A non-adhesive laminated polyimide flexible copper clad laminate

Abstract

The present invention discloses a non-adhesive laminated polyimide flexible copper clad laminate. The structure of the non-adhesive laminated polyimide flexible copper clad laminate sequentially includes an upper copper foil layer, a dielectric layer, and a lower copper foil layer from top to bottom. The dielectric layer includes a polyimide composite layer; the polyimide composite layer includes a thermosetting polyimide layer and adhesive layers disposed on both the upper and lower sides of the thermosetting polyimide layer, and the adhesive layer is a modified polyimide layer; wherein, the modified polyimide layer is a polyimide modified by nanocrystalline cellulose and an epoxy silane coupling agent. The present invention realizes a structure in which the dielectric layer can contain multiple polyimide composite layers, greatly improves the thickness of the dielectric layer, and solves the deficiencies existing in the prior art. The non-adhesive laminated polyimide flexible copper clad laminate of the present invention has the advantages of excellent electrical properties, high peel strength, high tensile strength, and excellent dimensional stability, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing flexible copper clad laminates, and particularly to a non - adhesive laminated polyimide flexible copper clad laminate. Background Art

[0002] Flexible copper clad laminate (FCCL for short) has the characteristics of light weight, thinness, high heat resistance and flexibility. Therefore, FPC with flexible copper clad laminate as the substrate material is widely used in electronic devices, consumer electronics products, and electronic communication products. With the progress of technology, the requirements for miniaturization and high precision of electronic products are getting higher and higher. In addition to the functions of electrical connection, insulation, and mechanical support of general copper clad laminates, polyimide flexible copper clad laminates can be bent repeatedly. The flexible printed circuit board made of flexible copper clad laminate can make the wiring more reasonable, save installation space, and meet the requirements of electronic products for being thinner, lighter, shorter and smaller.

[0003] To meet the requirements of being thinner, lighter, shorter and smaller for equipment in the fields of medical treatment, industrial control, security, vehicle, communication electronics and aerospace, rigid - flexible printed circuit boards have emerged. Rigid - flexible printed circuit boards have both the characteristics of FPC and PCB. Therefore, it can not only reduce the volume of PCB boards and save the internal space of products, but also maintain the high integration of circuit board products, which is of great help to improving product performance.

[0004] However, the thickness of the non - adhesive polyimide layer of traditional polyimide flexible copper clad laminates is limited within 50μm (including 50μm). With the rapid development of technology, its performance has been difficult to meet the requirements of actual production and application.

[0005] Therefore, it is urgent to develop a new type of copper clad laminate that can effectively increase the thickness of the polyimide layer to solve the problems existing in the prior art. Summary of the Invention

[0006] Based on this, the present invention provides a non - adhesive laminated polyimide flexible copper clad laminate. The present invention uses modified polyimide as the bonding layer, which has the characteristics of being processable at high temperature and having strong adhesiveness. This non - adhesive laminated polyimide flexible copper clad laminate overcomes the defects and deficiencies of the prior art, and can broaden the thickness of the polyimide dielectric layer from 50μm to 200μm through different lamination methods.

[0007] An object of the present application is to provide a non - adhesive laminated polyimide flexible copper clad laminate. The structure of the non - adhesive laminated polyimide flexible copper clad laminate includes, from top to bottom, an upper copper foil layer, a dielectric layer, and a lower copper foil layer. The dielectric layer includes a polyimide composite layer;

[0008] The polyimide composite layer includes a thermosetting polyimide layer and adhesive layers disposed on the upper and lower sides of the thermosetting polyimide layer, and the adhesive layer is a modified polyimide layer;

[0009] Among them,

[0010] The modified polyimide layer is a polyimide modified with nanocrystalline cellulose and an epoxy silane coupling agent;

[0011] The preparation method of the polyimide modified with nanocrystalline cellulose and an epoxy silane coupling agent includes the following steps:

[0012] S1. Add the epoxy silane coupling agent to a solvent, adjust the pH and stir, then add nanocrystalline cellulose, stir and react, and obtain an intermediate product after centrifugation, washing and drying;

[0013] S2. Immerse the polyimide in an alkaline solution, wash and dry it, then immerse it in an acidic solution again, and obtain the pretreated polyimide after washing and drying;

[0014] S3. Add the pretreated polyimide to the intermediate product solution, then add a catalyst and a crosslinking agent, react in an inert gas atmosphere, and obtain the polyimide modified with nanocrystalline cellulose and an epoxy silane coupling agent after filtration, washing and drying.

