WO2016117720A1

WO2016117720A1 - Electromagnetic wave shielding sheet and manufacturing method of the same

Info

Publication number: WO2016117720A1
Application number: PCT/KR2015/000590
Authority: WO
Inventors: Seung Jin Yang; Shin Young Park; Yoon Hyun Kim
Original assignee: CHANG SUNG Co Ltd
Current assignee: CHANG SUNG Co Ltd
Priority date: 2015-01-20
Filing date: 2015-01-20
Publication date: 2016-07-28
Anticipated expiration: 2017-07-20
Also published as: KR20160103502A

Abstract

The present invention relates to an electromagnetic wave shielding sheet having an adhesive property, and more particularly, to an electromagnetic wave shielding sheet having an adhesive property and capable of improving electromagnetic wave shielding efficiency by adding epoxy and polyurethane to an electromagnetic wave shielding layer so as to control a sheet resistance as an index of a shielding property.

Description

ELECTROMAGNETIC WAVE SHIELDING SHEET AND MANUFACTURING METHOD OF THE SAME

Embodiments of the inventive concept relate to an electromagnetic wave shielding sheet, a manufacturing method of the same, and a forming method of the electromagnetic wave shielding sheet on a flexible printed circuit board, and more particularly, to an electromagnetic wave shielding sheet having an adhesive property and capable of securing a shielding characteristic with respect to an electromagnetic wave by obtaining an adhesive property and adjusting a sheet resistance with respect to a medium such as an FPCB (flexible printed circuit board), a manufacturing method of the same, and a forming method of the electromagnetic wave shielding sheet on the flexible printed circuit board.

A flexible printed circuit board (hereinafter, also referred to as "FPCB") may include a print circuit on at least one surface of a flexible insulating film such as a polyimide film or a polyester film with or without an adhesive interlaid therebetween. A flexible insulating film including an opening corresponding to a portion where a terminal for mounting a circuit component on an upper surface of the print circuit or a terminal for connection with an external substrate is formed may be attached with an adhesive as necessary. Alternately, a surface protective layer may be formed by forming an opening through coating, drying, exposing, developing, and heating processes to a photosensitive insulating resin.

In electronic devices such as mobile phones, video cameras, notebookcomputers, etc. of which miniaturization and high functionalization have been rapidly progressing in recent years, the FPCB has been used in various ways in order to insert a circuit into a complicated device. Further, with its excellent flexibility, the FPCB has been used to connect a moving unit such as a print head with a control unit. Electronic devices using an FPCB in various ways have been required to prepare a measure to shield an electromagnetic wave, and as for an FPCB used in a device, a shield flexible print circuit board (hereinafter, referred to as "shield FPCB") having a measure to shield an electromagnetic wave has been used.

For example, a shield FPCB disclosed in Patent Literature 1 is formed by coating a resin on one surface of a separate film so as to form a cover film (protective layer), laminating a shield layer on one side of the cover film (protective layer), and heating/pressing a shield film so as to attach the shield film while electrically connecting the shield layer to a ground circuit mounted on the FPCB with a conductive adhesive and then peeling off the separate film. However, even if the above-described processes are performed, an electromagnetic wave shielding film having an adhesive property and capable of effectively implementing the characteristic of the shield layer has not been achieved so far since adhesion with respect to the print circuit board is excessive or weak.

The present invention is conceived to solve the above-described problems, and directed to providing an electromagnetic wave shielding sheet having anadhesive property and capable of securing initial adhesion and a sheet resistance property by adding two elements epoxy and polyurethane to a conductive metal-based substance.

Further, the present invention is directed to providing a method for improvingelectromagnetic wave shielding performance by adding an epoxy resin to conductive metal powder to increase a cross-linkability in the metal powder and forming the electromagnetic wave shielding sheet on a flexible printed circuit board.

An electromagnetic wave shielding sheet having an adhesive property according to the present invention may include: a shielding layer including a conductive substance containing Ag and Cu, bisphenol A added to the conductive substance, a polymer substance containing CTBN modified epoxy and thermoplastic polyurethane, a curing accelerator, an epoxy curing agent, and a solvent; and an insulating layer formed on one surface of the shielding layer.

The insulating layer includes a resin containing 5 to 15 wt% of a polyurethane resin, 2 to 4 wt% of bisphenol A-type epoxy, and 2 to 5 wt% of isocyanate and a filler containing 1 to 3 wt% of carbon black and 2 to 5 wt% of alumina, and may include ethyl acetate as the solvent.

The electromagnetic wave shielding sheet having an adhesive property may have an initial adhesion of 300 to 500 gf/inch.

The electromagnetic wave shielding sheet having an adhesive property may have a sheet resistance of 100 to 200 mΩ/sq.

