Method for preparing buried copper foil with low temperature coefficient of resistance

Abstract

The present invention discloses a method for preparing buried copper foil with low resistance temperature coefficient, which belongs to the technical field of buried copper foil and solves the problem that the existing technology cannot prepare buried copper foil with low resistance temperature coefficient and small resistance fluctuation and resistivity greater than 9×10 ‑4 The method addresses the problem of buried copper foil products. The method includes four steps: preparing a raw foil layer, preparing a surface treatment layer, reactively sputtering a resistor layer, and magnetron sputtering an anti-oxidation layer. The buried copper foil products produced using this method have the following advantages: a high resistivity of the resistor layer, achieving a higher square resistance value at the same resistor layer thickness; a low temperature coefficient of resistance (TCR) and good thermal stability; and a uniform and dense resistor layer, which can control the square resistance value tolerance within 3%. Compared to existing products on the market, this method offers significant advantages and has greater application prospects and commercial value.

Description

Technical Field

[0001] The invention belongs to the technical field of buried barrier copper foil, and in particular relates to a method for preparing a buried barrier copper foil with a low temperature coefficient of resistance. Background Art

[0002] With the rapid development of the electronic information industry, printed circuit boards (PCBs) are developing towards high density, multi-layer, easy packaging and miniaturization. Considering the reliability of PCB assembly, the stability of resistor devices and electrical performance, the embedding of resistor devices is very necessary. The emergence of embedded copper foil has solved this problem well.

[0003] On the one hand, due to the influence of the printed circuit board (PCB) processing process, the buried copper foil needs to have excellent resistance stability and reliability. The key lies in how to reduce the material's resistance temperature coefficient and reduce the tolerance range of resistance fluctuation. In the existing technology, because the buried copper foil is a new material, it is still limited to the research stage and mass production is limited. Some universities and research institutes use metal and non-metal doping to electro-deposit the resistor layer material in order to reduce the material's resistance temperature coefficient and reduce the tolerance range of resistance fluctuation. However, its disadvantages are:

[0004] ①The dispersion uniformity of metal materials in the electrolyte is difficult to control;

[0005] ②The uniformity of metal material after electrodeposition onto the copper foil surface is more difficult to control.

[0006] This results in a situation where one thing is sacrificed for another. Although the material's temperature coefficient of resistance is reduced, the tolerance range of resistance fluctuation becomes larger.

[0007] On the other hand, the downstream demand for the square resistance of buried copper foil covers 25Ω / □, 50Ω / □, 100Ω / □, 250Ω / □ and 1000Ω / □. According to the development trend, the square resistance value may be even higher in the future. The resistivity of the resistor layer is high, and a higher square resistance value can be obtained at the same thickness of the resistor layer. Conversely, according to the formula Rs=ρ / d, the higher the resistivity of the resistor layer, the thicker the resistor layer thickness is under the same square resistance value, which can reduce the downstream processing difficulty and improve the machinability of the material. In the existing technology, the maximum resistivity of similar products is 6-8×10 -4 The resistivity is greater than 9×10 -4 The adaptation of buried copper foil to downstream processes has always been a problem that has plagued the industry.

[0008] The reason is that it is impossible to break through the resistivity greater than 9×10 -4 This is because some domestic research basically uses water electroplating to prepare the buried barrier layer. This electroplating method has the following problems:

[0009] ① Due to the properties of materials with high resistivity, the current density distribution in the plating solution will be uneven, the tank voltage requirement will be high, and the side reactions will be aggravated, making it difficult to electroplate efficiently and with high quality. Materials with high resistivity cannot be electroplated;

[0010] ② The method of dispersing dopants in the plating solution. On the one hand, the dopants are not dispersed evenly in the plating solution. On the other hand, the uniformity of the distribution of the electroplated metal in the film layer after being deposited on the surface of the copper foil is also affected, which ultimately affects the stability and consistency of the product.

[0011] Regarding the above two technical problems, there is currently a lack of an effective method for preparing buried copper foil with low resistance temperature coefficient that can simultaneously overcome the two problems. Therefore, researchers have proposed a method for preparing buried copper foil with low resistance temperature coefficient. Summary of the Invention

[0012] The purpose of the present invention is to provide a method for preparing buried copper foil with low resistance temperature coefficient, so as to solve the problem that the existing technology cannot prepare buried copper foil with low resistance temperature coefficient and small resistance fluctuation and resistivity greater than 9×10 -4 The problem of buried copper foil products.