[0015] Furthermore, in the dielectric layer, there is one or more polyimide composite layers.

[0016] Figure 1 It is a schematic structural diagram of the adhesive-free laminated polyimide flexible copper clad laminate of the present invention;

[0017] Among them,

[0018] Figure 1 (a) is a schematic structural diagram of a structure with 2 polyimide composite layers;

[0019] Figure 1 (b) is a schematic structural diagram of a structure with 3 polyimide composite layers;

[0020] Figure 1 (c) is a schematic structural diagram of a structure with 4 polyimide composite layers.

[0021] The present invention modifies polyimide by grafting nano-crystalline cellulose with an epoxy silane coupling agent, introducing a large number of oxygen-containing groups on the surface of the polyimide, which are more likely to form covalent bonds of cupric oxide type with the surface of the copper foil during processing, significantly improving the peel strength between the copper foil and the dielectric layer; and the modification treatment also enhances the surface roughness of the polyimide, thereby increasing the bonding area and further improving the bonding performance of the polyimide; at the same time, the modified polyimide has a unique three-dimensional network cross-linked structure, which not only improves the bonding performance of the dielectric layer but also ensures strong mechanical properties, further enhancing the product stability.

[0022] Further, the thickness of the bonding layer is 3 - 10 μm, and the thickness of the thermosetting polyimide layer is 19 - 42 μm.

[0023] Further, in the upper copper foil layer and the lower copper foil layer, the Rz value of the copper teeth of the copper foil is 0.7 - 2.8 μm, and the thickness of the copper foil is 6 - 70 μm.

[0024] Further, the epoxy silane coupling agent is 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0025] Further, in step S1, the pH value is 4 - 4.5.

[0026] Further, in step S1, the mass ratio of the epoxy silane coupling agent to the nano-crystalline cellulose is (4 - 8):1.

[0027] Further, in step S3, the concentration of the intermediate product solution is 3 - 6%.

[0028] Further, the structure of the adhesive-free laminated polyimide flexible copper clad laminate further includes a protective film.

[0029] Further, the adhesive-free laminated polyimide flexible copper clad laminate is prepared by high-temperature hot pressing using an equal-pressure double steel belt machine. In the high-temperature hot pressing, at least 8 sending shafts are required at the pressing and sending end, among which 2 sending shafts are used to send the protective film, 2 sending shafts are used to send the copper foil layer, and the remaining 4 sending shafts are used to send the dielectric layer.

[0030] Further, before the high-temperature hot pressing, the moisture content of the dielectric layer is made ≤1% by baking.

[0031] Reducing the moisture content of the dielectric layer to below 1% can solve the problem of board explosion caused by water vapor volatilization during the high-temperature pressing of multi-layer polyimide film laminates.

[0032] The present invention has the following beneficial effects:

[0033] The adhesive - free laminated polyimide flexible copper clad laminate of the present invention uses polyimide modified with nanocrystalline cellulose and epoxy silane coupling agent as the bonding layer, which significantly enhances the bonding strength between the polyimide composite layer and the copper foil layer as well as between the multi - layer polyimide composite layers. At the same time, it ensures that the product has strong mechanical properties, thus realizing a structure in which the dielectric layer can contain multiple polyimide composite layers, greatly increasing the thickness of the dielectric layer and solving the deficiencies existing in the prior art. The adhesive - free laminated polyimide flexible copper clad laminate of the present invention has the advantages of excellent electrical properties, high peel strength, high tensile strength, and excellent dimensional stability, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic structural diagram of the adhesive - free laminated polyimide flexible copper clad laminate of the present invention;

[0035] Among them,

[0036] Figure 1 (a) is a schematic structural diagram of the structure with 2 polyimide composite layers;

[0037] Figure 1 (b) is a schematic structural diagram of the structure with 3 polyimide composite layers;

[0038] Figure 1 (c) is a schematic structural diagram of the structure with 4 polyimide composite layers.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS: 1 - copper foil layer; 2 - bonding layer; 3 - thermosetting polyimide layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] In order to more clearly illustrate the technical solutions of the present invention, the following examples are listed. The raw materials, reactions, and post - treatment means appearing in the examples are all common raw materials on the market and technical means well - known to those skilled in the art, unless otherwise specified.

