JPH05258790A - Anisotropically conductive adhesion film and connecting structure using it - Google Patents

Abstract

PURPOSE:To provide an anisotropically conductive adhesion film, which is free from risk of slipping-off of a metal substance put fully in each minute through hole, can seal the connection part certainly with resin, and ensures a high reliance upon the electric connection. CONSTITUTION:Minute through hole 2 is provided in the direction across the width of an insulative film 1, for example made of polyimide, and filled with 21 metal substance 3 using a means such as plating, and bump--shaped metal protrusions 4 are made in rivet form at the two ends of this through hole 2. A layer 5 of thermoplastic polyimide resin whose melt viscosity at 400 deg.C is below 10<8> poise is formed at least, on one surface of this insulative film 1, and thereby an anisotropic conductive adhesion film is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anisotropic conductive adhesive film and a connection structure using the same.

[0002]

2. Description of the Related Art In recent years, electronic devices have become more multifunctional and smaller and lighter. In the semiconductor field, wiring circuit patterns have been highly integrated and fine patterns with a large number of pins and a narrow pitch have been adopted. In order to cope with such fine patterning of circuits, a method of interposing an anisotropic conductive film in the connection between a plurality of conductor patterns formed on a substrate and the conductor patterns or ICs or LSIs connected thereto has been attempted. There is.

For example, Japanese Unexamined Patent Publication No. 55-161306 discloses a sheet in which holes in selected regions of an insulating porous sheet are plated with metal to provide anisotropic conductivity. However, since such a sheet does not have a metal protrusion on the surface, it is necessary to form bump electrodes (bumps) on the connection pads on the IC side when connecting an IC or the like, which complicates the connection process.

Further, JP-A-62-43008, JP-A-63-40218, and JP-A-63-94504.
Japanese Patent Laid-Open Publication No. 2004-242242 discloses a structure in which fine holes provided in the thickness direction of an insulating film are filled with a metal substance to make it anisotropically conductive, and the metal substance is projected in bumps from the film surface to facilitate connection. There is. Furthermore, JP-A-54-6320
The publication discloses that a large number of conductors are oriented in the thickness direction of an insulating film to make it anisotropically conductive, and an adhesive layer is formed on both sides of the film in order to improve workability.

[0005]

However, in such an anisotropically conductive film, since the metal substance filled is generally structured as shown in FIG. 5, the filled metal substance and the insulating film are There is a risk that the electrical connection reliability will be poor due to the lack of sufficient adhesion, the metal substance falling off, and the fine pores that must originally have conductivity, not exhibiting conductivity.

As the anisotropic conductive adhesive film, as shown in FIG. 6, the conductive powder 12 is dispersed in a bonding material 13 made of an adhesive thermoplastic resin or thermosetting resin. Things are known. However, when connecting a connected object using this film, the conductive powder 12 dispersed in the bonding material 13 may flow due to pressurization or heating to cause anisotropic conductivity failure or connection failure. .. Further, when such an anisotropic conductive film is used when mounting a semiconductor element such as a liquid crystal display driving IC or LSI, the film does not have sufficient self-holding property (shape retaining property), so that the mounting part is sealed. It does not function sufficiently as a stopping material, and is still insufficient in practical use. In addition, since the above-mentioned conventional adhesive film usually has poor heat resistance, it is difficult to apply it to heat resistant applications.

[0007]

Therefore, the present inventors have solved the above-mentioned problems of the conventional anisotropic conductive film, and are capable of surely making the anisotropic conductive film to have high connection reliability, and further to improve the adhesiveness. The present invention has been completed through intensive studies in order to provide an anisotropic conductive adhesive film which has a sealing function for surely sealing the connection part.

That is, according to the present invention, the insulating film has fine through holes which are independently conducted in the thickness direction, and at least one end of both ends of the through hole on the front and back surfaces of the film is an opening of the through hole. A thermoplastic polyimide resin layer which is closed by bump-like metal protrusions having a bottom area larger than the area and has a melt viscosity at 400 ° C. of 1 × 10 ⁸ poise or less is formed on at least one surface of the film. A first gist of the present invention is to provide an anisotropic conductive adhesive film, and a connection structure using an anisotropic conductive adhesive film in which this film is interposed between connected bodies. The second gist is to provide.

The present invention will be described below with reference to the drawings. FIG. 1 is an enlarged sectional view showing an example of the anisotropic conductive adhesive film of the present invention.