[0013] In order to solve the above problems, the technical solution of the present invention is:

[0014] A method for preparing a buried copper foil with a low temperature coefficient of resistance, the method comprising the following steps:

[0015] S1. Preparing a raw foil layer;

[0016] According to the existing technology, green foil is prepared by electrochemical deposition using a green foil machine, and green foil with qualified physical properties is obtained by adjusting the speed of the green foil machine, the current density, and the composition of the electroplating solution;

[0017] S2. Preparation of surface treatment layer;

[0018] According to the existing technology, the raw foil is roughened and non-copper metal is electroplated in a surface treatment machine to form a surface treatment layer on the basis of the raw foil layer, which is the finished foil.

[0019] S3. Reactive sputtering resistor layer;

[0020] S3.1 Preprocessing;

[0021] First, an ion source is used to bombard the treated surface of the finished foil with ions. The pretreatment effect is controlled by adjusting the ion source and its power, the working gas and its filling volume, and the treatment time to clean the surface of the finished foil.

[0022] S3.2 Preparation of the resistor layer using vacuum reactive sputtering coating technology;

[0023] Through vacuum reactive sputtering coating technology, the resistor material is deposited in the form of a compound on the surface of the pre-treated finished foil. The thickness and composition of the resistor layer can be controlled by adjusting the target material, coating power, reactive gas and its filling volume.

[0024] This step obtains a resistance layer on the basis of the surface treatment layer;

[0025] S4. Magnetron sputtering anti-oxidation layer;

[0026] Through vacuum magnetron sputtering coating technology, anti-oxidation material is deposited on the surface of copper foil after sputtering resistor material. The thickness of the anti-oxidation layer can be controlled by adjusting the target material, coating power, working gas and its filling volume.

[0027] This step obtains an anti-oxidation layer on the basis of the resistance layer;

[0028] Finally, the buried copper foil product is obtained.

[0029] Furthermore, in step S3.1, the ion source is one of an anode layer ion source, a Hall ion source, a Kaufman ion source, an ICP ion source, and a pulse bias ion source;

[0030] Set processing power 0.5-10KW;

[0031] The working gas is one or more of argon, nitrogen, oxygen, nitrous oxide, carbon dioxide, carbon monoxide and hydrogen;

[0032] The working gas flow rate is 50-500sccm;

[0033] The processing time is 1-10 minutes.

[0034] Furthermore, in step S3.2, the target material is a nickel-chromium alloy target with a mass ratio greater than 5:5;

[0035] Coating power is 1-15KW;

[0036] The reaction gas and the charging amount are:

[0037] The argon filling amount is 100-300 sccm, with a purity of 99.99%; the oxygen filling amount is 0-200 sccm, with a purity of 99.99%; the nitrogen filling amount is 0-200 sccm, with a purity of 99.99%;

[0038] The film thickness is 20-500nm.

[0039] Furthermore, in step S4, the target material is a titanium target or a chromium target with a purity greater than 99.99%;

[0040] Coating power is 1-15KW;

[0041] The working gas is one of the inert gases helium, neon, and argon;

[0042] The working gas charge is 100-300 sccm; the purity is 99.99%;

[0043] The film thickness is 5-100nm.

[0044] Furthermore, in step S1 , the raw foil is one of HTE series raw foil, RTF series raw foil, VLP series raw foil, or HVLP series raw foil.

[0045] Furthermore, in step S1, the foil machine has a speed of 1-10 m / min and a current density of 10-100 A / dm 2 .

[0046] Furthermore, in step S1, the properties of the raw foil are as follows:

[0047] Thickness 4.5-130μm, roughness Rz0.4-10μm, surface density 40-1200g / m 2 , tensile strength 200-800Mpa and elongation 1-20%.

[0048] Furthermore, in step S2, the properties of the finished foil are as follows:

[0049] The thickness of the finished foil is 4.5-130μm, the roughness Rz is 0.4-10μm, and the surface density is 40-1200g / m 2 , tensile strength is 200-800Mpa, and elongation is 1-20%.

