Composite metal foil, metal-clad laminated board and circuit board

Abstract

The invention discloses a composite metal foil, a metal-clad laminated board and a circuit board. The composite metal foil includes: a resistive layer; the resistance layer has a temperature coefficient, and the activation energy of the resistance layer is 0.6-9.2 * 10 <-2 > eV. According to the embodiment of the invention, heating monitoring and even feedback adjustment of the electronic component can be realized, and the thermal management precision is high.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of electronic technology, and in particular to a composite metal foil, a metal-clad laminate and a circuit board. Background Art

[0002] With the continuous advancement of the electronics industry and information technology, electronic components are developing towards high performance and miniaturization. However, electronic components will generate heat during operation. As the operating temperature increases, the electronic components will not be able to operate normally. Therefore, it is necessary to control the temperature of the electronic components to keep them operating normally. To achieve this goal, temperature control elements are often set on the surface or side of the electronic components, or chip thermistors are attached to the surface of the electronic components to monitor the temperature of the electronic components.

[0003] At present, the volume of temperature control elements is relatively large. Setting temperature control elements or surface-mounted thermistors on the surface of electronic components to achieve temperature monitoring is not conducive to the integration of circuit boards and occupies space on the circuit boards. Due to the limited location of its use, it is not possible to set temperature monitoring elements on many small electronic components, and it is also difficult to monitor the heat generation of most electronic components. Inadequate heat monitoring may result in the unmonitored electronic components being burned or failing due to overheating, affecting the normal operation of the circuit board and the terminal.

[0004] The resistance of a chip thermistor increases or decreases with temperature changes. However, due to its large size and high thickness, it is impossible to directly make a thermistor in the circuit and can only be soldered to the pad after subsequent circuit processing. At present, the industry does not use embedded resistor copper foil as a thermistor for temperature monitoring of electronic components.

[0005] At present, the thermal cycle performance of existing thermistor products has passed the requirements, but the detection accuracy is not enough. Specifically, at slight temperatures, the resistance value of the resistor layer does not change much, the response accuracy is low, and it is easily submerged by conventional noise. It can only respond when the temperature changes greatly, resulting in low thermal management efficiency and poor results. Summary of the invention

[0006] The present invention provides a composite metal foil, a metal-clad laminate and a circuit board, which have high thermal management accuracy and can monitor and even feedback-regulate the heating of electronic components.

[0007] According to one aspect of the present invention, there is provided a composite metal foil, characterized in that it comprises: a resistance layer;

[0008] The resistance layer has a temperature coefficient, and the activation energy of the resistance layer is 0.6-9.2×10 -2 eV.

[0009] Optionally, the relationship between the resistance value of the resistance layer and the temperature is expressed as follows:

[0010]

[0011] Wherein, R is the resistance value of the resistance layer, R0 is the pre-exponential factor, the resistance value range of R0 is 20kΩ~100kΩ, E a is the activation energy of the resistor layer, k is the Boltzmann constant, T is the temperature of the resistor layer, the unit is K, and the calculation is dimensionless.

[0012] Optionally, the material of the resistance layer includes at least one of iron oxide, manganese oxide, nickel oxide, cobalt oxide, copper oxide, nickel-iron oxide, nickel-zinc oxide, zinc oxide, ferrite, aluminum oxide, and titanium oxide.

[0013] Optionally, the mass proportion of the nickel-iron oxide is greater than the mass proportion of the aluminum oxide.

[0014] Optionally, for every 5° C. change in temperature, the resistance change rate of the resistance layer is greater than 2%.

[0015] Optionally, for every 1° C. change in temperature, the resistance change rate of the resistance layer is greater than 0.5%.

[0016] Optionally, the temperature rises from 25° C. to 150° C. and then drops to 25° C. as one temperature cycle, and within at least one temperature cycle, the resistance recovery deviation of the resistor layer is less than 8%.

[0017] Optionally, within N temperature cycles, the resistance recovery deviation of the resistor layer is less than 13%, wherein N≥200.

[0018] Optionally, the resistance layer has a thickness ranging from 50 nm to 3 μm.

[0019] Optionally, the resistance range of the resistance layer is greater than or equal to 500Ω.

[0020] Optionally, the composite metal foil further includes a conductive layer, and the resistance layer is arranged on one side of the conductive layer.

