WO2001084899A1

WO2001084899A1 - Electro-magnetic interference shielding structure with thin film comprising buffer layer and preparing process therefor

Info

Publication number: WO2001084899A1
Application number: PCT/KR2000/000699
Authority: WO
Inventors: Jin-Bong Jung
Original assignee: Hantech Co., Ltd.
Priority date: 2000-05-01
Filing date: 2000-06-30
Publication date: 2001-11-08
Also published as: AU5577200A; KR20010100358A; KR100371931B1

Abstract

An electro-magnetic interference (EMI) shielding structure, and a preparing method therefor are provided. The EMI shielding structure includes a non-conductive material, a conductive layer formed on at least one side of the non-conductive material, and a buffer layer having an affinity for both the non-conductive material and the conductive layer, the buffer layer interposed between the non-conductive material and the conductive layer.

Description

ELECTRO-MAGNETIC INTERFERENCE SHIELDING STRUCTURE WITH THIN FILM COMPRISING BUFFER LAYER AND PREPARING PROCESS THEREFOR

Technical Field

The present invention relates to an electro-magnetic interference shielding structure and a preparing process therefor, and more particularly, to an electromagnetic interference shielding structure with improved adhesion strength of a conductive film to a polymer material, and a preparing method therefor

Background Art

As plastic replaces metal as the outer packaging material of various electric and electronic products, electro-magnetic interference (EMI) generated from the electric and electronic products becomes serious EMI causes abnormal noise, malfunction or performance degradation of computers, airplanes, various communication equipment, and the like, and even has an harmful effect on human bodies A research result has been reported that EMI generated from cellular phones can cause brain tumors

Thus, advanced nations prepare for related laws and regulations for restricting harmful EMI, extend their application target from domestic products to imported products, and prohibit production and import of products which do not confirm with the laws and regulations Accordingly, manufacturers of various electric and electronic products have devised several measures for shielding EMI

EMI can be shielded by two methods of (1 ) mixing a conductive material with a resin composition for molding a plastic material, to provide a conductive plastic material, and (2) forming a thin conductive EMI shielding film on a non-conductive plastic material The first method, which is molding plastic by mixing a conductive filler such as aluminum, carbon, metallic power, carbon fiber or flake with the plastic, does not require a secondary process, and has no cracking or peeling which is generated during coating However, in the first method, a great amount of filler must be used to produce a uniform shielding effect, thus increasing the thickness of a housing and deteriorating the performance of plastic itself Also, in the first method, when black filler such as black carbon or carbon fiber is used, the surface becomes black, which requires a secondary coating process Furthermore, since a highly conductive plastic is a good conductor, if it is used, there is a danger of getting shocked

A method of forming a thin conductive shielding film on a non-conductive plastic material includes, for example, a method of laminating a metal plate on a plastic surface, a method of spray coating or vacuum depositing metallic powder, a wet plating method, and a conductive paint coating method However, the conductive paint coating method causes environmental pollution and threatens the health of workers since a poisonous solvent such as toluene is used Also, a conductive paint used in the conductive paint coating method must be totally imported, so that this method has low cost-competitiveness In this method, the thickness of a coated layer must be significantly increased to attain the same EMI shielding effect as when a plastic material is coated with only a pure metal Thus, this method does not match with a tendency toward small and light weight electronic devices

In the wet plating method in which a strongly-catalytic metal such as nickel or cobalt is used as a coating material, a chemical reducing agent is added to a plating solution, thus causing environmental pollution Also, in this method, a film layer is formed by dipping a substrate in a plating solution, so that selective cross-section plating is impossible That is, if cross-section plating must be performed, other surfaces desired not to be plated must be masked, which degrades the productivity Hence, the use of a vacuum deposition method and a sputtering method rapidly increases

A vacuum deposition method is a method of forming a conductive thin film on the surface of a material by heating a material to be deposited in a vapor state, in a vacuum This vacuum deposition method is a simple process, and does not cost much in the way of equipment However, a plastic material is unstable against heat generated during deposition, and it is less adhesive since only a small amount of energy is used to form a thin film Furthermore, the formed thin film has a low density, so that its durability is poor In a sputtering method, deposition is performed at a low temperature, and a stoichiometnc ratio can be easily controlled Also, in the sputtering method in which a deposition material is formed into a thin film by generated plasma, the magnitude of deposition energy reaches several hundreds of times of the deposition energy in a vacuum deposition method, thus providing excellent adhesiveness A thin film formed in this way has a high density, and thus it is durable Furthermore, it is easy to minutely adjust the thickness of the thin film