In FIG. 1, the insulating film 1 is provided with fine through holes 2 in the thickness direction, and the conductive paths filled with the metal substance 3 reach the front and back surfaces. Bump-shaped metal protrusions 4 having a bottom area larger than the opening area of the through hole 2 are formed at both ends of the through hole 2, and close the through hole 2 in a so-called rivet shape. Thermoplastic polyimide resin layers 5 are formed on both surfaces (front and back surfaces) of this insulating film 1, and it is effective in heating and adhering to an adherend to seal the connection part. In the present invention, the thermoplastic polyimide resin layer 5 may be formed not only on both sides but also on one side (not shown). Further, FIG. 1A shows a case where the thermoplastic polyimide resin layer 5 is formed so as to entirely cover the bump-shaped metal protrusions 4.
(B) shows that the thermoplastic polyimide resin layer 5 is formed in advance on the insulating film 1, the fine through holes 2 are formed including the resin layer 5, and the metal substance 3 is filled in the through holes 2 to form the front and back surfaces. A conductive path exposing the metal protrusion 4 is formed on the surface.

2 (A) and 2 (B) are enlarged cross-sectional views showing another example of the anisotropic conductive adhesive film of the present invention, showing the through holes 2 formed in the insulating film 1. A bump-shaped metal protrusion 4 having a bottom area larger than the opening area of the through hole 2 is formed only on one end portion, and the thermoplastic polyimide resin layer 5 is formed on both surfaces as in FIG.
Are formed. Note that (A) and (B) in FIG.
Shows the formation state (non-exposed state and exposed state of metal protrusion) of the same thermoplastic polyimide resin layer 5 as in FIGS. 1 (A) and 1 (B).

In each of the above figures, the diameter of the fine through hole 2 is
It can be set according to the purpose of use, but usually 15 to
The pitch is 100 μm, preferably 20 to 50 μm, and the pitch is 15 to 200 μm, preferably 40 to 100 μm.

The insulating film 1 for imparting self-supporting property and insulating property to the anisotropic conductive adhesive film of the present invention is not limited in its material as long as it is a film having electric insulating properties, and it may be a polyester resin or an epoxy resin. Resins, urethane resins, polystyrene resins, polyethylene resins, polyamide resins, polyimide resins, ABS resins, polycarbonate resins, silicone resins and other thermosetting resins or thermoplastic resins can be selected according to the purpose. Of these resins, heat-resistant resins such as polyimide, polyether sulfone, and polyphenylene sulfide, particularly polyimide resins, are preferably used as the resin having good heat resistance. Although the thickness of the insulating film 1 can be set arbitrarily, it is usually 5 to 200 μm, preferably 10 to 100 μm from the viewpoint of accuracy (variation) of film thickness and hole diameter accuracy of formed through holes.

The fine through holes 2 provided in the insulating film 1 may be formed by a mechanical processing method such as punching, a dry etching method using laser or plasma, or a chemical wet etching method using chemicals or a solvent. In the case of the etching method, a mask having a desired hole shape, for example, a circle, a square, or a rhombus is brought into close contact with the insulating film 1, and an indirect etching method in which the mask is processed, or a laser beam with a narrowed spot is applied to the film. Alternatively, there are a dry etching method in which a laser beam is imaged on a film through a mask, a direct etching method in which fine holes are patterned in advance using a photosensitive resist and then wet etching is performed. Incidentally, a dry etching method or a wet etching method is preferable in order to correspond to a fine pattern of a circuit, and particularly a dry etching method using ablation by an ultraviolet laser such as an excimer laser is preferable since a high aspect ratio can be obtained.

For example, when the fine through holes 4 are formed in the film 1 by laser light, the diameter of the through hole on the film surface on the side irradiated with the laser light is the same as the through hole formed on the film surface on the opposite side as shown in FIG. It is larger than the hole diameter. In addition, in FIGS. 1 and 2, the formation angle α of the through hole 2 is set to 90 ± 20 degrees, and the area of the planar shape of the through hole 2 is made larger than [film thickness × 1/1] ² . In terms of the wettability of the plating solution, it becomes effective in the subsequent metal filling.

As described above, the fine through holes 4 provided in the insulating film 1 are filled with the metal substance 3 serving as a conduction path, and bump-shaped metal protrusions 4 are formed at both ends thereof. ing. As such a metal substance, for example, various metals such as gold, silver, copper, tin, lead, nickel, cobalt and indium, or various alloys containing these as components are used. If the purity of this metal substance is too high, it is difficult to form bumps. Therefore, it is preferable to use a metal substance or an alloy containing a known amount of an organic substance or an inorganic substance. Various methods such as sputtering, various vapor depositions, and various platings can be adopted as the method of forming the conductive path. In the case of using the plating method, it is possible to grow the metal protrusion 4 in a bump shape by prolonging the plating time.