[0021] Optionally, the roughness Rz of the side surface of the conductive layer close to the resistance layer ranges from 1 μm to 7 μm.

[0022] Optionally, the composite metal foil further includes an adjustment layer, and the adjustment layer is arranged on a side of the resistance layer away from the conductive layer.

[0023] According to another aspect of the present invention, there is provided a metal-clad laminate, wherein the metal-clad laminate comprises the composite metal foil according to any embodiment of the present invention.

[0024] According to another aspect of the present invention, there is further provided a circuit board, wherein the circuit board comprises a circuit made of the composite metal foil described in any embodiment of the present invention.

[0025] The technical solution of the embodiment of the present invention provides a thermistor composite metal foil material, which is integrated into the circuit of the circuit board through an embedded design, does not occupy other packaging positions, and is conducive to the use of small-volume circuit boards. In addition, the thermistor composite metal foil material has a high activation energy, which represents the energy required to excite electrons from the valence band to the conduction band. When the temperature rises, more electrons obtain enough energy to cross the energy gap and enter the conduction band to participate in conduction. The higher the activation energy, the more obvious the effect of temperature rise on conductivity. Therefore, the composite metal foil can maintain the sensitivity of the resistor layer to temperature in a wider temperature range, thereby improving the circuit sensitivity and response accuracy of the thermistor in the circuit board and improving thermal management efficiency.

[0026] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 is a schematic structural diagram of a composite metal foil provided according to an embodiment of the present invention;

[0029] Figure 2 It is a schematic diagram of the structure of another composite metal foil provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0031] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0032] Figure 1 is a schematic diagram of the structure of a composite metal foil provided according to an embodiment of the present invention, Figure 1 The embodiment of the present invention provides a composite metal foil, characterized in that it includes: a resistance layer 10; the resistance layer 10 has a temperature coefficient, and the activation energy of the resistance layer 10 is 0.6-9.2×10 -2 eV.

[0033] Optionally, the resistance layer may be formed by spraying, electroplating, chemical plating, evaporation plating, ALD, PVD, CVD or other forming methods.

[0034] Specifically, the resistance layer 10 is formed on one side of the substrate by magnetron sputtering once or multiple times.

[0035] The composition ratio of transition metal oxides has a significant effect on the temperature sensitivity of NTC thermistors, because different transition metal oxides have different conductivity, activation energy, and response characteristics to temperature changes. Adjusting the ratio of these oxides can change the resistance-temperature characteristics of the thermistor, making it show higher sensitivity or stability within a specific temperature range.

[0036] The higher the activation energy of the material, the more sensitive the conductivity of the NTC thermistor is to temperature changes, and the larger the negative temperature coefficient, that is, the more significant the decrease in resistance as the temperature increases. By adjusting the activation energy, thermistors in different temperature ranges can be designed to meet the temperature sensitivity requirements of specific applications.

[0037] The technical solution of the embodiment of the present invention provides a thermistor composite metal foil material, which is integrated into the circuit of the circuit board through an embedded design, does not occupy other packaging positions, and is conducive to the use of small-volume circuit boards. In addition, the thermistor composite metal foil material has a high activation energy, which represents the energy required to excite electrons from the valence band to the conduction band. When the temperature rises, more electrons obtain enough energy to cross the energy gap and enter the conduction band to participate in conduction. The higher the activation energy, the more obvious the effect of temperature rise on conductivity. Therefore, the composite metal foil can maintain the sensitivity of the resistor layer to temperature in a wider temperature range, thereby improving the circuit sensitivity and response accuracy of the thermistor in the circuit board and improving thermal management efficiency.

[0038] Furthermore, the relationship between the resistance value R of the resistor layer and the temperature T is expressed as follows:

[0039]

[0040] Among them, R is the resistance value of the resistor layer, and R0 is the pre-exponential factor, which represents the resistance value of the material without the influence of activation energy (that is, theoretically at infinite high temperature). The resistance range of R0 is 20kΩ~100kΩ, and E a is the activation energy of the resistor layer, k is the Boltzmann constant (8.617×10 -5 eV / K), T is the temperature of the resistor layer, the unit is K, and the calculation is dimensionless.

[0041] This relationship establishes a functional relationship between the resistance value R and the temperature T, which limits the resistance change trend under temperature changes. Under this change trend, the detection accuracy of the thermistor can be guaranteed, the thermal management efficiency in the terminal can be improved, and the production cost can be reduced and the economic benefits can be improved.

