Metal foil for spring members and method for manufacturing spring members for electronic devices

Abstract

To provide a spring member for electronic apparatus capable of suppressing variation of a width in a thickness direction on a spring member formed of metal foil, and a method of manufacturing the spring member for electronic apparatus.SOLUTION: A spring member for electronic apparatus uses metal foil 10 for a spring member, and also has a first difference value between a maximum value and a minimum value of a first thickness at each point on a straight line along a rolling direction and a second difference value between a maximum value and a minimum value of a second thickness at each point on a straight line along a width direction orthogonal to the rolling direction. An absolute value of the difference value obtained by subtracting the second difference value from the first difference value is 0.8 μm or less. A standard deviation in the spring width is 2.1 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a spring member for an electronic device and a method for manufacturing a spring member for an electronic device. [Background technology]

[0002] Camera modules installed in electronic devices with cameras, such as tablet terminals and smartphones, are equipped with drive mechanisms that enable autofocus and zoom. Known drive mechanisms include a lens drive system and a sensor drive system. A lens drive system drive mechanism is equipped with a leaf spring that enables the position of the lens to be changed in the direction of the lens's optical axis. In contrast, a sensor drive system drive mechanism is equipped with a leaf spring that enables the position of the image sensor to be changed in the direction of the lens's optical axis (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-059345 [Patent Document 2] Japanese Patent Publication No. 2020-170170 Summary of the Invention [Problem to be solved by the invention]

[0004] However, leaf springs are required to satisfy a specific spring load or deflection within a limited volume, and to satisfy the spring load and deflection requirements, leaf springs must be made from a metal with high hardness.

[0005] The width and thickness of a leaf spring significantly affect its spring load and deflection. The metal foil that is the raw material for leaf springs is rolled to a predetermined thickness. Because metal foil is made of a high-hardness metal, it is more difficult to achieve a uniform thickness by rolling than when it is made of a low-hardness metal.

[0006] On the other hand, leaf springs are formed by wet etching of metal foil. Variations in the thickness of the metal foil cause variations in the amount of etching, which in turn causes variations in the width of the leaf spring along its thickness. Since variations in the width of the leaf spring along its thickness cause variations in the spring load and deflection of the leaf spring, it is necessary to suppress variations in the spring width along its thickness. [Means for solving the problem]

[0007] A spring component for an electronic device that solves the above-mentioned problems is a spring component for an electronic device that uses a metal foil for a spring component. The difference between the maximum and minimum values ​​of a first thickness at each point on a line along the rolling direction of the metal foil for a spring component is a first difference value, and the difference between the maximum and minimum values ​​of a second thickness at each point on a line along the width direction perpendicular to the rolling direction is a second difference value. The absolute value of the difference value obtained by subtracting the second difference value from the first difference value is 0.8 μm or less. The standard deviation of the spring width is 2.1 μm or less.

[0008] A method for manufacturing a spring component for an electronic device that solves the above-mentioned problems is a method for manufacturing a spring component for an electronic device using a metal foil for a spring component. The manufacturing method includes forming resist masks on the front and back surfaces of the metal foil for a spring component and wet-etching the metal foil for a spring component using the resist mask. A first differential value is a difference between the maximum and minimum values ​​of a first thickness at each point on a line along the rolling direction of the metal foil for a spring component, and a second differential value is a difference between the maximum and minimum values ​​of a second thickness at each point on a line along the width direction perpendicular to the rolling direction. The absolute value of the difference value obtained by subtracting the second differential value from the first differential value is 0.8 μm or less. The standard deviation of the spring width is 2.1 μm or less.

[0009] According to each of the above configurations, the absolute value of the difference obtained by subtracting the second difference value from the first difference value is 0.8 μm or less, so that the thickness variation in the metal foil for a spring member is suppressed, and therefore, the spring member formed by wet etching the metal foil for a spring member has a reduced width variation in the thickness direction.

[0010] In the above spring component for electronic devices, the maximum value of the first thickness may be a first maximum value, the maximum value of the second thickness may be a second maximum value, and the absolute value of the difference obtained by subtracting the second maximum value from the first maximum value may be 0.8 μm or less.

[0011] In the above-mentioned method for manufacturing a spring component for an electronic device, in the metal foil for the spring component, the maximum value of the first thickness may be a first maximum value, the maximum value of the second thickness may be a second maximum value, and the absolute value of the difference value obtained by subtracting the second maximum value from the first maximum value may be 0.8 μm or less.

[0012] When wet etching is used to form through-holes in the metal foil for a spring member that penetrate the metal foil for a spring member along the thickness direction of the metal foil, thinner portions of the metal foil for a spring member are more likely to be penetrated, and thicker portions of the metal foil for a spring member are less likely to be penetrated. Even if through-holes are formed in thinner portions of the metal foil for a spring member, the through-holes contribute to the formation of a flow of etching solution in the thickness direction of the metal foil for a spring member, but are less likely to contribute to the progression of isotropic etching in a direction perpendicular to the penetration direction. In contrast, thicker portions of the metal foil for a spring member require longer wet etching time than other portions, and therefore contribute to the isotropic etching that progresses in the metal foil for a spring member.

[0013] In this regard, in the metal foil for spring members, by having the absolute value of the difference obtained by subtracting the second maximum value from the first maximum value be 0.8 μm or less, the degree of isotropic etching occurring in the metal foil for spring members is prevented from varying in the rolling direction and width direction, and as a result, the variation in the spring width in the thickness direction of the spring member is reduced.

[0014] In the spring member for an electronic device, a difference value obtained by subtracting the minimum value from the maximum value of the thickness at each point on the metal foil for a spring member may be 2.6 μm or less.

[0015] In the method for manufacturing a spring component for an electronic device, a difference value obtained by subtracting the minimum value from the maximum value of the thickness at each point on the metal foil for a spring component may be 2.6 μm or less. According to each of the above configurations, the difference between the maximum and minimum thickness values ​​at each point on the metal foil for spring members is 2.6 μm or less, making it possible to suppress thickness variations throughout the metal foil for spring members.

[0016] In the above spring member for an electronic device, the spring member for an electronic device may include any one selected from the group consisting of stainless steel alloy, beryllium copper, nickel-tin copper, phosphor bronze, Corson alloy, and titanium copper.

