A method for testing pinholes of ultra-thin copper foil

Abstract

The application discloses a kind of ultra-thin copper foil pinhole testing methods, comprising the following steps: S1, selecting standard size copper foil, copper foil is laid between two backing plates, form test unit, the backing plate is made of light-transmitting and can be softened at high temperature Material is made, the copper foil between interlayer can be observed through any one side of two side backing plates;S2, the upper and lower sides of test unit are covered with pressing plate, put into high-temperature vacuum press, and pressure is applied to the upper and lower sides of test unit under high-temperature vacuum environment;S3, the test unit is taken out from high-temperature vacuum press for cooling, the pressing plate is removed, and the test unit is placed together on the window of the dark box with built-in light source, so that the light transmitted from the window transmits through the copper foil, the number and position of pinholes on the surface of the copper foil are tested and counted.The application can solve the problem that existing optical microscope or image processing technology is difficult to quickly locate pinhole position on ultra-thin copper foil in a large range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of copper foil physical property detection, in particular to a testing method for pinholes of ultra-thin copper foil. BACKGROUND

[0002] As an important part of the electronic material field, the copper foil industry is undergoing significant changes and development under the dual driving of technological innovation and market demand in recent years. One of the most notable trends is that copper foil is accelerating its development towards the ultra-thin field.

[0003] Ultra-thin copper foil is widely used in various fields due to its excellent electrical conductivity, good flexibility and high strength. In the field of lithium-ion batteries, ultra-thin copper foil as negative electrode current collector can significantly improve the energy density and cycle performance of the battery; in the field of 5G communication, ultra-thin copper foil can meet the demand of high-frequency high-speed signal transmission, improve communication quality and stability; in addition, in the field of flexible electronics, wearable devices, etc., ultra-thin copper foil also plays an irreplaceable role.

[0004] The use of ultra-thin copper foil has significant advantages for both the lithium battery industry and the electronic circuit industry. For lithium battery copper foil, by reducing the thickness of the copper foil, the amount of active material can be increased without changing the size of the battery, thereby increasing the thickness of the slurry coating and improving the energy density of the battery. For example, compared with 8-micron copper foil, 6-micron and 4.5-micron copper foil can increase the energy density by 5.11% and 8.82%, respectively.

[0005] For electronic circuit copper foil, as electronic products become increasingly smaller, lighter and more powerful, the traditional thickness of copper foil has been difficult to meet the design requirements of modern electronic devices for thinness and lightness. Therefore, engineers have improved production processes such as electrolysis and calendering, and the thickness of copper foil has been continuously reduced, and ultra-thin copper foil with a thickness of only a few microns can now be produced.

[0006] During the production of ultra-thin copper foil, factors such as the poor filtration effect of electrolyte, the generation of bubbles or foreign crystals, and the uneven size of grains during electroplating can cause pinholes on the surface of the copper foil. These pinholes not only affect the electrical conductivity and mechanical strength of the copper foil, but also can cause quality defects such as resin penetration, line loss, and open circuit during subsequent processing, thereby affecting the performance and reliability of the entire electronic product. Moreover, the problem of pinholes in electrolytic copper foil becomes more prominent as the thickness of the copper foil continues to thin out. Due to the randomness of the number and location of pinholes, combined with the poor anti-wrinkle ability of ultra-thin copper foil itself, traditional optical microscopes or image processing techniques are difficult to quickly and widely locate pinhole problems. This brings some difficulties to the detection method of copper foil pinholes. SUMMARY

[0007] The application provides a kind of ultra-thin copper foil pinhole test method, can solve the problem that existing optical microscope or image processing technology is difficult to quickly locate to ultra-thin copper foil on pinhole position.

[0008] To achieve the above object, the application provides the following technical scheme: a kind of ultra-thin copper foil pinhole test method, comprising the following steps:

[0009] S1: select standard size copper foil, copper foil is laid between two backing plates, form test unit, the backing plate is made of light-transmitting and softening material at high temperature, the copper foil between layers can be observed through any one side of the two side backing plates;

[0010] S2: cover the upper and lower sides of test unit with pressing plate, put into high temperature vacuum press, apply pressure to the upper and lower sides of test unit in high temperature vacuum environment;

[0011] S3: take out test unit from high temperature vacuum press for cooling, remove pressing plate, place test unit together on the window of dark box with built-in light source, make the light from the window transmit through copper foil, test the number and position of pinholes on the surface of copper foil, and count.

[0012] As preferred, the backing plate is made of polyethylene or polycarbonate, which has low material cost and can meet the requirements of light transmission and high temperature softening.

[0013] As preferred, the light transmittance of the backing plate is greater than 50%, and the surface flatness is less than 0.03mm, which ensures that the light and the line of sight can be seen through, and the small surface flatness can reduce the wrinkles and deformation of the surface of copper foil 3.

