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

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

TODO:

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

Continue lapping same settings