TWI526150B - An electromagnetic wave shielding film, a flexible substrate using the same, and a method for manufacturing the flexible substrate - Google Patents

Description

Electromagnetic wave shielding film, flexible substrate using the same, and manufacturing method of the same

The present invention relates to an electromagnetic wave shielding film, a flexible substrate using the same, and a method of manufacturing the same, and more particularly to an electromagnetic wave shielding film which can maintain an electromagnetic wave shielding effect after long-term sliding, and is formed using the same. A flexible substrate with electromagnetic wave shielding, and a method of manufacturing the flexible substrate.

The technology that has been hitherto has been to form an electromagnetic wave shielding film on a flexible substrate (FPC) disposed on a mobile phone hinge portion or the like to shield electromagnetic waves. The electromagnetic wave shielding film contains at least a conductive layer and a protective layer, and the conductive layer is formed by using a conductive adhesive (conductive paste) in which a metal powder is dispersed in a binder resin.

Such an electromagnetic wave shielding film is required to be thinner than ever with the thinning of a mobile phone. However, as long as other conditions are the same, the filming property is reduced as the filming property is lowered. . In addition, since it is a flexible substrate to be shielded by electromagnetic waves, it is used for a mobile phone or the like because it is used for bending and sliding. Therefore, as the use period increases, the electromagnetic wave shielding effect is lowered. Therefore, its solution is also expected.

In order to improve the performance of the electromagnetic wave shielding film, much work has been done on the shape and particle diameter of the metal particles. For example, in Patent Document 1, in order to improve conductivity, adhesion, and shielding of electromagnetic waves, it is disclosed that silver particles having an average particle diameter of 0.5 μm to 20 μm and granular silver particles having an average particle diameter of primary particles of 50 nm or less are required. Use under a certain ratio. Further, in Patent Document 2, in order to obtain a conductive paste composition which satisfies the bending characteristics required for a flexible substrate, it is disclosed that scaly silver powder having an average particle diameter of 2.0 to 5.0 μm and an average particle diameter of 10 to 19 μm are used. A mixed powder of dendritic silver-plated copper powder.

However, the current state of the art is that it has not been able to obtain an electromagnetic wave shielding film that has been bent for hundreds of thousands of times and still has sufficient electromagnetic shielding properties after sliding.

Prior technical literature

Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-294254

Patent Document 2: Japanese Laid-Open Patent Publication No. 2009-230952

In view of the above, an object of the present invention is to provide an electromagnetic wave shielding film which has excellent electromagnetic wave shielding properties even when it is thinned, and which is used for bending and sliding frequently, such as a hinge portion of a mobile phone. The initial electromagnetic wave shielding can also last for a long time. Further, a flexible substrate in which an electromagnetic wave shielding layer is formed using the film and a method of manufacturing the flexible substrate are provided.

That is, the electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film formed by laminating a protective layer on a conductive layer composed of (A) metal powder and (B) a binder resin, and in order to solve the above problems, the conductive layer is contained ( a) and (b) formed as a conductive paste of the metal powder, wherein (a) is a flaky metal powder having an average thickness of 50 to 300 nm and an average particle diameter of 3 to 10 μm, and (b) an average particle diameter of 3 to 3 Needle or dendritic metal powder of 10 μm.

In the electromagnetic wave shielding film, the ratio of the (A) metal powder to the (B) binder resin is in the range of A:B=50:50 to 80:20 by weight ratio (however, in terms of solid form) The ratio of the above (a) flaky metal powder to (b) acicular or dendritic metal powder is preferably in the range of a:b = 20:80 to 80:20 by weight.

In the manufacturing method of the flexible substrate of the present invention, the electromagnetic wave shielding film of the present invention is placed on the flexible substrate, and then the flexible substrate is heated together with the electromagnetic shielding film while being pressed in the thickness direction. A method of forming an electromagnetic wave shielding layer on a substrate.