[0042] Specifically, the influence of activation energy on negative temperature coefficient and its principle: Relationship between activation energy and conductivity: In NTC thermistor materials, the relationship between conductivity (or resistivity) and temperature change can usually be described by the following Arrhenius formula:

[0043]

[0044] Where R(T) is the conductivity of the material at temperature T, R0 is the pre-exponential factor (constant, material-dependent), E a is the activation energy of the material, k is the Boltzmann constant, and T is the absolute temperature in Kelvin.

[0045] The formula shows that the conductivity (or resistivity) of a material changes exponentially with increasing temperature, and the activation energy controls the magnitude of this change. The greater the activation energy, the more sensitive the material's conductivity is to temperature changes.

[0046] It should be noted that the effect of activation energy on negative temperature coefficient (NTC): Negative temperature coefficient (NTC) refers to the property that the resistance of a material decreases as the temperature increases. Activation energy plays a key role in this:

[0047] High activation energy materials: If the activation energy of a material is high, then its conductivity is more temperature-dependent, i.e., when the temperature rises, the conductivity increases significantly and the resistance decreases significantly. Such materials have a higher negative temperature coefficient and therefore exhibit greater resistance changes under larger temperature changes, and have higher sensitivity.

[0048] Low activation energy materials: If the activation energy of a material is low, the conductivity changes less with temperature and the resistance changes less with temperature. Therefore, the negative temperature coefficient of the material is small and the temperature sensitivity is relatively low.

[0049] Specific influencing mechanism: The specific influencing mechanism of activation energy in thermistor materials is related to the carrier generation and migration of the materials.

[0050] Electron excitation: Activation energy represents the energy required to excite electrons from the valence band to the conduction band. When the temperature rises, more electrons gain enough energy to cross the energy gap and enter the conduction band to participate in conduction. Therefore, the higher the activation energy, the more obvious the effect of temperature rise on conductivity.

[0051] Ion migration: In metal oxide materials, carriers include not only electrons, but also holes and ions. The higher the activation energy, the more dependent the excitation and migration of carriers in the material are on temperature changes, resulting in a faster decrease in resistance with temperature.

[0052] Alternatively, the activation energy of thermistor materials can be adjusted through material design (such as adjusting the composition, doping with trace elements, etc.), thereby controlling the sensitivity of the resistance to temperature changes. For example:

[0053] Improving activation energy: By increasing the proportion of manganese (Mn) or cobalt (Co) oxides, the activation energy of the material can be increased, making it more temperature sensitive in the high temperature region.

[0054] Optionally, the material of the resistance layer includes at least one of iron oxide, manganese oxide, nickel oxide, cobalt oxide, copper oxide, nickel-iron oxide, nickel-zinc oxide, zinc oxide, ferrite, aluminum oxide, and titanium oxide.

[0055] It should be noted that the activation energy and the temperature coefficient of resistance: the working principle of NTC thermistors is based on the negative temperature coefficient effect, that is, as the temperature increases, the resistance value decreases. This characteristic is determined by the activation energy of the material (which controls the temperature dependence of the carrier concentration). Different transition metal oxides have different activation energies, so they respond differently to temperature. Adjusting the composition ratio will affect the overall activation energy of the material, which in turn affects the temperature coefficient of resistance.

[0056] Oxides with high activation energy (such as manganese oxides) usually maintain higher sensitivity over a wider temperature range.

[0057] Oxides with low activation energy (such as nickel oxide) have better temperature response characteristics at lower temperatures. Influence of the composition ratio of transition metal oxides: The temperature sensitivity of the thermistor can be optimized by adjusting the composition ratio of different oxides.

[0058] The activation energy of the material is crucial to the negative temperature coefficient (NTC) thermistor because it is directly related to how the material's conductivity changes with temperature. Specifically, the higher the activation energy, the greater the change in the resistance value of the NTC thermistor with increasing temperature, that is, the higher the temperature sensitivity.

[0059] Specifically, the mass proportion of nickel iron oxide is greater than the mass proportion of aluminum oxide.

