Method for reducing chemical copper plating and diffusion plating of laser activated flexible substrate

Abstract

The invention provides a method for reducing chemical copper plating and diffusion plating of a laser activated flexible substrate, is suitable for the field of printed circuit manufacturing, and particularly relates to a flexible substrate modification solution and an application process thereof. The method comprises the following steps: (1) cleaning a sample; (2) coating the surface of the sample with a modified layer; (3) performing mask exposure treatment on the surface of the sample; (4) activating the surface of the sample by laser; compared with a traditional laser activation chemical copper plating process, the method has the advantages that the diffusion coating phenomenon of a copper layer is remarkably reduced, the roughness of the boundary of the copper layer is reduced, and the consistency of the copper plating width is improved, so that the improvement of the high-frequency performance of a manufactured electronic circuit is facilitated, and meanwhile, the reliability of a system can also be improved. In addition, the method can be widely applied to metallization requirements of non-metal substrates in the fields of electronic circuit manufacturing, micro-nano processing and the like in the high-frequency field of flexible substrates.

Description

Technical Field

[0001] The present invention belongs to the technical field of printed circuit materials, and particularly relates to a method for reducing copper penetration in electroless copper plating of laser-activated flexible substrates. Background Art

[0002] Electroless copper plating is a technique for depositing a copper layer on the surface of a substrate through a catalytic reduction reaction. Its remarkable feature is that it does not require an external current, so it is suitable for surface treatment of various complex shapes. This technique has extensive and important applications in modern industry and science. First of all, electroless copper plating can endow non-conductive materials (such as plastics, ceramics, glass, polyimide, etc.) with conductivity, which is particularly important in electronic manufacturing. For example, in the production of printed circuit boards (PCBs), electroless copper plating is used for via hole metallization to achieve electrical connection between multiple layers, and at the same time, it can also build high-quality conductive paths in flexible printed circuit boards and flexible electronic devices. Secondly, the copper layer deposited by electroless copper plating has good electrical conductivity, thermal conductivity and welding performance, and is widely used in the conductive layers of electronic components, the surfaces of heat sinks and electromagnetic shielding devices. Its high uniformity and controllable layer thickness make it an ideal choice for depositing on the surfaces of substrates with complex geometries. In addition, electroless copper plating can not only provide a certain degree of corrosion protection for the substrate, but also improve the decorativeness, and is often used for the bottom plating of decorative metal coatings. In terms of functionality, the electroless copper plating technique can also be used for the preparation of catalysts or catalytic carriers. By depositing a copper layer and then performing an oxidation treatment, the material is given specific catalytic properties. It is also widely used for repairing damaged metal parts or filling small defects, reducing material waste and extending the life of parts. In emerging fields, the electroless copper plating technique is being applied to the manufacturing of flexible electronics, Internet of Things devices and 3D electronic components, becoming a core technology for building the next generation of intelligent devices. Its low cost, high efficiency and compatibility with various substrates make it irreplaceable in the fields of electronics, decoration, industry and scientific research.

[0003] Traditional electroless copper plating technology performs excellently when dealing with flat rigid substrates because it relies on uniform surface pretreatment and the chemical deposition process of the catalytic layer. However, when applied to flexible substrates such as PI films, this technology faces significant challenges. The catalytic layer in the traditional process often has insufficient adhesion, and the process flow is complex, making it difficult to meet the special requirements of flexible substrates. In the Chinese invention patent "Metal Pattern on the Surface of Insulating Substrate and Additive Manufacturing Method" (CN202211686359.X), Zhou Guoyun et al. proposed to achieve electroless copper plating by chemically reducing the catalytic layer on the flexible substrate to form active sites; in the Chinese invention patent "Method for Electroless Copper Plating without Palladium on the Surface of Flexible Nanofiber Membrane" (CN202210078721.9), Wang Dong et al. achieved electroless copper plating by using silver nitrate solution to activate the flexible nanofiber membrane. However, for flexible substrates such as PI films with low surface energy, due to the insufficient surface energy of the flexible substrate to ensure the uniform adhesion of the catalytic layer, this often may lead to copper layer peeling off or uneven thickness, seriously affecting the electroplating effect and quality stability. In addition, the traditional electroless copper plating process requires multiple cleaning, surface pretreatment, and activation steps. This not only takes a long time but also increases production costs and process uncertainty, making it difficult to meet the requirements of modern manufacturing for efficiency and stability.

