Composite metal foil and circuit board

Abstract

The embodiment of the invention discloses a composite metal foil and a circuit board. The composite metal foil comprises a first resistance layer; the first resistance layer is a thermistor layer; the preset percentage area of the first resistive layer has or does not have gaps in the forming process, and when the first resistive layer has the gaps, the number of the gaps is smaller than 50 within any 50 [mu] m range in the plane direction of the first resistive layer; wherein the notches are gullies which are observed in the slicing state of the composite metal foil and are formed in the thickness direction of the first resistance layer. The number of the notches in the first resistance layer is limited, and the composite metal foil is light and thin and small in size, so that the problem that the temperature control element or the thermistor in the prior art is large in size when heating monitoring is carried out on an electronic component is solved; the integration of the circuit board is not facilitated; and small components cannot be monitored.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of electronic devices, and in particular to a composite metal foil 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. Summary of the invention

[0004] The embodiment of the present invention provides a composite metal foil and a circuit board, which solves the technical problems that the temperature control element or thermistor in the prior art has a large size when monitoring the heat of electronic components, does not utilize the integration of the circuit board, and cannot monitor small components.

[0005] An embodiment of the present invention provides a composite metal foil, the composite metal foil comprising a first resistance layer;

[0006] The first resistance layer is a thermistor layer;

[0007] A preset percentage area of ​​the first resistor layer has or does not have notches during the formation process, and when notches are present, the number of the notches is less than 50 within any 50 μm range along the plane direction of the first resistor layer;

[0008] The notch is a groove formed along the thickness direction of the first resistor layer when the composite metal foil is observed in a sliced ​​state.

[0009] Furthermore, the number of the notches is less than 20 within any range of 25 μm along the plane direction of the first resistance layer.

[0010] Furthermore, the maximum width of the gap is less than 20 nm, wherein the width of the gap refers to a dimension along a plane direction of the first resistor layer, and the plane direction of the first resistor layer is perpendicular to a thickness direction.

[0011] Further, in the thickness direction of the first resistor layer, within a distance from one surface to another surface of the first resistor layer, the number of the gaps is greater than or equal to 0 and less than a first preset number.

[0012] Furthermore, along the planar direction of the first resistor layer, the shortest distance between two adjacent gaps is greater than 100 nm, wherein the two adjacent gaps refer to two gaps along the thickness direction of the first resistor layer that are consistent with the distance from the surface of one side of the first resistor layer away from the conductive layer.

[0013] Furthermore, the thickness difference of the first resistance layer in the plane direction is less than 400 nm.

[0014] Furthermore, the composite metal foil further comprises a conductive layer;

[0015] The first resistance layer is disposed on one side surface of the conductive layer.

[0016] Furthermore, the composite metal foil further includes a second resistance layer;

[0017] The second resistance layer is disposed on the other side of the conductive layer away from the first resistance layer.

[0018] Furthermore, the roughness of the surface of the conductive layer close to the first resistance layer is 1-7 μm.

[0019] Furthermore, the composite metal foil further includes an adjustment layer, and the adjustment layer is arranged on a surface of the first resistance layer away from the conductive layer.

[0020] Furthermore, the first resistor layer has a negative temperature coefficient, and within a temperature variation range of 25° C., a resistance variation rate of the first resistor layer is greater than 5%.

[0021] Furthermore, in a temperature cycle from 25° C. to 150° C. and then back to 25° C., the resistance recovery deviation of the first resistance layer is less than 10%.

[0022] An embodiment of the present invention further provides a circuit board, the circuit board comprising the composite metal foil described in any of the above embodiments;

[0023] The composite metal foil is used for laying the circuits on the circuit board, or the composite metal foil is laid on the surface of at least one layer of the circuit board.

