Ultrathin copper foil for fine circuit as well as preparation method and application of ultrathin copper foil

Abstract

The invention relates to an ultra-thin copper foil for a fine circuit and a preparation method and application of the ultra-thin copper foil. The ultra-thin copper foil comprises a substrate supporting layer, an ultra-thin copper layer and a fine roughening layer from bottom to top, the matrix supporting layer is made of a low-melting-point substance with the melting point not exceeding 200 DEG C. According to the ultra-thin copper foil, a stripping layer does not need to be designed between the supporting layer and the ultra-thin copper layer, on one hand, the structure of a traditional strippable ultra-thin carrier-attached copper foil is simplified, and on the other hand, mutual separation between the supporting layer and the ultra-thin copper layer can be achieved in the thermocompression bonding process; and after pressing is completed, no extra operation of separating the carrier layer is needed, so that the method has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic circuit copper foil processing, and particularly relates to an extremely thin copper foil for fine lines, a preparation method thereof, and an application thereof. Background Art

[0002] At the present stage, lightness, thinness, miniaturization are the clear development directions and trends in the field of electronic circuits. Printed circuit boards (PCBs) are an essential key component in electronic circuit devices. With the reduction of device size and the improvement of functional requirements, new and higher requirements are put forward for the wiring density and processability of PCBs. The processability of copper foil is one of the key factors for realizing the lightness, thinness, and miniaturization of PCBs.

[0003] In the production process of PCBs, electronic circuit copper foils need to be etched into patterned lines to form functional partitions of conductive regions and insulating regions. Therefore, the etching performance of copper foil is an important index to characterize the processability of copper foil. The etching performance of copper foil can be quantified by the etching factor (Etching factor, EF). The PCB line etching process and the etching factor of the line are as Figure 1 shown. During the etching process, a chemical reaction occurs between copper and the etching solution, and elemental copper is oxidized to copper ions. Under the combined action of surface tension and gravity, the etching solution will chemically react with copper in the vertical and horizontal directions. Usually, the etching of copper by the etching solution in the horizontal direction is called side etching. Affected by the side etching effect, the cross-section of copper after etching treatment will show non-vertical characteristics. The etching factor of the copper foil etched to form a line can be calculated by Formula 1.

[0004]

[0005] Where EF is the etching factor of the line, Wt is the minimum width at the top of the line, Wb is the width at the bottom of the line, and T is the thickness of the copper layer.

[0006] Generally, in order to ensure the insulation reliability between adjacent lines, it is necessary to control the etching factor of the copper foil after etching. The higher the etching factor of the line, the better the verticality of the line, and the lower the risk of short circuit between adjacent lines. The miniaturization development of terminal applications has put forward new and higher requirements for the wiring density of PCB boards. As the line density per unit area increases, the spacing between lines is gradually compressed. Therefore, ultra-fine lines characterized by ultra-fine line widths and line pitches have gradually become the mainstream of high-end and high-performance PCBs.

[0007] The ultra-thin peelable carrier copper foil is a successful solution to reduce the adverse effects of chemical etching on copper foil processing and ensure the processability of ultra-fine circuits. On the one hand, by selecting a carrier with good processing performance as the support, the wrinkling problem that occurs during the processing of ultra-thin copper foils with a thickness less than 12 μm can be effectively solved. On the other hand, selecting an ultra-thin copper layer with a thickness less than 12 μm, or even 5 μm, as the functional layer is conducive to improving the circuit processing accuracy, and ultra-fine circuits with a line width-line pitch not exceeding 25 μm / 25 μm can be achieved.

[0008] At the present stage, the ultra-thin peelable carrier copper foil needs to select a suitable carrier as the support for the ultra-thin functional layer during production and processing on the one hand, and prepare a peeling layer with an appropriate separation force to achieve the mutual separation between the carrier layer and the ultra-thin functional copper layer on the other hand.

[0009] In the actual application process, copper foil is selected as the carrier layer of the carrier copper foil. Usually, after laminating and separating the carrier copper layer from the ultra-thin functional copper layer, the carrier copper layer loses its functionality and can only be recycled and processed as waste. Therefore, there is a large room for improvement in the utilization efficiency of the carrier copper layer.

[0010] The peeling layer is an indispensable key component to ensure the stable separation between the ultra-thin copper layer and the carrier layer. When the separation force is too small, delamination will occur during the production of the ultra-thin peelable carrier copper foil, affecting the normal production of the ultra-thin peelable carrier copper foil. When the separation force is too large, the ultra-thin copper layer and the carrier layer cannot be separated, affecting the downstream processing of the ultra-thin peelable carrier copper foil. Therefore, selecting a suitable peeling layer is the key to ensuring the stable separability between the ultra-thin copper layer and the carrier layer.

