阅读说明：本技术 一种挠性基材表面覆铜箔的制备方法 (Preparation method of copper foil coated on surface of flexible substrate ) 是由 陈苑明 冯弘宬 续振林 何为 李毅峰 王守绪 周国云 杨文君 何耀忠 陈嘉彦 于 2021-09-23 设计创作，主要内容包括：本发明公开了一种挠性基材表面覆铜箔的制备方法,属于印制电路制造领域。所述方法为先将挠性基材进行等离子处理,使挠性基材表面产生空洞和极性基团；再将铜箔进行氧化处理,使铜箔形成具有氧基团的粗糙表面；随后将氧化铜箔置于三甲基铝水解产生的甲基铝氧烷中使得甲基铝氧烷吸附在氧化铜箔表面；最后将挠性基材与吸附了甲基铝氧烷的氧化铜箔热压得到复合材料。所述挠性基材表面覆铜箔的方法简单,避免了纯胶的使用,大大降低了最终产品的厚度,符合电子产品轻薄化的趋势；工艺方案中所需设备与现有生产设备兼容,所需生产条件容易达到；得到的复合材料剥离强度高,可达工业应用的标准。(The invention discloses a preparation method of a copper foil coated on the surface of a flexible substrate, belonging to the field of printed circuit manufacturing. The method comprises the steps of firstly carrying out plasma treatment on a flexible base material to generate cavities and polar groups on the surface of the flexible base material; then carrying out oxidation treatment on the copper foil to enable the copper foil to form a rough surface with oxygen groups; then, the copper oxide foil is placed in methylaluminoxane generated by hydrolysis of trimethylaluminum, so that the methylaluminoxane is adsorbed on the surface of the copper oxide foil; finally, the flexible base material and the oxidized copper foil absorbed with the methylaluminoxane are hot-pressed to obtain the composite material. The method for coating the copper foil on the surface of the flexible substrate is simple, avoids the use of pure glue, greatly reduces the thickness of a final product, and accords with the trend of lightness and thinness of electronic products; the equipment required in the process scheme is compatible with the existing production equipment, and the required production conditions are easy to achieve; the obtained composite material has high peel strength and can reach the standard of industrial application.)

1. A preparation method of a copper foil coated on the surface of a flexible substrate is characterized by comprising the following steps:

step A: carrying out plasma treatment on the surface of the flexible base material to generate cavities and polar groups on the surface of the base material;

and B: carrying out oxidation etching treatment on the surface of the copper foil by adopting an alkaline aqueous solution to form a rough shape with an oxygen group on the surface of the copper foil;

and C: b, placing the copper foil subjected to the oxidation and etching treatment in the step B into a trimethyl aluminum aqueous solution for soaking treatment, so that methylaluminoxane generated by hydrolysis of trimethyl aluminum is adsorbed on the surface of the copper foil;

step D: and C, carrying out hot pressing treatment on the flexible base material after the plasma treatment and the copper foil after the treatment in the step C to obtain the surface-coated copper foil of the flexible base material.

2. The method for preparing the surface-coated copper foil of the flexible substrate according to claim 1, wherein the flexible substrate is polyethylene terephthalate polyester, polyimide or liquid crystal polymer.

3. The method for preparing a surface-coated copper foil on a flexible substrate according to claim 1, wherein the gas component for plasma treatment of the substrate surface in the step A is oxygen, argon or a mixed gas of one of oxygen and argon.

4. The method for preparing a surface-coated copper foil for a flexible substrate according to claim 3, wherein the gas flow rate of the plasma treatment is 0.5 to 3L/min, the plasma treatment temperature is 20 to 80 ℃, and the plasma treatment time is 5 to 120 min.

5. The method for preparing the surface-coated copper foil of the flexible substrate as claimed in claim 1, wherein the oxidation etching treatment in step B is NaOH and NaNO₂The mixed aqueous solution of (2) is used for soaking the copper foil.

6. The method for preparing the copper foil coated on the surface of the flexible substrate as claimed in claim 5, wherein the mass fraction of NaOH in the mixed aqueous solution is 1% -10%, and the NaNO is₂The mass fraction of (A) is 1-10%; the temperature of the soaking treatment is 30-110 ℃, and the soaking treatment time is 10-600 s.