[0050] Furthermore, in step S2, the finished foil is one of HTE series raw foil, RTF series raw foil, VLP series raw foil, or HVLP series raw foil.

[0051] Furthermore, in step S2, the vehicle speed, the current density index of each link, and the composition of the electroplating solution are controlled to ensure that the finished foil with qualified performance is obtained, wherein: the vehicle speed is 5-40m / min, the roughening current density is 10-40A / dm 2 , curing current density is 10-40A / dm 2 , blackening current density is 0.1-10A / dm 2 , ashing current density is 0.1-10A / dm 2 , passivation current density is 0.1-10A / dm 2 .

[0052] The beneficial effects of the present invention are as follows:

[0053] 1. In the method of the present invention, the raw foil categories applicable to S1 include raw foil categories of almost all production fields, such as HTE series raw foil, RTF series raw foil, VLP series raw foil, or HVLP series raw foil. The finished foil in S2 is limited to a thickness of 4.5-130μm, a roughness Rz of 0.4-10μm, and an area density of 40-1200g / m 2 , tensile strength 200-800Mpa, elongation 1-20%, almost covering all finished foil categories in the circulation field, that is, there is almost no special restriction on "raw materials", and it has a very wide range of applications and industrialization prospects.

[0054] In the present invention S3, a vacuum reactive sputtering coating technology is creatively used to prepare a resistance layer on the treated surface of the finished copper foil, which is different from the water electroplating and vacuum magnetron sputtering methods in the prior art:

[0055] In the traditional field of water electroplating, high resistivity of the plating solution means poor ion conductivity, uneven current density distribution during metal reduction deposition, and poor quality of the deposited film. Moreover, as the electroplating voltage requirement increases, excessively high voltage will lead to electrolyte decomposition and other side reactions, affecting deposition efficiency, metal layer properties, and film adhesion. This makes it difficult to electroplate materials with high resistivity efficiently and with high quality. -4 A technological breakthrough has been achieved in the field of buried barrier copper foil.

[0056] The film quality produced by vacuum magnetron sputtering is better than that of traditional water electroplating, and the thickness and composition can be more precisely controlled. However, high-resistivity targets are also not suitable for this purpose because poorly conductive targets affect the electron transmission of the entire circuit, making it difficult to generate glow discharge.

[0057] The pretreatment step of the present invention cleans the surface of the finished foil through ion bombardment to prevent impurities from affecting the adhesion and uniformity of the final film layer; the ion source power specified in this step can ensure that the surface of the copper foil substrate is effectively cleaned without causing irreversible damage to the substrate; and the flow rate of oxygen is limited to ensure that it can activate the surface of the copper foil substrate, form active functional groups, and enhance the adhesion or bonding force between the subsequent resistor layer and the copper foil substrate. On this basis, vacuum reactive sputtering combines the advantages of physical vapor deposition and chemical reactions, so that the various metal elements sputtered out react chemically with each other or with the reaction gas in a vacuum environment and are deposited on the substrate surface in the form of compounds. On this basis, the anti-oxidation layer is further magnetron sputtered to extend the anti-oxidation cycle of the product. The ultimate breakthrough is the resistivity of the buried copper foil at 6-8×10 -4 The current state of technology between.

[0058] 2. The present invention has a broad range of properties for raw copper foil and raw copper foil because the resistivity can be effectively improved by regulating the amount of reactive gas and the sputtering process during the preparation of the resistive layer using vacuum reactive sputtering coating technology. Specifically, the resistive layer material of the present invention, nickel-chromium alloy, is deposited on the surface of the finished foil in an oxidized state, including Ni x O y The resistivity of the resistive material deposited on copper foils of different roughness is different. Qia Qia can adjust the oxygen injection amount and sputtering power to obtain Ni oxides of different valence states, such as Ni3O4, Ni2O3, and NiO, thereby adjusting the resistivity of the material.

