Composite metal foil and metal-clad laminate

Abstract

The application discloses a composite metal foil and a metal-clad laminate, the composite metal foil comprising a substrate layer, a transition layer and a thermistor layer which are sequentially stacked; the transition layer is an electrically conductive amorphous film, and the sheet resistance of the transition layer is less than or equal to 50 Ω / □. By arranging the transition layer between the substrate layer and the thermistor layer, and the transition layer being an electrically conductive amorphous film, a completely uniform surface without grain boundary interference can be provided, the influence of the crystal lattice of the substrate layer is blocked, the resistance uniformity of the thermistor layer is effectively improved, internal stress can be released, and the problem of internal stress concentration can be avoided; in addition, by limiting the sheet resistance of the transition layer to be less than or equal to 50 Ω / □, it can be ensured that the substrate layer forms a resistance circuit with the thermistor layer through the transition layer after etching the window, and the resistance characteristics of the thermistor layer can be avoided from being affected, so that the stability of the thermosensitive characteristics of the thermistor layer is improved, and the high-precision temperature sensing requirement can be met.

Description

Technical Field

[0001] This invention relates to the field of electronic information materials technology, and in particular to a composite metal foil and a metal-clad laminate. Background Technology

[0002] With the rise of artificial intelligence, electronic components are gradually developing towards high performance and miniaturization. Electronic components are prone to heat generation during operation, and increased operating temperatures can cause them to malfunction. Therefore, temperature monitoring and control are necessary to ensure the normal operation of electronic components. Currently, due to the development of thin-film resistor technology, some circuit boards use embedded thin-film thermistor layers for thermal management monitoring, ensuring a smaller overall size and thickness of the circuit board.

[0003] In existing technologies, in order to set a thin-film thermistor layer in a metal foil, a resistive layer is usually sputtered directly onto a carrier metal layer. Before sputtering, the surface of the carrier metal layer generally has an anti-oxidation layer containing nickel, which is used to protect the carrier metal layer from oxidation before sputtering. However, the nickel in this anti-oxidation layer can easily cause the growth rate and orientation of the subsequently sputtered resistive layer to be different on different grains, which may lead to problems such as uneven resistance and internal stress concentration. This results in poor stability of its thermistor properties (such as the material constant B value), making it difficult to meet the subsequent high-precision temperature sensing requirements. Summary of the Invention

[0004] This invention provides a composite metal foil and a metal-clad laminate, which can improve the resistance uniformity of the thermistor layer obtained by sputtering and avoid the problem of internal stress concentration, thereby effectively improving the stability of the thermistor layer's thermal properties to meet the requirements of high-precision temperature sensing.

[0005] To address the aforementioned technical problems, a first aspect of the present invention provides a composite metal foil comprising a substrate layer, a transition layer, and a thermistor layer stacked sequentially; wherein the transition layer is a conductive amorphous thin film, and the sheet resistance of the transition layer is less than or equal to 50Ω / □.

[0006] As a preferred embodiment, the amorphous thin film is an amorphous metal nitride, an amorphous metal carbide, or an amorphous transition metal chalcogenide formed by reactive sputtering.

[0007] As a preferred embodiment, the amorphous metal nitride is at least one of titanium nitride, chromium nitride, zirconium nitride, hafnium nitride, tantalum nitride, molybdenum nitride, and tungsten nitride; and / or, the amorphous metal carbide is at least one of titanium carbide, chromium carbide, and tungsten carbide; and / or, the amorphous transition metal chalcogenide is at least one of tantalum disulfide and titanium disulfide.

[0008] As a preferred embodiment, the thickness of the transition layer is 5nm~100nm.

[0009] As a preferred embodiment, the thermistor layer is formed on the transition layer by one or more sputtering processes.

[0010] As a preferred embodiment, the thickness of the thermistor layer is 50nm~800nm, and the ratio between the thickness of the thermistor layer and the thickness of the transition layer is greater than or equal to 5.

[0011] As a preferred embodiment, the thermistor layer is made of a metal oxide with a spinel structure as the main phase, and the metal oxide includes at least Ni, Fe and O elements.

[0012] As a preferred embodiment, the metal oxide further includes one or more of the elements Mn, Co, Cu, and Al.

[0013] As a preferred embodiment, the surface roughness Rz of the substrate layer near the transition layer is ≤3μm; And / or, the ratio of the maximum to the minimum value among the N sheet resistance values ​​corresponding to any N sheet resistance test areas arbitrarily selected in the thermistor layer is less than or equal to 30%; where N is a positive integer and N≥10.

