COF (chip on film) tape design for improving adhesive force of printing ink

Abstract

The invention discloses a COF (chip on film) winding tape design for improving ink adhesive force, which comprises the following steps: providing a circuit substrate and a mask plate, carrying out light leakage design on the mask plate, coating positive photoresist on the surface of the circuit substrate, and then carrying out exposure operation; developing operation is carried out, and a copper surface in the circuit substrate is exposed; etching is carried out, so that the exposed copper surface in the circuit substrate and the light leakage area of the mask plate are etched away; and after degumming and water washing are conducted, tin plating and solder resist printing are conducted in sequence, finally drying is conducted, and the COF tape is obtained. The contact surface area of the ink and the metal coating is increased; compared with the prior art that no hole is formed in the circuit, the contact surface area of the ink and the metal coating on the surface of the hole is increased, and the contact surface area of the ink and the PI surface below the hole is increased, so that the adhesive force between the ink and the metal coating and the PI surface is improved.

Description

Technical Field

[0001] This invention belongs to the field of COF tape manufacturing, and specifically relates to a COF tape design that improves ink adhesion. Background Technology

[0002] COF, often referred to as flip-chip film, is a die-on flexible film packaging technology that fixes integrated circuits (ICs) onto flexible circuit boards. It uses a flexible attached circuit board as a chip packaging carrier to combine the chip with the flexible substrate circuit, or simply refers to a flexible attached circuit board without a packaged chip.

[0003] The manufacturing process of COF (Chip-on-Foil) includes: coating → exposure → development → etching → tin plating → solder resist printing, etc. In the solder resist printing process, ink is applied to the metal plating layer of the circuit area. To protect the circuit from contamination or scratches, the protective effect is closely related to the adhesion between the ink and the metal plating layer, and the adhesion between the ink and the PI (polyimide) surface. Adhesion is often measured using cross-cut adhesion test and pencil hardness test to ensure the protective effect of the ink.

[0004] The ink serves to protect the circuitry of the COF tape, but in practical applications, the ink layer on the metal plating may peel off. This is mainly because the adhesion between the ink layer and the metal plating is significantly lower than that between the ink layer and the PI layer. When subjected to significant external force, the ink layer above the metal plating will peel off, exposing the metal plating underneath. Foreign matter or moisture can then enter between the metal plating layers. When the conductive copper layer is energized, the conductive copper layer will burn out (because foreign matter or moisture can cause a short circuit between the conductive copper layers). Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a COF tape design that improves ink adhesion.

[0006] A COF tape design for improving ink adhesion includes: providing a copper foil, and sequentially performing coating, exposure, development, etching, resist removal, tin plating, solder resist printing, and baking on the copper foil; wherein, in the exposure step: providing a mask, and opening light-leaking holes in the chromium film of the mask.

[0007] As a preferred embodiment, the coating step includes: After coating the surface of the copper foil with a 1.2μm~1.6μm thick positive photoresist, it is cured at 100℃~120℃.

[0008] As a preferred embodiment, in the exposure step, the exposure intensity is controlled to be 55mw / cm2~100mw / cm2, and the exposure amount is 70mj~80mj.

[0009] As a preferred embodiment, the light-leaking hole is circular with a diameter of 3μm to 100μm.

[0010] As a preferred embodiment, in the development step, the exposed product is controlled to pass through an alkaline developing solution with pH > 13 at a speed of 2 m / min to 6 m / min. The alkaline developing solution is used to etch away the exposed positive photoresist, so that the pattern on the photomask appears on the positive photoresist.

[0011] As a preferred embodiment, the etching step employs wet etching, where the etching solution etches the areas of the copper foil surface without positive photoresist. Through processes of copper breaking, coarse etching, downward etching, and fine etching, the copper foil is transformed into copper circuitry. Since light-leaking patterns are formed on the chromium film of the photomask, the etching solution will etch holes into the circuitry in the light-leaking areas of the chromium film.

[0012] As a preferred embodiment, the degumming step is carried out in an alkaline solution at 50°C~60°C and pH>13.

[0013] As a preferred embodiment, in the tin plating operation, the tin plating solution is plated on the copper surface and the inner wall of the openings in the circuit board.