[0014] As preferred, when the test unit and the pressing plate are put into the high temperature vacuum press, high temperature soft pads are placed on the upper and lower sides of the test unit, which can prevent the pressure of the high temperature vacuum press from damaging the backing plate and the copper foil product.

[0015] As preferred, the test unit in step S2 includes a heating stage and a holding stage in the high temperature vacuum press, which ensures that the backing plate in the test unit can be fully softened and fully attached to the surface of the copper foil at a stable temperature.

[0016] As preferred, in step S3, the copper foil is placed on the window with the front side up and the back side up in turn for testing, and the number and position of pinholes on the front and back sides of the copper foil are compared, which can verify the number and position of pinholes by comparing the front and back sides of the copper foil.

[0017] As preferred, the size of the window is smaller than the size of the copper foil, which can prevent the light source from affecting the judgment of pinholes through side refraction.

[0018] As preferred, the window is arranged on the top of the dark box, the light source is arranged on the inner side wall and the bottom wall of the dark box, the window on the top facilitates the placement and movement of the test unit, and the light source is arranged to generate relatively uniform light emitted from the window, reduce reflection and have no dead angle.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] The operation is simple, the light-transmitting backing plate and the copper foil are high-temperature pressed, the copper foil is packaged between the two backing plates in a high-temperature planar pressing manner by using the characteristics of high-temperature softening and room-temperature curing of the special backing plate, the cleanliness of the sample to be tested is ensured, the ultra-thin copper foil will not be wrinkled by external force to affect the test, the pinhole position and quantity are quickly judged by using the light transmission method, the repeated test requirement of the sample can be met, the repeatability and reproducibility of the test process are improved, the process capacity of the measurement system is improved, and the large-area pinhole condition can be judged by using the large-area backing plate and pressing plate on the dark box. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a test method flowchart of the present application;

[0022] Figure 2 is a combination schematic view of the test unit and the pressing plate of the present application;

[0023] Figure 3 is a test schematic view of the present application;

[0024] Figure 4 is a structure view of the dark box of the present application.

[0025] REFERENCE SIGNS:

[0026] 1, pressing plate, 2, backing plate, 3, copper foil, 4, dark box, 5, window, 6, test unit, 7, light source. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

[0028] The present application solves the problem that the existing optical microscope or image processing technology is difficult to quickly and large-scale locate the pinhole position on the ultra-thin copper foil. Figures 1-4 As shown in the drawings, the following technical solutions are provided: a test method for an ultra-thin copper foil pinhole, comprising the following steps:

[0029] S1: selecting a standard size copper foil 3, placing the copper foil 3 between two backing plates 2 to form a test unit 6, the backing plates 2 are made of light-transmitting and high-temperature softening materials, and the copper foil 3 between the layers can be observed through any one side of the two backing plates 2;

[0030] S2: Covering the upper and lower sides of the test unit 6 with the press plate 1, and putting it into the high-temperature vacuum press to apply pressure to the upper and lower sides of the test unit 6 in a high-temperature vacuum environment;

[0031] S3: Taking the test unit 6 out of the high-temperature vacuum press for cooling, removing the press plate 1, and placing the test unit 6 together on the window 5 of the light source built-in dark box 4, so that the light transmitted from the window 5 transmits through the copper foil 3, and the number and position of pinholes on the surface of the copper foil 3 are tested and counted.

[0032] Specifically, generally, copper foil products used for transmission of circuit signals are not allowed to have pinholes, especially in the electronic circuit industry, the presence of pinholes can easily cause the circuit to be open, and for large quantities of copper foil products, the pinhole determination standard only has two results of the presence of pinholes and the absence of pinholes. However, when the light is seen to be emitted from the pinhole on the surface of the copper foil 3, it means that there is a pinhole on the sample copper foil. At the same time, the number and position of pinholes can be quickly counted and marked, and some problems in the production process of the ultra-thin copper foil can be deduced.

[0033] In this embodiment, the backing plate 2 is preferably a relatively thin plate, which can have a thickness of 2-4 mm, and two backing plates 2 are consumed for each test unit 6. The two backing plates 2 will soften under high temperature and will be in full contact with the copper foil 3 under the action of pressure, and will fill the pits on the surface of the copper foil 3 or flatten the wrinkles, so that the pinholes can be fully exposed. Moreover, the air between the copper foil 3 and the backing plate 2 can be extracted under vacuum state, preventing air bubbles from appearing between the copper foil 3 and the backing plate 2, which affects the accuracy of the test.