[0004] Laser chemical copper plating technology is a surface treatment method that combines laser processing technology with traditional chemical copper plating process, with significant advantages, especially showing strong application potential in the preparation of high-precision and complex-shaped conductive circuits. The early application of this technology was the Laser Direct Structuring process of LPKF Company in Germany. The technical solution of this technology is to fabricate electrical wires and patterns with electrical functions on the surface of an injection-molded plastic housing, directly install components on the housing and make their electrical interconnections, so as to realize the electrical interconnection function of the circuit board, the function of supporting components, the support and protection functions of the plastic housing, and functions such as shielding and antenna generated by the combination of mechanical entities and conductive patterns, integrating them into one, forming a "three-dimensional molded interconnect (mechatronic integration) device". Its technical approach: injection molding - laser activation - chemical copper plating + electroless nickel immersion gold. The research on special laser-activatable plastics has always been concerned by the industry, but this technical solution requires special plastics as the basis, and this special plastic contains components that can be laser-activated, directly restricting its application scope due to cost. Panasonic has also developed a high-polymer surface metallization technology called Microscopic integrated processing technology (MIPTEC). Its main steps: First, use plasma to treat the surface of the molded part, and form a copper thin film on its surface through physical vapor deposition (PVD); then, use a laser beam to remove the copper layer around the required pattern; electroplate on the surface of the required pattern to increase the thickness of the copper layer; use a soft etching method to remove the remaining unnecessary metal parts; finally, electroplate nickel and gold layers on the copper layer as a protective layer, and the completed parts enter the subsequent chip mounting process. However, some disadvantages of MIPTEC limit its extended application: (1) The additional equipment required for plasma treatment and PVD metal spraying steps significantly increases the cost; (2) The surface of the substrate needs to be completely covered with a metal thin film by the PVD process, but the large-area metal layer is removed in the subsequent laser etching step, resulting in a large amount of waste of metal materials and increasing the cost. It is mentioned and studied in articles such as Ren Jun's "Research on Laser Processing Technology for Three-Dimensional Surface Metal Deposition of Polymer Materials" and Zhang, Yang's "Laser Induced Selective Activation For Subsequent Autocatalytic Electroless Plating".Subsequently, to avoid the drawbacks of the overall activation component in the substrate material and the excessive actual process cost, local activation technology has been developed. For example, Li Jiujuan et al. proposed a method of laser-activating a flexible substrate to achieve electroless copper plating in the Chinese invention patent "Method and Pattern for Depositing Conductive Copper Pattern on Flexible Substrate Based on Laser Activation" (CN202410349184.6). However, during the laser processing, when the substrate surface absorbs the laser pulse energy, local melting occurs and rapidly solidifies to form a molten structure after cooling. This process may cause the polymer to diffuse to the edge of the activation area, leading to the phenomenon of infiltration plating, which becomes a key problem in the laser electroless copper plating technology. Based on the fact that laser activation is the result of the interaction between the laser spot and the substrate material, the irregularity of the spot edge and the behavior of light diffraction directly cause the infiltration plating phenomenon in the subsequent electroless plating stage, which has an adverse impact on the electrical conductivity and structural integrity of the coating, and affects the smoothness and roughness of the surface of the fabricated electronic circuit. According to electromagnetic theory, high-frequency signals tend to propagate along the surface of the conductor (skin effect). The thinning and uneven thickness of the copper layer will exacerbate signal attenuation, thereby affecting the high-frequency performance of electronic products. Secondly, the irregularity of the copper layer caused by infiltration plating may lead to signal reflection and crosstalk problems, further reducing the electromagnetic compatibility (EMC) of the circuit. In high-frequency applications, this interference will significantly weaken the device performance and even cause the failure of key components. In addition, infiltration plating may also cause anode failure, weaken the conductivity of the anode area, and affect the normal functioning of the anode. The diffusion of copper ions may trigger electrochemical reactions on the substrate, accelerate the aging of the anode material, and further reduce the long-term stability of the product.

