CN107556501A - Polyimide film and preparation method and application thereof - Google Patents

Abstract

The invention discloses a polyimide film, the glass transition temperature of which is 360-380°C, the tensile strength is 200-220MPa, and the average linear expansion coefficient in the range of 50-300°C is 18-20ppm/K; The chemical composition of polyimide film is polyimide, and the structural formula of described polyimide is as shown in formula I below: Wherein, n and m represent the degree of polymerization of the polymer, m:n is 3:1-17:3, and n is any positive integer. The polyimide in the present invention has excellent film-forming properties, and the polyimide film has ultra-high heat resistance and mechanical strength, and especially has an average linear expansion coefficient almost similar to that of copper foil in a certain high temperature range.

Description

A kind of polyimide membrane and its preparation method and application

technical field

The invention relates to the technical field of polyimide membranes. More specifically, it relates to a polyimide film and its preparation method and application.

Background technique

Flexible circuit board is a kind of flexible printed circuit board, which has the characteristics of high wiring density, light weight, small size, thin thickness and good bendability. At present, communication equipment, consumer electronics products, computers and other related products are the three largest application fields of flexible circuit boards, accounting for about 80% of the total market demand. In recent years, mobile electronic devices and wearable smart devices have also expanded the development space of flexible circuit boards.

Because polyimide has excellent properties such as high heat resistance, high strength, high modulus, and high dimensional stability, it has been widely used in flexible circuits as an insulating layer. However, one disadvantage of polyimide flexible circuit boards is that the adhesion between polyimide and copper foil is poor, and an adhesive layer is required. However, the traditional adhesive layer is epoxy resin or acrylic resin, which has poor heat resistance and toughness, and has a large difference in linear expansion coefficient with the base material, so the flexibility and life of the circuit board are limited.

In recent years, in order to solve the problems of poor adhesion between polyimide and copper foil and avoid the use of traditional adhesives, various manufacturing methods have emerged abroad. One of them is to use thermoplastic polyimide as the adhesive layer, and then press under high temperature and high pressure to obtain good adhesion. The research focus of this false two-layer flexible circuit board is the thermoplastic polyimide used as the bonding layer, and its mechanical properties and electrical properties are required to be no lower than the polyimide resin used for the core layer. At the same time, it must have high adhesion to polyimide and copper foil for the core layer, good manufacturability and low cost of hot pressing. In addition, it should have high elongation, low elastic modulus, low thermal expansion coefficient, etc. The other is to use a casting process to directly coat polyimide resin on the surface-activated copper foil, and then heat-treat it to form a film. This double-layer flexible circuit board has good dimensional stability due to only polyimide and copper foil. The polyimide resin here must have excellent adhesion properties to copper foil and good dimensional stability.

As a film for flexible copper clad laminates, in addition to the thermal stability and mechanical properties of the material, its thermal expansion coefficient and bonding performance with the substrate are very important. In microelectronic devices, polyimide should be bonded to substrates such as copper and silicon wafers. Since the thermal expansion coefficients of these materials are different, when subjected to cold and heat, especially when the polyimide precursor polyamic acid is cooled after high-temperature (350-400°C) thermal imidization, it will expand due to the thermal expansion of the two materials. The phenomenon of warping, cracking and even delamination occurs due to the mismatch of coefficients.

Therefore, it is necessary to provide a polyimide film having an average linear expansion coefficient close to that of copper in the range of 50-350°C.

Contents of the invention

One object of the present invention is to provide a polyimide film.

Another object of the present invention is to provide a method for preparing a polyimide film.

