A high-performance flexible chip-on-film

Abstract

The present application relates to the technical field of chip-on-film (COF) and discloses a high-performance flexible COF. The flexible COF is prepared by the following steps: S1. Modifying the surface of a flexible substrate using a silane coupling agent containing an epoxy group, and then grafting dextran onto the surface of the flexible substrate; S2. Cross-linking the dextran on the surface of the flexible substrate using a cross-linking agent to obtain a first modified flexible substrate; S3. Soaking the obtained first modified flexible substrate in a silver ion solution for reaction, and then reducing the silver ions on the surface of the first modified flexible substrate to silver, to obtain a second modified flexible substrate; S4. Electroplating the obtained second modified flexible substrate to electroplate a silver layer on the surface of the second flexible substrate, thereby obtaining a third modified flexible substrate; S5. Sequentially subjecting the obtained third modified flexible substrate to a photolithography process and an etching process to obtain the flexible COF. The present application can improve the stability of the flexible COF.

Description

Technical Field

[0001] The present application relates to the technical field of chip-on-films, and in particular to a high-performance flexible chip-on-film. Background Art

[0002] As electronic products become thinner, lighter, more portable, and more intelligent, the demand for flexible electronic devices is growing. As a key component of flexible electronic devices, flexible chip-on-film plays an important role in signal transmission and packaging protection.

[0003] In the preparation process of flexible chip-on-film, an appropriate material (such as polyimide) is first selected as the substrate, and then a conductive layer is made on the flexible substrate. Then, a layer of photoresist is coated on the conductive layer. A photolithography machine is used to project the required pattern onto the photoresist. Through the development step, the circuit pattern on the photoresist is transferred to the conductive layer. Then, the conductive layer not protected by the photoresist is removed by etching, thereby completing the production of the conductive circuit.

[0004] When making a conductive layer on the surface of a flexible substrate, the commonly used process includes electroplating. First, a conductive seed layer (silver seed layer) is coated on the flexible substrate, and then it is placed in an electroplating solution. Through an electrochemical reaction, a layer of silver is electroplated on the conductive seed layer to form a conductive silver layer. As a key component of flexible electronic devices, flexible on-chip film plays an important role in signal transmission and packaging protection. The conductive silver layer currently prepared has a problem of reduced conductivity in the use environment of multiple bending, resulting in the disadvantage of poor signal transmission stability, which in turn limits its application in flexible electronic devices. Summary of the Invention

[0005] In order to better maintain the performance of the flexible chip-on-chip film after multiple bending, the present application provides a high-performance flexible chip-on-chip film. The present application chemically grafts a dextran layer on the surface of a flexible substrate, and the dextran layer can form a three-dimensional porous network structure after cross-linking, thereby stably loading a layer of silver particles through cross-linked dextran, so that the flexible substrate can be used for electroplating, and then a silver layer is electroplated on its surface. When the flexible substrate is bent, the cross-linked dextran layer can form an elastic buffer, so that the silver particles can still abut each other after bending, thereby reducing the gaps between the silver particles.

[0006] This application adopts the following technical solutions:

[0007] A high-performance flexible chip-on-film is prepared by the following steps:

[0008] S1. After modifying the surface of a flexible substrate using a silane coupling agent containing an epoxy group, dextran is grafted onto the surface of the flexible substrate;

[0009] S2. cross-linking the dextran on the surface of the flexible substrate using a cross-linking agent to obtain a first modified flexible substrate;

[0010] S3, immersing the obtained first modified flexible substrate in a silver ion solution for reaction, then washing and drying in sequence, and then reducing the silver ions on the surface of the first modified flexible substrate to silver, thereby loading a silver particle layer on the surface of the flexible substrate to obtain a second modified flexible substrate;

[0011] S4, using the surface of the second modified flexible substrate as a cathode and pure silver as an anode, electroplating in an electroplating solution to electroplate a silver layer on the surface of the second flexible substrate, washing, and drying, thereby obtaining a third modified flexible substrate;

[0012] S5. Performing a photolithography process and an etching process on the obtained third modified flexible substrate in sequence to obtain the flexible chip-on-film.

