KR102222040B1 - Flexible printed circuit board - Google Patents

Abstract

The present specification is a polyimide film; A printing layer provided on the polyimide film; And a plating layer provided on at least one surface of the printing layer,
The printed layer relates to a flexible printed circuit board in which conductive particles are dispersed in a polymer matrix derived from a binder including a urethane-based compound, an epoxy-based resin, and a polyester-based resin.

Description

Flexible printed circuit board {FLEXIBLE PRINTED CIRCUIT BOARD}

The present invention relates to a flexible printed circuit board, and more particularly, to a flexible printed circuit board including a printed layer having excellent adhesion to a polyimide film, which is a flexible substrate, and excellent in chemical resistance.

In general, printed circuit boards (PCBs) and flexible printed circuit boards (FPCBs) used in small wireless devices and electronic products are formed by forming patterns on a copper clad laminate or a copper clad laminate polymer film, and then etching unnecessary parts except for a desired circuit pattern. Prepared by the method. However, in order to obtain a circuit pattern through this method, there is a disadvantage in that it must undergo complex processes such as development, corrosion, peeling, and water washing. In addition, there is a problem of polluting the environment by using a considerable amount of chemicals such as a photosensitive agent, a photoresist, and an etching solution in the etching process.

Therefore, by using a screen printing method, a conductive circuit is formed only in a necessary part, and a metal and/or a conductive material having excellent oxidation stability and electrical properties is electroplated or electrolessly plated on the outer side of the conductive circuit. There is a need for a conductive paste that allows fabrication of an FPCB having low resistance and low cost. In order to solve such a problem, Korean Patent Application Publication No. 10-2010-0013033 discloses a method of preventing penetration and corrosion of a plating solution by minimizing voids between metal particles to produce a pattern having a dense microstructure. The microstructure is effective in preventing penetration and corrosion, but there is a problem that it is not suitable for mass production due to the difficult paste manufacturing process and sintering process.

In addition, in the case of FPCB, the adhesive force between the printed layer and the polymer film (especially, polyimide film) is low, and the problem that the polymer film and the printed layer are peeled off due to the bending of the flexible substrate has not yet been solved. have.

Accordingly, there is a need to develop a flexible printed circuit board capable of preventing the separation of the printed layer due to bending of the polyimide film, which is a flexible substrate.

An object of the present invention is to provide a flexible printed circuit board having a printed layer having excellent adhesion to a polyimide film, in particular, flexural adhesion due to the bending of the polyimide film.

An exemplary embodiment of the present invention, according to the present invention, a polyimide film; A printing layer provided on the polyimide film; And a plating layer provided on at least one surface of the printing layer,

The printed layer provides a flexible printed circuit board in which conductive particles are dispersed in a polymer matrix derived from a binder including a urethane-based compound, an epoxy-based resin, and a polyester-based resin.

The flexible printed circuit board according to an exemplary embodiment of the present invention has excellent adhesion between the polyimide film and the printed layer, and in particular, has excellent flexural adhesion between the polyimide film and the printed layer according to the bending of the polyimide film, which is a flexible substrate, There is an advantage of excellent product reliability of a flexible printed circuit board using a polyimide film.

1 is a schematic diagram of a cross-sectional structure of a flexible printed circuit board (FPCB) according to an exemplary embodiment of the present invention.

In this specification, when a member is positioned "on" another member, this includes not only the case where the member is in contact with the other member, but also the case where another member exists between the two members.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

In the present specification, the unit "parts by weight" may mean a ratio of weight between each component.

In the case of forming a printed layer on a polyimide film used for a flexible printed circuit board using an existing conductive paste, the present inventors have a problem in that the printed layer is damaged due to low chemical resistance during the plating process and/or warpage of the polyimide film. Recognizing that there is a problem in that adhesion cannot be maintained depending on the characteristics, it was confirmed that the above problem can be solved by forming a printing layer using a new composition of conductive paste composition for plating that can solve this problem. We came to the completion of the invention.

Hereinafter, the present invention will be described in detail.