[0017] In the above-described method for manufacturing a spring component for an electronic device, the spring component for an electronic device may include any one selected from the group consisting of stainless steel alloy, beryllium copper, nickel-tin copper, phosphor bronze, Corson alloy, and titanium copper.

[0018] According to each of the above configurations, the metal foil for a spring member can have high hardness, and therefore the durability of the spring member formed from the metal foil for a spring member can be increased. [Effects of the Invention]

[0019] According to the present disclosure, it is possible to reduce variations in the spring width in the thickness direction of a spring member formed from metal foil. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a perspective view showing a structure of a metal foil for a spring member in one embodiment. [Figure 2]2 is a plan view showing the structure of the spring member for an electronic device in the embodiment. FIG. [Figure 3] 3A to 3C are process diagrams illustrating a method for manufacturing a metal foil for a spring member in the embodiment. [Figure 4] 3A to 3C are process diagrams illustrating a method for manufacturing a metal foil for a spring member in the embodiment. [Figure 5] 3A to 3C are process diagrams illustrating a method for manufacturing a metal foil for a spring member in the embodiment. [Figure 6] 3 is a process chart for explaining a method for manufacturing the spring member for an electronic device shown in FIG. 2. [Figure 7] 3 is a process chart for explaining a method for manufacturing the spring member for an electronic device shown in FIG. 2. [Figure 8] 3 is a process chart for explaining a method for manufacturing the spring member for an electronic device shown in FIG. 2. [Figure 9] 3 is a process chart for explaining a method for manufacturing the spring member for an electronic device shown in FIG. 2. [Figure 10] 3 is a process chart for explaining a method for manufacturing the spring member for an electronic device shown in FIG. 2. [Figure 11] FIG. 3 is a plan view illustrating a location where the thickness of the metal foil for a spring member is measured. [Figure 12] 1 is a table showing measurement results for metal foils of Examples and Comparative Examples. [Figure 13] 10 is a graph showing the relationship between the absolute value of the difference value obtained by subtracting the second difference value from the first difference value and the difference value of the width. [Figure 14] 10 is a graph showing the relationship between the absolute value of the difference value obtained by subtracting the second maximum value from the first maximum value and the difference value of the width. DETAILED DESCRIPTION OF THE INVENTION

[0021] 1 to 14, an embodiment of a metal foil for a spring member, a spring member for an electronic device, a method for manufacturing a metal foil for a spring member, and a method for manufacturing a spring member for an electronic device will be described. [Metal foil for spring components] The metal foil for a spring member will be described with reference to FIG.

[0022] In the metal foil for spring members (hereinafter also referred to as metal foil) 10 shown in FIG. 1, the region where the spring member is formed is the first region 10R1. The first region 10R1 has a square shape with a side length of 300 mm. The metal foil 10 is a rolled material formed from a metal having a high degree of hardness capable of realizing the spring load or deflection required for the spring member. The metal foil 10 has a strip shape extending along the rolling direction DR. The direction perpendicular to the rolling direction DR is the width direction DW. The thickness T of the metal foil 10 is, for example, 200 μm or less, and preferably 50 μm or more and 200 μm or less. The thickness of the metal foil 10 is uniform such that the ratio of the difference between the maximum and minimum thickness values ​​of the metal foil 10 to the average thickness of the substrate is 3% or less.

[0023] In the first region 10R1, the difference between the maximum and minimum values ​​of the thickness in the rolling direction DR is the first difference value. That is, the thickness at each point on a line along the rolling direction DR is the first thickness, and the difference between the maximum and minimum values ​​of the first thickness is the first difference value. In the first region 10R1, the difference between the maximum and minimum values ​​of the thickness in the width direction DW is the second difference value. That is, the thickness at each point on a line along the width direction DW is the second thickness, and the difference between the maximum and minimum values ​​of the second thickness is the second difference value. The metal foil 10 satisfies the following condition 1.

[0024] (Condition 1) The absolute value of the difference value obtained by subtracting the second difference value from the first difference value is 0.8 μm or less. The absolute value of the difference value obtained by subtracting the second difference value from the first difference value is the first absolute value.

[0025] Since the first absolute value is 0.8 μm or less, it is possible to reduce variations in thickness in the metal foil 10. Therefore, in the spring member formed by wet etching the metal foil 10, variations in spring width in the thickness direction are reduced.

[0026] The metal foil 10 has a front surface 10F and a back surface 10B opposite to the front surface 10F. The thickness T of the metal foil 10 is the distance between the front surface 10F and the back surface 10B. The maximum and minimum values ​​of the thickness in the rolling direction DR are determined as follows. That is, a first measurement region R1R having a strip shape extending along the rolling direction DR is set for the first region 10R1. The length of the first measurement region R1R in the width direction DW is, for example, 20 mm. Of the thicknesses of the metal foil 10 measured at each of multiple points in the first measurement region R1R, the largest value is the maximum value and the smallest value is the minimum value.

[0027] The maximum and minimum thickness values ​​in the width direction DW are determined as follows. That is, a second measurement region R1W having a strip shape extending along the width direction DW is set in the first region 10R1. The length of the second measurement region R1W in the rolling direction DR is, for example, 20 mm. Of the thicknesses of the metal foil 10 measured at each of a plurality of points in the second measurement region R1W, the largest value is the maximum value and the smallest value is the minimum value.

[0028] In the metal foil 10, thickness variation in the rolling direction DR decreases as the material used to produce the metal foil 10 is repeatedly rolled. Therefore, from the perspective of suppressing variation in the rolling direction DR, it is preferable to increase the number of rolling operations performed during the production of the metal foil 10. However, metal foil 10 for spring members must have a thickness greater than or equal to a predetermined value in order to achieve the spring load or deflection required for the spring member. Therefore, it is difficult to perform rolling operations a sufficient number of times during the production of metal foil 10 for spring members to eliminate thickness variation in the rolling direction DR. In contrast, thickness variation in the metal foil 10 in the width direction DW is controlled by the surface condition of the rolling rollers used in rolling, and therefore variation is suppressed regardless of the number of rolling operations. Therefore, in the metal foil 10, the second difference value is equal to or less than the first difference value.