[0041] The terms "preferred", "preferably", "more preferably", etc. in the present invention refer to embodiments of the present invention that can provide certain beneficial effects in certain cases. However, in the same or other cases, other embodiments may also be preferred. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present invention.

[0042] It should be understood that unless otherwise indicated in any operating example or otherwise, all numbers representing the amounts of ingredients used in the specification and claims should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters set forth in the following specification and appended claims are approximations that vary depending on the desired properties to be obtained by the present invention.

[0043] The thermosetting polyimide in the embodiments of the present invention is purchased from SKC.

[0044] The nanocrystalline cellulose in the embodiments of the present invention is purchased from Tianjin Wood Elf Biotechnology Co., Ltd.

[0045] The preparation method of the modified polyimide in the embodiments of the present invention includes the following steps:

[0046] S1. Add 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane into the ethanol / water mixed solution, then add glacial acetic acid to adjust the pH to 4.0. After stirring for 2 h, add nanocrystalline cellulose (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane:nanocrystalline cellulose = 5:1, m / m), and stir and react for 24 h. After centrifugation, washing, and drying, an intermediate product is obtained;

[0047] S2. Ultrasonically clean the polyimide (purchased from Ube NVT) with 50% ethanol for 2 h, then wash it with deionized water and dry it. Then, soak it hermetically in a 5% NaOH solution at 60 °C for 1 h, wash it with deionized water and dry it. Again, soak it hermetically in a 2% HCl solution at 60 °C, wash it with deionized water and dry it to obtain the pretreated polyimide;

[0048] S3. Add the pretreated polyimide into an excessive 5% intermediate product solution, then add a catalyst (0.5% AlCl3 and 0.3% p-toluenesulfonic acid by mass fraction of the system) and a crosslinking agent (0.4% 1,2,3,4-butanetetracarboxylic acid by mass fraction). React at 70 °C for 5 h under a nitrogen atmosphere. Then, ultrasonically clean the solid product with acetone and deionized water for 1 h respectively, and dry it to obtain the polyimide modified by nanocrystalline cellulose and epoxy silane coupling agent.

[0049] The copper foil in the embodiments of the present invention is Nisshin BHY-82F-T, the Rz value of the copper teeth is 1.1 μm, and the thickness of the copper foil is 18 μm.

[0050] The protective film in the embodiments of the present invention is a polyimide film with a thickness of 50 μm.

[0051] Example 1

[0052] A non-adhesive laminated polyimide flexible copper clad laminate, the structure of the non-adhesive laminated polyimide flexible copper clad laminate includes, from top to bottom, a protective film, an upper copper foil layer, a dielectric layer, a lower copper foil layer, and a protective film;

[0053] The dielectric layer includes 2 layers of polyimide composite layers,

[0054] Among them,

[0055] One layer is a polyimide composite layer with a thickness of 25 μm, which sequentially includes a 3-μm modified polyimide layer, a 19-μm thermosetting polyimide layer, and a 3-μm modified polyimide layer from top to bottom;

[0056] The other layer is a polyimide composite layer with a thickness of 50 μm, which sequentially includes a 4-μm modified polyimide layer, a 42-μm thermosetting polyimide layer, and a 4-μm modified polyimide layer from top to bottom.

[0057] The preparation method of the above adhesive-free laminated polyimide flexible copper clad laminate includes the following steps:

[0058] L1. Bake the polyimide composite layers with thicknesses of 25 μm and 50 μm at a constant temperature of 100 °C for 6 h to make the moisture content ≤ 1%;

[0059] L2. Perform high-temperature hot pressing using an equal-pressure double steel belt machine, and the lamination structure is as follows:

[0060] Table 1 High-temperature hot pressing lamination structure

[0061]

[0062]

[0063] Through hot pressing, an adhesive-free laminated polyimide flexible copper clad laminate with a 75-μm thick dielectric layer is obtained.