[0014] A second aspect of the present invention provides a metal-clad laminate, the metal-clad laminate comprising a composite metal foil as described in any one of the first aspects.

[0015] Compared to existing technologies, the beneficial effects of this invention are as follows: by providing a transition layer between the substrate layer and the thermistor layer, and the transition layer being a conductive amorphous thin film, a completely uniform surface free from grain boundary interference can be provided, blocking the lattice influence of the substrate layer. This effectively improves the resistance uniformity of the thermistor layer and releases internal stress, avoiding the problem of internal stress concentration. Furthermore, by limiting the sheet resistance of the transition layer to less than or equal to 50Ω / □, it can be ensured that after etching the window, the substrate layer forms a resistance circuit with the thermistor layer through the transition layer, and the resistance characteristics of the thermistor layer can be avoided, thereby improving the stability of the thermistor layer's thermal characteristics to meet the requirements of high-precision temperature sensing. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the first composite metal foil in the embodiments of the present invention; Figure 2 This is a schematic diagram of the composite metal foil after etching and windowing in an embodiment of the present invention; Figure 3This is a schematic diagram of the structure of the second type of composite metal foil in this embodiment of the invention; Figure 4 This is a schematic diagram of the etching and windowing process of the composite metal foil in an embodiment of the present invention; The structure consists of: 1. base layer; 2. transition layer; 3. thermistor layer. Detailed Implementation

[0017] 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, and not all embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0019] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used in this application are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0020] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] Please see Figure 1 The first aspect of the present invention provides a composite metal foil, comprising a base layer 1, a transition layer 2 and a thermistor layer 3 stacked sequentially; the transition layer 2 is a conductive amorphous thin film, and the sheet resistance of the transition layer 2 is less than or equal to 50Ω / □.

[0022] It is worth noting that the substrate layer 1, as the support of the composite structure, is used for etching to form circuits after the resistive side of the composite metal foil is subsequently pressed onto the circuit board substrate, so that the patterned resistive layer can take effect. The substrate layer 1 is preferably made of copper, and can be made of electrolytic copper foil or rolled copper foil. Besides copper, other conductive materials can also be used, such as gold, silver, iron, aluminum, or other metals and non-metals; this embodiment does not specifically limit the use of copper.

[0023] The thermistor layer 3 exhibits excellent temperature sensitivity, with its resistance displaying a stable non-linear relationship with temperature changes. This allows for precise temperature measurement; for example, it may exhibit NTC (Negative Temperature Coefficient) characteristics, meaning its resistance decreases as temperature increases, or PTC (Positive Temperature Coefficient) characteristics, meaning its resistance increases as temperature increases. When the composite metal foil is placed on a circuit board for temperature monitoring, the thermistor layer 3's thermal effect monitors temperature changes in the circuitry, thereby enabling heat monitoring and even feedback regulation of electronic components.

[0024] To improve the resistance uniformity of the thermistor layer 3, this embodiment provides a transition layer 2 between the substrate layer 1 and the thermistor layer 3. Firstly, this transition layer 2 creates a gradient transition in the coefficient of thermal expansion between the substrate layer 1 and the thermistor layer 3, which can release internal stress and act as an interface stress buffer, ensuring the overall stability of the composite metal foil structure. Furthermore, the transition layer 2 is a conductive amorphous thin film, which, through its conductivity, ensures the stability of the composite metal foil structure under various conditions. Figure 2After the etching window is shown, the portion of the substrate layer 1 on both sides of the window can contact the thermistor layer 3 and form a resistive circuit. On the other hand, the amorphous state of the transition layer 2 provides a completely uniform surface free from grain boundary interference. After the thermistor layer 3 is formed, it can block the lattice influence of the substrate layer 1, greatly improving the resistance uniformity of the sputtered thermistor layer 3, thereby improving the stability of the thermistor properties of the thermistor layer 3. In addition, the amorphous structure has higher atomic freedom and diffusion ability. During the deposition process, atoms are more likely to form a dense and tough interface with nickel atoms on the anti-oxidation surface of the substrate layer 1, fundamentally improving the reliability of the interface between the substrate layer 1 and the thermistor layer 3, and enhancing the adhesion between the amorphous thin film and the substrate layer 1. Furthermore, this embodiment also limits the sheet resistance of the transition layer 2 to less than or equal to 50Ω / □. For example, its sheet resistance is 50Ω / □, 45Ω / □, 42Ω / □, 38Ω / □, 36Ω / □, 31Ω / □, 29Ω / □, 25Ω / □, 20Ω / □, 18Ω / □, 15Ω / □, 13Ω / □, 10Ω / □, 5Ω / □, etc. This embodiment does not make specific limitations here. The sheet resistance value of the transition layer 2 can be measured using a four-probe tester. Since the thermistor... The surface of the resistive layer 3 will be laminated onto the circuit board substrate. Then, the base layer 1 and the transition layer 2 will be etched with an etching solution to expose the bottom resistive layer. At this time, the base layer 1 on both sides of the window will contact the thermistor layer 3 through the bottom transition layer 2 to form a resistive circuit. Therefore, the sheet resistance of the transition layer 2 will be limited to within 50Ω / □ to ensure that it has a small resistivity and meets the conductivity requirements. This will avoid affecting the resistance characteristics when the thermistor layer 3 is exposed by subsequent etching, thereby improving the temperature sensing accuracy in later applications.