The bump-like metal protrusion 4 formed in the opening of the through hole 2 has a bottom area larger than the plane area of the through hole 2, preferably 1.1 times or more. In the present invention, by increasing the bottom area in this way, the conductive path formed in the through hole 2 does not fall off, and sufficient strength against shearing force in the thickness direction of the insulating film 1 is obtained. Therefore, the reliability of electrical connection is improved.

A thermoplastic polyimide resin layer 5 is formed on at least one surface of the insulating film for temporarily adhering to the adherend and for sealing the connection portion with resin. The thermoplastic polyimide resin forming the layer has a melt viscosity at 400 ° C. of 1 × 10 ⁸ poise or less, preferably 1 × 10 ³ to 1 × 10 ⁷ poise, from the viewpoint of heat resistance. The structure is not particularly limited as long as it has a satisfactory polyimide skeleton. If the melt viscosity is high such that it exceeds 10 ⁸ poise, it cannot be melted sufficiently at the time of bonding with a body to be connected, and a reliable connection structure cannot be obtained. Further, it is preferable to use a glass transition temperature of 473 K or higher from the viewpoint of heat resistance. Examples of such a thermoplastic polyimide resin include Ultem 1000 (polyether imide manufactured by General Electric Co.), LARC-TPI (polyimide manufactured by Mitsui Toatsu Co., Ltd.), 4,4′-oxydiphthalic acid dianhydride and 3,3. Examples include polyimide obtained from'-diaminodiphenyl sulfone, and these may be used alone or in combination of two or more. In addition, additives such as a colorant, an adhesion improver, and an inorganic filler (silica, carbon, etc.) are added to the thermoplastic polyimide resin layer 5 as needed, as long as characteristics such as adhesiveness and heat resistance are not impaired. May be blended in any amount.

When a semiconductor element is used as the object to be connected, a silane coupling agent or a silane compound is added to the thermoplastic polyimide resin layer 5 in order to improve the adhesion between the thermoplastic polyimide resin layer 5 and the semiconductor element. It is preferable to contain or apply to the surface of the layer 5.

The thickness of such a thermoplastic polyimide resin layer 5 is not particularly limited, but is usually 3 to 500 μm, preferably 5 to 100 μm from the viewpoint of thickness accuracy (variation) and connection reliability.

The method for obtaining the anisotropic conductive adhesive film of the present invention includes, for example, a method comprising the following steps.

A conductive layer is laminated on the surface opposite to the laminated surface of the insulating film on which the thermoplastic polyimide resin layer is laminated, with or without an adhesive, to finely penetrate the insulating film and the thermoplastic polyimide resin layer. Laminating a conductive layer on a laminated film of an insulating film having holes or fine through holes and a thermoplastic polyimide multilayer (provided that the conductive layer is laminated so that the fine holes penetrate or is removed after lamination) ), A resist layer is formed on the surface of the conductive layer to insulate the surface, and then the through hole is etched to form a rivet-shaped groove in the conductive layer portion in contact with the through hole.

A step of filling the fine through holes with a metal substance by a plating method such as electrolytic plating or electroless plating to form bump-shaped metal protrusions.

A step of removing the conductive layer and the resist layer laminated on the insulating film by a chemical etching solution or electrolytic corrosion.

The thermoplastic polyimide resin layer in the above step may be laminated after the step without being laminated on the insulating film in advance.

In the above step, the bump-shaped metal protrusion may be formed after the step, and after the above step, the surface (exposed side) of the thermoplastic polyimide resin layer may be prevented from being contaminated. It is preferable to coat with a separator during storage.

When a bump-shaped metal protrusion is formed on one side of the insulating film in the anisotropic conductive adhesive film of the present invention, it is formed on the film surface on the side where the through-hole has a small hole diameter as shown in FIG. It is preferable to form bump-shaped metal protrusions. Therefore, the insulating film 1 as shown in FIG.
In, the conductive layer in the above step is formed on the side where the bump-shaped metal protrusion 4 is formed (the lower surface side in the figure).

In order to form a bump-shaped metal protrusion, it is preferable that the state of the metal crystal is a fine crystal. Note that when electrolytic plating is performed at a high current density, a dendritic crystal is formed, so that the bump may not be formed. In addition, a smooth and uniform protrusion can be obtained by adjusting the deposition rate of metal crystals, adjusting the type of plating solution and the temperature of the plating bath.

In the present invention, in order to make the bump-shaped metal protrusion have a bottom area larger than the opening area of the through hole, the plating film is formed at the time of the plating as compared with the opening surface, that is, the insulating film surface. It is necessary to grow high and also to grow laterally from the through-hole like a rivet, and the height can be arbitrarily set according to the hole pitch and the application, and is usually adjusted to 5 μm or more, preferably 5 to 100 μm. To be done.

