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bonding:removal

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bonding:removal [2020/04/30 22:00] – mcmasterbonding:removal [2020/10/25 06:06] (current) – mcmaster
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   * Providing a clear view of the die surface for imaging   * Providing a clear view of the die surface for imaging
  
-TLDR: +Bare die TLDR 2020-04-30: 
-  * Gold: for best results, use a ladle to dip the die in a solder pot +  * Gold wire: use 60/40 solder with a PTFE watch glass, temp controlled heatgun, and carbon fiber tweezers 
-  * Aluminum: pluck or briefly sonicate in a corrosive solution +  * Aluminum pad: briefly sonicate in a corrosive solution 
-  * If you want quick results and are okay risking some damage, use tweezers to pluck wires off+  * Pluck w/ tweezers 
 + 
 +Rebond die TLDR 2020-04-30: 
 +  * Gold wire: use mercury or shear 
 +  * Copper wire: moderate strength nitric acid (say 50%) 
 + 
 +2020-10-24: I've had good luck with swab method. It might see more use moving forward
  
  
 ====== Mechanical methods ====== ====== Mechanical methods ======
 +
 +===== Swab =====
 +
 +I've had good luck removing bond wires using optical cleaning swabs. They are soft and don't damage the die surface, but bond wires tend to get caught on them. This allows bond wires to be quickly pushed off without scratching the die. In theory the gold could scratch the surface, but as long as light pressure is used they shouldn't be able to press in
  
 ===== Ultrasound ===== ===== Ultrasound =====
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 {{:bond:bond_pad_01_neo20_cropped.jpg?300}} {{:bond:bond_pad_01_neo20_cropped.jpg?300}}
  
-====== Chemical methods ====== 
  
-===== Aluminum bond pads =====+====== Aluminum bond pad: chemical ======
  
 Weak nitric acid eats aluminum.  Since most bond pads are aluminum, one can simply put a chip in weak nitric acid and all the bond wires will fall off. Don't leave it in too long as it will start to etch under the overglass and eat top metal.  Aqua regia also works and is much more aggressive as it will work even when weak at room temperature. As with shearing, this method destroys the pads resulting in a die which cannot be re-bonded. Weak nitric acid eats aluminum.  Since most bond pads are aluminum, one can simply put a chip in weak nitric acid and all the bond wires will fall off. Don't leave it in too long as it will start to etch under the overglass and eat top metal.  Aqua regia also works and is much more aggressive as it will work even when weak at room temperature. As with shearing, this method destroys the pads resulting in a die which cannot be re-bonded.
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 The discolored area above and into the the left green area is from acid seeping relatively far into the die.  Similarly, there is a second patch with excessive acid damage near the bottom.  Note how the center of the die typically does not sustain any damage due to overglass passivation. The discolored area above and into the the left green area is from acid seeping relatively far into the die.  Similarly, there is a second patch with excessive acid damage near the bottom.  Note how the center of the die typically does not sustain any damage due to overglass passivation.
  
-===== Copper bond wire =====+====== Copper bond wire: chemical ======
  
-Copper bond wires are difficult to preserve during decapsulation and will disintegrate at the slightest provocation. If by some miracle a bit of copper bond remains on the pad, concentrated nitric acid will remove it cleanly with minimal damage to aluminum bond pads. This leaves a very clean substrate which is perfect for re-bonding. There is typically a shallow crater in the bond pad caused by pressure from the previous bond, but this does not appear to prevent successful re-bonding.+Copper bond wires are difficult to preserve during nitric acid decapsulation and will disintegrate at the slightest provocation. If by some miracle a bit of copper bond remains on the pad, concentrated nitric acid will remove it cleanly with minimal damage to aluminum bond pads. This leaves a very clean substrate which is perfect for re-bonding. There is typically a shallow crater in the bond pad caused by pressure from the previous bond, but this does not appear to prevent successful re-bonding.
  
 {{:bonding:002.jpg?300|}} {{:bonding:002.jpg?300|}}
-===== Gold bond wire  =====+ 
 + 
 +====== Gold bond wire: chemical ======
  
 Gold mining literature reveals a number of ways to dissolve gold.  Gold mining tends to be more selective to stay cost effective which is what we want.  NaCN tends to be the chemical of choice with thoria less toxic but less economically viable. Gold mining literature reveals a number of ways to dissolve gold.  Gold mining tends to be more selective to stay cost effective which is what we want.  NaCN tends to be the chemical of choice with thoria less toxic but less economically viable.
  
