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TEC/TOB bias bonds

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

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TEC/TOB bias bonds

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  1. TEC/TOB bias bonds Susanne Kyre University of California, Santa Barbara

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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)

  10. 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)

  11. 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

  12. 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

  13. 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

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