Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Die bond
Reexamination Certificate
2000-07-26
2002-07-30
Clark, Jasmine J. B. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Die bond
C257S787000, C257S788000, C257S789000, C257S790000
Reexamination Certificate
active
06426566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an anisotropic conductive film, a method for mounting a semiconductor chip, and a semiconductor device, and more particularly, to an anisotropic conductive film which appropriately mounts a semiconductor chip to a substrate with an active element formation surface of the chip facing the substrate, a method for mounting a semiconductor chip, and a semiconductor device.
2. Description of Related Art
Anisotropic conductive films are typically employed for so-called flipchip mounting, in which a semiconductor chip is mounted with the surface thereof bearing electrodes looking downward. An anisotropic conductive adhesive is formed in a sheet, and is called ACF (anisotropic conductive film). The thickness of the ACF is 50 &mgr;m approximately. The ACF has an elongated tape-like configuration, and before use, a cover film remains attached on both sides of the ACF.
The ACF is typically produced by applying electrically conductive particles, such as epoxy resin particles plated with a metal such as Ni or Au, to an epoxy-based or polyurethane-based thermosetting resin. Also occasionally in use are metal-coated resin particles which are further coated with a resin. In such a case, when the resin particles are in contact with each other or in contact with a bump of a semiconductor chip, the surface resin coatings are destroyed, assuring electrical conduction therebetween.
A typical mounting method of a semiconductor chip employing a conventional anisotropic conductive film is now discussed. FIGS.
8
(A) and
8
(B) are cross-sectional views showing a semiconductor chip using a conventional anisotropic conductive film. FIG.
8
(A) is the cross-sectional view showing the semiconductor chip that is thermo-compression bonded through the conventional anisotropic conductive film, and FIG.
8
(B) is the cross-sectional view showing the semiconductor chip that is mounted on a warped substrate using a conventional anisotropic conductive film. Referring to FIG.
8
(A), the anisotropic conductive film
3
is glued onto the substrate
2
having a wiring pattern
21
thereon. The semiconductor chip
1
is mounted on the anisotropic conductive film
3
with bumps
11
formed on electrodes of the semiconductor chip
1
facing the wiring pattern
21
. Using a thermo-compression tool
51
, the semiconductor chip
1
is heated from the surface thereof opposite to the surface bearing the bumps
11
while being pressed in the direction of an arrow A.
When heated, the anisotropic conductive film
3
gains fluidity, filling the space surrounding the bump
11
and the wiring pattern
21
, and furthermore flows out of bonding surfaces between the semiconductor chip
1
and the substrate
2
, and clings to the sides of the semiconductor chip
1
. Some of electrically conductive particles
36
are clamped between the bump
11
and the wiring pattern
21
.
After the thermo-compression process, when the setting of the anisotropic conductive film
3
is completed, the semiconductor chip
1
and the substrate
2
are bonded through the anisotropic conductive film
3
. The anisotropic conductive film
3
clinging to the sides of the semiconductor chip
1
forms a fillet
34
, reinforcing the mechanical bond between the semiconductor chip
1
and the substrate
2
. The electrically conductive particles
36
clamped between the bump
11
and the wiring pattern
21
serve as an electrically conductive medium.
SUMMARY OF THE INVENTION
The above-referenced conventional art suffers from the following drawback.
When the fluidity of the anisotropic conductive film
3
is relatively large, the anisotropic conductive film
3
easily flows and clings not only to the sides of the semiconductor chip
1
but also to the thermo-compression tool
51
, as represented by a deposit
35
as shown in FIG.
8
(A), when the semiconductor chip
1
is heated and pressed by the thermo-compression tool
51
. The management of the steps involved in the thermo-compression process of the semiconductor chip increases if part of the anisotropic conductive film
3
frequently clings to the thermo-compression tool
51
, the thermo-compression tool
51
frequently needs cleaning.
When the fluidity of the anisotropic conductive film
3
is small, the anisotropic conductive film
3
tends to remain between the bump
11
and the wiring pattern
21
when the semiconductor chip
1
is heated and pressed by the thermo-compression tool
51
. There occurs a variation in connection resistance of the bumps
11
. Particularly when the substrate
2
has a warp, the anisotropic conductive film and the substrate fail to properly join each other, and some of the bumps
11
and the wiring pattern
21
suffer from a point contact as represented by a point contact area
39
. In extreme cases, no electrical connection is established between the bump
11
and the wiring pattern
21
.
The present invention resolves the above conventional problems. It is an object of the present invention to provide an anisotropic conductive film which reliably assures electrical connection between a substrate and a semiconductor chip and prevents the anisotropic conductive film from clinging to a thermo-compression tool, thereby permitting manufacturing steps to be easily managed.
It is another object of the present invention to provide a semiconductor device incorporating the anisotropic conductive film.
To achieve the above objects, as recited in accordance with one exemplary embodiment of the present invention, an anisotropic conductive film of the present invention, which bonds a semiconductor chip to a substrate while serving as an electrically conductive medium between the semiconductor chip and the substrate, includes in lamination a first layer including at least one layer structure having electrically conductive particles, and a second layer including at least one layer structure having a fluidity higher than the fluidity of the first layer.
When heated, the anisotropic conductive film of claim 1, as constructed, creates a different fluidity between the first layer and the second layer. With the first layer less fluid and thus higher in hardness, the anisotropic conductive film is prevented from flowing out from between the semiconductor chip and the substrate when the semiconductor chip is bonded to the substrate by thermo-compression. The number of electrically conductive particles interposed between the electrodes of the semiconductor chip and the electrodes of the substrate is thus increased. On the other hand, with the second layer being more fluid and softer than the first layer, the anisotropic conductive film easily flows outward from between the semiconductor chip and the substrate when the semiconductor chip is bonded by thermo-compression to the substrate. This arrangement forms the fillet clinging to the sides of the semiconductor chip without impeding the contact between the chip electrodes and the substrate electrodes.
Compared to the amount of resin flowing out in the conventional anisotropic conductive film, the amount of resin flowing out from between the semiconductor chip and the substrate is reduced. This arrangement prevents the anisotropic conductive film from clinging to the thermo-compression tool. As a result, the mechanical bond between the semiconductor chip and the substrate is securely maintained while the reliability of the electrical connection therebetween is increased. The management of the bonding step of the semiconductor chip to the substrate is simplified.
In order to reduce the amount of the anisotropic conductive film clinging to the sides of the semiconductor chip, the thickness of the above anisotropic conductive film is preferably equal to the thickness of the conventional film. If the density of the electrically conductive particles contained in the electrically conductive particle containing layer is equal to that of the conventional anisotropic conductive film, the number of the electrically conductive particles per unit volume will be smaller than tha
Clark Jasmine J. B.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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