The third object of the present invention is to provide a kind of application of polyimide film

In order to achieve the above-mentioned first object, the present invention adopts the following technical solutions:

The polyimide film has a glass transition temperature of 360-380°C, a tensile strength of 200-220MPa, and an average linear expansion coefficient (CTE) of 18-20ppm/K within the range of 50-300°C. The chemical composition of described polyimide film is polyimide, and the molecular structure of described polyimide is as shown in following formula I:

Among them, n and m only represent the degree of polymerization of the polymer, not the number of molecules of each segment, m:n is 3:1-17:3, and n is any positive integer. In some specific embodiments of the present invention, the m:n may be, for example, 3:1-4:1, 4:1-17:3, etc., more preferably 4:1. The technicians of the present invention have confirmed through a large number of experiments that when m:n is 4:1, the average linear expansion coefficient of the polyimide film in the range of 50-300° C. is closest to that of copper. In the present invention, the molecular weight of the polyimide has no influence or little influence on the average linear expansion coefficient of the polyimide film.

Preferably, n shown is a positive integer ranging from 10 to 150.

Preferably, the polyimide is composed of 4,4'-diaminodiphenyl ether (ODA), 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) and benzophenone tetraacid di Anhydride (BTDA) prepared by copolymerization, in which, 4,4'-diaminodiphenyl ether (ODA), 2-(4-aminophenyl)-5-aminobenzimidazole (DAPBI) and benzophenone tetraacid di The molar ratio of the anhydride is n:m:n+m±1, that is, n:m:((n+m-1)˜(n+m+1)), more preferably n:m:n+m. The amount ratio of ODA, DAPBI and BTDA affects the ratio of m:n in polyimide and the molecular weight of polyimide in the present invention.

In order to achieve the above-mentioned second purpose, the present invention adopts the following technical solutions:

A method for preparing the above polyimide film comprises the following steps: the polyimide film is prepared by casting a polyamic acid solution into a film and thermal imidization.

Preferably, the polyamic acid solution is obtained by polymerizing ODA, DAPBI and BTDA in a polar solvent, wherein the molar ratio of ODA, DAPBI and BTDA is n:m:n+m±1, more preferably n:m :n+m.

Preferably, the polyamic acid solution has a viscosity of 2-10 Pa·s, preferably 2-6 Pa·s.

Preferably, the polar solvent is N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP).

Preferably, the thermal imidization is a gradient temperature rise under vacuum or inert gas conditions, from room temperature to temperature, and after removing the solvent, keep at any temperature of 200-250°C for 5-30min, and keep at any temperature of 250-300°C 5-20min, keep at 300-350°C for 5-20min, keep at any temperature of 350-400°C for 10-20min.

In order to achieve the above-mentioned third purpose, the present invention adopts the following technical solutions:

The application of the above-mentioned polyimide film as an electronic thin film material in the fields of flexible printed circuit boards, flexible display devices and the like.

The present invention also provides a polyimide copper-clad laminate, the polyimide copper-clad laminate comprises a copper foil layer and a polyimide layer arranged on the copper foil layer, and the material of the polyimide layer is The above-mentioned polyimide film. In the polyimide copper-clad laminate of the present invention, the adhesion between the polyimide layer and the copper foil layer is good, and no other bonding layer is needed.

Preferably, the polyimide layer has a thickness of 10-50 μm. In some specific embodiments of the present invention, the thickness of the polyimide layer may be, for example, 10-20 μm, 20-50 μm, etc., more preferably 20 μm. In the more preferred scheme of the present invention, the product performance obtained is better.

Preferably, the thickness of the copper foil layer is 8-50 μm. In some specific embodiments of the present invention, the thickness of the copper foil layer may be, for example, 8-13 μm, 13-50 μm, etc., more preferably 13 μm. In the more preferred scheme of the present invention, the product performance obtained is better.

Preferably, the warpage of the polyimide copper clad laminate is less than 6 mm, and the T-peel strength is greater than 5 N/cm. More preferably, the polyimide copper-clad laminate has a warpage of 3 mm and a T-peel strength of 6.4 N/cm.

The invention also provides a preparation method of polyimide copper-clad laminate, which is prepared by applying polyamic acid solution on copper foil and thermal imidization.