7. The method for preparing the copper foil coated on the surface of the flexible substrate according to claim 1, wherein the temperature of the aqueous solution of trimethylaluminum in the step C is 10-50 ℃, and the soaking time is 30 s-1 h.

8. The method for preparing the surface-coated copper foil of the flexible substrate according to claim 1, wherein the pressure of the hot pressing treatment in the step D is 1-15 MPa, the temperature of the hot pressing treatment is 120-210 ℃, and the time of the hot pressing treatment is 60-600 s.

Technical Field

The invention belongs to the field of printed circuit manufacturing, and particularly relates to a preparation method of a copper foil coated on the surface of a flexible substrate.

Background

With the development of communication technology, electronic devices are becoming wearable and Flexible, and Flexible Printed Circuit boards (FPCs) are playing an increasingly important role as carriers for electrical interconnection. With the rapid development of electronic technology, the functions of electronic products are becoming more and more powerful, and the increase of the number of stacked layers of circuits becomes an increasingly important research direction.

Currently, the most commonly used flexible substrates in FPCs include polyethylene terephthalate Polyester (PET), Polyimide (PI), and Liquid Crystal Polymer (LCP), among others. Compared with PET and PI, LCP has better heat resistance, lower water absorption, lower dielectric constant and dielectric dissipation factor. Therefore, the LCP can keep better bonding force when used in a high-temperature high-humidity environment, and can keep good dielectric property and signal transmission integrity when applied in a high-frequency scene.

The process for preparing the flexible film copper-clad foil is usually prepared by a compression method and a coating method. The patent application with the application number of 201911390853.X introduces a method of preparing a copper-clad foil by adopting a plurality of times of high-temperature flat plate hot pressing after plasma treatment, which can achieve the effect of the copper-clad foil, but the preparation process is too complex and the production efficiency is not high; redhwan et al respectively carry out plasma treatment on LCP film and copper foil in a Direct bonding of copper and liquid crystal polymer and then a method of laminating improves the bonding force of the film and the copper foil, the maximum bonding force obtained by the experiment is 587-683g/cm (5.75-6.69N/cm), the bonding force performance is poor, and the phenomenon that copper diffuses to the LCP side occurs in the analysis of the bonding force generation, which possibly influences the transmission performance of electric signals on the copper foil; yung et al compared the effect of different plasma gas combination treatments on the subsequent copper plating binding force in the article Impact of plasma etching technology of liquid crystal polymer printed circuit board, but the adopted copper plating method is difficult to continuously produce, and the phenomenon of copper plating failure even occurs after the adopted partial plasma gas combination treatment, and is not suitable for improving the binding force between LCP and copper; jia et al, in the Direct bonding of copper foil and liquid crystal polymer by laser ablation and welding, have adopted the laser ablation and welding method to promote the cohesion between film and copper foil, the laser ablation welding needs the larger etching area, and the laser parameter has greater difference with the machine for common drilling, need to introduce new apparatus and debug, and the surface roughness of the copper foil after laser ablation varies greatly, will influence the integrality of high-frequency signal transmission; the liquid crystal polymer coating method is adopted in the preparation of the liquid crystal polymer flexible copper-clad foil by the Liangli et al article coating method to prepare the copper-clad foil, and the performance of the copper-clad foil is compared with that of the copper-clad foil prepared by the compression method, while the coating method process adopted for preparing the LCP flexible film has the problem of being not suitable for continuous production in the FPC industry.

Disclosure of Invention

The invention provides a new method for covering copper foil on the surface of a flexible base material in an FPC. The method comprises the steps of carrying out plasma treatment on a flexible base material to generate a cavity and a polar group, then carrying out oxidation etching on a copper foil to obtain a rough surface, enabling methylaluminoxane obtained after hydrolysis of trimethylaluminum to be adsorbed on the surface of the copper oxide foil, and finally enabling the copper oxide foil and the flexible base material to generate a binding force through a hot pressing process. The invention has simple process, reduces the pressing temperature and is more convenient to operate compared with the scheme adopted in the current research; compared with the existing glue bonding, the thickness of the composite material can be obviously reduced, and the requirement of lightness and thinness of products is met.

