Low-profile electrolytic copper foil for high-density interconnection circuit board

Abstract

The present invention relates to the field of copper foil, and in particular to low-profile electrolytic copper foil for a high-density interconnection circuit board. The electrolytic copper foil sequ

Description

TECHNICAL FIELD The invention relates to the field of copper clad, particularly to a low-profile electrolytic copper clad for high-density interconnected circuit boards. BACKGROUND As copper electronic products are being developed to be light-weighted, thin, small, wearable and multi-functional, new requirements are constantly put forward for copper clad for multilayer circuit boards, and higher requirements are put forward in terms of copper clad area quality, copper clad thickness and allowable deviation, surface roughness of copper clad, dimensional stability, heat resistance, high-frequency and high-speed characteristics and fine circuit processing, so as to continuously promote the development of copper clad for circuit boards. Copper Clad Laminate (CCL) is the mam component of the circuit boards, which is made by laminating insulating film and upper and lower copper clads and hot pressing, and then etching to form the required circuit, that is, the core board of the circuit board. However, at present, the conventional common copper clad m copper clad laminate cannot meet the requirements of high-density interconnected circuit boards, the performance of thm ware width and small wire spacing, and the capability of carrying large current. Moreover, due to the problems of excessive roughness and low elongation at high temperatures, the conventional copper clad is prone to signal short circuit caused by the conduction of the upper and lower copper materials on the core board and hot cracking of the copper clad caused by thermal expansion and cold contraction of the film during the process of high-temperature and high-pressure pressing, which will adversely affect the quality and reliability of the subsequently manufactured circuit. SUMMARY Aiming at some problems existing in the prior art, the first aspect of the invention provides a low-profile electrolytic copper clad, which sequentially comprises a copper clad layer, a coarsening layer, a protective barrier layer, a passivation layer and a silane coupling agent layer; the thickness of the copper clad layer is 6-35 pm, the weight per unit area is 50-305 g / m2, the weight deviation per unit area is less than 5%, the tensile strength at 25 °C is more than or equal to 350 N / mm2, the elongation at 25 °C is more than or equal to 4%, the peel strength is more than or equal to 0.7 kg / cm, the smooth surface Ra is less than or equal to 0.43 pm, and the rough surface Rzis less than or equal to 3.5 pm. As a preferred technical scheme of the invention, the copper clad layer is obtained by electroanalysis in electrolyte containing copper ions; the electrolyte comprises 250-350 g / L copper salt, 70-150 g / L inorganic acid, 10-80 mg / L chloride salt and 1.5-45 mg / L leveling agent. As a preferred technical scheme of the invention, the leveling agent includes nonionic cellulose ether and leveling agent-1, and the nonionic cellulose ether-1 contains amino and carboxyl. As a preferred technical scheme of the invention, the nonionic cellulose ether contains methoxy, the content of the methoxy is 22-30wt%, and the degree of substitution is 1.3-2.5. As a preferred technical scheme of the invention, the nonionic cellulose ether also contains hydroxy ethyl, the content of hydroxy ethyl is 2.0-14wt%, and the degree of substitution is 0.06-0.5. As a preferred technical scheme of the invention, the weight-average molecular weight of the leveling agent-1 is 50,000-60,000. As a preferred technical scheme of the invention, the concentration ratio of the nonionic cellulose ether to the leveling agent -1 is 1: (2-5). As a preferred technical scheme of the invention, the protective barrier material is selected from one or more of nickel, titanium, tin, tungsten, molybdenum and zinc. As a preferred technical scheme of the invention, the silane coupling agent layer material is a silane coupling agent selected from one or more of 3-glycidyl ether oxy propyl trimethoxy silane, 3-aminopropyl triethoxy silane, vinyl triethoxy silane, vinyl trimethoxysilane, vinyl tri (P-methoxyethoxy) silane, vinyl benzyl aminoethyl aminopropyl trimethoxy silane and 3-(methacryloxy) propyl trim ethoxy silane, 3-(methacryloxy) propyl triethoxysilane or 3-(methacryloxy) propyl methyl dimethoxy silane. The second aspect of that invention provide an application of the low-profile electrolytic copper clad in a high-density interconnected circuit board. Compared with the prior art, the invention has the following beneficial effects: The electrolytic copper clad provided by the invention is simple in raw materials, nontoxic, harmless, safe and environment-friendly, has excellent tensile strength at normal temperature and high temperature, has good high-temperature oxidation resistance, able to withstand high temperatures of 200-300°C, can meet requirements for better flatness and low profile simultaneously, is simple to operate, can fully meet the market requirements for electrolytic copper clad for high-density interconnected circuit boards, has high added value, wide environmental applicability and remarkable market competitiveness. Description of the Invention The invention will be illustrated by specific embodiments below, but not limited to the specific embodiments given below. The