A composite metal foil and circuit board

Abstract

This invention discloses a composite metal foil and a circuit board. The composite metal foil includes a conductive layer and a resistive layer stacked together. The conductive layer has a plurality of protrusions on its surface near the resistive layer. The top regions of the protrusions are distributed with coarsened particles. In a cross-section along the thickness direction from the top to the bottom of the protrusion, the coarsened particles cover at least 40% of the height of the protrusion. Furthermore, in the cross-section, the coarsened particles are distributed on both sides of the top of the protrusion. The resistive layer covers the protrusions and the coarsened particles, thereby optimizing the adhesion between the resistive layer and the conductive layer while improving the deposition uniformity of the resistive layer.

Description

Technical Field

[0001] This invention relates to the field of circuit board materials technology, and more particularly to a composite metal foil and circuit board. Background Technology

[0002] As high-frequency and high-speed electronic circuits develop towards higher integration, buried copper foil integrates resistors with copper foil and integrates resistors into the circuit through etching. This replaces traditional soldered chip resistors, resulting in smaller size, shorter transmission paths, and simplified process flow. It can effectively improve the integration of printed circuit boards (PCBs) and meet the new demands for miniaturization, high density, high frequency, and high speed. Therefore, in the field of high frequency and high speed, buried copper foil is gradually being used to replace traditional resistors.

[0003] To ensure the adhesion between the copper foil and the circuit board, a large number of copper tooth structures need to be set on the copper foil bonding surface. However, too many or too large copper tooth structures will affect the uniformity of the resistive layer deposition, thereby affecting the electrical performance of the resistive layer. Summary of the Invention

[0004] This invention provides a composite metal foil and circuit board that optimizes the adhesion between the resistive layer and the conductive layer while improving the deposition uniformity of the resistive layer.

[0005] In a first aspect, embodiments of the present invention provide a composite metal foil, comprising a conductive layer and a resistive layer stacked together. The conductive layer has a plurality of protrusions on one side surface near the resistive layer. The top regions of the protrusions are distributed with coarsened particles. In a cross section along the thickness direction from the top to the bottom of the protrusion, the coarsened particles cover at least 40% of the height of the protrusion. Furthermore, in the cross section, the coarsened particles are distributed on both sides of the top of the protrusion. The resistive layer covers the protrusions and the coarsened particles.

[0006] Optionally, the number of coarsened particles distributed on each of the protrusions is 3 to 20.

[0007] Optionally, the projected area of ​​all the coarsened particles on each of the protrusions on the surface of the conductive layer accounts for 5% to 40% of the projected area of ​​the protrusion on the surface of the conductive layer.

[0008] Optionally, the maximum profile peak height Rp of the conductive layer on the side of the surface closest to the resistive layer is 5 μm to 20 μm.

[0009] Optionally, the arithmetic mean roughness Rq of the surface of the conductive layer near the resistive layer is 0.8 μm to 2 μm.

[0010] Optionally, the ratio of the vertical height h of the protrusion to the width w of the protrusion is in the range of 0.5 to 1.

[0011] Optionally, within a preset observation area, the number of protrusions accounts for more than 80%, and the ratio of the overall height h1 of the coarsened particles on the protrusions to the vertical height h of the corresponding protrusions ranges from 0.1 to 0.35.

[0012] Optionally, the ratio of the sheet resistance range of the resistive layer to the average sheet resistance of the resistive layer is less than 12%.

[0013] Optionally, the composite metal foil further includes a bonding layer, which is disposed on the side of the resistive layer opposite to the conductive layer, and is used to bond with the circuit board.

[0014] Optionally, the ratio of the thickness of the bonding layer to the thickness of the resistive layer is 0.01 to 0.2.

[0015] Secondly, embodiments of the present invention provide a circuit board, the material of which includes the composite metal foil described in any embodiment of the present invention.