[0025] As a preferred embodiment, the amorphous thin film is an amorphous metal nitride, an amorphous metal carbide, or an amorphous transition metal chalcogenide formed by reactive sputtering.

[0026] It is worth noting that the amorphous thin film in this embodiment is formed on the substrate 1 by reactive sputtering. Specifically, it is formed on the anti-oxidation surface of the substrate 1 by reactive sputtering. Since the reactive sputtering product has good adhesion to the Ni (nickel) element on the anti-oxidation surface, it can ensure excellent adhesion on the substrate 1 and avoid delamination of the composite metal foil.

[0027] Furthermore, this embodiment uses amorphous metal nitrides, amorphous metal carbides, or amorphous transition metal chalcogenides as materials for forming amorphous thin films. On the one hand, the amorphous nature of these materials ensures that the surface of the transition layer 2 is extremely smooth, which facilitates the formation of a thermistor layer 3 with high resistance uniformity and avoids local stress concentration caused by grain boundaries. On the other hand, amorphous metal nitrides, amorphous metal carbides, and amorphous transition metal chalcogenides all have good conductivity and can be removed by subsequent etching processes.

[0028] As a preferred embodiment, the amorphous metal nitride is at least one of titanium nitride (TiN), chromium nitride (CrN), zirconium nitride (ZrN), hafnium nitride (HfN), tantalum nitride (TaN), molybdenum nitride (MoN), and tungsten nitride (WN).

[0029] In this embodiment, the amorphous metal nitride can be one of titanium nitride (TiN), chromium nitride (CrN), zirconium nitride (ZrN), hafnium nitride (HfN), tantalum nitride (TaN), molybdenum nitride (MoN), and tungsten nitride (WN), or a combination of two or more of them. This embodiment does not make a specific limitation. These metal nitrides are easy to prepare amorphous thin films without sharp crystal diffraction peaks, random crystal orientations, and grain boundaries. They can fundamentally eliminate the problems of bonding force differences and internal stress concentration caused by mismatch between the nickel grain orientation and the anti-oxidation surface of the substrate 1. Moreover, the sheet resistance can meet the requirement of less than or equal to 50Ω / □, which has excellent conductivity and is easy to remove in subsequent etching processes.

[0030] Taking the sputtering of amorphous titanium nitride (TiN) to form a transition layer 2 as an example, an electrolytic copper foil (18 μm thick) with a nickel anti-oxidation layer (approximately 50 nm to 200 nm thick) was selected as the substrate layer 1. A titanium target was used as the target material on this substrate layer 1, and magnetron sputtering was performed using nitrogen (N2) as the reactive gas. The stage temperature was 100°C, the argon (Ar) flow rate was adjusted to 40 sccm, the nitrogen flow rate was 10 sccm, the chamber working pressure was maintained at 0.3 Pa, the nitrogen to argon flow rate ratio was 1:4, and the DC sputtering power was set to 150 W. After 10 minutes of deposition, a titanium nitride transition layer film with a thickness of approximately 30 nm was obtained on the substrate layer 1. X-ray diffraction analysis (XRD) showed that the deposited titanium nitride transition layer film had almost no sharp crystal diffraction peaks, confirming its amorphous structure. Then, sheet resistance was measured using a four-probe tester, and the sheet resistance value was 25±5Ω / □, which meets the conductivity requirements. Furthermore, the surface roughness Rq of the titanium nitride transition layer film was detected to be less than 0.5nm using atomic force microscopy (AFM), confirming that it has achieved the goal of providing an atomically smooth growth interface.

[0031] In the aforementioned magnetron sputtering process, by controlling the stage temperature below 150°C and maintaining the nitrogen to argon flow ratio within the range of 1:3 to 1:5, transition metal nitride thin films exhibiting both amorphous properties and electrical conductivity can be prepared. Furthermore, when using chromium, zirconium, or tantalum targets and introducing nitrogen or hydrocarbon gases, similar processes can be employed to prepare amorphous CrN, ZrN, or WC thin films, all with sheet resistances below 50 Ω / □ and exhibiting good electrical conductivity.