first aspect of the invention provides the low-profile electrolytic copper clad, which sequentially comprises the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent layer. Copper Clad Laver In one embodiment, the thickness of the copper clad layer is 6-35 pm, the weight per unit area is 50-305 g / m2, the weight deviation per unit area is less than 5%, the tensile strength at 25 °C is more than or equal to 350 N / mm2, the elongation at 25°C is more than or equal to 4%, the peel strength is more than or equal to 0.7 kg / cm, the smooth surface Ra is less than or equal to 0.43 pm, and the rough surface Rzis less than or equal to 3.5 pm. In one embodiment, the copper clad layer is obtained by electroanalysis in electrolyte containing copper ions; the electrolyte comprises 250-350 g / L copper salt, 70-150 g / L inorganic acid, 10-80 mg / L chloride salt and 1.5-45 mg / L leveling agent. In a preferred embodiment, the electrolyte comprises 320 g / L copper salt, 100 g / L inorganic acid, 20 mg / L chloride salt and 4.5 mg / L leveling agent. <Copper Salt> The copper salt in the invention is not particularly specified, but can be routinely selected by those skilled in the art. In one embodiment, the copper salt is copper sulfate pentahydrate. In the invention, as the main component of the plating solution, copper sulfate pentahydrate is subject to the electrode process. The concentration of copper sulfate pentahydrate is too high, the dispersion ability of copper ions is poor, the concentration of anhydrous copper sulfate is too low, and the copper clad layer of the high current layer is burnt. < Inorganic Acid > The inorganic acid in the invention is not particularly specified, but can be routinely selected by those skilled in the art. In one embodiment, the inorganic acid is sulfuric acid. In the invention, as the main component of the plating solution, sulfuric acid participates in the electrode process together with copper sulfate pentahydrate, and the sulfuric acid and the copper sulfate pentahydrate is interdependent in the electroplating process. Sulfuric acid can also prevent the decomposition of copper sulfate pentahydrate in the invention and increase the conductivity at the same time. < Chloride Salt> The chloride salt in the invention is not particularly specified, but can be routinely selected by those skilled in the art. In one embodiment, the chlorine salt is hydrochloric acid. According to the invention, hydrochloric acid, copper sulfate pentahydrate and sulfuric acid are interdependent, and the uniformity and compactness of grain texture of the copper clad layer are improved under the condition of improving the conductivity of the plating solution. < Leveling Agent> Leveling agent is a substance that can be added to electroplating solution to improve the flatness of coating and make the obtained coating smoother than the laminate surface. In the process of electroplating, the leveling agent is more easily adsorbed at the microscopic peak than at the valley on the surface of the plated piece, so that the deposition resistance at valley is larger and the deposition rate is slower. After a certain period of time, the microscopic valleys are gradually filled by the coating, so that the coating is levelled. For example, adding butynediol or pyridine and quinoline compounds to bright nickel plating solution can not only make the coating bright but also have a good leveling effect. In one embodiment, the leveling agent includes nonionic cellulose ether and leveling agent-1. Preferably, the leveling agent-1 contains amino groups and carboxyl groups; further preferably, the weight-average molecular weight of the leveling agent -1 is 50,000-60,000. It is found that adding leveling agent-1 to the electrolyte, which contains amino and carboxyl, can improve the leveling effect to a certain extent, but its leveling effect is limited. At the same time, it is also found that the tensile strength of the obtained copper clad layer decreases, and unexpectedly found that when the weight-average molecular weight of the leveling agent -1 is 50,000-60,000, the leveling effect can be significantly improved, and the tensile strength of the obtained copper clad layer is enhanced. The applicant guesses that the possible reason is that the molecular structure of the leveling agent-1 with the weight-average molecular weight of 50,000-60,000 has many flexible snake chains with irregular shapes, which can be effectively adsorbed on the bumps and cover a large area. At the same time, during the electrolysis process, the molecule of the leveling agent-1 with the weight-average molecular weight of 50,000-60,000 has larger internal rigidity, higher probability of molecular movement, and the probability of covering it with electrolytic copper clad is reduced, so that rigidity does not decrease. In one embodiment, the nonionic cellulose ether contains methoxy, the content of the methoxy is 22-30wt%, and the degree of substitution is 1.3-2.5. Preferably, the nonionic cellulose ether also contains hydroxyethyl, the content of hydroxy ethyl is 2.0-14wt% and the degree of substitution is 0.06-0.5. More preferably, the nonionic cellulose ether has a viscosity of 5-200,000 mps at 20°C in a 2wt% aqueous solution. It is unexpectedly found that the obtained copper clad layer has a good leveling effect when the nonionic cellulose ether contains methoxy with the content of22-3 0wt% and the degree of substitution of 1.3-2.5, the nonionic cellulose ether contains also contains hydroxyethyl with the content of hydroxy ethyl