Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-02-25
2001-05-08
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S767000, C361S807000, C361S808000, C257S778000, C257S780000, C257S737000, C257S738000, C174S050510, C174S050510, C174S259000, C174S260000, C174S262000
Reexamination Certificate
active
06229711
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a flip-chip mount board and a flip-chip mount structure, and particularly relates to a flip-chip mount board provided with a plurality of conductor patterns to which a plurality of bumps provided on an electronic component can be connected via a connection medium provided on the conductor patterns.
2. Description of the Related Art
Recently, there is an improvement in the density of electronic components such as semiconductor chips. Accordingly, finer pitch is required for external connection terminals, such as bumps, provided on electronic components.
Therefore, as for a mount board, it is necessary to provide connection pads at a considerably high density. The mount board, to which the above-described electronic components are to be mounted, is hereinafter referred to as a flip-chip mount board. Also, a high reliability is required when flip-chip mounting the electronic components.
Now, a flip-chip mounting process of an electronic component, e. g., a semiconductor chip, onto a flip-chip mount board will be described. First of all, connection part conductor patterns (hereinafter referred to as conductor patterns) are formed on the flip-chip mount board. Then, the conductor patterns are provided with solder serving as a connection medium. Finally, the flip-chip mounting process is completed by connecting the bumps (e.g., gold bumps) provided on the semiconductor chip to the conductor patterns.
FIGS. 1 and 2
are an enlarged perspective diagram and a plan view, respectively, partially showing a flip-chip mount board
1
. As shown in
FIGS. 1 and 2
, the flip-chip mount board
1
includes a circuit board
2
, conductor patterns
3
A,
3
B, a solder resist
4
and solder lumps
5
.
The conductor patterns
3
A,
3
B are provided on an upper surface of the circuit board
2
so as to form a predetermined pattern. As shown in
FIG. 3
, a bump
8
made of gold, for example, provided on a semiconductor chip
7
may be connected to a part of the conductor pattern
3
A,
3
B. Hereinafter, a part of the conductor pattern
3
A,
3
B, to which part the gold bump
8
is to be connected, will be referred to as a connection pad
9
.
Now, the width of the connection pad
9
will be described in detail. As shown in
FIG. 2
, the conductor pattern
3
A,
3
B including the connection pad
9
has a uniform width W
3
along the whole length. The width W
3
is approximately 30 to 60 &mgr;m.
Also, the solder resist
4
serving as an insulator is provided over the circuit board
2
, except for positions over the conductor patterns
3
A,
3
B to which positions the semiconductor chip
7
may connected.
In other words, the solder resist
4
is provided with an opening
4
a
at a position where the semiconductor chip
7
and the conductor patterns
3
A,
3
b
are connected. The gold bumps
8
will be connected to the parts of the conductor patterns
3
A,
3
B exposed by the opening
4
a.
Therefore, the remaining parts of the conductor patterns
3
A,
3
B are covered, and thus protected, by the solder resist
4
.
As shown in
FIG. 2
, the conductor pattern
3
A is covered by the solder resist
4
on both ends. The conductor pattern
3
B is covered by the solder resist
4
on one end. The other end of the conductor pattern
3
B terminates before reaching the solder resist
4
.
Generally, in order to mount a semiconductor chip securely on a flip-chip mount board, it is necessary to provide a solder layer having a uniform thickness onto connection pads. In order to achieve a uniform thickness, it is advantageous to increase an area of the connecting pad because the total number of solder particles provided on the connection pad will be also be increased. In other words, unwanted effects due to the variation in the number of solder particles provided on the connection pad can be reduced.
However, when the area of the connection pads is comparatively large, the solder lump
5
may be created when solder particles are coated on the surface of the conductor patterns
3
A,
3
B with flux, and then fused. This is because a surface tension is produced in the fused solder, which is in a liquid state. The solder lump
5
thus formed on the conductor pattern
3
A,
3
B has a height H of approximately 20 to 40 &mgr;m. The solder lump
5
serves so as to electrically and mechanically connect the gold bump
8
and the conductor pattern
3
A,
3
B.
It is also noted that with a recent semiconductor chip having a high-density structure, the pitch between the gold bumps is comparatively fine. Thereby, the width of the connection pad, i.e., the conductor pattern, is also reduced.
Accordingly, in order to increase the area of the connection pad while reducing the width thereof, it is necessary to increase the length of the connection pad. In the related art, since the width of the connection pad is equal to the width of the conductor pattern, increasing the length of the connection pad is equivalent to increasing the length of the conductor pattern.
However, when the width of the connection pad, or the conductor pattern is reduced while increasing the length thereof, a uniform solder layer cannot be obtained since solder lumps will be produced at irregular positions. For example, the connection pad has a width of less than 60 &mgr;m and a length of more than 300 &mgr;m, and it is attempted to form a uniform solder layer having a thickness of approximately 10 to 20 &mgr;m. In such case, a uniform solder layer can not be obtained, since, as shown in
FIG. 1
, the solder lumps
5
will be formed on the conductor patterns
3
A,
3
B at irregular positions.
Since the solder lumps
5
are provided at irregular positions, positions of the connection pads
9
and positions of the solder lumps
5
will not correspond to each other. Therefore, as shown in
FIG. 3
, when the semiconductor chip
7
is positioned above the flip-chip mount board
1
, the positions of gold bumps
8
and the solder lumps
5
will not correspond to each other.
It is only solder films
6
that are provided at the positions corresponding to the gold bumps
8
.
FIG. 4
shows a state where the semiconductor chip
7
is mounted on the flip-chip mount board
1
. In this state, the solder films
6
do not provide a sufficient joining force between the gold bumps
8
and the connection pads
9
. Therefore, there is a need for a mount board which has a higher mounting reliability.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a flip-chip mount board and a flip-chip mount structure which satisfy the needs described above.
It is another and more specific object of the invention to provide a flip-chip mount board which can achieve a highly reliable connection between bumps provided on an electronic component and connection pads provided on the flip-chip mount board via a connection medium.
In order to achieve the above object,
a conductor pattern comprises at least one wiring pattern and a connection pad, the wiring pattern serving as an interconnection, the connection pad being provided at a position corresponding to one of bumps, the at least one wiring pattern and the connection pad being provided in an integrated manner, and
a width (W
1
) of the connection pad being formed so as to be greater than a width (W
2
) of the wiring pattern (W
1
>W
2
).
With the flip-chip mount board described above, the connection medium is always gathered on the connection pad and forms a connection medium lump at a position corresponding to the bump, i.e., on the connection pad. Also, the connection medium may be solder. The circuit board may be a printed-circuit board. The insulating layer may be a solder resist. The electronic component may be a semiconductor chip. Also, the bumps provided on the connection pad may primarily be made of a material having gold (Au).
It is yet another object of the invention to provide a flip-chip mounting board which can form connection medium lumps on connection pads with an improved reliability.
In or
Foster David
Gaffin Jeffrey
Shinko Electric Industries Co. Ltd.
Staas & Halsey , LLP
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