[0032] Furthermore, the amorphous metal carbide is at least one of titanium carbide (TiC), chromium carbide (CrC), and tungsten carbide (WC).

[0033] Specifically, the amorphous metal carbide in this embodiment can be one of titanium carbide (TiC), chromium carbide (CrC), and tungsten carbide (WC), or a combination of two or more of them. This embodiment does not impose specific limitations. These materials are all highly conductive ceramic materials that maintain low resistivity even in their amorphous state, meeting the requirement of a sheet resistance less than or equal to 50 Ω / □ when fabricating the transition layer 2. Furthermore, these amorphous metal carbides are easily formed into an amorphous state through reactive sputtering, and after reflective sputtering, they exhibit good adhesion to the Ni element on the anti-oxidation surface of the substrate layer 1, significantly improving the bonding strength between the transition layer 2 and the substrate layer 1, and preventing delamination or peeling during subsequent processes.

[0034] Furthermore, the amorphous transition metal chalcogenide is at least one of tantalum disulfide (TaS2) and titanium disulfide (TiS2).

[0035] Specifically, in this embodiment, when using an amorphous transition metal chalcogenide to form the transition layer 2, only tantalum disulfide (TaS2) or titanium disulfide (TiS2) can be used, or both tantalum disulfide (TaS2) and titanium disulfide (TiS2) can be used simultaneously. This embodiment does not make specific limitations here. Both tantalum disulfide (TaS2) and titanium disulfide (TiS2) can easily form amorphous thin films without grain boundaries and random crystal orientations through reactive sputtering. Both are typical layered conductive chalcogenides. Even in the amorphous state, they still have high carrier mobility and high conductivity concentration. The sheet resistance of the film prepared by sputtering can be stably controlled within 50Ω / □, which can ensure that after etching and opening the window, the substrate layer 1 and the thermistor layer 3 form a stable resistance circuit through the transition layer 2, avoiding interference of the temperature sensing accuracy of the thermistor layer 3 by the resistance of the transition layer 2 itself.

[0036] In addition, the aforementioned amorphous metal nitrides, amorphous metal carbides, and amorphous transition metal chalcogenides can all provide a gradient transition effect in the coefficient of thermal expansion between the substrate layer 1 and the thermistor layer 3, effectively releasing the interfacial stress caused by temperature changes during the operation of electronic components, avoiding cracking of the thermistor layer 3 and drift of the B value due to stress concentration, and ensuring the long-term stability of thermistor properties.

[0037] As a preferred embodiment, the thickness of the transition layer 2 is 5nm~100nm.

[0038] Specifically, in this embodiment, the thickness of the transition layer 2 is further limited to 5nm~100nm. For example, its thickness can be 5nm, 10nm, 14nm, 18nm, 23nm, 27nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 83nm, 86nm, 90nm, 95nm, 100nm, etc. This embodiment does not make a specific limitation here, so as to ensure that the thickness of the transition layer 2 is relatively thin. On the one hand, it can avoid the overall thickness of the composite metal foil being too thick. On the other hand, it can ensure that before processing and etching, most of the current still flows through the thermistor layer 3 body, so as to minimize the shunting interference of the transition layer 2 on the resistance measurement signal and ensure the accuracy of the resistance characteristics of the thermistor layer 3 body.

[0039] As a preferred embodiment, the thermistor layer 3 is formed on the transition layer 2 by one or more sputtering processes.

[0040] Specifically, in this embodiment, the thermistor layer 3 can be formed on the transition layer 2 by one or more sputtering processes, depending on factors such as the required resistor thickness or resistance value. That is, the thermistor layer 3 can present as one or more layers in the slice display state. For example, ... Figure 3 As shown, the thermistor layer 3 has a three-layer structure. In this embodiment, the number of layers of the thermistor layer 3 is not specifically limited.

[0041] like Figure 4 As shown, the etching and windowing process of the composite metal foil with copper foil as the base layer 1 in this embodiment is as follows: First, a thermistor layer 3 with NTC characteristics is formed on the transition layer 2 on the base copper foil by magnetron sputtering to obtain the composite metal foil; then, the resistive side of the composite metal foil is pressed onto a PP (Polypropylene) sheet at high temperature, and a resistive coating is applied to the other side. Based on the local area where the circuit needs to be formed, the part outside the area is exposed and developed, and then acid etching is used to retain the composite metal foil part used to form the circuit, and the resistive coating is removed from the remaining part; further, the remaining composite metal foil part on the PP sheet is coated with a second layer of resist, and then the area where the window needs to be opened to expose the thermistor layer 3 is exposed and developed, and the base layer 1 and transition layer 2 in the area are etched by alkaline etching to finally expose the thermistor layer 3, and then the resistive coating is removed from the remaining coated circuit area.