An exemplary embodiment of the present invention is a polyimide film; A printing layer provided on the polyimide film; And a plating layer provided on at least one surface of the printing layer,

The printed layer provides a flexible printed circuit board in which conductive particles are dispersed in a polymer matrix derived from a binder including a urethane-based compound, an epoxy-based resin, and a polyester-based resin.

Polymer matrix

According to an exemplary embodiment of the present invention, the polymer matrix may be formed by curing a material constituting the binder. Specifically, the polymer matrix may be a cured product of the binder. More specifically, the polymer matrix may be formed using the following conductive paste composition for plating.

According to an exemplary embodiment of the present invention, the polymer matrix may be a cured product of a binder consisting of 30 parts by weight to 45 parts by weight of a urethane-based compound, 15 parts by weight to 30 parts by weight of an epoxy resin, and the balance of a polyester-based resin.

According to an exemplary embodiment of the present invention, the polymer matrix is an organic solvent; A binder including a urethane-based compound, an epoxy-based resin, and a polyester-based resin; And it may be derived from a conductive paste composition for plating including conductive particles. Specifically, the polymer matrix may be a cured product of the conductive paste composition for plating.

bookbinder

In the present invention, the binder includes at least a urethane-based compound, an epoxy-based resin, and a polyester-based resin. That is, the conductive paste composition for plating according to the present invention contains at least three materials as described above at the same time, thereby greatly improving the adhesion between the printing layer and the polyimide film, and further securing the chemical resistance of the printing layer to form a plating layer. In this case, damage to the printed layer by the plating solution can be prevented and a homogeneous plating layer can be formed. In particular, the binder may play a role of preventing the printed layer from having elasticity and deteriorating adhesion according to the bending properties of the polyimide film.

In order to implement such characteristics, the content of the binder may be adjusted to 15 parts by weight to 25 parts by weight based on 100 parts by weight of the conductive paste composition for plating. Specifically, the content of the binder may be 18 parts by weight to 23 parts by weight based on 100 parts by weight of the total composition.

In addition, when the content of the binder is within the above range, the sheet resistance of the printed layer formed by using the conductive paste composition for plating may be as low as 1 Ω/□ or less.

Urethane compound

In the present invention, the urethane-based compound may be at least one of a urethane-based compound containing a urethane bond and a polyurethane resin containing a monomer unit containing a urethane bond.

According to an exemplary embodiment of the present invention, the urethane-based compound may be a carbamic acid ester, specifically at least one of ethyl carbamate and methyl carbamate, more specifically ethyl carbamate.

According to an exemplary embodiment of the present invention, the polyurethane resin may be a reactant between a polyester polyol and a polyisocyanate compound, or a reactant between a polyether polyol and a polyisocyanate compound.

Examples of the polyester polyol include lactone-based polyester polyol and adipic acid-based polyester polyol. The adipic acid-based polyester polyol is made by polymerization of a polyfunctional carboxylic acid compound and a polyfunctional alcohol compound, and adipic acid may be used as the polyfunctional carboxylic acid used at this time, and diol (diol) as the polyfunctional alcohol compound. ) Or triol can be used.

The polyether polyol may be prepared by adding propylene oxide (PO) or ethylene oxide (EO) to an initiator having two or more activated hydrogens (-OH, NH _{2 ), for example, polyethylene glycol,} It may be polypropylene glycol, polytetramethylene glycol, or a copolymer of the above material.

The polyisocyanate compound may be used in the art to form a urethane bond, and for example, an aromatic isocyanate, an aliphatic isocyanate, and an alicyclic isocyanate may be used. Specifically, the polyisocyanate compound is diphenylmethane diisocyanate (MDI; diphenyl methane diisocyanate), toluene diisocyanate (TDI; tolunene diisocyanate), hexamethylene diisocyanate (HDI; hexamethylene diisocyanate), dicyclohexylmethane diisocyanate (H12MDI; dicyclohexylmethane diisocyanate) or a mixture of two or more thereof.

The urethane-based compound enables the flexibility of the printing layer to be secured, thereby preventing the printing layer from being peeled off due to the bending of the polymer substrate.

In order to implement the above characteristics, the content of the urethane-based compound may be 30 parts by weight to 45 parts by weight based on 100 parts by weight of the total binder. Specifically, the content of the urethane-based compound may be 30 parts by weight to 37 parts by weight, or 32 parts by weight to 37 parts by weight based on 100 parts by weight of the total binder.