[0059] 3. The buried copper foil product prepared by the method of the present invention has the following advantages:

[0060] (1) The resistivity of the resistor layer is high, and a higher square resistance value can be obtained at the same resistor layer thickness;

[0061] (2) The product has a low temperature coefficient of resistance (TCR), a stable electronic structure, and a small change in crystal texture with temperature, and has good thermal stability;

[0062] (3) The resistance layer is uniform and dense, and the tolerance of the square resistance value can be controlled within 3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 The structure diagram of the buried copper foil prepared by the method of the present invention;

[0064] Figure 2 The scanning electron microscope plan view (5K) of the buried copper foil sample 1 prepared in Example 1

[0065] times);

[0066] Figure 3 The cross-sectional electron microscope image (5K) of the buried copper foil sample 1 prepared in Example 1

[0067] times);

[0068] Figure 4 This is a cross-sectional electron microscope image (100K magnification) of the buried copper foil sample 1 prepared in Example 1.

[0069] The reference numerals are as follows:

[0070] 1. Raw foil layer; 2. Surface treatment layer; 3. Resistance layer; 4. Anti-oxidation layer. DETAILED DESCRIPTION

[0071] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0072] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention but is merely representative of selected embodiments of the present invention.

[0073] Example 1

[0074] A method for preparing a buried copper foil with a low temperature coefficient of resistance, the method comprising the following steps:

[0075] First, use existing technology to prepare the raw foil layer 1 and the surface treatment layer 2, such as Figure 1 shown.

[0076] S1. Preparing a raw foil layer;

[0077] The raw foil is prepared by electrochemical deposition using a raw foil machine, and the raw foil with qualified physical properties is obtained by adjusting the speed of the raw foil machine, the current density and the electroplating solution formula.

[0078] In this embodiment, a foil machine is used to prepare HTE series green foil with a thickness of 18 μm. The specific process parameters are as follows:

[0079] Cu 2+ Concentration: 100g / L;

[0080] H2SO4 concentration: 140g / L;

[0081] Cl - Concentration: 20mg / L;

[0082] Collagen concentration: 5g / L;

[0083] Collagen addition flow rate: 35L / h;

[0084] Temperature: 55℃;

[0085] Flow rate: 50m 3 / h;

[0086] Current density: 60A / dm 2 ;

[0087] Cathode roller speed: 5m / min;

[0088] This step ultimately produces a green foil layer 1 .

[0089] S2. Preparation of surface treatment layer;

[0090] The raw foil is roughened and electroplated with non-copper metals using a surface treatment machine. Finished foil with acceptable peel resistance, oxidation resistance, and chemical resistance is achieved by controlling the machine speed, current density, and plating solution formulation.

[0091] The raw foil is transferred to the winding system of the surface treatment machine at a speed of 30m / min. The process parameters are as follows:

[0092] S2.1 Pickling;

[0093] H2SO4 concentration: 120g / L;

[0094] Temperature: 28°C

[0095] Flow rate: 5m 3 / h;

[0096] S2.2 coarsening;

[0097] Cu 2+ Concentration: 20g / L;

[0098] H2SO4 concentration: 140g / L;

[0099] Sodium tungstate concentration: 20 mg / L;

[0100] Temperature: 28°C

[0101] Flow rate: 8m 3 / h;

[0102] Current density: 30A / dm 2 ; S2.3 solidification;

[0103] Cu 2+ Concentration: 70g / L;

[0104] H2SO4 concentration: 100g / L;

[0105] Temperature: 55℃;

[0106] Flow rate: 8m 3 / h;

[0107] Current density: 30A / dm 2 ;S2.4 blackening;

[0108] Ni 2+ Concentration: 2g / L;

[0109] K4P2O7 concentration: 80g / L;

[0110] Temperature: 40℃;

[0111] Flow rate: 4m 3 / h;

[0112] pH: 10;

[0113] Current density: 0.3A / dm 2 ;S2.5 ashing;

[0114] Zn 2+ Concentration: 1.5g / L;

[0115] K4P2O7 concentration: 70g / L;

[0116] Temperature: 40℃;

[0117] Flow rate: 4m 3 / h;

[0118] pH: 11;

[0119] Current density: 0.3A / dm 2 ;

[0120] S2.6 passivation;

[0121] Cr 6+ Concentration: 1g / L;

[0122] Temperature: 30℃;

[0123] Flow rate: 5m 3 / h;

[0124] pH: 12;

[0125] Current density: 20A / dm 2 ;

[0126] There are water washing and water squeezing functions in each independent link. The copper foil after passivation treatment is washed, dried and rolled.

