Resistance-embedded metal foil and protection method thereof

Abstract

The invention relates to a buried resistor metal foil and a protection method thereof. The buried resistor metal foil sequentially comprises a conductive layer, a resistive layer, a passivation layer and a protection layer, the buried resistance metal foil is provided with the passivation layer through a chemical reaction, and the protection layer is arranged through a coating, electroplating or physical vapor deposition method. Through the arrangement of the passivation layer and the protection layer, the corrosion resistance and the mechanical damage resistance of the buried resistance metal foil are effectively enhanced through double guarantee, the resistance fluctuation of the buried resistance metal foil is reduced, and the service life of the buried resistance metal foil is prolonged; wherein the protective layer can be removed without damage through a physical or chemical method before PCB processing, and a stable, precise and low-fluctuation buried resistance metal foil is provided for the PCB.

Description

Technical Field

[0001] The invention belongs to the technical field of printed circuit boards, and in particular relates to a buried barrier metal foil and a protection method thereof. Background Art

[0002] With the advancement of society, today's electronic products are rapidly developing towards miniaturization and higher quality. Resistors, as a common component, occupy a significant amount of PCB panel space. Embedded metal foil allows the resistor to be integrated onto the metal foil, reducing the space occupied by the resistor, eliminating the need for extensive soldering, and minimizing external influences on the resistor. Furthermore, with high-frequency and high-speed digital signal transmission, parasitic effects can cause the characteristic impedance of chip resistors to vary by up to 40%. However, signal transmission has little effect on the characteristic impedance of embedded resistors.

[0003] Currently, embedded resistor manufacturing technologies are primarily categorized into five categories: 1. Etched metal film resistor technology; 2. Screen-printed thick film resistor technology; 3. Spray-coated ink resistor technology; 4. Electroplated metal film resistor technology; and 5. Sputtered metal film resistor technology. The resistor films produced by these embedded resistor manufacturing technologies are generally in roll or sheet form. However, both roll and sheet forms undergo cutting and other operations during processing, which can scratch the resistor film, severely damaging the embedded resistor layer and causing uncontrollable deviations between the designed resistance value and the actual resistance value in the subsequent graphical resistance design step of the embedded resistor metal foil. For example, patent CN117684229A merely washes and then dries the electroplated embedded copper foil, lacking protective measures for the embedded copper foil. Another example is patent CN116367407A, which employs chromate coating on the resistor layer to enhance the rust and corrosion resistance of the embedded metal foil. However, this carries the risk of impacting the product's electrical performance, resistance volatility, and signal transmission capabilities. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a buried barrier metal foil and a protection method thereof, which effectively enhances the corrosion resistance and mechanical damage resistance of the buried barrier metal foil and reduces the resistance fluctuation of the buried barrier metal foil, thereby extending the service life of the buried barrier metal foil.

[0005] The present invention provides a buried barrier metal foil, which comprises a conductive layer, a resistor layer, a passivation layer and a protective layer in sequence; the buried barrier metal foil is used to set the passivation layer by chemical reaction, and is used to set the protective layer by coating, electroplating or physical vapor deposition.

[0006] Preferably, the resistivity of the resistance layer is 58 to 580 times that of the conductive layer; the ratio of the roughness of the resistance layer to the roughness of the conductive layer is 0.8 to 1.2; and the texture aspect ratio of the conductive layer to the resistance layer is 0.5 to 1.

[0007] Preferably, the conductive layer comprises one or more alloys of copper, aluminum, gold, iron, and silver.

[0008] Preferably, the resistance layer material includes any one of nickel, chromium, platinum, palladium, titanium, aluminum, silicon, molybdenum, manganese, thallium, tungsten, iron, and phosphorus, or an alloy of at least two of nickel, chromium, platinum, palladium, titanium, aluminum, silicon, molybdenum, manganese, thallium, tungsten, iron, and phosphorus.

[0009] Preferably, the passivation solution used in the passivation layer includes one or more of nitric acid, sulfuric acid, phosphoric acid, citric acid, and chromic acid. In addition to the relevant strong acid solution, a strong oxidant such as hydrogen peroxide or potassium permanganate may also be added to the passivation solution depending on the characteristics of the resistor layer.

[0010] Preferably, the protective layer comprises one of titanium and its alloys, polyimide coating, silicone coating, and silver.