Further, the flexible substrate of the present invention is one which comprises an electromagnetic wave shielding layer composed of the electromagnetic wave shielding film of the present invention.

The electromagnetic wave shielding film of the present invention has an excellent electromagnetic wave shielding effect, and when the electromagnetic wave shielding layer is mounted on the flexible substrate, electromagnetic wave shielding capable of maintaining a high level even after bending or sliding for several hundred thousand times can be obtained. The effect.

Moreover, according to the method of manufacturing a substrate provided with an electromagnetic wave shielding layer according to the present invention, the flexible substrate having the electromagnetic wave shielding layer having a long-lasting superior electromagnetic wave shielding effect can be easily obtained.

Simple illustration

Fig. 1 is a schematic end view showing a method of measuring sheet resistance.

Fig. 2 is a schematic end view showing the method of measuring the connection resistance, and (b) is a partial enlarged view of (a).

Figure 3 shows a schematic end view of the method of the sliding test.

Form for implementing the invention

Hereinafter, the electromagnetic wave shielding film of the present invention and a method of manufacturing the flexible substrate using the same will be described in detail.

As described above, the electromagnetic wave shielding film of the present invention contains at least a conductive layer and a protective layer composed of a metal powder and a binder resin, and is used as a metal powder in combination with a flaky metal powder and a needle-like or dendritic metal powder. Its characteristics.

In the present invention, the term "sheet-like metal powder" is generally referred to as a scaly shape or a sheet shape, and the shape of the flat surface is not particularly limited as long as it is a flat plate shape. The scaly metal powder formed by various shapes of particles or crushed or crushed is suitable for use because it is advantageous in terms of cost or productivity.

The type of metal of the flaky metal powder includes gold, silver, silver plated copper, copper, nickel, etc., of which silver or silver plated copper is preferred. Further, the flaky metal powder preferably has an average thickness of 50 to 300 nm and an average particle diameter of 3 to 10 μm. When the average thickness is more than 300 nm, the melting point of the flaky metal powder is not easily lowered; and if the average thickness is less than 50 nm, the production cost is greatly increased. Further, when the average particle diameter is more than 10 μm, the dispersibility is lowered. When the average particle diameter is less than 3 μm, the conductivity tends to decrease when the filler is low.

On the other hand, the "needle-like or dendritic metal powder" may be needle-shaped, dendritic (dendritic), or a mixture of the two. The term "dendritic shape" as used herein is not limited to those having a branch portion which can be clearly identified as a dendritic portion, and includes those having a protrusion like a gold-sweet sugar or a protrusion having a shape of various sizes. The type of the acicular or dendritic metal powder is also the same as described above, and there are gold, silver, silver plated copper, copper, nickel, etc., of which silver-plated copper is preferred. The size is preferably in the range of 3 to 10 μm in the average particle diameter. When the average particle diameter is more than 10 μm, the film formation of the masking film becomes difficult. When the average particle diameter is less than 3 μm, the formation of the protrusion shape of the metal powder becomes difficult.

The average particle diameter or average thickness of the aforementioned metal powder can be measured by a laser diffraction scattering method.

By using a flaky metal powder together with a needle-like or dendritic metal powder as described above, when using any of these metal powders alone or in combination with other shapes (for example, flaky metal powder and spherical metal) The powder is used in combination, and the durability of the electromagnetic wave shielding effect of the repeated bending and sliding can be considered to be significantly improved. In the conventional technique, the increase in the shielding effect with time is considered to be caused by the deterioration of the film and the deterioration of the contact state of the metal particles of the conductive layer. From this, it is presumed that when the flaky metal powder is used in combination with the acicular or dendritic metal powder, the acicular or dendritic metal powder forms a physical bond of spurs or the like in the flaky metal powder portion. Further, by the step of simultaneously pressing at the time of heating, the metal powder should produce a metal bond or a strong bond with it. Further, the bonding strength should be made stronger by the step of reflowing described later.