[0013] By adopting the above technical solution, the surface of the flexible substrate is modified by an epoxy silane coupling agent, so that the surface of the flexible substrate is provided with epoxy groups. Dextran contains a large number of hydroxyl groups. Through the reaction between the epoxy groups and the hydroxyl groups, the dextran is grafted to the surface of the flexible substrate. After cross-linking, the dextran can form a three-dimensional network structure on the surface of the flexible substrate, and the groups of the cross-linked dextran can coordinate with silver ions, thereby fixing silver ions on the surface and inside of the cross-linked dextran. After the silver ions are reduced, a stable silver particle layer can be formed on the surface and inside of the dextran, and the flexible substrate is endowed with the ability to conduct electricity. Then, the flexible substrate can be electroplated. In the present application, the silver particle layer is connected to the flexible substrate by chemical grafting of the cross-linked dextran, and the three-dimensional network structure of the dextran itself also has a certain amount of silver particles in the pores. When the flexible substrate is bent multiple times, the silver particle layers can maintain good contact, thereby reducing the impact on subsequent signal transmission.

[0014] Optionally, in step S1, the flexible substrate is first surface-modified using an epoxy silane coupling agent and a mercapto silane coupling agent to obtain a coupling agent-modified flexible substrate; a dextran solution is prepared, and the coupling agent-modified flexible substrate is immersed in the dextran solution, and 4-dimethylaminopyridine is added, and the reaction is followed by washing and drying.

[0015] By adopting the above technical solution, the surface of the flexible substrate is modified by using an epoxy silane coupling agent and a mercapto silane coupling agent, thereby grafting epoxy groups and mercapto groups on the surface of the flexible substrate. Under the promotion of 4-dimethylaminopyridine, the epoxy groups can be used to react with the hydroxyl groups of dextran, thereby grafting the dextran to the surface of the flexible substrate through chemical bonds; and the mercapto groups have the ability to complex with silver ions, so that the silver ions can be better fixed, so that more silver is present in the dextran, and the existence is more stable, and the silver is less likely to fall off after bending.

[0016] Optionally, in step S2, a crosslinking agent solution is prepared and the pH of the crosslinking agent solution is adjusted to be between 7 and 9. The flexible substrate obtained in S1 is immersed in the crosslinking agent solution to perform a crosslinking reaction to obtain a first modified flexible substrate.

[0017] By adopting the above technical solution, in an alkaline environment, the cross-linking agent better promotes the cross-linking of dextran, and after cross-linking, the dextran can form a three-dimensional network structure with a porous structure, thereby having better mechanical properties. Silver particles can be loaded inside and on the surface of the dextran. When the flexible substrate is bent, the silver particle layers can also abut against each other, and rigid cracks are not easily generated.

[0018] Optionally, the weight ratio of the epoxy silane coupling agent to the mercapto silane coupling agent is (1-5):1.

[0019] By adopting the above technical solution, the grafting effect of dextran and the fixation effect of silver are taken into consideration, thereby achieving better stability.

[0020] Optionally, in step S1, the flexible substrate is first subjected to plasma surface treatment, and then the surface of the flexible substrate is modified using an epoxy silane coupling agent and a mercapto silane coupling agent.

[0021] By adopting the above technical solution, plasma can excite more active groups on the surface of the flexible substrate. The plasma treatment process conditions are: the treatment medium is nitrogen or argon; the gas flow rate is 60cm 3 / min-90cm 3 / min, the plasma power is 350w-400w, and the processing time is 40-80s. The plasma processing power is mainly related to the thickness of the flexible substrate. The thicker the thickness, the longer the processing time can be.

[0022] Optionally, the dextran solution further contains a surfactant.

[0023] By adopting the above technical solution, the surfactant can improve the compatibility between the flexible substrate surface and dextran, thereby promoting the reaction between dextran and epoxy groups.

[0024] Optionally, the cross-linking agent is selected from epichlorohydrin.

[0025] Optionally, in step S3, a reducing agent solution is prepared, and the first modified flexible substrate soaked in the silver ion solution is immersed in the reducing agent solution to reduce the silver ions.

[0026] By adopting the above technical solution, silver ions enter the solution of the reducing agent and can be quickly reduced to silver. The reducing agent can be selected from ammonium persulfate, sodium sulfite, ascorbic acid, sodium borohydride solution, etc.

[0027] Optionally, the epoxy silane coupling agent is selected from 3-glycidyloxypropyltriethoxysilane, and the mercapto silane coupling agent is selected from 3-mercaptopropyltrimethoxysilane.

[0028] Optionally, the molecular weight of the dextran is 6000-10000.