[0016] The composite metal foil provided by this invention reduces obstruction to the deposition path by concentrating coarsened particles only on the top and upper sidewalls of the protrusions, rather than densely covering the entire surface. During vertical deposition, the resistive material can smoothly cover the coarsened particles on the top and sides of the protrusions and fill the gaps between adjacent protrusions, forming a continuous and uniform resistive film. The coarsened particles form bonding points with the conductive layer in areas above 40% of the protrusion height, significantly improving the adhesion between the resistive and conductive layers and preventing peeling during subsequent hot pressing or reflow soldering. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a composite metal foil provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the electron microscope morphology of a conductive layer under vertical observation, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the morphology of a conductive layer observed at a 45° angle in an embodiment of the present invention. Figure 4 This is a schematic diagram of a cross-sectional structure of a conductive layer provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the process for providing a composite metal foil according to an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Currently, the common production methods for buried copper foil in the industry are chemical plating and magnetron sputtering. Among them, sputtered resistor layers have better density and stability, and magnetron sputtering has a wide range of selectable resistor materials, high material utilization, and no waste liquid, making it the preferred method for the production of resistor materials in the future.

[0020] However, buried resistive copper foil produced by magnetron sputtering has strict requirements on the morphology of the sputtered copper foil substrate. On the one hand, to ensure the adhesion between the copper foil and PTFE, it is generally desirable to have as many copper teeth on the copper foil surface as possible, and the higher the density, the better. On the other hand, during magnetron sputtering, the resistive material is usually deposited vertically on the copper foil substrate. The dense copper teeth on the copper foil surface can hinder the uniform deposition of the resistive layer, resulting in an uneven thickness of the resistive layer formed on the copper foil surface. At the bottom of different roughened copper teeth, the resistive layer may not even be deposited. The uneven thickness of the resistive layer does not have abnormal electrical performance under normal conditions, but after high-temperature processing, such as lamination and reflow soldering, open circuits may occur, leading to resistor failure, or the device may fail during use after resistor assembly.

[0021] In view of this, Figure 1 This is a schematic diagram of a composite metal foil provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the electron microscope morphology of a conductive layer observed vertically, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the electron microscope morphology of a conductive layer observed at a 45° angle, provided as an embodiment of the present invention. Figure 4 This is a schematic diagram of a cross-sectional structure of a conductive layer provided in an embodiment of the present invention. See also: Figures 1-4 The composite metal foil includes a conductive layer 110 and a resistive layer 120 stacked together. The conductive layer 110 has a plurality of protrusions 111 on one side surface near the resistive layer 120. The top regions of the protrusions 111 are distributed with coarsened particles 112. In a cross section along the thickness direction from the top to the bottom of the protrusions 111, the coarsened particles 112 cover at least 40% of the height of the protrusions 111. In the cross section, coarsened particles 112 are distributed on both sides of the top of the protrusions 111. The resistive layer 120 covers the protrusions 111 and the coarsened particles 112.

[0022] Specifically, the conductive layer 110 is composed of a highly conductive material, such as one or more combinations of copper, gold, silver, iron, aluminum, graphite, conductive polymers, and carbon fiber composites. In this embodiment, the conductive layer 110 can be made of copper. A resistive layer 120 can be formed on the surface of the conductive layer 110, and the resistive layer 120 is used to provide stable surface resistance. The resistive layer 120 can be composed of a multi-element conductive alloy. For example, the resistive layer 120 contains at least two of titanium (Ti), nickel (Ni), chromium (Cr), silicon (Si), phosphorus (P), aluminum (Al), cobalt (Co), manganese (Mn), iron (Fe), nitrogen (N), oxygen (O), and carbon (C). Exemplary multi-element conductive alloys may include nickel-chromium alloys, nickel-phosphorus alloys, or composite structures thereof.

[0023] In this process, the surface of the conductive layer 110 near the resistive layer 120 is roughened to form multiple protrusions 111. Each protrusion 111 extends upwards along the thickness direction of the conductive layer 110 and can have a cone-shaped, pyramid-shaped, cauliflower-shaped, dendritic, crown-shaped, cluster-shaped, clump-shaped, coral-shaped, columnar, or irregular peak-shaped form. At the apex of each protrusion 111, near its highest point, multiple roughened particles 112 are distributed. These roughened particles 112 are nanoscale particles attached to the surface of the protrusions 111, used to enhance the interfacial bonding between the conductive layer 110 and the resistive layer 120. These roughened particles 112 are not randomly scattered but are concentrated at specific locations on the protrusions 111 through process control. When viewed in a cross-section along the thickness direction of the protrusion 111, i.e., perpendicularly from the top to the bottom, the coarsening particles 112 cover at least 40% of the height of the protrusion 111. This means that the coarsening particles 112 not only exist at the top point but also extend downwards along the sidewalls of the protrusion 111 for a certain distance. Simultaneously, in the cross-section, coarsening particles 112 are distributed on both sides of the top of the protrusion 111. The coarsening particles 112 can be spatially symmetrically or approximately symmetrically distributed, avoiding stress shifts or interface weakness caused by unilateral deposition.