[0060] Nickel oxide shows better sensitivity in low temperature areas. Increasing the proportion of nickel oxide helps optimize the performance of the thermistor at low temperatures, making it more sensitive in a lower temperature range (such as 0°C to 100°C). Iron oxide (Fe2O3): Iron oxide can improve the stability and durability of the thermistor, and can also help control the range of resistance value changes. The right amount of iron oxide helps provide better sensitivity and smooth temperature response in the medium temperature range (100°C to 300°C).

[0061] By precisely controlling the ratio of different metal oxides, the thermistor can be made to respond more sensitively and stably within a specific temperature range.

[0062] In one embodiment, the resistance change rate of the resistor layer is greater than 2% for every 5°C temperature change. Exemplarily, the resistance change rate of the resistor layer is 2%, 3%, 4%, 5%, 6%, 8%, 10%, 15% or other values ​​for every 5°C temperature change. This makes the resistance change rate of the thermistor greater within a specific temperature range, thereby improving the response speed of the thermal management circuit to small temperature changes, and the accuracy can meet the use of the thermistor in the terminal, thereby improving the detection sensitivity.

[0063] Furthermore, for every 1°C change in temperature, the resistance change rate of the resistor layer is greater than 0.5%. Exemplarily, for every 1°C change in temperature, the resistance change rate of the resistor layer is 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.1%, 1.2%, 1.5% or other values. This can further improve the response speed of the thermal management circuit to small temperature changes, and can have a larger resistance value change within a 1°C temperature change, thereby causing a change in voltage, current or level, further improving the response speed, meeting the use of thermistors in the terminal, and improving detection sensitivity.

[0064] Optionally, the resistance change rate per unit temperature may be increased by changing the composition, adjusting the thickness or other improvement methods.

[0065] In this embodiment, by adding manganese oxide to the resistor layer, the proportion of which is within 5%, increasing the proportion of manganese oxide can improve the sensitivity of the thermistor in the high temperature range, because manganese oxide has a higher activation energy, making the resistor layer suitable for working in the high temperature zone.

[0066] Specifically, the operating temperature of the components to be tested can be monitored in real time through the resistance change of the composite metal foil resistor layer. When the preset temperature is exceeded, timely protection can be provided through other temperature control circuits, thereby protecting the components to be tested and preventing the electronic components from being burned out due to excessive temperature.

[0067] In one embodiment, the temperature rises from 25° C. to 150° C. and then drops to 25° C. as one temperature cycle. In at least one temperature cycle, the resistance value recovery deviation of the resistor layer is less than 8%.

[0068] Specifically, within at least one temperature cycle, the resistance recovery deviation of the resistor layer is less than 13%, ensuring that the resistance of the composite metal foil in the temperature measurement circuit is stable, thereby ensuring that the voltage change in the temperature measurement circuit is stable, avoiding large jumps in voltage, ensuring the normal operation of the temperature measurement circuit, and avoiding large voltage differences during the temperature measurement of the composite metal foil that affect the use of other active devices.

[0069] Furthermore, within N temperature cycles, the resistance recovery deviation of the resistor layer is less than 13%, wherein N≥200.

[0070] Specifically, after multiple cycles, the resistance of the resistor layer can still be restored to near the initial value, and the resistance value still changes steadily, thereby ensuring that the composite metal foil has a longer service life and improving the quality of the circuit board and the terminal using it.

[0071] Continue to refer Figure 1 Optionally, the thickness of the resistance layer 10 is in the range of 50 nm to 3 μm.

[0072] Specifically, the resistor layer 10 is formed on one side of the copper foil by magnetron sputtering once or multiple times (or formed by other physical or chemical plating processes), with a thickness of 50nm to 3μm. Within this range, the thickness is adjusted to increase the resistance value, so that the temperature coefficient is increased and the detection accuracy is improved. When the film thickness is very thin, the carriers may jump between different conductive areas through the quantum tunneling effect, causing the conductivity to be very sensitive to temperature, thereby increasing the temperature coefficient of resistance (TCR). The thinner the film, the greater the residual stress is usually, especially in physical vapor deposition processes such as sputtering. Residual stress can cause microstructural defects, such as an increase in grain boundaries and vacancy density, thereby increasing the temperature sensitivity of the resistor and improving the TCR. The thinner the film, the shorter the heat diffusion path and the faster the local temperature changes in the material, which will accelerate the temperature response of the film and increase the TCR. When the film thickness is very thin, the carriers may jump between different conductive areas through the quantum tunneling effect, causing the conductivity to be very sensitive to temperature, thereby improving the TCR.