of 2.0-14wt% and the degree of substitution of 0.06-0.5, and at the same time, the viscosity in 2wt% aqueous solution is 5-200,000 mps at 20°C. The possible reason is that under appropriate conditions, nonionic cellulose ether has proper molecular structure and good dispersibility, can well control the gradual increase of fine copper particles at the copper clad bumps, and realizes the copper plating process step by step, with smooth top of particles and increased flatness. At the same time, the nonionic cellulose ether under this condition has stronger adsorption to impurity ions in electrolyte, which can avoid the pinhole of electrolytic copper clad. At the same time, the nonionic cellulose ether under this condition has stronger adsorption to impurity ions in electrolyte, which can avoid the pinhole of electrolytic copper clad. In one embodiment, the concentration ratio of the leveling agent-1 to the nonionic cellulose ether is (2-5): 1. Preferably, the concentration ratio of the leveling agent -1 to the nonionic cellulose ether is 3.5: 1. It is unexpectedly found that when the concentration ratio of leveling agent-1 to nonionic cellulose ether is (2-5): 1, the tensile strength of electrolytic copper clad at high-temperature can also be improved. The possible reasons are as follows: on one hand, when the concentration ratio of the leveling agent-1 to the nonionic cellulose ether is (2: 5): 1, a suitable hydrogen bond structure is formed between molecule of the leveling agent -1 with a weight-average molecular weight of 50,000-60,000 and the nonionic cellulose ether, which can further refine the copper particles, keep the unit area weight of the electrolytic copper clad at the same level, reduce the error and improve the mechanical properties at high temperatures; on the other hand, nonionic cellulose ether has a good protective effect on the leveling agent-1, avoiding the loss of the activity of leveling agent-1 during electrolysis, which leads to coarse copper particles and affects the uniformity of weight per unit area. In addition, leveling agent-1 molecules with a weight-average molecular weight of 50,000-60,000 with appropriate concentration can also avoid the defect of strength reduction of electrolytic copper clad caused by hydroxyethyl cellulose. In one embodiment, the preparation method of the copper clad layer comprises the following steps: (1) electrolyte preparation: uniformly mixing copper salt, inorganic acid, chloride salt and leveling agent in the electrolyte at 40-60°C, and placing in an electrolytic bath; (2) electrochemical reaction: applying direct current, precipitating copper clad from the cathode at the current density of 40-80 A / dm2, and peeling. In a preferred embodiment, the preparation method of the copper clad layer comprises the following steps: (1) electrolyte preparation: uniformly mixing copper salt, inorganic acid, chloride salt and leveling agent in the electrolyte at 50°C, and placing in an electrolytic bath; (2) electrochemical reaction: applying direct current, precipitating copper clad from the cathode at the current density of 70 A / dm2, and peeling. Coarsening Laver The coarsening treatment improves theadhesion between the copper clad and the substrate. In coarsening treatment, copper powder is produced and solidified by the current density higher than the limit current density, which makes the surface of copper clad form a firm granular structure with highly developed rough surface and high specific surface area. In this way, the adhesion and embedding force of resin infiltration can be strengthened and the affinity between copper and resin can be increased. If the crystal layer of the copper clad is flat and the spreading degree is small in coarsening treatment, the bonding force between the copper clad and the substrate will be insufficient, which will further adversely affect properties of the board. In one embodiment, the coarsening layer is obtained by electrolysis of the copper clad layer in the coarsening treatment solution. In one embodiment, the coarsening treatment solution comprises 10-50 g / L copper sulfate, 50-150 g / L sulfuric acid and 1.2-40 g / L additive. In a preferred embodiment, the coarsening treatment solution includes 38 g / L copper sulfate, 75 g / L sulfuric acid and 2 g / L additive. In the invention, copper sulfate is used as the main salt of the coarsening solution to form a star-shaped roughened surface on the surface of the copper clad layer. If the content of copper sulfate is too high, the generated copper powder is easy to fall off, which adversely affects the coarsening effect; if the content of copper sulfate is too low, the coarsening effect is not obvious. In the invention, sulfuric acid as the main component of the coarsening treatment solution can promote the precipitation of copper sulfate on the surface of the copper clad layer, and improve the stability of the coarsening treatment solution. In one embodiment, that additive is selected from one or more of sodium tungstate, titanium sulfate and tin sulfate. Preferably, the additives are sodium tungstate, titanium sulfate and tin sulfate; further preferably, the concentration ratio of sodium tungstate, titanium sulfate and tin sulfate is 1: (7-10): (1-5); more preferably, the concentration ratio of sodium tungstate, titanium sulfate and tin sulfate is 1: 8: 3. The additive in the invention is arsenic-free, non-toxic, safe and healthy, and at the same time, sodium tungstate, titanium sulfate and tin sulfate interact to promote the formation of loose nodules