The flaky metal powder (a) and the acicular or dendritic metal powder (b) are preferably used in a ratio of a:b=20:80 to 80:20 by weight ratio. When the ratio of the acicular or dendritic metal powder to the flaky metal powder does not exceed the above range, the decrease in conductivity due to bending or sliding becomes large. That is, the shadowing effect is greatly reduced.

Next, as the binder resin, a thermosetting resin such as an epoxy resin, a polyurethane resin, an acrylic resin, a polyimide resin, a phenol resin, or a melamine resin can be used without particular limitation. Among them, polyurethane resins are favorably used because of their superior flexibility.

The addition ratio of the above (A) metal powder and (B) binder resin is preferably in the range of A:B=50:50 to 80:20 by weight ratio (however, it is converted in a solid form), and the weight ratio is preferably It is preferably in the range of A:B=55:45 to 70:30. When the weight ratio of the metal powder is less than 50%, the display of conductivity becomes difficult; and if the weight ratio is more than 80%, the flexibility or the adhesion is lowered.

The method for producing an electromagnetic wave shielding film from the metal powder and the binder resin is not particularly limited. For example, the paste made of the metal powder and the binder resin is prepared, and coated on a release paper or the like to form a conductive layer. The film. The thickness of the film is preferably 8 to 28 μm, and preferably 5 to 25 μm after the press step described later. If the thickness after the press step is less than 5 μm, it is difficult to obtain sufficient electromagnetic shielding, and if the thickness exceeds 25 μm, it is not suitable for the film formation.

A well-known additive which does not depart from the object of the present invention may be added to the aforementioned conductive layer as needed. Examples of the additive include a flame retardant, a leveling agent, a viscosity adjuster, and the like. As the flame retardant, an inorganic or organic flame retardant such as a phosphorus system can be suitably used.

The electromagnetic wave shielding film of the present invention can be obtained by laminating a film constituting a protective layer on a film constituting the above-mentioned conductive layer. Alternatively, a film constituting the protective layer may be formed first, and a film constituting the conductive layer may be laminated on the film.

The film constituting the protective layer may be formed of an epoxy resin, a polyurethane resin or the like. In addition, it is preferable that the surface hardness of the protective layer is from H to 4H, and a surface-hardened layer such as a ketone system may be laminated on the layer composed of the epoxy resin or the polyurethane resin as needed. When the surface hardness of the protective layer is less than the pencil hardness H, the film is easily damaged. On the other hand, if it is larger than 4H, the flexibility is small and the sliding property is lowered.

Further, the thickness of the film constituting the protective layer is preferably from 3 to 15 μm, and is preferably from 2 to 12 μm after the press step described later. If the thickness after the press step is less than 2 μ, the strength of the protective layer is insufficient, and if it exceeds 12 μm, it is not preferable for the film formation.

In addition, as for the entire electromagnetic wave shielding film, the thickness before the pressing step described later is preferably 11 to 30 μm, and preferably 7 to 28 μm after the pressing step.

Next, as a method of producing a flexible substrate of the present invention, the electromagnetic wave shielding film of the present invention can be placed on a flexible substrate, and a press step of pressurizing at a pressure of 1 to 5 MPa at the same time as heating can be applied to the flexible substrate. An electromagnetic wave shielding layer is formed thereon. The heating temperature in the pressing step is preferably 140 to 200 °C.

Further, by applying the reflow step to the flexible substrate in which the electromagnetic wave shielding layer is formed by the press step, the sliding property can be more significantly improved. The conditions for the reflow can be carried out under the condition that the weld bead is melted, and although it is not particularly limited, it is usually about 260 ° C for 4 seconds. Since the melting point of the metal through the thin film is lowered, the flaky metal powder used in the present invention, for example, a high melting point metal such as silver having a melting point of 962 ° C, is melted by a reflow step in this temperature range. This results in the aforementioned metal bond or a strong bond to which it is.