[0024] The embodiment of the present invention discloses a composite metal foil and a circuit board, wherein the composite metal foil includes a first resistor layer; the first resistor layer is a thermistor layer; a preset percentage area of ​​the first resistor layer has or does not have notches during the formation process, and when there are notches, the number of notches is less than 10 within any 10 μm range along the plane direction of the first resistor layer; wherein the notches are grooves formed along the thickness direction of the first resistor layer observed in the composite metal foil in a sliced ​​state. The present application limits the number of notches on the first resistor layer, and because the composite metal foil is relatively light and thin and has a small volume, it solves the technical problem that the temperature control element or thermistor in the prior art is large in volume when monitoring the heating of electronic components, which is not conducive to the integration of the circuit board and the inability to monitor small components, and achieves the technical effect of improving the accuracy of component heating monitoring without affecting the integration of the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a structural diagram of a composite metal foil provided by an embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of a notch in the first resistance layer provided by an embodiment of the present invention;

[0027] Figure 3 is a structural diagram of another composite metal foil provided by an embodiment of the present invention;

[0028] Figure 4 This is a structural diagram of another composite metal foil provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0030] It should be noted that the terms "first", "second", etc. in the specification, claims and drawings of the present invention are used to distinguish different objects, rather than to limit a specific order. The following embodiments of the present invention can be implemented separately, or in combination with each other, and the embodiments of the present invention do not impose specific limitations on this.

[0031] Figure 1 It is a structural diagram of a composite metal foil provided in an embodiment of the present invention. Figure 2 Schematic diagram of the notch of the first resistance layer provided in an embodiment of the present invention.

[0032] like Figure 1As shown, an embodiment of the present invention provides a composite metal foil, which includes a first resistor layer 10; the first resistor layer 10 is a thermistor layer; a preset percentage area of ​​the first resistor layer 10 has or does not have a notch 11 during the formation process, and when there is a notch, the number of the notches 11 is less than 50 within any range of 50μm along the plane direction of the first resistor layer 10; wherein the notch 11 is a gully formed along the thickness direction of the first resistor layer 10 observed in the composite metal foil in a sliced ​​state.

[0033] It should be noted that the notch 11 is a disconnection point of the first resistance layer 10 with a maximum width greater than 5 nm and a maximum depth greater than 5 nm in a slice cross-section state.

[0034] Specifically, the material of the first resistor layer 10 may include Ni (nickel), Cr (chromium), Zn (zinc), Al (aluminum), Sn (tin), O (oxygen), N (nitrogen), Cu (copper), Mn (manganese), Fe (iron) or other elements that can achieve good thermal sensitivity.

[0035] Specifically, the material of the first resistor layer 10 is a nickel-iron oxide alloy. Nickel-iron oxide belongs to ferrite material, has good temperature sensitivity, and its resistance shows a stable nonlinear relationship with temperature change. It can be used to accurately measure temperature changes, and can work in a wide temperature range. It has chemical and thermal stability, can maintain stable performance in long-term use or harsh environments (such as high temperature or high humidity), has relatively low manufacturing costs, and is suitable for large-scale production. By changing the ratio of nickel to iron or doping other elements (such as manganese and zinc), its resistance-temperature characteristics can be adjusted to meet specific application requirements.

[0036] Furthermore, in the first resistor layer 10, the composition ratio is preferably: Fe content is less than 30%, Ni content is greater than 30%, and O content is less than 60%. Such a composition ratio can make etching easier on the one hand, and on the other hand can further improve temperature sensitivity and thermal stability, thereby improving the use quality of the composite metal foil.

[0037] When the composite metal foil is arranged in a circuit board for thermal management temperature monitoring, the voltage, current or level change of the circuit in the circuit board is monitored through the thermal effect of the first resistor layer 10, thereby realizing the heating monitoring and even feedback regulation of the electronic components.

[0038] Optionally, the first resistor layer 10 may be formed by PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), spraying, evaporation, magnetron sputtering or other processing methods.

[0039] When manufacturing the circuit board, the side of the first resistor layer 10 facing away from the conductive layer 20 is connected to the circuit board. In order to ensure the bonding force between the composite metal foil and the substrate during lamination, it is necessary to ensure that the side of the conductive layer 20 close to the first resistor layer 10 is uneven, referred to as the rough surface. Taking the conductive layer 20 as copper foil as an example, the first resistor layer 10 is processed on the rough surface. During the processing, due to process and material problems, the formation process of the first resistor layer 10 will grow vertically, resulting in Figure 2 The nanometer-scale hole gap in the red circle cannot be observed by naked eyes. Figure 2 The FIB (Focused Ion Beam) sliced ​​state shown shows downward-pointing grooves.