The technical scheme adopted by the invention is as follows:

a preparation method of a copper foil coated on the surface of a flexible substrate is characterized by comprising the following steps:

step A: the surface of the flexible base material is subjected to plasma treatment to generate voids and polar groups on the surface of the base material. The surface of the flexible base material is subjected to plasma treatment, so that cavities are generated on the surface of the flexible base material, the number of organic polar groups on the surface of the flexible base material is increased, and the bonding force between the flexible base material and the copper foil is increased during the hot-press molding of the copper foil of the base material.

And B: and carrying out oxidation etching treatment on the surface of the copper foil by adopting an alkaline aqueous solution to form a rough shape with oxygen groups on the surface of the copper foil. The surface of the copper foil after the oxidation and etching treatment of the alkaline aqueous solution can be etched to remove part of copper atoms to form a rough surface appearance; and meanwhile, the rough surface of the copper foil is partially oxidized to form copper oxide, so that an oxygen ion bond is introduced into the rough surface of the copper foil, the methyl aluminum oxide group in the subsequent step C is favorably adsorbed, and the binding force of the methyl aluminum oxide group and the copper foil is increased, so that the binding force of the flexible substrate and the copper foil is increased when the substrate copper foil is subjected to hot press molding.

And C: and B, placing the copper foil subjected to the oxidation and etching treatment in the step B into an aqueous solution of trimethylaluminum for soaking treatment, so that methylaluminoxane generated by hydrolysis of the trimethylaluminum is adsorbed on the surface of the copper foil. After absorbing the methylaluminoxane group on the surface of the copper foil, the methylaluminoxane group can be strongly absorbed with the polar group on the surface of the flexible base material treated in the step A, so that the binding force between the flexible base material and the copper foil during the hot press molding of the base material copper foil is obviously increased.

Step D: and C, carrying out hot pressing treatment on the flexible base material after the plasma treatment and the copper foil after the treatment in the step C to obtain the surface-coated copper foil of the flexible base material.

Further, the flexible substrate is a polyethylene terephthalate polyester, a polyimide, or a liquid crystal polymer.

Further, the gas component for plasma treatment of the substrate surface in step a is oxygen, argon or a mixed gas of one of them and nitrogen.

Further, the gas flow rate of the plasma treatment is 0.5-3L/min, the plasma treatment temperature is 20-80 ℃, and the plasma treatment time is 5-120 min.

Further, the oxidation etching treatment method in the step B adopts NaOH and NaNO₂The mixed aqueous solution of (2) is used for soaking the copper foil.

Further, the mass fraction of NaOH in the mixed aqueous solution is 1% -10%, and NaNO is₂The mass fraction of (A) is 1-10%; the temperature of the soaking treatment is 30-110 ℃, and the soaking treatment time is 10-600 s.

Further, the temperature of the aqueous solution of the trimethylaluminum in the step C is 10-50 ℃, and the soaking time is 30 s-1 h.

Further, the pressure of the hot pressing treatment in the step D is 1-15 MPa, the temperature of the hot pressing treatment is 120-210 ℃, and the time of the hot pressing treatment is 60-600 s.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, the cavity is generated on the surface of the flexible base material by adopting a plasma treatment mode, and the surface of the copper foil is etched at the same time, so that the surfaces of the base material and the copper foil are both in rough shapes, and the chelating strength between the base material and the copper foil is increased; more importantly, the method can introduce the methylaluminoxane group on the surface of the copper foil through the oxidation etching treatment of the copper foil and the soaking treatment of the aqueous solution of the trimethylaluminum, and the methylaluminoxane group can strongly attract the organic polar group on the surface of the base material, so that the binding force between the base material and the copper foil is obviously increased; in addition, the oxygen ion bond generated by partial oxidation of the surface of the copper foil in the oxidation etching treatment process of the copper foil can also increase the attraction force between the oxygen ion bond and the organic polar group on the surface of the base material, thereby increasing the binding force between the base material and the copper foil.