Further, the electromagnetic wave shielding film of the present invention is excellent in adhesion to the flexible substrate to be coated, and preferably has a bonding strength of 2° or more with respect to the polyimide.

Example

Embodiments of the invention are disclosed below, but the invention is not limited to the following examples.

[Examples, Comparative Examples]

By coating a 6 μm thick epoxy resin on the release film, after drying, the acrylic surface hardening treatment liquid is applied thereon, and after drying, the epoxy soft layer and the acrylic system are formed. A protective layer composed of a two-layer structure of the surface-hardened layer (symbol 1 in the first and second figures to be described later). The conductive paste prepared by applying the ratios shown in Tables 1 and 2 was applied to the protective layer, and after drying, a conductive layer was formed (the same as in the first drawing and the second reference numeral 2) to obtain an electromagnetic wave shielding film. The following evaluation was carried out using the electromagnetic wave shielding film obtained thereby. The details of the binder resin and metal powder used are as follows.

Adhesive resin: Da Ri Jing Chemical Industry Co., Ltd., polyurethane resin UD1375

Metal powder: (a) scaly silver powder: average thickness 100 nm, average particle diameter 5 μm, melting point about 250 ° C

(b) Dendritic silver-plated copper powder: average particle size 5 μm

However, in Comparative Example 3, spherical silver-plated copper powder (average particle diameter: 6 to 7 μm) was used instead of (b) dendritic silver-plated copper powder.

(1) sheet resistance

The cube-shaped electrodes A and B shown in Fig. 1 were placed on the conductive layer 2 (electrode area: 1 cm ² (L1 = L2 = L3 = 1 cm), electrode spacing d = 1 cm, electrode surface: gold plating treatment) The electrode was added with a weight of 4.9 N in the direction indicated by the arrow, and the resistance between the AB electrodes was measured by a 4-terminal method, and the value after 1 minute from the start of the measurement was used as the electric resistance. The atmospheric temperature was measured to be 18 to 28 ° C, and a cut sample of 249 mm × 50 mm was used for measurement. Table 1 shows the average number of experiments with n=5.

(2) 180° peel strength

The conductive layer of the electromagnetic wave shielding film was attached to the test plate via a polyimide film (Toray, DuPont, Kaitong 100H (trade name)), and the protective layer side was also pasted with the adhesive layer. The upper polyimine film (with Kaitong 100H) was peeled off from the polyimide film at 50 mm/min. Table 1 shows the average number of experiments with n=5.

(3) Connection resistance

The above-mentioned electromagnetic wave shielding film was placed on a flexible printed circuit board (thickness: 53.5 μm), heated at 170 ° C for 30 minutes, and pressed at a pressure of 3 MPa to prepare a sample for evaluation of a flexible substrate (FPC). The electromagnetic wave shielding film having the cross-sectional shape shown in Figs. 2(a) and (b) is provided, and then reflowing is performed five times. In Figs. 2(a) and 2(b), reference numeral 1 denotes a protective layer of an electromagnetic wave shielding film, and reference numeral 2 denotes a conductive layer. Further, reference numeral 3 denotes a polyacrylonitrile layer of FPC (thickness: 12.5 μm), reference numeral 4 denotes a copper layer (Cu: 18 μm), and reference numeral 5 denotes an electroless nickel-gold plating layer (Ni: 3 to 5 μm, Au: 0.05 to 0.1) Μm), symbol 6 denotes an adhesive layer (thickness 35 μm), and symbol 7 denotes a polyimide layer (thickness 25 μm). a is the bottom diameter. (b) is an enlarged view of the bottom of (a). The bottom diameter (a) was measured at 0.5 mm ψ, 0.8 mm ψ, and 1.0 mm, and the resistance value R (connection resistance) thereof was measured. Tables 1 and 2 show the average number of experiments as n=5.

