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Description  |
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The present invention pertains to the formation of leads of a semiconductor
package and the testing of the package through the interconnected, formed
leads.
BACKGROUND OF THE INVENTION
In the semiconductor industry, once electronic circuits are formed on
semiconductor chips and the chips are packaged, it is necessary to
completely test the package to ensure correct operation. Generally, the
electronic circuits are formed in the semiconductor chip and the chip is
attached to a lead frame or the like. The chip is then encapsulated with
the leads extending straight out from the package in a common plane. In
one prior art process, the circuitry within the package is tested at this
time, because it is easier to contact the leads when they are in a common
plane, and generally because it is difficult to make contact to preformed
leads.
The major problem with this prior method is that the leads are formed after
testing of the circuitry is completed. However, in many instances the
process of forming the leads causes damage to the leads and, in some
instances, can even cause the leads to be loosened from the chip and/or
breakage of the encapsulation. Thus, it has become common to perform an
open/short test after the lead forming process, which extends the
manufacturing and testing procedure and increases the manufacturing costs.
However, difficulty in contacting the formed leads applies also to this
test. Further, intermittent wire bonds are impossible to detect because
the pulling force on the leads that caused the wire bond failure has been
relieved when the device left the forming station, which is the final
assembly step, and no further testing is performed.
Because devices and packages are becoming smaller, it is becoming even more
difficult to make reliable contact on the preformed leads. Contact failure
on preformed leads is currently at about 0.5%. Excess contact pressure
applied to the leads in an attempt to ensure a reliable electrical contact
with the leads has a potential to deform the leads out of specification.
Accordingly, it is desirable to perform tests on semiconductor packages
which reliably contact the leads and determine failures caused by
formation of the leads.
It is a purpose of the present invention to provide a new and improved lead
forming and package testing method.
It is another purpose of the present invention to provide a new and
improved lead forming and package testing method in which constant and
reliable contact with the leads is made.
It is a further purpose of the present invention to provide a new and
improved lead forming and package testing method in which failures caused
by lead formation can be determined.
It is still another purpose of the present invention to provide a new and
improved lead forming and package testing method in which testing time and
expense is reduced.
Yet a further purpose of the present invention is to provide a new and
improved lead forming and package testing method which improves detection
of lead forming induced failures, including intermittents.
A still further purpose of the present invention is to provide a new and
improved lead forming and package testing method in which bending of the
leads out of specification is substantially reduced and tested packages
can be placed directly into final outgoing packages, i.e. tapes and reels.
SUMMARY OF THE INVENTION
The above problems and others are at least partially solved and the above
purposes and others are realized in a method of forming leads and testing
circuitry of a semiconductor package, including the steps of providing a
semiconductor package including an electronic circuit therein, and the
package having unformed leads electrically connected to the circuit, and
contacting the leads of the package for testing the package, and forming
the leads with the contacting step.
In a specific embodiment of the above method, the step of contacting and
forming the leads includes providing a forming and testing station with a
support for receiving the package, and dies with electrical test equipment
attached thereto movably positioned adjacent the support for contacting
and forming the leads. The package is positioned on the support and the
station is used for lead forming and final electrical contacting.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to the drawings:
FIG. 1 is a simplified flow chart illustrating a prior art testing and lead
forming process;
FIG. 2 is a simplified flow chart illustrating a testing and lead forming
process in accordance with the present invention;
FIG. 3 is a front plan view of a forming/testing station, with
semiconductor package in place, prior to lead forming and testing in
accordance with the method of FIG. 2;
FIG. 4 is a front plan view of the testing station of FIG, 3, with
semiconductor package in place, during lead forming and testing in
accordance with the method of FIG. 2; and
FIG. 5 is a perspective view of portions of the testing station of FIG. 3,
illustrating the operating relationship.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring specifically to FIG. 1, a simplified flow chart of a prior art
method of testing and forming leads on a semiconductor package is
illustrated. In a first step, subsequent to the fabrication and packaging
of the semiconductor device, one half of the final test is performed to
determine that the semiconductor device operates properly. A second test
is then performed to complete the second half of the final test.
Generally, the final test is performed in two steps because it can be
accomplished faster and is easier to perform. Also, most catastrophic
in-process failures are detected in the first half and the package can be
discarded without expending the time and effort required to perform the
complete final test.
With the final test completed and the determination made that the package
operates satisfactorily, the package is moved to a lead forming station
where the leads are formed into the desired final shape. However, because
the forming process creates substantial forces on the package and the
leads, it is necessary to perform a lead test on the package, which
generally tests for shorts and opens in the leads. This test is difficult
and unreliable because contacting the preformed leads is difficult,
especially with small packages and/or those with many leads. Efforts to
increase the reliability of the contacts with the leads by increasing the
contact pressure of the testing contacts generally results in many
deformed leads and contacts.
Referring specifically to FIG. 2, a simplified flow chart is illustrated
which shows steps in an improved method embodying the present invention.
In the improved method, one half of the final test is performed initially
to find semiconductor devices which include problems introduced during
manufacturing. It will be understood that this step is optional and that
the complete final test could be performed in one step, if desired.
However, it has been found that substantial testing time can be saved by
performing the first half of the final test in a separate step so as to
find semiconductor devices in which a catastrophic in-process failure has
occurred and removing them from the process before expending additional
testing and forming time.
In the next step of the new and improved method, the second half of the
final test is performed during or immediately after the leads are formed.
The device forming the leads has test equipment attached to it and,
because sufficient pressure must be applied to form the leads, good
electrical contact is also made. Thus, the leads are formed and the final
test of the package is completed in one step. Because the test is
performed during or immediately after the leads are formed, any
intermittents, shorts, or opens caused by the forming step are detected in
this testing step and an additional test of the leads is not required.