A manufacturing method of an electromagnetic wave shielding sheet having an adhesive property according to an exemplary embodiment of the present invention may include: (a) a step of forming a first protective film layer made of poly ethylene terephethalate (PET) (S10); (b) a step of preparing an insulating layer coating solution by mixing an insulating layer composition (S20); (c) a step of coating and drying the insulating layer coating solution on the first protective film layer (S30); (d) a step of preparing a shielding layer coating solution by mixing and dispersing a shielding layer composition (S40); (e) a step of coating the shielding layer coating solution on the insulating layer (S50); and (e) a step of laminating a second protective film layer on the shielding layer (S60).

A forming method of an electromagnetic wave shielding sheet on a flexible printed circuit board according to an exemplary embodiment of the present invention may include: (A) a step of removing the second protective film layer from the electromagnetic wave shielding sheet manufactured according to claim 6 (S110); (B) a step of temporarily bonding the electromagnetic wave shielding sheet, from which the second protective film layer is removed, to an upper surface of an FPCB (flexible printed circuit board) by way of hot pressing (S120); (C) a step of bonding the temporarily bonded electromagnetic wave shielding sheet to the upper surface of an FPCB by pressing at a high temperature (S130); and (D) a step of removing the first protective film layer from the electromagnetic wave shielding sheet (S140).

According to an electromagnetic wave shielding sheet having an adhesive property in an exemplary embodiment of the present invention, it is possible to appropriately adjust adhesion with respect to a metal layer, and, thus, a release property is excellent when the electromagnetic wave shielding sheet is attached to the metal layer. Further, the electromagnetic wave shielding sheet includes a conductive substance, and, thus, it is possible to provide the electromagnetic wave shielding sheet having an excellent electromagnetic wave shielding performance.

According to a forming method of an electromagnetic wave shielding sheet on a flexible printed circuit board in an exemplary embodiment ofthe present invention, an adhesive property between the electromagnetic wave shielding sheet and the flexible printed circuit board can be secured and an electromagnetic wave shielding property can be improved. Thus, it is possible to solve EMI by shielding an electromagnetic wave emitted from the flexible printed circuit board.

Figure 1 is a schematic diagram showing a configuration of an electromagnetic wave shielding sheet according to an exemplary embodiment of the present invention.

Figure 2 is a figure showing a device capable of performing an adhesive property test to an electromagnetic wave shielding sheet having an adhesive property according to an exemplary embodiment of the present invention.

Figure 3 provides figures respectively showing results of adhesive property tests according to Example 2 of the present invention and Comparative Examples 3 and 4.

Figure 4 is a graph comparing and showing the sheet resistance and an electromagnetic wave shielding property.

Figure 5 is a graph showing electromagnetic wave shielding efficiency according to an exemplary embodiment of the present invention.

Figure 6 provides figures showing a process of measuring a step coverage of an electromagnetic wave shielding sheet manufactured according to an exemplary embodiment of the present invention.

Figure 7 provides figures showing results of measurement of a step coverage according to Experimental Example 4.

Figure 8 schematically shows steps of forming an electromagnetic wave shielding sheet on an FPCB according to an exemplary embodiment of the present invention.

Advantages and features of the present invention, and inventions for accomplishing the same will be more clearly understood from exemplary embodiments described below with reference to the accompanying drawings. However, the present invention is not limited to the following exemplary embodiments but may be implemented in various different forms. The exemplary embodiments are defined only to complete disclosure of the present invention and to fully provide those skilled in the art to which the present invention pertains with the category of the invention. In the accompanying drawings, respective layers and regions may be exaggerated in size and relative size for clarity of explanation

Hereinafter, an electromagnetic wave shielding sheet according to an exemplary embodiment will be described in detail.

Figure 1 is a cross-sectional view of an electromagnetic wave shielding sheet according to an exemplary embodiment of the present invention.

An electromagnetic wave shielding sheet 100 according to an exemplary embodiment of the present invention may include: a shielding layer 130 including a conductive substance containing Ag and Cu, bisphenol A-type epoxy added to the conductive substance, a polymer substance containing CTBN modified epoxy and thermoplastic polyurethane, a curing accelerator, and an epoxy curing agent; and an insulating layer 120 formed on one surface of the shielding layer 130.

The resin contained in the conductive substance may function as a bonding material of the conductive substance with respect to the shielding layer 130. For the function as a bonding material of the conductive substance as described above, a polymer resin may be included.

The polymer resin may include a bisphenol A-type epoxy resin, a CTBN modified epoxy resin, and a thermoplastic polyurethane resin.