(4) Sliding characteristics

a four-layer structure of FPC13 made of the upper laminate layer in the order of the polyimide layer (12.5 μm), the adhesive layer (15 μm), the copper foil layer (12 μm), and the polyimide layer (12.5 μm), The lower two-layer electromagnetic wave shielding films 14, 15 (length 100 mm, width 12 mm) were used to prepare samples for evaluation. The upper side of the FPC 13 is bent in the longitudinal direction so that the sample is bent in the longitudinal direction. As shown in Fig. 3, the sample is sandwiched by the fixing plate 11 and the sliding plate 12 (bending radius b: 1.0 mm). The terminals at both ends in the longitudinal direction of the conductive layers of the electromagnetic shielding films 14 and 15 are connected to each other by a copper foil (not shown) to measure the respective resistance values of the films 14 and 15 as the initial resistance of the shielding layer. Then, the black point is used as the base point to make a reciprocating stroke in the direction of the arrow (sliding width 50 mm (c=c'=25 mm), 60 reciprocation/minute), and the number of strokes when the shielding layer resistance reaches 100 Ω (reciprocating as one time) is investigated as " Sliding characteristics." Further, the same test was also carried out on the sample after the above-mentioned evaluation sample was subjected to the three-time reflow step. The results are shown in Tables 1 and 2. In the table, "inner bend" indicates the resistance value of the electromagnetic wave shielding film 15 which becomes the inside of the FPC 13 at the time of bending, and "outer bend" indicates the resistance value of the electromagnetic wave shielding film 15 which becomes the outer side of the FPC 13.

Industrial availability

In addition to a mobile phone, the electromagnetic wave shielding film of the present invention is also generally applicable to a flexible substrate mounted in a machine such as a digital camera having a bent portion or a sliding portion.

1. . . The protective layer

2. . . Conductive layer

3. . . Polyimine layer

4. . . Copper layer

5. . . Nickel-gold plating

6. . . Subsequent layer

7. . . Polyimine layer

c=c'. . . Sliding amplitude

11. . . Fixed plate

12. . . Sliding plate

13. . . FPC

14. . . Electromagnetic wave shielding film

15. . . Electromagnetic wave shielding film

A. . . electrode

B. . . electrode

a. . . Bottom diameter

b. . . Bending radius

d. . . Electrode spacing

R. . . resistance

Fig. 1 is a schematic end view showing a method of measuring sheet resistance.

Fig. 2 is a schematic end view showing a method of measuring the connection resistance, and (b) is a partial enlarged view of (a).

Figure 3 shows a schematic end view of the method of the sliding test.

Claims (3)

An electromagnetic wave shielding film which is formed by laminating a protective layer on a conductive layer composed of (A) a metal powder and (B) a binder resin, wherein the conductive layer is formed of a conductive paste, and the conductive paste The following metal powders (a) and (b) are contained: (a) a flaky metal powder having an average thickness of 50 to 300 nm and an average particle diameter of 3 to 10 μm; and (b) an acicular shape having an average particle diameter of 3 to 10 μm. Or a dendritic metal powder; the ratio of the (A) metal powder to the (B) binder resin in the conductive layer is in the range of A:B=50:50-80:20 by weight ratio (however, as a solid component) The ratio of the above-mentioned (a) flaky metal powder to (b) acicular or dendritic metal powder is in the range of a:b=20:80 to 80:20 by weight ratio; and, the electromagnetic wave shielding The thickness of the film before the stamping step is 11 to 30 μm, and the thickness after the stamping step is 7 to 28 μm and is thinner than the thickness before the stamping step. A method of manufacturing a flexible substrate, wherein an electromagnetic wave shielding film according to claim 1 of the patent application is placed on a flexible substrate, and then the flexible substrate is heated together with the electromagnetic shielding film while being pressed in a thickness direction. Thereby, an electromagnetic wave shielding layer is formed on the flexible substrate. A flexible substrate having an electromagnetic wave shielding layer composed of an electromagnetic wave shielding film according to claim 1 of the patent application.