Inert vapor lonization, which is a method of directly vaporizing a deposition material due to the collision of ionized vapor with the target surface, occurs at an abnormal glow discharge region The ionized vapor collides with a cathode surface by the influence of an electric field Accordingly, in a sputtering method, a plastic material can be coated with a pure metal using a target as a cathode and using a vacuum vessel or a sputtering material as an anode Therefore, the sputtering method can reduce a resistance per unit thickness and provide an excellent adhesiveness, compared to a case when plastic is coated with conductive paint Thermoplastic engineering plastics, such as polycarbonate, polyamide, polyacetal, polybuthylene terephthalate, or polyphenylene oxide, can be taken as examples of a plastic material which replaces the materials of various metallic parts of electric electronic products and the outer packaging materials thereof Polycarbonate has a high resistance to atmospheric corrosion, a high physical strength, and high impact resistance, so that its use is extended to all electronic products

Polycarbonate, which is representative of engineering plastic, is generally polyester produced by reacting phosgene with bisphenol A or other types of phenol as in the following Reaction formula 1

Polycarbonate melts at 230 °C, is thermally deformed at 120 to 140 °C, has a high physical strength, and is highly impermeable to water In particular, polycarbonate has a high impact resistance, a high elastic modulus, and an excellent light resistance To be more specific, some physical properties of polycarbonate and an alloy for diecasting are compared as in the following Table 1

[Table 1]

Resin which is difficult to etch and is non-polar, such as polycarbonate, is very difficult to etch and to surface-catalyze to obtain a good adhesion strength Accordingly, when conductive paint is sprayed on a material such as the above- described resin, and also when sputtering is performed, a sufficient level of adhesion strength cannot be obtained, thus causing a big problem to the performance of products Most component parts of a product are operated by fine current However, if part of an EMI shielding film which covers the exteriors of component parts peels off due to an inferior adhesive strength and interrupts the flow of current, an electrical short circuit may result, causing products to malfunction

Disclosure of the Invention

An objective of the present invention is to provide an electro-magnetic interference (EMI) shielding structure with improved adhesion strength between a non-conductive material and a metal layer, even when the non-conductive material has a low affinity for metal like polycarbonate, when a non-conductive material is coated with the conductive material, and a preparing method therefor

To achieve the above objective, the present invention provides an electro- magnetic interference (EMI) shielding structure including a non-conductive material, a conductive layer formed on at least one side of the non-conductive material, and a buffer layer having an affinity for both the non-conductive material and the conductive layer, the buffer layer interposed between the non-conductive material and the conductive layer According to a preferred embodiment of the present invention, the non- conductive material may be formed of one or more materials selected from the group consisting of polycarbonate, polyamide, pol acetal, polybuthylene terephthalate, and polyphenylene oxide

According to a preferred embodiment of the present invention, the conductive s layer may be formed of one or more materials selected from the group consisting of silver, aluminum, copper, gold, platinum, stainless steel and an alloy of two or more of these materials

According to a preferred embodiment of the present invention, the buffer layer may be formed of one or more materials selected from the group consisting of o polytetrafluoroethylene, polyethylene and acrylonitπle-butadiene-styrene copolymer According to another preferred embodiment of the present invention, the buffer layer may be formed of one or more materials selected from the group consisting of stainless steel, nickel, titanium, cobalt, copper and a compound of two or more of these materials 5 According to preferred embodiments of the present invention, the buffer layer may formed by one of sputtering, vacuum deposition, vacuum deposition with ion assistance, and electron beam vacuum deposition

In order to achieve the above objective, the present invention provides a method of manufacturing an EMI shielding structure, the method including o preparing for a non-conductive material, forming a buffer layer on at least one surface of the non-conductive material layer, the buffer layer formed of a material which has an affinity for both the non-conductive material and one or more conductive materials selected from the group consisting of silver, aluminum, copper, gold, platinum, stainless steel, and an alloy of two or more of these materials, and forming a conductive layer on the exposed surface of the buffer layer, the conductive layer formed of one or more conductive materials selected from the group consisting of silver, aluminum, copper, gold, platinum, stainless steel and an alloy of two or more of these materials

Brief Description of the Drawings

FIG 1 is a cross-sectional view schematically illustrating an electro-magnetic interference (EMI) shielding structure according to the present invention,

FIG 2 is an AES depth profile illustrating an analysis of the depth distribution of each element with respect to an EMI shielding structure according to an embodiment of the present invention, and