Bisphenol A is an organic compound prepared by condensation of one molecule of acetone and two molecules of phenol. The bisphenol A has been mainly used as a synthetic material of polycarbonate plastic and epoxy resins. The bisphenol A has a low resistance since it is greatly contracted during curing, and may impart adhesion when the electromagnetic wave shielding sheet according to the exemplary embodiment of the present invention is bonded.

The polyurethane resin may be a polyurethane prepolymer which is obtained by reacting organic isocyanate with polyol in the presence of a silicon modifier. The organic isocyanate may include those known in the art for preparing polyurethane and may be selected from aromatic, aliphatic, cycloaliphatic, and aromatic polyisocyanates. The polyol has a molecular weight Mw of 400 to 6000, preferably, 1000 to 4000, in order for the polyurethane resin to maintain viscosity at a certain level. It is desirable to use a product having -OH of 35 to 250, preferably, 35 to 180. The polyurethane resin may improve the adhesion of the electromagnetic wave shielding layer 130 according to the exemplary embodiment of the present invention. Further, the polyurethane resin may improve a surface characteristic of the electromagnetic wave shielding layer 130. At the time of release after a temporary bond, hard release can be achieved. If the polyurethane resin is increased, a sheet resistance of the electromagnetic wave shielding layer 130 may be decreased, and, thus, the electromagnetic wave shielding efficiency may be decreased.

The CTBN (Carboxylic Terminated Butadiene Acryylonitrile) modified epoxy resin is compatible with a typical epoxy resin and has an excellent adhesion strength and may have an excellent elasticity. The CTBN modified epoxy resin may improve workability of the electromagnetic wave shielding sheet 100 having an adhesive property and make it possible to softly release the electromagnetic wave shielding sheet 100 during a temporary bond.

Therefore, when the CTBN modified epoxy resin is added to DGEBA (diglycidyl ether of bisphenol A)-based epoxy, it is possibleto prevent brittle fracture by reducing a high cross-linking structure of DGEBA and also possible to improve flexibility, adhesion, etc. by mixing a liquid elastomer such as CTBN rubber.

The electromagnetic wave shielding sheet 100 having an adhesive property according to the exemplary embodiment of the present invention may include copper, silver, or silver-coated copper as the conductive filler. The silver, copper, or silver-coated copper may be contained in an amount of about 30 to 40 wt% with respect to the total weight of the shielding layer composition.

The silver-coated copper (Ag-coated Cu) may be in the form of dendrite, flake, or spherical copper powder coated with about 5 to 25 wt% of silver particles as a measure to solve the problem of high reactivity of copper occurring when copper is used solely. Since the silver-coated copper is contained in the composition of the electromagnetic wave shielding layer 130 having an adhesive property, it is possible to reduce reactivity of copper and improve an electromagnetic wave shielding property.

The shielding layer 130 may have a thickness of 5 to 20㎛.

If the thickness of the shielding layer 130 is smaller than 5㎛, the electromagnetic wave shielding performance may be decreased. If the thickness of the shielding layer 130 is greater than 20㎛, the shielding performance may be increased but flexibility may be decreased.

In addition, an epoxy curing agent or a curing accelerator may be further added.

As the curing accelerator, trimethyl phosphate may be included.

The electromagnetic wave shielding sheet 100 having an adhesive property according to the exemplary embodiment of the present invention may include the insulating layer 120.

The insulating layer 120 includes a resin containing 5 to 15 wt% of a polyurethane resin, 2 to 4 wt% of bisphenol A-type epoxy, and 2 to 5 wt% of isocyanate and a filler containing 1 to 3 wt% of carbon black and 2 to 5 wt% of alumina, and may include ethyl acetate as the solvent.

The filler included in the insulating layer 120 protects a surface of the shielding layer 130 and prevents a possibility of an electrical short from the external environment. The filler mixed in a resin composition can minimize resin flow occurring at a high temperature and minimize product modification caused by heat. Further, even under repeated sliding bending loads, the filler can prevent damage to the surface and the shape caused by physical wear.

The electromagnetic wave shielding sheet 100 having an adhesive property according to the exemplary embodiment of the present invention may include a second protective film layer 140 containing silicon-coated PET. The second protective film layer 140 may have an adhesive force of 200 gf/inch to 300 gf/inch.

The electromagnetic wave shielding sheet 100 may have an adhesive property. The adhesive property refers to a temporary bond of the sheet so as to be attachable to and detachable from the printed circuit board. In order for the electromagnetic wave shielding sheet 100 according to the exemplary embodiment of the present invention to have the adhesive property, the shielding layer 130 including the conductive filler may include an adhesive resin. The adhesive resin may include 10 to 30 wt% of bisphenol A-type epoxy, 2 to 10 wt% of CTBN modified epoxy, and 1 to 5 wt% of thermoplastic polyurethane with respect to the total weight of the shielding layer. Herein, any one or more of toluene, MEK (methyl ethyl ketone), and ethyl acetate may be mixed and used as the solvent. The solvents may be mixed so as to account for the rest of the weight.