[0040] Specifically, the notch 11 will affect the continuity of the first resistor layer 10 and the uniformity of the square resistance. The composite metal foil can be used to lay the circuit in the circuit board. If the notch 11 is made in the circuit, the resistance value will increase or even cause the circuit to be interrupted, resulting in poor circuit production quality. In order to avoid such a situation, the production process is adjusted to reduce the number of notches 11 per unit length in the slicing state, that is, the notch 11 is less than 50 within any 50μm range along the plane direction of the first resistor layer 10, so as to ensure the uniformity and stability of the first resistor layer 10, meet the circuit production and use, ensure the reliability of the circuit, and then ensure the thermal management effect.

[0041] For example, see Figure 2 , with two gaps 11 (i.e. Figure 2 The depth of the notch 11 observed in the sliced ​​state ranges from 20 nm to 600 nm, and may be in the form of penetrating the first resistor layer 10 (e.g. Figure 2 There is a through hole in the area indicated by the red circle on the left side of the figure), or it is a blind hole in the first resistor layer 10, or it is a discontinuous hole (such as Figure 2 As shown in the right red circle, there are two connection points in the middle, forming three holes. The straight-line distance between two adjacent notches 11 is greater than 0.2 μm, and the thickness difference of the first resistance layer 10 is less than 200 nm.

[0042] In the embodiment of the present invention, the number of notches on the first resistor layer is limited, and because the composite metal foil is relatively thin and small in size, the technical problems that the temperature control element or thermistor in the prior art is large in size when monitoring the heat of electronic components, which is not conducive to the integration of circuit boards and small components cannot be monitored are solved, and the technical effect of improving the heat monitoring accuracy of components without affecting the integration of circuit boards is achieved.

[0043] In one embodiment, the number of the notches 11 is less than 20 within any range of 25 μm along the plane direction of the first resistance layer 10 .

[0044] Specifically, in order to further ensure the uniformity and stability of the first resistor layer 10, the number of notches 11 of the first resistor layer 10 in the selected composite metal foil can be limited to less than 20 within any 25 μm range along the plane direction of the first resistor layer 10. Under the performance of this composite metal foil, better resistance continuity can be achieved, the sudden increase of the resistance value of the first resistor layer is further reduced, the stability and reliability of circuit manufacturing are improved, and the thermal management effect is guaranteed.

[0045] In one embodiment, the maximum width of the notch 11 is less than 20 nm, wherein the width of the notch refers to the dimension along the plane direction of the first resistor layer 10 , and the plane direction of the first resistor layer 10 is perpendicular to the thickness direction.

[0046] Specifically, in order to ensure the uniformity and stability of the first resistor layer 10, the maximum width of the gap 11 is limited. Experimental verification shows that the maximum width of the gap 11 is less than 20 nm, which can ensure that the first resistor layer is continuous during magnetron sputtering processing and can well ensure the square resistance uniformity of the first resistor layer 10.

[0047] In one embodiment, in the thickness direction of the first resistor layer 10 , within a distance from one surface to another surface of the first resistor layer 10 , the number of the notches 11 is greater than or equal to 0 and less than a first preset number.

[0048] Specifically, see Figure 2 , there are three gaps 11 in the thickness direction of the first resistor layer 10 in the red circle on the right. Obviously, the best solution to achieve resistance continuity and ensure square resistance uniformity is to have no gaps 11, that is, the number of gaps 11 is 0. When the number of gaps 11 is within the above range, the production cost can be reduced while ensuring the stability of the electrical performance of the first resistor layer 10 to meet the circuit etching requirements.

[0049] In one embodiment, along the planar direction of the first resistor layer 10, the shortest distance between two adjacent notches 11 is greater than 100 nm, wherein the two adjacent notches 11 refer to two notches 11 along the thickness direction of the first resistor layer 10, which are consistent with the distance from the surface of one side of the first resistor layer 10 away from the conductive layer 20.