Preferably, the application method is spin coating or blade coating.

The invention adds rigid and flexible structural units into the molecular structure from the molecular point of view to adjust and optimize the performance of the polymer. The invention uses two kinds of diamines ODA, DAPBI, and dianhydride BTDA as the basic units of the molecular structure, and obtains a copolymer containing different proportions of ODA-BTDA chain segments and DAPBI-BTDA chain segments coexisting through copolymerization. The ODA-BTDA segment with a curved and flexible structure in the copolymer is used as a flexible segment to enhance the toughness of the copolymer; while the DAPBI-BTDA segment is used to increase the rigidity and regularity of the main chain of the polymer molecule. At the same time, the H on the N atom in DAPBI will form an intermolecular hydrogen bond with the carbonyl on the imine ring of the adjacent molecular chain, increasing the interaction force between the molecular chains. Therefore, the DAPBI-BTDA segment is used to improve the mechanical properties, dimensional stability and heat resistance of the copolymer. By adjusting the ratio of bending flexible ODA-BTDA segment to bending rigid DAPBI-BTDA segment, the toughness and dimensional stability of the film material were optimized, in order to obtain a high-performance polyimide film material with a linear expansion coefficient similar to that of copper foil.

In addition, unless otherwise specified, the raw materials used in the present invention can be obtained commercially, and any range described in the present invention includes the end value and any value between the end value and the end value or any value between the end value Any subrange formed by .

The beneficial effects of the present invention are as follows:

(1) The polyimide in the present invention has excellent film-forming properties, and the polyimide film has ultra-high heat resistance and mechanical strength, especially in a certain high temperature range with almost similar average lines of copper foil Coefficient of expansion.

(2) The polyimide copper-clad laminate prepared by polyimide and copper foil provided by the present invention has excellent flexibility and can be bent arbitrarily; the polyimide layer and copper foil have excellent adhesion, and the The polyimide copper clad laminate omits the traditional adhesive during the preparation process; it has very little warpage. It belongs to the true double-layer flexible printed circuit board.

Description of drawings

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

FIG. 1 shows the relationship between the coefficient of linear expansion and temperature of the polyimide film and copper foil in Example 1, Comparative Example 1 and Comparative Example 3 of the present invention.

Fig. 2 (a) shows the photo of polyimide film in the embodiment of the present invention 1; Fig. 2 (b) shows the photo of polyimide copper clad board in the embodiment of the present invention 2; Fig. 2 (c) shows The photo of the polyimide copper-clad laminate in the embodiment of the present invention 2; Fig. 2 (d) shows the photo of the polyimide copper-clad laminate in the comparative example 1 of the present invention; Fig. 3 shows the polyimide copper-clad laminate in the embodiment of the present invention 2 Schematic diagram of the structure of the amine copper clad laminate, in which, 1-copper foil layer, 2-polyimide layer.

FIG. 4 shows a test curve of the peeling performance of the polyimide copper-clad laminate in Example 2 of the present invention.

detailed description

In order to illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and accompanying drawings. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not limit the protection scope of the present invention.

The raw materials used in the invention can be obtained commercially. The preparation process of polyamic acid is a process familiar to those in the industry. It can be obtained by equimolar diamine and dianhydride in the polar solvent N,N-dimethylethane It can be prepared by polymerization in amide (DMAc), N,N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP); it can also be prepared by adjusting the ratio of diamine to dianhydride and using dianhydride-capped polymerization Polyamic acid with fixed molecular weight; the molecular weight of polyamic acid can also be regulated by end-capping agent phthalic anhydride.