[0024] The resistive layer 120 is formed on the conductive layer 110 by a vertical incidence deposition process such as physical vapor deposition, sputtering, or atomic layer deposition. If there are dense and irregularly shaped copper teeth on the surface of traditional copper foil, the deposition particles cannot reach the valley area evenly due to the shadowing effect during the deposition of resistive material, which will cause the resistive layer 120 to be too thin in some areas or even open circuit, seriously affecting the sheet resistance consistency.

[0025] In this embodiment of the invention, by concentrating the coarsened particles 112 only on the top and upper sidewalls of the protrusion 111, rather than densely covering the entire surface, the obstruction of the deposition path is reduced. During vertical deposition, the resistive material can smoothly cover the coarsened particles 112 on the top and sides of the protrusion and fill the gaps between adjacent protrusions, forming a continuous and uniform resistive film. The coarsened particles 112 form bonding points with the conductive layer 110 in areas where the height of the protrusion 111 is above 40%, significantly improving the adhesion between the resistive layer 120 and the conductive layer 110 and preventing peeling during subsequent hot pressing or reflow soldering.

[0026] Optionally, the number of coarsened particles 112 distributed on each protrusion 111 is 3 to 20.

[0027] Specifically, the number of coarsened particles 112 can affect the distribution of the resistive layer 120. If the number of coarsened particles 112 is too small, an effective bonding connection cannot be formed around the protrusion 111, resulting in insufficient interfacial bonding force between the resistive layer 120 and the conductive layer 110. If the number of coarsened particles 112 is too large, the particle density is too high, which easily leads to agglomeration or accumulation at the top of the protrusion. This not only blocks the vertical deposition path of the subsequent resistive material but may also cause local stress concentration, thereby reducing the uniformity and reliability of the film layer. In this embodiment of the invention, by limiting the number of coarsened particles 112 distributed on each protrusion 111 to 3 to 20, a multi-point bonding structure is formed on a single protrusion 111, effectively enhancing the peel strength. Furthermore, by ensuring that the number of coarsened particles 112 is not excessive, it is possible to avoid blocking the deposition of the resistive layer 120, ensuring the uniformity of the deposition of the resistive layer 120. For example, aerosol spraying combined with electrostatic adsorption, or electrophoretic deposition under specific pH and potential conditions, is used to selectively enrich the coarsened particles 112 at the tip regions of each protrusion 111. By adjusting the deposition time, particle concentration, and electric field strength, the number of particles captured by each protrusion 111 is controlled to fall within the range of 3–20. Finally, a vertical incidence physical vapor deposition process, such as magnetron sputtering or electron beam evaporation, is used to deposit the resistive material on the entire surface of the structure, forming a continuous and dense resistive layer 120. Because the number of coarsened particles 112 on each protrusion 111 is moderate and the spatial distribution is controllable, the resistive material can uniformly coat the particles and fill the gaps during the deposition process, avoiding unevenness of the resistive layer 120 caused by shadows due to excessive particle density. By limiting the number of coarsened particles 112 on each protrusion 111 to 3 to 20, a performance balance is achieved between interfacial adhesion, film uniformity, and process feasibility.

[0028] The number of coarsened particles 112 can be counted by electron microscopy, EBSD slice observation, automatic image recognition or other methods.

[0029] Optionally, the projected area of ​​all the coarsened particles 112 on the surface of the conductive layer 110 on each protrusion 111 accounts for 5% to 40% of the projected area of ​​the protrusion 111 on the surface of the conductive layer 110.