[0005] The innovation of the present invention lies in using a photoresist dry film to attach to the surface of the sample to reduce the generation of molten substances adhering outside the preset activation area during subsequent laser activation of the sample, thereby reducing the occurrence of infiltration plating during subsequent electroless copper plating. Summary of the Invention

[0006] During the laser processing, the surface of the sample absorbs the energy of the laser pulse, resulting in the melting of the surface thin layer, which is then rapidly cooled by the environment. During this process, the polymer substrate rapidly solidifies to form a melt-like structure. However, due to the fluidity of the molten polymer, some polymers may diffuse to the edge or even the external area of the target activation area, forming an uneven activation distribution, thereby leading to the infiltration plating phenomenon during the electroless copper plating process. The present invention provides a method for reducing the infiltration plating of laser-activated flexible substrate electroless copper plating.

[0007] To achieve the above-mentioned invention purpose, the technical solution provided by the present invention is as follows:

[0008] A method for reducing the infiltration plating of laser-activated flexible substrate electroless copper plating, comprising the following steps:

[0009] Step 1: Clean the sample

[0010] Place the cut flexible substrate in an ultrasonic cleaner and alternately clean it with anhydrous ethanol and deionized water in sequence to remove surface impurities. Subsequently, put the cleaned flexible substrate into an oven to dry and obtain a clean substrate;

[0011] Step Two: Coating a modification layer on the sample surface

[0012] Take an appropriate amount of the prepared modification solution and evenly spin-coat it on the surface of the clean flexible substrate with a homogenizer. Subsequently, put the coated flexible substrate into an oven at 70 °C to dry for 4 hours to form a solidified modification coating;

[0013] Step Three: Mask exposure treatment on the sample surface

[0014] Perform mask treatment on the sample with the modification coating prepared in Step Two using a laminator, and then use an ultraviolet exposure machine to perform exposure curing treatment on the covering film on the sample;

[0015] Step Four: Laser activation of the sample surface

[0016] Use laser treatment to activate the masked sample in Step Three;

[0017] Step Five: Demasking treatment on the sample surface

[0018] Put the activated sample in Step Four into an alkaline solution for soaking treatment until the excess covering film completely falls off, and then use deionized water to clean the sample;

[0019] Step Six: Electroless copper plating on the sample surface

[0020] Place the sample treated in Step Five in an electroless copper plating solution to deposit copper. During electroless copper plating, use magnetic stirring to improve the stability of the plating solution and promote the volatilization of bubbles in the plating solution; after electroless copper plating is completed, use deionized water to clean the copper-plated sample, then perform antioxidant treatment, and finally dry it to obtain the final sample.

[0021] As a preferred method, the composition of the modification solution in Step Two is: 5 - 25 ml of propylene glycol methyl ether, 0.2 - 1.0 g of triethanolamine or thiourea, 10 - 30 g of bisphenol A diglycidyl ether, 0.1 - 0.6 g of silver nitrate or copper acetate, and 0.2 - 1 g of epoxy resin curing agent.

[0022] As a preferred method, the preparation method of the modification solution in Step Two includes the following steps:

[0023] First Step: Add propylene glycol methyl ether, triethanolamine or thiourea, and bisphenol A diglycidyl ether into a clean glass bottle and magnetically stir at room temperature for 12 h to obtain a transparent solution;

[0024] Step 2: Add silver nitrate or copper acetate to the obtained transparent solution and magnetically stir it at room temperature for 12 h to obtain a light yellow solution or a blue solution;

[0025] Step 3: Before using the obtained modified solution, add an epoxy resin curing agent thereto and stir it at room temperature for 20 min to obtain a final modified solution.

[0026] Preferably, the flexible substrate is a polyimide film, a polyether ether ketone film, or a PET film.

[0027] Preferably, the film used in the laminator in Step 3 is a photoresist dry film, and the exposure time of the ultraviolet exposure machine to the sample is 5 - 10 minutes.

[0028] Preferably, the laser used for activation in Step 4 is a 355 nm ultraviolet laser, and its laser parameters are as follows: the frequency is 15 - 35 kHz, the pulse width is 10 - 30 ns, the scanning speed is 200 - 400 mm / s, and the line spacing is 10 - 20 μm.

[0029] Preferably, the alkaline solution used in Step 5 is a 1 - 3 mol / L sodium hydroxide or potassium hydroxide solution.