[0042] As a preferred embodiment, the thickness of the thermistor layer 3 is 50nm~800nm, and the ratio between the thickness of the thermistor layer 3 and the thickness of the transition layer 2 is greater than or equal to 5.

[0043] Specifically, this embodiment further limits the thickness of the thermistor layer 3 to 50nm~800nm. For example, the thickness of the thermistor layer 3 can be 50nm, 100nm, 145nm, 182nm, 203nm, 220nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 647nm, 694nm, 711nm, 745nm, 785nm, 800nm, etc. This embodiment does not make a specific limitation here, so as to ensure that the thickness of the thermistor layer 3 is thick enough to enable its main function to achieve the thermal characteristics. Moreover, within this thickness range, it can ensure that its resistance is relatively large and its density is good, which can improve the resistance uniformity and thermal stability of the thermistor layer 3. In addition, considering the principle of parallel circuits, the current tends to flow to the path with lower resistance. By ensuring that the thermistor layer 3 has a certain thickness, it can be ensured that most of the current still flows through the thermistor layer 3 body. At the same time, it can avoid the thermistor layer 3 being too thick. For example, if its thickness exceeds 1μm, it is easy to cause its sheet resistance value to be too low, which is not conducive to forming a thermistor layer 3 with a large sheet resistance.

[0044] Furthermore, this embodiment also limits the ratio between the thickness of the thermistor layer 3 and the thickness of the transition layer 2 to be greater than or equal to 5. For example, the ratio can be 5, 6, 7, 8, 9, 10, 11, 12, etc. This embodiment does not make a specific limitation here, so as to ensure that the thickness of the thermistor layer 3, which is the main functional layer, is sufficiently thick compared with the thickness of the transition layer 2, avoiding excessive interference to the resistance measurement signal due to the excessive thickness of the conductive transition layer 2 with low resistance, and further ensuring that most of the current still flows through the thermistor layer 3 body.

[0045] As a preferred embodiment, the thermistor layer 3 is made of a metal oxide with a spinel structure as the main phase, and the metal oxide includes at least Ni, Fe and O elements.

[0046] Specifically, in this embodiment, the thermistor layer 3 is made of a metal oxide with a spinel structure as the main phase, such as nickel oxide or iron oxide. In order to form the thermistor layer 3, the metal oxide with a spinel structure as the main phase can be directly pre-made into a target material. Then, the metal oxide target material is directly sputtered on the transition layer 2 to form the main functional layer. This ensures that the thermistor layer 3, as the main working area of ​​the NTC effect or PTC effect, has a uniform and dense structure, which ensures the high stability and low dispersion of the core parameters of the thermistor layer 3 (such as resistivity (ρ) and material constant (B value)).

[0047] Furthermore, in this embodiment, the thermistor layer 3 is primarily composed of Ni, Fe, and O elements, making it a nickel-iron oxide alloy. Nickel-iron oxide is a ferrite material with excellent temperature sensitivity; its resistance exhibits a stable nonlinear relationship with temperature changes, allowing for precise temperature measurement. It can operate over a wide temperature range, possesses chemical and thermal stability, and maintains stable performance even under long-term use or harsh environments (such as high temperature or high humidity). Its relatively low manufacturing cost makes it suitable for mass production. By changing the ratio of nickel to iron or doping with other elements (such as manganese or zinc), its resistance-temperature characteristics can be adjusted to meet specific application requirements.

[0048] Preferably, in the thermistor layer 3, the content of Fe element is less than 30%, the content of Ni element is greater than 30%, and the content of O element is less than 60%. Such a composition ratio makes etching easier and further improves temperature sensitivity and thermal stability, thereby enhancing the quality of the composite metal foil.

[0049] As a preferred embodiment, the metal oxide further includes one or more of the elements Mn, Co, Cu, and Al.

[0050] Specifically, in this embodiment, the thermistor layer 3 can also be doped with one or more of Mn, Co, Cu and Al elements. By combining multiple metal oxides, the resistivity composition can be enriched and the B value of the thermistor layer 3 can be further improved.

[0051] As a preferred embodiment, the surface roughness Rz of the base layer 1 near the transition layer 2 is ≤3μm.