[0011] Preferably, the thickness of the resistance layer is between 50 nm and 2000 nm; the thickness of the passivation layer is between 2 nm and 20 nm; and the thickness of the protective layer is between 50 nm and 20 μm.

[0012] Preferably, the resistance layer is prepared by one of vacuum evaporation, sputtering, chemical vapor deposition, sol-gel, slit coating, electroplating, spraying, and gas adsorption.

[0013] Preferably, the protective layer can be removed by an etching solution, and the etching solution is classified into one of acetone etching solution, isopropyl alcohol etching solution, zinc chloride and ammonium chloride mixed etching solution, and silver nitrate etching solution according to the type of the protective layer.

[0014] The present invention also provides a method for protecting a buried barrier metal foil, comprising the following steps: S1: Use dilute nitric acid solution to clean the surface of the buried metal foil resistor layer to remove oxides and contaminants, and then rinse with clean water to remove acid residue; S2: placing the buried metal foil in step S1 in a passivation solution to form a passivation layer on the surface of the resistor layer; S3: preparing a protective layer on the surface of the buried metal foil resistor layer forming the passivation layer to obtain a buried metal foil.

[0015] Preferably, the concentration of the dilute nitric acid in step S1 is in the range of 0.5 mol / L to 6 mol / L.

[0016] Beneficial effects The present invention provides a passivation layer and a protective layer to provide dual protection, thereby effectively enhancing the corrosion resistance and mechanical damage resistance of the buried barrier metal foil, reducing the resistance fluctuation of the buried barrier metal foil, and extending the service life of the buried barrier metal foil. The protective layer can be removed without damage by physical or chemical methods before PCB processing, providing a stable, precise, and low-fluctuation buried barrier metal foil for the PCB. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of the buried metal foil of the present invention; wherein, 101 is a conductive layer, 201 is a first resistance layer, 202 is a second resistance layer, 301 is a passivation layer, and 401 is a protective layer.

[0018] Figure 2 The flowchart of the protection method of the buried barrier metal foil of the present invention is shown. DETAILED DESCRIPTION

[0019] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0020] Depend on Figure 1 As shown, the present invention provides a buried metal foil, which includes a conductive layer, a resistance layer, a passivation layer and a protective layer in sequence.

[0021] Specifically, the conductive layer includes one or more alloys of copper, aluminum, gold, iron, and silver.

[0022] Specifically, the resistivity of the resistor layer is 58 to 580 times that of the conductive layer. The first and second resistor layers may be collectively referred to as resistor layer 200. However, it should be noted that, depending on specific requirements, the resistivities of the first and second resistor layers may be the same or different. The roughness of the first resistor layer is similar to that of the second resistor layer. Because the resistor layer is thinner than the conductive layer, the roughness Rz of the resistor layer is similar to that of the conductive layer.

[0023] Specifically, the Str (texture aspect ratio) of the conductive layer and the resistive layer is between 0.5 and 1. The texture aspect ratio represents the degree of isotropy of the roughness particles that cause the roughness variation. An Str value less than 0.3 indicates an anisotropic distribution of the roughness particles. In the present invention, the Str value range is between 0.5 and 1, indicating that the roughness particles are isotropic. Preferably, the isotropy is perpendicular to the conductive layer.

[0024] Specifically, the thickness of the passivation layer is between 2nm and 20nm. Preferably, nickel-chromium material is used as the material of the resistance layer 200 of the buried metal foil. Most of the nickel-chromium alloy is FCC structure, which ensures the uniformity of the alloy. The passivation layer is obtained by the reaction of a strong acidic solution with the resistance layer material. During the acid passivation process, an acidic solution is used to remove pollutants, impurities, slight oxides and intermediate corrosion products on the metal surface to purify the metal surface. After cleaning, the nickel and chromium react with oxygen in an acidic environment to form a layer containing Cr2O3 and NiO X The passive film is formed spontaneously and self-healing, effectively preventing the penetration of oxygen and corrosive media from the external environment. Prolonged acid treatment or proper adjustment of acid treatment conditions (such as temperature, time, and concentration) can enhance the stability and thickness of the protective film, thereby further improving the corrosion resistance of the material.

