Minutes of the GLAST Tracker Technical Meeting
July 12, 2000

Present: Perugia, Trieste, SLAC, Hytec, Pisa, UCSC

Gwelen related experiences with wire bonding rows of wires on Ossie’s laser-cut 
test Si wafers.  The bonding worked very well.  He put rows of 322 bonds spaced 
at 194 microns (as in the BTEM).  He did have problems with vacuuming down 
the wafers, due to Si burrs along the cut edges.  He also had problems with the 
wafers chipping very easily, probably due to weakening of the edges from the 
laser cutting.  Ossie will make some diamond-cut laser marked wafers which will 
allow visual programming of the wire bonder.  He would like to test the potting 
with a pitch somewhat smaller than that which is planned, to be on the safe side.  
He will work out the details offline with Gwelen.

Ossie said that he will be going to the Semicon West conference in San 
Francisco and will make contact with Si suppliers while there.  He is waiting on 
quotes from some vendors.

Ossie is waiting on the return of Eduardo to work out final plans for adhesive 
testing.  He remarked that the ASTM specs might be hard to follow because of 
the load that the tests would put on the silicon.  Two-sided tests as suggested by 
Hytec might work well.

Ossie will meet tomorrow with an AI-Tech representative in Santa Clara.  He 
learned from them that there is a program in the government that will pay a 
company for space qualification testing if there is evidence presented that the 
product is being considered for use by a NASA project.

Ossie reminded us that the Nusil products cost about $150 each time a sample is 
mixed, so it would be best to plan to test it on a lot of parts in parallel.

John updated us on the status of the ladder gluing jig.  It was retouched twice on 
a better mill and is now flat to about 20 microns and the reference edge is 
straight to about 4 microns (not sure I got that right---seems too good).  He now 
needs good wafers for testing.  He is working on the design of a dipping fixture 
for application of the adhesive.  It will dip in a different spot of glue each time.  
Gwelen asked that he run a sketch of the concept by the rest of us before 
prototyping.

Hartmut talked about some investigation he made of Colleen’s analysis of the 
temperature and leakage-current data taken by Hytec on the ladder test 
structures.  He finds that for temperatures greater than about 30C the currents 
never settle down, due to self heating of the detectors.  At lower temperatures 
they do settle down and one can derive an exponent for the temperature 
dependence of the current.  He also sees some hint of stress-dependent currents 
at the lowest temperatures.  A few more days are needed for further study of the 
data.

Gwelen gave a status report on the new fixture for ladder thermal testing.  The 
machining is all done, and in the next few days they will glue up the layers of 
converter and kapton and put the detectors down.  He remarked that the new 
thermal testing chamber arrived at UCSC, so they will also look at the behavior of 
the fixture in the thermal chamber without any payload to work out the 
appropriate ramping rate.  Ossie said that the strain gauges have been ordered 
and will arrive in about 1.5 weeks.

Ossie remarked that there was some confusion about the CTE of Si, since it is 
temperature dependent.  However, everybody now agrees that the value is about 
2.6E-6 per degree C within about 50 degrees of room temperature.  He is 
interested to know whether the precise value depends on the crystal orientation 
in the wafer (100 versus 111).

There was some discussion of the group from Pisa that will travel next week to 
UCSC and SLAC.  Gloria and Nick will be in lodging near SLAC, while Andrea 
and Alessandro will be lodged in Santa Cruz.  They will arrive on the 18th and 
19th and stay for up to 4 weeks.  They would like to return to Pisa with a working 
readout system, including if possible two trays.  They also remarked that Andrea 
is associated with the department of aerospace engineering in Pisa, where we 
can take advantage of facilities and personnel to do testing (such as vibration) 
and development of composites.  Their electronics group is also available to 
begin contributing to the ASIC design.

Hartmut has put the draft tracker top-level requirements document on the web 
and requests comments.

Hartmut said that ST is sending 8 detectors with good IV characteristics to SLAC.  
The specs and test structures for the new detectors have been settled on.  He 
would like for ST and Micron to include the same test structures as HPK.