[0050] Specifically, see Figure 2 , Figure 2The distance between the position where the gap 11 in the red circle on the left is a from the surface of the first resistor layer 10 away from the conductive layer 20 and the position where the gap 11 in the red circle on the right is b from the surface of the first resistor layer 10 away from the conductive layer 20 is greater than 0.2 μm. Obviously, a=b. Figure 2 The two gaps in the middle satisfy the condition that the shortest distance between two adjacent gaps 11 is greater than 100 nm. Two adjacent gaps with a distance greater than 100 nm can avoid the gap position as much as possible through wiring during the etching process, thereby meeting the use requirements and improving quality reliability.

[0051] In one embodiment, the thickness difference of the first resistance layer 10 in the plane direction is less than 400 nm.

[0052] Specifically, in order to ensure the uniformity of square resistance, control production costs, improve the yield rate, and meet application requirements, in the process of forming the first resistance layer 10, the difference between the maximum thickness and the minimum thickness of the first resistance layer 10 is made less than 400nm. Figure 2 exemplarily shows a composite metal foil in which the thickness difference of the first resistance layer 10 is less than 200 nm.

[0053] In one embodiment, Figure 1 As shown, the composite metal foil further includes a conductive layer 20 ; the first resistance layer 10 is disposed on one side surface of the conductive layer 20 .

[0054] Optionally, the conductive layer 20 may be made of copper, silver, gold, aluminum, nickel, chromium, manganese, zinc, titanium, platinum or other conductive materials.

[0055] Specifically, the conductive layer 20 is a copper foil, such as an electrolytic copper foil or a rolled copper foil, and the thickness of the conductive layer 20 ranges from 5 μm to 100 μm, preferably 18 μm. The first resistor layer 10 is formed on one side of the conductive layer 20 by magnetron sputtering once or multiple times (or formed by other physical or chemical plating processes), and the thickness of the first resistor layer 10 is 50 nm to 800 nm. The conductive layer 20 can be used as a circuit manufacturing material, and a circuit is formed on a substrate by a circuit etching process, and an embedded thermistor is formed by exposing the position of the first resistor layer 10, which is conducive to use in a very small space and improves the circuit integration.

[0056] In one embodiment, Figure 3 As shown, Figure 3 1 is a structural diagram of another composite metal foil provided in an embodiment of the present invention. The composite metal foil further includes a second resistance layer 30 . The second resistance layer 30 is disposed on the other side surface of the conductive layer 20 away from the first resistance layer 10 .

[0057] Specifically, the second resistor layer 30 is used to change the resistance of the component or circuit board where the composite metal foil is located, that is, the role of the second resistor layer 30 is different from the thermal sensitive effect of the first resistor layer 10. It is used as an ordinary pull-up resistor or pull-down resistor and is used in conjunction with the first resistor layer 10. It can more effectively drive the voltage to change with temperature, which is beneficial to improving the response accuracy of thermal management.

[0058] In one embodiment, the roughness Rz of the surface of the conductive layer 20 close to the first resistance layer 10 is 1-7 μm.

[0059] Specifically, by limiting the surface roughness of the first resistor layer 10 , the uniformity of the square resistance of the composite metal foil can be effectively improved, and the heat generation monitoring of the circuit board or electronic components can be better achieved.

[0060] In one embodiment, Figure 4 As shown, Figure 4 The composite metal foil further comprises an adjustment layer 40 , which is disposed on a surface of the first resistance layer 10 away from the conductive layer 20 .

[0061] Specifically, the adjustment layer 40 is usually a silane coupling agent, which is used to enhance the bonding force between the composite metal foil pressed on the substrate and the substrate to prevent it from falling off. It should be noted that the surface of the second resistor layer 30 away from the conductive layer 20 does not need to be combined with the substrate, so there is no need to set an adjustment layer, which will not be repeated here.

[0062] In one embodiment, the first resistor layer 10 has a negative temperature coefficient, and the resistance change rate of the first resistor layer 10 is greater than 3% within a temperature change range of 25° C.

[0063] Specifically, under this range of change rates, it has higher detection accuracy and response speed, thereby improving the overall thermal management accuracy after being applied to the circuit board.