on the surface of the copper clad layer, and at the same time, the precipitation of copper ions in copper sulfate on the surface of the copper clad layer is not affected, so that the copper layer can cover the nodules in time, the formation of dendritic copper is prevented, and the production of copper powder is inhibited. In one embodiment, the method for preparing the roughened layer includes the following steps: (1) pickling: pickling the copper clad layer in pickling solution at 10-50 °C for 2-20 s, wherein the pickling solution comprises 80-250 g / L copper sulfate and 50-150 g / L sulfuric acid; (2) electrolyzing the material obtained in step (1) at 25 °C and current density of 5-10 A / dm2 for 2-20 s to obtain the roughened layer. In a preferred embodiment, the method for preparing the roughened layer comprises the following steps: (1) pickling: pickling the copper clad layer in pickling solution at 27°C for 10 s, wherein the pickling solution comprises 130 g / L copper sulfate and 80 g / L sulfuric acid; (2) electrolyzing the material obtained in step (1) at 25 °C and current density of 10 A / dm2 for 10 s to obtain the roughened layer. Protective Barrier Layer In one embodiment, that protective barrier layer material is selected from one or more of nickel, titanium, tin, tungsten, molybdenum and zinc. Preferably, the protective barrier layer is a nickel and / or zinc layer; further preferably, the protective barrier layer is the nickel and zinc layer. Zinc coating is the earliest barrier layer, which has the advantages of stable process, convenient operation and low cost. After passivation and organic film coating, the galvanized copper clad has good heat resistance and high bonding strength with the laminate, but it has some disadvantages such as poor corrosion resistance and easy discoloration due to the active chemical properties of zinc. Nickel coating has good resistance to discoloration at high temperature. Besides, nickel coating has better acid resistance than zinc coating, and it has high resistance to Cu2+ migration because of slow diffusion of nickel. However, it is not easy for nickel coating to be etched in alkaline ammonium persulfate etchant, and it will also leave spots on printed boards and cause pollution. In this application, the nickel and zinc layers can not only integrate the advantages of the nickel layer and the zinc layer, but also effectively coat the coarsening layer to improve the bonding strength between the coarsening layer and the protective barrier layer. In one embodiment, the protective barrier layer is obtained by electroanalysis on the surface of the coarsening layer in the protective barrier fluid. In an embodiment, the protective barrier fluid comprises 20-100 g / L sulfuric acid, 0.25-2 g / L Ni2+, 0.50-5 g / L Zn2+ and 50-300 mg / L protective barrier fluid additive. In a preferred embodiment, the protective barrier fluid comprises 20-100 g / L sulfuric acid, 1 g / L Ni2+, 3 g / L Zn2+ and 150 mg / L protective barrier fluid additive. The concentration of sulfuric acid in the protective barrier fluid of the invention is adjusted to pH=3.0-6.0, and the pH is preferably 5. The pH value in the protective barrier fluid of this application is 3.0-6.0, which ensures the dispersion ability of ions in the protective barrier fluid on one hand, and on the other hand, ensures the stable deposition of nickel ions and zinc ions with good uniformity. In one embodiment, the protective barrier fluid additive is saccharin and / or benzyl triethylammonium bromide. Preferably, the protective barrier fluid additive is benzyl triethylammonium bromide. In the invention, benzyl triethylammonium bromide can uniformly electroplate the nickel and zinc layers on the surface of the coarsening layer, thereby improving the surface smoothness of electrolytic copper clad. In one embodiment, the method for preparing the protective barrier layer comprises the following step: electrolyzing the coarsening layer at 30-60°C and 0.5-2.0 A / dm2 for 2-10 s. In a preferred embodiment, the method for preparing the protective barrier layer includes: electrolyzing the coarsening layer at 50°C and 1.5 A / dm2 for 8 s. Passivation Laver In one embodiment, the passivation layer is obtained by electroanalysis on the surface of the protective barrier layer in passivation treatment fluid. In an embodiment, the passivation fluid comprises 2.0-20 g / L Na2SO4, 0.2-3.0 g / L Zn2+ and 0.5-5.0 g / L CrOv Preferably, the passivation fluid comprises 15 g / L Na2SO4, 1.8 g / L Zn2+ and 3.2 g / L CrO3. Passivation treatment fluid with appropriate concentration makes the passivation treatment layer in this application dense and fine, and forms a dense and complex film layer on the surface of the protective barrier layer, so that protective barrier layer will not be oxidized and discolored by direct contact with air; meanwhile, the bonding strength between the film layer and the protective barrier layer is high, and the protection duration is long. In one embodiment, the method for preparing the passivation layer includes: electrolyzing the protective barrier layer at 30-60°C and 0.5-5 A dm2 for 1-10 s. In a preferred embodiment, the method for preparing the passivation layer includes: electrolyzing the protective barrier layer for 2-8 s at 40 °C and 3.2A / dm2. Silane Coupling Agent Layer In one embodiment, the silane coupling agent layer material is a silane coupling agent selected from one or more of 3-glycidyl ether oxy propyl trimethoxy si lane, 3-aminopropyl triethoxysilane, vinyl triethoxysilane, vinyl trimethoxysilane, vinyl tri (P-methoxyethoxy) silane, vinyl benzyl aminoethyl aminopropyl trimethoxysilane and 3-(methacryloxy) propyl trimethoxy silane, 3-(methacryloxy) propyl tri ethoxysilane or 3-(methacryloxy) propyl methyl dimethoxy silane. Preferably, the silane coupling agent is 3-glycidyl ether oxy propyl trimethoxysilane. 