Work holders – Relatively movable jaws – Means to actuate jaw
Reexamination Certificate
2000-01-07
2001-08-14
Watson, Robert C. (Department: 3723)
Work holders
Relatively movable jaws
Means to actuate jaw
C269S903000
Reexamination Certificate
active
06273409
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to screw mechanisms, and more particularly, to a locking screw mechanism with a screw nut having a front screw nut and a back screw nut for minimizing the force required for loosening the locking screw mechanism.
BACKGROUND OF THE INVENTION
The locking screw mechanism of the present invention is described for locking a magazine that holds strips of integrated circuit packages in a solder plating machine during manufacture of integrated circuit packages. However, the locking screw mechanism of the present invention may advantageously be used for locking any other object in place, as would be apparent to one of ordinary skill in the art from the present description herein.
Referring to
FIG. 1
, a magazine
12
is locked into place in a solder plating machine during manufacture of integrated circuit packages by four locking screw mechanisms including a first locking screw mechanism
14
, a second locking screw mechanism
16
, a third locking screw mechanism
18
, and a fourth locking screw mechanism
20
. The magazine
12
holds a first strip
22
, a second strip
24
, and a third strip
26
with each of the strips
22
,
24
, and
26
comprising a plurality of integrated circuit packages. For example, the first strip
22
is comprised of a first integrated circuit package
102
, a second integrated circuit package
104
, and a third integrated circuit package
106
. A magazine typically includes more than three strips. For example, the magazine
12
typically holds eighty strips stacked within the magazine
12
. However, the magazine
12
of
FIG. 1
includes the three strips
22
,
24
, and
26
for clarity of illustration.
Each of the strips
22
,
24
, and
26
is comprised of a plurality of integrated circuit packages during manufacture of the integrated circuit packages.
FIG. 1
shows a side view of the strips
22
,
24
, and
26
stacked within the magazine
12
. Referring to
FIG. 2
for example, a top view of the first strip
22
shows a top view of the first integrated circuit package
102
, the second integrated circuit package
104
, and the third integrated circuit package
106
. A strip typically includes more than three integrated circuit packages, but the strips
22
,
24
, and
26
of
FIGS. 1 and 2
include three integrated circuit packages for clarity of illustration.
Each of the integrated circuit packages on a strip has a plurality of leads. Referring to
FIG. 3
for example, the first integrated circuit package
102
includes a first lead
112
, a second lead
114
, a third lead
116
, and a fourth lead
118
on one side of the integrated circuit package
102
. The first integrated circuit package
102
also includes a fifth lead
120
, a sixth lead
122
, a seventh lead
124
, and an eighth lead
126
on the other side of the integrated circuit package
102
. An integrated circuit package typically includes more than eight leads, but the integrated circuit packages
102
,
104
, and
106
of
FIGS. 2 and 3
include eight leads for clarity of illustration.
Referring to
FIG. 1
, the strips
22
,
24
, and
26
of integrated circuit packages are stacked within the magazine
12
, and the magazine
12
is clamped to a solder plating machine by the locking screw mechanisms
14
,
16
,
18
, and
20
to plate the leads of the integrated circuit packages with solder which typically is comprised of tin (Sn) and lead (Pb). Referring to
FIG. 4
, a side view of one of the locking screw mechanisms
14
,
16
,
18
, and
20
of the prior art illustrates a screw head
150
and a screw nut
152
that clamp the magazine
12
in place in the solder plating machine. (Elements having the same reference number in
FIGS. 1 and 4
refer to elements having similar structure and function.) Referring to
FIGS. 1 and 4
, the magazine
12
is placed between the screw head
150
and the screw nut
152
.
The screw nut
152
is then threaded about a screw shaft
154
to move the screw nut
152
toward the magazine
12
(in accordance with the right hand rule as known to one of ordinary skill in the art of mechanics). Referring to
FIGS. 4 and 5
, the screw nut
152
is threaded about the screw shaft
154
toward the magazine
12
until the screw nut
152
contacts and presses the magazine
12
against the screw head
150
such that the magazine
12
is firmly held between the screw head
150
and the screw nut
152
. (Elements having the same reference number in
FIGS. 1
,
4
, and
5
refer to elements having similar structure and function.)
Referring to
FIG. 5
, the screw head
150
has a first contact surface
156
and the screw nut
152
has a second contact surface
158
. Referring to
FIGS. 1 and 5
, when the magazine
12
is clamped between the screw head
150
and the screw nut
152
, the magazine
12
makes contact with a portion of the first contact surface
156
of the screw head
150
and with a portion of the second contact surface
158
of the screw nut
152
. For example,
FIG. 6
illustrates the second contact surface
158
of the screw nut
152
that surrounds the screw shaft
154
. The portion of the second contact surface
158
of the screw nut
152
that makes contact with the magazine
12
(when the magazine is clamped between the screw head
150
and the screw nut
152
) is shown as the shaded contact area
160
. (Elements having the same reference number in
FIGS. 1
,
4
,
5
, and
6
refer to elements having similar structure and function.)
Referring to
FIG. 1
, the magazine
12
holding a plurality of strips
22
,
24
, and
26
of integrated circuit packages is clamped to a solder plating machine by the plurality of locking screw mechanisms
14
,
16
,
18
, and
20
for plating the leads of the plurality of integrated circuit packages with solder during manufacture of the integrated circuit packages. After this solder plating process, the magazine
12
is released from the solder plating machine by loosening the plurality of locking screw mechanisms
14
,
16
,
18
, and
20
. The magazine
12
holding the plurality of strips
22
,
24
, and
26
of integrated circuit packages is then transferred to another station for further processing of the integrated circuit packages in the manufacture of the integrated circuit packages.
Referring to
FIG. 5
, for loosening the locking screw mechanism, the screw nut
152
is dethreaded about the screw shaft
154
away from the magazine
12
(in accordance with the right hand rule as known to one of ordinary skill in the art of mechanics). The force required to turn the screw nut
152
for initially dethreading the screw nut
152
away from the magazine
12
(while the magazine
12
is clamped between the screw head
150
and the screw nut
152
) is determined predominantly by two counter-forces. A first counter-force is the frictional force between the threading of the screw shaft
154
and the threading within the screw nut
152
.
Referring to
FIG. 6
, a second counter-force is the fictional force in the contact area
160
between the screw nut
152
and the magazine
12
. When the magazine
12
is clamped between the screw head
150
and the screw nut
152
, the screw nut
152
is pressed against the magazine
12
at the contact area
160
. When the screw nut
152
is initially loosened, the screw nut
152
turns against the magazine at the contact area
160
with a frictional force as the screw nut
152
is turned during the dethreading of the screw nut
152
about the screw shaft
154
.
The force required for loosening the screw nut
152
must overcome the above described frictional counter forces. In the prior art locking screw mechanism of
FIGS. 4
,
5
, and
6
, such a force required for loosening the screw nut
152
when the magazine
12
is clamped between the screw head
150
and the screw nut
152
may be too high because of the large frictional counter forces. In particular, in the locking screw mechanism of the prior art of
FIG. 6
, the contact area
160
is relatively large leading to a relatively high frictional force between the screw nut
1
Prommate Wanus
Treerawat Montri
Advanced Micro Devices , Inc.
Choi Monica H.
Watson Robert C.
LandOfFree
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