[0025] Specifically, the protective layer includes: any one of titanium and its alloys, polyimide coating, silicone coating, and silver. It should be noted that the protective layer can be removed by etching or physical means depending on its type. Furthermore, the titanium alloy can be deposited on the passivation layer by electroplating or sputtering, which can well protect the buried metal foil. The process of etching titanium with a mixture of zinc chloride and ammonium chloride mainly relies on the corrosion effect caused by chemical reactions and complexation. In the mixed solution, ammonium chloride can decompose to produce hydrochloric acid, and the generated ammonium chloride is an active ingredient. Zinc chloride provides stable zinc ions in the solution, usually helps to stabilize the generated chloride and may participate in the corrosion process under certain conditions. Hydrochloric acid then reacts with the titanium alloy to generate titanium chloride, causing titanium to dissolve. The entire protective layer removal process is accompanied by the complexation of ammonia, which increases solubility while ensuring the continued dissolution of titanium, NH 4+ and Zn 2+ It also participates in the reaction of complexing titanium ions, maintaining the dissolution process until the titanium is completely dissolved. Similarly, when polyimide is used as a protective layer, it can be dissolved and removed using a strong acid solution (such as hydrochloric acid, nitric acid, or sulfuric acid). Alternatively, it can be decomposed and removed using high temperatures. Similarly, when a silicone coating is used as a protective layer, it can be dissolved and removed using acetone or isopropyl alcohol. Alternatively, physical heat treatment can be used to remove the protective layer. Similarly, when silver is used as a protective layer, an ammonia complex formed by silver nitrate and water can be used as an etching solution, along with a mixture of potassium ferricyanide and hydrochloric acid. Optionally, plasma etching, using oxygen or chlorine plasma, can completely remove the silver protective layer, providing the PCB with a mechanically damage-free, low-resistance buried metal foil.

[0026] Example 1 This embodiment provides a buried metal foil, which includes a conductive layer, a resistance layer, a passivation layer and a protective layer in sequence.

[0027] The resistivity of the resistive layer is 465 times that of the conductive layer.

[0028] The ratio of the roughness of the resistive layer to the roughness of the conductive layer is 1.1.

[0029] The material of the resistance layer is nickel-chromium alloy.

[0030] The Str (texture aspect ratio) of the conductive layer and the resistive layer is 0.9.

[0031] The thickness of the resistance layer is 160 nm.

[0032] The thickness of the passivation layer is 5 nm.

[0033] The resistance layer is prepared by sputtering; the sputtering power is 4.2Kw; the background vacuum is 1.5*10 -3 Pa; the coating vacuum degree is 0.3Pa; the ventilation volume is 150sccm.

[0034] This embodiment also provides a method for protecting a buried metal foil, the specific steps of which include: S1: Surface pretreatment of buried metal foil: Use dilute nitric acid solution to clean the surface of the resistor layer to remove oxides and contaminants, and then rinse with clean water to remove acid residues; S2: Passivation treatment: Place the copper foil in step S1 in the passivation solution; S3: Preparing a protective layer: Preparing a protective layer on the resistive layer of the passivated copper foil; S4: Protective layer removal treatment: Use physical methods or relevant etching solutions to etch away the protective layer.

[0035] The concentration of dilute nitric acid in step S1 is 1 mol / L.

[0036] The passivation solution in step S2 is sulfuric acid passivation solution with a concentration of 3 mol / L.

[0037] The protective layer is made of titanium metal; the thickness of the protective layer is 200nm, and the titanium is plated by thermal evaporation process, wherein the background vacuum is 5*10 -4 Pa, the deposition rate was 10Å / S, the substrate temperature was 500°C, and the evaporation distance was 40cm.

[0038] The protective layer is etched with a mixed solution of zinc chloride and ammonium chloride, wherein the concentration of ammonium chloride is 1.5 mol / L, the concentration of zinc chloride is 2 mol / L, the balance is pure water, and the etching temperature is 50±10°C.

[0039] The titanium protective layer offers excellent lightweighting, aesthetics, high-temperature resistance, mechanical abrasion resistance, and corrosion resistance, protecting the buried barrier foil from mechanical damage during transportation. Furthermore, the subsequent vacuum evaporation of titanium in the roll-to-roll production process only takes an additional 200 seconds, virtually impacting production capacity. This method provides high-quality, low-resistance, and mechanically damage-free buried barrier foil for the PCB.

[0040] Example 2 This embodiment provides a buried metal foil, which includes a conductive layer, a resistance layer, a passivation layer and a protective layer in sequence.

[0041] The resistivity of the resistive layer is 465 times that of the conductive layer.

[0042] The ratio of the roughness of the resistive layer to the roughness of the conductive layer is 1.1.