[0030] Specifically, the orthographic projection area is the area of ​​the contour formed by projecting the image onto the plane of the conductive layer 110 along a direction perpendicular to the surface of the conductive layer 110. For example, if a protrusion 111 is circular in a top view with a diameter of 20 μm, then the orthographic projection area is approximately 314 μm. 2 The protrusion 111 has multiple coarsened particles 112 distributed on it. The sum of the projected surfaces of these particles under the same viewing angle should be between 5% and 40% of the orthographic projection area of ​​the protrusion 111, i.e., 15.7 μm. 2 Up to 125.6μm 2 between.

[0031] It should be noted that the projected area can be calculated automatically by processing the electron microscope image, such as using software like ImageJ, MATLAB, or OpenCV for automatic recognition and calculation, or by other calculation methods.

[0032] If the projection ratio of all coarsened particles 112 on the same protrusion 111 to the protrusion 111 is less than 5%, it indicates that the coverage density of the coarsened particles 112 is too low, failing to form effective bonding points. This results in insufficient interfacial bonding strength between the resistive layer 120 and the conductive layer 110, making it prone to peeling under thermal stress or mechanical bending. If the projection ratio of all coarsened particles 112 on the same protrusion 111 to the protrusion 111 exceeds 40%, the particles are too dense. This not only obstructs the deposition path of subsequent resistive materials, causing uneven local thickness of the resistive layer 120, but may also lead to micropores or defects due to particle aggregation, reducing the film's density and electrical performance stability. This embodiment of the invention controls the spatial coverage density of the coarsened particles 112 to avoid deposition obstruction caused by excessively dense coarsened particles 112, thereby improving the uniformity of the resistive layer 120.

[0033] Optionally, the maximum profile peak height Rp of the conductive layer 110 on the side of the surface near the resistive layer 120 is 5 μm to 20 μm.

[0034] Specifically, the maximum profile peak height Rp is the vertical distance from the profile centerline to the highest profile peak within a preset sampling length; it reflects the height of the most prominent peak on the surface. If the maximum profile peak height Rp is too high and the sidewalls are steep, the back side of the tall peak will be difficult to be covered by the resistive material due to obstruction during vertical incidence physical vapor deposition processes such as magnetron sputtering, resulting in insufficient film thickness or even open circuit areas. If the maximum profile peak height Rp is too low, the surface will be too flat, lacking effective bonding points, which is not conducive to bonding with the resistive layer 120.

[0035] In this embodiment of the invention, by limiting the maximum profile peak height Rp to 5 μm to 20 μm, when Rp is greater than or equal to 5 μm, the conductive layer 110 forms microscopic protrusions 111 of sufficient height on its surface without being too steep. During deposition, the resistive layer 120 can encapsulate these peaks and fill the surrounding voids, forming a stable bond. In actual processes, coarsening particles 112 are further attached to the surface of the protrusions 111 to enhance interface performance. A moderate maximum profile peak height Rp provides a well-defined apex, facilitating the selective enrichment of coarsening particles 112 at the peak apex and preventing the coarsening particles 112 from randomly scattering at the valley bottom.

[0036] In some embodiments, the arithmetic mean roughness Rq of the surface of the conductive layer 110 near the resistive layer 120 may be further defined or limited to be 0.8 μm to 2 μm.

[0037] Specifically, the arithmetic mean roughness Rq, also known as the root mean square roughness, is the root mean square value of the vertical distance from a surface point to the centerline within the sampling length. The arithmetic mean roughness Rq is more sensitive to extreme peaks and valleys, and can more accurately characterize the distribution of microstructure undulations. When the arithmetic mean roughness Rq is greater than 2 μm, it indicates severe surface undulations and excessively large local peak-valley differences. When using vertical incidence physical vapor deposition processes such as magnetron sputtering, deep valley areas are prone to insufficient deposition due to obstruction, resulting in uneven resistivity layer thickness, increased porosity, or even open circuits.

[0038] In this embodiment of the invention, by limiting the arithmetic mean roughness Rq of the surface of the conductive layer 110 near the resistive layer 120 to 0.8 μm to 2 μm, the surface undulations are ensured to be within a controllable range, making it less likely to form deposition breakpoints, thus enabling the resistive layer 120 to continuously and uniformly cover the entire surface of the conductive layer 110. When the arithmetic mean roughness Rq is greater than or equal to 0.8 μm, it indicates that there are sufficient micro-undulations on the surface, which can provide effective bonding points for the subsequently deposited resistive layer 120.