[0052] Specifically, in order to further improve the resistance uniformity of the thermistor layer 3, this embodiment roughens the surface of the substrate layer 1 and the transition layer 2, and the surface roughness Rz is less than or equal to 3μm. For example, the surface roughness Rz of this side surface is 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, etc. This embodiment does not make a specific limitation, so that the surface of the substrate layer 1 near the transition layer 2 is a low profile surface, which can provide a uniform adhesion substrate for the thermistor layer 3 formed by subsequent sputtering, avoid the uneven resistance of the thermistor layer 3 due to the unevenness of this side surface, greatly improve the sheet resistance uniformity of the thermistor layer 3, and ensure the consistency of product performance.

[0053] Furthermore, the ratio of the maximum to the minimum value among the N sheet resistance values ​​corresponding to any N sheet resistance test areas arbitrarily selected in the thermistor layer 3 is less than or equal to 30%; where N is a positive integer and N≥10.

[0054] Specifically, to further ensure the sheet resistance uniformity of the thermistor layer 3, this embodiment employs a four-probe sheet resistance test method to perform sheet resistance tests on at least 10 randomly selected sheet resistance test areas in the thermistor layer 3. Among the at least 10 sheet resistance values ​​obtained, the ratio of the maximum and minimum values ​​is calculated, limiting the ratio of the maximum to the minimum value to be less than or equal to 30%. For example, the ratio of the maximum to the minimum value could be 30%, 25%, 20%, 15%, 10%, 5%, 3%, etc. This embodiment does not impose specific limitations here, thereby ensuring that the sheet resistance range of the thermistor layer 3 is small and the sheet resistance uniformity is good. It is worth noting that during the sheet resistance test, one side of the thermistor layer 3 on the composite metal foil needs to be pressed onto the circuit board substrate. Then, a portion of the base layer 1 is etched to expose a portion of the thermistor layer 3. Multiple sheet resistance test areas are divided along the TD or MD direction on the exposed surface of the thermistor layer 3. These sheet resistance test areas can be evenly spaced or randomly divided; this embodiment does not impose specific limitations here.

[0055] A second aspect of the present invention provides a metal-clad laminate, the metal-clad laminate comprising a composite metal foil as described in any embodiment of the first aspect.

[0056] The composite metal foil and metal-clad laminate provided in the embodiments of the present invention have at least the following beneficial effects: (1) By setting a transition layer 2 between the substrate layer 1 and the thermistor layer 3, and the transition layer 2 is a conductive amorphous thin film, a completely uniform surface without grain boundary interference can be provided, blocking the lattice influence of the substrate layer 1, effectively improving the resistance uniformity of the thermistor layer 3 and releasing internal stress, avoiding the problem of internal stress concentration; In addition, by limiting the sheet resistance of the transition layer 2 to less than or equal to 50Ω / □, it can be ensured that after etching the window, the substrate layer 1 forms a resistance circuit with the thermistor layer 3 through the transition layer 2, and the resistance characteristics of the thermistor layer 3 can be avoided, thereby improving the stability of the thermal characteristics of the thermistor layer 3, so as to meet the high-precision temperature sensing requirements.

[0057] (2) By limiting the thickness of the transition layer 2 to 5nm~100nm, it is possible to ensure that the thickness of the transition layer 2 is relatively thin. On the one hand, this avoids the overall thickness of the composite metal foil being too thick. On the other hand, it ensures that before the etching process, most of the current still flows through the thermistor layer 3 body, so as to minimize the shunting interference of the transition layer 2 on the resistance measurement signal and ensure the resistance characteristic accuracy of the thermistor layer 3 body.

[0058] (3) By limiting the thickness of the thermistor layer 3 to 50nm~800nm, and the ratio between the thickness of the thermistor layer 3 and the thickness of the transition layer 2 is greater than or equal to 5, it can be ensured that the thickness of the thermistor layer 3 is thick enough to achieve the thermal characteristics of its main function. Moreover, within this thickness range, it can ensure that its resistance is relatively large and its density is good, which can improve the resistance uniformity and thermal stability of the thermistor layer 3. In addition, it can also ensure that most of the current still flows through the thermistor layer 3 body, avoiding excessive interference from the shunting of the resistance measurement signal due to the excessive thickness of the conductive transition layer 2 with low resistance.

[0059] (4) By limiting the surface roughness Rz of the base layer 1 near the transition layer 2 to ≤3μm, the surface of the base layer 1 near the transition layer 2 is a low profile surface, which can provide a uniform substrate for the thermistor layer 3 formed by subsequent sputtering, avoid the uneven resistance of the thermistor layer 3 due to the unevenness of the surface on this side, and greatly improve the sheet resistance uniformity of the thermistor layer 3.