[0064] In one embodiment, in a temperature cycle from 25° C. to 150° C. and then back to 25° C., the resistance recovery deviation of the first resistor layer 10 is less than 10%.

[0065] For example, the resistance recovery deviation of the first resistor layer 10 is 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value in between. Furthermore, the number of temperature cycles is within 30,000 times. In this way, the overall service life of the circuit board made of the composite metal foil can be guaranteed, while ensuring the stability of the recovery accuracy, thereby improving the thermal management efficiency.

[0066] Specifically, the Temperature Coefficient of Resistance (TCR) indicates the relative change in resistance when the temperature changes by 1 degree Celsius, in units of ppm / °C. Generally, a resistor can have a negative temperature coefficient, a positive temperature coefficient, and a critical temperature coefficient at which the resistance value changes suddenly at a certain temperature.

[0067] By limiting the resistance temperature coefficient of the first resistor layer 10 of the composite metal foil in the embodiment of the present invention and the corresponding parameters of the change relationship between temperature and resistance, the thermal performance of the composite metal foil can be effectively improved, the terminal working reliability and service life can be ensured, and the heat monitoring of circuit boards or electronic components can be better realized.

[0068] The performance of the composite metal foil provided in this application is introduced below with a specific embodiment.

[0069] For example, taking the copper layer as an example of the conductive layer, the copper layer used is an electrolytic copper foil, and then the first resistance layer is formed on the surface of the copper layer by vacuum sputtering. The square resistance test method is to use a square resistance meter to test the first resistance layer on the surface of the composite metal foil. The test conditions are: using a four-probe test head, connecting the square resistance meter to the test head, and applying a DC voltage of 1V to the test head. Then use the four-probe test head to test the 2cm*2cm area. Among them, the surface curvature of the probe is Sr=0.9mm, the pressure of the probe is 0.45±0.15N or 50±15gf, and the probe spacing is 3mm. The specific structural parameters are as follows:

[0070] Group 1: The first resistor layer was magnetron sputtered on the surface of conventional copper foil A1 to prepare thermistor B1; wherein the first resistor layer was nickel iron oxide with a thickness of 366nm. After FIB slicing, the number of notches within any 50μm range along the plane direction of the first resistor layer was 8, and the notch width was between 3-16nm.

[0071] The second group: The first resistor layer was magnetron sputtered on the surface of conventional copper foil A1 to prepare thermistor B2; wherein the first resistor layer was nickel iron manganese oxide with a thickness of 536nm. After FIB slicing, the number of notches within any 50μm range along the plane direction of the first resistor layer was 14, and the notch width was between 11-18nm.

[0072] The third group: The first resistance layer was magnetron sputtered on the surface of conventional copper foil A1 to prepare thermistor B2; wherein the first resistance layer was nickel iron aluminum oxide with a thickness of 418nm, the number of notches within any 50μm range along the plane direction of the first resistance layer was 21, and the notch width was between 2-19nm.

[0073] Group 4: Different from Group 3, the material of the first resistor layer is Ni-P oxide. After FIB sectioning, the number of notches in any 50μm range along the plane direction of the first resistor layer is 63, and the notch width is between 11-38nm.

[0074] Group 5: Different from Group 4, after FIB sectioning, the number of notches within any 25 μm range along the plane direction of the first resistor layer is 44, and the notch width is between 11-34 nm.

[0075] Thermistors B1-B5 in the five experimental groups were tested for square resistance according to the above test method and the square resistance uniformity was calculated. The test results are shown in Table 1. The upper limit value of square resistance uniformity calculation = (M max -M ave ) / M ave ×100%;Lower limit=(M ave -M min ) / M ave ×100%; where M max is the maximum value, M min is the minimum value, M ave is the average value.

[0076] Table 1. Square resistance uniformity of thermistors in different experimental groups

[0077] serial number B1 B2 B3 B4 B5 Upper limit of square resistance uniformity 8.9％ 8.3％ 11.9％ 21.1％ 33.5％ Lower limit of square resistance uniformity -9.5％ -7.2％ -11.4％ -19.6％ -56.1％

[0078] According to the test results of the above embodiments, it can be seen that the composite metal foil prepared according to the structure and structural parameters provided by this solution has better square resistance uniformity and can adapt to the current high-performance circuit boards.