[0011] Selective etching of copper foil is the main method for processing circuits in PCB. During the PCB circuit processing, the copper foil in the part where the circuit needs to be formed is retained, and the copper foil between the circuits is etched away to obtain the designed patterned circuit. It should be noted that: the etching of copper foil by the etching solution mainly occurs along the grain boundaries of the copper foil (intergranular corrosion). The boundary between adjacent crystals in the copper foil (grain boundary) is the main site for the chemical reaction between the copper foil and the etching solution. Usually, the higher the grain boundary density of the copper foil, the more sites for the etching reaction between the copper foil and the etching solution, and the corresponding etching rate is also faster. However, the crystal structure of the copper foil will change during the hot pressing process, and the mutual fusion between adjacent grains will lead to a decrease in the grain boundary density, and the corresponding etching rate will also be adversely affected. Summary of the Invention

[0012] The specific problems to be solved by the present invention are as follows: (1) The problem of the reuse of the carrier layer and the reuse efficiency. In view of the low utilization rate and low reuse efficiency of the metal foil or polymer film carrier widely used at present, a new solution for the carrier layer material is proposed; (2) The problem of the selection of the release layer material. In view of the limited composition of the release layer material of the extremely thin peelable copper foil with carrier at present, a structure of an extremely thin copper layer is redesigned to achieve a solution of an extremely thin copper foil without a release layer; (3) The problem of the crystal structure stability of the extremely thin copper layer. In view of the problem that the crystal structure change of the copper foil during the hot pressing process may affect the etching processing performance, the microscopic crystal structure of the copper foil is redesigned to improve the crystal structure stability of the functional extremely thin copper layer.

[0013] The present invention provides an extremely thin copper foil for fine circuits, which comprises a substrate support layer, an extremely thin copper layer and a micro-roughened layer from bottom to top; the substrate support layer is a low-melting-point substance with a melting point not exceeding 200 °C.

[0014] Preferably, the low-melting-point substance is one or more of tin-bismuth alloy, tin-lead alloy, cadmium-indium-tin alloy, tin-lead-antimony-copper alloy, bismuth alloy, and zinc alloy.

[0015] Preferably, the thickness of the extremely thin copper layer does not exceed 1.5 μm.

[0016] Preferably, the extremely thin copper layer is obtained by electrochemically depositing with the assistance of additive A; the micro-roughened layer is obtained by micro-roughening the extremely thin copper layer with the assistance of additive B.

[0017] Preferably, additive A includes a brightening agent and a leveling agent; additive B is a grain refiner.

[0018] More preferably, the brightening agent is one or more of selenium dioxide, SH110, MPS, and APS; the leveling agent is one or more of glutamic acid, aspartic acid, and cysteine.

[0019] Furthermore, the extremely thin copper foil further includes a non-copper metal functional layer and a chemical bonding layer.

[0020] The present invention also provides a method for preparing an extremely thin copper foil for fine circuits, which comprises the following steps:

[0021] S1. Select a substrate support layer and perform pretreatment;

[0022] S2. Electrochemically deposit on the surface of the pretreated substrate support layer with the assistance of additive A to obtain an extremely thin copper layer;

[0023] S3. Perform micro-roughening treatment on the surface of the extremely thin copper layer with the assistance of additive B to obtain a micro-roughened layer, thus obtaining the extremely thin copper foil for fine circuits.

[0024] Preferably, the pretreatment in step S1 includes alkali washing, acid washing and water washing.

[0025] Preferably, the process parameters of the electrochemically depositing in step S2 are as follows: the temperature of the electrolyte is 30-60 °C, and the current density is 70-100 A / dm 2 .

[0026] Preferably, the micro-roughening treatment in step S3 includes roughening treatment and curing treatment.

[0027] Furthermore, the preparation method further includes electrochemically depositing a non-copper metal functional layer and constructing a chemical bonding layer.

[0028] The present invention also provides an application of an extremely thin copper foil for fine circuits in the preparation of a copper clad laminate.