[0127] This step obtains a surface treatment layer 2 on the basis of the raw foil layer 1 to form a finished foil.

[0128] The properties of the finished foil are as follows:

[0129] The finished foil has a thickness of 130 μm, a roughness of Rz10 μm, and an area density of 1200 g / m 2 , tensile strength 800Mpa, elongation 20%.

[0130] S3. Reactive sputtering resistor layer;

[0131] S3.1 Preprocessing;

[0132] First, an ion source is used to bombard the treated surface of the finished foil with ions. The pretreatment effect is controlled by adjusting the ion source and its power, the working gas and its filling volume, and the treatment time to clean the surface of the finished foil.

[0133] Specifically, in this embodiment:

[0134] The copper foil obtained in S2.6 was transferred to the winding system of the vacuum coating machine, and the speed was set to 10m / min.

[0135] The ion source is an anode layer ion source, the working gas is argon, the set power is 0.5KW, the flow rate is 50sccm, and the processing time is 10min.

[0136] S3.2 Preparation of resistor layer by vacuum reactive sputtering coating technology (resistance layer of oxide component obtained by mixing with other metals)

[0137] Through vacuum reactive sputtering coating technology, the resistor material is deposited in the form of a compound on the surface of the pre-treated finished foil. The thickness and composition of the resistor layer can be controlled by adjusting the target material, coating power, reactive gas and its filling volume.

[0138] In this embodiment, the resistor layer is prepared by vacuum reactive sputtering coating technology, and the target material is a nickel-chromium alloy target with a mass ratio of 7:3; the coating power is 15KW; the argon filling amount is 300sccm, the oxygen filling amount is 200sccm, and the nitrogen filling amount is 20sccm, and the purity is all 99.99%; the film thickness is 500nm.

[0139] This step obtains the resistance layer 3 on the basis of the surface treatment layer 2, such as Figure 1 shown.

[0140] S4. Magnetron sputtering anti-oxidation layer;

[0141] Through vacuum magnetron sputtering coating technology, anti-oxidation material is deposited on the surface of copper foil after sputtering resistor material. The thickness of the anti-oxidation layer is controlled by adjusting the coating power, time and the inflation volume of the working gas.

[0142] In this embodiment, the anti-oxidation layer is prepared by DC magnetron sputtering. The target material is a titanium target with a purity greater than 99.99%. The coating power is 15KW. The neon gas injection amount is 300sccm with a purity of 99.99%. The film thickness is 100nm.

[0143] This step obtains an anti-oxidation layer 4 on the basis of the resistance layer 3, such as Figure 1 shown.

[0144] Finally, the buried copper foil product 1 is obtained.

[0145] Example 2

[0146] The difference from Example 1 is that:

[0147] S2 raw foil is RTF series raw foil.

[0148] The properties of the finished foil are as follows:

[0149] The finished foil has a thickness of 18 μm, a roughness of Rz3.5 μm, and an area density of 151 g / m 2 , tensile strength 315Mpa, elongation 7%.

[0150] The ion source in S3.1 is a Kaufman ion source with a set power of 8 kW; the working gases are carbon monoxide and hydrogen, with a carbon monoxide flow rate of 200 sccm and a hydrogen flow rate of 50 sccm; the processing time is 4 minutes.

[0151] The target material in S3.2 is a nickel-chromium alloy target with a mass ratio of 8:2; the coating power is 9KW; the argon filling amount is 180sccm, the oxygen filling amount is 100sccm, and the purity of both is 99.99%; the film thickness is 350nm.

[0152] The target material in S4 is a chromium target with a purity greater than 99.99%; the coating power is 10KW; the helium filling amount is 200sccm, with a purity of 99.99%; and the film thickness is 80nm.

[0153] Finally, the buried copper foil product 2 is obtained.

[0154] Take a sample at any position and scan its plane and cross-section at 5K times the electron microscope image, as shown in the figure below. Figure 2 、 Figure 3 The cross-sectional details under the 100kx electron microscope are shown as follows. Figure 4 shown.

[0155] Visible: It can be found that the film layer is uniform and dense, and each layer is clearly visible.