Compared with the conventional viscose glue laminating method in industrial production, the preparation method for the surface-coated copper foil of the flexible base material reduces the use of pure glue and reduces the thickness of the product; the prepared flexible substrate with the copper foil coated on the surface can ensure the peeling strength of the copper foil (can ensure the binding force between the substrate and the copper foil); the invention combines the methylaluminoxane with the base materials and the copper foils on the two sides, simplifies the process, reduces the temperature required by the hot pressing process and improves the compatibility with the existing production equipment.

Drawings

FIG. 1 is an SEM image of the surface topography of an LCP film before plasma treatment of example 1, step A;

FIG. 2 is an SEM image of the surface topography of an LCP film after the plasma treatment of example 1, step A;

FIG. 3 is a graph of the results of the water contact angle test of the LCP film surface before plasma treatment of example 1, step A;

FIG. 4 is a graph of the results of the water contact angle test of the LCP film surface after the plasma treatment of example 1, step A;

FIG. 5 is an SEM image of the surface topography of the copper foil before oxidation treatment of example 1 step B;

FIG. 6 is an SEM image of the surface topography of the copper foil after oxidation treatment of example 1 step B;

FIG. 7 is a FIB-SEM image of the cross-sectional profile of example 1 after step D hot pressing is complete;

FIG. 8 is an SEM image of the surface topography of the copper foil after peel strength testing of example 1;

FIG. 9 is an SEM image of the surface morphology of the LCP film of example 1 after peel strength testing.

Detailed Description

The present invention will be further described with reference to the following examples, which are not intended to limit the scope of the present invention in any way. The starting reagents employed in the examples of the present invention are, unless otherwise specified, those that are conventionally purchased.

Example 1

Step A: subjecting the flexible film to plasma treatment: the LCP film is selected in the embodiment, the gas selected for plasma treatment is oxygen, the gas flow is 2.5L/min, the treatment power is 6kW, the treatment time is 30min, and the vacuum degree is 220 mTorr.

And B: carrying out oxidation etching treatment on the surface of the copper foil, and specifically comprising the following steps:

step B-1: alkali washing for oil removal: using water as solvent, according to Na₂CO₃ 50g/L、C₆H₅Na₃O₇ 50g/L、Na₂HPO₃·H₂Preparing alkaline cleaning oil liquid according to the proportion of O50g/L, soaking a copper foil in the alkaline cleaning oil liquid at 50 ℃ for 120s, taking out, washing with water and drying;

step B-2: oxidation and etching: using water as solvent according to NaOH 50g/L, NaNO₂Preparing an oxidation solution at a ratio of 50g/L, soaking the deoiled copper foil in the oxidation solution at 100 ℃ for 120s, taking out, washing with water and drying.

And C: the hydrolysis of trimethyl aluminum and the adsorption of methylaluminoxane specifically comprise the following steps:

step C-1: hydrolysis of trimethylaluminum: preparing 5% trimethyl aluminum water solution, performing hydrolysis reaction, and standing for 10 min;

step C-2: adsorption of Methylaluminoxane: and C, placing the copper foil subjected to the oxidation etching treatment in the step B-2 into the trimethyl aluminum hydrolysis solution obtained in the step C-1, standing for 5min at the temperature of 25 ℃, taking out the copper foil, and drying the copper foil by blowing.

Step D: and C, carrying out hot-pressing treatment on the flexible film treated in the step A and the copper foil treated in the step C: and (3) using a four-opening rapid press, setting the pressing pressure to be 12MPa, the pressing temperature to be 180 ℃, and the pressing time to be 300s, and taking out to obtain the composite material combining the film and the copper foil.

And D, carrying out peel strength test on the film-copper foil composite material obtained in the step D, wherein an apparatus for testing the peel strength is Donggangbolede BLD-1028A, and the peel strength test result is 8.92N/cm.

FIG. 1 is an SEM image of the surface topography of an LCP film before plasma treatment in step A of example 1, and it can be seen that the surface of the film without plasma treatment has a relatively flat topography.

