JP2000036515A - Bare chip mounting structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To connect a bump-less IC chip with the terminal of a circuit board at low costs, by using an anisotropic conductive bounding material, and to maintain the high operation stability of the IC chip. SOLUTION: A bump-less chip IC1 in which an organic insulating film 6 is formed on a passivation film 4 and a circuit board 10 are connected by an anisotropic conductive bonding material 20 including hard conductive particles 23, at least whose surfaces are metal in this bare chip mounting structure. It is desired that the hardness of the hard conductive particles 23 is 300 kgf/mm2 or more as compressed hardness K value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bare chip mounting structure for flip-chip mounting an IC chip at low cost without forming bumps.

[0002]

2. Description of the Related Art In recent years, as market needs for electronic devices with higher functionality, lighter weight, thinner, and smaller sizes have increased, flip-chip mounting in which bare chips are directly mounted on printed wiring boards and other substrates has been performed. ing.

In this flip chip mounting, generally, as shown in FIG. 2, gold, solder or the like is previously placed on an Al electrode pad 2 of an IC chip 1 through a barrier layer such as Ti if necessary. To form bumps 3 and circuit board 1
0 terminal 11 and conductive particles 21 and insulating adhesive 22
The connection is made with an anisotropic conductive adhesive 20 made of.

[0004]

However, since it takes time and cost to form the bumps 3 on the IC chip 1, a product having a mounting structure as shown in FIG. 2 cannot improve the productivity. The cost is increased. In addition, since the formation of the bumps 3 is usually entrusted to a specialized trader, a maker who mounts the IC chip 1 on the circuit board 10 and manufactures an electronic device has a problem that the secret of the IC chip 1 is leaked to the outside. Becomes

To solve such a problem, as shown in FIG. 3, the Al electrode pad 2 is directly connected to the terminal 11 of the circuit board 10 without forming a bump on the Al electrode pad 2 of the IC chip 1. Connecting with an anisotropic conductive adhesive 20 is conceivable.

In the IC chip 1 in which no bump is formed on the Al electrode pad 2 as described above, an Al oxide film is formed on the surface of the Al electrode pad 2. In order to make connection, the conductive particles used for the anisotropic conductive adhesive 20 are hard particles (hard conductive particles) that break the Al oxide film on the surface of the Al electrode pad 2 to enable electrical conduction during connection. 23)
You need to use Therefore, the hard conductive particles 2
As 3, metal particles such as Ni are used.

However, when the hard conductive particles 23 such as metal particles are used as the conductive particles, the amount of the bumps is reduced by the absence of bumps.
The distance between the passivation film 4 of the chip 1 and the circuit board 10 or its terminals 11 is reduced. Therefore, when connecting the IC chip 1 and the circuit board 10 using the anisotropic conductive adhesive 20, cracks 5 are formed on the passivation film 4 by the action of the hard conductive particles 23 in the anisotropic conductive adhesive 20.
And the circuit under the passivation film 4 is easily corroded, and the operation stability of the IC chip 1 is reduced.

[0008] The present invention solves the above-mentioned problem of flip-chip mounting a bare chip on a substrate by connecting a bumpless IC chip and a terminal of a circuit board at low cost using an anisotropic conductive adhesive. It is another object of the present invention to prevent cracks from entering the passivation film of the IC chip and to maintain high operation stability of the IC chip.

[0009]

In order to achieve the above object, the present invention provides a bumpless bear chip IC having an organic insulating film formed on a passivation film and a circuit board, wherein at least the surface is formed of hard conductive particles having a metal surface. The present invention provides a bare chip mounting structure characterized by being joined by an anisotropic conductive adhesive containing:

Since the bare chip IC used in the present invention does not have bumps, when mounted on a circuit board, its bare chip
An Al oxide film is formed on the electrode pad surface. However, as the conductive particles of the anisotropic conductive adhesive for connecting the IC chip and the circuit board, hard conductive particles having at least a metal surface are used. The conductive particles break the Al oxide film, and it is possible to secure conduction between the Al electrode pad of the IC chip and the terminal of the circuit board.

