PI2611 Polyimide Recipe  v 1.2, 30 June 2001

*** 50 um wide flexures with 4 um thick polyimide ***

see data sheet at www.hdmicrosystems.com

warning- wear coat, latex gloves, goggles and work under fumehood
with polyimide


o pre-heat vacuum oven to 200 degrees C (max temperature ~ 1 hour)

o (if not already in small container, thaw PI2611 and pour into small
   plastic bottle. cap tightly after use) replace PI2611 in freezer
  * warm to room temperature - I suggest a warm water bath for the small
   bottle. Cooler temperature will be viscous and too thick *

o prepare slide with double sided GelPak X4 to hold SS

o attach 12 um stainless, sand lightly with silicon carbide, 600 grit

o clean debris from SS with acetone on Q tip until tip is clean

o turn on vacuum for spin coater and position slide. Make sure slide is 
  securely held

o pour PI2611 from small bottle in center of SS, being careful not to
  introduce bubbles, let sit ~ 1 minute to partially spread out
  
o spin on KW4A timer 1: 18 sec, 2:00 on dial
               timer 2: 50 sec, 3:00 on dial

   (this gives 4 um thick polyimide)

o place slide+gelpak+stainless steel in oven for 2 minutes.
  SS will curl up and release from gel pak. Pull SS off of gelpak with
  tweezers, and remove gelpak from oven so it doesn't burn. Polyimide
  will still be tacky, so don't stick anything on it.

o place stainless steel on shelf (sticky side up). Seal door, apply vacuum,
  (to 25" Hg). This should keep toxic fumes out of lab. Heat at
  200 degrees C for 30 minutes, ``Soft bake''.
  Turn on vacuum pump, open inlet partially to exhaust fumes up
  fumehood. (Maybe 2-3 minutes?). Remove SS piece.

o Sandwich SS+polyimide piece between 2 glass slides to ensure uniform
  heating. Place on hotplate.  Turn on hotplate heat to #9, 
  ``hard bake'' for 30 minutes. 
  (Do not place cold glass slides on hotplate at high heat- they shatter,
  instead, ramp temperature.) 
  After soft bake, polyimide does not stick to glass. 
  [possible problem with polyimide outgassing and bubbling? ramp
   temperature to avoid problems?]
  This hard bake step seems to increase strength 3-4X compared to softbake.
  (This is hot enough to burn/ignite paper and melt solder so be careful).

_____________________ masking+patterning  ____________________

o apply procedure above using PI2579 (0.5 um thick) as mask, ``soft bake''
  and ``hard bake'' to avoid outgassing problems laster in process.
  Thinner layer of polyimide seems to provide cleaner edges in laser cutting,
  and hence less stress concentration at flexures.

o thin polyimide is easily cut with the laser on green, low power ~600 50X,
  or high power ~600 at 20X for ~150 um flexures. Edge of polyimide
  should be clean.  Blast just polyimide, not SS.

_____________________ etching  ____________________

o put S.S. in small beaker with ferric chloride, use magnetic stirrer
  at 3-4, hotplate on #2-3 for 3-10 minutes.
  Check every 2-3 minutes- pull out with plastic tweezers, rinse in 
  flask of tap water. Ferric chloride does not seem to affect polyimide.
  Magnetic stirrer will tear weak flexures. 1 cm ``hard baked''
  flexures survived ok.