Example 1

A kind of polyimide film, its preparation method comprises the steps:

1) Synthesis of polyamic acid (PAA) solution: Carry out according to the molar ratio of BTDA:ODA:DAPBI=5:1:4, first add two kinds of diamine monomers ODA and DAPBI with a molar ratio of 1:4 into the metered In DMAc, make the total solid content 15%, then mechanically stir under the protection of nitrogen, then add BTDA which is equimolar to the total amount of the two diamines in batches, and make it continue to react for 5 hours below 25 ° C in a nitrogen atmosphere to obtain Viscous polyamic acid solution. The polyamic acid solution was sealed and placed in the refrigerator for use, and its viscosity was measured to be 5.3 Pa·s after 24 hours.

2) Preparation of polyimide film: cast the PAA solution prepared in step 1) on a clean glass plate to form a film, keep it in a blast oven at 60°C for 30min, at 100°C for 30min, and at 150°C for 30min, then Continue in the vacuum oven, keep at 250°C for 20min, at 300°C for 20min, and at 380°C for 20min to complete the thermal imidization process.

The obtained polyimide film has a glass transition temperature of 370°C, a thermal decomposition temperature of 525°C, a tensile strength of 210MPa, and an average linear expansion coefficient within the range of 50-300°C of 19.6ppm/K. Its structural formula is as follows,

m:n=4:1.

The curve of the relationship between the linear expansion coefficient and temperature of the obtained polyimide film is shown in FIG. 1 , and the linear expansion coefficients in different temperature ranges are listed in Table 1.

Table 1 Coefficient of linear expansion of polyimide film and copper foil

In conjunction with Fig. 1 and Table 1, it can be seen that the coefficient of linear expansion of the polyimide film in Comparative Example 1 is too high, and the coefficient of linear expansion of the polyimide film in Comparative Example 3 is too low, both of which do not match the copper foil and cannot It is used in the field of double-layer flexible printed circuit. The coefficient of linear expansion of the polyimide in Example 1 in the range of 50-300° C. is consistent with that of copper foil in this range, and can be used in the fields of double-layer flexible printed circuit boards and flexible displays. And it has been confirmed by a large number of experiments by the technicians of the present invention that the polyimide membrane obtained in Example 1 has the best performance effect.

Example 2

A polyimide copper-clad laminate, as shown in Figure 3, comprises a copper foil layer and a polyimide layer disposed on the copper foil layer, wherein the thickness of the copper foil layer is 13 μm, and the thickness of the polyimide layer is 20 μm; its preparation includes the following steps:

The PAA solution prepared in Example 1 was spin-coated on the copper foil, and then the thermal imidization process was completed using the same thermal imidization process as in Example 1 to obtain a polyimide copper-clad laminate.

The polyimide copper-clad laminate in this embodiment has very good flatness, and the polyimide layer and the copper foil layer have very good adhesion performance, see FIG. 2(b) and FIG. 2(c). A polyimide copper clad laminate with a width of 0.5cm and a length of 5cm was used to test the peel performance. 6.4N/cm.

Example 3

A kind of polyimide film, its preparation method comprises the steps:

1) Synthesis of polyamic acid solution: Carry out according to the molar ratio of BTDA:ODA:DAPBI=4:1:3, firstly add ODA and DAPBI two diamine monomers with a molar ratio of 1:3 into the metered DMAc, Make the total solid content 15%, then mechanically stir under the protection of nitrogen, then add BTDA which is equimolar to the total amount of the two diamines in batches, and continue to react for 5 hours under the nitrogen atmosphere below 25°C to obtain viscous Polyamic acid solution. The polyamic acid solution was sealed and placed in a refrigerator for use, and its viscosity was measured to be 5.0 Pa·s after 24 hours.

2) Preparation of polyimide film: cast the PAA solution prepared in step 1) on a clean glass plate to form a film, keep it in a blast oven at 60°C for 30min, at 100°C for 30min, and at 150°C for 30min, then Continue in the vacuum oven, keep at 250°C for 20min, at 300°C for 20min, and at 380°C for 20min to complete the thermal imidization process.