[0039] Furthermore, in high-frequency applications, excessively high surface roughness can exacerbate current path disturbances due to the skin effect, increasing conductor losses. Simultaneously, sharp peaks and valleys may cause localized electric field concentration, leading to signal reflection or crosstalk. By limiting the arithmetic mean roughness Rq of the surface of the conductive layer 110 near the resistive layer 120 to 0.8 μm to 2 μm, sufficient interfacial adhesion is provided while avoiding high-frequency losses caused by extreme roughness.

[0040] See also Figure 4 Optionally, the ratio of the vertical height h of the protrusion 111 to the width w of the protrusion 111 is in the range of 0.5 to 1.

[0041] Specifically, the vertical height h of the protrusion 111 is the vertical distance from the original substrate plane of the conductive layer 110 to the highest point of the protrusion 111. The width w of the protrusion 111 is the maximum projected dimension of the protrusion 111 on the surface of the conductive layer 110 in the horizontal direction. The ratio of the vertical height h to the width w reflects the steepness of the protrusion 111.

[0042] When the ratio of vertical height h to width w is less than 0.5, the surface exhibits insufficient undulation, making it difficult to form an effective bond. This results in weak interfacial adhesion between the resistive layer 120 and the conductive layer 110, making them prone to peeling. When the ratio of vertical height h to width w is greater than or equal to 0.5, the protrusion 111 has sufficient height and is no longer a flat bulge, thus forming an effective bonding point. During the coating process, the resistive layer 120 can wrap around the top of the protrusion and fill the surrounding gaps, enhancing the bonding force. If the ratio of vertical height h to width w is greater than 1, the sidewalls of the protrusion 111 are steep. When using vertical incidence physical vapor deposition processes such as magnetron sputtering, the towering sidewalls of the protrusion can lead to insufficient film thickness in some areas. Limiting the ratio of vertical height h to width w to less than or equal to 1 ensures a gentle slope on the sidewalls of the protrusion, allowing sputtered particles to effectively reach the sides and bottom of the protrusion, achieving uniform coverage of the entire surface.

[0043] In high-frequency circuits, an excessively high ratio of vertical height h to width w can cause the local electric field to concentrate at sharp peaks, resulting in additional insertion loss and return loss; while an excessively low ratio of vertical height h to width w cannot provide sufficient interface bonding, which may lead to microcracks during long-term use and indirectly affect signal stability.

[0044] In this embodiment of the invention, by limiting the ratio of vertical height h to width w to a range of 0.5-1, the protrusion 111 formed has a gentle slope structure, which can avoid electric field distortion and maintain interface reliability.

[0045] Optionally, within a preset observation area, the number of protrusions 111 accounts for more than 80%, and the ratio of the overall height h1 of the coarsened particles 112 on the protrusions 111 to the vertical height h of the corresponding protrusions 111 ranges from 0.1 to 0.35.

[0046] Specifically, the preset observation area is a standard test area used to evaluate the coverage of surface microstructures; for example, it can be 100 μm. 2The square field of view can be observed and statistically analyzed using a scanning electron microscope, white light interferometer, or atomic force microscope. The percentage of protrusions 111 is the actual number of protrusions 111 within the preset observation area relative to the theoretical maximum number of protrusions. That is, it is the percentage of the total number of protrusions that can be accommodated when the periodic array is fully filled. For example, if the theoretical maximum number of protrusions is 100, and 85 are actually observed, then the percentage is 85%. This embodiment of the invention limits the percentage of protrusions 111 to greater than 80%, so that bonding points can be formed in most areas of the conductive layer 110 surface, avoiding localized weak adhesion caused by large flat areas.