[0034] The backing plate 2 will automatically solidify at room temperature, so that the copper foil 3 and the backing plate 2 form a whole, i.e. the test unit 6, and the copper foil 3 will not be deformed or damaged by external force. The test unit 6 can be repeatedly detected and sample saved.

[0035] The high-temperature vacuum press can use conventional equipment on the market, which has low requirements, or can use a vacuum flat plate vulcanizing machine or a vacuum hot press forming machine, which can be freely selected.

[0036] As shown in Figure 2 The press plate 1 is used to assist in tightly attaching the two backing plates and the copper foil therebetween, and has an area greater than that of the backing plate 2 and a certain weight, such as a 2KG steel press plate 1.

[0037] In the embodiment, the liner plate 2 is made of polyethylene or polycarbonate, which has low material cost and can meet the effects of light transmission and high-temperature softening of the liner plate 2. The light transmission rate of the liner plate 2 is greater than 50%, and the surface flatness is less than 0.03 mm, so that the light and the line of sight can be seen through, and the small surface flatness can reduce the wrinkles and deformation of the surface of the copper foil 3.

[0038] In the embodiment, when the test unit 6 and the pressing plate 1 are placed in the high-temperature vacuum pressing machine, high-temperature soft pads are placed on the upper and lower sides of the test unit 6, which can prevent the pressure of the high-temperature vacuum pressing machine from damaging the liner plate 2 and the copper foil 3. The high-temperature soft pads can be made of high-temperature rubber pads or high-temperature silica gel pads, which can be purchased on the market.

[0039] In the embodiment, the test unit 6 in step S2 includes a temperature rising stage and a temperature maintaining stage in the high-temperature vacuum pressing machine, so that the liner plate 2 in the test unit 6 can be fully softened and fully combined with the surface of the copper foil 3 at a stable temperature. For example, the temperature is raised to 120°C at a temperature rising rate of 10 ℃ / min, and then maintained for 30 min.

[0040] Since the local areas of the front and back surfaces of the copper foil 3 can have different color block areas or wrinkles, if only one surface of the copper foil 3 is tested, the missed pinholes can be generated. Therefore, in step S3, the copper foil 3 can be placed on the window 5 with the front surface upward and the back surface upward in sequence, and the number and positions of the pinholes on the front and back surfaces of the copper foil 3 are compared. The front and back surfaces of the copper foil 3 can be used to verify the number and positions of the pinholes, so as to ensure the accuracy of the detection.

[0041] The size of the window 5 is smaller than the size of the copper foil 3, so that the light source can not refract through the side edges to affect the judgment of the pinholes. Meanwhile, the window 5 is arranged on the top of the dark box 4, the inner side wall and the bottom wall of the dark box 4 are both provided with the light source 7, the window 5 is arranged on the top to facilitate the placement and movement of the test unit 6, and the light source 7 is arranged in this way to generate relatively uniform light from the window 5, so as to reduce the reflection and have no dead angle.

[0042] As a first specific case in the embodiment:

[0043] Embodiment 1:

[0044] A 3 μm-thick copper foil 3 with a size of 300*300 mm is cut by a sampler, and is placed on the central layer between two 350*350 mm-sized liner plates 2. The liner plate 2 is made of polyethylene with a light transmission rate greater than 50% and a thickness of 3 mm, and has a smooth surface with a surface flatness of 0.03 mm.

[0045] The two sides of the backing plate 2 are covered with a steel pressing plate 1 with a weight of 2 kg and a size of 370*370 mm, which is tightly attached to the polyethylene backing plate 2, to help tightly attach the two backing plates 2 to the copper foil 3 therebetween. If multiple groups of samples are to be tested, the test units are continuously stacked upwards in this structure.

[0046] The two sides of the test unit are padded with high-temperature-resistant soft pads, and the test unit is placed in a high-temperature vacuum press. The vacuum is extracted to 0.05 MPa, the pressure is set to 28 PSI, the temperature is raised to 120°C at a rate of 10°C / min, and the temperature is maintained for 30 min. After cooling to room temperature, the test unit is removed.

[0047] After the test sample is removed, the outer high-temperature-resistant soft pads are peeled off and the pressing plate 1, and the sample can be clearly observed to have interlayer copper foil 3 on either side of the two backing plates 2. The test sample is placed as shown in Figure 3 the windowed dark box window, which has a size of 270*270 mm and is smaller than the size of the copper foil cut, to prevent light from the light source from being refracted through the side edges and affecting the pinhole judgment. The dark box 4 has light sources 7 on the bottom and sides, which can be adjusted between 500-2500 lumens according to the power.

[0048] The position of the test unit 6 is adjusted until the size of the middle copper foil 3 completely covers the light source, and the number and position of pinholes are tested in steps with light sources of 500, 1000, 1500, 2000, and 2500 lumens, and the number of pinholes in the copper foil is 10 after the test.