3-glycidyl ether oxy propyl trimethoxysilane is a coupling agent containing epoxy groups, and a uniform organic film layer can be easily formed on the surface of the passivation layer of the invention, thereby further improving the anti-oxidation ability. At the same time, 3-glycidyl ether oxy propyl trimethoxysilane and has good wettability with the surface of passivation layer, and good bonding strength is obtained. In addition, the obtained silane coupling layer has good bonding strength with the laminate. In one embodiment, the method for preparing the silane coupling agent layer includes spraying 0. l-3wt% of silane coupling agent on the surface of the passivation layer. Preferably, the method for preparing the silane coupling agent layer comprises spraying 2wt% silane coupling agent on the surface of the passivation layer. The solvents of the electrolyte, the coarsening treatment fluid, the protective barrier fluid and the passivation treatment fluid are all water. In one embodiment, the water is deionized. The second aspect of the invention provides an application of the electrolytic copper clad in a high-density interconnected circuit board. Embodiments Hereinafter the invention will be described in more detail by embodiments, but it should be understood that these embodiments are only illustrative and not restrictive. Unless otherwise stated, the raw materials used in the following embodiments are all commercially available. Embodiment 1 Embodiment 1 of the invention provides the low-profde electrolytic copper clad for high-density interconnected circuit boards, which is sequentially composed of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent layer. The copper clad layer is obtained by electroanalysis in electrolyte containing copper ions; the electrolyte is 250 g / L copper salt, 70 g / L inorganic acid, 10 mg / L chloride salt and 1.5 mg / L leveling agent. The copper salt is copper sulfate pentahydrate, the inorganic acid is sulfuric acid, the chlorine salt is hydrochloric acid, the leveling agent is nonionic cellulose ether and leveling agent-1; the leveling agent-1 contains amino groups and carboxyl groups, the average molecular weight is 50,000-60,000, and the CAS is 9000-70-8, which is purchased fromDe LOCKE; the nonionic cellulose ether contains methoxy and hydroxyethyl, the content of methoxy is 22-30wt%, and the degree of substitution is 1.3-2.5; the hydroxyethyl content is 2.0-14wt%, the degree of substitution is 0.06-0.5, and the viscosity of 2wt% aqueous solution is 5-200,000 mps at 20°C; and the concentration ratio of the leveling agent-1 to nonionic cellulose ether is 2: 1. The method for preparing the copper clad layer comprises the following steps: (1) electrolyte preparation: uniformly mixing copper salt, inorganic acid, chloride salt and leveling agent in the electrolyte at 40°C, and placing in an electrolytic bath; (2) electrochemical reaction: applying direct current, precipitating copper clad from the cathode at the current density of 40 A / dm2, and peeling. The coarsening layer is obtained by electrolysis of the copper clad layer in the coarsening treatment solution. The coarsening treatment solution comprises 10 g / L copper sulfate, 50 g / L sulfuric acid and 1.2 g / L additive. The additives are sodium tungstate, titanium sulfate and tin sulfate and the concentration ratio of sodium tungstate, titanium sulfate and tin sulfate is 1: 7: 1. The method for preparing the coarsening layer comprises the following steps: (1) pickling: pickling the copper clad layer in pickling solution at 10°C for 20 s, wherein the pickling solution comprises 80 g / L copper sulfate and 50 g / L sulfuric acid; (2) electrolyzing the material obtained in step (1) at 25 °C and current density of 5 A / dm2 for 20 s to obtain the coarsening layer. The protective barrier layer is the nickel and zinc layer. The protective barrier layer is obtained by electroanalysis on the surface of the coarsening layer in the protective barrier fluid. The protective barrier fluid comprises 20 g / L sulfuric acid, 0.25 g / L Ni2+, 0.50 g / L Zn2+ and 50 mg / L protective barrier fluid additive. The protective barrier fluid additive is benzyl triethylammonium bromide. The method for preparing the protective barrier layer comprises the following step: electrolyzing the coarsening layer at 30°C and 2.0 A dm2 for 10 s. The passivation layer is obtained by electroanalysis on the surface of the protective barrier layer in passivation treatment fluid. The passivation fluid comprises 2.0 g / L Na2SO4, 0.2 g / L Zn2+ and 0.5 g / L CrOs. The method for preparing the passivation layer includes: electrolyzing the protective barrier layer at 30°C and 0.5 A / dm2 for 10 s. The method for preparing the silane coupling agent layer includes spraying 0.1 wt% of silane coupling agent on the surface of the passivation layer. The silane coupling agent is 3-glycidyl ether oxy propyl trimethoxysilane. Embodiment 2 Embodiment 2 of the invention provides the low-profile electrolytic copper clad for high-density interconnected circuit boards, which is sequentially composed of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent layer. The copper clad layer is obtained by electroanalysis