[0047] The overall height h1 of the roughened particles 112 is the vertical distance from the original top surface of the protrusion 111 to the highest point of the roughened particle 112 accumulation layer, reflecting the thickness of the additional roughened layer formed after the roughened particles 112 are attached. The ratio of the overall height h1 of the roughened particles 112 on the protrusion 111 to the vertical height h of the corresponding protrusion 111 is used to quantify the relative height of the roughened particles 112 relative to the protrusion 111. In this embodiment of the invention, the ratio of the overall height h1 of the roughened particles 112 on the protrusion 111 to the vertical height h of the corresponding protrusion 111 is limited to a range of 0.1 to 0.35. If the ratio of the overall height h1 of the roughened particles 112 on the protrusion 111 to the vertical height h of the corresponding protrusion 111 is less than 0.1, then the roughened particles 112 are too thin and cannot effectively increase the specific surface area, resulting in limited interface enhancement effect. If the ratio of the overall height h1 of the coarsened particles 112 on the protrusion 111 to the vertical height h of the corresponding protrusion 111 is greater than 0.35, the coarsened particles 112 will be stacked too high, easily forming a shield during the physical vapor deposition process, resulting in poor coverage of the resistive layer 120 at the particle gaps, or even producing pores or uneven thickness. This embodiment of the invention limits the ratio of the overall height h1 of the coarsened particles 112 on the protrusion 111 to the vertical height h of the corresponding protrusion 111 to a range of 0.1 to 0.35, thus fully utilizing the binding effect of the coarsened particles 112 while ensuring the continuous and dense film formation of the resistive layer 120, thereby guaranteeing consistent electrical performance.

[0048] Optionally, the ratio of the sheet resistance range of the resistive layer 120 to the average sheet resistance of the resistive layer 120 is less than 12%.

[0049] Specifically, sheet resistance, measured in Ω / □, is a parameter that measures the resistance of a thin film material per unit square area. The mean sheet resistance is the arithmetic mean of sheet resistance values ​​measured at multiple sampling points across the entire resistive layer 120 or a specified test area. The sheet resistance range is the difference between the maximum and minimum sheet resistance values ​​at all sampling points within the same test area. The ratio of the sheet resistance range to the mean sheet resistance reflects the electrical uniformity of the resistive layer 120 over the entire area.

[0050] Through the structural design of the composite metal foil in the above embodiments, for example, within a preset observation area, the proportion of protrusions 111 is greater than 80%, the ratio of the vertical height h of the protrusions 111 to the width w of the protrusions 111 is in the range of 0.5 to 1, or the ratio of the overall height h1 of the coarsened particles 112 on the protrusions 111 to the vertical height h of the corresponding protrusions 111 is in the range of 0.1 to 0.35, etc., the bonding advantages of the coarsened particles 112 can be retained, and the interference on the uniformity of the resistor layer 120 can be reduced. Both are conducive to achieving a ratio of the sheet resistance difference of the resistor layer 120 to the average sheet resistance of the resistor layer 120 of less than 12%, thereby improving device consistency and yield. In mass production, the scrap caused by local resistance deviation can be significantly reduced.

[0051] Optionally, the composite metal foil also includes a bonding layer disposed on the side of the resistive layer 120 opposite to the conductive layer 110, and the bonding layer is used to bond with the circuit board.

[0052] Specifically, the bonding layer is located on the side of the resistive layer 120 away from the conductive layer 110. It is a functional layer used to achieve reliable bonding or thermo-press bonding with the external circuit board. The material can be selected from epoxy resin modified acrylate, thermosetting polyimide precursor, or metal oxide containing functional groups. Its main function is to provide interfacial adhesion and thermal / mechanical buffering performance.

[0053] Optionally, the thickness ratio of the bonding layer to the resistor layer 120 is 0.01-0.2. This prevents excessively thick bonding layers from introducing unnecessary stress concentration or affecting overall flexibility, while maintaining the conductive layer 110 as the main structural layer. The bonding layer of the composite metal foil is thermo-pressed to the circuit board. The conductive layer 110 and the resistor layer 120 are patterned using photolithography and etching processes to form the required circuitry and resistive components.

