tec/tob bias bonds

Susanne KyreTracker week, October 2005

TEC/TOB bias bonds

Susanne Kyre

University of California, Santa Barbara


TEC/TOB bias bonds• Wirebonds will be added to the back of all TEC

and TOB modules to add redundancy to the bias connection

• On TOB modules a bondable tab needs to be added to the module frame

• New modules• Existing modules are retrofitted (~2600 modules)

• TEC modules already have a gold plated area on the module frame, where wirebonds can be placed

• All bias bonds get encapsulated to protect them from damage during handling


New TOB modules• Two small tabs (gold plated

kapton) are soldered to the module frame

• During module assembly the tabs are glued to the back side of the sensor


Existing TOB modules I• For modules that have

little or no silver epoxy under the the gold plated hole in the kapton of the module frame, a small tab (gold plated kapton) gets glued with silver epoxy to the gold

• The tab is also glued to the sensor

• Most of the 1200 modules at UCSB will be retrofitted using this method


Existing TOB modules II• For modules that have a lot of

silver epoxy under the gold plated hole in the kapton of the module frame, a wire is soldered to the resistor on front side of the module

• The wire gets looped around the edge of the frame to the back side

• A small tab (gold plated kapton), which has previously been soldered to the wire, gets glued to the sensors straddling the gap between the sensors

• All 1400 FNAL modules and about 80 UCSB modules will be retrofitted using this method


Bias wirebonding• Height requirement: Maximum

encapsulant height must be below the highest point on the module frame

• Wirebond loop height is kept to 280 microns

• Encapsulant height is kept below 630 microns

• After the front side of the module is wirebonded, the module gets removed from the module carrier, turned over and placed on a special vacuum fixture

• 15 wire bonds are placed on each of the 2 bias bond areas on the backside of the modules


Bias bond encapsulation

• For the detailed procedure see:http://hep.ucsb.edu/cms/cms_procedures/tec-encapsulation-procedure.pdf

• For the drawings of UCSB designed tools see:

http://hep.ucsb.edu/cms/mechanical.html


Material and Preparation• Sylgard 186 Silicone

Elastomer, 2 part kit, 10:1 mixing ratio (manufacturer: Dow-Corning)

• Mixing cups

• Mixing sticks

• Digital bench scale

• Small vacuum chamber or centrifuge for degassing


Dispensing Equipment• Pneumatic glue dispenser

with foot pedal and timed pulse option (manufacturer: EFD model: Ultra 1400) www.efd-inc.com

• 3ccm syringe barrel and piston (EFD)

• Smooth-flow tapered tips, gage 20 (EFD)


Set up Equipment• Base plate (UCSB

design), to hold the module on a module carrier upside down

• Plastic trowel (UCSB design), to spread the encapsulant over the wirebonds and to keep the height of the encapsulant below the maximum height

• Stereo microscope (optional)


Procedure I• Mix encapsulant, degas

the mixture and fill syringe

• Set pneumatic dispenser to 15 psi and 1 second dispense time

• Set module in carrier upside down onto base plate

• Dispense a line of encapsulant across the width of the wirebonds


Procedure II• Position the trowel with

one leg on the sensor, one leg on the kapton

• Spread the encapsulant over all 15 wirebonds by sliding the trowel across the bonds

• Once the trowel is past the wirebonds, lift it up and clean it off with a dry tissue paper


Procedure III• Check that all wirebonds

are covered completely with the encapsulant (this can be done with or without a stereo microscope)

• If necessary apply more silicone and repeat the troweling procedure

• Cure for 24 hours with the backside of the module facing up to avoid beading up of the encapsulant

tec/tob bias bonds

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