Optical: systems and elements – Lens – Afocal
Reexamination Certificate
2002-12-19
2004-01-27
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Afocal
C356S153000, C356S399000, C356S400000, C356S615000, C228S105000, C250S559340
Reexamination Certificate
active
06683731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bonding apparatus and more particularly to a bonding apparatus that calculates the amount of offset between a bonding tool and a position detection camera that takes images of a workpiece.
2. Prior Art
Manufacturing process of semiconductor assemblies such as ICs, etc. includes a wire bonding steps. In such bonding steps, a wire
4
is, as shown in
FIG. 7
, connected to a pad (a first bonding point)
1
a
of the semiconductor chip
1
of a workpiece
3
and a lead (second bonding point)
2
a
of a lead frame
2
.
The above wire bonding steps are performed by, for instance, a wire bonding apparatus
10
shown in FIG.
8
.
First, a deviation from normal positions of at least two fixed points on a semiconductor chip
1
and at least two fixed points on a lead frame
2
is detected by a position detection camera
11
, and bonding coordinates stored in memory (not shown) beforehand are corrected based upon such detected values. When this detection is done by the position detection camera
11
, an X-axis motor
12
and a Y-axis motor
13
are first driven so that the optical axis
11
a
of the position detection camera
11
is positioned directly above a measurement point. After the bonding coordinates are corrected as described above, a bonding tool (called “tool”)
5
is moved in the directions of the X and Y axes (or moved horizontally) and in the direction of the Z axis (or moved vertically), and a wire
4
that passes through the tool
5
is wire-bonded to the first bonding point
1
a
and the second bonding point
2
a.
In the above structure, the optical axis
1
a
of the position detection camera
11
and the axial center
5
a
of the tool
5
are offset by a distance W. Accordingly, after the deviation of the fixed points is detected by the position detection camera
11
and the bonding coordinates are corrected, the XY table
15
is moved by an amount equal to the offset amount W by the X-axis motor
12
and Y-axis motor
13
, thus positioning the tool
5
above the first bonding point
1
a
. Afterward, the wire
4
is wire-bonded at the above-described corrected bonding coordinates by the movement of the XY table
15
in the directions of the X and Y axes by the X-axis motor
12
and Y-axis motor
13
and by the movement of the tool
5
in the direction of the Z axis by the vertical movement (or swinging movement) of the bonding arm
16
caused by the Z-axis motor
14
.
In
FIG. 8
, the bonding arm
16
is disposed on a bonding head
17
so that the bonding arm
16
is free to swing, and the position detection camera
11
is fastened to the bonding head
17
via a camera holding arm
18
. Xw refers to an X-axis component of the offset amount W, and Yw refers to a Y-axis component of the offset amount W.
The position detection camera
11
is for determining the reference points for ascertaining the position to which the tool
5
is moved. Accordingly, it is extremely important to know exactly how far the position detection camera
11
is offset from the tool
5
. However, the actual offset amount varies from instant to instant as a result of thermal expansion of the camera holding arm
18
and bonding arm
16
caused by radiant heat from the high-temperature bonding stage and heat transferred from the heated air. Accordingly, it is necessary to correct the offset amount when bonding work is initiated and at an appropriate timing during intervals between bonding operations.
Japanese Patent No. 2982000 (Japanese Patent Application Laid-Open (Kokai) No. 2000-021923), for instance, discloses a conventional means for determining an accurate offset amount. However, this offset amount determining means requires a special offset correction camera used for offset correction in addition to the position detection camera that detects the positions of bonding points. Thus, the construction is complicated and expensive.
Japanese Patent Application Laid-Open (Kokai) No. 2001-203234 discloses a system that solves the above problems. In this system, an optical means that conducts image light of a tool and a reference member disposed in a specified position to a position detection camera is employed. As a result, the position detection camera that detects a position of the workpiece is used also for imaging the tool and reference member. Thus, this prior art shows that there is no need to use a special offset correction camera even in cases where a reference member is used.
The above-identified Japanese Patent Application Laid-Open (Kokai) No. 2001-203234 discloses various embodiments. One of the embodiments uses a telecentric lens as the lens of the position detection camera. The “telecentric lens” refers to a telecentric optical system or to an optical system which is constructed so that principal light rays that are focused as an image pass through the rear-side focal point of a lens. A telecentric lens has a broad tolerance range with respect to positional deviations in the direction that face the image focusing plane. Especially, even in a case in which transmitted light consisting of parallel light is illuminated, the size of the image (i.e., the distance from an optical axis) does not vary even if the object position fluctuates.
The optical system of the position detection camera in this prior art is similar to telecentric; strictly speaking, however, such an optical system is not telecentric; and if the object deviates from the focal position when the object is illuminated with parallel light, the image becomes more or less blurred.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a bonding apparatus that can easily obtain a clear image regardless of the focal position when illumination is made with parallel light.
The above object is accomplished by a unique structure of the present invention for a bonding apparatus that comprises a bonding tool through which a wire passes and which performs bonding on a workpiece, a position detection camera which takes images of the workpiece, a reference member which is disposed in a specified position of the apparatus, and an optical means which conducts the image of the tool and reference member to the position detection camera; and in the present invention, an afocal system is employed which is constructed by a combination of a lens disposed in the position detection camera and a lens disposed in the optical means.
In the above structure, the afocal system is a Kepler type afocal system.
Instead, the afocal system can be a Galileo type afocal system.
REFERENCES:
patent: 5566876 (1996-10-01), Nishimaki et al.
patent: 6337489 (2002-01-01), Matsumoto et al.
patent: 6449516 (2002-09-01), Kyomasu et al.
patent: 6464126 (2002-10-01), Hayata et al.
patent: 2003/0098426 (2003-05-01), Hayata
patent: 2003/0099049 (2003-05-01), Hayata
patent: 2982000 (1999-09-01), None
patent: 2001-203234 (2001-07-01), None
Dinh Jack
Epps Georgia
Kabushiki Kaisha Shinkawa
Koda & Androlia
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