[0054] For example, Figure 5 This is a schematic diagram of a composite metal foil provided in an embodiment of the present invention. See [link / reference]. Figure 5 The overall process includes the stages of raw foil preparation, copper tooth roughening, and silane surface treatment, specifically including: S110, Raw foil stage Specifically, a base copper foil, i.e., conductive layer 110, is prepared on a titanium roller cathode using electrolytic deposition. The target roughness is achieved on the non-titanium roller surface by adjusting the plating bath composition and electrochemical parameters. Specifically, the copper ion concentration in the plating bath is controlled at 80-100 g / L, the sulfuric acid concentration at 90-110 g / L, the temperature is maintained at 36-45℃, and the current density is set at 40 A / dm³. 2 Simultaneously added SPS (bis(3-sulfopropyl) disulfide) 15±2ppm, gelatin 10±2ppm, PEG (polyethylene glycol) 2±0.1g / L and Cl -40±5ppm. Among them, SPS and high current density work together to effectively promote grain refinement and surface micro-protrusion formation, that is, to form protrusion 111, so that the roughness of the obtained copper foil surface is stably controlled at 4-6μm, providing a good physical basis for subsequent interface bonding.

[0055] S120, Coarsening Stage of Copper Teeth To enhance surface adhesion, a copper tooth structure, i.e., protrusion 111, is further constructed on the rough surface of the raw foil. This step employs an additive-free pure copper electrodeposition process to avoid introducing impurities that could cause high-frequency signal interference or structural detachment. The plating bath uses a high-copper, medium-acid formulation: copper ion concentration of 30±3 g / L, sulfuric acid concentration increased to 160±10 g / L, and an application of 35±2 A / dm². 2 The high current density and roughening time are controlled within 6-10 seconds. Due to the tip discharge effect, copper preferentially deposits on the top of the rough surface micro-protrusions, thus forming roughened particles 112.

[0056] S130, silane coupling treatment stage To improve the interfacial adhesion between copper foil and low surface energy dielectric layers such as polytetrafluoroethylene (PTFE), a fluorosilane coupling agent is coated onto the roughened copper foil for fluorosilane surface modification. The fluorosilane coupling agent includes one or more of tridecafluorooctyltrimethoxysilane and heptadecafluorodecyltrimethoxysilane. A 1%–1.5% fluorosilane solution is applied by spraying at a pressure of 0.35 MPa and a processing speed of 1 m / min. Silane molecules form a dense self-assembled monolayer on the copper surface, with one end bonded to copper oxide and the other end providing hydrophobic functional groups compatible with PTFE. This significantly improves the adhesion strength and resistance to damp heat at the copper-dielectric interface during subsequent lamination processes.

[0057] To verify the technical advantages of the composite metal foil of the present invention in terms of interfacial bonding strength and resistance uniformity, the following comparative examples and experimental cases were set up and systematic tests were conducted.

[0058] Experimental Example Composite metal foils were prepared according to the preparation method as experimental samples, wherein, in the cross section in the thickness direction, the coarsening particles 112 covered at least 40% of the height of the protrusions 111, and the number of coarsening particles 112 distributed on each protrusion 111 was 3 to 20.

[0059] Comparative Example A conventional composite metal foil was used as a comparative sample. The conventional composite metal foil was not designed with the high coverage protrusion structure and controllable coarsening particles 112 as described in the embodiments of the present invention.

[0060] After laminating the composite metal foil with a polytetrafluoroethylene (PTFE) dielectric layer, the peel strength was tested according to the standard method with a sample width of 3.175 mm and a tensile angle of 90°.

[0061] Table 1 compares the electrical resistance of conventional copper foil and the copper foil of the present invention after sputtering. The comparative sample's three parallel peel strength tests yielded values ​​of 1.157 N / mm, 1.162 N / mm, and 1.153 N / mm, with an average peel force of 1.157 N / mm. The experimental sample from this embodiment of the invention yielded values ​​of 1.250 N / mm, 1.313 N / mm, and 1.189 N / mm, with an average peel force of 1.251 N / mm, representing an improvement of approximately 8.1% compared to the comparative sample.

[0062] Sheet resistance distribution was measured after sputtering a 120-layer resistive layer onto the surface of the experimental and comparative samples.