Since no additional testing or reforming of the leads is required, the now
completed and quality-verified semiconductor packages are placed directly
into final outgoing packages, i.e. tapes and reels, etc. The testing is
much more reliable and constant because the lead forming pressure is
constant and electrical contact with the leads is constant and reliable.
Further, because the final test is performed as the final manufacturing
step after the leads are formed, all prior potentially damaging
manufacturing steps are successfully screened. This improved method of
testing as a final manufacturing step assures quality and outgoing
reliability of the final product and substantially reduces the forming and
testing time and cost by combining both steps into one.
Referring to FIG. 3, an embodiment of a specific testing and forming
station 10 for performing the improved method is illustrated. Station 10
includes a support 12, which is essentially a block shaped structure with
a planar upper surface for receiving a semiconductor package 15 thereon.
It should be noted that support 12 is appropriately electrically insulated
from blocks 25. A vacuum pickup 20, or the like, is utilized to pick
semiconductor packages from a feed track or other source and place them in
the correct position on the upper surface of support 12. At this point,
semiconductor package 15 could be partially tested to ensure that further
operations are warranted, and a plurality of leads 17 connected to
semiconductor package 15 are as yet unformed.
A plurality of lower contact blocks 25, one for each lead 17 of
semiconductor package 15, are positioned adjacent the sides of support 12
and in a position to receive leads 17 to complete their form and position.
Each lower contact block 25 has an electrical connection 26 associated
therewith which is electrically connected to test equipment 30 (see FIG.
4). Also, lower contact blocks 25 are constructed to complete an
electrical circuit between leads 17 of semiconductor package 15 and test
equipment 30 when leads 17 are bent into contact with lower contact blocks
25. This can be accomplished by forming lower contact blocks 25 completely
of a good electrical conductor or by providing an electrically conductive
surface layer.
A plurality of upper contact members 35 are pivotally mounted adjacent
support 12. Members 35 are mounted for vertical, diagonal, horizontal
pivotal or rolling movement between a first or loading position
(illustrated in FIG. 3) and a second position in which members 35
electrically contact and form, in cooperation with lower contact blocks
25, leads 17 (illustrated in FIG. 4). Plurality of members 35 include one
member 35 for each lead 17 of semiconductor package 15 and an electrical
connection 36 associated therewith which is electrically connected to test
equipment 30. In this specific embodiment, each lower contact block 25 and
associated upper contact member 35 cooperate to form a die 40 that bends a
lead 17 into a desired and predetermined shape.
Generally, in this specific embodiment, member 35 rotates downwardly from
the first toward the second position and, at some time during the downward
movement, member 35 is also cammed inwardly to press leads 17 against
contact blocks 25 or to the body of semiconductor package 15. It will of
course be understood that the formation of different shapes of leads will
require different shapes and/or positions for dies 40 and, in some
instances different movements of components thereof.
Dies 40 are movably positioned adjacent support 12 for simultaneously
contacting and forming leads 17. Further, in this specific embodiment both
lower contact block 25 and upper contact member 35 of each die 40
electrically contacts leads 17 to ensure a constant and reliable
electrical connection between leads 17 and test equipment 30. It will of
course be understood that a single contact on the upper or lower surface
of each lead 17 might be sufficient in some applications. Also, while
station 10 is described herein as including a plurality of separate dies
40, it should be understood that a single die could be formed with
electrical insulation between contacts for each lead 17. Also, in actual
manufacturing and testing environments, a plurality of semiconductor
packages may be operated upon in a single step.
Referring specifically to FIG. 5, lower contact blocks 25 and upper contact
members 35 of dies 40 are illustrated in a perspective view to add to the
understanding of the construction thereof. Here it can be seen that
members 35 are essentially fingers with a 90.degree. corner at the lower
edge thereof and an insulating space or layer therebetween. Lower contact
blocks 25 are formed with a layer of insulation 45 extending upwardly
therebetween. Insulation 45 not only serves to electrically separate each
lower contact block 25 from adjacent contact blocks 25, but also extends
upwardly between members 35 when they are in the second position to guide
the leads 17 to ensure lead spacing and also to assist removal of foreign
matter from therebetween. It should be understood that the insulation can
be positioned for upward and/or downward cleaning action. The contacting
and forming process has a tendency to break off small particles of leads
17, which particles can collect in the spaces between members 35 and cause
errors in the tests. Insulating layers 45 assist in removing these
particles and ensure adequate and accurate testing for each semiconductor
package.
Thus, semiconductor package 15 is completely tested and leads 17 are formed
into the desired shape in one forming and testing final manufacturing
step. Semiconductor package 15, of known quality, is moved directly into
final outgoing packages, i.e. tape and reel, trays, magazines, shipping
tubes, etc. A new and improved lead forming and package testing method is
disclosed in which constant and reliable contact with the leads is made.
Further, the new and improved lead forming and package testing method can
quickly and efficiently detect failures caused by lead formation. Also,
forming and testing time and expense is reduced and the improved lead
forming and testing method substantially improves detection of lead
forming as well as prior process induced failures, including
intermittents. In addition, the new and improved lead forming and package
testing method substantially reduces bending and surface marring of the
leads out of specification during testing, and tested packages of known
quality can be placed directly into final outgoing packages, i.e. tapes
and reels, etc.
While we have shown and described specific embodiments of the present
invention, further modifications and improvements will occur to those
skilled in the art. We desire it to be understood, therefore, that this
invention is not limited to the particular forms shown and we intend in
the appended claims to cover all modifications that do not depart from the
spirit and scope of this invention.
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