Further, when the conductive layer on the bottom surface of the through hole is removed to form rivet-shaped bumps (when bumps are formed on both sides), the etching is preferably performed at 1.1 times or more the diameter of the through hole. .. If it is less than 1.1 times, the effect as a rivet-shaped bump becomes poor and the desired effect may not be exhibited.

3 and 4 show a flexible printed circuit (FPC) using the anisotropic conductive adhesive film of the present invention.
The lead portion 11 of the electrode 10 is connected to the electrode 8 on the printed wiring board 9.
It is sectional drawing which shows the connection structure before mounting and after mounting. For example, as a thermoplastic polyimide resin, polyetherimide (Ultem 1 manufactured by General Electric Co., Ltd.)
000) is used by hot pressing at 320 ° C.
The connection structure as shown in FIG. 4 is obtained by heating and pressure bonding for about 10 minutes under the condition of 0 kg / cm ² .

[0032]

EXAMPLES Examples of the present invention will be shown below and will be described more specifically.

A polyimide precursor solution was applied onto a copper foil so as to have a thickness of 1 mil after drying and cured to prepare a two-layer film of a copper foil and a polyimide film. Then, the surface of the polyimide film is irradiated with KrF excimer laser light with an oscillation wavelength of 248 nm through a mask to perform dry etching, and the polyimide film layer has a fine through hole of 60 μmφ and a pitch of 200 μm in an area of 5 cm / mm and 8 cm ² . Set up in.

Next, a resist was applied to the surface of the copper foil, cured to insulate it, and immersed in a chemical polishing solution at 50 ° C. for 2 minutes.

After washing this with water, the copper foil portion was connected to the electrode and immersed in a cyanide gold plating bath at 60 ° C., the copper foil was used as a negative electrode, and gold plating was grown in the through-hole portion of the two-layer film. The plating process was interrupted when the gold crystals were slightly projected from the film surface (projection height was 5 μm).

Then, the coated resist layer is peeled off, and 2
The copper foil of the layer film was dissolved and removed with cupric chloride.

Finally, a thermoplastic polyimide resin layer (40 made of LARC-TPI (polyimide manufactured by Mitsui Toatsu) is used.
A melt viscosity at 0 ° C. of 8.3 × 10 ⁵ poise and a glass transition temperature of 451 K) was formed on one side or both sides of the insulating film to obtain an anisotropic conductive adhesive film of the present invention.

[0038]

EFFECT OF THE INVENTION Since the anisotropic conductive adhesive film of the present invention has the above-mentioned structure, the metal substance filled as the conductive path is sufficiently adhered to the insulating film, and the metal substance does not drop off. Originally, the micropores that originally have to have conductivity exhibit sufficient conductivity, and the electrical connection reliability is high.

Furthermore, since the thermoplastic polyimide resin layer is formed on at least one surface of the insulating film in the anisotropic conductive adhesive film of the present invention, the polyimide resin is applied by pressure and heat during connection during mounting. Even if the layer flows or deforms, the insulating material keeps the metal material layer serving as a conductive path fixed and the thermoplastic polyimide resin layer also seals the connection part so that no connection failure occurs. Exerts the effect. Also, because a polyimide resin layer having a specific property with good heat resistance is used, various FPCs, TABs, etc. as well as semiconductor elements can be mounted on an external circuit board, and the connection reliability during mounting is high. Will be much improved.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing an actual example of an anisotropic conductive adhesive film of the present invention.

FIG. 2 is an enlarged cross-sectional view showing another example of the anisotropic conductive adhesive film of the present invention.

FIG. 3 shows an FP using the anisotropic conductive adhesive film of the present invention.
It is sectional drawing which shows the state before mounting C on an external wiring board.

FIG. 4 is a cross-sectional view showing a state after mounting and connecting the state shown in FIG.

FIG. 5 is an enlarged cross-sectional view of a conventional anisotropic conductive film.

FIG. 6 is a cross-sectional view of another conventional anisotropic conductive film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating film 2 Micro through-hole 3 Metal substance 4 Bump-shaped metal protrusion 5 Thermoplastic polyimide resin layer

Claims (2)

[Claims] 1. An insulating film having fine through holes that conduct independently in the thickness direction, and at least one end of both ends of the through hole on the front and back surfaces of the film is larger than the opening area of the through hole. It is closed by a bump-shaped metal protrusion having a large bottom area, and a thermoplastic polyimide resin layer having a melt viscosity at 400 ° C. of 1 × 10 ⁸ poise or less is formed on at least one surface of the film. An anisotropic conductive adhesive film characterized in that 2. A connection structure using an anisotropic conductive adhesive film having the anisotropic conductive adhesive film according to claim 1 interposed between objects to be connected.