(Example 1)

A first protective film layer 110 was formed to a thickness of 50㎛.

On the first protective film layer 110, an insulating layer 120 including 2.5 wt% of epoxy (bisphenol A-type), 10 wt% of polyurethane, 4 wt% of isocyanate, 5 wt% of polyamide,2 wt% of carbon black, 5 wt% of Al₂O₃, and 71.5 wt% of ethyl acetate was formed and then dried. A thickness of the insulating layer 120 was 6㎛.

On the insulating layer, a shielding layer composition including Ag-coated copper limited to 34.1 wt%, 20.9 wt% of bisphenol A-type epoxy, 1.9 wt% of CTBN modified epoxy, 1.9 wt% of thermoplastic polyurethane, 1.3 wt% of an epoxy curing agent, 1.3 wt% of a curing accelerator, and 38.6 wt% of ethyl acetate as an organic solvent was coated and then dried by heating. A thickness of the shielding layer 130 was 10㎛.

On the first protective film layer 110, the insulating layer 120, and the shielding layer 130, a second protective film layer 140 was formed of releasable PET coated with silicon. The second protective film layer 140 was formed to a thickness of 75㎛.

(Example 2)

An electromagnetic wave shielding sheet was manufactured under the same conditions as Example 1 except that a shielding layer composition included 19 wt% of bisphenol A-type epoxy, 3.8 wt% of CTBN modified epoxy, and 1.9 wt% of thermoplastic polyurethane.

(Example 3)

An electromagnetic wave shielding sheet was manufactured under the same conditions as Example 1 except that a shielding layer composition included 18.6 wt% of bisphenol A-type epoxy, 1.9 wt% of CTBN modified epoxy, and 3.8 wt% of thermoplastic polyurethane.

(Comparative Example 1)

An electromagnetic wave shielding sheet 100 was manufactured under the same conditions as Example 1 except that a shielding layer composition included 24.7 wt% of bisphenol A-type epoxy, 0 wt% of CTBN modified epoxy, and 0 wt% of thermoplastic polyurethane.

(Comparative Example 2)

An electromagnetic wave shielding sheet 100 was manufactured under the same conditions as Example 1 except that a shielding layer composition included 20.9 wt% of bisphenol A-type epoxy, 3.8 wt% of CTBN modified epoxy, and 0 wt% of thermoplastic polyurethane.

(Comparative Example 3)

An electromagnetic wave shielding sheet 100 was manufactured under the same conditions as Example 1 except that a shielding layer composition included 17.1 wt% of bisphenol A-type epoxy, 3.8 wt% of CTBN modified epoxy, and 3.8 wt% of thermoplastic polyurethane.

(Comparative Example 4)

An electromagnetic wave shielding sheet 100 was manufactured under the same conditions as Example 1 except that a shielding layer composition included 20.9 wt% of bisphenol A-type epoxy, 0 wt% of CTBN modified epoxy, and 3.8 wt% of thermoplastic polyurethane.

(Experimental Example 1)

An adhesive property test was performed to the electromagnetic wave shielding sheets respectively manufactured under the conditions of Examples 1 to 3 and Comparative Examples 1 to 4.

The adhesive property refers to a temporary bond of the sheet so as to be attachable to and detachable from the printed circuit board. The adhesive property can be measured as initial adhesion (gf/inch).

Referring to Figure 2, the adhesive property test can be performed with a universal testing machine.

The adhesive property test was performed after the first protective film layer 110, the insulating layer 120, and the shielding layer 130 laminated in sequence were attached to a polyimide (KEPTON) film 150.

In order to perform the adhesive property test, the electromagnetic wave shielding sheet 100 was manufactured to 20 mm across ×100 mm wide and attached to the polyimide (Kapton) film of 25㎛ and then pressed under the hot pressing conditions (1000 gf/cm²) for 10 seconds. Then, under the conditions of 23℃ and a relative humidity of 50%, a 180 degree peel test was performed at a tension speed of 60 mm/min using a universal testing machine.

According to a result of the adhesive property test, in Comparative Examples 1 and 2 where thermoplastic polyurethane or CTBN modified epoxy was not included, the initial adhesion was not measured. This confirmed that thermoplastic polyurethane and CTBN modified epoxy are essential elements to attach the electromagnetic wave shielding sheet 100 to a flexible printed circuit board 200.