[0029] On the other hand, when wet etching is performed on the metal foil 10 to form through-holes that penetrate the metal foil 10 along the thickness direction of the metal foil 10, the thinner the portion of the metal foil 10, the shorter the time required for the through-holes to be formed. The through-holes formed in the metal foil 10 create a flow of etching solution between the front surface 10F and the back surface 10B of the metal foil 10, but they hardly contribute to the progress of isotropic etching of the metal foil 10 in a direction perpendicular to the penetration direction. In contrast, the thicker the portion of the metal foil 10, the longer the time required for the through-holes to be formed. Therefore, the thicker portions of the metal foil 10 greatly contribute to the progress of isotropic etching of the metal foil 10.

[0030] Therefore, the first difference value can be used as an index of the likelihood of isotropic etching occurring in the rolling direction DR in the thickness of the metal foil 10. Also, the second difference value can be used as an index of the likelihood of isotropic etching occurring in the width direction DW in the thickness of the metal foil 10. Furthermore, the first absolute value can be used as an index of the likelihood of isotropic etching occurring in the rolling direction DR, relative to the width direction DW, where isotropic etching is less likely to occur.

[0031] In this regard, when the metal foil 10 satisfies the above-mentioned condition 1, the tendency for isotropic etching to occur in the rolling direction DR is prevented from becoming excessively large when the tendency for isotropic etching to occur in the width direction DW is taken as a standard. Therefore, the spring member formed by etching the metal foil 10 can be easily formed into a desired shape.

[0032] In the first region 10R1, the maximum value of the thickness T in the rolling direction DR is a first maximum value. In the first region 10R1, the maximum value of the thickness T in the width direction DW is a second maximum value. It is preferable that the metal foil 10 satisfy at least one of the following conditions 2 and 3. That is, the metal foil 10 may satisfy only one of conditions 2 and 3, or may satisfy both conditions 2 and 3.

[0033] (Condition 2) The absolute value of the difference obtained by subtracting the second maximum value from the first maximum value is 0.8 μm or less. The absolute value of the difference obtained by subtracting the second maximum value from the first maximum value is the second absolute value. (Condition 3) In the first region 10R1, the difference obtained by subtracting the minimum thickness from the maximum thickness of the metal foil 10 is 2.6 μm or less.

[0034] As described above, even if through holes are formed in the thin portions of the metal foil 10, the through holes contribute to the formation of a flow of etching solution in the thickness direction of the metal foil 10, but are unlikely to contribute to the progress of isotropic etching. In contrast, the thick portions of the metal foil 10 require a longer time for wet etching than other portions, and therefore contribute to the isotropic etching that progresses in the metal foil 10.

[0035] In this regard, when the metal foil 10 satisfies condition 2, the degree of isotropic etching occurring in the metal foil 10 is reduced to a level that varies in the rolling direction DR and the width direction DW, and as a result, variation in the spring width in the thickness direction of the spring member is reduced.

[0036] Furthermore, when the metal foil 10 satisfies condition 3, it is possible to suppress variations in thickness throughout the metal foil 10. The maximum value of the thickness T of the metal foil 10 is the largest value among all the measured values ​​including the measured value of the thickness T in the rolling direction DR and the measured value of the thickness T in the width direction DW. In contrast, the minimum value of the thickness T of the metal foil 10 is the smallest value among all the measured values ​​including the measured value of the thickness T in the rolling direction DR and the measured value of the thickness T in the width direction DW.

[0037] As described above, the metal foil 10 is formed from a metal having a high enough hardness to achieve the spring load or deflection required for a spring member manufactured using the metal foil 10. The metal foil 10 may be formed from, for example, a stainless steel alloy or a copper alloy. The stainless steel alloy may be, for example, a stainless steel alloy specified in JIS G 4313:2011 "Stainless steel strip for springs." The copper alloy may be, for example, a copper alloy specified in JIS H 3130:2018 "Beryllium copper, titanium copper, phosphor bronze, nickel-tin copper, and nickel silver plate and strip for springs."

[0038] The metal foil 10 preferably contains any one selected from the group consisting of stainless steel alloy, beryllium copper, nickel-tin copper, phosphor bronze, Corson alloy, and titanium-copper, which allows the metal foil 10 to have high hardness, thereby increasing the durability of the spring member formed from the metal foil 10.

[0039] [Spring member] The spring member will be described with reference to Fig. 2. Fig. 2 schematically shows the planar structure of the spring member as viewed from a viewpoint opposite to the plane in which the spring member extends.

[0040] As shown in FIG. 2, the spring member 20 includes an outer frame portion 21, an inner frame portion 22, and a spring portion 23. The spring member 20 is a leaf spring. In the example shown in FIG. 2, the outer shape of the outer frame portion 21 is octagonal, and the outer shape of the inner frame portion 22 is circular. The spring portion 23 has a folded line shape. The outer shapes of the outer frame portion 21 and the inner frame portion 22 may be changed depending on the shapes of other members included in the drive mechanism of the camera module in which the spring member 20 is mounted, i.e., members other than the spring member 20. The inner frame portion 22 is located within an area defined by the outer frame portion 21. The spring portion 23 connects the inner frame portion 22 to the outer frame portion 21.

[0041] In the lens drive type drive mechanism, a pair of spring members 20 are arranged to sandwich the lens in the optical axis direction of the lens. In the optical axis direction, the position of the inner frame portion 22 connected to each outer frame portion 21 changes relative to that outer frame portion 21, thereby changing the position of the lens in the optical axis direction. This makes it possible for the lens drive type drive mechanism to correct camera shake.

[0042] In contrast, in a sensor-driven drive mechanism, a pair of spring members 20 are arranged to sandwich the image sensor in the optical axis direction of the lens. The position of the inner frame portion 22 connected to each outer frame portion 21 changes relative to that outer frame portion 21 in the optical axis direction, thereby changing the position of the image sensor in the optical axis direction of the lens. This makes it possible to correct camera shake using a sensor-driven drive mechanism.