The glass transition temperature of the obtained polyimide film is 365°C, the thermal decomposition temperature is 523°C, the tensile strength is 207MPa, and the average linear expansion coefficient in the range of 50-300°C is 20.1ppm/K. Its structural formula is as follows,

m:n=3:1.

Example 4

A polyimide copper-clad laminate, comprising a copper foil layer and a polyimide layer disposed on the copper foil layer, wherein the thickness of the copper foil layer is 13 μm, and the thickness of the polyimide layer is 20 μm; its preparation includes the following steps step:

The PAA solution prepared in Example 3 was spin-coated on the copper foil, and then the thermal imidization process was completed using the same thermal imidization process as in Example 3 to obtain a polyimide copper-clad laminate.

The polyimide copper-clad laminate in this embodiment has very good flatness, and the polyimide layer and the copper foil layer have very good adhesion performance, and the polyimide copper-clad laminate with a width of 0.5cm is used for peeling performance According to the test, the warpage of the copper clad laminate is 5.0 mm, and the T-peel strength with the 13 μm thick copper foil is 6.3 N/cm.

Example 5

A kind of polyimide film, its preparation method comprises the steps:

1) Synthesis of polyamic acid solution: Carry out according to the molar ratio of BTDA:ODA:DAPBI=20:3:17, firstly add ODA and DAPBI two diamine monomers with a molar ratio of 3:17 into the metered DMAc, Make the total solid content 15%, then mechanically stir under the protection of nitrogen, then add BTDA which is equimolar to the total amount of the two diamines in batches, and continue to react for 5 hours under the nitrogen atmosphere below 25°C to obtain viscous Polyamic acid solution. The polyamic acid solution was sealed and placed in a refrigerator for use, and its viscosity was measured to be 5.4 Pa·s after 24 hours.

2) Preparation of polyimide film: cast the PAA solution prepared in step 1) on a clean glass plate to form a film, keep it in a blast oven at 60°C for 30min, at 100°C for 30min, and at 150°C for 30min, then Continue in the vacuum oven, keep at 250°C for 20min, at 300°C for 20min, and at 380°C for 20min to complete the thermal imidization process.

The obtained polyimide film has a glass transition temperature of 382°C, a thermal decomposition temperature of 525°C, a tensile strength of 213MPa, and an average coefficient of linear expansion within the range of 50-300°C of 19.1ppm/K. Its structural formula is as follows,

m:n=17:3.

Example 6

A polyimide copper-clad laminate, comprising a copper foil layer and a polyimide layer disposed on the copper foil layer, wherein the thickness of the copper foil layer is 13 μm, and the thickness of the polyimide layer is 20 μm; its preparation includes the following steps step:

The PAA solution prepared in Example 5 was scraped onto the copper foil, and then the thermal imidization process was completed using the same thermal imidization process as in Example 5 to obtain a polyimide copper-clad laminate.

The polyimide copper-clad laminate in this embodiment has very good flatness, and the polyimide layer and the copper foil layer have very good adhesion performance, and the polyimide copper-clad laminate with a width of 0.5cm is used for peeling performance According to the test, the warpage of the copper clad laminate is 5.5mm, and the T-peel strength with the 13μm thick copper foil is 6.1N/cm.

Comparative example 1

A polyimide film, the preparation method of which is the same as that of Example 1, except that the PAA solution in step 1) is prepared according to the molar ratio of BTDA:ODA:DAPBI=5:2:3.

The glass transition temperature of the obtained polyimide film is 340°C, the thermal decomposition temperature is 524°C, the tensile strength is 206MPa, and the average linear expansion coefficient in the range of 50-300°C is 25.6ppm/K.

The curve of the relationship between the linear expansion coefficient and temperature of the obtained polyimide film is shown in FIG. 1 , and the linear expansion coefficients in different temperature ranges are listed in Table 1. As shown in Table 1, it has a higher coefficient of linear expansion than copper foil.