[0030] Preferably, the composition of the electroless copper plating solution used for electroless copper plating in Step 6 is as follows: 30 - 40 g / L of potassium sodium tartrate tetrahydrate, 1 - 3 g / L of disodium ethylenediaminetetraacetate dihydrate, 10 - 15 g / L of copper sulfate pentahydrate, 3 - 5 g / L of nickel sulfate hexahydrate, 5 - 20 mg / L of 2,2'-bipyridine, 10 - 25 mg / L of potassium ferrocyanide trihydrate, 10 - 15 g / L of sodium hydroxide, and 10 - 15 ml / L of formaldehyde solution. The electroless copper plating time is controlled to be 0.5 - 2 h, and the plating solution temperature is controlled to be 35 - 50 °C.

[0031] In summary, due to the adoption of the above - mentioned scheme conditions, the beneficial effects of the present invention are as follows:

[0032] In the present invention, by introducing a mask technology during the laser activation process and using a mask material with high temperature resistance and laser irradiation resistance, the laser action range is accurately defined, effectively avoiding the problem of non-target diffusion of the catalyst. The optimized mask fitting method ensures that the laser action area is completely consistent with the mask boundary, achieving precise control of the shape and size of the coating. The mask technology not only fundamentally reduces the problem of infiltration plating caused by the diffusion of molten polymer, improves the accuracy of the width of the electroless copper plating layer, but also ensures the reliability of the laser processing and electroless copper plating processes due to its heat resistance and stability. At the same time, the mask operation is simple and flexible, can be customized according to different substrates and requirements, and is easy to integrate into the existing production line, with wide industrial applicability, especially suitable for the metallization requirements in the fields of flexible electronics and micro-nano processing. The present invention significantly improves the quality control ability of the laser-activated electroless copper plating process, overcomes the technical bottlenecks of the traditional process, and provides an important theoretical support and practical basis for the development of high-precision metallization technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic flow diagram of the present invention;

[0034] Figure 2 is an optical microscope image of the copper layer in Example 1;

[0035] Figure 3 is an SEM image of the copper layer in Example 1;

[0036] Figure 4 is an XRD pattern of the copper layer in Example 1;

[0037] Figure 5 is a metallographic section image of the copper layer in Example 1;

[0038] Figure 6 is an optical microscope image of the copper layer in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0039] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] As Figure 1 shown, the embodiment provides a method for reducing infiltration plating in laser-activated electroless copper plating on flexible substrates, including the following steps:

[0041] Step 1: Cleaning the sample

[0042] Place the cut flexible substrate in an ultrasonic cleaner and wash it alternately with anhydrous ethanol and deionized water in turn to remove surface impurities. Subsequently, put the washed flexible substrate into an oven to dry and obtain a clean substrate;

[0043] Step 2: Coating a modification layer on the sample surface

[0044] Take an appropriate amount of the prepared modification solution and spin-coat it evenly on the surface of the clean flexible substrate with a homogenizer. Subsequently, put the coated flexible substrate into an oven at 70 °C to dry for 4 hours to form a cured modification coating;

[0045] Step 3: Mask exposure treatment on the sample surface

[0046] Perform mask treatment on the sample with the modification coating prepared in Step 2 using a laminator, and then use an ultraviolet exposure machine to perform exposure curing treatment on the cover film on the sample;

[0047] Step 4: Laser activation of the sample surface

[0048] Use laser treatment to activate the masked sample in Step 3;

[0049] Step 5: Demasking treatment on the sample surface

[0050] Put the activated sample in Step 4 into an alkaline solution for soaking treatment until the excess cover film completely falls off, and then wash the sample clean with deionized water;

[0051] Step 6: Electroless copper plating on the sample surface

[0052] Place the sample treated in Step 5 in an electroless copper plating solution to deposit copper. During electroless copper plating, use magnetic stirring to improve the stability of the plating solution and promote the volatilization of bubbles in the plating solution; after electroless copper plating, wash the copper-plated sample clean with deionized water, then perform an antioxidant treatment, and finally dry it to obtain the final sample.

[0053] Preferably, the composition of the modification solution in Step 2 is: 5 - 25 ml of propylene glycol methyl ether, 0.2 - 1.0 g of triethanolamine or thiourea, 10 - 30 g of bisphenol A diglycidyl ether, 0.1 - 0.6 g of silver nitrate or copper acetate, and 0.2 - 1 g of an epoxy resin curing agent.