[0043] The material of the resistance layer is nickel-chromium alloy.

[0044] The Str (texture aspect ratio) of the conductive layer and the resistive layer is 0.9.

[0045] The thickness of the resistance layer is 160 nm.

[0046] The thickness of the passivation layer is 5 nm.

[0047] The resistance layer is prepared by sputtering. The sputtering power is 4.2Kw; the background vacuum is 1.5*10 -3 Pa; the coating vacuum degree is 0.3Pa; the ventilation volume is 150sccm.

[0048] This embodiment also provides a method for protecting a buried metal foil, the specific steps of which include: S1: Surface pretreatment of buried metal foil: Use dilute nitric acid solution to clean the surface of the resistor layer to remove oxides and contaminants, and then rinse with clean water to remove acid residues; S2: Passivation treatment: Place the copper foil in step S1 in the passivation solution; S3: Preparing a protective layer: Preparing a protective layer on the resistive layer of the passivated copper foil; S4: Protective layer removal treatment: Use physical methods or relevant etching solutions to etch away the protective layer.

[0049] The concentration of dilute nitric acid in step S1 is 1 mol / L; The passivation solution in step S2 is sulfuric acid passivation solution with a concentration of 3 mol / L; The protective layer is a polyimide coating with a thickness of 2 μm. It can be completely removed using 95% concentrated sulfuric acid at a reaction temperature of 160°C in 5 minutes. Alternatively, the polyimide protective layer can be completely removed by heating the buried metal foil at 300°C for 1 minute and then randomly tearing off the polyimide protective layer.

[0050] The polyimide protective layer has excellent mechanical properties, electrical insulation, radiation resistance, and environmental tolerance, and can effectively protect the buried metal foil. This method can provide high-quality, low-resistance fluctuation, and mechanically damage-free buried metal foil for the PCB end.

[0051] Example 3 This embodiment provides a buried metal foil, which includes a conductive layer, a resistance layer, a passivation layer and a protective layer in sequence.

[0052] The resistivity of the resistive layer is 465 times that of the conductive layer.

[0053] The ratio of the roughness of the resistive layer to the roughness of the conductive layer is 1.1.

[0054] The material of the resistance layer is nickel-chromium alloy.

[0055] The Str (texture aspect ratio) of the conductive layer and the resistive layer is 0.9.

[0056] The thickness of the resistance layer is 160 nm.

[0057] The thickness of the passivation layer is 5 nm.

[0058] The resistance layer is prepared by sputtering. The sputtering power is 4.2Kw; the background vacuum is 1.5*10 -3 Pa; the coating vacuum degree is 0.3Pa; the ventilation volume is 150sccm.

[0059] This embodiment also provides a method for protecting a buried metal foil, the specific steps of which include: S1: Surface pretreatment of buried metal foil: Use dilute nitric acid solution to clean the surface of the resistor layer to remove oxides and contaminants, and then rinse with clean water to remove acid residues; S2: Passivation treatment: Place the copper foil in step S1 in the passivation solution; S3: Preparing a protective layer: Preparing a protective layer on the resistive layer of the passivated copper foil; S4: Protective layer removal treatment: Use physical methods or relevant etching solutions to etch away the protective layer.

[0060] The concentration of dilute nitric acid in step S1 is 1 mol / L.

[0061] The passivation solution in step S2 is sulfuric acid passivation solution with a concentration of 3 mol / L.

[0062] The protective layer is a silicone coating. Polydimethylsiloxane (PDMS) is dissolved in cyclohexane at a 1:1 volume ratio. The embedded metal foil is immersed in the prepared solution and cured at room temperature for 2 minutes. If the embedded metal foil needs to be processed after transportation, the protective layer can be completely removed by dissolving it with 99.5% pure acetone or heating it at 350°C.

[0063] Silicone coating has excellent electrical insulation, good ductility, UV resistance, aging resistance, water resistance, and easy preparation. This method can provide high-quality, low-resistance fluctuation, and mechanically damage-free buried metal foil for the PCB end.

[0064] Example 4 This embodiment provides a buried metal foil, which includes a conductive layer, a resistance layer, a passivation layer and a protective layer in sequence.

[0065] The resistivity of the resistive layer is 465 times that of the conductive layer.

[0066] The ratio of the roughness of the resistive layer to the roughness of the conductive layer is 1.1.

[0067] The material of the resistance layer is nickel-chromium alloy.