FIG 3 is an SEM image (x 10000) of the cross-section of an EMI shielding structure according to an embodiment of the present invention

Best mode for carrying out the Invention

FIG 1 is a magnified cross-sectional view of a conductive shielding structure 10 according to the present invention According to the present invention, when an electro-magnetic interference (EMI) shielding capability is provided to a non- conductive substrate 11 , such as polycarbonate, which is used to replace various metals by virtue of its excellent mechanical properties, a buffer layer 12 made of a material which has an affinity for both a substrate and a conductive material is interposed between a non-conductive substrate 11 and a conductive layer 13 in order to overcome the deficient affinity of the substrate 11 for a conductive material such as silver, aluminum, copper, gold, platinum, stainless steel or an alloy of two or more of these materials

A material, which has an affinity for both a non-conductive material, such as polycarbonate, and metal powder, is not limited to a particular material However, polytetrafluoroethylene, polyethylene and acrylonitπle-butadiene-styrene copolymer can be taken as examples of such a material Also, the above-described material is not limited to polymers That is, a metal having a high affinity for polymer, such as stainless steel, nickel, titanium, cobalt, copper or a compound of two or more of these materials, can be used instead of polymer

In case that the buffer layer is formed of polymer, it can be formed by general polymer thin film forming methods well-known to those skilled in the art These methods include casting, laminating, and the like Also, the buffer layer can be formed by deposition methods such as sputtering, vacuum deposition, vacuum deposition with ion assistance, and electron beam vacuum deposition It is preferable that an optimal method is used in consideration of the peculiar characteristics of each buffer material to be used In case that the buffer layer is formed of a metal or its compound, it can be formed by the above-described general metal thin film forming methods, most preferably, by sputtering

A non-conductive material used in a conductive shielding structure according to the present invention can be any material which requires a means for shielding EMI, and is not limited to engineering plastic

Any conductive material, which is widely used in the art to shield EMI, can be applied as the material of a conductive layer for shielding EMI Also, various methods prevalently used in the art can be used as a conductive layer forming method, but a sputtering method is the most preferable In case that the buffer layer is formed of polymer, the conductive layer forming method must be selected in consideration of the properties of the material to be used

In a sputtering method, which is a preferable method of manufacturing an EMI shielding structure according to the present invention, inert gas such as argon is supplied into a vacuum When direct current is applied, electrons jump out of a cathode and collide with vapor molecules Some of the stricken molecules are ionized, while most of them are not ionized The non-ionized molecules are excited and then immediately return to a stable state, emitting photons, this effect called a "glow discharge", and producing plasma Sputtering refers to a phenomenon in which a material is knocked out of a cathode and attached to a substrate by accelerating ions, for example, Ar⁺ ions of the plasma toward the cathode by the force of negative electricity A cathodic plate is set to be a target, and atoms having enough kinetic energy get out of the solid and fly into the reaction chamber space Here, a sputtering apparatus forms a thin film by accumulating sputter atoms which fly off a solid The sputtering apparatus accelerates positive ions of a plasma where glow charge occurred, to the target to which negative voltage has been applied, thereby colliding the positive ions with the target The rate of sputters flying when one ion collides with the target varies with the material of the target, the type of ion, and the energy of the ion The sputter etch rate (E) of the target is expressed as in the following Equation 1

wherein S denotes the sputter ratio, j denotes the current density applied to the target, M denotes the atomic weight, and p denotes the density of the target The probability that a sputter atom flying from the target reaches the substrate is affected by the geometrical shapes of the target and the substrate the relative positions of the target and the substrate, and the collision and scattering of sputter atoms and gas molecules in the space between the target and the substrate In case that the target and the substrate are stationary and face each other, the attaching speed (D) has the following relationship with the sputter etch rate (E) by a proportional integer (F)

D = F • E ...(2)

In a general sputtering apparatus, D is between about 0 1 A/mm and 0 5 A/mm When a particular sputtering apparatus and sputtering conditions are determined from Equations 1 and 2, the attaching speed of a film can be controlled by S andy In various sputtering apparatuses, the speed of forming a film is almost proportional to the power applied to the target

A sputtering method can be classified into a direct current 2-pole sputteπng method, an RF 2-pole sputtering method, a thermionic cathode sputtering method and a magnetron sputtering method, but the present invention is not limited to a particular sputtering method

Hereinafter, the present invention will be described in detail with reference to a preferred embodiment The embodiment is used only to facilitate understanding of the present invention, not to limit the scope of the present invention as set forth in the claims