[0054] Preferably, the preparation method of the modification solution in Step 2 includes the following steps:

[0055] First step: Add propylene glycol methyl ether, triethanolamine or thiourea, and bisphenol A diglycidyl ether into a clean glass bottle and magnetically stir at room temperature for 12 h to obtain a transparent solution;

[0056] Second step: Add silver nitrate or copper acetate to the obtained transparent solution and magnetically stir at room temperature for 12 h to obtain a light yellow solution or a blue solution;

[0057] Step 3: Before using the obtained modified solution, add an epoxy resin curing agent thereto and stir for 20 min at room temperature to obtain the final modified solution.

[0058] Preferably, the flexible substrate is a polyimide film, a polyether ether ketone film, or a PET film.

[0059] Preferably, the film used in the film laminator in Step 3 is a dry film photoresist, and the exposure time of the ultraviolet exposure machine to the sample is 5 - 10 minutes.

[0060] Preferably, the laser used for activation in Step 4 is a 355 nm ultraviolet laser, and its laser parameters are: frequency 15 - 35 kHz, pulse width 10 - 30 ns, scanning speed 200 - 400 mm / s, and line spacing 10 - 20 μm.

[0061] Preferably, the alkaline solution used in Step 5 is a 1 - 3 mol / L sodium hydroxide or potassium hydroxide solution.

[0062] Preferably, the composition of the electroless copper plating solution used for electroless copper plating in Step 6 is: 30 - 40 g / L of potassium sodium tartrate tetrahydrate, 1 - 3 g / L of disodium ethylenediaminetetraacetate dihydrate, 10 - 15 g / L of copper sulfate pentahydrate, 3 - 5 g / L of nickel sulfate hexahydrate, 5 - 20 mg / L of 2,2'-bipyridine, 10 - 25 mg / L of potassium ferrocyanide trihydrate, 10 - 15 g / L of sodium hydroxide, and 10 - 15 ml / L of formaldehyde solution. The electroless copper plating time is controlled to be 0.5 - 2 h, and the plating solution temperature is controlled to be 35 - 50 °C.

[0063] Example 1

[0064] (1) Preparation of the modified solution: Add 10 ml of propylene glycol methyl ether, 0.4 g of thiourea, and 7 g of bisphenol A diglycidyl ether into a clean glass bottle, and magnetically stir for 12 h at room temperature to obtain a transparent solution; then add 0.2 g of silver nitrate to the obtained transparent solution and magnetically stir for 12 h at room temperature to obtain a light yellow solution; finally, add 0.5 g of 593-type epoxy resin curing agent to the light yellow solution before use and stir for 20 min at room temperature to obtain the final light tan solution;

[0065] (2) Coating the modified layer on the sample surface: Place the cut PI film in an ultrasonic cleaner and alternately clean it with anhydrous ethanol and deionized water to remove surface impurities. Then, put the cleaned flexible substrate into an oven to dry to obtain a clean substrate. Take an appropriate amount of the prepared modified solution and spin-coat it evenly on the surface of the clean flexible substrate with a homogenizer. Then, put the coated flexible substrate into an oven at 70 °C and dry for 4 hours to form a cured modified layer.

[0066] (3) Mask exposure treatment of the sample surface: The prepared sample with a catalytic layer is pasted with a dry film of photoresist using a laminator, and then the film on the sample is exposed and cured using an ultraviolet exposure machine for 10 minutes;

[0067] (4) Laser activation of the sample surface: The sample after laminating is irradiated with ultraviolet laser with a wavelength of 355 nm. The laser parameters are: frequency 22.5 kHz, pulse width 120 ns, scanning speed 100 mm / s, and line spacing 15 μm.