[0049] Example 2

[0050] The difference between this example 2 and example 1 is that the thickness of the measured copper foil sample is adjusted, and a copper foil with a thickness of 35 μm and a pinhole number of 10 is used for testing. Moreover, the material of the backing plate 2 is changed, and a polycarbonate material is used as the backing plate for testing, which has a light transmittance of >50%. The surface flatness is 0.002 mm.

[0051] After testing, the number of pinholes on the surface of the copper foil is 10.

[0052] Example 3

[0053] The difference between this example 3 and example 1 is that the size of the measured copper foil sample is adjusted, and a copper foil with a size of 500*500 mm and a pinhole number of 10 is used for testing, and the size of the backing plate 2 is 550*550 mm, and the size of the pressing plate 1 is 570*570 mm.

[0054] After testing, the number of pinholes on the surface of the copper foil is 10.

[0055] On the contrary, the following are comparative examples without a test method:

[0056] Comparative Example 1:

[0057] The difference between the present comparative example 1 and example 1 is that the sample preparation of the copper foil test does not use a backing plate. The specific process is to directly cut the copper foil to cover the dark box window for verification, and the copper foil is flattened by hand.

[0058] After testing, the number of pinholes on the surface of the copper foil is 15, and they are mainly concentrated in the wrinkle area, and the sample cannot be repeatedly tested.

[0059] Comparative Example 2:

[0060] The difference between the present comparative example 1 and example 1 is that the flatness of the backing plate is 0.5 mm.

[0061] After testing, the number of pinholes on the surface of the copper foil is 12, and gas bubbles appear between the layers of the sample after pressing, affecting the light shielding of the sample and the observation of the number of pinholes.

[0062] Comparing the above example 1 with comparative examples 1 and 2, it can be seen that the schemes of comparative examples 1 and 2 result in inaccurate test results, and the results of examples 1-3 are accurate.

[0063] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative positional relationship, motion condition, etc. between the components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications will also change accordingly.

[0064] In addition, the description of "first level", "second level" and the like in the present application is only for description purposes, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first level" and "second level" can be explicitly or implicitly included at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0065] In the present application, unless otherwise specifically specified and limited, the terms "connection", "fixation" and the like should be understood broadly, for example, "fixation" can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection; can be directly connected, or indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise specifically limited. For ordinary skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0066] In addition, the technical solutions among various embodiments of the present application can be combined with each other, but it must be based on that a person skilled in the art can realize, when the combination of technical solutions appears contradictory or cannot be realized, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope required by the present application.

Claims

1. A method for testing pinholes of an ultra-thin copper foil, characterized by, It comprises the following steps: S1: select standard size copper foil (3), copper foil (3) is placed between two pieces of backing plate (2), forming a test unit (6), the backing plate (2) is made of light transmission and can be softened at high temperature material, through the two sides of the backing plate (2) can be observed from any side of the copper foil (3) between the layers; S2: cover the test unit (6) on both sides of the upper and lower pressure plate (1), and then put into the high temperature vacuum press after putting on the high temperature soft pad on both sides of the upper and lower, apply pressure to the upper and lower sides of the test unit (6) in high temperature vacuum environment, soften the backing plate (2) and the copper foil (3) surface by heating and heat preservation; S3: take out the test unit (6) from the high temperature vacuum press for cooling, remove the pressure plate (1) and soft pad, and place the test unit (6) together on the window (5) of the dark box (4) with built-in light source, so that the light from the window (5) transmits through the copper foil (3), the number and position of pinholes on the surface of the copper foil (3) are tested and counted.

2. The method of testing for pinholes in an ultra-thin copper foil according to claim 1, wherein: The backing plate (2) is made of polyethylene or polycarbonate.

3. The method of claim 1, wherein: The light transmittance of the backing plate (2) is greater than 50%, and the surface flatness is less than 0.03mm.

4. The method of testing for pinholes in an ultra-thin copper foil according to any one of claims 1 to 3, characterized in that: In step S3, the copper foil (3) is placed on the window (5) with the front side up and the back side up in turn for testing, and the number and position of pinholes on the front and back sides of the copper foil (3) are compared.

5. The method of testing for pinholes in an ultra-thin copper foil according to claim 4, wherein: The size of the window (5) is smaller than that of the copper foil (3).

6. The method of testing for pinholes in an ultra-thin copper foil according to claim 5, wherein: The window (5) is arranged on the top of the dark box (4), and the light source (7) is installed on the inner side wall and the bottom wall of the dark box (4). The size of the window (5) is smaller than that of the copper foil (3). The window (5) is arranged on the top of the dark box (4), and the light source (7) is installed on the inner side wall and the bottom wall of the dark box (4).

Images