Dispensing – Processes of dispensing – Molten metal
Reexamination Certificate
1999-09-14
2001-04-10
Kastler, Scott (Department: 1742)
Dispensing
Processes of dispensing
Molten metal
C222S591000, C222S593000, C228S033000
Reexamination Certificate
active
06213356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bump forming apparatus and a bump forming method for forming a bump on a land of a substrate or a pad of a chip.
2. Description of the Background Art
FIG. 15
is a sectional view typically showing the structure of a conventional bump forming apparatus (refer to Japanese Patent Laying-Open Gazette No. 3-60036 (1991)). An ink jet printer
121
has a head
123
, which is provided therein with a paste chamber
124
and an air chamber
125
. The paste chamber
124
is provided with a plurality of inner nozzles
126
, while the air chamber
125
is provided with outer nozzles
127
on portions opposite to the inner nozzles
125
respectively. A plurality of control electrodes
128
are provided on a lower surface of the paste chamber
124
around the inner nozzles
126
. A plurality of common electrodes
129
are provided on a lower surface of the air chamber
125
around the outer nozzles
127
.
A method of forming bumps with the ink jet printer
121
shown in
FIG. 15
is now described. First, a semiconductor element
130
is arranged oppositely to the head
123
. More specifically, the semiconductor element
130
, which is provided with a plurality of electrode pads
131
, is so located that the plurality of electrode pads
131
are opposed to the plurality of outer nozzles
127
respectively.
Then, compressed air is externally supplied into the air chamber
125
as shown by arrow X. The pressure of the compressed air is set to about 0.5 kg/cm
2
to several kg/cm
2
, for example. At this time, the paste chamber
124
holds conductor paste
122
therein. The conductor paste
122
consists of metal powder, a binder and an adhesive. The metal powder, which is chosen in consideration of the materials for bumps
132
to be formed and the electrode pads
131
or the like, is prepared from powder of solder, tin or lead. The binder, which is employed as a solvent, is prepared from volatile methyl alcohol, isopropyl alcohol or methyl ethyl ketone. The adhesive is prepared that having a flux action. The compressed air supplied into the air chamber
125
forms air flows Y to flow out through the outer nozzles
127
.
Then, voltage of about minus several 100 V is applied between the control electrodes
128
and the common electrodes
129
. Due to electrostatic force resulting from this voltage application, the conductor paste
122
is extracted in a constant amount from the paste chamber
124
successively through the inner nozzles
126
, the air chamber
125
and the outer nozzles
127
. At this time, the air flows Y guide the conductor paste
122
to the outer nozzles
127
and quickly push out the conductor paste
122
.
The conductor paste
122
discharged from the outer nozzles
127
splashes in the form of thin threads of about 10 &mgr;m to several 10 &mgr;m in diameter, for example, to adhere onto the electrode pads
131
of the semiconductor element
130
.
FIG. 15
sequentially illustrates conductive paste
122
a
starting to be discharged, discharged conductor paste
122
b
and conductor paste
122
c
starting to adhere onto one of the electrode pads
131
. Finally a bump
132
is formed on each electrode pad
131
.
However, the conventional bump forming apparatus, employing the ink jet printer
121
while simply using the conductor paste
122
in place of ink, has the following problems:
First, the inner and outer nozzles
126
and
127
, which are readily clogged with the conductor paste
122
containing the metal powder of solder or the like and the adhesive, tend to defectively discharge the conductor paste
122
.
Further, the conductor paste
122
has high viscosity due to the adhesive contained therein, while the air chamber
125
applies pressure of about 0.5 kg/cm
2
to everal kg/cm
2
to the inner nozzles
126
. Therefore, it takes a long time after the conductor paste
122
is temporarily discharged from the inner nozzles
126
until new conductor paste
122
fills up the inner nozzles
126
. Thus, it is difficult to discharge the conductor paste
122
at a high speed, while the amount of discharge is dispersed if the conductor paste
122
is discharged in a state incompletely filling up the inner nozzles
126
.
Further, since pressure is applied to the inner nozzles
126
from the air chamber
125
, air enters the paste chamber
124
from the air chamber
125
through the inner nozzles
126
when the conductor paste
122
is discharged from the inner nozzles
126
to form bubbles, which cause unstable discharge of the conductor paste
122
.
SUMMARY OF THE INVENTION
A bump forming apparatus according to a first aspect of the present invention comprises a first tank storing fused solder and having an outlet for the fused solder, a pipe having one end connected with the outlet, a cavity, arranged below the first tank, having an inlet for the fused solder connected with another end of the pipe, a nozzle, arranged on a lower portion of the cavity, having a first opening on its bottom surface, a pressure element properly pressurizing the fused solder in the cavity toward the first opening in order to drop the fused solder from the first opening, a first heater heating the first tank and the cavity, and a static pressure control part for keeping static pressure of the fused solder applied to the nozzle at a constant value.
According to the first aspect of the present invention, the static pressure of the fused solder applied to the nozzle is kept at a constant value, whereby discharge of the fused solder from the first opening can be stabilized.
According to a second aspect of the present invention, the pressure element of the bump forming apparatus according to the first aspect has a diaphragm arranged on an upper portion of the cavity and a piezoelectric element fixed to an upper surface of the diaphragm, and the diaphragm is capable of pressurizing the fused solder in the cavity toward the first opening and oppositely to the first opening.
According to the second aspect of the present invention, the fused solder discharged from the first opening breaks away well, whereby the amount of the fused solder discharged from the first opening can be stably ensured even if the fused solder has high viscosity.
According to a third aspect of the present invention, the static pressure control part of the bump forming apparatus according to the first aspect has a second tank, arranged above the first tank, storing solid solder and having a second opening on its bottom surface, a second heater provided around the second opening, a level detector detecting the surface level of the fused solder in the first tank and a control part controlling driving of the second heater on the basis of a detection signal from the level detector.
According to the third aspect of the present invention, the surface level of the fused solder in the first tank is kept constant, whereby the static pressure applied to the nozzle can be kept at a constant value.
According to a fourth aspect of the present invention, the bump forming apparatus according to the third aspect further comprises an inert gas introduction part introducing inert gas into the second tank and an inert gas discharge part discharging the inert gas from the second tank.
According to the fourth aspect of the present invention, the solid solder can be prevented from oxidation in the second tank.
According to a fifth aspect of the present invention, the bump forming apparatus according to the third aspect further comprises an inert gas introduction part introducing inert gas into the first tank and an inert gas discharge part discharging the inert gas from the first tank.
According to the fifth aspect of the present invention, the fused solder can be prevented from oxidation in the first tank.
According to a sixth aspect of the present invention, the static pressure control part of the bump forming apparatus according to the first aspect has an inert gas introduction part introducing inert gas into the first tank, a first gas flow rate control part controlling
Fukumoto Hiroshi
Kanda Makoto
Nakasu Yasufumi
Yoshida Masaharu
Kastler Scott
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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