Cover film and circuit board

Abstract

The invention discloses a cover film and a circuit board, the cover film comprises a cover film body, the cover film body is provided with a first surface and a second surface which are opposite to each other, and the brightness value of the first surface is greater than that of the second surface; and after at least two times of reflow soldering, the first color difference E1 of the first surface is smaller than or equal to 1, so that the high-temperature-resistant stability of the covering film is ensured, color change in the subsequent high manufacturing process of the circuit board is avoided, and the quality of the circuit board is effectively improved.

Description

Technical Field

[0001] Embodiments of the present invention relate to the technical field of electronic information materials, and in particular, to a cover film and a circuit board. Background Art

[0002] In existing circuit boards, a glue layer is usually provided on the surface of the circuit as a cover film for protection. The entire surface of the circuit board is covered by the cover film to play roles such as protection, moisture-proof, dust-proof, and interlayer insulation. At the same time, it also has certain identification and aesthetic functions. However, when installing electronic components on the circuit board covered with the cover film, high-temperature processes such as reflow soldering are required, and the maximum temperature range may reach 300 °C. After the high-temperature process, the cover film covering the surface of the circuit board is prone to discoloration, affecting the quality of the product. Summary of the Invention

[0003] The present invention provides a cover film and a circuit board to ensure the high-temperature stability of the cover film, avoid discoloration during subsequent high processes of the circuit board, and effectively improve the quality of the circuit board.

[0004] In a first aspect, an embodiment of the present invention provides a cover film, including a cover film body. The cover film body has opposite first and second surfaces, and the lightness value of the first surface is greater than the lightness value of the second surface;

[0005] And after at least 2 reflow soldering processes, the first color difference ΔE1 of the first surface is less than or equal to 1.

[0006] Optionally, the lightness value of the first surface in the Lab color model is greater than 60, and the lightness value of the second surface in the Lab color model is less than 40.

[0007] Optionally, the absolute value of the difference between the lightness value of the first surface and the lightness value of the second surface is greater than or equal to 30.

[0008] Optionally, before and after at least 2 reflow soldering processes, the absolute value of the difference between the lightness values of the first surface is less than or equal to 5.

[0009] Optionally, taking a cover film sample in a preset area, after at least 240 h under the conditions of a temperature of 85 °C and a humidity of 85% RH, the second color difference ΔE2 of the first surface of the cover film sample is less than or equal to 1.

[0010] Optionally, taking a cover film sample in a preset area and soaking it in 2 mol / L HCl and 10% NaOH solutions for 10 min respectively, the third color difference ΔE3 of the first surface of the cover film sample is less than or equal to 1.

[0011] Optionally, the covering film body includes a color-developing layer and an adhesive layer arranged in a stacked manner. The side of the color-developing layer away from the adhesive layer is the first surface of the covering film body, and the side of the adhesive layer away from the color-developing layer is the second surface of the covering film body.

[0012] Optionally, the thickness of the color-developing layer is greater than or equal to 2 times the thickness of the adhesive layer.

[0013] Optionally, the covering film body further includes a carrier layer, and the carrier layer is detachably arranged on the first surface.

[0014] In a second aspect, an embodiment of the present invention provides a circuit board, and the circuit board includes the covering film according to any of the embodiments of the present invention.

[0015] In the embodiment of the present invention, by defining that the lightness value of the first surface of the covering film body is greater than the lightness value of the second surface, the color difference between the two sides can be used not only for aesthetic and marking designs on the lighter first surface, but also because the lightness value of the second surface is lower and the color is darker, after covering the circuit board on the second surface, the surface of the circuit board can be effectively blocked. In addition, after the covering film has experienced at least 2 reflow soldering processes, the present invention also defines that the first color difference △E1 of the first surface is less than or equal to 1 to ensure the high-temperature stability of the covering film and avoid color change during subsequent high-processes of the circuit board, effectively improving the quality of the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic structural diagram of a covering film provided by an embodiment of the present invention;

[0017] Figure 2 is another schematic structural diagram of a covering film provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] Figure 1 is a schematic structural diagram of a covering film provided by an embodiment of the present invention, see Figure 1, the cover film includes a cover film body. The cover film body has opposite first surface 111 and second surface 121, and the lightness value of the first surface 111 is greater than that of the second surface 121; and after at least 2 reflow soldering processes, the first color difference △E1 of the first surface 111 is less than or equal to 1.