Referring to Figure 3, it can be seen that in Example 2, the electromagnetic wave shielding sheet 100 is softly released from the polyimide (PI) during the adhesive property test. However, it can be seen that in Comparative Example 3, adhesion between the shielding layer 130 and the polyimide (PI) is strong, and, thus, the first protective film layer 110 is peeled from the insulating layer 120. A black area in Figure 3(b) is a part of the insulating layer 120 from which the first protective film layer 110 is peeled.

Figure 3(c) relates to Comparative Example 4 where CTBN modified epoxy is not included but only thermoplastic urethane is included. In this case, it can be seen that the shielding layer 130 is stuck to the polyimide film 150. Such a phenomenon may cause a decrease in step coverage of the electromagnetic wave shielding sheet 100.

It can be seen that Comparative Example 4 where CTBN modified epoxy is not included has a high initial adhesion value (500 gf/inch) due to addition of 3.8 wt% of thermoplastic polyurethane, but does not have flexibility, and, thus, it is released hard during the adhesive property test and a shielding composition of a surface of the shielding layer 130 is stuck to a surface of the PI film.

(Experimental Example 2)

Measurement of a sheet resistance was conducted on the electromagnetic wave shielding sheets 100 respectively manufactured according to Examples 1 to 3 and Comparative Examples 1 to 4.

In order to measure a fabric conductivity of the electromagnetic wave shielding sheet 100, the second protective film layer 140 of the electromagnetic wave shielding sheet 100 was removed and then hot-pressed (pressed at a temperature of 150℃ under a pressure of 40 kgf/cm²for 1 hour) to a release paper layer. Then, a conductivity of the shielding sheet 100 was measured using a 4-point terminal measurement method (Mitsubishi Chemical. Co., apparatus: Loresta GP).

Table 1 shows a sheet resistance, electromagnetic wave shielding efficiency, initial adhesion, a status of a released surface, and presence or absence of a step crack.

Table 1

	Sheet resistance(mΩ/sq)	Shielding efficiency(dB＠1GHz)	Initial adhesion (gf/inch)	Peel testStatus of released surface after	StepCrackPresence or absence
Example 1	170	53,4	350	clean	x
Example 2	179	52.4	450	clean	x
Example 3	201	49.8	600	clean	x
Comparative Example 1	122	58.2	0	clean (No sticking)	o
Comparative Example 2	171	53,5	0	clean (No sticking)	x
Comparative Example 3	398	39.9	700	Protective film peeled off	x
Comparative Example 4	191	50.8	500	Shielding layer stuck	o

As can be seen from Table 1, in Examples 1 to 3, a sheet resistance was measured at 100 to 200 mΩ/sq. Meanwhile, it can be seen that in Comparative Examples 1 and 2, even if a sheet resistance meets the standard, plastic polyurethane is not contained and initial adhesion is not expressed, and, thus, the electromagnetic wave shielding sheet 100 cannot be used in a flexible printed circuit board.

It can be seen that in Comparative Example 3, in spite of a satisfactory initial adhesion, a sheet resistance is measured at 398 mΩ/sq,and, thus, the performance as a shielding sheet is not satisfactory.

(Experimental Example 3)

Measurement of electromagnetic wave shielding performance was conducted on the electromagnetic wave shielding sheets respectively manufactured according to Examples 1 to 3 and Comparative Examples 1 to 4.

Referring to Figure 4, it can be seen that as a sheet resistance increases, shielding efficiency decreases.

Generally, the following standard is applied to a level of a shielding effect. In a range from about 0 dB to about 10 dB, there is little shielding effect, and in a range from about 10 dB to about 30 dB, there is a shielding effect to a certain extent or more. Further, in a range from about 30 dB to about 60 dB, an average shielding effect can be expected, in a range from about 60 dB to about 90 dB, a shielding effect is above the average, and in a range of about 90 dB or more, almost all of electromagnetic waves can be shielded. Generally, it is known that electromagnetic wave shielding sheets using metals have a shielding effect of about 60 dB or more.

As for the electromagnetic wave shielding sheet according to the present invention, it was determined that shielding efficiency is not good in a range of 50 dB or less.