Epoxy resin

According to an exemplary embodiment of the present invention, the epoxy resin is a bisphenol A type epoxy resin, a hydrogenated bisphenol A type epoxy resin, a brominated bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, a novolac type epoxy. Resin, phenol novolak type epoxy resin, cresol novolac type epoxy resin, N-glycidyl type epoxy resin, bisphenol A novolak type epoxy resin, bixylenol type epoxy resin, biphenol type epoxy resin, chelate type epoxy resin, Glyoxal type epoxy resin, amino group-containing epoxy resin, rubber modified epoxy resin, dicyclopentadiene phenolic type epoxy resin, diglycidylphthalate resin, heterocyclic epoxy resin, tetraglycidyl xylenoylethane resin, silicone modified epoxy It may be at least one of resin and ε-caprolactone-modified epoxy resin.

The epoxy resin may improve the adhesion of the printing layer. Specifically, the epoxy resin may serve to improve adhesion of the printing layer to the polyimide film together with the urethane-based compound. Specifically, the epoxy resin makes it possible to secure a solid adhesive force between the printing layer and the polyimide film. In addition, the urethane-based compound used together with the epoxy resin secures the flexibility of the printing layer so that the adhesive strength of the printing layer due to the bending of the polyimide film can be secured.

Further, the epoxy resin may improve the chemical resistance of the printing layer, so that the corrosion resistance of the printing layer can be secured when the plating layer is formed.

In order to implement the above characteristics, the content of the epoxy resin may be 15 parts by weight to 30 parts by weight based on 100 parts by weight of the total binder. Specifically, the content of the polyester-based resin may be 20 parts by weight to 25 parts by weight based on 100 parts by weight of the total binder.

Polyester system Suzy

According to an exemplary embodiment of the present invention, the polyester resin may be a saturated polyester resin or an unsaturated polyester resin. Specifically, the polyester resin may be a saturated polyester resin.

Specifically, according to an exemplary embodiment of the present invention, the polyester-based resin may be used by selecting among products of the ES series of BASE KOREA, for example, ES-100, ES-110, ES-300, ES-350 , ES-360 and other products can be used. However, the present invention is not limited thereto, and any polyester resin capable of securing the physical properties of the conductive paste composition for plating may be applied without limitation.

The polyester-based resin may serve to improve compatibility of each composition in the conductive paste composition for plating. Specifically, the polyester-based resin is a thermoplastic resin, and when cured by heating after coating (or printing) the conductive paste composition for plating, at least a portion of the resin is dissolved and the bonding between the urethane-based compound and the epoxy-based resin is firmly maintained. It can, and furthermore, it is possible to bind the electroconductive particle to the print layer.

In order to implement the above characteristics, the content of the polyester-based resin may be the balance excluding the content of the urethane-based compound and the content of the epoxy-based resin based on 100 parts by weight of the total binder. Specifically, the content of the polyester-based resin may be 30 parts by weight to 45 parts by weight based on 100 parts by weight of the total binder. More specifically, the content of the polyester-based resin may be 35 parts by weight to 45 parts by weight, or 40 parts by weight to 45 parts by weight based on 100 parts by weight of the total binder.

Conductive particles

In the present invention, the conductive particles may serve as a conductor for forming a plating layer and electrical conductivity of the printed layer.

According to an exemplary embodiment of the present invention, the conductive particles may include metallic particles and carbon-based particles. Specifically, the metallic particles may be micro-sized particles, and the average diameter thereof may be 1 µm to 10 µm, specifically 3 µm to 10 µm, 3 µm to 7 µm, or 5 µm to 7 µm. In addition, the carbon-based particles may be nano-sized particles, and the average diameter thereof may be 10 nm to 500 nm.

The metallic particles have a relatively large particle diameter, and are partially exposed to the outside of the printing layer to serve as a conductor when forming the plating layer. Specifically, when forming a printing layer by curing the conductive paste composition for plating, the binder may partially shrink and the metallic particles may be partially exposed. In addition, since the carbon-based particles have a relatively small particle diameter, it is possible to fill the space between the metallic particles, increase the density of the conductive particles in the printing layer, and lower the resistance of the printing layer.