[0020] Specifically, when the cover film is laminated on the circuit board, the second surface 121 side of the cover film body is combined with the circuit board surface. In the embodiment of the present invention, the lightness value of the first surface 111 is greater than that of the second surface 121. The lightness value is a parameter in the Lab color model. The lightness value can be represented by L, and the value range of L is 0 - 100, which reflects the change from black to white. The lightness value can describe the brightness or darkness of a color. It reflects the position of the color in the black - white - gray scale. The higher the lightness value, the lighter the color; the lower the lightness value, the darker the color. The lightness value of the first surface 111 is greater than that of the second surface 121, that is to say, the color of the first surface 111 is lighter and the color of the second surface 121 is darker. The first surface 111 and the second surface 121 can form a lightness contrast, which is more conducive to distinguishing the first surface 111 and the second surface 121 of the cover film body during the preparation process of the circuit board, and aesthetic and marking designs can be carried out on the lighter - colored first surface 111. Further, when the second surface 121 is attached to the circuit board, the color of the circuit board and the circuits on the circuit board can be blocked by the second surface 121, improving the quality of the circuit board.

[0021] The first surface 111 with a higher lightness value usually includes inorganic materials with a high reflectivity in terms of material. It can not only improve the lightness of the first surface 111, but also has stronger chemical stability at high temperatures and is not prone to color change. Further, the thermal radiation absorption rate of the first surface 111 with a higher lightness value is reduced, which can also reduce the influence of temperature on the first surface 111. By limiting the lightness value of the first surface 111 to be greater than that of the second surface 121 in the cover film of the embodiment of the present invention, and after at least 2 reflow soldering processes, that is, after at least two high - temperature treatments, the first color difference △E1 of the first surface 111 is controlled to be less than or equal to 1 to ensure the high - temperature discoloration resistance ability of the cover film. The first color difference △E1 is used to characterize the degree of color difference of the first surface 111 before and after reflow soldering.

[0022] In the Lab color model, the color difference △E is used to characterize the degree of difference between two colors. The color difference △E is an auxiliary index parameter in the Lab color model and is usually represented in numerical form. The smaller the value of the color difference △E, the closer the color change before and after; conversely, the larger the value of the color difference, the more obvious the difference between the colors before and after.

[0023] The calculation method of △E is as follows:

[0024]

[0025] Among them, △L, △a, and △b respectively represent the differences in lightness, a-axis, and b-axis between two consecutive color samplings. The a-axis represents the axis from green to red, with negative values indicating the green direction and positive values indicating the red direction; the b-axis represents the axis from blue to yellow, with negative values indicating the blue direction and positive values indicating the yellow direction.

[0026] The first color difference △E1 of the first surface 111 can be obtained by using a color difference meter to perform color difference tests on the first surface 111 of the product, obtaining the initial L, a, and b values of the first surface 111 before reflow soldering, then curing the product, and then performing at least 2 reflow soldering operations on the entire circuit board. After reflow soldering, take out the circuit board product and perform color difference tests on the first surface 111 again to obtain the L1, a1, and b1 values of the first surface 111 after reflow soldering. Calculate the parameter values before and after reflow soldering according to the color difference formula to obtain the first color difference △E1 of the first surface 111 before and after reflow soldering. Moreover, the absolute value △L of the difference in lightness values of the first surface 111 before and after at least 2 reflow soldering operations can also be obtained.

[0027] In this embodiment, the peak zone temperature of reflow soldering is generally above 210°C. The temperature curve needs to be adjusted according to the type of board (such as FR-4, metal substrate, flexible board, etc.), and the solder joint quality control is carried out in combination with IPC standards (such as IPC-J-STD-001).

[0028] In the embodiment of the present invention, by defining that the lightness value of the first surface 111 of the cover film body is greater than the lightness value of the second surface 121, the color difference on both sides can be used not only for aesthetic and marking design on the lighter first surface 111, but also because the lightness value of the second surface 121 is lower and the color is darker, after covering the circuit board on the second surface 121, the surface of the circuit board can be effectively blocked. In addition, after the cover film has experienced at least 2 reflow soldering operations, the first color difference △E1 of the first surface 111 is less than or equal to 1 to ensure the high-temperature stability of the cover film and avoid color change during subsequent high-processes of the circuit board, effectively improving the quality of the circuit board.