[0029] The matrix support layer in the present invention mainly provides the function of mechanical strength during the production and processing of the extremely thin copper foil; the extremely thin copper layer in the present invention is an indispensable key component for making fine circuits; the micro-roughening layer in the present invention ensures that the extremely thin copper foil always maintains a good bonding force with the resin sheet during the processing and use. Compared with the traditional extremely thin peelable carrier copper foil, the extremely thin copper foil for fine circuits of the present invention has the following characteristics. On the one hand, a supported extremely thin copper foil of the present invention does not require a release layer to be designed between the support layer and the extremely thin copper layer, which simplifies the structure compared with the traditional peelable extremely thin carrier copper foil. On the other hand, the melting point of the support layer of a supported extremely thin copper foil of the present invention is lower than 200 °C, and the support layer is converted into a liquid state at a temperature higher than the melting point during the hot pressing process. The mutual separation between the support layer and the extremely thin copper layer can be achieved during the hot pressing process, and no additional operation of separating the carrier layer is required after the pressing is completed.

[0030] Beneficial effects

[0031] The extremely thin copper foil of the present invention does not require a release layer to be designed between the support layer and the extremely thin copper layer. On the one hand, it simplifies the structure of the traditional peelable extremely thin carrier copper foil. On the other hand, the mutual separation between the support layer and the extremely thin copper layer can be achieved during the hot pressing process, and no additional operation of separating the carrier layer is required after the pressing is completed, having good application prospects. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the copper foil etching process and the etching factor.

[0033] Figure 2 It is a schematic structural diagram of the extremely thin copper foil of the present invention; wherein, 101 is the matrix support layer, 201 is the extremely thin copper layer, and 301 is the micro-roughening layer.

[0034] Figure 3 Schematic diagram for preparing a copper clad laminate using the extremely thin copper foil of the present invention. Detailed implementation manners

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it 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 also fall within the scope defined by the appended claims of this application.

[0036] Embodiment 1

[0037] Step 1. Pretreatment of the carrier support layer

[0038] Select a tin-bismuth alloy with a thickness of 18 μm as the carrier support layer, and sequentially remove foreign substances such as organic and inorganic substances adsorbed on the surface of the support layer through alkali washing, acid washing, and water washing. The process parameters during the pretreatment of the carrier support layer are as follows:

[0039] Sodium carbonate Na 2 CO 3 Concentration: 1.0 mol / L -1 ;

[0040] Temperature of the alkali washing solution: 35 °C;

[0041] Alkali washing time: 10 s;

[0042] Concentration of hydrochloric acid HCl: 0.5 mol / L -1 ;

[0043] Temperature of the acid washing solution: 25 °C;

[0044] Acid washing time: 10 s;

[0045] Temperature of the water washing: 25 °C;

[0046] Water washing time: 10 s.

[0047] Step 2: Additive-assisted electrochemical deposition of an extremely thin copper layer

[0048] Using the support layer as the cathode, a DSA dimensionally stable anode plate as the anode, and pickling copper sulfate as the electrolyte, an extremely thin copper layer is electrochemically deposited under the action of an electric current. During the electrochemical deposition of the extremely thin copper foil, a brightener with grain refinement and an inhibitor with a leveling effect are introduced, and a low-profile extremely thin copper foil with small-sized grains is deposited under the action of a direct current electric field. The process parameters during the electrochemical deposition of the extremely thin copper foil are as follows:

[0049] Copper concentration: 100 g / L;

[0050] Sulfuric acid concentration: 115 g / L;

[0051] Chloride ion concentration: 20 mg / L;

[0052] Brightener concentration: 5 mg / L;

[0053] Leveling agent concentration: 15 mg / L;

[0054] Temperature: 50 °C;

[0055] Flow rate: 45 m 3 / h;

[0056] Current density: 70 A / dm 2 .

[0057] Step 3 Additive-assisted micro-roughening treatment

[0058] During the roughening treatment of surface treatment, additives with refined particle size are introduced to reduce the particle size of the roughened structure on the copper foil surface and increase the specific surface area of the copper foil surface. The micro-roughening treatment is divided into two sub-processes: roughening and curing. The electrolyte formulations and functions of the two processes are different. In the roughening process, in the electrolyte with high-concentration acid and low-concentration copper, the growth of the micro-roughened structure is achieved through electrochemical deposition. In the curing process, in the electrolyte with high-concentration copper and low-concentration acid, conformal coating of the micro-roughened structure formed in the roughening process is carried out through electrochemical deposition to enhance the bonding reliability between the roughened structure and the substrate copper layer. The process parameters during the micro-roughening treatment are as follows:

[0059] Roughening treatment process:

[0060] Copper concentration: 15 g / L;

[0061] Sulfuric acid concentration: 150 g / L;

[0062] Additive concentration: 15 mg / L;

[0063] Temperature: 25 °C;

[0064] Electroplating time: 7 s;

[0065] Current density: 40 A / dm 2 .