In the present invention, an IC chip having an organic insulating film formed on a passivation film is used as an IC chip to be mounted. The organic insulating film functions as a buffer between the hard conductive particles and the passivation film, and prevents the passivation film from being cracked.

Therefore, according to the present invention, it is possible to obtain an IC chip mounting structure which is inexpensive and has good operation stability of the IC chip. The mounting structure of the present invention is also useful for IC chip package applications, and is also useful for forming a multi-chip module by repeatedly forming this mounting structure.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The anisotropic conductive adhesive of the present invention will be described below in detail with reference to the drawings. In each figure,
The same reference numerals represent the same or equivalent components.

FIG. 1 is a sectional view of a bare chip mounting structure according to the present invention. As shown in the figure, in the present invention, the IC chip 1 has no bump on the Al electrode pad 2, has an organic insulating film 6 on the passivation film 4,
The structure is such that the C chip 1 and the terminal 11 of the circuit board 10 are connected using an anisotropic conductive adhesive 20.

Here, as the passivation film 4,
A known SiN film or the like formed as a surface protective film in the final stage of the production of the IC chip can be used as it is.

As the organic insulating film 6 on the passivation film 4, the hard conductive particles 23 in the anisotropic conductive adhesive 20 are used.
Functions as a buffer for the passivation film 4 of
Various insulating films can be formed as long as the generation of cracks in the passivation film 4 can be prevented.
For example, BT resin (bismaleimide triazine resin), PEEK (polyetheretherketone), PP
S (polyphenylene sulfide), POB (polyoxybenzoyl), PEI (polyetherimide), PAI
A film such as (polyamide imide) can be formed.
Among them, a polyimide film having a thickness of 1 to 10 μm is preferable from the viewpoint of buffering property and heat resistance.

The organic insulating film 6 can be formed by applying a photosensitive organic insulating film forming composition so that the Al electrode pad 2 is opened, exposed to light, and etched.

On the other hand, as the anisotropic conductive adhesive 20, a material having at least a surface made of hard conductive particles 23 of metal and an insulating adhesive 22 is used.

The conductive particles constituting the anisotropic conductive adhesive 20 include hard conductive particles 23 having at least a metal surface.
When the IC chip 1 and the circuit board 10 are connected to each other with the anisotropic conductive adhesive material 20, the Al oxide film formed on the Al electrode pad 2 is broken and the Al electrode pad 2 and the circuit board Conduction with the ten terminals 11 can be ensured.

As the hard conductive particles 23, it is preferable to use particles having a hardness of 300 kgf / mm ² or more as a compression hardness K value. This compression hardness K value is expressed by the following equation (I)

[0021]

K = E / (1−σ ² ) (I) (where E represents the elastic modulus of the sphere and σ represents the Poisson's ratio of the sphere), and the following equation (II)

[0022]

[Number 2] K = (3 / √2) · F · S -3/2 · R -1/2 (II) ( wherein, F is compressive force applied to the sphere, S is the amount of compressive deformation, R
Represents the radius of the sphere. ) Is a value approximately determined by the formula (1), and represents the hardness of the sphere universally and quantitatively. Therefore, the hardness of the fine particles can be quantitatively and uniquely represented by the K value.

This equation (II) is derived as follows. That is, the Landau-Lifshitz theoretical physics curriculum "Elasticity" (published by Tokyo Book, 1972), p.
Equations (1) and (2), which are equations for contact between two elastic spheres

[0024]

H = F ^2/3 [D ² (1 / R + 1 / R ′)] ^1/3 (1) D = (3/4) [(1−σ ² ) / E + (1−σ ′ ²⁾ ) / E '] (2) (where R and R' are the radii of the respective elastic spheres, h is the difference between the distance between R + R 'and the center of the two spheres, F is the compressive force, and E and E' are 2)
The elastic modulus of one elastic sphere, σ and σ ′, represent the Poisson's ratio of the two elastic spheres. ), One of the elastic spheres is replaced by a plate and compressed from both sides to make R ′ → ∞ and E≫E ′, thereby approximating the following equation (3).