[0029] By adopting the above technical solution and controlling the molecular weight of dextran, the ability of dextran to be grafted onto the surface of a flexible substrate and the stabilizing effect of dextran on silver particles after cross-linking can be taken into account.

[0030] In summary, this application has at least one of the following beneficial effects:

[0031] 1. By chemically grafting dextran onto a flexible substrate, the dextran can form a three-dimensional network structure after cross-linking. Silver particles can be loaded into the cross-linked dextran. When the flexible substrate is bent, a buffer zone can be formed between the cross-linked dextran, allowing the silver particles to continue to abut against each other after bending, thereby reducing the impact on signal transmission.

[0032] 2. The surface of the flexible substrate is modified by using an epoxy silane coupling agent and a mercapto silane coupling agent, so that dextran can be smoothly grafted onto the surface of the flexible substrate and silver particles can be better fixed through the mercapto group. DETAILED DESCRIPTION

[0033] Preparation Example 1

[0034] 3 parts of 3-glycidyloxypropyltriethoxysilane were dissolved in 100 parts of ethanol solution to obtain a coupling agent solution.

[0035] Preparation Example 2

[0036] 1.5 parts of 3-glycidyloxypropyltriethoxysilane and 1.5 parts of 3-mercaptopropyltrimethoxysilane were dissolved in 100 parts of ethanol solution to obtain a coupling agent solution.

[0037] Preparation Example 3

[0038] 2.25 parts of 3-glycidoxypropyltriethoxysilane and 0.75 parts of 3-mercaptopropyltrimethoxysilane were dissolved in 100 parts of ethanol solution to obtain a coupling agent solution.

[0039] Preparation Example 4

[0040] 2.5 parts of 3-glycidoxypropyltriethoxysilane and 0.5 parts of 3-mercaptopropyltrimethoxysilane were dissolved in 100 parts of ethanol solution to obtain a coupling agent solution.

[0041] Preparation Example 5

[0042] The flexible substrate is selected from polyimide, and the surface of the flexible substrate is modified using a plasma surface treatment device. The plasma treatment process conditions are: the treatment medium is nitrogen; the gas flow rate is 60cm 3 / min, the plasma generating power is 350w, and the processing time is 40s.

[0043] Example 1

[0044] The embodiment of the present application discloses a high-performance flexible chip-on-film, which specifically includes the following steps:

[0045] S1. Using the coupling agent solution of Preparation Example 1, the flexible substrate of Preparation Example 5 was immersed in the coupling agent solution and reacted for 5 hours, thereby modifying the surface of the flexible substrate; 4 parts of dextran (relative average molecular weight of 9000) were dissolved in 100 parts of water to prepare a dextran solution, and a surfactant was added to the dextran solution, wherein the surfactant was selected from sodium lauryl carboxylate. The flexible substrate modified by the coupling agent was immersed in the dextran solution, and 0.5 parts of 4-dimethylaminopyridine was added. The reaction was continued for 48 hours, and then washed and dried;

[0046] S2. Dissolve 5 parts of epichlorohydrin in 100 parts of ethanol to obtain a cross-linking agent solution, and use sodium hydroxide to adjust the pH of the cross-linking agent solution to 8, and adjust the temperature of the cross-linking agent solution to 40°C, soak the dextran-modified flexible substrate in S1 in the cross-linking agent solution, react for 5 hours, and then wash with distilled water and dry to obtain a first modified flexible substrate; S3. Prepare a silver nitrate solution with a mass fraction of 3wt% and a reducing agent solution with a mass fraction of 4wt%, wherein the reducing agent is selected from sodium borohydride; soak the obtained first modified flexible substrate in the silver nitrate solution, react for 2 hours, then rinse the excess silver nitrate solution on the surface with distilled water, and dry, then soak it in the reducing agent solution again to react for 10-15 minutes, rinse it with distilled water, and dry to obtain a second modified flexible substrate; silver ions are loaded on the surface of the flexible substrate by coordination with the groups in the dextran, and are reduced by the reducing agent, thereby loading a layer of conductive silver particles on the dextran;

[0047] S4. The surface of the second flexible modified substrate was used as a cathode and pure silver was used as an anode for electroplating in an electroplating solution, wherein the concentration of silver nitrate in the electroplating solution was 25 g / L, the concentration of potassium carbonate was 80 g / L, CFY-LA was 360 mL, CFY-A was 0.5 g / L, the pH of the electroplating solution was controlled at 11, the electroplating solution temperature was 40°C, and the current density was 0.4 A / dm 2 , after electroplating, a silver conductive layer can be plated on the surface of the second flexible substrate, thereby obtaining a third modified flexible substrate;

[0048] S5. Performing a photolithography process and an etching process on the obtained third modified flexible substrate in sequence to obtain the flexible chip-on-film.