[0029] Based on the above embodiment, optionally, the lightness value of the first surface 111 in the Lab color model is greater than 60, and the lightness value of the second surface 121 in the Lab color model is less than 40.

[0030] Specifically, by defining that the lightness value of the first surface 111 is greater than 60 and the lightness value of the second surface 121 is less than 40, the contrast between the two sides of the cover film can be further improved. After the second surface 121 of the cover film is attached to the circuit board, the lightness value of the second surface 121 is less than 40, and the second surface 121 can serve as a darker background, which can improve the shielding of the circuit board surface, thereby reducing the interference of reflected light on the circuit board and improving the accuracy of optical positioning when soldering or mounting devices on the circuit board. In the embodiment of the present invention, by defining that the lightness value of the first surface 111 is greater than 60, the reflectivity of the high-lightness first surface 111 is higher, thereby reducing the local heat radiation aggregation and the influence of heat radiation, and thus avoiding a large color difference on the first surface 111 after high-temperature processes.

[0031] Optionally, the absolute value of the difference between the lightness value of the first surface 111 and the lightness value of the second surface 121 is greater than or equal to 30. If the difference between the lightness value of the first surface 111 and the lightness value of the second surface 121 is small, the contrast between the first surface 111 and the second surface 121 is low, which will introduce signal noise of light during soldering or mounting devices on the circuit board and affect the accuracy of optical positioning of the devices on the circuit board. And because the contrast between the first surface 111 and the second surface 121 is low, the heat radiation absorption of the first surface 111 and the second surface 121 will be relatively similar, resulting in heat radiation aggregation between the first surface 111 and the second surface 121, which will cause discoloration in some areas of the first surface 111, and ultimately increase the first color difference △E1 of the first surface 111, failing to meet the application requirements. Therefore, in the embodiment of the present invention, it is defined that the absolute value of the difference between the lightness value of the first surface 111 and the lightness value of the second surface 121 is greater than or equal to 30 to ensure that the first surface 111 and the second surface 121 have a certain contrast, ensure the high-temperature resistance stability of the cover film, avoid a large color difference on the first surface 111 after high-temperature processes, and not meet the application requirements.

[0032] Furthermore, high temperature easily causes the cover film to denature and trigger color changes. By selecting the cover film material, for example, a high heat-resistant substrate can be selected to reduce the change in the lightness value of the first surface 111 after high temperature. The structure of the cover film can also be adjusted. For example, increasing the thickness of the film layer corresponding to the first surface 111 can reduce the influence of heat conduction on the cover film, or by coating a reflective coating on the first surface 111 to reduce the aggregation of heat radiation and reduce the change in the lightness value of the first surface 111 after high temperature. In the embodiment of the present invention, by defining that the absolute value of the difference between the lightness values of the first surface 111 before and after at least 2 reflow solders is less than or equal to 5, the high-temperature discoloration stability of the cover film is ensured.

[0033] In order to further ensure the color change stability of the cover film during application, in the embodiments of the present invention, after the cover film is placed in a high-temperature and high-humidity environment (for example, at a temperature of 85°C and a humidity of 85% RH) for at least a first preset time, the second color difference ΔE2 of the first surface 111 should be less than or equal to 1, so as to ensure the color change stability of the cover film in the high-temperature and high-humidity environment. Exemplarily, the test process of the second color difference ΔE2 can be as follows: Take a cover film sample in a preset area, press the second surface 121 of the cover film against the circuit board, tear off the carrier film to expose the first surface 111 of the product, use a color difference meter to perform a color difference test on the first surface 111 of the product to obtain the initial L, a, b values of the first surface 111, and then cure the product. After at least 240 hours under the conditions of a temperature of 85°C and a humidity of 85% RH, take out the circuit board product, and perform a color difference test on the first surface 111 again to obtain the L2, a2, b2 values of the first surface 111 after the high-temperature and high-humidity environment test. Calculate according to the color difference formula to obtain the second color difference ΔE2 of the first surface 111.