[0156] Example 3

[0157] The difference from Example 1 is that:

[0158] The raw foil in S2 is VLP series raw foil. The properties of the finished foil are as follows:

[0159] The finished foil has a thickness of 4.5 μm, a roughness of Rz2.0 μm, and an area density of 40 g / m 2 , tensile strength 200Mpa, elongation 1%.

[0160] In S3.1, the ion source is a Hall ion source with a set power of 5 kW; the working gas is nitrous oxide with a flow rate of 500 sccm; and the processing time is 5 min.

[0161] The target material in S3.2 is a nickel-chromium alloy target with a mass ratio of 9:1; the coating power is 13KW; the argon filling amount is 250sccm, the oxygen filling amount is 20sccm, and the nitrogen filling amount is 200sccm, all with a purity of 99.99%; and the film thickness is 400nm.

[0162] The target material in S4 is a titanium target with a purity greater than 99.99%; the coating power is 10KW; the neon gas filling amount is 250sccm with a purity of 99.99%; and the film thickness is 40nm.

[0163] Finally, the buried copper foil product 3 is obtained.

[0164] Example 4

[0165] The difference from Example 1 is that:

[0166] S2 raw foil is HVLP series raw foil. The properties of the finished foil are as follows:

[0167] The finished foil has a thickness of 12 μm, a roughness of Rz0.4 μm, and an area density of 107 g / m 2 , tensile strength 300Mpa, elongation 8%.

[0168] In S3.1, the ion source is an ICP ion source with a set power of 10 kW. The working gases are carbon dioxide and nitrogen with a carbon dioxide flow rate of 300 sccm and a nitrogen flow rate of 50 sccm. The processing time is 2 min.

[0169] The target material in S3.2 is a nickel-chromium alloy target with a mass ratio of 6:4; the coating power is 1KW; the argon filling amount is 100sccm, the oxygen filling amount is 30sccm, and the nitrogen filling amount is 50sccm, all with a purity of 99.99%; and the film thickness is 20nm.

[0170] The target material in S4 is a titanium target with a purity greater than 99.99%; the coating power is 1KW; the helium filling amount is 100sccm, with a purity of 99.99%; and the film thickness is 5nm.

[0171] Finally, the buried copper foil product 4 is obtained.

[0172] Example 5

[0173] The difference from Example 1 is that:

[0174] The raw foil in S2 is HTE series raw foil. The properties of the finished foil are as follows:

[0175] The finished foil has a thickness of 18 μm, a roughness of Rz7.0 μm, and an area density of 155 g / m 2 , tensile strength 530Mpa, elongation 11%.

[0176] The ion source in S3.1 is an anode layer ion source, the set power is 3KW, the working gas is oxygen, the flow rate is 250sccm, and the processing time is 1min.

[0177] The target material in S3.2 is a nickel-chromium alloy target with a mass ratio of 8:2; the coating power is 6KW; the argon filling amount is 150sccm, the oxygen filling amount is 50sccm, and the purity of both is 99.99%; the film thickness is 300nm.

[0178] The target material in S4 is a chromium target with a purity greater than 99.99%; the coating power is 7KW; the argon gas filling amount is 150sccm, with a purity of 99.99%; and the film thickness is 30nm.

[0179] Finally, the buried copper foil product 5 is obtained.

[0180] Example 6

[0181] The difference from Example 1 is that:

[0182] The raw foil in S2 is RTF series raw foil. The properties of the finished foil are as follows:

[0183] The finished foil has a thickness of 35 μm, a roughness of Rz4.0 μm, and an area density of 285 g / m 2 , tensile strength 420Mpa, elongation 8%.

[0184] In S3.1, the ion source is an anode layer ion source, the set power is 2KW, the working gas is nitrogen, the flow rate is 300sccm, and the processing time is 8min.

[0185] The target material in S3.2 is a nickel-chromium alloy target with a mass ratio of 8:2; the coating power is 5KW; the argon filling amount is 200sccm, the nitrogen filling amount is 100sccm, and the purity of both is 99.99%; the film thickness is 150nm.

[0186] The target material in S4 is a chromium target with a purity greater than 99.99%; the coating power is 6KW; the argon gas filling amount is 200sccm, with a purity of 99.99%; and the film thickness is 50nm.