[0068] (5) Demasking treatment of the sample surface: The sample after laser activation is immersed in a 1 mol / L sodium hydroxide alkaline solution for treatment until the excess covering film completely falls off; then the sample is cleaned with deionized water;

[0069] (6) Electroless copper plating on the sample surface: The sample after demasking treatment is placed in an electroless copper plating solution for copper deposition. The electroless copper plating solution used for electroless copper plating is 32 g / L of potassium sodium tartrate tetrahydrate, 2 g / L of disodium ethylenediaminetetraacetate dihydrate, 12 g / L of copper sulfate pentahydrate, 5 g / L of nickel sulfate hexahydrate, 5 mg / L of 2,2'-bipyridine, 10 mg / L of potassium ferrocyanide trihydrate, 10 g / L of sodium hydroxide, and 12 ml / L of formaldehyde solution. The electroless copper plating time is controlled at 1 h, and the plating solution temperature is controlled at 45 °C. During electroless copper plating, magnetic stirring is used to improve the stability of the plating solution and promote the volatilization of bubbles in the plating solution. After the electroless plating is completed, the sample is cleaned with deionized water, then subjected to antioxidant treatment, and finally dried to obtain the final sample.

[0070] As Figure 2 shown, after electroless copper plating, the width of the preset area activated by laser is 750 μm, which is observed through an optical microscope. The penetration width of the copper layer after electroless plating is 16.443 μm, and the actual width of the copper layer only increases by 2.19% compared with the preset width. The penetration phenomenon is slight, and the impact on the product quality is very small.

[0071] As Figure 3 、 4 and 5 shown, a pure copper chemical plating layer has been successfully formed on the sample surface. It can be observed that there is a good bonding force between the copper layer and the substrate surface, and the presence of copper oxide grains is not detected, indicating that the purity of the plating layer is relatively high. Further analysis shows that the copper layer particles are evenly distributed, and the particles are tightly connected to form a continuous and dense plating layer structure.

[0072] Comparative Example 1

[0073] (1) Preparation of the modified solution: Add 10 ml of propylene glycol monomethyl ether, 0.4 g of triethanolamine, and 7 g of bisphenol A diglycidyl ether into a clean glass bottle, and magnetically stir for 12 h at room temperature to obtain a transparent solution; then add 0.2 g of silver nitrate into the obtained transparent solution, and magnetically stir for 12 h at room temperature to obtain a light yellow solution; finally, add 0.5 g of curing agent type 593 into the light yellow solution before use, and stir for 20 min at room temperature to obtain the final light tan solution;

[0074] (2) Coating the modified layer on the sample surface: Place the cut PI film in an ultrasonic cleaner, and alternately clean it with anhydrous ethanol and deionized water in turn to remove surface impurities. Then, put the cleaned flexible substrate into an oven to dry, and obtain a clean substrate. Take an appropriate amount of the prepared modified solution, and spin-coat it evenly on the surface of the clean flexible substrate with a homogenizer. Then, put the coated flexible substrate into an oven at 70 °C and dry for 4 hours to form a cured catalytic layer.

[0075] (3) Laser activation of the sample surface: The ultraviolet laser used for the masked sample is a 355 nm laser, and its laser parameters are: frequency is 22.5 kHz, pulse width is 120 ns, scanning speed is 100 mm / s, and line spacing is 15 μm.

[0076] (4) Electroless copper plating on the sample surface: Place the laser-activated sample in an electroless copper plating solution to deposit copper. The electroless copper plating solution used for electroless copper plating is potassium sodium tartrate tetrahydrate 32 g / L, disodium ethylenediaminetetraacetate dihydrate 2 g / L, copper sulfate pentahydrate 12 g / L, nickel sulfate hexahydrate 5 g / L, 2,2'-bipyridine 5 mg / L, potassium ferrocyanide trihydrate 10 mg / L, sodium hydroxide 10 g / L, and formaldehyde solution 12 ml / L. The electroless copper plating time is controlled for 1 h, and the plating solution temperature is controlled at 45 °C. During electroless copper plating, magnetic stirring is used to improve the stability of the plating solution and promote the volatilization of bubbles in the plating solution. After the electroless plating is completed, clean the sample with deionized water, then perform an antioxidant treatment, and finally dry it to obtain the final sample.

[0077] The optical microscope image of the copper layer after electroless copper plating in Comparative Example 1 is as Figure 6 shown. The preset width of the laser-activated preset area is 750 μm, while the width of the copper layer in the overplated part after the sample electroless plating is 59.879 μm, and the actual copper layer width exceeds the preset width by 7.98%. The overplating phenomenon is relatively serious and does not meet the requirements of the fine copper layer circuit.