[0034] In the embodiments of the present invention, it is also ensured that the color change stability of the cover film in acidic and alkaline environments by defining that after the cover film is immersed in an acidic and alkaline environment (for example, in 2 mol / L HCl and 10% NaOH solutions) for a second time, the third color difference ΔE3 of the first surface 111 of the cover film sample is less than or equal to 1. Exemplarily, the test process of the third color difference ΔE3 can be as follows: Take a cover film sample in a preset area, press the second surface 121 of the cover film against the circuit board, tear off the carrier film to expose the first surface 111 of the product, use a color difference meter to perform a color difference test on the first surface 111 of the product to obtain the initial L, a, b values of the first surface 111, and then cure the product. Immerse it in 2 mol / L HCl and 10% NaOH solutions for 10 minutes respectively, take out the circuit board product, and perform a color difference test on the first surface 111 again to obtain the L3, a3, b3 values of the first surface 111 after the acidic and alkaline tests. Calculate according to the color difference formula to obtain the third color difference ΔE3 of the first surface 111.

[0035] Combined with Figure 1 , the cover film body includes a color display layer 110 and an adhesive layer 120 arranged in a stacked manner. The side of the color display layer 110 away from the adhesive layer 120 is the first surface 111 of the cover film body, and the side of the adhesive layer 120 away from the color display layer 110 is the second surface 121 of the cover film body.

[0036] Specifically, the color display layer 110 is used to provide color, pattern or text information for differentiating circuit function areas, identifying pad positions or tracing production information. Through the control of lightness value (L value), hue (a / b value), etc., the optical color change, light reflection and other properties of the circuit board can be optimized. Among them, the material of the color display layer 110 can be polyimide, etc. The color display layer 110 should have the characteristics of high temperature resistance, acid and alkali resistance, stable lightness value, etc. In the embodiments of the present invention, by defining that before and after at least 2 reflow soldering processes, the absolute value of the difference in lightness value of the first surface 111 is less than or equal to 5, the second color difference △E2 of the first surface 111 in high temperature and high humidity environments should be less than or equal to 1, and / or the third color difference △E3 of the first surface 111 in acidic and alkaline environments is less than or equal to 1, so as to ensure the stability of the cover film color change. The adhesive layer 120 is used to bond the color display layer 110 to the circuit board to prevent the color display layer 110 from falling off.

[0037] In the embodiments of the present invention, the color display layer 110 of the cover film can be white, for example, a white ink layer or a film adhesive layer is used, so that the color display layer 110 is a light color system. The adhesive layer 120 can be black, for example, a black film adhesive layer is used, so that the adhesive layer 120 is a dark color system. The color difference between the color display layer 110 and the adhesive layer 120 is relatively obvious. The color display layer 110 provides the first surface 111, and the adhesive layer 120 provides the second surface 121, so that the lightness value of the first surface 111 is greater than that of the second surface 121, and the adhesive layer 120 can effectively play a shielding role. Among them, the thickness of the color display layer 110 is at least twice the thickness of the adhesive layer 120. By increasing the thickness of the color display layer 110, the transmittance of external light is reduced, the shielding property of the cover film is further enhanced, and at the same time, the color display layer 110 with sufficient thickness can effectively slow down the color change degree of the cover film during high-temperature processes and reduce the possibility of its appearance of miscellaneous colors.

[0038] Figure 2 For another structural schematic diagram of the cover film provided by the embodiments of the present invention, see Figure 2 The cover film body further includes a carrier layer 130, and the carrier layer 130 is detachably disposed on the first surface 111. Generally, when pressing the cover film, a carrier layer 130 is set as an intermediate medium. After the cover film is thermally pressed on the surface of the circuit board through the carrier layer 130, the carrier layer 130 can be peeled off.

[0039] The embodiments of the present invention also provide a circuit board, which includes a printed circuit board, a PCB, etc. The cover film of any embodiment of the present invention is attached to the surface of the circuit board. Because it includes the cover film of any embodiment of the present invention, it has the same beneficial effects and will not be elaborated here.

[0040] According to the comparative verification of the color change stability of the cover film in the embodiments of the present invention, combined with Figure 1In addition, the operating conditions or processes for reflow soldering in the following examples and comparative examples are kept consistent.

[0041] Example 1

[0042] This example provides a cover film. Among them, the lightness value of the first surface 111 is 65, and the lightness value of the second surface 121 is 28. Before reflow soldering, the initial L, a, and b values of the first surface are measured through color difference testing. After 2 times of reflow soldering, the current L1, a1, and b1 values of the first surface are measured through color difference testing. According to the color difference formula, the first color difference △E1 of the first surface 111 before and after 2 times of reflow soldering is 0.59, and the lightness difference △L is 2.6.