The average particle diameter may mean an average diameter of particles randomly sampled after analyzing a powder including particles through an electron microscope or the like.

The metallic particles are platinum (Pt), gold (Au), copper (Cu), nickel (Ni), silver (Ag), tin (Sn), cobalt (Co), iron (Fe), nickel (Ni), and It may include metal particles including at least one metal of aluminum (Al). In addition, the metallic particles may be metal particles having a core-shell structure including two or more different metals. Specifically, the core-shell structured metal particles may be particles in which silver (Ag) is coated on the surface of copper (Cu) particles.

The carbon-based particles may include at least one of carbon black, ketjen black, acetylene black, graphite, graphene, and carbon nanotubes. Specifically, the carbon-based particles may include graphite and carbon nanotubes together, or may include graphene and carbon nanotubes together.

The content of the conductive particles may be 60 parts by weight to 75 parts by weight based on 100 parts by weight of the conductive paste composition for plating. Specifically, the content of the conductive particles may be 65 parts by weight to 70 parts by weight based on 100 parts by weight of the conductive paste composition for plating.

Further, according to an exemplary embodiment of the present invention, the content of the conductive particles may be 70 parts by weight to 85 parts by weight based on 100 parts by weight of the printing layer. Specifically, the content of the conductive particles may be 70 parts by weight to 80 parts by weight, or 74 parts by weight to 80 parts by weight based on 100 parts by weight of the printing layer.

Further, the content of the metallic particles may be 98 parts by weight to 99.9 parts by weight based on 100 parts by weight of the total conductive particles. In addition, the content of the carbon-based particles may be 0.05 parts by weight to 0.3 parts by weight based on 100 parts by weight of the total conductive particles.

Within the content range of the conductive particles as described above, the effects of the conductive particles described above may be implemented.

Organic solvent

In the present invention, the organic solvent serves to disperse the composition, and makes it possible to secure the fluidity of the conductive paste composition for plating. Further, after applying (or printing) the conductive paste composition for plating, when heat is applied at a predetermined temperature, the organic solvent is volatilized and the binder is cured to form a printed layer.

The organic solvent may include a hydrocarbon-based solvent having a high boiling point, and may prevent plate dryness when printing the conductive paste composition for plating by a method such as silk screen printing. Specifically, the organic solvent may be a hydrocarbon-based solvent, specifically hexane, octane, decane, tetradecane, tetradecene, hexadecane, 1-hexadecene, octadecene, 1-octadecine, chlorobenzoic acid, solvent naphtha , Xylene, N-methylpyrrolidone, and may include one or more of N-ethyl-2-pyrrolidone.

According to an exemplary embodiment of the present invention, the organic solvent may be a non-toluene-free organic solvent. That is, since the organic solvent does not contain toxic toluene, environmental pollution and work safety can be further improved.

The content of the organic solvent may be the remainder of the plating conductive paste excluding the content of components based on 100 parts by weight of the plating conductive paste composition. Specifically, the content of the organic solvent may be 5 parts by weight to 20 parts by weight based on 100 parts by weight of the conductive paste composition for plating. Specifically, the content of the organic solvent may be 5 parts by weight to 15 parts by weight, or 5 parts by weight to 10 parts by weight based on 100 parts by weight of the conductive paste composition for plating.

additive

According to an exemplary embodiment of the present invention, the conductive paste composition for plating may further include one or more additives selected from the group consisting of a dispersant, a colorant, a leveling agent, a thixotropic agent, and a stabilizer. Additives such as a dispersant, a colorant, a leveling agent, a thixotropic agent, and a stabilizer may be used without limitation, those generally used in the art.

The content of the additives may be 0.05 parts by weight to 5 parts by weight, or 0.1 parts by weight to 3 parts by weight, respectively, based on 100 parts by weight of the plating conductive paste composition. In addition, the total content of the additive may be 1 to 5 parts by weight, or 2 to 4 parts by weight based on 100 parts by weight of the conductive paste composition for plating.

