensitive adhesive tape transfer technology replaces laser / chemical etching, reducing costs and avoiding damage.

[0023] Copper paste containing glass powder is limited by high-temperature sintering (650°C) and cannot be used on flexible substrates such as PET / PI (it will carbonize and decompose). This invention achieves reliable integration of copper film on any flexible substrate by using a low-temperature organic carrier and an alumina substrate for temporary loading.

[0024] The above description only illustrates the preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All modifications made within the scope of the independent claims of this invention are also within the scope of protection of this invention.

Claims

1. A method for preparing a cold strippable high performance conductive copper film, characterized by: The conductive copper film is prepared from a glass-free copper paste. The glass-free copper paste comprises, by mass percentage, 40-61 wt% micron-sized copper powder, 25-30 wt% nano-sized copper powder, 10-20 wt% acrylic resin, 3-8 wt% diethylene glycol butyl ether acetate, 0.5-1 wt% antioxidant, and 0.5-1 wt% leveling agent. The preparation method includes the following steps: S1: Micron-sized and nano-sized copper powders are mixed using a planetary mixer to form a uniform dry powder mixture of micron-sized and nano-sized powders; S2: Place acrylic resin and diethylene glycol butyl ether acetate in a beaker according to the mass ratio and heat in a constant temperature water bath while stirring until they are completely dissolved. Then cool to room temperature to prepare the organic carrier. S3: Place the mixed dry powder, organic carrier, antioxidant and leveling agent in a mixer and stir rapidly to form a copper paste precursor; S4: The copper paste precursor is rolled several times at the same speed by reducing the gap between the feed port and the discharge port in stages using a three-roll mill to obtain a uniform printing copper paste. The printing copper paste is then sintered at high temperature using an alumina substrate and nitrogen gas to form a copper film, thereby achieving the densification of copper particles and the formation of a conductive network. S5: The copper film is cold-peeled and transferred to any flexible substrate using pressure-sensitive adhesive tape, and the cold-peeled copper film is fixed on the flexible substrate using acrylic resin. At the same time, a double layer of polydimethylsiloxane with a thickness of 90-110μm is used as an encapsulation film to isolate the copper film from oxidation, so as to form a low sheet resistance flexible copper film with a sheet resistance of 6.3-12.5mΩ / □. The preparation of the copper film in step S4 specifically includes the following steps: S4.4: Copper paste is screen-printed onto an alumina substrate to form a preset circuit pattern, with a printing thickness of 10-20 μm; S4.5: Place the printed alumina substrate in an oven and preheat at 80-100℃ for 5-15 minutes to remove the solvent and pre-cure the paste to obtain the sample; S4.6: Transfer the sample to a tube furnace, introduce nitrogen gas at a flow rate of 450-550 sccm, heat to 600-700℃ at a rate of 8-12℃ / min, and hold for 20-40 minutes to achieve densification of copper particles and formation of a conductive network.

2. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that: The particle sizes of the micron-sized and nano-sized copper powders both conform to a normal distribution. The D50 particle size of the micron-sized copper powder is 0.5-1.5 μm, and the D50 particle size of the nano-sized copper powder is 130-170 nm.

3. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that: The stirring speed in step S1 is 1800-2200 rpm, and the stirring time is 10-20 min.

4. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that: The water bath heating temperature in step S2 is 60-70℃, and the stirring speed is 250-350r / min.

5. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that: The stirring speed in step S3 is 1000-3000 rpm, and the stirring time is 30-90 s.

6. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that: The rolling process in step S4 specifically includes the following steps: S4.1: Rolling 3-8 times with a feed inlet gap of 150-180 μm, a discharge inlet gap of 75-90 μm, and a rotation speed of 100-150 r / min; S4.2: Adjust the feed inlet gap to 100-130μm, the discharge outlet gap to 50-65μm, and roll at the same speed 3-8 times; S4.3: Adjust the feed inlet gap to 50-80μm, the discharge outlet gap to 25-40μm, and roll at the same speed of 100-150r / min for 6-14 times to obtain the desired printing copper paste.

7. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that: The antioxidant in step S3 is a benzotriazole compound.

8. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that: The leveling agent in step S3 is a polyether-modified siloxane.

9. The method for preparing a cold-peelable high-performance conductive copper film according to claim 1, characterized in that, In step S4, after sintering, the copper film is naturally cooled to room temperature to form a copper film. The copper film and the substrate are only in physical contact and naturally separate after cooling. The peeling force is ≤0.1 N / cm to achieve non-destructive cold peeling.

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