in electrolyte containing copper ions; the electrolyte is 350 g / L copper salt, 150 g / L inorganic acid, 80 mg / L chloride salt and 45 mg / L leveling agent. The copper salt is copper sulfate pentahydrate, the inorganic acid is sulfuric acid, the chlorine salt is hydrochloric acid, the leveling agent is nonionic cellulose ether and leveling agent-1; the leveling agent-1 contains amino groups and carboxyl groups, the weightaverage molecular weight is 50,000-60,000, and the CAS is 9000-70-8, which is purchased from DE LOCKE DE LOCKE; the nonionic cellulose ether contains methoxy and hydroxyethyl, the content of methoxy is 22-30wt%, and the degree of substitution is 1.3-2.5; the hydroxyethyl content is 2.0-14wt%, the degree of substitution is 0.06-0.5, and the viscosity of 2wt% aqueous solution is 5-200,000 mps at 20°C; and the concentration ratio of the leveling agent-1 to nonionic cellulose ether is 5: 1. The method for preparing the copper clad layer comprises the following steps: (1) electrolyte preparation: uniformly mixing copper salt, inorganic acid, chloride salt and leveling agent in the electrolyte at 60°C, and placing in an electrolytic bath; (2) electrochemical reaction: applying direct current, precipitating copper clad from the cathode at the current density of 80 A / dm2, and peeling. The coarsening layer is obtained by electrolysis of the copper clad layer in the coarsening treatment solution. The coarsening treatment solution comprises 50 g / L copper sulfate, 150 g / L sulfuric acid and 40 g / L additive. The additives are sodium tungstate, titanium sulfate and tin sulfate and the concentration ratio of sodium tungstate, titanium sulfate and tin sulfate is 1: 10: 5. The method for preparing the coarsening layer comprises the following steps: (1) pickling: pickling the copper clad layer in pickling solution at 50 °C for 2 s, wherein the pickling solution comprises 250 g / L copper sulfate and 150 g / L sulfuric acid; (2) electrolyzing the material obtained m step (1) at 25 °C and current density of 10 A / dm2 for 2 s to obtain the coarsening layer. The protective barrier layer is the nickel and zinc layer. The protective barrier layer is obtained by electroanalysis on the surface of the coarsening layer in the protective barrier fluid. The protective barrier fluid comprises 100 g / L sulfuric acid, 2.0 g / L Ni2+, 5.00 g / L Zn2+ and 300 mg / L protective barrier fluid additive. The protective barrier fluid additive is benzyl triethylammonium bromide. The method for preparing the protective barrier layer comprises the following step: electrolyzing the coarsening layer at 60°C and 2.0 A / dm2 for 2 s. The passivation layer is obtained by electroanalysis on the surface of the protective barrier layer in passivation treatment fluid. The passivation fluid comprises 20 g / L Na2SO4, 3 g / L Zn2+ and 5 g / L CrO3. The method for preparing the passivation layer includes: electrolyzing the protective barrier layer at 60 °C and 5 A dm2 for 3 s. The method for preparing the silane coupling agent layer includes spraying 3wt% of silane coupling agent on the surface of the passivation layer. The silane coupling agent is 3-glycidyl ether oxy propyl trimethoxysilane. Embodiment 3 Embodiment 3 of the invention provides the low-profile electrolytic copper clad for high-density interconnected circuit boards, which is sequentially composed of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent layer. The copper clad layer is obtained by electroanalysis in electrolyte containing copper ions; the electrolyte is 320 g / L copper salt, 100 g / L inorganic acid, 20 mg / L chloride salt and 4.5 mg / L leveling agent. The copper salt is copper sulfate pentahydrate, the inorganic acid is sulfuric acid, the chlorine salt is hydrochloric acid, the leveling agent is nonionic cellulose ether and leveling agent-1; the leveling agent-1 contains amino groups and carboxyl groups, the weightaverage molecular weight is 50,000-60,000, and the CAS is 9000-70-8, which is purchased from DE LOCKE; the nonionic cellulose ether contains methoxy and hydroxyethyl, the content of methoxy is 22-30wt%, and the degree of substitution is 1.3-2.5; the hydroxyethyl content is 2.0-14wt%, the degree of substitution is 0.06-0.5, and the viscosity of 2wt% aqueous solution is 5-200,000 mps at 20°C; and the concentration ratio of the leveling agent-1 to nonionic cellulose ether is 3.5: 1. The method for preparing the copper clad layer comprises the following steps: (1) electrolyte preparation: uniformly mixing copper salt, inorganic acid, chloride salt and leveling agent in the electrolyte at 50°C, and placing in an electrolytic bath; (2) electrochemical reaction: applying direct current, precipitating copper clad from the cathode at the current density of 70 A / dm2, and peeling. The coarsening layer is obtained by electrolysis of the copper clad layer in the coarsening treatment solution. The coarsening treatment solution comprises 38 g / L copper sulfate, 75 g / L sulfuric acid and 2 g / L additive. The additives are sodium tungstate, titanium sulfate and tin sulfate and the concentration ratio of sodium tungstate, titanium sulfete and tin sulfate is 1: 8: 3. The method for preparing the coarsening layer comprises the following steps: (1) pickling: pickling the copper clad layer in pickling solution at 27°C for 10 s, wherein the pickling solution comprises 130 g / L copper sulfate and 80 g / L sulfuric acid; (2) electrolyzing the material obtained in step (1) at 25 °C and current density of 10 A / dm2 for 10 s to obtain the