<Embodιment>

A stainless steel target SUS 304, and a polycarbonate substrate are installed so that they face each other, within the vacuum chamber of a sputtering apparatus MRC 903 (which is a product of MRC company) A circuit is constructed such that a cathode is positioned toward a target, and an anode is positioned toward a plastic material The pressure of the vacuum chamber is maintained at the initial vacuum degree of 5x 10 ⁶ Torr and at the process vacuum degree of 8χ 10 ⁴ Torr Argon and oxygen are mixed in a ratio of 9 to 1 , respectively, and plasma is produced for 4 minutes by applying 150W to the circuit An SUS oxide buffer layer is formed to a thickness of about 2000 A, and an SUS with a thickness of about 3000 A is formed

A polycarbonate substrate having a buffer layer formed thereon is again installed toward the anode, and Cu is sputtered by the same method as that described above, thereby forming a conductive layer to a thickness of about 20000

A

The line resistance of a conductive shielding structure manufactured according to this embodiment measures 0 8 Ω/cm, which is a satisfactory result

Adhesion is estimated using a KS-0254 adhesive tape test A 10mmχ10mm conductive layer is cut into 1 mmχ1 mm squares, and tape is attached to the

10mmχ10mm conductive layer and then detached therefrom At this time, the number of 1 mmχ1 mm squares remaining on the conductive layer is measured According to the measurement, most of the area of the conductive layer remains without damage, from which it can be seen that the conductive layer has excellent adhesion

Meanwhile, an analysis is made on the depth distribution of each element with respect to an EMI shielding structure manufactured according to this embodiment FIG 2 shows depth profiles obtained by analyzing a 20 m^χ20 m sample under the conditions of an electron beam of 10KeV (60nA), sputtering Ar⁺ ions of 5KeV (5mA), and an etch time of 100 to 250 sec using an AES (VG

MICROLAB 300R) apparatus It can be seen from FIG 2 that SUS was totally oxidized FIG 3 is a 10000 times-magnified SEM picture of the cross-section of an EMI shielding structure manufactured according to this embodiment The thickness of a conductive layer Cu is about 1 935 m, and an SUS oxide buffer layer measures 5,300 A

Industrial Applicability

In an EMI shielding structure according to the present invention, a buffer layer made of a material which has an affinity for both a non-conductive material and a metal is interposed when a non-conductive material having excellent mechanical properties but having a low affinity for a metal is coated with a conductive layer for shielding EMI Therefore, the conductive layer has excellent adhesion strength, so that the EMI shielding structure of the present invention can be successfully applied to all electric and electronic products which require EMI shielding

Claims

What is claimed is

1 An electro-magnetic interference (EMI) shielding structure comprising a non-conductive material, a conductive layer formed on at least one side of the non-conductive material, and a buffer layer having an affinity for both the non-conductive material and the conductive layer, the buffer layer interposed between the non-conductive material and the conductive layer

2 The EMI shielding structure of claim 1 , wherein the non-conductive material is formed of one or more materials selected from the group consisting of polycarbonate, polyamide, polyacetal, polybuthylene terephthalate, and polyphenylene oxide

3 The EMI shielding structure of claim 1 , wherein the conductive layer is formed of one or more materials selected from the group consisting of silver, aluminum, copper, gold, platinum, stainless steel and an alloy of two or more of these materials

4 The EMI shielding structure of claim 1 , wherein the buffer layer is formed of one or more materials selected from the group consisting of polytetrafluoroethylene, polyethylene and acrylonitπle-butadiene-styrene copolymer

5 The EMI shielding structure of claim 1 , wherein the buffer layer is formed of one or more materials selected from the group consisting of stainless steel, nickel, titanium, cobalt, copper and a compound of two or more of these materials

6 The EMI shielding structure of claim 1 , wherein the buffer layer is formed by one of sputtering, vacuum deposition, vacuum deposition with ion assistance, and electron beam vacuum deposition

7. A method of manufacturing the EMI shielding structure of claim 1 , the method comprising: preparing for a non-conductive material; forming a buffer layer on at least one surface of the non-conductive material layer, the buffer layer formed of a material which has an affinity for both the non- conductive material and one or more conductive materials selected from the group consisting of silver, aluminum, copper, gold, platinum, stainless steel, and an alloy of two or more of these materials; and forming a conductive layer on the exposed surface of the buffer layer, the conductive layer formed of one or more conductive materials selected from the group consisting of silver, aluminum, copper, gold, platinum, stainless steel and an alloy of two or more of these materials.