As can be seen from Figure 5, in Comparative Example 1(3) where only bisphenol A-type epoxy was employed, due to a high cross-linking density, the resin was greatly contracted during curing, which is advantageous to contacts in powder. Thus, the sheet resistance value was low and the shielding efficiency was the highest and measured at 58.2 dB. In Comparative Example 2(2) where 3.8 wt% of CTBN modified epoxy was mixed, due to addition of epoxy modified into CTBN as a liquid elastomer, a cross-linking density was slightly lower than that of bisphenol A-type epoxy, and, thus, the sheet resistance value was increased to 171 mΩ/sq and the shielding efficiency was decreased to 53.5 dB. In Comparative Example 3(1) where CTBN modified epoxy and thermoplastic polyurethane were mixed together in an amount of 3.8 wt% each, the resistance was remarkably increased as compared with Comparative Examples 1 and 2, and, thus, the measured shielding efficiency was low, which seems to be caused by effects of thermoplastic polyurethane which was not involved in cross-linking and CTBN modified epoxy decreased in cross-linking density. It can be seen that in order to reach 50 dB as a target electromagnetic wave shielding efficiency, it is necessary to mix appropriate amounts of a CTBN modified epoxy resin and a thermoplastic polyurethane resin with a bisphenol A-type resin as shown the results of the electromagnetic wave shielding efficiency in Examples 1 to 3(4).

That is, it can be seen that the adhesive property and the electromagnetic wave shielding property can be controlled by varying the amounts of bisphenol A-type epoxy,CTBN modified epoxy, and thermoplastic polyurethane in the shielding layer 130 of the present invention.

(Experimental Example 4)

Presence or absence of a step crack was checked by varying the amounts of bisphenol A-type epoxy, CTBN modified epoxy, and thermoplastic polyurethane in shielding layers 130 respectively included in an exemplary embodiment of the present invention and Comparative Example.

Referring to Figure 6, two FR-4 substrates 160 each having a thickness of 0.2 mm were placed with a gap of 2 cm on a polyimide (PI) film 150 and bonded to the PI film 150 under hot pressing conditions (at 150℃ under a pressure of 40 kgf/cm² for 1 hour). A electromagnetic wave shielding sheet 100 manufactured into 2 cm wide 10 cm long was placed on a plate including a step and bonded under hot pressing conditions (at 150℃ under a pressure of 40 kgf/cm² for 1 hour). Finally, a first protective film layer 110 was removed, and the stepped portion was observed with a microscope to check presence or absence of a crack.

Referring to Figure 7, it can be seen that in Examples 1 to 3, a crack did not occur at the stepped portion, but in Comparative Examples 1 and 4 among Comparative Examples 1 to 4, a crack occurred. It can be seen that the above-described result is caused by a decrease in flexibility since CTBN modified epoxy is not added.

Hereinafter, a manufacturing method of an electromagnetic wave shielding sheet according to an exemplary embodiment of the present invention will be described in detail.

A manufacturing method of an electromagnetic wave shielding sheet according to an exemplary embodiment of the present invention may include: (a) a step of forming a first protective film layer 110 made of poly ethylene terephethalate (PET) (S10); (b) a step of preparing an insulating layer coating solution by mixing an insulating layer composition (S20); (c) a step of coating and drying the insulating layer coating solution on the first protective film layer 110(S30); (d) a step of preparing a shielding layer coating solution by mixing and dispersing a shielding layer composition (S40); (e) a step of coating the shielding layer coating solution on the insulating layer 120 (S50); and (e) a step of laminating a second protective film layer on the shielding layer (S60).

Preferably, a matted release film may be used as the first protective film layer 110. The matted release film may be a matted PET film. Examples of a method of matting a PET film include a method of forming a matted layer on a surface of a typical PET film to form a dual structure and a method of matting a PET film itself to form a single structure. The matted PET film is rough (surface roughness of 30% or more) as compared with the typical PET film. Therefore, the matted PET film has a small adhesive surface and a small contact area and thus has a high peeling force and is stable in change with lapse of time.

Preferably, the first protective film layer 110 may have adhesion of 180 gf/in or more and less than 250 gf/in. If the adhesion is less than 180 gf/in, the first protective film layer 110 may be peeled off more easily than the second protective film layer 140 attached on the shielding layer 130, and, thus, it may be difficult to perform a bonding operation with respect to a printed circuit board (PCB). If the adhesion is more than 250 gf/in, it may be difficult to perform a release operation after attachment of the electromagnetic wave shielding sheet 100 by way of hot pressing.

The step (S20) of coating and drying the insulating layer composition on the first protective film layer 110 may be performed. The insulating layer composition includes a resin containing 5 to 15 wt% of a polyurethane resin, 2 to 4 wt% of bisphenol A-type epoxy, and 2 to 5 wt% of isocyanate and a filler containing 1 to 3 wt% of carbon black and 2 to 5 wt% of alumina, and may include ethyl acetate as the solvent.

After the insulating layer composition is formed on the first protective film layer 110, the step (S20) of coating the insulating layer composition may include coating with a microgravure coater or a slot die.