[0025]

F = (2 ^1/2/3 ) (S ^3/2 ) (E · R ^1/2 ) (1-σ ² ) (3) (where S represents the amount of compressive deformation) And this equation (3)
Is applied to the above-described definition equation (I) of K to obtain the above-described equation (II).

Specific examples of the hard conductive particles 23 include N
i, metal particles made of hard solder, Co, Cu, or the like; and particles obtained by forming a metal layer of Ni, Co, Cu, etc. on the surface of a hard plastic as a core material. When solder particles are used, a low α-ray type having a low Pb content is preferable from the viewpoint of memory protection of the IC.

The particle size of the hard conductive particles 23 depends on the material for forming the organic insulating film 6, but is preferably not less than the thickness of the organic insulating film 6, particularly preferably 150% to 400% of the film thickness. Usually, it is preferably 1.5 to 20 μm. Thereby, the hard conductive particles 23 can be effectively deformed, and the connection reliability can be secured.

As the insulating adhesive 22 constituting the anisotropic conductive adhesive 20, various thermosetting adhesives or thermoplastic adhesives can be used. From the viewpoint of reliability after mounting the IC chip 1, epoxy resin, urethane resin,
It is preferable to use a thermosetting adhesive such as an acrylate resin or a BT resin. When preparing an insulating adhesive from these resin components, a single type of resin component may be used, or a plurality of types may be mixed and used.

As the anisotropic conductive adhesive 20, one prepared by mixing the hard conductive particles 23 and the insulating adhesive 22 to prepare a liquid or a film can be used. It is preferable to use a film-like material from the viewpoint of workability.

There is no particular limitation on the circuit board 10 on which the IC chip 1 is mounted. A well-known film-shaped or plate-shaped printed wiring board can be used.

An IC using the anisotropic conductive adhesive 20 described above
In connecting the chip 1 and the circuit board 10 to obtain the mounting structure of the present invention, an anisotropic conductive adhesive 20 is provided between the IC chip 1 and the circuit board 10 and heated and pressed.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Examples 1 to 3 and Comparative Examples 1 and 2 As shown in FIG. 4, on the entire surface of the IC chip 1, Al patterns 7 at 2 μm intervals were used as crack check patterns.
Was formed thereon, and a passivation film was formed thereon so that the Al electrode pad 2 formed over the entire periphery of the IC chip 1 was opened. Further, in Examples 1 to 3, a polyimide film having a thickness of 2 μm or 5 μm was provided on the passivation film as shown in Table 1. The pattern of the polyimide film was formed by applying a photosensitive polyimide film, exposing it to light, and etching.

On the other hand, an anisotropic conductive adhesive was prepared from an insulating adhesive containing a phenoxy resin, an epoxy resin, and a curing agent in a weight ratio of 50:50:30, and the conductive particles shown in Table 1. This was formed into a film so as to have a dry film thickness of 20 μm to obtain an anisotropic conductive film. The obtained anisotropic conductive film is stuck on a wiring board, and the above-mentioned IC chip is superimposed thereon, and the temperature is set to 180 ° C. and the pressure is set to 400 kgf / cm ² for 20 minutes.
The IC chip was mounted by heating and pressing for 2 seconds. In addition, instead of forming the anisotropic conductive film and attaching it to the wiring board, an IC chip can be similarly formed by directly applying an anisotropic conductive adhesive on the wiring board so as to have a dry film thickness of 20 μm. Could be implemented.

Evaluation Regarding the mounting structure of the IC chips manufactured in the examples and comparative examples, (1) the presence or absence of cracks in the passivation film immediately after mounting and after aging, and (2) the conductivity were evaluated as follows. Table 1 shows the results.