[0049] Example 2

[0050] The difference between this example and Example 1 is that the coupling agent solution of Preparation Example 1 in Example 1 is replaced by an equal amount of the coupling agent solution of Preparation Example 2, and the other steps remain unchanged.

[0051] Example 3

[0052] The difference between this example and Example 1 is that the coupling agent solution of Preparation Example 1 in Example 1 is replaced by an equal amount of the coupling agent solution of Preparation Example 3, and the other steps remain unchanged.

[0053] Example 4

[0054] The difference between this embodiment and Example 1 is that the coupling agent solution of Preparation Example 1 in Example 1 is replaced by an equal amount of the coupling agent solution of Preparation Example 4, and the other steps remain unchanged.

[0055] Example 5

[0056] The difference between this embodiment and embodiment 1 is that the crosslinking agent solution is different. The crosslinking agent solution is prepared by dissolving 1 part of epichlorohydrin in 100 parts of ethanol to obtain the crosslinking agent solution. The other steps remain unchanged.

[0057] Example 6

[0058] The difference between this embodiment and embodiment 1 is that the crosslinking agent solution is different. The crosslinking agent solution is prepared by dissolving 10 parts of epichlorohydrin in 100 parts of ethanol to obtain the crosslinking agent solution. The other steps remain unchanged.

[0059] Comparative Example 1

[0060] This comparative example discloses a high-performance flexible chip-on-film, which specifically includes the following steps:

[0061] S1, using the coupling agent solution of Preparation Example 2, immersing the flexible substrate in Preparation Example 5 in the coupling agent solution and reacting for 5 hours, thereby modifying the surface of the flexible substrate;

[0062] S2. Prepare a silver nitrate solution with a mass fraction of 3 wt% and a reducing agent solution with a mass fraction of 4 wt%, wherein the reducing agent is selected from sodium borohydride; immerse the obtained first modified flexible substrate in the silver nitrate solution, react for 2 hours, then rinse the excess silver nitrate solution on the surface with distilled water and dry, then immerse the substrate in the reducing agent solution again for 10-15 minutes, rinse with distilled water, and dry to obtain a second modified flexible substrate; silver ions are loaded on the surface of the flexible substrate by coordination with groups in dextran, and are reduced by the reducing agent, thereby loading a layer of conductive silver particles on the dextran;

[0063] S3. The surface of the second flexible modified substrate was used as a cathode and pure silver was used as an anode for electroplating in an electroplating solution, wherein the concentration of silver nitrate in the electroplating solution was 25 g / L, the concentration of potassium carbonate was 80 g / L, CFY-LA was 360 mL, CFY-A was 0.5 g / L, the pH of the electroplating solution was controlled at 11, the temperature of the electroplating solution was 40°C, and the current density was 0.4 A / dm 2 , after electroplating, a silver conductive layer can be plated on the surface of the second flexible substrate, thereby obtaining a third modified flexible substrate;

[0064] S4. Performing a photolithography process and an etching process on the obtained third modified flexible substrate in sequence to obtain the flexible chip-on-film.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that the average molecular weight of the dextran used is 600, and the other steps remain unchanged.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 1 is that the average molecular weight of the dextran used is 20,000, and the other steps remain unchanged.

[0069] Performance Testing

[0070] The resistance of the flexible chip-on-film was measured using a two-point probe method. The sample was then cyclically bent 500 times using a bending machine. The resistance of the sample after cyclic bending was measured, and the stability of the sample was calculated. Stability = 1 - (resistance after test - original resistance) / original resistance * 100%. The higher the stability, the higher the stability after 500 bending tests.

