Metal fusion bonding – Process – With measuring – testing – indicating – inspecting – or...
Reissue Patent
1996-09-26
2001-10-02
Heinrich, Samuel M. (Department: 1725)
Metal fusion bonding
Process
With measuring, testing, indicating, inspecting, or...
C228S105000, C228S180500
Reissue Patent
active
RE037396
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor manufacturing and specifically to semiconductor wire bonding processes. More particularly, the present invention relates to an improved method for teaching the location of a bond site on a lead finger of a leadframe during a wire bonding process.
BACKGROUND OF THE INVENTION
In semiconductor manufacture a wire bonding process is used to electrically connect bond pads formed on semiconductor dice to the lead fingers of a
leadfree
leadframe
strip. Apparatus for wire bonding semiconductor dice are well known in the art. U.S. Pat. No. 3,894,671 to configuration which matches the peripheral configuration of a semiconductor die. Mounting paddle connecting members
58
attached to the strip rails
34
connect and support mounting paddles
32
on the
leadfree
leadframe
strip
30
.
The bond wire is typically a fine gold or copper wire that is threaded through the bonding tool. The end of the wire is heated by an electrical discharge or a hydrogen torch to a molten state. This forms a ball of molten metal on the end of the bond wire. For bonding a selected bond pad of the heated die, the molten ball is pressed by the bonding tool against the bond pad. This mechanically bonds the bond pad and the bond wire to one another. The bonding tool is then moved over a bonding site on a selected lead finger and the heated bond wire is pressed against the bond site. This mechanically bonds the bond wire and the lead finger to one another. The bond wire is then tensioned and sheared. This process is repeated for each bond pad on the die.
A critical requirement of the wire bonding process is precisely locating the bonding tool with respect to each bonding pad and to a bond site of an appropriate lead finger. Earlier versions of wire bonding apparatus were manually operated by an operator viewing the semiconductor dice through a microscope to precisely locate the bonding tool. More recently, automated wire bonding apparatus include vision systems for automatically sensing the locations of the bond pads on the dice and lead fingers of the leadframe to automatically perform the wire bonding process. U.S. Pat. No. 4,441,205 to Berkin et al. discloses a representative vision system for wire bonding apparatus.
In general, such vision systems are adapted to sense the lateral edges of the lead fingers and to teach a bond site in the middle of the lead finger somewhere along the longitudinal axis of the lead finger. There is, however, no provision for precisely locating the bond site on a lead finger an exact distance from the tip of the lead finger. Typically, the bonding tool is programmed by an operator to move a set distance away from the bond pad for placing the bond site along the longitudinal axis of a lead finger. This is not an accurate or consistent method for teaching a bond site location on a lead finger. In addition, this method of locating a bond site tends to use more bond wire than is necessary because the length of the bond wire is consistently oversized.
This situation is shown in FIG.
1
. With reference to
FIG. 1
, a semiconductor die
10
is shown during a wire bonding process. The semiconductor die
10
has been attached to a die mounting paddle
12
of a leadframe
14
. The semiconductor die
10
includes a plurality of bond pads
18
which connect to various integrated circuits formed on the die
10
. The leadframe
14
includes an arrangement of lead fingers
16
which will ultimately become the external leads of the completed semiconductor package. During the wire bonding process, fine bond wires
26
are bonded to the bond pads
18
and to bond sites
20
on the lead fingers
16
.
For teaching the location of a bond site
20
′ on particular lead finger
16
′, the locations of the lateral edges
22
′,
24
′ of the lead finger
16
′ are sensed by the vision system of the wire bonding apparatus. The wire bonding apparatus is then programmed to determine a midpoint between the edges
22
,
24
of the lead finger
16
′. This is the dimension “Y” in FIG.
1
. Accordingly, axis
28
′ is the longitudinal axis of the lead finger
16
′. Following this determination, the bonding tool of the wire bonding apparatus is programmed to move along the longitudinal axis
28
′ of the lead finger
16
′, a predetermined distance “X” from the appropriate bond pad
18
on the semiconductor die
10
, to locate the bond site
20
′ and make the bond.
A problem with this method of teaching or locating the bond site
20
′ on the lead finger
16
′ is that the location of the lead finger
16
′ with respect to the die
10
my vary from die to die. As an example, the location of the die
10
on the mounting paddle
12
may vary by up to 10 mils in any direction from the nominal position. The distance “X” is therefore imprecise. In addition, more bond wire than necessary tends to be used in order to insure that the bond site
20
will be located on the lead finger
16
.
In view of these shortcomings of the prior art, it is an object of the present invention to provide an improved method for wire bonding semiconductor dice to the lead fingers of a leadframe and for teaching a bond site location on a lead finger during wire bonding. It is a further object of the present invention to provide an improved method for precisely locating a bond site along a longitudinal axis of a lead finger a predetermined distance from a terminal edge of a tip portion of the lead finger during wire bonding. It is a yet another object of the present invention to provide a wire bonding method in which a length of the bond wire is controlled during the wire bonding process and less bond wire is used. It is a further object of the present invention to provide an improved wire bonding method that is simple, efficient, and adaptable to large scale semiconductor manufacture.
SUMMARY OF THE INVENTION
In accordance with the invention an improved method for teaching a bond site location on a lead finger of a semiconductor
leadfree
leadframe
during a wire bonding process is provided. In a wire bonding process, bond pads formed on a semiconductor die are bonded to lead fingers on a leadframe using fine bond wires. The method of the invention, broadly stated, comprises locating a bond site on the lead finger along a longitudinal axis of the lead finger a predetermined distance from a terminal edge of a tip portion of the lead finger. The predetermined distance between the bond site and the terminal edge is equal to the distance between a lateral edge of the lead finger and a longitudinal axis of the lead finger. Stated differently, the predetermined distance is equal to the width of a lead finger divided by two.
More particularly stated, the method of the invention includes the following steps: sensing a location of the terminal edge and lateral edges of a tip portion of a lead finger of a leadfree; determining a distance from a lateral edge of the lead finger to a longitudinal axis of the lead finger; locating a bond site along the longitudinal axis and spaced from the terminal edge of the lead finger by the predetermined distance.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of the invention as illustrated in the accompanying drawings.
REFERENCES:
patent: 3894671 (1975-07-01), Kulicke, Jr. et al.
patent: 4441205 (1984-04-01), Berkin et al.
patent: 4671446 (1987-06-01), Sherman
patent: 4813588 (1989-03-01), Srivastava et al.
patent: 4853968 (1989-08-01), Berkin
patent: 4877173 (1989-10-01), Fujimoto et al.
patent: 4886200 (1989-12-01), Tsumura
patent: 4899207 (1990-02-01), Hallowell et al.
patent: 4951120 (1990-08-01), Hagiware et al.
patent: 4978050 (1990-12-01), Amador
patent: 4979663 (1990-12-01), Sofia et al.
patent: 5082165 (1992-01-01), Ishizuka
patent: 5097406 (1992-03-01), Narasimhan et al.
patent: 5111989 (1992-05-01), Holdgrafer et al.
patent: 5119436 (1992-06-01), Holdgrafer
patent: 5137201
Heinrich Samuel M.
Micro)n Technology, Inc.
TraskBritt
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