JPH03266306A - Anisotropic conductive film - Google Patents

Abstract

PURPOSE:To attain high-reliability of electric connection by providing a fine through-hole in an insulating film in the direction of the thickness and filling the through-hole with metal material by plating, etc., to form a metal protrusion from both ends of the through-hole in a rivet shape. CONSTITUTION:Fine through-holes 2 of about 20-50mum dia. are made at pitches of about 40-100mum in an electrically insulating film 1 such as a polyimide film in the direction of the thickness by means of a machining method by punching or a dry/wet etching method. Each through-hole 2 filled with metal material 3 by plating, etc., to form a bump-like metal protrusion 4 from both ends of the through-hole 2 in a rivet shape. By making the base area of the metal protrusion 4 larger than the plane area of the through-hole 2, falling of the protrusion 4 is prevented and the reliability of electric connection is increased. The metal material filled as a conductive passage is thus fully stuck to the insulating film without falling of the metal material, so giving the fine hole satisfactory conductivity and increasing the reliability of electric connection.

Description

[Detailed description of the invention]

[0001)

[Industrial application field]

The present invention relates to an anisotropic conductive film. [00023

[Background Art] As electronic devices have become more multifunctional and smaller and lighter in recent years, wiring circuit patterns in the semiconductor field have become highly integrated, and fine patterns with many pins and narrow pitches have been adopted. In order to respond to such fine patterning of circuits, a method has been attempted in which an anisotropic conductive film is interposed between a plurality of conductor patterns formed on a substrate and a conductor pattern connected thereto, or an IC or LSI. There is. [0003] For example, JP-A-55-161306 discloses a sheet in which holes in selected areas of an insulating porous sheet are plated with metal to make them anisotropically conductive. However, since such a sheet does not have a metal protrusion on its surface, when connecting an IC or the like, it is necessary to form a protruding electrode (bump) on the connection pad on the IC side, which complicates the connection process. [0004] Also, JP-A-62-43008 and JP-A-63-4
No. 0218 and Japanese Unexamined Patent Publication No. 63-94504 disclose that micropores provided in the thickness direction of an insulating film are filled with a metal substance to make it conductive anisotropically, and the metal substance is made to protrude from the surface of the film in the form of bumps. Disclosed is one that facilitates the connection. JP-A-3-26-306 (3) [Problem to be Solved by the Invention] However, since such an anisotropic conductive film generally has a structure as shown in FIG. If the adhesion between the metal material and the insulating film is insufficient, the metal substance may fall off, and the micropores that should be conductive may not exhibit conductivity, resulting in a lack of reliability in electrical connection. [0006]

[Means to solve the problem]