[0078] The above embodiments are only used to illustrate the principles and effects of the present invention, rather than to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for reducing electroless copper plating on a laser activated flexible substrate, characterized in that The following steps are involved: Step 1: Clean the sample The cut flexible substrate is placed in an ultrasonic cleaner, and is cleaned alternately with anhydrous ethanol and deionized water to remove surface impurities. Subsequently, the cleaned flexible substrate is placed in an oven to dry to obtain a clean substrate; Step 2: Coating the modified layer on the sample surface Take an appropriate amount of the prepared modified solution and evenly spin-coat it on the surface of a clean flexible substrate using a homogenizer. Then, place the coated flexible substrate in an oven at 70°C and dry it for 4 hours to form a cured modified coating. Step 3: Mask exposure treatment on sample surface The modified coating sample prepared in step 2 is subjected to masking treatment using a film laminating machine, and then the covering film on the sample is subjected to exposure and curing treatment using a UV exposure machine; Step 4: Laser activation of sample surface Activate the masked sample in step 3 by laser treatment; Step 5: Sample surface de-mold treatment The activated sample in step 4 is immersed in an alkaline solution to completely remove the excess covering film, and then the sample is cleaned with deionized water; Step 6: Chemical copper plating on sample surface The sample treated in step five is placed in a chemical copper plating solution to deposit copper. During the chemical copper plating, magnetic stirring is used to improve the stability of the plating solution and promote the volatilization of bubbles in the plating solution. After the chemical copper plating is completed, the copper-plated sample is cleaned with deionized water, and then an antioxidant treatment is performed, and finally drying is performed to obtain the final sample.

2. A method for reducing electroless copper plating on a laser activated flexible substrate according to claim 1, characterized in that: The modified solution in step 2 is composed of: 5-25 ml propylene glycol methyl ether, 0.2-1.0 g triethanolamine or thiourea, 10-30 g bisphenol A diglycidyl ether, 0.1-0.6 g silver nitrate or copper acetate, and 0.2-1 g epoxy resin curing agent.

3. The method for reducing electroless copper plating on a laser activated flexible substrate according to claim 1, characterized in that: The preparation method of the modified solution in step 2 comprises the following steps: Step 1: Add propylene glycol methyl ether, triethanolamine or thiourea, and bisphenol A diglycidyl ether into a clean glass bottle and stir magnetically at room temperature for 12 hours to obtain a transparent solution; Step 2: Add silver nitrate or copper acetate to the obtained transparent solution, and stir magnetically for 12 hours at room temperature to obtain a light yellow solution or a blue solution; Step 3: Before using the modified solution, add epoxy resin curing agent and stir at room temperature for 20 minutes to obtain the final modified solution.

4. The method for reducing electroless copper plating on a laser activated flexible substrate according to claim 1, characterized in that: The flexible substrate is a polyimide film, a polyetheretherketone film and a PET film.

5. The method for reducing electroless copper plating on a laser activated flexible substrate according to claim 1, characterized in that: Step 3: The film used by the film laminating machine is a photoresist dry film, and the UV exposure machine exposes the sample for 5 to 10 minutes.

6. The method for reducing electroless copper plating on a laser activated flexible substrate according to claim 1, characterized in that: The laser used for activation in step 4 is a 355nm ultraviolet laser, and its laser parameters are: frequency of 15-35kHz, pulse width of 10-30ns, scanning speed of 200-400mm / s, and line spacing of 10-20μm.

7. The method for reducing electroless copper plating on a laser activated flexible substrate according to claim 1, characterized in that: The alkaline solution used in step 5 is 1-3 mol / L sodium hydroxide or potassium hydroxide solution.

8. The method for reducing electroless copper plating on a laser activated flexible substrate according to claim 1, characterized in that: Step 6: The chemical copper plating solution used for chemical copper plating is composed of: 30-40 g / L potassium sodium tartrate tetrahydrate, 1-3 g / L disodium ethylenediaminetetraacetic acid dihydrate, 10-15 g / L copper sulfate pentahydrate, 3-5 g / L nickel sulfate hexahydrate, 5-20 mg / L 2,2'-bipyridine, 10-25 mg / L potassium ferrocyanide trihydrate, 10-15 g / L sodium hydroxide, and 10-15 ml / L formaldehyde solution. The chemical copper plating time is controlled to be 0.5-2 h, and the plating solution temperature is controlled to be 35-50 ° C.

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