Electric heating – Inductive heating – Specific heating application
Reexamination Certificate
1999-07-29
2001-09-11
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
Specific heating application
C219S603000, C219S616000, C219S651000, C219S673000, C219S677000
Reexamination Certificate
active
06288376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method of melting a bump. In particular, the invention relates to a method of melting a bump that is improved to melt, in the dry process, a bump formed on a metal interconnection provided on a substrate or a bump formed an electrode of a semiconductor device such that the bump is sphered. The invention further relates to an apparatus for melting a bump improved to realize such a method of melting a bump. The invention still further relates to a method of manufacturing a semiconductor device including such a method of melting a bump.
2. Description of the Background Art
FIG. 12
is a plan view of a substrate on which solder bumps are produced.
FIG. 13
is a partial cross sectional view along the line XIII—XIII in FIG.
12
.
Referring to these figures, a substrate
2
is formed of resin such as glass epoxy or polyimide. A patterned copper foil
21
is mounted on one surface of substrate
2
. A solder resist
22
is applied onto substrate
2
to cover copper foil
21
. Laser drilling of the other surface of substrate
2
and laser drilling of solder resist
22
produce respectively an outer electrode portion
21
b
and an inner electrode portion
21
a
. Inner electrode portion
21
a
and outer electrode portion
21
b
are formed of plating of Ni/Au, Ni/Pd/Au or the like. Ball bonding of a solder wire to inner electrode portion
21
a
produces a solder bump
21
c
. Substrate
2
onto which flux is applied is passed through a reflow furnace to make solder bump
21
c
into a sphere. Substrate
2
and an electrode of a semiconductor chip are bonded together with solder bump
21
c
therebetween. The resultant product is entirely sealed with resin and an outer ball of solder is attached to outer electrode
21
b
. The product is then cut into separate packages as final products.
The conventional art discussed above is hereinafter described in detail with reference to figures.
FIG. 14
is a plan view illustrating a conventional art of applying flux for generating solder balls on a substrate.
FIG. 15
is a plan view of a reflow furnace for melting solder.
FIG. 16
is a cross sectional view along the line XVI—XVI in FIG.
15
.
FIG. 17
shows a temperature profile in the reflow furnace.
Referring to these figures, substrate
2
enters a melting reflow furnace
3
from a reflow furnace in-loader
31
, and moves from the first zone to the fourth zone by use of a reflow carrier belt
33
. Substrate
2
is heated by an upper heater
32
a
and a lower heater
32
b
. Solder bump
21
c
is melted to be sphered under the profile temperature conditions shown in
FIG. 17
, namely at 140-160° C. for 70±20 seconds in the second zone and at 200-220° C. for 90 seconds or less in the fourth zone, and under a condition of an oxygen concentration of 1000 ppm or less. Substrate
2
is thereafter taken out from an unloader
34
.
In order to remove the flux, a cleaning process with solvent and a drying process are carried out. A similar method is employed for a process of bonding solder to an outer electrode and a process of forming solder on elements on a printed circuit board.
The conventional art discussed above has the following problems.
The first problem is that four processes of applying the flux, reflowing, cleaning, and drying are required after generating the bump of the inner electrode portion, leading to reduction in productivity, and the residue of the flux deteriorates the reliability of the product.
The second problem is that contaminants in the cleaning fluid attach to the surface of the outer electrode on the bottom surface of the substrate in the cleaning process, and thus disturb sticking of solder paste used for bonding the outer ball after sealing process, resulting in peeling off of the ball.
The third problem is that the temperatures of bump
21
c
and substrate
2
rise to almost the same value within the reflow furnace so that the substrate is melted before the bump is melted if the reflow temperature is set at the glass transition point Tg or more. Therefore, medium temperature solder such as Sn—Ag and Sn—Sb and refractory metals such as Au and Cu cannot be used. Then, those products that satisfy both of the requirements of product quality and cost cannot be manufactured.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a method of melting a bump improved to omit processes of flux application, reflow, cleaning and drying for any bonding material formed on a substrate or a chip.
Another object of the invention is to provide a method of melting a bump improved to enhance the quality of bonding.
Still another object of the invention is to provide a method of melting a bump improved to freely set the range of control temperature and to increase the range of the melting point which can be treated.
A further object of the invention is to provide an apparatus for melting a bump improved to realize such methods of melting a bump.
A further object of the invention is to provide a method of manufacturing a semiconductor device improved to reduce the time for bonding a substrate with a chip and thus enhance the productivity.
According to a method of melting a bump in the first aspect of the invention, a bump formed on a substrate is heated to be melted by electromagnetic induction using an induction heating coil in an ambient of low oxygen concentration.
According to a method of melting a bump in the first aspect of the invention, the heat is generated by current induced in the bump itself not by heat transfer or radiant heat originating from a heat source outside the bump, and the bump is sphered without an oxide film generated on its surface.
According to a method of melting a bump in the second aspect of the invention, the temperature of the substrate is measured and the amount of current applied to the induction heating coil is controlled according to the measured temperature.
According to the method of melting a bump in the second aspect of the invention, the amount of current applied to the induction heating coil can appropriately be controlled.
According to a method of melting a bump in the third aspect of the invention, the magnetic field of the induction heating coil is applied perpendicularly to the surface of the substrate, the induction heating coil is moved horizontally relative to the surface of the substrate, and the substrate is heated by a heater in order to reduce the current applied to the induction heating coil.
The method of melting a bump in the third aspect of the invention achieves a high productivity.
According to a method of melting a bump in the fourth aspect of the invention, the bump is melted while the substrate is cooled using a Peltier device.
The method of melting a bump in the fourth aspect of the invention allows a bump of refractory metal to be melted into a sphere shape without damage to the substrate.
An apparatus for melting a bump in the fifth aspect of the invention relates to an apparatus for melting a bump formed on a substrate. The apparatus includes ambient supply means for supplying an ambient of low oxygen concentration onto the substrate, and an induction heating coil for heating the bump by electromagnetic induction.
The apparatus for melting a bump in the fifth aspect of the invention can sphere the bump without oxide film generated on its surface.
In an apparatus for melting a bump in the sixth aspect of the invention, the induction heating coil is U-shaped in plan view.
The apparatus for melting a bump in the sixth aspect of the invention provides a manufacturing method with a high productivity.
In an apparatus for melting a bump in the seventh aspect of the invention, the induction heating coil includes a cylindrical section through which cooling water flows, and a high-frequency current applying section extending downward from the cylindrical section with high frequency current flowing therethrough.
The apparatus for melting a bump in the seventh aspect of the invention prevents the induction heating coil i
Leung Philip H.
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
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