FIG. 2 is an SEM image of the surface topography of the LCP film after the plasma treatment of step A of example 1, and it can be seen that some void structures are formed on the surface of the film after the plasma treatment.

FIG. 3 is a graph of the results of the water contact angle test of the LCP film surface before plasma treatment in step A of example 1, and it can be seen that the water contact angle of the non-plasma treated surface is 81.0 deg., and the hydrophilicity is poor.

FIG. 4 is a graph of the results of the water contact angle test of the LCP film surface after the plasma treatment of step A of example 1, and it can be seen that the water contact angle of the plasma treated surface is 56.4 deg., and the hydrophilicity is improved.

FIG. 5 is an SEM image of the surface morphology of the copper foil before the oxidation etching treatment of step B of example 1, and it can be seen that the surface of the copper foil without the oxidation etching treatment has no regular particles.

FIG. 6 is an SEM image of the surface morphology of the copper foil after the oxidation and etching treatment in step B of example 1, which shows that the copper foil surface after the oxidation and etching treatment has regular particles with different sizes, thereby achieving the effect of roughening the copper foil surface.

Fig. 7 is an FIB-SEM image of the cross-sectional morphology after the hot pressing in step D of example 1, in which the area a is a copper foil layer, the area b is a particle layer produced by oxidation etching of the copper foil, the area c is a methylaluminoxane layer, and the area D is an LCP film layer, it can be seen that the interfaces between the layers of the material prepared by the method are clear and distinguishable, the boundary between the particle layer produced by oxidation etching and the methylaluminoxane layer is very tortuous, the joints are staggered, and the thickness of the particle layer produced by oxidation etching and the methylaluminoxane layer are both 100nm, which greatly reduces the thickness compared with the pure glue used in the industry.

Fig. 8 is an SEM image of the surface morphology after peel strength test of the copper foil in example 1, and it can be seen that a part of LCP (light part in the figure) remained on the surface of the copper foil after the peel test, and the LCP has a torn morphology.

Fig. 9 is an SEM image of the surface morphology of the LCP film after the peel strength test in example 1, and it can be seen that the internal tearing of the LCP occurs, and it is proved that the fracture failure in the peel strength test occurs inside the LCP flexible film, thereby proving that the bonding force of the flexible film and the copper foil is good.

Example 2

Step A: in this example, the LCP film was selected and no plasma treatment was performed.

And B: carrying out oxidation etching treatment on the surface of the copper foil, and specifically comprising the following steps:

step B-1: alkali washing for oil removal: using water as solvent, according to Na₂CO₃ 50g/L、C₆H₅Na₃O₇ 50g/L、Na₂HPO₃·H₂Preparing alkaline cleaning oil liquid according to the proportion of O50g/L, soaking a copper foil in the alkaline cleaning oil liquid at 50 ℃ for 120s, taking out, washing with water and drying;

step B-2: oxidation and etching: using water as solvent according to NaOH 50g/L, NaNO₂Preparing an oxidation solution at a ratio of 50g/L, soaking the deoiled copper foil in the oxidation solution at 100 ℃ for 120s, taking out, washing with water and drying.

And C: the hydrolysis of trimethyl aluminum and the adsorption of methylaluminoxane specifically comprise the following steps:

step C-1: hydrolysis of trimethylaluminum: preparing 5% trimethyl aluminum water solution, performing hydrolysis reaction, and standing for 10 min;

step C-2: adsorption of Methylaluminoxane: and C, placing the copper foil subjected to the oxidation etching treatment in the step B-2 into the trimethyl aluminum hydrolysis solution obtained in the step C-1, standing for 5min at the temperature of 25 ℃, taking out the copper foil, and drying the copper foil by blowing.

Step D: and C, carrying out hot-pressing treatment on the flexible film treated in the step A and the copper foil treated in the step C: and (3) using a four-opening rapid press, setting the pressing pressure to be 12MPa, the pressing temperature to be 180 ℃, and the pressing time to be 300s, and taking out to obtain the composite material combining the film and the copper foil.

And D, carrying out peel strength test on the film-copper foil composite material obtained in the step D, wherein an instrument for testing the peel strength is Dongguan Bolede BLD-1028A, the copper foil and the LCP flexible film do not generate good bonding force in the peel strength test, and a tension meter completely peels once pulling, and effective tension data are not displayed.