[0073] Continue to refer Figure 1 Optionally, the resistance range of the resistance layer 10 is 500Ω to 10MΩ.

[0074] Specifically, the resistance of the resistance layer 10 is set to 500Ω-10MΩ, which can meet the production requirements of different circuits.

[0075] Figure 2 is a schematic diagram of the structure of another composite metal foil provided according to an embodiment of the present invention, Figure 2 Optionally, the composite metal foil further includes a conductive layer 20, and the resistor layer 10 is disposed on one side of the conductive layer 20. By stacking the conductive layer 20 and the resistor layer 10, pressing them on the substrate, and forming a circuit through a circuit manufacturing process, the resistor can be buried in the circuit, thereby improving the compactness of the circuit design and helping to reduce the volume of the circuit.

[0076] It should be noted that the resistance value test condition of the resistor layer is to measure on a resistor layer material with an aspect ratio of 1:1.

[0077] Optionally, the conductive layer material includes a single metal layer and / or an alloy layer; wherein the single metal layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0078] Specifically, the conductive layer is copper foil. Figure 2, further, the thickness of the conductive layer 20 is 5 to 100 μm. The roughness Rz of the side of the conductive layer 20 close to the resistor layer 10 is in the range of 1 μm to 7 μm. When the resistor layer 10 is a copper layer, it can be used to directly etch a temperature measurement circuit to meet the needs of circuit etching, and improve the stability of current transmission while controlling the cost of use. The roughness within the above range can further ensure the bonding force between the resistor layer 10 and the conductive layer 20, and at the same time ensure the bonding force between the composite metal foil and the substrate after pressing, to prevent the circuit from falling off.

[0079] Continue to refer Figure 2 In one embodiment, the composite metal foil further includes an adjustment layer 30 , and the adjustment layer 30 is disposed on a side of the resistance layer 10 away from the conductive layer 20 .

[0080] Optionally, the material of the adjustment layer 30 may be a coupling agent, an adhesive or other materials.

[0081] Specifically, the adjustment layer 30 is a silane coupling agent, and the function of the adjustment layer 30 is to enhance the bonding force between the thermistor copper foil pressed on the substrate and the substrate to prevent it from falling off.

[0082] Embodiment 1

[0083] A composite metal foil comprises a resistance layer and a conductive layer. The conductive layer is made of Cu and has a thickness of 18 μm. The resistance layer is made of a mixture of ferrite and nickel-iron oxide and has a thickness of 300 nm. The activation energy of the resistance layer is 1.4×10 -3 eV. Under the test environment, when the temperature rises from 25°C to 125°C, the relationship between the resistance value of the resistor layer and the temperature satisfies the formula:

[0084]

[0085] Among them, the resistance value of R0 is 95kΩ.

[0086] Embodiment 2

[0087] The difference from Example 1 is that the material of the resistance layer is a mixture of ferrite and nickel-zinc oxide, and the thickness of the resistance layer is 500 nm. -3 eV, the relationship between the resistance value of the resistor layer and the temperature satisfies the above relationship, and the resistance value of R0 is 120kΩ.

[0088] Embodiment 3

[0089] Different from the first embodiment, the composite metal foil further includes an adjustment layer, which is arranged on a side of the resistance layer away from the conductive layer, and the material of the adjustment layer is a silane coupling agent.

[0090] Comparative Example 1

[0091] The composite metal foil includes a resistance layer and a conductive layer, wherein the conductive layer is made of Cu and has a thickness of 15 μm, and the resistance layer is made of nickel phosphorus oxide and has a thickness of 800 nm. The activation energy of the resistance layer is 0.4×10 -3 eV.

[0092] Comparative Example 2

[0093] Different from comparative example 1, the thickness of the resistor layer is 2.5 μm. Under the test environment, when the temperature rises from 25°C to 125°C, the relationship between the resistance value of the resistor layer and the temperature satisfies the formula:

[0094]

[0095] Among them, the resistance value of R0 is 15kΩ.