[0014] As a preferred embodiment, in the solder resist printing, ink is printed in the non-lead area of ​​the COF tape.

[0015] As a preferred embodiment, the baking temperature in the baking step is >110°C.

[0016] The implementation principle of this invention is as follows: Figure 1 As shown: 1. For lines that require openings, a light leakage design is made on the photomask so that the light leakage area of ​​the photomask is equal to the area of ​​the opening on the line. After processes such as coating, exposure, development, etching and resist removal, a conductive copper layer is formed in the hole, where the conductive copper layer is a copper line.

[0017] 2. When no holes are made in the circuit, the thickness of the ink on the metal plating layer is 5~15μm. After holes are made, the ink is embedded in the conductive copper layer, and the ink thickness becomes 13~23μm. The thicker the ink, the better the adhesion between the ink and the metal plating layer and the PI surface. The metal plating layer is a tin layer.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. Increased the contact surface area between the ink and the metal plating, and increased the contact surface area between the ink and the PI surface (due to the opening of holes in the line, such as...). Figure 2As shown, compared to not having holes in the conductive copper layer, this increases the contact surface area between the ink and the metal plating on the hole surface, and also increases the contact surface area between the ink and the PI surface below the hole, thereby improving the adhesion between the ink and the metal plating and the PI surface.

[0019] 2. Because there are holes in the line, the ink fills the holes, which is equivalent to a rivet being embedded in the conductive copper layer, thereby improving the adhesion of the ink to the metal layer and the PI surface. Attached Figure Description

[0020] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the implementation principle of the COF tape preparation method of the present invention. Figure 2 This is a schematic diagram of the conductive copper layer hole process in this invention; Figure 3 This is a comparison image of the chromium film on the mask plate before and after the circular holes are opened in the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention. Example

[0022] This embodiment provides a COF tape design to improve ink adhesion (for the fine conductive copper layer of COF tape), specifically including the following steps: S1. Coating: A 1.4μm thick layer of positive photoresist is uniformly coated on the surface of the copper foil. The positive photoresist is then baked and cured in a PB oven at a temperature of 120℃ for 120s. S2. Exposure: A projection-type exposure machine is used, with an exposure illuminance of 80 mW / cm². 2 With an exposure of 75mJ, the pattern on the photomask is transferred onto the positive photoresist. S2-1: The light emitted by the light source of the projection exposure machine cannot pass through the chromium film on the mask. Light leakage holes are created in the chromium film (e.g., ...). Figure 3 As shown), the shape of the light-leaking hole can be circular (e.g., Figure 3 As shown), the diameter of the circular hole is 3μm; S3. Development: Using a tank-type immersion developer, the exposed COF carrier is passed through an alkaline developer with pH=14 at a speed of 4m / min. The alkaline developer etches away the exposed positive photoresist, allowing the pattern on the photomask to appear on the positive photoresist. S4. Etching: Wet etching is used to etch the copper surface without positive photoresist. Through copper breaking, coarse etching, down etching, and fine etching, the copper foil is finally turned into copper circuit. S4-1: Since there are light leakage patterns on the chromium film of the mask, the etching solution will etch holes in the light leakage area of ​​the chromium film on the line. S5. Removal of photoresist: Use an alkaline solution with pH=13 and temperature of 60℃ to remove the positive photoresist above the circuit. S6. Tin plating: Tin liquid is plated onto the copper surface through an electroless electroplating method. At the same time, the tin liquid is also plated on the inner wall of the copper circuit hole. S7, Solder mask printing: Ink is printed on the non-lead area of ​​the COF tape. During the ink printing process, the ink is also printed into the holes of the circuit. The ink thickness is ≥20μm. S8. Baking: Bake in an oven at 120°C for 30 minutes to cure the ink.