Example 3

Step A: subjecting the flexible film to plasma treatment: the LCP film is selected in the embodiment, the gas selected for plasma treatment is oxygen, the gas flow is 2.5L/min, the treatment power is 6kW, the treatment time is 30min, and the vacuum degree is 220 mTorr.

And B: the method for cleaning the surface of the copper foil comprises the following steps:

step B-1: alkali washing for oil removal: using water as solvent, according to Na₂CO₃ 50g/L、C₆H₅Na₃O₇ 50g/L、Na₂HPO₃·H₂Preparing alkaline cleaning oil liquid according to the proportion of O50g/L, soaking the copper foil in the alkaline cleaning oil liquid at 50 ℃ for 120s, taking out, washing with water and drying.

And C: the hydrolysis of trimethyl aluminum and the adsorption of methylaluminoxane specifically comprise the following steps:

step C-1: hydrolysis of trimethylaluminum: preparing 5% trimethyl aluminum water solution, performing hydrolysis reaction, and standing for 10 min;

step C-2: adsorption of Methylaluminoxane: and C, placing the copper foil subjected to the oxidation etching treatment in the step B-2 into the trimethyl aluminum hydrolysis solution obtained in the step C-1, standing for 5min at the temperature of 25 ℃, taking out the copper foil, and drying the copper foil by blowing.

Step D: and C, carrying out hot-pressing treatment on the flexible film treated in the step A and the copper foil treated in the step C: and (3) using a four-opening rapid press, setting the pressing pressure to be 12MPa, the pressing temperature to be 180 ℃, and the pressing time to be 300s, and taking out to obtain the composite material combining the film and the copper foil.

And D, carrying out peel strength test on the film-copper foil composite material obtained in the step D, wherein an instrument for testing the peel strength is Dongguan Bolede BLD-1028A, the copper foil and the LCP flexible film do not generate good bonding force in the peel strength test, and a tension meter completely peels once pulling, and effective tension data are not displayed.

Example 4

Step A: subjecting the flexible film to plasma treatment: the LCP film is selected in the embodiment, the gas selected for plasma treatment is oxygen, the gas flow is 2.5L/min, the treatment power is 6kW, the treatment time is 30min, and the vacuum degree is 220 mTorr.

And B: carrying out oxidation etching treatment on the surface of the copper foil, and specifically comprising the following steps:

step B-1: alkali washing for oil removal: using water as solvent, according to Na₂CO₃ 50g/L、C₆H₅Na₃O₇ 50g/L、Na₂HPO₃·H₂Preparing alkaline cleaning oil liquid according to the proportion of O50g/L, soaking a copper foil in the alkaline cleaning oil liquid at 50 ℃ for 120s, taking out, washing with water and drying;

step B-2: oxidation and etching: using water as solvent according to NaOH 50g/L, NaNO₂Preparing an oxidation solution at a ratio of 50g/L, soaking the deoiled copper foil in the oxidation solution at 100 ℃ for 120s, taking out, washing with water and drying.

And C: and (3) carrying out hot-pressing treatment on the flexible film treated in the step A and the copper foil treated in the step B: and (3) using a four-opening rapid press, setting the pressing pressure to be 12MPa, the pressing temperature to be 180 ℃, and the pressing time to be 300s, and taking out to obtain the composite material combining the film and the copper foil.

And D, carrying out peel strength test on the film-copper foil composite material obtained in the step C, wherein an instrument for testing the peel strength is Dongguan Bolede BLD-1028A, the copper foil and the LCP flexible film do not generate good bonding force in the peel strength test, and the tension meter is completely peeled once being pulled, and effective tension data are not displayed.

The foregoing has described in detail the principles and features of the invention, together with the advantages thereof. The present invention is not limited by the above embodiments, which are described only for illustrating the principle of the present invention, but various modifications can be made without departing from the spirit and scope of the present invention, and these modifications are intended to fall within the scope of the claimed invention. The scope of the invention is defined by the appended claims and equivalents thereof.