Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
2000-03-24
2001-08-28
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S668000, C257S780000, C257S747000
Reexamination Certificate
active
06281571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor device having a substrate provided with an through hole to which a protruding electrode such as a solder ball is provided.
Recently, in association with reduction in the size of semiconductor devices and increase in density of circuits in semiconductor devices, the fine pitch BGA (Ball Grid Array) structure has become widely used for semiconductor devices. A semiconductor device having the fine pitch BGA structure comprises a substrate whose front surface is provided with a semiconductor chip and a resin package molding the semiconductor chip. The back surface of the substrate is provided with solder balls as external connection electrodes.
In order to further reduce the size of the semiconductor device having the fine pitch BGA structure and further increase the density of circuits in the semiconductor device having the fine pitch BGA, the pitch of the solder balls must be further reduced. However, since a high reliability is required for semiconductor devices, a predetermined level of reliability must be maintained even when the pitch of the solder balls is reduced.
2. Description of the Related Art
FIGS. 1 and 2
show parts of semiconductor devices
1
A and
1
B having a typical fine-pitch ball grid array (FBGA) structure, respectively.
The semiconductor device
1
A shown in
FIG. 1
is generally referred to as an over molding type BGA. The semiconductor device
1
A comprises a substrate
2
, a semiconductor chip
3
, a plastic package
8
and solder balls
10
(only one shown in the figure).
The substrate
2
is made of a plastic film. The semiconductor chip
3
is mounted on the substrate
2
via an adhesive
4
. Through holes
7
are formed at predetermined positions of the substrate
2
. Only one through hole
7
is shown in FIG.
1
. The opening of the through hole
7
on the surface on which the semiconductor chip
3
is mounted is closed by an electrode film
5
which is formed by copper (Cu) or gold (Au) plating.
A via part
9
is formed inside the through hole
7
. The solder ball
10
is bonded to the via part
9
. Accordingly, the solder ball
10
is electrically connected to the electrode film
5
via the via part
9
. The solder ball
10
protrudes from the surface of the substrate
2
so as to serve as an external connection terminal.
In the over molding type semiconductor device
1
A shown in
FIG. 1
, an electrode of the semiconductor chip
3
is electrically connected to the electrode
5
by a wire
6
. The plastic package
8
is formed by, for example, transfer molding so as to protect the semiconductor chip
3
, the electrode film
5
and the wire
6
.
The semiconductor device
1
B shown in
FIG. 2
is generally referred to as a flip-chip type FBGA. In
FIG. 2
, parts that are the same as the parts shown in
FIG. 1
are given the same reference numerals, and descriptions thereof will be omitted. Stud bumps
11
are formed on the semiconductor chip
3
(only one stud bump
11
is shown in FIG.
2
). The stud bumps
11
may be solder bumps. The semiconductor chip
3
is flip chip bonded to the electrode films
5
.
Each of the semiconductor devices
1
A and
1
B has solder balls
10
as external connection electrodes. Accordingly, the manufacturing process of each of the semiconductor devices
1
A and
1
B includes a ball mounting process to mount the solder balls
10
onto the substrate
2
.
FIGS. 3 through 5
show a method for mounting the solder ball
10
to the substrate
2
. It should be noted that
FIGS. 3 through 5
show a method for manufacturing the semiconductor device
1
A shown in FIG.
1
.
In the ball mounting method shown in
FIG. 3
, an appropriate amount of flux
12
(or solder paste) is previously applied to the solder ball
10
, and the solder ball
10
is inserted into the through hole
7
formed in the substrate
2
.
FIG. 4
shows a state in which the solder ball
10
is inserted into the through hole
7
.
Conventionally, a pitch (ball pitch) between the adjacent solder balls is as large as about 0.8 mm. Thus, the diameter L
1
of the through hole
7
can be as large as 0.30 mm to 0.40 mm. The diameter R of the solder ball
10
is 0.40 mm to 0.50 mm. Accordingly, when the solder ball
10
is applied to the through hole
7
, the entirety of the solder ball
10
is accommodated in the through hole
7
as shown in
FIG. 4
, or most of the solder ball
10
is accommodated in the through hole
7
.
After the solder ball
10
is accommodated in the through hole
7
, a solder reflow process (heating process) is performed. Conventionally, since the entirety or most of the solder ball
10
is accommodated in the through hole
7
, the melted solder ball
10
positively fills the through hole
7
and is bonded to the electrode film
5
. Additionally, excess solder forms the solder ball
10
on the substrate
2
due to a surface tension of the melted solder ball
10
. As a result, the semiconductor device
1
A shown in
FIG. 1
is formed.
On the other hand, in the ball mounting method shown in
FIG. 5
, an appropriate amount of solder paste
13
is applied to the interior of the through hole
7
according to a screen printing method. As mentioned above, the diameter L
1
of the conventional through hole
7
is sufficiently large, therefore an appropriate amount of the solder paste
13
can be easily applied inside the through hole
7
. It should be noted that the solder paste
13
is a mixture of the flux made of an organic material and a solder powder.
Thereafter, the solder ball
10
is applied to the through hole
7
in which the solder paste
13
is applied, and a solder reflow process is performed. Thereby, the organic component contained in the solder paste
13
scatters, and the solder powder is melted, which fills the through hole
7
. Additionally, the solder ball
10
is also melted and brought into contact with the melted solder in the through hole
7
, which results in formation of the semiconductor device
1
A shown in FIG.
1
.
As mentioned above, the number of terminals provided in a single semiconductor device has been increased due to increase in the density of the semiconductor chips. Additionally, there is a demand for the semiconductor devices to be further reduced in size since the electronic equipment in which the semiconductor devices are incorporated is required to be smaller.
Accordingly, the ball pitch of the solder balls provided in the semiconductor device has become as small as 0.5 mm. In order to achieve the ball pitch of 0.5 mm, the diameter L
1
of each through hole must be in the range of 0.20 mm to 0.25 mm. Additionally, the diameter of each solder ball must be about 0.3 mm.
If the ball mounting method mentioned with reference to
FIGS. 3 and 4
is used to form the solder balls of the semiconductor device having the above-mentioned small ball pitch, each solder ball cannot be appropriately inserted into the respective through hole
7
since the diameter of the through hole
7
is much smaller than the diameter of the solder ball
10
. Accordingly, a large distance remains between the solder ball
10
and the electrode film
5
. Thus, even if the solder reflow process is performed, there is a problem in that the solder ball
10
is not electrically connected to the electrode film
5
.
FIGS. 6A and 6B
show an example in which the ball mounting method mentioned with reference to
FIG. 5
is applied to the substrate
2
having a through hole
14
having a diameter of 0.20 mm. When the diameter of the through hole
14
is as small as 0.20 mm to 0.25 mm as shown in
FIG. 6A
, an appropriate amount of the solder paste
13
cannot be filled into the through hole
14
by using a screen printing method. That is, the solder paste
13
is applied to only a limited area near the opening of the through hole
14
.
If the solder reflow process is performed after providing the solder ball
10
to the through hole, the melted solder paste
13
in the through hole
14
is ab
Ando Fumihiko
Kosakai Kazunari
Kumagaya Yoshikazu
Sato Mitsuru
Suzuki Takashi
Armstrong Westerman Hattori McLeland & Naughton LLP
Clark Sheila V.
Fujitsu Limited
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