Flexible printed circuit board

According to an exemplary embodiment of the present invention, the flexible printed circuit board includes a printed layer formed using the aforementioned conductive paste composition for plating, and a polyimide film may be used as a flexible substrate.

According to an exemplary embodiment of the present invention, in order to secure adhesion between the polyimide film and the printing layer, the polyimide film may not be provided with a surface coating layer.

According to an exemplary embodiment of the present invention, the height of the printing layer may be within the range of the average particle diameter of the conductive particles. Specifically, the height of the printing layer may be 1 µm to 10 µm, specifically 3 µm to 10 µm, 3 µm to 7 µm, or 5 µm to 7 µm. Specifically, the conductive paste composition for plating may be applied within the range of the average diameter of the metal particles, specifically, the average diameter of the metal particles, and when curing it to form a printing layer, the conductive paste composition for plating The organic solvent is volatilized and the binder partially shrinks, thereby partially exposing the aforementioned metallic particles. The metal particles exposed in this way may serve as a conductor when forming the plating layer. That is, the height of the printing layer may be within the range of the average diameter of the metallic particles described above.

The plating layer may be formed on at least one surface of the printing layer using an electroless plating method generally known in the art. In addition, the plating layer may include two or more plating layers made of different metals. Specifically, the plating layer may be formed of 1 to 5 plating layers, and metals constituting each plating layer may be different from each other. For example, according to an exemplary embodiment of the present invention, a copper plating layer, a nickel plating layer, a palladium plating layer, and a gold plating layer may be sequentially provided on the printing layer by using electroless plating.

Hereinafter, examples will be described in detail in order to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various forms, and the scope of the present invention is not construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely describe the present invention to those of ordinary skill in the art.

[ Example ]

Organic solvents including N-ethyl-2-pyrrolidone, dimethyl benzene, and solvent naphtha; Urethane-based compounds (CAS No. 51-79-6), polyester-based resins (Base Korea's ES-100) and epoxy resins (CAS No. 25068-38-6) as binders; Cu particles coated with Ag having an average particle diameter of about 5 µm (Ag content: about 10 wt%) as metallic particles; As carbon-based particles, graphite (grapheneol) and carbon nanotubes (CNT) (LION SPECIALTY CO., LTD.) were mixed in the composition shown in Table 1 to prepare a conductive paste composition for plating.

Further, after silkscreen printing the prepared conductive paste composition for plating to a thickness of about 5 μm on a polyimide film, heat was applied at about 140° C. for about 40 minutes to form a printed layer. Then, a copper plating layer was formed on the surface of the printed layer by using an electroless plating method including degreasing and palladium catalyst treatment.

[ Comparative example And Reference example ]

Using the materials used in the examples, a conductive paste composition for plating was prepared by mixing in the composition shown in Table 1 below, and a printing layer was formed on the polyimide film in the same manner as in the examples. Then, a copper plating layer was formed on the surface of the printed layer by using an electroless plating method including degreasing and palladium catalyst treatment.

Example
(Part by weight) Comparative Example 1
(Part by weight) Comparative Example 2
(Part by weight) Reference Example 1
(Part by weight) Reference Example 2
(Part by weight) Organic solvent 8.69 8.69 8.69 7.64 9.43 bookbinder Urethane compound 7.05 - 9.45 10.58 3.45 Epoxy resin 4.57 7.73 - 6.89 2.32 Polyester resin 8.53 12.42 10.7 12.7 4.21 Metallic particles Ag coated Cu 68.11 68.11 68.11 59.97 77.32 Carbon-based particles Graphite 0.05 0.05 0.05 0.04 0.05 CNT 0.05 0.05 0.05 0.04 0.05 Other additives 2.95 2.95 2.95 2.14 3.17

[ Experimental example One] Printed layer Measurement of flat adhesion

In order to measure the flat adhesion of the printed layer according to the Examples, Comparative Examples and Reference Examples to the polyimide film, a cross cut test was performed according to ASTM D3359 standard and evaluated as 0B to 5B. Measurement results according to Experimental Example 1 are shown in Table 2 below.

