Download Preliminary Report of Pull Tests for Wire Bonds between Kapton and

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Document #
LAT-TD-00202
Prepared by(s)
Edward Mulder
Robert Johnson
GLAST LAT TECHNICAL DOCUMENT
Date Effective
5/30/01
Supersedes
None
Subsystem/Office
Tracker Subsystem
Document Title
Results of Pull Tests on Prototype Pitch Adapter Circuits
Gamma-ray Large Area Space Telescope
(GLAST)
Large Area Telescope (LAT)
Results of Pull Tests on Prototype Pitch Adapter Circuits
Hard copies of this document are for REFERENCE ONLY and should not be
considered the latest revision.
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CHANGE HISTORY LOG
Revision
Effective Date
6/26/01
Description of Changes
DCN #
Initial release
LAT-TD-00202
Hard copies of this document are for REFERENCE ONLY and
should not be considered the latest revision.
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Results of Pull Tests on Prototype Pitch Adapter Circuits
June 25, 2001
Edward Mulder
Santa Cruz Institute for Particle Physics
1. Introduction
The purpose of performing the pull tests was to see if the wire-bonding machine
in the clean room could create acceptable wire bonds for Kapton to Kapton on a section
of pitch adapter flex circuit. This was necessary first to see if the particular wire bonding
process in use here at SCIPP would work satisfactorily on this material (the reliability for
wire bonding to the flex circuits was not as high as desired in the BTEM construction).
Secondly, due to a change of vendor supplying the material, we needed to be sure that the
product supplied by this vendor would perform satisfactorily in this context.
2. Set up
On 6/15/01 Bill Rowe and I started up the wire-bonding machine in the clean
room (an ultra-sonic wedge bonder using aluminum wire of 25-micron diameter) again
after an extended period of inactivity. There were no major problems during the start up,
the calibration, or the programming of the machine. Minor problems that occurred
included initial failure to follow some commands and some unknown error warnings that
came up occasionally. However, all these minor problems seemed to correct themselves
and did not hamper the tests in any way.
The program for the machine was such that there were two “reference systems,”
the “die” reference system, and the “outer lead” reference system. In turn, each reference
system used two reference points. After these were entered, the machine was then taught
each wire position for each series of measurements. There were a total of 64 wires in
each series.
The set up for the Kapton to Kapton that was bonded consisted of sections of
Pitch Adapter from Q-Flex. These were bonded to ¾ mm thick copper coated G10 using
the 1838 B/A green epoxy adhesive. This, in turn, was attached to the aluminum dovetail
plate with pink circuit bonding tape for the first series of bonds done on 6/20/01, and was
bonded to the aluminum dovetail plate using the 2-part 5-minute Epoxi-Patch bonder for
the second series of bonds done on 6/22/01.
The dovetail plate was then slid into the dovetail fixture on the bonding machine.
During the first series of bonds done on 6/20/01, in order to get the pitch adapter aligned
correctly with the cross hairs on the monitor screen, we sighted along the upper bus bar
of the adapter and then taped it down. For the second series of bonds done on 6/22/01, we
first laid down a smooth layer of the 2-part 5-minute Epoxi-Patch bonder onto the
dovetail plate, placed the adapter onto the plate, then sighted along the upper bus bar of
the adapter as we did with the first series. Once the adapter was aligned with the crosshairs, we then weighted it down with a piece of plexi-glass and then waited 5 minutes for
the bond to dry.
Hard copies of this document are for REFERENCE ONLY and
should not be considered the latest revision.
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For the first series, no real effort was made to clean the pitch adapter before
bonding, as a visual inspection revealed no large specs or pieces of material. For the
second series, the pitch adapter was carefully wiped with a swab soaked in alcohol while
being visually examined at the inspection station.
3.
Measurements
The first series of pull measurements were done on wire bonds that were created
in several different modes on date 6/20/01. The first set of bonds was created in “teach,”
or manual mode. The second set was created in “semi-automatic” mode, and the last two
sets were created in “automatic” mode. The second series of pull measurements were
done on wire bonds that were all created in the “automatic” mode on date 6/22/01.
The pull measurements were done at the inspection station using a Samfy tester
gauge with hook. While peering under the microscope at the station, the hook of the
tester gauge is placed squarely under the middle of the wire and then the tester is pulled
straight up until one of the bonds is broken. The force required to break one of the bonds
is then registered on the gauge of the tester in gm.
The results of the first series of measurements can be seen on the attached sheet
labeled Pull Test for Wire Bonds 6/20/01. The pull test specifications for aluminum wire
of 25-micron diameter were found in the IPC Standards and Specifications TM 650 and
turned out to be 2.5 g. Since the gauge readings for the first series of measurements were
rounded off to the nearest gram, the percentage of bonds  3 g were looked at for each set
of measurements. For teach mode this was 87.5%, for semi-automatic mode it was
78.1%, and for the two automatic mode sets it was 90.6% and 93.8% respectively. This
was deemed not satisfactory, so it was determined that a second series of bondings and
measurements would be done with greater attention paid to both the cleaning of the pitch
adapter and the rigidity of the bond to the dovetail plate, by replacing the pink circuit
bonding tape with the 2-part 5-minute Epoxi-Patch bonder.
The results of the second series of measurements can be seen on the attached
sheet labeled Pull Test for Wire Bonds 6/22/01. The gauge readings for the second series
were rounded off to the nearest 0.5 g, so the percentage of bonds  2.5gm were looked at
for each set of measurements corresponding to the actual IPC standards. As can be seen,
for each of the last three sets of measurements this percentage was 100%.
For the first two sets of measurements, after the bonding machine applied the
bonds, we got a “Missing Wire Detector” error message indicating that not all of the
bonds were successful. When doing the pull test on the first set of bonds, the missing
wire was obvious by visual inspection for one wire, and a pull test on another wire
indicated that perhaps that wire with a gauge reading of 2 g might be “missing” as well.
For the second set of bonds, the missing wire was not detectable by visual inspection, but
became readily apparent during the pull test. For these two sets of bonds, we are not
worried about the percentage of bonds  2.5 g since we know these sets to be defective
before the pull test.
4.
Conclusion
In conclusion, it is apparent that the final series of tests form 6/22/01 more than
satisfied the pull test specifications of 2.5 g for 25-micron diameter wire found in the IPC
Hard copies of this document are for REFERENCE ONLY and
should not be considered the latest revision.
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TM 650. Thus it would seem that the wire-bonding machine in the clean room can create
acceptable wire bonds for Kapton to Kapton on a section of pitch adapter. The secondary
reason for testing, namely the questions as to whether the product supplied by this vendor
would perform satisfactorily in this context, has been positively affirmed as well.
Hard copies of this document are for REFERENCE ONLY and
should not be considered the latest revision.
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Hard copies of this document are for REFERENCE ONLY and
should not be considered the latest revision.