[0071] Table 1 Test results of Examples 1-6 and Comparative Examples 1-3

[0072] stability / % Example 1 90.7％ Example 2 92.6％ Example 3 93.1％ Example 4 92.8％ Example 5 87.7％ Example 6 85.8％ Comparative Example 1 75.3％ Comparative Example 2 81.3％ Comparative Example 3 82.3％

[0073] The stability of the conductivity of the flexible chip-on-film determines the stability of signal transmission. Referring to the comparison of Examples 1-4, it can be seen that the epoxy silane coupling agent and the mercapto silane coupling agent are used in combination, wherein the epoxy group is used to stably graft dextran to the surface of the flexible substrate, and the mercapto group is used to cooperate with the dextran to chemically coordinate silver ions, thereby making the stability to silver ions better; and the cross-linked dextran has a porous three-dimensional structure, in which nanosilver particles are loaded, and the silver particles abutting each other form a conductive channel. When bent, the silver particles can return to the state of abutting each other, thereby improving the stability of signal transmission after bending.

[0074] With reference to Examples 1 and 5 and 6, it can be seen that the concentration of the cross-linking agent solution determines the degree of cross-linking of the dextran. Excessive or insufficient cross-linking is not conducive to the fixation of silver particles and the stability of the silver particle layer.

[0075] By comparing Example 1 with Comparative Examples 2 and 3, it can be seen that the molecular weight of dextran also has a relatively important influence on stability. Dextran with too small a molecular weight has a weak effect on the silver particles after cross-linking, and the signal transmission stability of the flexible chip-on-film is low. Dextran with too large a molecular weight has low activity when grafted onto the flexible substrate, and the subsequent effect on the silver particles is small, so that the molecular weight of dextran also affects the stability of signal transmission of the flexible chip-on-film.

[0076] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A high-performance flexible chip-on-film, characterized by: The flexible flip chip is prepared by the following steps: S1. After modifying the surface of a flexible substrate using a silane coupling agent containing an epoxy group, dextran is grafted onto the surface of the flexible substrate; the dextran has a molecular weight of 6000-10000; S2. cross-linking the dextran on the surface of the flexible substrate using a cross-linking agent to obtain a first modified flexible substrate; S3, immersing the obtained first modified flexible substrate in a silver ion solution for reaction, then washing and drying in sequence, and then reducing the silver ions on the surface of the first modified flexible substrate to silver, thereby loading a silver particle layer on the surface of the flexible substrate to obtain a second modified flexible substrate; S4, using the surface of the second modified flexible substrate as a cathode and pure silver as an anode, electroplating in an electroplating solution to electroplate a silver layer on the surface of the second flexible substrate, washing, and drying, thereby obtaining a third modified flexible substrate; S5. Performing a photolithography process and an etching process on the obtained third modified flexible substrate in sequence to obtain the flexible chip-on-film.

2. The high-performance flexible chip-on-film according to claim 1, characterized in that: In step S1, the flexible substrate is first surface-modified using an epoxy silane coupling agent and a mercapto silane coupling agent to obtain a coupling agent-modified flexible substrate; A dextran solution is prepared, and the coupling agent-modified flexible substrate is immersed in the dextran solution. 4-dimethylaminopyridine is added, and the substrate is washed and dried after the reaction.

3. The high-performance flexible chip-on-film according to claim 2, characterized in that: In step S2, a crosslinking agent solution is prepared and the pH of the crosslinking agent solution is adjusted to be between 7 and 9. The flexible substrate obtained in S1 is immersed in the crosslinking agent solution to perform a crosslinking reaction to obtain a first modified flexible substrate.

4. The high-performance flexible chip-on-film according to claim 2, characterized in that: The weight ratio of the epoxy silane coupling agent to the mercapto silane coupling agent is (1-5):

1.

5. The high-performance flexible chip-on-film according to claim 2, characterized in that: In step S1, the flexible substrate is first subjected to plasma surface treatment, and then the surface of the flexible substrate is modified using an epoxy silane coupling agent and a mercapto silane coupling agent.

6. The high-performance flexible chip-on-film according to claim 2, characterized in that: The dextran solution also contains a surfactant.

7. The high-performance flexible chip-on-film according to claim 3, characterized in that: The cross-linking agent is selected from epichlorohydrin.

8. The high-performance flexible chip-on-film according to claim 1, characterized in that: In step S3, a reducing agent solution is prepared, and the first modified flexible substrate soaked in the silver ion solution is immersed in the reducing agent solution to reduce the silver ions.

9. The high-performance flexible chip-on-film according to claim 2, characterized in that: The epoxy silane coupling agent is selected from 3-glycidyloxypropyltriethoxysilane, and the mercaptosilane coupling agent is selected from 3-mercaptopropyltrimethoxysilane.