The microgravure coater enables continuous process and mass production unlike coating methods such as ESD (electro static deposition), aerosol jetting using an air pressure, etc. In particular, unlike the ESD coating method or the aerosol jetting method using an air pressure, it is possible to form a film layer having a stable surface roughness after a coating process. The microgravure coating methodis a kind of simple precise coating method in which a radius of a coating roll is reduced to minimize a wrap angle between a fabric and the coating roll during a kiss coating operation, thereby minimizing a vortex range of paint and ink on the roll surface and processed fabric, and, thus, the paint and ink is uniformly coated in a thin film.

Slot die coating refers to supplying a liquefied fluid (slurry, an adhesive, a hard coating agent, ceramic, etc.) to a space between upper and lower mold plates having the interior designed by Rheology called slot die and processed, by using a pulseless pump or a piston pump to coat the fluid supplied through a liquid supply pipe with a uniform thickness in a widthwise direction of a proceeding direction of a fabric, a film, a glass plate, or a sheet.

The above-described insulating layer 120 can be formed in a semi-cured state by drying the insulating layer 120 at a temperature of 100 to 150℃.

On the insulating layer 120 formed as described above, a shielding layer composition may be formed by the same method as the method of coating the insulating layer. The insulating layer may be formed to a thickness of 3 to 10㎛ .

The shielding layer 130 may be electrically conductive and may have adhesiveness. The shielding layer 130 is designed to have adhesiveness in order to improve a bonding force with respect to a flexible printed circuit board.

The electromagnetic wave shielding layer 130 may include a polymer resin in order to improve adhesion. The polymer resin may include a bisphenol A-type epoxy resin, a CTBN modified epoxy resin, and a thermoplastic polyurethane resin.

A process of coating the shielding layer composition using a slot die coater or a comma coater and drying the shielding layer composition at 100 to 150C may be included. Through the above-described drying process, a shielding layer 130 in a semi-cured state can be formed.

After the shielding layer 130 is formed as described above, the second protective film layer 140 may be laminated. As thesecond protective film layer 140, a silicon-coated PET release film may be used.

Hereinafter, a forming method of an electromagnetic wave shielding sheet having an adhesive property on a flexible printed circuit board according to an exemplary embodiment of the present invention will be described in detail.

A forming method of an electromagnetic wave shielding sheet on a flexible printed circuit board according to an exemplary embodiment of the present invention may include: (A) a step of removing the second protective film layer 140 from the manufactured electromagnetic wave shielding sheet (S110); (B) a step of temporarily bonding the electromagnetic wave shielding sheet 100, from which the second protective film layer 140 is removed, to an upper surface of an FPCB (flexible printed circuit board) by way of hot pressing (S120); (C) a step of bonding the temporarily bonded electromagnetic wave shielding sheet 100 to the upper surface of an FPCB 200 by pressing at a high temperature (S130); and (D) a step of removing the first protective film layer 110 from the electromagnetic wave shielding sheet 100 (S140). The flexible printed circuit board 200 may include a stepped portion, including an FR-4 (Flame Retardant-4), on a surface layer. The FR-4 refers toa laminate of glass fiber in which an epoxy resin is immersed.

Referring to Figure 8, the second protective film layer 140 can be removed from the electromagnetic wave shielding sheet 100 having an adhesive property (S110). The electromagnetic wave shielding sheet 100 from which the second protective film layer 140 is removed can be temporarily bonded to the flexible printed circuit board 200 (S120). The temporary bonding step is maintained at a temperature of 40 to 80℃ under a pressure of 1000 gf/cm² for 1 minute.

The temporarily bonded electromagnetic wave shielding sheet 100 can be bonded under hot pressing conditions (maintained at 120 to 200℃ under 30 to 50 kgf/cm² for 1 hour) (S130). Through the above-described bonding step, the shielding layer 130 can be attached to the surface of the FPCB 200.

The first protective film layer 110 can be removed from the electromagnetic wave shielding sheet 100 after the bonding step. The first protective film layer 110 has a low bonding force, and, thus, it can be easily removed.

Although the present invention has been described with reference to the accompanying drawings, this is just one of various exemplary embodiments including the subject matter of the present invention and intends to allow those skilled in the art to easily implement the present invention. It is clear that the present invention is not limited to the above-described exemplary embodiments. Therefore, the scope of the present invention should be construed by the following claims. Without departing from the subject matter of the present invention, all the technical spirits within the scope equivalent to the subject matter of the present invention is included in the right scope of the present invention by modifications, substitutions, changes, and the like. Also, it is clear that some of the drawing configuration are intended for more clearly describing the configuration and are more exaggerated or shortened than the actual ones.

Embodiments of the inventive concept relate to an electromagnetic wave shielding sheet, a manufacturing method of the same, and a forming method of the electromagnetic wave shielding sheet on a flexible printed circuit board.