[0187] Finally, the buried copper foil product 6 is obtained.

[0188] Comparative Example 1

[0189] Compared with Example 1, the difference of Comparative Example 1 is that the S3.1 pretreatment step is eliminated, and the rest remains unchanged.

[0190] Comparative Example 2

[0191] Compared with Example 2, the difference of Comparative Example 2 is that a nickel-chromium alloy target with a mass ratio of 3:7 is used in step S3.2, and the rest remains unchanged.

[0192] Comparative Example 3

[0193] Compared with Example 5, Comparative Example 3 differs in that the resistive layer is formed by vacuum magnetron sputtering in step S3.2. Specifically, a nickel-chromium alloy target with a mass ratio of 8:2 is used, 99.99% pure argon is introduced at a rate of 150 sccm, the DC power supply output is set to 6 kW, and the coating thickness is 300 nm. All other conditions remain unchanged.

[0194] To more intuitively demonstrate the effectiveness of the present invention, all samples were laminated with PTFE under high-temperature vacuum. After etching away the raw foil and surface treatment layers from the entire surface of a 15×15 cm sheet, the sheet resistance at nine points was measured using a square resistance meter, and the mean and fluctuation values ​​were recorded. After reflow soldering, the sheet resistance at nine points was measured, and the mean and fluctuation values ​​were recorded. After window processing of multiple 30×30 μm patterns on the 15×15 cm sheet, the resistance was measured using a micro-ohmmeter, and the mean and fluctuation values ​​were recorded. The thickness of the resistor layer was measured using a scanning electron microscope. The temperature coefficient of resistance (TCR) of the samples was measured using the MIL-STD-202-304 method. The peel strength between the samples and PTFE was measured using the IPC-TM-650 method. Detailed data are shown in Table 1.

[0195] Table 1 Physical properties of buried copper foil in examples and comparative examples

[0196]

[0197]

[0198] By comparing Example 1 and Comparative Example 1, it can be found that: in Example 1, which was pre-treated with an ion source, the fluctuation value of the square resistance after the PTFE pressing plate was 1.8%, the fluctuation value of the square resistance after reflow soldering was 2.3%, and the fluctuation value of the square resistance after processing and opening the window was 2.8%; in Comparative Example 1, which was not pre-treated with an ion source, the fluctuation value of the square resistance after the PTFE pressing plate was 9.8%, the fluctuation value of the square resistance after reflow soldering was 10.4%, and the fluctuation value of the square resistance after processing and opening the window was 12.4%. This shows that ion source treatment can effectively reduce the fluctuation of the square resistance and improve stability.

[0199] By comparing Example 2 and Comparative Example 2, it can be found that: when the mass ratio of the nickel-chromium alloy target is less than 5:5, the temperature coefficient of resistance TCR becomes very poor, increasing from 110 PPM / °C to 335 PPM / °C, and the thermal stability deteriorates, which causes a serious drift in the mean between the PTFE pressing plate, reflow soldering and processing window, affecting product quality.

[0200] By comparing Example 5 with Comparative Example 3, it can be found that the resistivity of Example 5, which uses the vacuum reactive sputtering method to prepare the resistor material, is 1.1×10 -3 Ω·cm; Comparative Example 3 of the resistor material prepared by vacuum magnetron sputtering method has a resistivity of 1.7×10 -4 Ω·cm. The resistivity is increased by nearly 10 times. According to the formula It can be seen that under the same thickness d, the higher the resistivity ρ, the greater the R □ The larger the resistance value, the better the performance. The larger the resistance value, the better the performance.

[0201] Furthermore, the resistivity of the buried copper foil has exceeded the limit of 6-8×10 -4 The current state of technology between them exceeds 9×10 -4 Ω·cm, especially in Examples 2, 5, and 6, the resistivity is directly increased to 1.0×10 -3 Ω·cm and above, which also has huge technical advantages for meeting the trend of buried copper foil in the future.

[0202] In summary, the buried copper foil prepared by the present invention has a high resistivity of the resistor layer, and a higher square resistance value can be obtained at the same resistor layer thickness; the product has a low temperature coefficient of resistance (TCR) and good thermal stability; the resistor layer is uniform and dense, and the tolerance of the square resistance value can be controlled within 3%.