[0064] Example 2

[0065] An adhesive-free laminated polyimide flexible copper clad laminate, the structure of the adhesive-free laminated polyimide flexible copper clad laminate sequentially includes a protective film, an upper copper foil layer, a dielectric layer, a lower copper foil layer, and a protective film from top to bottom;

[0066] The dielectric layer includes 2 layers of polyimide composite layers,

[0067] Both of the 2 layers of polyimide composite layers are polyimide composite layers with a thickness of 50 μm, and each layer sequentially includes a 4-μm modified polyimide layer, a 42-μm thermosetting polyimide layer, and a 4-μm modified polyimide layer from top to bottom.

[0068] The preparation method of the above adhesive-free laminated polyimide flexible copper clad laminate includes the following steps:

[0069] L1. Bake the 2 layers of polyimide composite layers with a thickness of 50 μm at a constant temperature of 100 °C for 6 h to make the moisture content ≤ 1%;

[0070] L2. Perform high-temperature hot pressing using an equal-pressure double steel belt machine, and the lamination structure is as follows:

[0071] Table 2 High-temperature hot pressing lamination structure

[0072] Serial number Material The first layer Protective film The second layer Copper foil The third layer 50μm polyimide composite layer The fourth layer 50μm polyimide composite layer The fifth layer Copper foil The sixth layer Protective film

[0073] The adhesive - free laminated polyimide flexible copper clad laminate with a 100 - μm - thick dielectric layer is obtained by pressing.

[0074] Example 3

[0075] An adhesive - free laminated polyimide flexible copper clad laminate, the structure of the adhesive - free laminated polyimide flexible copper clad laminate includes, from top to bottom, a protective film, an upper copper foil layer, a dielectric layer, a lower copper foil layer, and a protective film;

[0076] The dielectric layer includes 3 layers of polyimide composite layers.

[0077] Among them,

[0078] Two layers are polyimide composite layers with a thickness of 50 μm. Each layer includes, from top to bottom, a 4 - μm modified polyimide layer, a 42 - μm thermosetting polyimide layer, and a 4 - μm modified polyimide layer.

[0079] One layer is a polyimide composite layer with a thickness of 25 μm, which includes, from top to bottom, a 3 - μm modified polyimide layer, a 19 - μm thermosetting polyimide layer, and a 3 - μm modified polyimide layer.

[0080] The preparation method of the above - mentioned adhesive - free laminated polyimide flexible copper clad laminate includes the following steps:

[0081] L1. Bake 2 layers of polyimide composite layers with a thickness of 50 μm and 1 layer of polyimide composite layer with a thickness of 25 μm at a constant temperature of 100 °C for 6 h to make the moisture content ≤ 1%.

[0082] L2. Use an equal - pressure double - steel - belt machine for high - temperature hot pressing. The pressing stack structure is as follows:

[0083] Table 3 High - temperature hot - pressing stack structure

[0084] Serial number Material The first layer Protective film The second layer Copper foil The third layer 50μm polyimide composite layer The fourth layer 25μm polyimide composite layer The fifth layer 50μm polyimide composite layer The sixth layer Copper foil The seventh layer Protective film

[0085] The adhesive - free laminated polyimide flexible copper clad laminate with a 125 - μm - thick dielectric layer is obtained by pressing.

[0086] Example 4

[0087] An adhesive - free laminated polyimide flexible copper clad laminate, the structure of the adhesive - free laminated polyimide flexible copper clad laminate includes, from top to bottom, a protective film, an upper copper foil layer, a dielectric layer, a lower copper foil layer, and a protective film;

[0088] The dielectric layer includes 4 layers of polyimide composite layers.

[0089] Each of the four-layer polyimide composite layers is a polyimide composite layer with a thickness of 50 μm. Each layer includes a modified polyimide layer with a thickness of 4 μm, a thermosetting polyimide layer with a thickness of 42 μm, and a modified polyimide layer with a thickness of 4 μm from top to bottom in sequence.

[0090] The preparation method of the above-mentioned adhesive-free laminated polyimide flexible copper clad laminate includes the following steps:

[0091] L1. Bake the four 50-μm-thick polyimide composite layers at a constant temperature of 100 °C for 6 h to make the moisture content ≤ 1%.

[0092] L2. Perform high-temperature hot pressing using an equal-pressure double steel belt machine. The lamination structure for pressing is as follows:

[0093] Table 4 Lamination structure for high-temperature hot pressing

[0094] Serial number Material The first layer Protective film The second layer Copper foil The third layer 50μm polyimide composite layer The fourth layer 50μm polyimide composite layer The fifth layer 50μm polyimide composite layer The sixth layer 50μm polyimide composite layer The seventh layer Copper foil The eighth layer Protective film

[0095] An adhesive-free laminated polyimide flexible copper clad laminate with a 200-μm-thick dielectric layer is obtained through pressing.

