Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Wire contact – lead – or bond
Reexamination Certificate
1999-05-06
2001-08-07
Wong, Don (Department: 2821)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Wire contact, lead, or bond
C257S775000, C228S110100, C228S104000, C438S018000
Reexamination Certificate
active
06271601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wire bonding method and apparatus for interconnecting electronic parts by using electrically conductive wires, and to a semiconductor device. Particularly, the inventive method and apparatus are applied suitably to semiconductor devices which are intended for high-speed switching of large currents in automobile equipment controllers, electric-car drive controllers and other vehicle-installed motor controllers.
2. Description of the Prior Art
In the manufacturing process of semiconductor devices which include multiple semiconductor chips and electronic parts, a scheme of wire bonding is used for the electrical connection between the electrodes of semiconductor chips and electronic parts and between the terminals of electronic parts.
A typical conventional wire bonding apparatus will be explained first with reference to FIG.
14
.
FIG. 14
is a side view of the conventional wire bonding apparatus. This wire bonding apparatus is designed to feed a wire
101
, which is supplied from a bobbin (not shown), to the groove of wire press section
112
of a bonding tool
111
by way of a through-hole
115
formed in a horn
110
and a gap of clamp section of a wire clamp mechanism
120
.
With ultrasonic vibration being applied to the bonding tool
111
which is fixed to the tip section of the horn
110
, the wire
101
is pressed onto the electrode of a semiconductor chip
102
as one part of connection so that the wire
101
is joined to it, and next the wire
101
is fed and brought by the bonding tool
111
to the terminal
104
of another electronic part, e.g., a resistor, as another part of connection and joined to it in the same manner.
The wire clamp mechanism
120
is located between the wire press section
112
of the bonding tool
111
and the through-hole
115
of the horn
110
, and it serves to hold and guide the wire
101
when it is fed out. The bonding tool
111
and horn
110
are supported on a vertical moving mechanism and horizontal moving table so that they can move vertically and horizontally relative to the semiconductor chip
102
and electronic part.
Automobile equipment controllers and electric-car drive controllers are required to be made much smaller in size and weight. The drive controller incorporates semiconductor devices which implements high-speed switching of large currents for producing a.c. power for driving motors by being supplied with power from such a d.c. power source as battery.
Electronic components have their operating currents increasing to match with the trend of higher-power drive controllers, and therefore wires of large diameters are used for the electrical connection between semiconductor chips and between semiconductor chips and electronic parts of semiconductor devices. For wires of large diameters, aluminum wires which are inexpensive and light are used, instead of wires having higher electrical conductivity that mainly consist of expensive gold. Aluminum wires are thicker due to the lower electrical conductivity than gold wires, and aluminum wires with diameters of 100-600 &mgr;m are necessary for high-power semiconductor devices.
Semiconductor devices used in automobile equipment controllers and electric-car drive controllers are required to be durable against severe heat cycles and power cycles thereby to last long, in addition to the demand of compactness and light weight. In order to meet these requirements, it is necessary to improve the strength of wire joints.
There is a limit in widening the joint area based merely on pressing the wire
101
having a circular cross section onto the planar target joint surface, and there is also a limit in improving the strength and life of joints based merely on the application of ultrasonic vibration to the limited joint area. Specifically, the conventional wire bonding scheme works for joining by pressing the wire
101
having a circular cross section onto a planar target joint surface so that the wire is deformed, and the pressing force needs to be increased progressively to overcome the increasing resistance of deformation.
Accordingly, in order for the conventional wire bonding scheme to improve the strength and life of wire joints by raising the degree of deformation of the wire
101
while retaining the mechanical strength of the deformed section of the wire
101
, it is necessary to increase the ultrasonic output for the metallic joint process thereby to increase the pressing force of the wire
101
. However, an excessive pressing force by the increased ultrasonic output can result in the breakage of the electronic part or semiconductor chip
102
having the target joint surface.
On this account, conventionally, there is a limit in widening the joint area, and thus there is a limit in improving the strength and life of wire joints.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the foregoing prior art deficiency, and its prime object is to provide a wire bonding method and apparatus capable of accomplishing wire joints which are durable against severe heat cycles and power cycles thereby to have a long life, and are useful for semiconductor devices which implement high-speed switching of large currents.
Another object of the present invention is to provide a high-power semiconductor device which is smaller in size and weight and durable against severe heat cycles and power cycles thereby to have a long life based on the enhanced strength of wire joints.
In order to achieve the above objective, the inventive wire bonding method comprises a step of implementing the flatly thinner plastic deformation for the joint section of a wire on the feed side thereof, and a step of joining the wire to a target joint surface by feeding out and positioning the flatly deformed wire joint section processed by the wire deforming step to the target joint surface, and pressing the positioned wire joint section, with vibration being applied, onto the target joint surface with a ultrasonic wire bonder. Preferred wire diameters range from 100 to 600 &mgr;m.
Alternatively, the inventive wire bonding method comprises a step of implementing the flatly thinner plastic deformation for the joint section of a wire on the feed side thereof to match with the intended length of wire loop, and a step of joining the wire to a target joint surface by feeding out and positioning the flatly deformed wire joint section processed by the wire deforming step to the target joint surface, and pressing the positioned wire joint section, with vibration being applied, onto the target joint surface with a ultrasonic wire bonder. Preferred wire diameters range from 100 to 600 &mgr;m.
Wires used for the inventive wire bonding method are preferably made of aluminum or aluminum alloy.
Preferably, the wire deforming step of the inventive wire bonding method implements the flatly thinner plastic deformation for the joint section of the wire at a ratio of 2 or more in terms of deformation factor W/D, where W is the width of deformed wire at the joint section and D is the original wire diameter.
Preferably, the wire joining step of the inventive wire bonding method joins the joint section of the wire to the target joint surface at a deformation factor W/D of a ratio 2 or more, where W is the width of deformed wire at the joint section and D is the original wire diameter.
More preferably, the wire joining step of the inventive wire bonding method joins the joint section of the wire to the target joint surface at a deformation factor W/D of a ratio in the range from 4 to 6, where W is the width of deformed wire at the joint section and D is the original wire diameter.
In order to achieve the above objective, the inventive wire bonding apparatus comprises means of implementing the flatly thinner plastic deformation for the joint section of a wire on the feed side thereof, and means of joining the wire to a target joint surface by feeding out and positioning the flatly deformed wire joint section processed by the wire deforming mean
Shigemura Tatsuya
Suzuki Osamu
Taneda Yukinori
Yamamoto Noriaki
Yamamura Hirohisa
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Vo Tuyet T.
Wong Don
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