[0079] An embodiment of the present invention further provides a circuit board, which includes the composite metal foil in any of the above embodiments; the composite metal foil is used to lay the circuits on the circuit board, or the composite metal foil is laid on the surface of at least one layer of the circuit board.

[0080] Specifically, the composite metal foil can be used as a material for laying the circuits on the circuit board. The circuit board is made by burying the composite metal foil with thermistor characteristics in the circuit with a line width of micron level. This does not occupy the placement position of the circuit board components, and is combined with a temperature monitoring circuit. The changes in voltage and current in the circuit caused by temperature changes can be used to monitor the heat generation of electronic components and even feedback regulation. Alternatively, the composite metal foil can also be buried in a single-layer board or a multi-layer board that needs to be monitored for heat generation, and then the chip is packaged on the circuit board to achieve heat generation monitoring of various positions on the circuit board.

[0081] The circuit board provided in the embodiment of the present invention includes the composite metal foil in the above embodiment, so the circuit board provided in the embodiment of the present invention also has the beneficial effects described in the above embodiment, which will not be described in detail here.

[0082] In the description of the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0083] Finally, it should be noted that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A composite metal foil, characterized in that: The composite metal foil includes a first resistance layer; The first resistance layer is a thermistor layer; A preset percentage area of ​​the first resistor layer has or does not have notches during the formation process, and when there are notches, the number of the notches is less than 50 within any 50 μm range along the plane direction of the first resistor layer; The notch is a groove formed along the thickness direction of the first resistor layer when the composite metal foil is observed in a sliced ​​state.

2. The composite metal foil according to claim 1, characterized in that: The number of the notches is less than 20 within any range of 25 μm along the plane direction of the first resistance layer.

3. The composite metal foil according to claim 1, characterized in that: The maximum width of the notch is less than 20 nm, wherein the width of the notch refers to a dimension along a plane direction of the first resistor layer, and the plane direction of the first resistor layer is perpendicular to a thickness direction.

4. The composite metal foil according to claim 1, characterized in that: In the thickness direction of the first resistance layer, within a distance from one surface to another surface of the first resistance layer, the number of the notches is greater than or equal to 0 and less than a first preset number.

5. The composite metal foil according to claim 1, characterized in that: Along the plane direction of the first resistor layer, the shortest distance between two adjacent gaps is greater than 100 nm, wherein the two adjacent gaps refer to two gaps along the thickness direction of the first resistor layer, which are consistent with the distance between the first resistor layer and the surface of one side away from the conductive layer.

6. The composite metal foil according to claim 1, characterized in that: The thickness difference of the first resistance layer in the plane direction is less than 400 nm.

7. The composite metal foil according to claim 1, characterized in that: The composite metal foil further includes a conductive layer; The first resistance layer is disposed on one side surface of the conductive layer.

8. The composite metal foil according to claim 7, characterized in that: The composite metal foil further includes a second resistance layer; The second resistance layer is disposed on the other side of the conductive layer away from the first resistance layer.

9. The composite metal foil according to claim 7, characterized in that: The roughness of the surface of the conductive layer close to the first resistance layer is 1-7 μm.

10. The composite metal foil according to claim 7, characterized in that: The composite metal foil further includes an adjustment layer, and the adjustment layer is arranged on a surface of the first resistance layer away from the conductive layer.

11. The composite metal foil according to claim 1, characterized in that: The first resistor layer has a negative temperature coefficient. Within a temperature variation range of 25° C., the resistance value variation rate of the first resistor layer is greater than 3%.

12. The composite metal foil according to claim 1, characterized in that: In a temperature cycle from 25° C. to 150° C. and then back to 25° C., the resistance recovery deviation of the first resistance layer is less than 10%.

13. A circuit board, characterized in that: The circuit board comprises the composite metal foil as described in any one of claims 1 to 12; The composite metal foil is used for laying the circuits on the circuit board, or the composite metal foil is laid on the surface of at least one layer of the circuit board.

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