[0063] Table 2 shows the resistance performance of the comparative samples. Table 3 shows the resistance performance of the experimental samples. In a 200-point test grid (20 rows × 10 columns), the comparative sample had a mean sheet resistance of 50.41 Ω / □, a maximum of 56.03 Ω / □, a minimum of 46.06 Ω / □, and a range of 9.97 Ω / □. The ratio of the range to the mean was 19.8%, indicating poor uniformity in resistance distribution. In the same 200-point test grid, the experimental sample had a mean sheet resistance of 49.77 Ω / □, a maximum of 52.47 Ω / □, a minimum of 47.60 Ω / □, and a range of 4.87 Ω / □. The ratio of the range to the mean was 9.8%, significantly lower than the comparative sample's 19.8%, thus meeting the high uniformity requirement of less than 12%.

[0064] The present invention enhances the bonding force between the composite metal foil and PTFE by designing coarsening particles 112 to cover at least 40% of the height of the protrusion 111 in the cross section in the thickness direction, and the peel force is stable at more than 1.25 N / mm, which is superior to conventional composite metal foils.

[0065] The comparative example, due to the random surface microstructure and lack of height control, resulted in large fluctuations in film thickness during sputtering, with a sheet resistance range / mean ratio reaching 19.8%. In contrast, the structural design of this invention effectively suppresses the sputtering shadowing effect, resulting in a highly concentrated sheet resistance distribution and reducing the range / mean ratio to 9.8%, thus meeting the stringent requirements for resistance consistency in high-frequency devices.

[0066] In summary, the composite metal foil structure and preparation process proposed in the embodiments of the present invention not only improve the bonding force of the resistive layer 120, but also improve the electrical uniformity of the resistive functional layer.

[0067] This invention also provides a circuit board, also known as a printed circuit board, PCB, electronic board, or simply circuit board, which is an important electronic component. It includes a composite metal foil according to any embodiment of this invention. The composite metal foil is used to fabricate resistive circuits. When fabricating the resistive circuits, the conductive layer 110 and the resistive layer 120 of the composite metal foil are etched according to a preset resistive circuit image to obtain the desired resistive circuit. The circuit board of this invention, because it incorporates the composite metal foil of any embodiment of this invention, has the same beneficial effects, which will not be elaborated further here.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite metal foil, characterized in that, The device includes a conductive layer and a resistive layer stacked together. The conductive layer has a plurality of protrusions on the surface near the resistive layer. The top regions of the protrusions are distributed with coarsened particles. In a cross section along the thickness direction from the top to the bottom of the protrusion, the coarsened particles cover at least 40% of the height of the protrusion. In the cross section, the coarsened particles are distributed on both sides of the top of the protrusion. The resistive layer covers the protrusions and the coarsened particles.

2. The composite metal foil according to claim 1, characterized in that, The number of coarsened particles distributed on each of the protrusions is 3 to 20.

3. The composite metal foil according to claim 1, characterized in that, The projected area of ​​all the coarsened particles on each of the protrusions on the conductive layer surface accounts for 5% to 40% of the projected area of ​​the protrusion on the conductive layer surface.

4. The composite metal foil according to claim 1, characterized in that, The maximum profile peak height Rp of the conductive layer on the side of the resistive layer is 5 μm to 20 μm; and / or, the arithmetic mean roughness Rq of the conductive layer on the side of the resistive layer is 0.8 μm to 2 μm.

5. The composite metal foil according to claim 1, characterized in that, The ratio of the vertical height h of the protrusion to the width w of the protrusion is in the range of 0.5 to 1.

6. The composite metal foil according to claim 1, characterized in that, Within the preset observation area, the number of protrusions accounts for more than 80%, and the ratio of the overall height h1 of the coarsened particles on the protrusions to the vertical height h of the corresponding protrusions ranges from 0.1 to 0.

35.

7. The composite metal foil according to claim 1, characterized in that, The ratio of the sheet resistance range of the resistive layer to the average sheet resistance of the resistive layer is less than 12%.

8. The composite metal foil according to claim 1, characterized in that, It also includes a bonding layer disposed on the side of the resistive layer opposite to the conductive layer, the bonding layer being used to bond with the circuit board.

9. The composite metal foil according to claim 8, characterized in that, The ratio of the thickness of the bonding layer to the thickness of the resistive layer is 0.01 to 0.

2.

10. A circuit board, characterized in that, The circuit board is made of composite metal foil as described in any one of claims 1-9.

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