Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With bumps on ends of lead fingers to connect to semiconductor
Reexamination Certificate
2000-10-18
2002-10-15
Ho, Hoai (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With bumps on ends of lead fingers to connect to semiconductor
C257S737000, C257S780000, C438S613000
Reexamination Certificate
active
06465879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure for mounting a semiconductor device wherein a surface mount semiconductor device provided with bumps (protruded electrodes) is electrically and mechanically connected with a circuit board provided with circuit electrodes, and a method of mounting the same. Further, the invention is concerned with a semiconductor device suitable for use in obtaining the structure for mounting, and a method of fabricating the semiconductor device.
2. Description of the Related Art
Surface mount semiconductor devices have come to be in widespread use as a semiconductor device making up an integrated circuit (IC), a large scale integrated circuit (LSI), and so forth.
Among the surface mount semiconductor devices, there is one provided with a multitude of bumps placed in lines on the surface thereof for electrical and mechanical connection with circuit electrodes of a circuit board when mounting the same on the circuit board provided with the circuit electrodes.
FIG. 35
is a schematic view showing the construction in section of a semiconductor device provided with bumps formed in a straight-wall shape by way of example.
With the semiconductor device
10
, a multitude of electrode pads
14
for connecting integrated circuits (not shown in the figure) with an external circuit are provided on the surface (in
FIG. 35
, the upper face) of a semiconductor chip
11
, with the integrated circuits formed therein, in such a way as to run along side edges of the semiconductor chip
11
in the direction orthogonal to the plane of the figure. In
FIG. 35
, there is shown only one of a plurality of the electrode pads
14
placed in respective lines running along the side edge on both sides of the semiconductor chip
11
.
An insulation film
16
having an opening formed over the respective electrode pads
14
in such a way as to cover the peripheral region of the respective electrode pads
14
while exposing the inside of the respective peripheral regions is formed across the surface of the semiconductor chip
11
. A lower electrode
19
is provided so as to be in intimate contact with the peripheral region of the respective openings of the insulation film
16
and an exposed part of the respective electrode pads
14
. Further, on top of the each lower electrode
19
, a bump
22
formed in a straight-wall shape is provided.
There are also bumps formed in the shape of a mushroom wherein the top part of the respective bumps is larger in width than the base thereof. However, the bumps formed in a straight-wall shape are more suitable for reducing lateral spread thereof along a semiconductor chip, and to that extent, placement density of the bumps can be increased, so that a pitch at which connection thereof with an external circuit is made can be rendered minuscule.
FIG. 36
shows a conventional mounting structure wherein a semiconductor device provided with such bumps is mounted on a circuit board provided with circuit electrodes.
In
FIG. 36
, the semiconductor device
10
in a posture inverted from that shown in
FIG. 35
is disposed on a circuit board
26
such that the bumps
22
are positioned on the underside of the semiconductor device
10
, thereby bonding the semiconductor device
10
with the circuit board
26
by use of an anisotropic conductive adhesive
44
.
The anisotropic conductive adhesive
44
is composed of a multitude of electrically conductive particles
42
dispersed in an insulating adhesive
46
, and the respective bumps
22
are electrically connected with the respective circuit electrodes
28
on the circuit board
26
by the agency of the electrically conductive particles
42
while the semiconductor device
10
is mechanically connected with the circuit board
26
by agency of the insulating adhesive
46
.
Herein, a method of fabricating the conventional semiconductor device shown in
FIG. 35
is briefly described with reference to
FIGS. 33 and 34
, and a conventional method of mounting the same is described with reference to FIG.
36
.
First, as shown in
FIG. 33
, across the surface of a semiconductor substrate
12
provided with integrated circuits (not shown) for a plurality of semiconductor chips and a plurality of electrode pads for connecting the integrated circuits with an external circuit, the insulation film
16
is formed, and an opening
16
a
is formed over the respective electrode pads
14
by photo etching method such that most of respective electrode pads
14
are exposed, leaving only the peripheral region thereof covered.
FIGS. 33 and 34
are enlarged sectional views showing only a portion (a region slightly larger than that corresponding to a unit of a semiconductor device) of the semiconductor substrate
12
, respectively.
Subsequently, an aluminum film, a chromium film, and a copper film are sequentially deposited in that order by the sputtering method on the entire surface of the insulation film
16
and a portion of the respective electrode pads
14
exposed inside the respective openings
16
a
, on the semiconductor substrate
12
, thereby forming a common electrode film
18
made up of layered films of aluminum-chromium-copper.
Thereafter, a photosensitive resin film
20
shown in
FIG. 34
is formed to a thickness of 20 to 25 &mgr;m on the entire surface of the common electrode film
18
by the spin coater method, and an opening
20
a
of substantially the same size as the respective electrode pads
14
is formed on portions of the photosensitive resin film
20
, over the respective electrode pads
14
, by photolithography method.
Subsequently, the semiconductor substrate
12
is immersed in a gold plating bath composed of sodium gold sulfite, and by means of electroplating using the common electrode film
18
as a plating electrode, the bump
22
shown in
FIG. 34
is formed to a thickness of 15 &mgr;m to 20 &mgr;m on the common electrode film
18
inside the respective openings
20
a
of the photosensitive resin film
20
.
Thereafter, the photosensitive resin film
20
is removed, the common electrode film
18
is etched using the bumps
22
as etching masks, and most of the common electrode film
18
, other than portions thereof underneath the bumps
22
, is removed, thereby forming lower electrodes
19
shown in FIG.
35
. Thus, a structure wherein the bump
22
is individually installed over the respective electrode pads
14
with the respective lower electrodes
19
interposed therebetween.
Subsequently, a dicing step is applied to the semiconductor chips
12
whereby the semiconductor chips
12
are cut into the individual semiconductor chips
11
, thereby fabricating the semiconductor device
10
as shown in FIG.
35
.
In mounting the semiconductor device
10
on the circuit board, the anisotropic conductive adhesive
44
composed of the electrically conductive particles
42
dispersed in the insulating adhesive
46
made of epoxy resin is interposed between the semiconductor device
10
having a plurality of the bumps
22
and the circuit board
26
having a plurality of the circuit electrodes
28
disposed opposite to the semiconductor device
10
, whereupon pressure and heat are applied between the bumps
22
and the circuit electrodes
28
.
As a result, the electrically conductive particles
42
are sandwiched between the respective bumps
22
and the respective circuit electrodes
28
, thereby effecting electrical connection therebetween. At the same time, the semiconductor device
10
is mechanically connected with the circuit board
26
, and connections between the respective bumps
22
and the respective circuit electrodes
28
are sealed by the agency of the insulating adhesive
46
.
However, with such a conventional structure for mounting a semiconductor device, and a method of mounting the same as described above, ten or more pieces of the electrically conductive particles
42
need to be maintained between the respective bumps
22
and the respective circuit electrodes
28
on the circuit board
26
in order to ensure a sufficiently small co
Armstrong Westerman & Hattori, LLP
Citizen Watch Co. Ltd.
Ho Hoai
Huynh Andy
LandOfFree
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