[0068] The Str (texture aspect ratio) of the conductive layer and the resistive layer is 0.9.

[0069] The thickness of the resistance layer is 160 nm.

[0070] The thickness of the passivation layer is 5 nm.

[0071] The resistance layer is prepared by sputtering. The sputtering power is 4.2Kw; the background vacuum is 1.5*10 -3 Pa; the coating vacuum degree is 0.3Pa; the ventilation volume is 150sccm.

[0072] This embodiment also provides a method for protecting a buried metal foil, the specific steps of which include: S1: Surface pretreatment of buried metal foil: Use dilute nitric acid solution to clean the surface of the resistor layer to remove oxides and contaminants, and then rinse with clean water to remove acid residues; S2: Passivation treatment: Place the copper foil in step S1 in the passivation solution; S3: Preparing a protective layer: Preparing a protective layer on the resistive layer of the passivated copper foil; S4: Protective layer removal treatment: Use physical methods or relevant etching solutions to etch away the protective layer.

[0073] The concentration of dilute nitric acid in step S1 is 1 mol / L.

[0074] The passivation solution in step S2 is sulfuric acid passivation solution with a concentration of 3 mol / L.

[0075] The protective layer is metallic silver.

[0076] Optionally, the protective layer is made of electroplated silver, using 50g / L silver nitrate solution to provide silver ions, 100g / L sodium sulfate as a conductive salt, pH maintained between 4-6, electrolyte temperature at 45°C, and buried metal foil as the cathode to deposit a 1um silver protective layer. Alternatively, the protective layer is made of vacuum evaporation with a background vacuum of 5*10 -4 Pa, the deposition rate is 20Å / S, the substrate temperature is 960℃, and the evaporation distance is 40cm to deposit a 1um metallic silver protective layer.

[0077] The metallic silver protective layer has excellent ductility, aesthetics, conductivity, corrosion resistance, and resistance to mechanical damage. This method can provide the PCB end with high-quality, low-resistance fluctuation, and mechanically damage-free buried metal foil.

[0078] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the embodiments of the present invention are not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the embodiments of the present invention. Therefore, although the embodiments of the present invention are described in more detail through the above embodiments, the embodiments of the present invention are not limited to the above embodiments. Without departing from the concept of the embodiments of the present invention, the embodiments of the present invention may also include more other equivalent embodiments, and the scope of the embodiments of the present invention is determined by the scope of the appended claims.

Claims

1. A buried barrier metal foil, characterized in that: It comprises a conductive layer, a resistance layer, a passivation layer and a protective layer in sequence; the buried metal foil is used to form the passivation layer by chemical reaction, and is used to form the protective layer by coating, electroplating or physical vapor deposition.

2. The buried barrier metal foil according to claim 1, wherein: The resistivity of the resistance layer is 58 to 580 times that of the conductive layer; the ratio of the roughness of the resistance layer to the roughness of the conductive layer is 0.8 to 1.2; and the texture aspect ratio of the conductive layer to the resistance layer is 0.5 to 1.

3. The buried barrier metal foil according to claim 1, wherein: The conductive layer includes one or more alloys of copper, aluminum, gold, iron, and silver.

4. The buried barrier metal foil according to claim 1, wherein: The material of the resistance layer includes any one of nickel, chromium, platinum, palladium, titanium, aluminum, silicon, molybdenum, manganese, thallium, tungsten, iron, and phosphorus, or an alloy of at least two of nickel, chromium, platinum, palladium, titanium, aluminum, silicon, molybdenum, manganese, thallium, tungsten, iron, and phosphorus.

5. The buried barrier metal foil according to claim 1, wherein: The passivation solution used in the passivation layer includes one or more of nitric acid passivation solution, sulfuric acid passivation solution, phosphoric acid passivation solution, citric acid passivation solution, and chromic acid passivation solution.

6. The buried barrier metal foil according to claim 1, wherein: The protective layer comprises one of titanium and its alloys, polyimide coating, organic silicon coating and silver.

7. A method for protecting a buried metal foil, comprising the following steps: S1: Use dilute nitric acid solution to clean the surface of the buried metal foil resistor layer to remove oxides and contaminants, and then rinse with clean water to remove acid residue; S2: placing the buried metal foil in step S1 in a passivation solution to form a passivation layer on the surface of the resistor layer; S3: preparing a protective layer on the surface of the buried metal foil resistor layer forming the passivation layer to obtain a buried metal foil.

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