Example Comparative Example 1 Comparative Example 2 Reference Example 1 Reference Example 2 Cross cut 5B 5B 1B 5B 3B

[ Experimental example 2] Printed layer Measurement of flexural adhesion

In order to measure the bending adhesion of the polyimide film of the printed layer according to the above Examples, Comparative Examples and Reference Examples, the prepared samples were bent in opposite directions for 10 times. The case where it did not come off was evaluated as ○, and the case where at least part of the printed layer was separated from the polyimide film was evaluated as x. Measurement results according to Experimental Example 2 are shown in Table 3 below.

Example Comparative Example 1 Comparative Example 2 Reference Example 1 Reference Example 2 Flexural adhesion ○ × × ○ ×

[ Experimental example 3] Printed layer Sheet resistance Measure

For the printed layers according to Examples, Reference Example 1 and Reference Example 2, sheet resistance was measured using a 4-point probe.

As a result of the measurement, the sheet resistance of the printed layer according to the example was measured to be less than 1 Ω/□. In addition, the sheet resistance of the printed layer according to Reference Example 1, in which the total content of the binder is about 30 parts by weight, was measured to be about 7 Ω/□, and the sheet resistance of the printed layer according to Reference Example 2, in which the total content of the binder is about 10 parts by weight, was about It was measured as 0.6 Ω/□. As a result of Experimental Example 3, it was confirmed that the printed layer according to the example had a sheet resistance of a sufficiently low value for electroless plating, and it was confirmed that the copper plating layer was uniformly electrodeposited.

As a result of the above Experimental Examples 1 to 3, it was confirmed that the printed layer according to the example had excellent both flat adhesion and flexural adhesion to the polymer substrate, and further, the sheet resistance of the printed layer was lower than 1 Ω/□. .

On the other hand, the printed layer according to Comparative Example 1, which did not contain a urethane-based compound as a binder, exhibited excellent flat adhesion to the polymer substrate, but exhibited very poor flexural adhesion. It is believed that this is due to the absence of a urethane-based compound that serves to secure the flexibility of the printed layer.

Further, the printed layer according to Comparative Example 2, which did not contain an epoxy resin as a binder, showed poor adhesion to the polymer substrate in both plane and flexure. It is believed that this is due to the absence of an epoxy resin that serves to secure the adhesion of the printed layer.

In addition, it was confirmed that the printed layer according to Reference Example 1 in which the total content of the binder was more than 25 parts by weight of the composition had an excessively high content of the binder, so that the sheet resistance of the printed layer was significantly increased. In addition, the printed layer according to Reference Example 2 in which the total content of the binder is less than 15 parts by weight with respect to the composition has a very low sheet resistance value, but the content of the binder is too low, so that both the planar adhesion of the printed layer to the polymer substrate and the flexural adhesion are poor Appeared.

10: polyimide film
20: printed layer
30: plating layer

Claims (8)

Polyimide film; A printing layer provided on the polyimide film; And a plating layer provided on at least one surface of the printing layer,
In the printed layer, conductive particles are dispersed in a polymer matrix derived from a binder containing a urethane-based compound, an epoxy-based resin, and a polyester-based resin,
The polymer matrix is a cured product of a binder consisting of 30 parts by weight to 45 parts by weight of a urethane-based compound, 15 parts by weight to 30 parts by weight of an epoxy resin, and the balance of a polyester-based resin. delete The method according to claim 1,
The conductive particle is characterized in that it comprises a metal-based particle and a carbon-based particle, the flexible printed circuit board. The method according to claim 1,
The content of the conductive particles is characterized in that 70 parts by weight to 85 parts by weight based on 100 parts by weight of the printed layer, the flexible printed circuit board. The method according to claim 1,
The flexible printed circuit board, characterized in that the height of the printed layer is within the range of the average particle diameter of the conductive particles. The method according to claim 1,
The flexible printed circuit board, characterized in that the polyimide film is not provided with a surface coating layer. The method according to claim 1,
The plating layer is characterized in that it comprises two or more plating layers made of different metals, the flexible printed circuit board. The method of claim 6,
The plated layer is a copper plated layer, a nickel plated layer, a palladium plated layer and a gold plated layer, characterized in that provided in sequence, the flexible printed circuit board.

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