Silicon Prawn

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====== McMaster notes ======

===== 2021-04-21 =====

  * Goal: set RP2-B0 in wax on Allied sample holder
  * RP2-B0
    * Decapped 2x "live" from photo shoot to bare die
    * Around 277 um thick. Later measurement 281 um
  * Sacrificial dies
    * Samsung k4h560438e-tcb0
    * 324 um
  * Area
    * Samsung: 5.3 x 11.1 = 58.8 mm2
    * RPI: maybe 4 mm2
    * Net: maybe 60 mm2
  * Etchant: 20% w/v KOH in water
    * https://cleanroom.byu.edu/koh
    * Approx 250 um / hour heated => 4.15 um / min
  * Etch
    * Etch 1
      * 25 min @ 177F hotplate
      * 306 um
    * Etch 2
     * 30 min?
      * raised temp?
      * 297, 302 um
      * High spots forming (was warned might be uneven at this conc)
    * Etch 3
      * Now hotplate at 220F
      * 286 um, 291 um
      * 14 um in 30 min
      * (286 - 277) * 2 = 18 more min?
      * Lots of metal flaking off
    * Etch 4
      * 20 min
      * Ultrasound. Lots of stuff flaked off
      * Didn't note final thickness...
  * Check all dies for thickness before mounting
    * Not all started at exactly the same time, although was close
  * Order replacement lapping gauge
    * 543-452B, ID-C125EB
      * 1 um resolution
      * 25 mm travel
      * Long
      * Flat carbide tip. Will need to switch to new unit
    * Skips
    * Can't modify spares to be long enough
    * One that might work I can't get to power up. Completely broken?
  * Set in wax
    * 0.4 mm gap in area(s). Not ideal but may still work




===== 2021-04-23 =====

Goal: setup lapping machine, lap RPI chip from other day

TODO:
  * Level head
  * Review Allied recommendations
  * Characterize um / rev
    * Gauge skips, but is stable over say 1 mm
  * Setup slurry feed
    * Can I make this nicer?

Inventory:
  * 2x MultiPrep systems w/ arm
    * Both were surplus / in bad condition
    * One is more "ready to go"
  * Lots of lapping disks
  * Is my old colloidial silica still good?

Notes:
  * Installed old magnetic polishing cloth
  * Post 1.49"
    * Could I mount stopcock to it somehow?
  * Feeler gauge test
    * Pointed inside
    * About 30 um variation
    * Good enough for now: not great but not terrible
  * Main crank 40 TPI
    * Wheel is marked in um (635 um)
  * Allied-Parallel-Lapping-Integrated-Circuits.pdf
    * If gauge is moving its already too much pressure
    * Instead use recommended distances
    * Based on 500 um die
    * Imperial Polishing Cloth, #50-150-500: 0.840 mm
    * 277 um die => 724 + 277 = 1001 um offset?
    * Sample load set to full
    * Using spare holder to measure
    * Distance from Platen to bottom of polishing fixture = Ts - Tc - Td + 0.116 mm
      * Ts = Spacer thickness (0.500")
      * Tc = Cloth Thickness
      * Td = Die Thickness
    * So...
      * Ts: 12.65 mm
      * Tc: 0.840 mm
      * Td: 0.277 mm
      * Net: 12.65 - 0.840 - 0.277 + 0.116 = 11.649
    * ...but I'm using magnetic sheet. Not the same
      * 50-500-500 instead of 50-150-500
      * Magnet: 735 um
      * Cloth: 450 um (840 um official)
    * Let's use official number
      * 12.65 - 0.840 - 0.735 - 0.277 + 0.116 = 10.914 mm
      * Crank: 25.4 / 40 = 0.635 mm
      * 10.914 / 0.635 = 17.2 cranks
        * Remainder: 0.119 mm
    * Settings
      * 225 RPM CCW
      * Rotation: full speed (8)
      * Osc: 3
    * 0.05 um silica

===== 2021-04-24 =====

Continue lapping
same settings