coarsening layer. The protective barrier layer is the nickel and zinc layer. The protective barrier layer is obtained by electroanalysis on the surface of the coarsening layer in the protective barrier fluid. The protective barrier fluid comprises 60 g / L sulfuric acid, 1 g / L Ni2+, 3 g / L Zn2+ and 150 mg / L protective barrier fluid additive. The protective barrier fluid additive is benzyl triethylammonium bromide. The method for preparing the protective barrier layer comprises the following step: electrolyzing the coarsening layer at 50°C and 1.5 A / dm2 for 8 s. The passivation layer is obtained by electroanalysis on the surface of the protective barrier layer in passivation treatment fluid. The passivation fluid comprises 15 g / L Na2SO4, 1.8 g / L Zn2+ and 3.2 g / L CrOs. The method for preparing the passivation layer includes: electrolyzing the protective barrier layer at 40°C and 3.2 A / dm2 for 8 s. The method for preparing the silane coupling agent layer includes spraying 2wt% of silane coupling agent on the surface of the passivation layer. The silane coupling agent is 3-glycidyl ether oxy propyl trimethoxysilane. Embodiment 4 Embodiment 4 of the invention provides the low-profile electrolytic copper clad for high-density interconnected circuit boards, the specific implementation of which is the same as that of Embodiment 3, except that the leveling agent is nonionic cellulose ether, which contains methoxy and hydroxy ethyl, the content of methoxy is 22-3 0wt%, and the degree of substitution is 1.3-2.5; the hydroxy ethyl content is 2.0-14wt%, the degree of substitution is 0.06-0.5, and the viscosity of 2wt% aqueous solution is 5-200,000 MPs at 20°C. The preparation methods of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent are the same as those in Embodiment 3. Embodiment 5 Embodiment 5 of the invention provides the low-profde electrolytic copper clad for high-density interconnected circuit boards, the specific implementation of which is the same as that of Embodiment 3. The difference is that the leveling agent is nonionic cellulose ether and leveling agent-1, and the nonionic soluble cellulose ether contains methoxy and hydroxy ethyl, which is purchased from Anhui Zhonghong Bioengineering Co., Ltd. with the article number of 123456; the leveling agent-1 contains amino groups and carboxyl groups, the weight-average molecular weight is 50,000-60,000, the CAS is 9,000-70-8, and the concentration ratio of the leveling agent-1 to nonionic cellulose ether is 3.5: 1. The preparation methods of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent are the same as those in Embodiment 3. Embodiment 6 Embodiment 6 of the invention provides the low-profile electrolytic copper clad for high-density interconnected circuit boards, the specific implementation of which is the same as that of Embodiment 3, except that the leveling agent is nonionic cellulose ether and leveling agent-1, the nonionic cellulose ether is hydroxy ethyl cellulose, the degree of substitution (D*S) is 1.8-2.0, and the viscosity of 2wt% aqueous solution is 30,000-40,000 mps, which is purchased from Jiekesite Biotechnology; the levelling agent-1 contains amino groups and carboxyl groups, the weight-average molecular weight is 50,000-60,000, and the CAS is 9000-70-8, which is purchased from DE LOCKE; the concentration ratio of the leveling agent-1 to nonionic cellulose ether is 3.5: 1. The preparation methods of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent are the same as those in Embodiment 3. Embodiment 7 Embodiment 7 of the invention provides the low-profde electrolytic copper clad for high-density interconnected circuit boards, the specific implementation of which is the same as that of Embodiment 3, except that the leveling agent is leveling agent-1, which contains amino groups and carboxyl groups, and the weight-average molecular weight is 50000-60000, and CAS is 9000-70-8. The preparation methods of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent are the same as those in Embodiment 3. Embodiment 8 Embodiment 8 of the invention provides the low-profile electrolytic copper clad for high-density interconnected circuit boards, and the specific implementation is the same as that of Embodiment 3, except that the concentration ratio of the leveling agent-1 to nonionic cellulose ether is 7: 1. The preparation methods of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent are the same as those in Embodiments. Embodiment 9 Embodiment 9 of the invention provides the low-profile electrolytic copper clad for high-density interconnected circuit boards, and its specific implementation is the same as that of Embodiment 3, except that the concentration ratio of the leveling agent-1 to nonionic cellulose ether is 0.8: 1. The preparation methods of the copper clad layer, the coarsening layer, the protective barrier layer, the passivation layer and the silane coupling agent are the same as those in Embodiments. Performance Evaluation 1. Weight per unit area: the weight per unit area of the copper clad layers obtained in Embodiments 1-9 is tested according to GB / T 5230-1995 standard, and each embodiment is tested for 10 times. The weight deviation per unit area is calculated out. The weight deviation per unit area is less than 3.0%, which is recorded as excellent; the weight deviation per unit area is 3-5.0%, which is recorded as good; and weight deviation per unit area is more than 5%, which is recorded as poor. 2. Roughness: the roughness of copper clad layers obtained in Embodiments 1-9 is tested