Therefore, the present inventors have made extensive studies to solve the above-mentioned problems of conventional anisotropic conductive films, and to provide an anisotropic conductive film that can be reliably made anisotropically conductive and has high connection reliability.
The present invention has now been completed. [0007] That is, the present invention has fine through-holes that conduct independently in the thickness direction of an insulating film, 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. An object of the present invention is to provide an anisotropic conductive film characterized in that it is closed by bump-shaped metal protrusions having a larger base area than the area of the anisotropic conductive film. [00083] The present invention will be explained below using the drawings. FIG. 1 is a sectional view showing an example of the anisotropic conductive film of the present invention. In FIG. 1, an insulating film 1 is provided with minute through holes 2 in the thickness direction, and conductive paths filled with a metal substance 3 reach the front and back surfaces. A bump-shaped metal protrusion 4 having a larger bottom area than the opening area of the through hole 2 is formed at both ends of the through hole 2, and closes the through hole 2 in a so-called rivet shape. [0009] FIG. 2 is a sectional view showing another example of the anisotropic conductive film of the present invention, in which a metal protrusion 4 on a bump is formed at one end of a through hole 20 provided in an insulating film 1. It is something that has been done. [0010] The diameter of the fine through holes 2 is usually 15 to 100 μm, preferably 20 to 50 μm, and the pitch is 15 to 200 A1 m, preferably 40 to 50 μm.
It is set to 100 μm. [0011] In the present invention, the material of the insulating film 1 is not limited as long as it has electrical insulation properties, and may include polyester resin, epoxy resin, urethane resin, polystyrene resin, polyethylene resin, and polyamide resin. ,
Any thermosetting resin or thermoplastic resin, such as polyimide resin, ABS resin, polycarbonate resin, or silicone resin, can be selected depending on the purpose. For example, if flexibility is required, it is preferable to use an elastic material such as silicone rubber, urethane rubber, or fluorine rubber; if heat resistance is required, heat resistant materials such as polyimide, polyether sulfone, or polyphenylene sulfide are used. Preferably, resin is used. Further, the thickness of the insulating film 1 is usually 5 to 200 μm, preferably 10 to 100 μm, from the viewpoint of the accuracy (variation) of the thickness of the thin film, which can be selected arbitrarily, and the accuracy of the diameter of the through holes to be formed. [0012] Examples of the metal substance 3 serving as a conductive path and the metal substance forming the bump-shaped metal protrusion 4 filling the fine through-holes provided in the insulating film 1 include gold, silver, copper, tin-lead, nickel, Various metals such as cobalt and indium, or various alloys containing these as components are used. If the purity of such metal substances is too high, it is difficult to form bumps, so
It is preferable to use a metal substance or alloy mixed with a small amount of a known organic or inorganic substance. As a method for forming the conductive path, various methods such as sputtering, various types of vapor deposition, and various types of plating can be adopted. In addition, when using the plating method, by increasing the plating time, the metal protrusions 4 are formed in a bump shape.
can grow. [0013] The fine through-holes 2 formed in the insulating film 1 can be formed by a mechanical processing method such as punching, a dry etching method using laser plasma or the like, or a chemical wet niche leg method using chemicals, solvents, or the like. In the case of the etching method, the insulating film 1 is shaped into a desired flower shape, such as round, square, etc.
An indirect etching method in which a mask with a diamond shape or the like is placed in close contact with the mask and the process is performed from above the mask, and a laser beam with a narrowed spot is applied. There are dry etching methods in which a laser beam is imaged onto the film by exposing it to a lonorm or through a mask, and direct etching methods in which fine holes are patterned in advance using a photosensitive resist and wet etching is performed. Dry etching and wet etching are preferable for patterning, and dry etching using ablation with an ultraviolet laser such as an excimer laser is particularly preferable because a high aspect ratio can be obtained. [0014] For example: , fine through holes 4 are formed in the film 1 by laser light.
3, the diameter of the through hole in the film surface on the side irradiated with laser light is larger than the diameter of the through hole formed in the film surface on the opposite side. In addition, in FIGS. 1 and 2, the formation angle α of the through hole 2 is 90±2
0 degrees, and the area of the planar shape of the through hole 2 is [film thickness x
5/4] By making it larger than 2, it becomes effective in the subsequent metal filling in terms of wettability of the plating liquid into the hole. [0015] The bump-shaped metal protrusion 4 formed at the opening of the through hole 2 has a bottom area larger than the planar 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 the insulating film 1 has sufficient strength against shearing force in the thickness direction. This improves electrical connection reliability. [0016] As a method for obtaining the anisotropic conductive film of the present invention,
For example, a method consisting of the following steps can be mentioned. [0017] ■Laminated film of insulating film and conductive layer (3-layer film with adhesive or 2-layer film directly laminated)
Either provide fine through holes only in the insulating film, or laminate a conductive layer on the insulating film provided with the fine through holes (however, the conductive layer is laminated so that the fine holes penetrate through it, or the lamination solution is removed). . After forming a resist layer on the surface of the conductive layer to insulate the surface, etching the through hole to form a rivet-like groove in the portion of the conductive layer in contact with the through hole. [0018] (2) 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 a bump-shaped metal protrusion. [0019] (1) A step of removing the conductive layer and resist layer laminated on the insulating film using a chemical etching solution or electrolytic corrosion. [0020] Note that in the above step (1), the formation of bump-shaped metal protrusions may be performed after the step (2). [0021] When forming a bump-shaped metal protrusion on one side of the insulating film in the anisotropic conductive film of the present invention, as shown in FIG. It is preferable to form metal protrusions of the shape. Therefore, in the insulating film 1 as shown in FIG. 3, the conductive layer in step (2) is formed on the side where the bump-shaped metal protrusions 4 are formed (lower surface side in the figure). [0022] In order to form a bump-shaped metal protrusion, it is preferable that the metal crystal is in a fine crystal state. Note that when electrolytic plating is performed at a high current density, dendritic crystals are formed, so the bump-like shape may not be obtained. Moreover, smooth and uniform protrusions can be obtained by adjusting the precipitation rate of metal crystals, the type of plating solution, and the temperature of the plating bath. [0023] In the present invention, in order to make the bump-shaped metal protrusion have a larger bottom area than the opening area of the through hole, the plating film is placed on the opening surface, that is, the insulating film surface, during the plating. It is necessary to grow high and also to grow laterally from the through hole in a rivet-like manner, and the height can be set arbitrarily depending on the hole pitch and purpose, and is usually adjusted to 5 μm or more, preferably in the range of 5 to 100 μm. be done. [0024] Furthermore, when forming rivet-like bumps by removing the conductive layer at the bottom of the through-hole (Tokuhohei 3-26G30G (7) When forming bumps on both sides), etching is performed at 1 part of the diameter of the through-hole. .1 times or more is preferable. When it is less than 1.1 times, the effect as a rivet-like bump becomes poor and the desired effect may not be exhibited. [0025]

