Metal fusion bonding – Process – Preplacing solid filler
Reexamination Certificate
1999-03-24
2002-10-01
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
Process
Preplacing solid filler
C228S180210
Reexamination Certificate
active
06457633
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method of forming a semiconductor device, a method of forming a circuit board, and a semiconductor-device forming device. The present invention particularly relates to a method of forming a semiconductor device having solder balls thereof arranged at small holes formed in a board, and a method of forming a circuit board used in such a semiconductor device, and a semiconductor-device forming device for manufacturing such a semiconductor device.
In recent years, a fine-pitch BGA (ball-grid array) has been widely used to respond to the demand for miniaturization and increased circuit density of semiconductor devices.
The fine-pitch BGA includes a semiconductor chip mounted on a surface of a board and a resin package to cover the semiconductor chip, and further includes solder balls provided as external connection terminals on the other surface of the board.
In order to further pursue miniaturization and increased circuit density of the semiconductor device, pitches between the solder balls need to be further narrowed. Since reliable semiconductor devices are expected, a certain degree of reliability must be maintained even when pitches of the solder balls are further narrowed.
2. Description of the Related Art
FIG. 1
is an illustrative drawing showing a semiconductor device
1
A having a FBGA (fine-pitch ball-grid array) structure. The semiconductor device
1
A of
FIG. 1
is an “overmold” type. The semiconductor device
1
A mainly includes a board
2
, a semiconductor chip
3
, a resin package
8
, and a solder ball
10
.
The board
2
is formed from a resin film, and has the semiconductor chip
3
mounted thereon via an adhesive. The board
2
has a hole
7
formed at a predetermined location thereof. A conductive sheet
5
is formed by plating copper (Cu) or gold (Au) at the hole
7
on the side where the semiconductor chip
3
is mounted. The conductive sheet
5
serves as an electrode, and is hereinafter referred to as an electrode sheet
5
. In this configuration, one end of the hole
7
is closed by the electrode sheet
5
.
In the hole
7
, a via portion
9
is formed by using solder. The via portion
9
is connected to the solder ball
10
to together form a single inseparable part. In this manner, the solder ball
10
is electrically connected to the electrode sheet
5
through the via portion
9
. The solder ball
10
serves as an external connection terminal, and is provided to project from the surface of the board
2
.
In the semiconductor device
1
A of the overmold type as shown in
FIG. 1
, the semiconductor chip
3
and the electrode sheet
5
are connected by a wire
6
. The resin package
8
is formed by using a transfer mold method, for example, and serves to protect the semiconductor chip
3
, the electrode sheet
5
, and the wire
6
.
FIG. 2
is an illustrative drawing showing a semiconductor device
1
B having a FBGA structure of a flip-chip type. In the semiconductor device
1
B of
FIG. 2
, a stud bump
11
is formed on the semiconductor chip
3
, and is connected to the electrode sheet
5
via flip-chip bonding. In some configurations, a solder bump is used in place of the stud bump
11
. In
FIG. 2
, the same elements as those of
FIG. 1
are referred to by the same numerals.
The semiconductor device
1
A and the semiconductor device
1
B having the FBGA structure described above have the solder ball
10
serving as an external connection terminal. A manufacturing process for forming the semiconductor device
1
A or the semiconductor device
1
B thus necessarily includes a ball mounting step for mounting the solder ball
10
on the board
2
.
FIGS. 3 through 5
are illustrative drawings showing related-art methods of mounting the solder ball
10
on the board
2
. It should be noted that the methods shown in
FIGS. 3 through 5
are directed to the semiconductor device
1
A of FIG. l.
In
FIG. 3
, the solder ball
10
with a flux
12
(or solder paste) applied thereto in advance is inserted into the hole
7
of the board
2
.
FIG. 4
shows the way the solder ball
10
is inserted into the hole
7
.
In the related art, it is possible for adjacent solder balls to have as large a pitch as 0.8 mm therebetween, so that a diameter L
1
of the hole
7
can be proportionally large (e.g., can be 0.30 to 0.40 mm). In such a case, a diameter R of the solder ball
10
may generally range from 0.40 mm to 0.50 mm. When the solder ball
10
is inserted into the hole
7
, the solder ball
10
may be completely buried in the hole
7
, or may be partially but almost entirely cloistered in the hole
7
, depending on the diameter R of the solder ball
10
.
After the solder ball
10
is inserted into the hole
7
, a reflow process (i.e., heating process) is performed to melt the solder ball
10
. Since the solder ball
10
is completely or almost entirely cloistered in the hole
7
, the melted solder ball
10
fills the hole
7
securely so as to contact the electrode sheet
5
. Solder in excess of the volume of the hole
7
forms the solder ball
10
on the board
2
with help of the surface tension. In this manner, the semiconductor device
1
A shown in
FIG. 1
is created.
FIG. 5
shows another ball mounting method. In this method, the solder paste
13
is provided in the hole
7
by applying a printing method (i.e., a screen printing method) to the board
2
. As described above, the diameter L
1
of the hole
7
is relatively large in the relate-art configuration, so that the screen printing easily fills the hole
7
with the solder paste
13
. Here, the solder paste
13
is a mixture of organic flux and solder powder.
The solder ball
10
is inserted into the hole
7
filled with the solder paste
13
, and a reflow process is performed. This disperses organic components from the solder paste
13
, and the solder powder is melted to fill the hole
7
. The solder ball
10
is also melted so as to blend with the solder in the hole
7
. In this manner, the semiconductor device
1
A shown in
FIG. 1
is created.
As a circuit density of the semiconductor chip
3
is increased, the number of external terminals tends to increase as has been observed in recent years. Also, semiconductor devices are expected to be increasingly smaller in order to produce an ever smaller electronics equipment.
Against this background, pitches between balls in semiconductor devices are now required to be as small as 0.5 mm. In order to achieve this dimension, a diameter L
1
of a hole needs to be as small as 0.20 to 0.25 mm, and a diameter of a solder ball needs to be about 0.3 mm.
If the ball mounting method as described in connection with
FIGS. 3 and 4
is used in such a small-dimension configuration as described above, an attempt to insert the solder ball
10
into the hole
7
ends up having the solder ball
10
only partially cloistered in the hole
7
because of the relatively small size of the hole
7
compared to the size of the solder ball
10
. This creates a large gap between the solder ball
10
and the electrode sheet
5
. Because of the size of the gap, the reflow process may not be able to electrically connect the solder ball
10
to the electrode sheet
5
.
FIGS. 6A and 6B
are illustrative drawings showing a case in which the ball mounting method of
FIG. 5
is applied to the board
2
having a hole
14
with a diameter L
2
of 0.20 mm. As shown in
FIG. 6A
, an attempt to insert the solder paste
13
in the hole
14
by using a screen printing method fails to sufficiently fill the hole
14
with the solder paste
13
when the diameter L
2
of the hole
14
is as small as 0.20 mm to 0.25 mm. Namely, as shown in the figure, the solder paste
13
may be provided only around the end of the hole
14
.
When the solder ball
10
is mounted in the hole
14
and a reflow process is then performed, solder of the solder paste
13
is absorbed by the melted solder ball
10
, resulting in such a situation as no solder exists inside the hole
14
as shown in FIG.
6
B. In this manner, the ball
Kamimura Kazuya
Kumagaya Yoshikazu
Takashima Akira
Armstrong Westerman & Hattori, LLP
Elve M. Alexandra
Fujitsu Limited
Johnson Jonathan
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