Claims

1. A method for preparing a buried copper foil with a low temperature coefficient of resistance, characterized in that: The method is divided into the following steps: S1. Preparing a raw foil layer; According to the existing technology, green foil is prepared by electrochemical deposition using a green foil machine, and green foil with qualified physical properties is obtained by adjusting the speed of the green foil machine, the current density, and the composition of the electroplating solution; S2. Preparation of surface treatment layer; According to the existing technology, the raw foil is roughened and non-copper metal is electroplated in a surface treatment machine to form a surface treatment layer on the basis of the raw foil layer, which is the finished foil. S3. Reactive sputtering resistor layer; S3.1 Preprocessing; First, an ion source is used to bombard the treated surface of the finished foil with ions. The pretreatment effect is controlled by adjusting the ion source and its power, the working gas and its filling volume, and the treatment time to clean the surface of the finished foil. S3.2 Preparation of the resistor layer using vacuum reactive sputtering coating technology; The vacuum reactive sputtering coating technology is used to deposit the resistor material in the form of a compound on the surface of the pre-treated finished foil. The thickness and composition of the resistor layer can be controlled by adjusting the target material, coating power, reactive gas and its filling volume, as follows: The target material is a nickel-chromium alloy target with a mass ratio greater than 5:5; Coating power is 1-15KW; The reaction gas and the charging amount are: The argon filling amount is 100-300 sccm, with a purity of 99.99%; the oxygen filling amount is 0-200 sccm, with a purity of 99.99%; the nitrogen filling amount is 0-200 sccm, with a purity of 99.99%; The film thickness is 20-500nm; This step obtains a resistance layer on the basis of the surface treatment layer; S4. Magnetron sputtering anti-oxidation layer; Through vacuum magnetron sputtering coating technology, anti-oxidation material is deposited on the surface of copper foil after sputtering resistor material. The thickness of the anti-oxidation layer can be controlled by adjusting the target material, coating power, working gas and its filling volume. This step obtains an anti-oxidation layer on the basis of the resistance layer; Finally, the buried copper foil product is obtained.

2. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S3.1, the ion source is one of an anode layer ion source, a Hall ion source, a Kaufman ion source, an ICP ion source, and a pulse bias ion source; Set processing power 0.5-10KW; The working gas is a combination of one or more of argon, nitrogen, oxygen, nitrous oxide, carbon dioxide, carbon monoxide and hydrogen; The working gas flow rate is 50-500sccm; The processing time is 1-10 minutes.

3. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S4, the target material is a titanium target or a chromium target with a purity greater than 99.99%; Coating power is 1-15KW; The working gas is one of the inert gases helium, neon, and argon; The working gas charge is 100-300 sccm; the purity is 99.99%; The film thickness is 5-100nm.

4. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S1, the raw foil is one of HTE series raw foil, RTF series raw foil, VLP series raw foil, or HVLP series raw foil.

5. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S1, the foil machine has a speed of 1-10 m / min and a current density of 10-100 A / dm2.

6. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S1, the properties of the raw foil are as follows: Thickness 4.5-130μm, roughness Rz0.4-10μm, surface density 40-1200g / m2, tensile strength 200-800Mpa and elongation 1-20%.

7. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S2, the properties of the finished foil are as follows: The finished foil has a thickness of 4.5-130 μm, a roughness Rz of 0.4-10 μm, an area density of 40-1200 g / m2, a tensile strength of 200-800 MPa, and an elongation of 1-20%.

8. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S2, the finished foil is one of HTE series raw foil, RTF series raw foil, VLP series raw foil, or HVLP series raw foil.

9. The method for preparing a buried copper foil with a low temperature coefficient of resistance according to claim 1, wherein: In step S2, the vehicle speed, the current density index of each link, and the composition of the electroplating solution are controlled to ensure that the finished foil with qualified performance is obtained, wherein: the vehicle speed is 5-40 m / min, the roughening current density is 10-40 A / dm2, the curing current density is 10-40 A / dm2, the blackening current density is 0.1-10 A / dm2, the ashing current density is 0.1-10 A / dm2, and the passivation current density is 0.1-10 A / dm2.

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