Claims

An electromagnetic wave shielding sheet having an adhesive property comprising:

a shielding layer including a conductive substance containing Ag and Cu, bisphenol A-type epoxy added to the conductive substance, a polymer substance containing CTBN modified epoxy and thermoplastic polyurethane, a curing accelerator, and an epoxy curing agent; and

an insulating layer formed on one surface of the shielding layer.
The electromagnetic wave shielding sheet having an adhesive property of claim 1,

wherein the insulating layer includes a resin containing 5 to 15 wt% of a polyurethane resin, 2 to 4 wt% of bisphenol A-type epoxy, and 2 to 5 wt% of isocyanate and a filler containing 1 to 3 wt% of carbon black and 2 to 5 wt% of alumina, and includes ethyl acetate as a solvent.
The electromagnetic wave shielding sheet of claim 1,

wherein the conductive substance containing Ag and Cu has the form of Cu coated with Ag, and

the Cu is in the form of dendrite, flake, or sphere.
The electromagnetic wave shielding sheet having an adhesive property of claim 1,

wherein the electromagnetic wave shielding sheet has an initial adhesion of 300 to 500 gf/inch.
The electromagnetic wave shielding sheet having an adhesive property of claim 1,

wherein the electromagnetic wave shielding sheet has a sheet resistance of 100 to 200 mΩ/sq.
A manufacturing method of an electromagnetic wave shielding sheet comprising:

(a) a step of forming a first protective film layer made of poly ethylene terephethalate (PET) (S10);

(b) a step of preparing an insulating layer coating solution by mixing an insulating layer composition (S20);

(c) a step of coating and drying the insulating layer coating solution on the first protective film layer (S30);

(d) a step of preparing a shielding layer coating solution by mixing and dispersing a shielding layer composition (S40);

(e) a step of coating the shielding layer coating solution on the insulating layer (S50); and

(e) a step of laminating a second protective film layer on the shielding layer (S60).
The manufacturing method of an electromagnetic wave shielding sheet having an adhesive property of claim 6,

wherein the first protective film layer is a matted release liner.
The manufacturing method of an electromagnetic wave shielding sheet having an adhesive property of claim 6,

wherein in the step (S20) of coating and drying the insulating layer composition on the first protective film layer,

the insulating layer composition includes a resin containing 5 to 15 wt% of a polyurethane resin, 2 to 4 wt% of bisphenol A-type epoxy, and 2 to 5 wt% of isocyanate and a filler containing 1 to 3 wt% of carbon black and 2 to 5 wt% of alumina, and includes ethyl acetate as a solvent, and

the step of coating includes coating with a microgravure coater or a slot die.
The manufacturing method of an electromagnetic wave shielding sheet having an adhesive property of claim 6,

wherein in the step (S50) of coating the shielding layer coating solution on the insulating layer,

the shielding layer coating solution includes a conductive substance containing Ag and Cu, bisphenol A-type epoxy added to the conductive substance, a polymer substance containing CTBN modified epoxy and thermoplastic polyurethane, a curing accelerator, an epoxy curing agent, and a solvent, and

the shielding layer coating solution is coated using a slot die coater or a comma coater and dried at 100 to 150℃.
The manufacturing method of an electromagnetic wave shielding sheet of claim 6,

wherein the shielding layer has a thickness of 5 to 20㎛.
A forming method of an electromagnetic wave shielding sheet on a flexible printed circuit board comprising:

(A) a step of removing the second protective film layer from the electromagnetic wave shielding sheet manufactured according to claim 6 (S110);

(B) a step of temporarily bonding the electromagnetic wave shielding sheet, from which the second protective film layer is removed, to an upper surface of an FPCB (flexible printed circuit board) by way of hot pressing (S120);

(C) a step of bonding the temporarily bonded electromagnetic wave shielding sheet to the upper surface of an FPCB by pressing at a high temperature (S130); and

(D) a step of removing the first protective film layer from the electromagnetic wave shielding sheet (S140).
The forming method of an electromagnetic wave shielding sheet on a flexible printed circuit board of claim 11,

wherein the flexible printed circuit board includes a stepped portion, including a FR-4, on a surface layer.
The forming method of an electromagnetic wave shielding sheet on a flexible printed circuit board of claim 11,

wherein the step (S120) of temporarily bonding the electromagnetic wave shielding sheet, from which the second protective film layer is removed, to the upper surface of the FPCB is performed at 40 to 80℃.
The forming method of an electromagnetic wave shielding sheet on a flexible printed circuit board of claim 11,

wherein the step (S130) of bonding the temporarily bonded electromagnetic wave shielding sheet to the upper surface of the FPCB by pressing at a high temperature is performed at a temperature of 120 to 200℃ .under a pressure of 30 to 50kgf/cm².