Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Bump leads
Reexamination Certificate
2000-07-18
2002-11-19
Thomas, Tom (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Bump leads
C257S738000, C257S734000, C257S778000, C257S787000, C257S785000, C257S780000, C257S690000
Reexamination Certificate
active
06483190
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a semiconductor chip element to which ultrasonic bonding is applied, a semiconductor chip element mounting structure and a semiconductor chip element mounting device and mounting method.
(2) Description of the Related Art
FIG. 1A
shows a conventional semiconductor chip element
10
to be ultrasonically bonded. The semiconductor chip element
10
comprises a silicon chip
11
on a bottom surface
11
a
of which an integrated circuit
12
is formed and electrodes
13
made of aluminum formed at a periphery of the bottom surface
11
a,
on top of which are formed signal stud bumps
14
, power stud bumps
15
, ground stud bumps
16
(not shown in the diagram) and dummy stud bumps (not shown in the diagram). The signal stud bumps
14
, power stud bumps
15
, ground stud bumps
16
(not shown in the diagram) and dummy stud bumps (not shown in the diagram) are all made from 99.99% pure gold in order to lower the electrical resistance of the connecting portion connecting to a circuit board of the semiconductor chip element.
It should be noted that the stud bumps
14
,
15
are formed by using a wire bonding device from the nozzle of which a gold wire is extended, and moving the wire bonding device in generally the same pattern as when performing wire bonding, with this difference: Whereas in wire bonding the wire is extended continuously from bond to bond, in forming the stud bumps
14
,
15
the wire is cut at each bump, giving the bumps the substantially onion-domed shape shown in the diagrams.
As shown in
FIG. 1B
, the semiconductor chip element
10
is mounted in a face down position on a circuit board
30
that is itself fixedly mounted on top of a table
20
, in such a way that each stud bump
14
,
15
is aligned with a corresponding gold electrode
31
. Under room-temperature conditions, the semiconductor chip element
10
is pressed with a tool
21
and at the same time ultrasonic vibrations are applied for a period of, for example, several seconds, with the surfaces of the stud bumps
14
,
15
and the electrodes
31
(both made of gold) rubbed against each other so as to ultrasonically bond the stud bumps
14
,
15
and the electrodes
31
.
With the semiconductor chip element
10
in the state described above, using a device (not shown in the diagrams) an underfill
41
is injected into a gap
40
between the underside of the semiconductor chip element
10
and the circuit board
30
as shown in
FIG. 1C
, after which the underfill undergoes thermosetting.
As shown in
FIG. 1C
, the semiconductor chip element
10
is mounted on the circuit board
30
in a state in which the stud bumps
14
,
15
are ultrasonically bonded to the electrodes
31
and the gap
40
is filled with the underfill
41
which is an epoxy resin. The underfill
41
strengthens the attachment of the semiconductor chip element
10
to the circuit board
30
and protects the integrated circuit
12
.
It should be noted that the 99.99% pure gold only has a hardness of 75 Hv on the Vickers hardness scale, that is, is soft. As a result, it sometimes happens that the stud bumps
14
,
15
suffer substantial deformation when ultrasonically bonded to the electrodes, in which case a height A of the gap
40
described above narrows sharply, to approximately 10 &mgr;m. When the gap
40
narrows, not enough of the underfill
41
enters the gap
40
to fill the gap
40
completely and so an unfilled space indicated in
FIG. 1C
by reference numeral
42
is left.
It will be appreciated that the presence of the unfilled space
42
reduces the effectiveness of the underfill
41
and hence reduces the strength of the attachment or mounting of the semiconductor chip element
10
on the circuit board
30
, and additionally, fails to fully protect the integrated circuit
12
.
It is possible to maintain the gap
40
at a height A greater than 10 &mgr;m by raising a height h of the stud bumps
14
,
15
. However, since the stud bumps
14
,
15
are formed in much the same way that wire bonding is performed, if the height h is increased then a diameter d of the stud bumps
14
,
15
also increases, yet at the same time the pitch of the stud bump alignment imposes limitations on the diameter of the stud bumps
14
,
15
. As a result, there is a practical limit to the extent to which the height h of the stud bumps
14
,
15
can be increased.
SUMMARY OF THE INVENTION
Accordingly, the present invention has as its object to provide a semiconductor chip element, a semiconductor chip element mounting device and mounting method in which, under the above-described conditions, the above-described disadvantage is eliminated.
The above-described object of the present invention is achieved by the invention according to one embodiment, comprising a semiconductor chip element including a chip as well as signal stud bumps and non-signal stud bumps dispersedly aligned on a bump formation surface of the chip and the semiconductor chip element being adapted to be bonded and mounted by using ultrasonic vibrations, the semiconductor chip element characterized by having the non-signal stud bumps made of a material having a hardness greater than a hardness of a material from which the signal stud bumps are made.
According to the invention described above, the degree to which the non-signal stud bumps deform when ultrasonically bonded is reduced, and accordingly, a relatively wide gap as compared to the conventional art can be maintained between a bottom surface of the semiconductor chip element and a circuit board when the former is mounted on the latter, thus improving the filling of the gap with an underfill.
Additionally, the above-described object of the present invention is also achieved by the invention, comprising the semiconductor chip element described above, characterized in that the signal stud bumps are made of gold (Au) and the non-signal stud bumps are made of a gold-palladium alloy.
According to the invention described above, the non-signal stud bumps made of gold-palladium alloy are harder than the signal stud bumps made of pure gold. The signal stud bumps made of pure gold have a reduced electrical resistance.
Additionally, the above-described object of the present invention is also achieved by the invention, comprising a semiconductor chip element including a chip as well as signal stud bumps and non-signal stud bumps dispersedly aligned on a bump formation surface of the chip and the semiconductor chip element being adapted to be bonded and mounted by using ultrasonic vibrations, characterized by having plated bumps on the bump formation surface of the chip and the stud bumps formed on top of the plated bumps to form combination stacked bumps.
According to the invention described above, the plated bumps do not deform as easily as the stud bumps during ultrasonic treatment, so a relatively wide gap as compared to the conventional art can be maintained between a bottom surface of the semiconductor chip element and a circuit board when the former is mounted on the latter, thus improving the filling of the gap with an underfill.
Additionally, the above-described object of the present invention is also achieved by the invention, comprising a semiconductor chip described above, characterized in that the stud bumps are made of gold and the plated bumps are made of gold.
According to the invention described above, the gold plated bumps are of the same material as the gold stud bumps, so the quality of the connection of the stud bumps to the plated bumps is improved. The stud bumps may be dispensed with plated bumps, where the plated bumps are previously made of a gold-palladium alloy. Combination stacked bumps may also be used, where the plated bump portion is made of a gold-palladium alloy and the stud bump portion is made of gold.
Additionally, the above-described object of the present invention is also achieved by the invention, comprising a semiconductor chip element mounting structure, in which the semiconductor chip element is ultrasonically
Kainuma Norio
Kira Hidehiko
Okada Toru
Parekh Nitin
Thomas Tom
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