[0023] Example 2: This embodiment provides a COF tape design to improve ink adhesion (for coarse lines of COF tape, such as PASS line lines), specifically including the following steps: S1. Coating: A 1.4μm thick layer of positive photoresist is uniformly coated on the surface of the copper foil. The positive photoresist is then baked and cured in a PB oven at a temperature of 120℃ for 120s. S2. Exposure: A projection-type exposure machine is used, with an exposure illuminance of 80 mW / cm². 2 With an exposure of 75mJ, the pattern on the photomask is transferred onto the positive photoresist. S2-1: The light emitted by the light source of the projection exposure machine cannot pass through the chromium film on the mask. A light-leaking circular hole with a diameter of 80μm is opened on the chromium film. S3. Development: Using a tank-type immersion developer, the exposed COF carrier is passed through an alkaline developer with pH=14 at a speed of 4m / min. The alkaline developer etches away the exposed positive photoresist, allowing the pattern on the photomask to appear on the positive photoresist. S4. Etching: Wet etching is used to etch the copper surface without positive photoresist. Through copper breaking, coarse etching, down etching, and fine etching, the copper foil is finally turned into copper circuit. S4-1: Since there are light leakage patterns on the chromium film of the mask, the etching solution will etch holes in the light leakage area of ​​the chromium film on the line. S5. Removal of photoresist: Use an alkaline solution with pH=13 and temperature of 60℃ to remove the positive photoresist above the circuit. S6. Tin plating: Tin liquid is plated onto the copper surface through an electroless electroplating method. At the same time, the tin liquid is also plated on the inner wall of the copper circuit hole. S7, Solder mask printing: Ink is printed on the non-lead area of ​​the COF tape. During the ink printing process, the ink is also printed into the holes of the circuit. The ink thickness is ≥20μm. S8. Baking: Bake in an oven at 120°C for 30 minutes to cure the ink.

[0024] The only difference between this comparative example and Example 1 is that the diameter of the light-leaking circular holes on the chromium film is <2μm.

[0025] At this point, the diameter of the holes on the circuit is small, which cannot effectively improve the adhesion of the ink to the circuit.

[0026] The only difference between this comparative example and Example 1 is that the diameter of the light-leaking circular holes on the chromium film is >5μm.

[0027] At this point, a larger aperture will affect the signal transmission of the copper layer of the fine wires in the COF tape.

[0028] The only difference between this comparative example and Example 2 is that the diameter of the light-leaking circular holes on the chromium film is >100μm.

[0029] At this point, a larger aperture will affect the signal transmission of the coarse conductive copper layer on the COF tape. The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A COF tape design for improving ink adhesion, characterized in that, include: A copper foil is provided, and the copper foil is subjected to the following steps in sequence: coating, exposure, development, etching, resist removal, tin plating, solder resist printing and baking; wherein, in the exposure step: a mask is provided, and light-leaking holes are formed on the chromium film of the mask.

2. The COF tape design for improving ink adhesion according to claim 1, characterized in that, The coating step includes: After coating the surface of the copper foil with a 1.2μm~1.6μm thick positive photoresist, it is cured at 100℃~120℃.

3. The COF tape design for improving ink adhesion according to claim 1, characterized in that, In the exposure step, the exposure intensity is controlled to be 55 mw / cm. 2 ~100mw / cm 2 The exposure level is 70mj~80mj.

4. The COF tape design for improving ink adhesion according to claim 1 or 3, characterized in that, The light-leaking hole is circular with a diameter of 3μm to 100μm.

5. The COF tape design for improving ink adhesion according to claim 1, characterized in that, In the development step, the exposed product is controlled to pass through an alkaline developing solution with pH > 13 at a speed of 2 m / min to 6 m / min. The alkaline developing solution is used to etch away the exposed positive photoresist, so that the pattern on the photomask appears on the positive photoresist.

6. The COF tape design for improving ink adhesion according to claim 1, characterized in that, The etching process employs wet etching, which involves etching the copper foil surface without positive photoresist. Through copper breaking, coarse etching, down etching, and fine etching, the copper foil is transformed into copper circuitry.

7. The COF tape design for improving ink adhesion according to claim 1, characterized in that, The degumming step is carried out in an alkaline solution at 50℃~60℃ and pH>13.

8. The COF tape design for improving ink adhesion according to claim 1, characterized in that, In the tin plating operation, the tin plating solution is plated on the copper surface and the inner wall of the openings in the circuit board.

9. The COF tape design for improving ink adhesion according to claim 1, characterized in that, In the solder resist printing process, ink is printed in the non-lead area of ​​the COF tape.

10. The COF tape design for improving ink adhesion according to claim 1, characterized in that, In the baking step, the baking temperature is >110℃.

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