[0043] In the spring member 20, when viewed from a plane opposite to the plane in which the spring member 20 extends, the length of the spring member 20 in a direction perpendicular to the direction in which each side of the outer frame portion 21 extends is the width of the spring member 20 at the outer frame portion 21. Furthermore, when viewed from a plane opposite to the plane in which the spring member 20 extends, the length of the inner frame portion 22 along the radial direction of the inner frame portion 22 is the width of the spring member 20 at the inner frame portion 22. Furthermore, when viewed from a plane opposite to the plane in which the spring member 20 extends, the line width of the folding lines of the spring portion 23 in the plan view is the width of the spring portion 23, i.e., the spring width SW.

[0044] The electronic device in which the camera module having the spring member 20 is mounted may be, for example, a mobile phone terminal, a smartphone, a tablet terminal, or a notebook personal computer.

[0045] [Method for manufacturing metal foil for spring components] A method for producing the metal foil 10 will be described with reference to FIGS. The method for manufacturing the metal foil 10 includes rolling a base material, preparing a plurality of rolled materials obtained by rolling the base material, and then selecting the metal foil 10 from the plurality of rolled materials. In selecting the metal foil 10, a rolled material that satisfies the above-mentioned condition 1 is selected as the metal foil 10 from the plurality of rolled materials. Furthermore, the method for manufacturing the metal foil 10 may further include at least one of the above-mentioned conditions 2 and 3 as conditions for selecting the metal foil 10 from the plurality of rolled materials.

[0046] The method for producing the metal foil 10 will be described in more detail below with reference to the drawings. 3 and 4 show a schematic diagram of the process of rolling the base material to form the metal foil 10. FIG.

[0047] 3, when the metal foil 10 is manufactured, first, a strip-shaped base material BM1 extending along a rolling direction DR is prepared. Next, the base material BM1 is transported along the transport direction toward a rolling mill RE equipped with a pair of rolling rollers RL1 and RL2 so that the rolling direction DR of the base material BM1 and the transport direction in which the base material BM1 is transported are parallel to each other.

[0048] When the base material BM1 reaches between the pair of rolling rollers RL1, RL2, the base material BM1 is rolled by the pair of rolling rollers RL1, RL2. This reduces the thickness of the base material BM1 and stretches the base material BM1 along the conveying direction, thereby obtaining a rolled material BM2. The rolled material BM2 is wound around a core C. Note that the rolled material BM2 may be handled in a stretched strip shape without being wound around the core C. The thickness of the rolled material BM2 is, for example, 200 μm or less, and preferably 50 μm or more and 200 μm or less.

[0049] As shown in Figure 4, in order to remove residual stress accumulated inside the rolled material BM2 formed by rolling the base material BM1, the rolled material BM2 is annealed using an annealing device AE. This results in the annealed rolled material BM3. The annealing of the rolled material BM2 is performed while pulling the rolled material BM2 along the transport direction, so the rolled material BM3 has reduced residual stress compared to the rolled material BM2 before annealing.

[0050] As described above, the material forming the base material BM1 may include any one selected from the group consisting of stainless steel alloy, beryllium copper, nickel-tin copper, phosphor bronze, Corson alloy, and titanium-copper. Because these metals have high hardness, in other words, they are less likely to stretch than metals with lower hardness, i.e., softer metals, variations in the degree of rolling are likely to occur within the base material BM1. Furthermore, variations in the degree of rolling are likely to occur among multiple base materials BM1. Therefore, it is highly effective to include the above-described condition 1 in the selection conditions for the metal foil 10 formed by rolling the base material BM1.

[0051] FIG. 5 shows a schematic diagram of a process for measuring the thickness of the metal foil 10 formed through the rolling process. As shown in Figure 5, after preparing a plurality of rolled materials BM3 obtained through rolling, the thickness of a first region of each rolled material BM3 for forming the spring member 20 is measured using a measuring device ME. As a result, at least the above-mentioned first absolute value is calculated for the first region of each rolled material BM3. Then, from the plurality of rolled materials BM3, a rolled material BM3 that satisfies the above-mentioned first condition is selected as the metal foil 10, and the selected metal foil 10 is used to manufacture the spring member 20.

[0052] The above-described first maximum value, second maximum value, and maximum and minimum values ​​in the thickness T of the rolled material BM3 may be calculated for the first region of each rolled material BM3. At least one of the above-described conditions 2 and 3 may be added to the conditions for sorting the metal foil 10 from the rolled material BM3. That is, only one of conditions 2 and 3, or both of conditions 2 and 3, may be added to the conditions for sorting the metal foil 10 from the rolled material BM3. Furthermore, the measuring device ME may be a contact measuring device or a non-contact measuring device.

[0053] A length gauge, for example, can be used as a contact-type measuring device. A non-contact-type measuring device, for example, can be used as a measuring device equipped with an irradiation unit that irradiates X-rays and a detection unit that detects fluorescent X-rays. When using this measuring device, first, the irradiation unit is used to irradiate X-rays onto the metal foil 10, and the fluorescent X-rays emitted from the metal foil 10 are detected by the detection unit. Since the intensity of the fluorescent X-rays detected by the detection unit depends on the thickness of the metal foil 10, it is possible to determine the thickness of the metal foil 10 from the intensity of the fluorescent X-rays.

[0054] The first absolute value, the second absolute value, and the difference between the maximum and minimum values ​​of the thickness T of the metal foil 10 can be changed by changing at least one of the following: the rotational speed of the rolling rollers RL1 and RL2, the pressing force between the rolling rollers RL1 and RL2, the temperature of the rolling rollers RL1 and RL2, and the quantity of the rolling rollers RL1 and RL2. That is, only one of the rotational speed of the rolling rollers RL1 and RL2, the pressing force between the rolling rollers RL1 and RL2, the temperature of the rolling rollers RL1 and RL2, and the quantity of the rolling rollers RL1 and RL2 may be changed. Alternatively, any two or more of the rotational speed of the rolling rollers RL1 and RL2, the pressing force between the rolling rollers RL1 and RL2, the temperature of the rolling rollers RL1 and RL2, and the quantity of the rolling rollers RL1 and RL2 may be changed.

[0055] [Method for manufacturing spring components] A method for manufacturing the spring member 20 will be described with reference to FIGS. 6, when manufacturing the spring member 20, first, a first resist layer PR1 is formed on the front surface 10F of the metal foil 10, and a second resist layer PR2 is formed on the back surface 10B. Note that, although the resist layers PR1 and PR2 are formed from positive photoresists in the examples described with reference to FIGS. 6 to 10, each of the resist layers PR1 and PR2 may be formed from negative photoresists.