[0060] (5) By limiting the ratio of the maximum to the minimum of the N sheet resistance values ​​corresponding to any N sheet resistance test areas in the thermistor layer 3 to be less than or equal to 30%, it can be ensured that the sheet resistance range of the thermistor layer 3 is small and the sheet resistance uniformity is good.

[0061] To fully demonstrate the beneficial effects of the composite metal foil and metal-clad laminate provided in the embodiments of the present invention, the following description is provided in conjunction with specific embodiments and comparative examples.

[0062] Example 1 A composite metal foil includes a base layer, a transition layer and a thermistor layer stacked sequentially; the base layer is made of electrolytic copper foil, the transition layer is an amorphous metal nitride thin film formed by reactive sputtering, and the sheet resistance of the transition layer is 25Ω / □.

[0063] Example 2 A composite metal foil includes a substrate layer, a transition layer, and a thermistor layer stacked sequentially. The substrate layer is made of electrolytic copper foil, and the transition layer is an amorphous metal nitride thin film formed by reactive sputtering, with a sheet resistance of 40 Ω / □. The thickness of the transition layer is 20 nm. The thermistor layer is formed on the transition layer by a single sputtering process.

[0064] Example 3 A composite metal foil includes a substrate layer, a transition layer, and a thermistor layer stacked sequentially. The substrate layer is made of electrolytic copper foil. The transition layer is an amorphous metal carbide thin film formed by reactive sputtering, and the sheet resistance of the transition layer is 35 Ω / □. The thickness of the transition layer is 30 nm. The thermistor layer is formed on the transition layer by two sputtering operations. The thickness of the thermistor layer is 180 nm, and the ratio of the thickness of the thermistor layer to the thickness of the transition layer is 6.

[0065] The thermistor layer is made of a metal oxide with a spinel structure as the main phase, which includes Ni, Fe, and O elements. The surface roughness of the substrate layer near the transition layer is 1 μm.

[0066] Example 4 A composite metal foil includes a substrate layer, a transition layer, and a thermistor layer stacked sequentially. The substrate layer is made of electrolytic copper foil. The transition layer is an amorphous transition metal chalcogenide thin film formed by reactive sputtering, and the sheet resistance of the transition layer is 25 Ω / □. The thickness of the transition layer is 60 nm. The thermistor layer is formed on the transition layer by five sputtering operations. The thickness of the thermistor layer is 420 nm, and the ratio of the thickness of the thermistor layer to the thickness of the transition layer is 7.

[0067] The thermistor layer is made of a metal oxide with a spinel structure as the main phase, which includes Ni, Fe, and O elements. The surface roughness of the substrate layer near the transition layer is 1.5 μm. The ratio of the maximum to the minimum sheet resistance value among 10 randomly selected sheet resistance test areas in the thermistor layer is 20%.

[0068] Example 5 A composite metal foil includes a substrate layer, a transition layer, and a thermistor layer stacked sequentially. The substrate layer is made of electrolytic copper foil. The transition layer is an amorphous metal nitride thin film formed by reactive sputtering, and the sheet resistance of the transition layer is 15 Ω / □. The thickness of the transition layer is 70 nm. The thermistor layer is formed on the transition layer by five sputtering operations. The thickness of the thermistor layer is 560 nm, and the ratio of the thickness of the thermistor layer to the thickness of the transition layer is 8.

[0069] The thermistor layer is made of a metal oxide with a spinel structure as the main phase, which includes Ni, Fe, and O elements. The surface roughness of the substrate layer near the transition layer is 0.5 μm. The ratio of the maximum to the minimum sheet resistance value among 12 randomly selected sheet resistance test areas in the thermistor layer is 15%.

[0070] Comparative Example 1 A composite metal foil includes a base layer and a thermistor layer stacked sequentially.

[0071] Comparative Example 2 A composite metal foil includes a base layer, a transition layer and a thermistor layer stacked sequentially, wherein the transition layer is an organic thin film and the sheet resistance of the transition layer is greater than 200Ω / □.