(1) Presence or Absence of Cracks in Passivation Film When the conductive particles cause cracks in the passivation film and reach the Al pattern 7, the Al pattern 7 in FIG.
Was short-circuited, and the presence or absence of cracks in the passivation film immediately after mounting was determined by checking the presence or absence of short-circuits by a continuity test. Further, when humidification aging is performed in an oven at a temperature of 85 ° C. and a humidity of 85%, if cracks enter the passivation film, moisture penetrates and the Al pattern 7 is corroded. Was observed and the presence or absence of the corrosion was examined to determine the presence or absence of cracks in the passivation film after aging.

(2) Conductivity A 1 mA current is applied to the connection between the IC chip and the terminal of the wiring board by the anisotropic conductive film by the four-terminal method, the voltage applied to the connection is measured, and the resistance of the connection is measured. (See FIG. 4). In this case, the resistance of the connection portion was measured immediately after mounting the IC chip and after humidification aging in an oven at a temperature of 85 ° C. and a humidity of 85%. When the resistance after humidification and aging became twice or more as large as the resistance immediately after mounting, conduction was evaluated as unstable, and less than twice was evaluated as good.

[0038]

[Table 1] Example 1 Example 2 Example 3 Example 3 Polyimide film thickness 2 μm 2 μm 5 μm Conductive particles (particle size) Ni (6 μm) Plastic core (5 μm) Leadless solder (5 μm) Ni plating (0.2 μm) Compression hardness K value (kgf / mm ² ) Approx.6000 800 Approx.4000 hash film crack Immediately after mounting None None None After aging None None None Conductivity Immediately after mounting Good Good Good After aging Good Good Good Comparative example 1 Comparative example 2 Polyimid film None None Conductive particles (particle size) Ni (6 μm) Plastic core (5 μm) Ni plating (0.2 μm) Compression hardness K value (kgf / mm ² ) Approx. 6000 200 Immediately Yes No After post-acquisition Yes No Conductivity Immediately after mounting Good Unstable Post-acquisition Good Unstable

From the results shown in Table 1, it can be seen that cracks in the passivation film can be prevented by providing the polyimide film on the IC chip. Further, it can be seen that if the conductive particles are soft, sufficient conduction with the Al electrode pad cannot be obtained (Comparative Example 2).

[0040]

According to the present invention, the IC chip and the terminal of the substrate are connected at low cost by using an anisotropic conductive adhesive, and in this case, the passivation film of the IC chip can be formed without forming bumps. Cracks do not occur, and the operation stability of the IC chip can be kept high.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mounting structure of an IC chip of the present invention.

FIG. 2 is a cross-sectional view of a conventional IC chip mounting structure.

FIG. 3 is a cross-sectional view of a bumpless mounting structure of a conventional IC chip.

FIG. 4 is a plan view of an Al pattern formed on an IC chip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 IC chip 2 Al electrode pad 3 Bump 4 Passivation film 5 Crack 6 Organic insulating film 7 Al pattern 10 Circuit board 11 Terminal 20 Anisotropic conductive adhesive 21 Conductive particles 22 Insulating adhesive 23 Hard conductive particles

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Motohide Takeichi 12-3 Satsukicho, Kanuma-shi, Tochigi Sony Chemical Corporation F-term (reference) 4M105 AA01 BB09 FF00 FF06

Claims (4)

[Claims] 1. A bumpless bear chip IC having an organic insulating film formed on a passivation film and a circuit board are bonded at least on their surfaces with an anisotropic conductive adhesive containing hard conductive particles of metal. Features a bare chip mounting structure. 2. The bare chip mounting structure according to claim 1, wherein the hardness of the hard conductive particles is 300 kgf / mm ² or more as a compression hardness K value. 3. The bare chip mounting structure according to claim 1, wherein the organic insulating film is a polyimide film. 4. The bare chip mounting structure according to claim 1, wherein the thickness of the polyimide film is 1 to 10 μm.