[0056] 7, a first photomask PM1 is placed on the first resist layer PR1, and a second photomask PM2 is placed on the second resist layer PR2. Then, the first resist layer PR1 is exposed using the first photomask PM1, and the second resist layer PR2 is exposed using the second photomask PM2.

[0057] As shown in FIG. 8, the exposed resist layers PR1 and PR2 are developed, thereby forming a first resist mask RM1 from the first resist layer PR1 and a second resist mask RM2 from the second resist layer PR2.

[0058] 9, the metal foil 10 is wet-etched using resist masks RM1 and RM2. During this process, the metal foil 10 is etched from both the front surface 10F and the back surface 10B. As a result, through-holes are formed in the metal foil 10, penetrating the metal foil 10 in the thickness direction, resulting in the formation of an outer frame portion 21, an inner frame portion 22 spaced from the outer frame portion 21, and spring portions 23 connecting the inner frame portion 22 to the outer frame portion 21.

[0059] In this case, because the metal foil 10 satisfies condition 1, it is easy to obtain a spring member 20 having a desired shape in the thickness direction of the metal foil 10. Furthermore, because the metal foil 10 satisfies condition 1, it is possible to obtain a spring member 20 in which the variation in spring width in the thickness direction of the spring member 20 is kept within a predetermined range, without changing the wet etching conditions in accordance with the variation in thickness of the metal foil 10. Therefore, in manufacturing the spring member 20, it is not necessary to change the wet etching conditions in accordance with the variation in thickness, and it is also possible to eliminate errors in the combination of the variation in thickness and the wet etching conditions.

[0060] As shown in FIG. 10, the resist masks RM1 and RM2 are removed from the etched metal foil 10, and then the spring member 20 is cut out from the etched metal foil 10, thereby obtaining the spring member 20.

[0061] [Example] An example and a comparative example will be described with reference to FIGS. [Example 1] First, a base material made of titanium copper was rolled to form a rolled material. Then, the rolled material was annealed. As a result, the metal foil of Example 1 having a design thickness of 120 μm was obtained.

[0062] [Examples 2 to 8 and Comparative Examples 1 to 3] In Example 1, when rolling the base material, at least one of the rotation speed of the rolling rollers, the pressing force between the rolling rollers, the temperature of the rolling rollers, and the number of rolling rollers was changed, while the rest was kept the same as in Example 1, thereby obtaining the metal foils of Examples 2 to 8 and Comparative Examples 1 to 3.

[0063] [Evaluation method] [Thickness measurement] A method for measuring the thickness of the metal foil 10 will be described with reference to FIG.

[0064] As shown in FIG. 11, square test foils 30 with sides measuring 300 mm were cut out from the metal foils of each example and comparative example. Each test foil 30 was cut out so that the direction in which the first side of the test foil 30 extended was parallel to the rolling direction DR of the metal foil, and the direction in which the second side of the test foil 30 extended was perpendicular to the width direction DW of the metal foil. Each test foil 30 had a square measurement area 30A including the center of the test foil 30, and a rectangular peripheral area 30B surrounding the measurement area 30A. The width W3 of the peripheral area 30B was set to 10 mm.

[0065] Furthermore, a first measurement region R1R having a strip shape extending along the rolling direction DR and a second measurement region R1W having a strip shape extending along the width direction DW were set within the measurement region 30A. At this time, the width W1 of the first measurement region R1R, which is the length in the width direction DW, was set to 20 mm, and the width W2 of the second measurement region R1W, which is the length in the rolling direction DR, was set to 20 mm.

[0066] The thickness of the metal foil was measured in all of the regions obtained by dividing the first measurement region R1R into 14 equal parts in the rolling direction DR. The thickness of the metal foil 30 for measurement was also measured in all of the regions obtained by dividing the second measurement region R1W into 14 equal parts in the width direction DW.

[0067] In each region, the thickness was measured at the point where the diagonal lines connecting two opposing corners intersected. For each metal foil, the thickness was measured at 14 points in the rolling direction DR and 14 points in the width direction DW. However, in the region where the first measurement region R1R and the second measurement region R1W intersect, the measurement point in the rolling direction DR and the measurement point in the width direction DW are the same point, so a total of 27 thickness measurements were performed for each metal foil. The measured values ​​were then rounded to the nearest tenth, resulting in the measured thickness for each region. From these measurements, the average, maximum, minimum, and first differential values ​​for the rolling direction thickness, which is the thickness in the rolling direction DR, were calculated from the measurements in the rolling direction DR. Furthermore, the average, maximum, minimum, and second differential values ​​for the width direction thickness, which is the thickness in the width direction DW, were calculated from the measurements in the width direction DW.

[0068] A contact-type thickness gauge (Nikon Corporation, MH-15M) was used to measure the thickness of the metal foil 30. When measuring the thickness, first, the gauge head was placed in contact with the base plate, and the plate thickness measuring device counter attached to the gauge head was turned on, thereby adjusting the zero point. Thereafter, the metal foil was placed between the gauge head and the base plate, and the gauge head was then lowered to measure the thickness of each part of the metal foil.

[0069] [Evaluation of etching patterns] Resist masks having a plurality of openings corresponding to the shape of the spring members 20 were formed on the front and back surfaces of each measurement metal foil 30, and the measurement metal foil 30 was wet-etched from both the front and back surfaces using the two resist masks. In the measurement region 30A, unit regions each corresponding to one spring member 20 and having a square shape of 20 mm on each side were arranged in a grid pattern so as to be densely packed in both the rolling direction DR and the width direction DW. Therefore, in each resist mask, unit patterns corresponding to the shape of one spring member 20 were also arranged in a grid pattern so as to be densely packed in both the rolling direction DR and the width direction DW.

[0070] In the unit pattern, in the portion of the spring member 20 that forms the spring portion 23 having a folded line shape, the opening width of the resist pattern corresponding to the gap between adjacent line segments that are parallel to each other in the spring portion 23 was set to 100 μm, and the pitch between the adjacent line segments was set to 200 μm. Here, the pitch between adjacent line segments refers to the distance between the center lines set for the adjacent line segments that are parallel to each other in the design of the etching pattern.