[0066] Curing treatment process:

[0067] Copper concentration: 50 g / L;

[0068] Sulfuric acid concentration: 100 g / L;

[0069] Additive concentration: 10 mg / L;

[0070] Temperature: 50°C;

[0071] Electroplating time: 7 s;

[0072] Current density: 50 A / dm 2 .

[0073] Step 4 Electrochemical deposition of non - copper metal functional layer

[0074] In order to ensure the processability and reliability of the copper foil for electronic circuits during downstream processing and use, it is necessary to construct a functional layer mainly composed of non - copper metals on the surface of the copper foil. The non - copper metal layer on the copper foil surface can generally be divided into a nickel - containing blackening layer for improving chemical resistance, a zinc - containing ashing layer for improving high - temperature resistance, and a chromium - containing passivation layer for improving weather resistance. The process parameters for the electrochemical deposition of the non - copper metal functional layer are as follows:

[0075] Blackening section

[0076] Ni concentration: 2.5 g / L;

[0077] Potassium pyrophosphate: 85 g / L;

[0078] pH value: 10;

[0079] Blackening solution temperature: 30°C;

[0080] Blackening solution flow rate: 10 m 3 / h;

[0081] Current density: 50 A / m 2 ;

[0082] Electroplating time: 7 s.

[0083] Ashing section

[0084] Zn concentration: 2.0 g / L;

[0085] Potassium pyrophosphate: 50 g / L;

[0086] pH value: 11.5;

[0087] Ashing solution temperature: 40°C;

[0088] Ashing solution flow rate: 10 m 3 / h;

[0089] Current density: 75 A / m 2 ;

[0090] Electroplating time: 7 s.

[0091] Passivation section

[0092] Chromium concentration: 1.0 g / L;

[0093] pH value: 12;

[0094] Passivation solution temperature: 35 °C;

[0095] Passivation solution flow rate: 10 m 3 / h;

[0096] Current density: 50 A / m 2 ;

[0097] Electroplating time: 7 s.

[0098] Step 5 Chemical bonding layer construction

[0099] Copper foil is a typical inorganic material, and the sheets used for the lamination of copper clad laminates mainly consist of organic resins. To improve the bonding strength between the copper foil and the sheets, it is usually necessary to construct a chemical bonding layer on the lamination surface of the copper foil and the sheets. A silane coupling agent is usually selected to improve the chemical bonding force between the copper foil and the sheets during the construction of the chemical bonding layer. The process parameters during the construction of the chemical bonding layer on the copper foil surface are as follows:

[0100] Silane coupling agent: KBM-403;

[0101] Silane coupling agent solution concentration: 0.8 wt%;

[0102] Silane coupling agent solution temperature: 28 °C;

[0103] Silane coupling agent solution flow rate: 2.5 m 3 / h;

[0104] Silane coupling agent coating time: 2 s.

[0105] Step 6 Lamination of copper clad laminates

[0106] Electrical circuit copper foil is a raw material for the processing of CCL and PCB. It needs to be laminated with sheets through hot pressing to form CCL, and further processed to form PCB products. The parameters during the lamination of copper clad laminates are as follows:

[0107] Resin composition of the sheets: BT;

[0108] Resin content RC of the sheets: 65%;

[0109] Glass cloth model: 1078;

[0110] Number of prepreg layers: 2 ply;

[0111] Lamination temperature: 225 °C;

[0112] Lamination pressure: 500 psi;

[0113] Lamination heat preservation time: 240 min;

[0114] Heating rate: 5 °C / min;

[0115] Cooling rate: 5 °C / min.

[0116] Step 7 Peel strength test

[0117] After the copper foil is laminated with the board, it is not allowed for the copper foil and the board to separate from each other during the downstream PCB processing and end - use. The peel strength is an important parameter characterizing the bonding strength between the copper foil and the board and the reliability of the PCB. The process parameters for the peel strength test between the copper foil and the board are as follows:

[0118] Spline width: 3.175 mm;

[0119] Spline length: 10 cm;

[0120] Peel angle: 90 °C;

[0121] Peel stroke: 25 mm;

[0122] Peel speed: 50 mm / min;

[0123] Copper layer thickness: 35 μm (12 μm copper foil electroplated to 35 μm);

[0124] Number of peel strength tests: 3 times.

[0125] Step 8 Fine line processing Reducing the line width and line pitch is the key to achieving high wiring density and miniaturization and thin - light of electronic circuit devices. The main method for forming lines is to etch the non - line area while retaining the copper foil in the line area during the process of processing the copper - clad laminate into a PCB. The parameters during the fine line processing are as follows:

[0126] Chloride ion concentration of the etching solution: 220 - 250 g / L;

[0127] Copper ion concentration of the etching solution: 90 - 130 g / L;

[0128] pH value of the etching solution: 1.5 - 2.5;

[0129] Temperature of the etching solution: 48 - 52 °C;

[0130] Etching running speed: 1.5 - 3.0 m / min.