according to GB / T 5230-1995 standard. The arithmetic mean deviation (Ra) of the profile and the ten-point mean height (Rz) of the microscopic roughness are tested, where Ra is the arithmetic mean of the absolute value of the profile deviation within the sampling length and Rz is the difference between the average of the five largest profile peak heights and the average of the five largest profile valley depths within the sampling length. Ra<0.15 pm is recorded as Grade I; Ra=0.15-0.3 pm, recorded as Grade II; and Ra>0.3 pm is recorded as Grade III. Rz<0.15 pm is recorded as Grade I; Rz=1.5-2.5 pm, recorded as Grade II; and Ra>0.3 pm is recorded as Grade III. 3. Tensile strength at normal temperature: the tensile strength of the copper clad layers obtained in Embodiments 1-9 is tested according to GB / T 5230-1995 standard at 25°C. Tensile strength^350 N / mm2 is recorded as qualified, and tensile strength <350 N / mm2 is recorded as unqualified. 4. Tensile strength at high temperature: tensile strength of the copper clad layer at high temperature obtained in Embodiments 1-9 at 200°C is tested according to GB / T 5230-1995 standard. The change rate of tensile strength is calculated, the change rate of tensile strength (%) = (tensile strength at normal temperature-tensile strength at high temperature) / normal temperature tensile strength *100%. The change rate of tensile strength <30% is recorded as Grade A, the change rate of tensile strength=30-50% is recorded as Grade B, and the change rate of tensile strength >50% is recorded as Grade C. Table 1 Embodi ment Weight deviation per unit area Ra Rz Tensile strength at normal temperature Tensile strength at high temperature 1 excellent Grade I Grade I qualified Grade A 2 excellent Grade I Grade I qualified Grade A 3 excellent Grade I Grade I qualified Grade A 4 good Grade II Grade II unqualified Grade C 5 good Grade II Grade II unqualified Grade B 6 good Grade II Grade III unqualified Grade B 7 poor Grade III Grade III unqualified Grade C 8 poor Grade II Grade III unqualified Grade C 9 poor Grade II Grade II unqualified Grade C The foregoing embodiments are only illustrative and are used to exp ain some features of the method of the invention. The appended claims are intended to claim the widest possible range imaginable, and the embodiments presented herein are only illustrative of the selected embodiments according to the combination of all possible embodiments. Therefore, it is the intention of the applicant that the appended claims are not limited by the choice of embodiments illustrating the features of the invention. Some numerical ranges used in the claims also include subranges within them, and changes in these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A low-profile electrolytic copper clad, characterized in that it sequentially comprises a copper clad layer, a coarsening layer, a protective barrier layer, a passivation layer and a silane coupling agent layer; the thickness of the copper clad layer is 6-35 pm, the weight per unit area is 50-305 g / m2, the weight deviation per unit area is less than 5%, the tensile strength at 25 °C is more than or equal to 350 N / mm2, the elongation at 25 °C is more than or equal to 4%, the peeling strength is more than or equal to 0.7 kg / cm, the smooth surface Ra is less than or equal to 0.43 pm, and the rough surface RZ is less than or equal to 3.5 pm.

2. The low-profile electrolytic copper clad according to claim 1, wherein the copper clad layer is obtained by electroanalysis in an electrolyte containing copper ions; the electrolyte comprises 250-350 g / L copper salt, 70-150 g / L inorganic acid, 10-80 mg / L chloride salt and 1.5-45 mg / L leveling agent.

3. The low- profile electrolytic copper clad according to claim 2, wherein the leveling agent comprises nonionic cellulose ether and leveling agent-1, and the leveling agent-1 contains amino groups and carboxyl groups.

4. The low-profile electrolytic copper clad according to claim 3, wherein the nonionic cellulose ether contains methoxy, the content of the methoxy is 22-3 0wt%, and the degree of substitution is 1.3-2.5.

5. The low-profile electrolytic copper clad according to claim 4, wherein the nonionic cellulose ether further contains hydroxyethyl, the content of hydroxy ethyl is 2.0-14wt%, and the degree of substitution is 0.06-0.5.

6. The low- profile electrolytic copper clad according to claim 3, wherein the weightaverage molecular weight of the leveling agent-1 is 50,000-60,000.

7. The low-profile electrolytic copper clad according to any one of claims 3-6, wherein the concentration ratio of the nonionic cellulose ether to the leveling agent-1 is 1: (2-5).

8. The low-profile electrolytic copper clad according to any one of claims 3-6, wherein the protective barrier material is one or more of nickel, titanium, tin, tungsten, molybdenum and zinc.

9. The low-profile electrolytic copper clad according to any one of claims 3-6, wherein the silane coupling agent layer material is a silane coupling agent selected from one or more of 3-glycidyl ether oxy propyl trimethoxy silane, 3-aminopropyl tri ethoxysilane, vinyl triethoxysilane, vinyl trimethoxysilane, vinyl tri (P-methoxy ethoxy) silane, vinyl benzyl aminoethyl aminopropyl trimethoxysilane and 3-(methacryloxy) propyl trimethoxysilane, 3- (methacryloxy) propyl triethoxysilane or 3-(methacryloxy) propyl methyl dimethoxy silane.

10. An application of the low-profile electrolytic copper clad according to any one of claims 1 -9 in high-density interconnection circuit boards.