[0096] The thermal management circuit test board was made by etching the composite metal foil of the above embodiment and comparative example, and the average resistance value change rate was measured every 25°C in the oven at a temperature range of 25°C to 125°C; the average resistance value change rate was measured every 5°C in the temperature change range of 25°C to 50°C; the average resistance value change rate was measured every 5°C in the temperature change range of 25°C to 35°C, and the change results are shown in Table 1 below:

[0097] Table 1

[0098]

[0099]

[0100] According to the comparative analysis of the test data, it can be seen that the resistance layer in Examples 1-3 has higher detection accuracy and can achieve faster response in a low temperature environment, thereby improving the thermal management effect inside the terminal.

[0101] An embodiment of the present invention provides a metal-clad laminate, which includes the composite metal foil according to any embodiment of the present invention.

[0102] Since the metal-clad laminate includes the composite metal foil provided by any embodiment of the present invention, the metal-clad laminate has the same beneficial effects as the composite metal foil, which will not be described in detail herein.

[0103] An embodiment of the present invention further provides a circuit board, which includes a circuit made of the composite metal foil according to any embodiment of the present invention.

[0104] Specifically, the composite metal foil can be a thermistor copper foil, which is embedded in a micron-level line width circuit to make a circuit board, without occupying the circuit board component placement position, and is matched with a temperature monitoring circuit. By using the changes in voltage and current in the circuit caused by temperature changes, the heating monitoring and even feedback adjustment of electronic components can be realized. The thermistor copper foil is embedded in a single-layer board or a multi-layer board, and then the chip is packaged on the circuit board.

[0105] Since the circuit board includes the composite metal foil provided by any embodiment of the present invention, the beneficial effects of the above-mentioned circuit board and the composite metal foil are the same, which will not be described in detail here.

[0106] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite metal foil, characterized in that: include: Resistor layer; The resistance layer has a temperature coefficient, and the activation energy of the resistance layer is 0.6-9.2×10 -2 eV.

2. The composite metal foil according to claim 1, characterized in that: The relationship between the resistance value of the resistance layer and the temperature is expressed as follows: Wherein, R is the resistance value of the resistance layer, R0 is the pre-exponential factor, the resistance value range of R0 is 20kΩ~100kΩ, E a is the activation energy of the resistor layer, k is the Boltzmann constant, T is the temperature of the resistor layer, the unit is K, and the calculation is dimensionless.

3. The composite metal foil according to claim 1, characterized in that: The material of the resistance layer includes at least one of iron oxide, manganese oxide, nickel oxide, cobalt oxide, copper oxide, nickel-iron oxide, nickel-zinc oxide, zinc oxide, ferrite, aluminum oxide, and titanium oxide.

4. The composite metal foil according to claim 3, characterized in that: The mass proportion of the nickel-iron oxide is greater than the mass proportion of the aluminum oxide.

5. The composite metal foil according to claim 1, characterized in that: For every 5°C change in temperature, the resistance change rate of the resistance layer is greater than 2%.

6. The composite metal foil according to claim 1, characterized in that: The resistance change rate of the resistance layer is greater than 0.5% for every 1°C change in temperature.

7. The composite metal foil according to claim 1, characterized in that: The temperature rises from 25° C. to 150° C. and then drops to 25° C. for one temperature cycle. In at least one temperature cycle, the resistance value recovery deviation of the resistor layer is less than 8%.

8. The composite metal foil according to claim 7, characterized in that: Within N temperature cycles, the resistance recovery deviation of the resistor layer is less than 13%, wherein N≥200.

9. The composite metal foil according to claim 1, characterized in that: The thickness of the resistance layer is in the range of 50 nm to 3 μm.

10. The composite metal foil according to claim 1, characterized in that: The resistance range of the resistance layer is greater than or equal to 500Ω.

11. The composite metal foil according to claim 1, characterized in that: It also includes a conductive layer, and the resistance layer is arranged on one side of the conductive layer.

12. The composite metal foil according to claim 11, characterized in that The roughness Rz of the side surface of the conductive layer close to the resistance layer is in the range of 1 μm to 7 μm.

13. The composite metal foil according to claim 11, characterized in that: It also includes an adjustment layer, which is arranged on a side of the resistance layer away from the conductive layer.

14. A metal-clad laminate, characterized in that: The metal-clad laminate comprises the composite metal foil according to any one of claims 1 to 13.

15. A circuit board, characterized in that: The circuit board comprises a circuit made of the composite metal foil described in any one of claims 1-13.

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