[0096] Comparative Example 1

[0097] A polyimide copper clad laminate. The difference between this comparative example and Example 1 is that in the dielectric layer of this comparative example, the polyimide of the adhesive layer is not modified, and other structures and preparation methods are the same as those in Example 1.

[0098] Comparative Example 2

[0099] A polyimide copper clad laminate. The difference between this comparative example and Example 1 is that in the preparation process of the modified polyimide in this comparative example, step S1 is omitted, and in step S3, nanocrystalline cellulose is used to replace the intermediate product to obtain polyimide modified only with nanocrystalline cellulose, and other structures and preparation methods are the same as those in Example 1.

[0100] Test Example

[0101] Perform performance tests on the copper clad laminates prepared in Examples 1-4 and Comparative Examples 1-2.

[0102] Test method:

[0103] Use the test method of IPC-TM-650 in the industry to conduct performance tests such as peel strength, tensile strength, elongation, dimensional stability, and thermal stress on the adhesive-free laminated flexible copper clad laminate materials prepared in the examples and comparative examples.

[0104] The test results are shown in Table 5.

[0105] Table 5 Performance results of copper clad laminates

[0106]

[0107] As can be seen from Table 5, Examples 1-4 using polyimide modified with nanocrystalline cellulose and epoxy silane coupling agent as the adhesive layer have good adhesion performance. The adhesion and peel strength between the dielectric layers and between the dielectric layer and the copper foil layer in the examples are significantly improved. At the same time, the stability and aging resistance of the copper clad laminate are also greatly improved, which is significantly better than Comparative Examples 1-2.

[0108] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0109] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A non-adhesive laminated polyimide flexible copper clad laminate, characterized in that, The structure of the adhesive-free laminated polyimide flexible copper clad laminate includes, from top to bottom, an upper copper foil layer, a dielectric layer, and a lower copper foil layer. The dielectric layer includes a polyimide composite layer; The polyimide composite layer includes a thermosetting polyimide layer and adhesive layers provided on both the upper and lower sides of the thermosetting polyimide layer. The adhesive layer is a modified polyimide layer; Wherein, The modified polyimide layer is a polyimide modified by nanocrystalline cellulose and an epoxy silane coupling agent; The preparation method of the modified polyimide includes the following steps: S1. Add an epoxy silane coupling agent to a solvent, adjust the pH and stir, then add nanocrystalline cellulose. After stirring and reacting, obtain an intermediate product through centrifugation, washing, and drying; S2. Immerse the polyimide in an alkaline solution, wash and dry it, then immerse it in an acidic solution again, and wash and dry it to obtain the pretreated polyimide; S3. Add the pretreated polyimide to the intermediate product solution, then add a catalyst and a crosslinking agent, react in an inert gas atmosphere, and obtain the modified polyimide through filtration, washing, and drying.

2. The adhesive-free laminated polyimide flexible copper clad laminate according to claim 1, wherein, In the dielectric layer, there is one or more layers of polyimide composite layers.

3. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 1, wherein The thickness of the adhesive layer is 3 - 10 μm, and the thickness of the thermosetting polyimide layer is 19 - 42 μm.

4. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 1, wherein In the upper copper foil layer and the lower copper foil layer, the Rz value of the copper teeth of the copper foil is 0.7 - 2.8 μm, and the thickness of the copper foil is 6 - 70 μm.

5. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 1, wherein, The epoxy silane coupling agent is 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

6. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 1, wherein In step S1, the value of the pH is 4 - 4.

5.

7. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 1, characterized in that, In step S1, the mass ratio of the epoxy silane coupling agent to nanocrystalline cellulose is (4 - 8):

1.

8. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 1, wherein, In step S3, the concentration of the intermediate product solution is 3 - 6%.

9. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 1, wherein The adhesive-free laminated polyimide flexible copper clad laminate is prepared by high-temperature hot pressing using an equal-pressure double-steel belt machine.

10. The non-adhesive laminated polyimide flexible copper clad laminate according to claim 9, characterized in that, Before the high-temperature hot pressing, the moisture content of the dielectric layer is made ≤1% by baking.

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