[0071] In addition, multiple unit patterns were formed on each resist mask so that, when viewed in a plane facing the surface of the measurement metal foil 30, the entirety of one unit pattern on the resist mask located on the surface of the measurement metal foil 30 overlaps the entirety of one unit pattern on the resist mask located on the back surface of the measurement metal foil 30.

[0072] Using such a resist mask, a plurality of etching patterns corresponding to the shape of the spring member 20 were formed in the measurement metal foil 30. In the etching patterns, the design value of the spring width of the spring portion 23 in a plan view was set to 30 μm.

[0073] After etching, the spring portion 23 of the spring member 20 present in each of the measurement metal foils 30 was embedded in a synthetic resin. Then, the embedded spring portion 23 was cut using a microtome to expose a cross section of the spring portion 23 in a plane perpendicular to the direction in which the line segments included in the spring portion extend.

[0074] The spring widths were measured at the following positions on the cross section of the spring portion 23. That is, the spring width on the front surface of the metal foil 30 for measurement, the spring width on the back surface of the metal foil 30 for measurement, and the spring widths on three planes sandwiched between the front and back surfaces of the metal foil 30 for measurement among the planes dividing the spring portion 23 into four equal parts in the thickness direction were measured. That is, when the depth on the front surface of the metal foil 30 for measurement was set to 0 μm, the spring width at a depth of 0 μm, a depth of approximately 30 μm, a depth of approximately 60 μm, a depth of approximately 90 μm, and a depth of approximately 120 μm were measured in the etching pattern. When measuring the spring width of the spring portion 23, a digital microscope (Keyence Corporation, VHX-7000) was used, and the magnification of the objective lens of the digital microscope was set to 200x.

[0075] For each unit pattern included in the measurement metal foil 30, the spring widths of all springs included in the spring portion 23 were measured at the five locations in the thickness direction. Then, the maximum and minimum values ​​were identified for each spring, and a difference value was calculated by subtracting the minimum value from the maximum value, and the average spring width was calculated. Next, the average of the maximum values ​​identified for all springs was calculated, and this average value was set as the maximum spring width for that measurement metal foil 30. The average of the minimum values ​​identified for all springs was calculated, and this minimum value was set as the minimum spring width for that measurement metal foil 30. The average of the difference values ​​calculated for all springs was calculated, and this average value was set as the difference value for that measurement metal foil 30. The average of the average values ​​calculated for all springs was calculated, and this average value was set as the average for that measurement metal foil 30.

[0076] In addition, for the etching patterns obtained from the test metal foils 30 of each example and each comparative example, the first standard value, the standard deviation of the spring width, the second standard value, and the percentage of 3σ relative to the average value of the spring width were calculated. When calculating the percentage of 3σ relative to the average value of the spring width, the average value set for each test metal foil 30 was used. The first standard value is the percentage of the difference value of the spring width relative to the design value of the spring width. The difference value set for each test metal foil 30 was used to calculate the first standard value. The second standard value is the percentage of the standard deviation of the spring width relative to the design value of the spring width.

[0077] When calculating the standard deviation of the spring width, first, the standard deviation of the spring width was calculated from the thickness measured at five points for each spring. Next, the average value of the standard deviations calculated for all springs was calculated, and this average value was set as the standard deviation of the spring width for that measurement metal foil 30. In addition, the standard deviation set for each measurement metal foil 30 was used to calculate the second standard value.

[0078] [Evaluation results] The evaluation results for the thickness of the metal foil 30 for measurement and the spring width of the etching pattern will be described with reference to FIGS.

[0079] Fig. 12 shows the results of measuring the thickness of each test metal foil 30 and the results of measuring the spring width of an etching pattern formed by wet etching each test metal foil 30. In Fig. 12, the third absolute value is the absolute value of the difference obtained by subtracting the minimum value of the width direction thickness, which is the thickness in the width direction DW, from the minimum value of the rolling direction thickness, which is the thickness in the rolling direction DR.

[0080] 12, the first difference value, which is the value obtained by subtracting the minimum value from the maximum value of the rolling direction thickness, which is the thickness in the rolling direction DR, was found to be 0.9 μm in Example 1, 1.8 μm in Example 2, 1.3 μm in Example 3, and 1.2 μm in Example 4. In addition, the first difference value was found to be 1.0 μm in Example 5, 1.0 μm in Example 6, 1.7 μm in Example 7, and 1.8 μm in Example 8. In addition, the first difference value was found to be 2.3 μm in Comparative Example 1, 1.8 μm in Comparative Example 2, and 1.9 μm in Comparative Example 3.

[0081] The second difference value, which is the value obtained by subtracting the minimum value from the maximum value of the width direction thickness, which is the thickness in the width direction DW, was found to be 0.6 μm in Example 1, 1.3 μm in Example 2, 1.0 μm in Example 3, and 0.4 μm in Example 4. The second difference value was also found to be 0.8 μm in Example 5, 1.0 μm in Example 6, 1.5 μm in Example 7, and 1.4 μm in Example 8. The second difference value was also found to be 0.7 μm in Comparative Example 1, 0.6 μm in Comparative Example 2, and 1.0 μm in Comparative Example 3.

[0082] As a result, it was found that the first absolute value was 0.3 μm in Example 1, 0.5 μm in Example 2, 0.3 μm in Example 3, and 0.8 μm in Example 4. It was also found that the first absolute value was 0.2 μm in Example 5, 0.0 μm in Example 6, 0.2 μm in Example 7, and 0.4 μm in Example 8. It was also found that the first absolute value was 1.6 μm in Comparative Example 1, 1.2 μm in Comparative Example 2, and 0.9 μm in Comparative Example 3.

[0083] Thus, it was found that the first absolute value was 0.8 μm or less in the measurement metal foils 30 of Examples 1 to 8, while the first absolute value was greater than 0.8 in the measurement metal foils 30 of Comparative Examples 1 to 3. It was also found that the first difference value was greater than or equal to the second difference value in all of the measurement metal foils 30 of Examples 1 to 8 and Comparative Examples 1 to 3.