[0043] Example 2

[0044] This example provides a cover film. Among them, the lightness value of the first surface 111 is 73, and the lightness value of the second surface 121 is 30. Before reflow soldering, the initial L, a, and b values of the first surface are measured through color difference testing. After 4 times of reflow soldering, the current L1, a1, and b1 values of the first surface are measured through color difference testing. According to the color difference formula, the first color difference △E1 of the first surface 111 before and after 4 times of reflow soldering is 0.749, and the lightness difference △L is 3.

[0045] Example 3

[0046] This example provides a cover film. Among them, the lightness value of the first surface 111 is 78, and the lightness value of the second surface 121 is 25. Before reflow soldering, the initial L, a, and b values of the first surface are measured through color difference testing. After 8 times of reflow soldering, the current L1, a1, and b1 values of the first surface are measured through color difference testing. According to the color difference formula, the first color difference △E1 of the first surface 111 before and after 8 times of reflow soldering is 0.949, and the lightness difference △L is 4.

[0047] Comparative Example 1

[0048] This example provides a comparative cover film. Among them, the lightness value of the first surface 111 is 45, and the lightness value of the second surface 121 is 71. The initial L, a, and b values of the first surface are measured through color difference testing. After 2 times of reflow soldering, the current L1, a1, and b1 values of the first surface are measured through color difference testing. According to the color difference formula, the first color difference △E1 of the first surface 111 after 2 times of reflow soldering is 3.32.

[0049] Comparative Example 2

[0050] This embodiment provides another comparative cover film. Among them, the lightness value of the first surface 111 is 33, and the lightness value of the second surface 121 is 65. The L, a, and b values of the initial first surface are measured through a color difference test. After 4 reflow soldering processes, the L, a, and b values of the current first surface are measured through a color difference test. According to the color difference formula, the first color difference △E1 of the first surface 111 before and after 4 reflow soldering processes is 4.42.

[0051] Table 1 Test parameters of each embodiment and comparative example

[0052]

[0053] According to the data in the above table, compared with the cover film of the comparative example, the lightness value of the first surface 111 of the cover film in the embodiment of the present invention is greater than that of the second surface 121. Not only can aesthetic and identification designs be carried out on the lighter first surface 111, but also after covering the circuit board on the second surface 121, the surface of the circuit board can be effectively blocked; and after at least 2 reflow soldering processes, the first color difference △E1 of the first surface 111 is less than or equal to 1, making the color difference change of the cover film in subsequent high-temperature processes smaller, and having a better effect of better stability at high temperatures.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A covering film, characterized in that, It includes a covering film body, the covering film body is provided with opposite first and second surfaces, and the lightness value of the first surface is greater than that of the second surface; And after at least 2 reflow soldering processes, the first color difference △E1 of the first surface is less than or equal to 1.

2. The cover film according to claim 1, characterized in that, The lightness value of the first surface in the Lab color model is greater than 60, and the lightness value of the second surface in the Lab color model is less than 40.

3. The cover film according to claim 2, wherein The absolute value of the difference between the lightness value of the first surface and the lightness value of the second surface is greater than or equal to 30.

4. The cover film according to claim 1, wherein Before and after at least 2 reflow soldering processes, the absolute value of the difference between the lightness values of the first surface is less than or equal to 5.

5. The cover film according to claim 1, characterized in that, Take a covering film sample in a preset area. After at least 240 h under the conditions of a temperature of 85 °C and a humidity of 85% RH, the second color difference △E2 of the first surface of the covering film sample is less than or equal to 1.

6. The cover film according to claim 1, characterized in that, Take a covering film sample in a preset area and soak it in 2 mol / L HCl and 10% NaOH solutions for 10 min respectively. The third color difference △E3 of the first surface of the covering film sample is less than or equal to 1.

7. The cover film according to claim 1, wherein The covering film body includes a color-developing layer and an adhesive layer arranged in a laminated manner. The side of the color-developing layer away from the adhesive layer is the first surface of the covering film body, and the side of the adhesive layer away from the color-developing layer is the second surface of the covering film body.

8. The cover film according to claim 7, wherein The thickness of the color-developing layer is greater than or equal to 2 times the thickness of the adhesive layer.

9. The cover film according to claim 1 or 7, characterized in that The covering film body further includes a carrier layer, and the carrier layer is detachably arranged on the first surface.

10. A circuit board, characterized in that, The circuit board includes the covering film according to any one of claims 1-9.

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