[0072] After etching the composite metal foil circuits using the above embodiments and comparative examples, a test board was fabricated. The resistance uniformity and resistance recovery accuracy of the thermistor layer were then tested. The resistance uniformity was tested by sampling multiple sheet resistance values ​​from the thermistor layer and calculating the average value. The difference between the maximum and minimum sheet resistance values ​​was then calculated. The ratio of this difference to the calculated average value is used to characterize the resistance uniformity; the higher the resistance uniformity, the smaller this ratio. The resistance recovery accuracy characterizes the stability of the thermistor characteristics. Specifically, it is defined as follows: assuming the initial resistance of the thermistor layer at room temperature is R0, after multiple temperature cycling tests, it is returned to room temperature. The resistance obtained at this point is recorded as R1. The resistance recovery accuracy is |R1-R0| / R0. The test results are shown in Table 1 below. Table 1. Test results of resistance uniformity and resistance recovery accuracy of the thermistor layer

[0073] Examples 1-5, by setting a transition layer between the substrate layer and the thermistor layer, wherein the transition layer is a conductive amorphous thin film with a sheet resistance of less than 50 Ω / □, provides a completely uniform surface free from grain boundary interference, blocking the lattice influence of the substrate layer and effectively improving the resistance uniformity of the thermistor layer. Specifically, in Examples 1-5, the ratio between the difference between the maximum and minimum sheet resistance values ​​and the average sheet resistance value is relatively small, indicating high resistance uniformity. Furthermore, the transition layer with a sheet resistance of less than 50 Ω / □ ensures that after etching and opening the window, the substrate layer forms a resistance circuit with the thermistor layer through the transition layer, avoiding any impact on the resistance characteristics of the thermistor layer, thereby improving the stability of the thermistor layer's thermal characteristics. As shown in Table 1 above, the resistance recovery accuracy of the thermistor layers in Examples 1-5 is relatively low, indicating good stability of their thermal characteristics.

[0074] In contrast, the composite metal foil in Example 1 lacks a transition layer between the substrate layer and the thermistor layer. Consequently, the nickel element in the antioxidant layer on the surface of the substrate layer causes the thermistor layer to grow at different rates and orientations on different grains, resulting in low resistance uniformity and poor thermistor stability. Its resistance recovery accuracy is as high as 19%.

[0075] Although the composite metal foil in Comparative Example 2 has a transition layer between the substrate layer and the thermistor layer, it is an organic thin film with a sheet resistance greater than 200 Ω / □. Therefore, compared with conductive amorphous thin films, it cannot provide a completely uniform surface free from grain boundary interference. After the thermistor layer is sputtered to form, the resistance uniformity of the thermistor layer is still low. Moreover, due to its excessive sheet resistance, the resistance characteristics of the thermistor layer are affected, resulting in poor thermistor stability and a resistance recovery accuracy as high as 16%.

[0076] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A composite metal foil, characterized in that, It includes a base layer, a transition layer and a thermistor layer stacked sequentially; the transition layer is a conductive amorphous thin film, and the sheet resistance of the transition layer is less than or equal to 50Ω / □.

2. The composite metal foil as described in claim 1, characterized in that, The amorphous thin film is an amorphous metal nitride, amorphous metal carbide, or amorphous transition metal chalcogenide formed by reactive sputtering.

3. The composite metal foil as described in claim 2, characterized in that, The amorphous metal nitride is at least one of titanium nitride, chromium nitride, zirconium nitride, hafnium nitride, tantalum nitride, molybdenum nitride, and tungsten nitride; and / or, the amorphous metal carbide is at least one of titanium carbide, chromium carbide, and tungsten carbide; and / or, the amorphous transition metal chalcogenide is at least one of tantalum disulfide and titanium disulfide.

4. The composite metal foil as described in claim 1, characterized in that, The thickness of the transition layer is 5nm~100nm.

5. The composite metal foil as described in claim 1, characterized in that, The thermistor layer is formed on the transition layer by one or more sputtering processes.

6. The composite metal foil as described in claim 1 or 4, characterized in that, The thickness of the thermistor layer is 50nm~800nm, and the ratio between the thickness of the thermistor layer and the thickness of the transition layer is greater than or equal to 5.

7. The composite metal foil as described in claim 1, characterized in that, The thermistor layer is made of a metal oxide with a spinel structure as the main phase, and the metal oxide includes at least Ni, Fe and O elements.

8. The composite metal foil as described in claim 7, characterized in that, The metal oxide also includes one or more of the elements Mn, Co, Cu, and Al.

9. The composite metal foil as described in claim 1, characterized in that, The surface roughness Rz of the base layer near the transition layer is ≤3μm; And / or, the ratio of the maximum to the minimum value among the N sheet resistance values ​​corresponding to any N sheet resistance test areas arbitrarily selected in the thermistor layer is less than or equal to 30%; where N is a positive integer and N≥10.

10. A metal-clad laminate, characterized in that, The metal-clad laminate comprises a composite metal foil as described in any one of claims 1 to 9.

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