【Example】

Examples of the present invention will be shown below and will be explained more specifically. [0026] Thickness of polyimide precursor solution after drying on copper foil: 1ml
It was coated and cured to produce a two-layer film of copper foil and polyimide film. [0027] Next, dry etching was performed by irradiating the surface of the polyimide film with KrF excimer laser light with an oscillation wavelength of 248 nm through a mask to form 5 fine through holes with a diameter of 60 μm and a pitch of 200 μm in the polyimide film layer.
It was set up in an area of 80 m2. [0028] Next, a resist was applied to the surface of the copper foil, cured, and insulated, and immersed in a chemical polishing solution at 50° C. for 2 minutes. [0029] After washing this with water, the copper foil part was connected to an electrode and immersed in a cyanide gold plating bath at 60°C, the copper foil was used as a negative electrode,
Gold plating was grown in the through-holes of the two-layer film, and the plating process was interrupted when all the crystals slightly protruded from the surface of the polyimide film (protrusion height 5 μm). [0030]Finally, the applied resist layer was peeled off and the copper foil of the two-layer film was dissolved and removed with cupric chloride to obtain an anisotropic conductive film of the present invention.

[0031]

【Effect of the invention】

Since the anisotropic conductive film of the present invention has the above structure, the metal substance filled as a conductive path is in sufficient contact with the insulating film, and the metal substance does not fall off and is inherently conductive. The fine pores that must be connected exhibit sufficient conductivity, and the connection reliability is high.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of an anisotropic conductive film of the present invention.

FIG. 2 is a sectional view showing another example of the anisotropic conductive film of the present invention.

[Figure 3] FIG. 2 is a cross-sectional view of a conventional anisotropic conductive film with bumps.

[Explanation of symbols]

1 Insulating film 2 Fine through holes 3 Metallic substances 4 Bump-shaped metal protrusions electricity

【Document name】

[Figure 1]

[Figure 2]

[Figure 3] drawing

Claims (1)

[Claims] Claim 1: An insulating film has 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. An anisotropic conductive film characterized in that it is blocked by bump-shaped metal protrusions having a large base area.