[0084] The second absolute value was found to be 0.0 μm in Example 1, 0.8 μm in Example 2, 0.4 μm in Example 3, and 0.1 μm in Example 4. The second absolute value was found to be 0.0 μm in Example 5, 0.0 μm in Example 6, 0.4 μm in Example 7, and 0.6 μm in Example 8. The second absolute value was found to be 1.5 μm in Comparative Example 1, 1.1 μm in Comparative Example 2, and 0.9 μm in Comparative Example 3. Thus, the second absolute value was found to be 0.8 μm or less in the measurement metal foils 30 of Examples 1 to 8, while the second absolute value was found to be greater than 0.8 μm in the measurement metal foils 30 of Comparative Examples 1 to 3.

[0085] Furthermore, it was found that the difference value obtained by subtracting the minimum value from the maximum value in the thickness of the metal foil 30 for measurement was 0.9 μm in Example 1, 2.6 μm in Example 2, 1.7 μm in Example 3, and 1.3 μm in Example 4. It was also found that the difference value obtained by subtracting the minimum value from the maximum value in the thickness of the metal foil 30 for measurement was 1.0 μm in Example 5, 1.0 μm in Example 6, 2.1 μm in Example 7, and 2.4 μm in Example 8. It was also found that the difference value obtained by subtracting the minimum value from the maximum value in the thickness of the metal foil 30 for measurement was 2.3 μm in Comparative Example 1, 1.8 μm in Comparative Example 2, and 1.9 μm in Comparative Example 3.

[0086] On the other hand, the difference value obtained by subtracting the minimum value from the maximum value in the spring width of the etching pattern was found to be 7.0 μm in Example 1, 7.5 μm in Example 2, 8.2 μm in Example 3, and 8.1 μm in Example 4. The difference value obtained by subtracting the minimum value from the maximum value in the spring width of the etching pattern was found to be 8.4 μm in Example 5, 8.4 μm in Example 6, 8.4 μm in Example 7, and 9.7 μm in Example 8. The difference value obtained by subtracting the minimum value from the maximum value in the spring width of the etching pattern was found to be 12.5 μm in Comparative Example 1, 13.7 μm in Comparative Example 2, and 14.3 μm in Comparative Example 3.

[0087] The first standard value was found to be 23.1% in Example 1, 24.9% in Example 2, 27.4% in Example 3, and 27.2% in Example 4. The first standard value was found to be 27.9% in Example 5, 28.0% in Example 6, 28.1% in Example 7, and 32.3% in Example 8. The first standard value was found to be 41.6% in Comparative Example 1, 45.6% in Comparative Example 2, and 47.5% in Comparative Example 3.

[0088] The standard deviation of the spring width was found to be 1.4 μm in Example 1, 1.4 μm in Example 2, 1.9 μm in Example 3, and 1.9 μm in Example 4. The standard deviation of the spring width was found to be 2.0 μm in Example 5, 1.7 μm in Example 6, 2.0 μm in Example 7, and 2.1 μm in Example 8. The standard deviation of the spring width was found to be 2.5 μm in Comparative Example 1, 2.6 μm in Comparative Example 2, and 2.6 μm in Comparative Example 3.

[0089] The second standard value was found to be 4.7% in Example 1, 4.7% in Example 2, 6.3% in Example 3, and 6.4% in Example 4. The second standard value was found to be 6.6% in Example 5, 5.7% in Example 6, 6.6% in Example 7, and 7.1% in Example 8. The second standard value was found to be 8.2% in Comparative Example 1, 8.5% in Comparative Example 2, and 8.5% in Comparative Example 3.

[0090] The percentage of 3σ with respect to the average value of the spring width was found to be 13.0% in Example 1, 13.0% in Example 2, 18.3% in Example 3, and 17.1% in Example 4. The percentage of 3σ with respect to the average value of the spring width was found to be 17.8% in Example 5, 16.0% in Example 6, 18.3% in Example 7, and 18.8% in Example 8. The percentage of 3σ with respect to the average value of the spring width was found to be 24.8% in Comparative Example 1, 26.4% in Comparative Example 2, and 22.0% in Comparative Example 3.

[0091] As described above, it was found that the metal foils for spring members of Examples 1 to 8 had smaller first standard values ​​for the spring width than the metal sheets for spring members of Comparative Examples 1 to 3. Therefore, it can be said that the metal foils for spring members of Examples 1 to 8 have less variation in the spring width in the thickness direction than the metal foils for spring members of Comparative Examples 1 to 3.

[0092] Furthermore, it was found that the standard deviation of the spring width was smaller in the metal foils for spring members of Examples 1 to 8 than in the metal sheets for spring members of Comparative Examples 1 to 3. Therefore, it can be said that the metal foils for spring members of Examples 1 to 8 have less variation in the spring width in the thickness direction than the metal foils for spring members of Comparative Examples 1 to 3.

[0093] Furthermore, it was found that the metal foils for spring members of Examples 1 to 8 had smaller second standard values ​​for the spring width than the metal foils for spring members of Comparative Examples 1 to 3. Therefore, it can be said that the metal foils for spring members of Examples 1 to 8 have less variation in the spring width in the thickness direction than the metal foils for spring members of Comparative Examples 1 to 3.

[0094] Furthermore, it was found that the percentage of 3σ relative to the average spring width was smaller in the metal foils for spring members of Examples 1 to 8 than in the metal foils for spring members of Comparative Examples 1 to 3. Therefore, it can be said that the metal foils for spring members of Examples 1 to 8 have less variation in spring width in the thickness direction than the metal foils for spring members of Comparative Examples 1 to 3.

[0095] FIG. 13 is a graph showing the relationship between the first absolute value and the difference value of the spring width. 13, when the first absolute value is 0.8 μm or less, the difference in the spring width of the etching pattern is found to be within the range of 6.0 μm to 10.0 μm. On the other hand, when the first absolute value is greater than 0.8 μm, the difference in the spring width of the etching pattern is found to exceed 12 μm. Thus, with the first absolute value, it is found that the variation in the spring width of the etching pattern varies greatly with 0.8 μm as the boundary.