[0131] Comparative example 1

[0132] The difference between this comparative example and Example 1 is that the carrier support layer is a 18 - micron copper foil.

[0133] Comparative example 2

[0134] The difference between this comparative example and Example 1 is that a release layer is introduced between the carrier support layer and the ultra-thin copper layer.

[0135] Table 1 Ultra-thin copper foil test data

[0136]

[0137] For conventional peelable carrier copper foils, a copper foil with a thickness of 18 μm is used as the support layer. After the ultra-thin copper layer is laminated with the resin sheet, the 18-μm support layer copper foil needs to be separated from the ultra-thin copper layer. Usually, the separated 18-μm carrier support layer copper foil is no longer used. Using a low-melting-point material as the carrier support layer not only facilitates the reuse of the carrier support layer but also eliminates the need to additionally construct a release layer on the surface of the carrier support layer, which helps simplify the production process of ultra-thin copper foils. Conventional peelable carrier copper foils require a release layer to be constructed at the cross-section between the carrier support layer and the ultra-thin copper layer to achieve the mutual separation between the carrier support layer and the ultra-thin copper layer after lamination. The release layer is an important indicator determining the processability of traditional peelable carrier copper foils. Only when the separation force is within an appropriate range can the processability of peelable carrier copper foils be ensured. If the separation force is too small, the peelable carrier copper foils may show delamination during production, directly affecting the production efficiency and yield of peelable carrier copper foils. If the separation force is too large, the carrier support layer and the ultra-thin copper layer may not be separable during downstream processing, affecting the downstream processing efficiency.

[0138] The ultra-thin copper foil for fine circuits of the present invention eliminates the release layer between the carrier support layer and the ultra-thin copper layer at the design stage and directly utilizes the energy during the hot lamination process to achieve the mutual separation between the carrier support layer and the ultra-thin copper layer. The low-melting-point carrier support layer and the design without a release layer not only help reduce the production cost of peelable carrier copper foils but also improve the convenience of ultra-thin copper foils at the processing stage. Therefore, the ultra-thin copper foil for fine circuits of the present invention has considerable practical value.

Claims

1. An ultra-thin copper foil for fine circuits, characterized in that: The ultra-thin copper foil comprises a base support layer, an ultra-thin copper layer and a fine roughening layer from bottom to top; the base support layer is made of a low melting point material with a melting point not exceeding 200°C.

2. The ultra-thin copper foil for fine circuits according to claim 1, characterized in that: The low melting point material is one or more of tin-bismuth alloy, tin-lead alloy, cadmium-indium-tin alloy, tin-lead-antimony-copper alloy, bismuth alloy and zinc alloy.

3. The ultra-thin copper foil for fine circuits according to claim 1, characterized in that: The thickness of the ultra-thin copper layer does not exceed 1.5 μm.

4. The ultra-thin copper foil for fine circuits according to claim 1, characterized in that: The ultra-thin copper layer is obtained by electrochemical deposition with the assistance of additive A; the micro-roughening layer is obtained by micro-roughening the ultra-thin copper layer with the assistance of additive B.

5. The ultra-thin copper foil for fine circuits according to claim 4, characterized in that: The additive A includes a brightener and a leveler; the additive B is a grain refiner.

6. The ultra-thin copper foil for fine circuits according to claim 1, characterized in that: The ultra-thin copper foil further comprises a non-copper metal functional layer and a chemical bonding layer.

7. A method for preparing an ultra-thin copper foil for fine circuits as claimed in any one of claims 1 to 6, comprising the following steps: S1. Select the substrate support layer and perform pretreatment; S2. Electrochemical deposition is performed on the surface of the pretreated substrate support layer with the aid of additive A to obtain an extremely thin copper layer; S3. The surface of the ultra-thin copper layer is subjected to a fine roughening treatment with the aid of additive B to obtain a fine roughening layer, that is, an ultra-thin copper foil for fine circuits.

8. The preparation method according to claim 7, characterized in that: The electrochemical deposition process parameters in step S2 are: electrolyte temperature 30-60°C, current density 70-100A / dm 2 .

9. The preparation method according to claim 7, characterized in that: The micro-roughening process in step S3 includes a roughening process and a curing process.

10. Use of the ultra-thin copper foil for fine circuits as claimed in any one of claims 1 to 6 in the preparation of copper-clad laminates.

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