Comparative example 2

A polyimide copper-clad laminate, the structure and preparation method of which are the same as those in Example 2, except that the PAA solution in Comparative Example 1 is used for preparation.

As a result, as shown in FIG. 2(d), warping toward the polyimide layer occurred when both the polyimide layer and the copper foil layer were laminated.

Comparative example 3

A polyimide film, the preparation method of which is the same as that of Example 1, except that the PAA solution in step 1) is prepared according to the molar ratio of BTDA:DAPBI=1:1.

The obtained polyimide film has a glass transition temperature of 397°C, a thermal decomposition temperature of 530°C, a tensile strength of 221MPa, and an average linear expansion coefficient within the range of 50-300°C of 15.9ppm/K. Its structural formula is as follows,

m is any integer.

The curve of the relationship between the linear expansion coefficient and temperature of the obtained polyimide film is shown in FIG. 1 , and the linear expansion coefficients in different temperature ranges are listed in Table 1. As shown in Table 1, it has a lower coefficient of linear expansion than copper foil.

Comparative example 4

A polyimide copper-clad laminate, the structure and preparation method of which are the same as those in Example 2, except that the PAA solution in Comparative Example 3 is used for preparation.

Result: When the polyimide layer and the copper foil layer were laminated, warpage appeared in the direction of the copper foil.

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. For those of ordinary skill in the art, on the basis of the above description, they can also make It is not possible to exhaustively list all the implementation methods here, and all obvious changes or changes derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims (10)

1. a kind of polyimide film, it is characterised in that the glass transition temperature of the polyimide film is 360~380 DEG C, is drawn It is 200~220MPa to stretch intensity, and the average coefficient of linear expansion in the range of 50~300 DEG C is 18~20ppm/K；The polyimides The chemical composition of film is polyimides, and the structural formula of the polyimides is as shown in following formula I：

Wherein, the degree of polymerization of n and m representation polymers, m:N is 3:1~17:3, n be any positive integer.

2. a kind of polyimide film according to claim 1, it is characterised in that the polyimides is n by mol ratio:m: The 4,4 ' of n+m ± 1-diaminodiphenyl ether, 2- (4- aminophenyls)-5- aminobenzimidazoles and benzophenone tetracarboxylic dianhydride copolymerization system It is standby to obtain.

3. a kind of preparation method of polyimide film as claimed in claim 1 or 2, comprises the following steps：The polyimides Film through hot imidization by by polyamic acid solution casting film-forming, being made.

4. preparation method according to claim 3, it is characterised in that the polyamic acid solution viscosity is 2~10pa s。

5. preparation method according to claim 3, it is characterised in that the hot imidization is in vacuum or inert gas bar Part Gradient heats up, and from room temperature, removes and keeps 5~30min after solvent at 200~250 DEG C of any temperature, and 250~300 5~20min is kept at DEG C any temperature, 5~20min are kept at 300~350 DEG C, 10 are kept at 350~400 DEG C of any temperature ~20min.

6. a kind of polyimide film as claimed in claim 1 or 2 is in flexible printed circuit board or flexible display device field Using.

7. a kind of polyimide copper clad lamination, it is characterised in that the polyimide copper clad lamination includes copper foil layer and located at copper foil layer On polyimide layer, the material of the polyimide layer is polyimide film as claimed in claim 1 or 2.

8. a kind of polyimide copper clad lamination according to claim 5, it is characterised in that the thickness of the polyimide layer is 10~50 μm, the thickness of the copper foil layer is 8~50 μm.

9. a kind of polyimide copper clad lamination according to claim 5, it is characterised in that the polyimide copper clad lamination sticks up Curvature is less than 6mm, and T-shaped peel strength is more than 5N/cm.

10. the preparation method of a kind of polyimide copper clad lamination as described in claim 7~9 is any, it is characterised in that described poly- Acid imide copper-clad plate is made by the way that polyamic acid solution is applied on copper foil through hot imidization.