[0096] FIG. 14 is a graph showing the relationship between the second absolute value and the difference value of the spring width. As shown in Figure 14, when the second absolute value is 0.8 µm or less, the difference in the spring width of the etching pattern is found to be within the range of 6.0 µm to 10.0 µm. On the other hand, when the second absolute value is greater than 0.8 µm, the difference in the spring width of the etching pattern is found to exceed 12 µm. Thus, with the second absolute value, it is found that the variation in the spring width of the etching pattern varies greatly with 0.8 µm as the boundary.

[0097] As described above, according to one embodiment of the metal foil for spring members, the spring member for electronic devices, the method for manufacturing the metal foil for spring members, and the method for manufacturing the spring member for electronic devices, the following effects can be obtained.

[0098] (1) Since the absolute value of the difference value obtained by subtracting the second difference value from the first difference value is 0.8 μm or less, the thickness variation in the metal foil 10 is suppressed. Therefore, in the spring member 20 formed by wet etching the metal foil 10, the variation in the spring width in the thickness direction is suppressed.

[0099] (2) Since the absolute value of the difference obtained by subtracting the second maximum value from the first maximum value is 0.8 μm or less, the degree of isotropic etching occurring in the metal foil 10 is prevented from varying in the rolling direction DR and the width direction DW, and as a result, the width variation in the thickness direction of the spring member 20 is reduced.

[0100] (3) Since the difference between the maximum and minimum thicknesses of the metal foil 10 is 2.6 μm or less, it is possible to suppress variations in thickness throughout the metal foil 10. (4) Since the metal foil 10 can have high hardness, the durability of the spring member 20 formed from the metal foil 10 can be increased.

[0101] The technical ideas derived from the above-described embodiment and modified examples are described below. [Appendix 1] A metal foil for a spring member for manufacturing a spring member, The spring member has a square shape with a side length of 300 mm and includes a first region for forming the spring member. a first maximum value of the first thickness at each point on a straight line along the rolling direction in the first region, the second maximum value of the thickness at each point on a straight line along the width direction of the metal foil for a spring member is a second maximum value, The absolute value of the difference obtained by subtracting the second maximum value from the first maximum value is 0.8 μm or less. Metal foil for spring components.

[0102] When wet etching is used to form through-holes in the metal foil for a spring member that penetrate the metal foil for a spring member along the thickness direction of the metal foil, thinner portions of the metal foil for a spring member are more likely to be penetrated, and thicker portions of the metal foil for a spring member are less likely to be penetrated. Even if through-holes are formed in thinner portions of the metal foil for a spring member, the through-holes contribute to the formation of a flow of etching solution in the thickness direction of the metal foil for a spring member, but are less likely to contribute to the progression of isotropic etching in a direction perpendicular to the penetration direction. In contrast, thicker portions of the metal foil for a spring member require longer wet etching time than other portions, and therefore contribute to the isotropic etching that progresses in the metal foil for a spring member.

[0103] In this regard, in the metal foil for spring members, by having the absolute value of the difference obtained by subtracting the second maximum value from the first maximum value be 0.8 μm or less, the degree of isotropic etching occurring in the metal foil for spring members is prevented from varying in the rolling direction and width direction, and as a result, the variation in the spring width in the thickness direction of the spring member is reduced. [Explanation of symbols]

[0104] 10...Metal foil for spring components 10R1…1st area 20...Spring member

Claims

1. A metal foil for a spring member for manufacturing a spring member, having a square shape with a side length of 300 mm, and including a first region for forming the spring member, wherein a difference value between a maximum value and a minimum value of a first thickness at each point on a straight line along the rolling direction within the first region is a first difference value, a difference value between a maximum value and a minimum value of a second thickness at each point on a straight line along the width direction orthogonal to the rolling direction is a second difference value, an absolute value of a difference value obtained by subtracting the second difference value from the first difference value is 0.8 μm or less, the metal foil for a spring member is a rolled material, and a thickness of the metal foil for a spring member is 50 μm or more Metal foil for a spring member.

2. In the first region, the maximum value of the first thickness is a first maximum value, the maximum value of the second thickness is a second maximum value, and an absolute value of a difference value obtained by subtracting the second maximum value from the first maximum value is 0.8 μm or less The metal foil for a spring member according to Claim 1.

3. In the first region, a difference value obtained by subtracting a minimum value from a maximum value of the thickness at each point on the metal foil for a spring member is 2.6 μm or less The metal foil for a spring member according to Claim 1 or 2.

4. the metal foil for a spring member includes any one selected from the group consisting of a stainless alloy, beryllium copper, nickel tin copper, phosphor bronze, Corson alloy, and titanium copper The metal foil for a spring member according to Claim 1 or 2.

5. A method for manufacturing a spring member for an electronic device using a metal foil for a spring member, including forming a resist mask on a front surface and a back surface of the metal foil for a spring member, and wet-etching the metal foil for a spring member using the resist mask, wherein a difference value between a maximum value and a minimum value of a first thickness at each point on a straight line along the rolling direction of the metal foil for a spring member is a first difference value, a difference value between a maximum value and a minimum value of a second thickness at each point on a straight line along the width direction orthogonal to the rolling direction is a second difference value, an absolute value of a difference value obtained by subtracting the second difference value from the first difference value is 0.8 μm or less, a standard deviation of the spring width is 2.1 μm or less, the metal foil for a spring member is a rolled material, and a thickness of the metal foil for a spring member is 50 μm or more Method for manufacturing a spring member for an electronic device.

6. The thickness of the metal foil for a spring member is 200 μm or less The method for manufacturing a spring member for an electronic device according to Claim 5.

7. In the metal foil for the spring member, the maximum value of the first thickness is the first maximum value, the maximum value of the second thickness is the second maximum value, the absolute value of the difference value obtained by subtracting the second maximum value from the first maximum value is 0.8 μm or less The method for manufacturing a spring member for an electronic device according to claim 5 or 6.

8. The difference value obtained by subtracting the minimum value from the maximum value of the thickness at each point on the metal foil for the spring member is 2.6 μm or less The method for manufacturing a spring member for an electronic device according to claim 5 or 6.

9. The spring member for an electronic device includes any one selected from the group consisting of a stainless alloy, beryllium copper, nickel tin copper, phosphor bronze, Corson alloy, and titanium copper The method for manufacturing a spring member for an electronic device according to claim 5 or 6.

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