-==== Tin ====+https://twitter.com/lukeweston/status/1253256917457137664?s=20 
 +  * "I think Aqua Regia is fastest, but it's harsh and not selective, corrosive to many things. Cyanides are apparently the "finest" etch for gold microelectronics, slow, gentle and gives good small, precise structures. Iodine is a good tradeoff, it's pretty harmless and selective." 
 + 
 + 
 +===== Gold I/NaI  ===== 
 + 
 +TLDR: not recommended. Eats aluminum 
 +  * Details w/ references: https://twitter.com/johndmcmaster/status/1256773931807043585 
 + 
 +https://twitter.com/lukeweston/status/1253256917457137664?s=20 
 +  * 2.5 g I 
 +  * 10 g NaI 
 +  * 100 mL H2O 
 + 
 +https://www.inrf.uci.edu/wordpress/wp-content/uploads/sop-wet-gold-etch-using-potassium.pdf 
 +  * 0.5 – 1 um/min at room temperature 
 +  * mix 
 +    * 1 g I2 (solid) 
 +    * 4 g KI (solid) 
 +    * 40 ml DI water  
 +  * glass or poly bottle 
 + 
 + 
 +https://www.sigmaaldrich.com/catalog/product/aldrich/651818?lang=en&region=US 
 +  * Etch rate of 28 angstrom/sec @ 25 °C. 
 +  * Synonym: Antistrumin, Potassium monoiodide 
 + 
 +http://engineering.tufts.edu/microfab/documents/sop_goldetch.pdf 
 +  * Has temp etch curve 
 +  * 30C: 400 um / min 
 +  * 45C: 800 um / min 
 +  * 60C: 1500 um / min 
 + 
 +===== Gold NaCN ===== 
 + 
 +McMaster: tried this and was too slow to be practical 
 + 
 + 
 +===== Gold thiourea ===== 
 + 
 +https://twitter.com/lukeweston/status/1253256917457137664?s=20 
 +  * "I don't know, I haven't used it or heard of it being used in a microfabrication context" 
 + 
 +====== Gold bond wire: amalgam ====== 
 + 
 +Use of liquid metals to dissolve gold 
 + 
 +Gold is soluble in molten Sn, will a Sn-based alloy work? 
 + 
 +Generally it seems the removal rate is more related to the solution temperature than the alloy used. However, lower temperature tends to be more gentle, making it more suitable for rebonding. This means that mercury is ideal followed by Wood's metal as lead melts at a relatively high temperature 
 +===== 2020-04-26 video ===== 
 + 
 +https://www.youtube.com/watch?time_continue=108&v=AAKWzC3O00k&feature=emb_logo 
 + 
 +Discusses misc metals to remove gold 
 + 
 +Discusses Wood's metal experiment. TLDR: works, but not any better than lead 
 + 
 +Move to PTFE watch glass + heatgun from solder pot
  
-FIXME: Gold is soluble in molten Sn, will a Sn-based alloy work?+Notes 
 +  * teflon melting point 620F (327C) 
 +  * 770F heatgun => 415F blob? 
 +  * 2020-05-04: 770F => 441F measured 
 +  * 60/40 melts around 190C => 374F
  
-==== Lead ====+===== Gold lead =====
  
 The most effective way to remove gold bond wires so far has been hot lead-gold amalgam.  Sometimes two metals can be melted together to form an alloy at much lower than their melting point.  Gold and lead form such a mixture. The most effective way to remove gold bond wires so far has been hot lead-gold amalgam.  Sometimes two metals can be melted together to form an alloy at much lower than their melting point.  Gold and lead form such a mixture.
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-=== mcmaster solder pot ===+==== mcmaster solder pot ====
  
 ^ Watt ^ Dial ^ Temp C ^ Note ^ ^ Watt ^ Dial ^ Temp C ^ Note ^
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-=== mcmaster procedure 10/27/2016 ===+==== mcmaster procedure 10/27/2016 ====
  
 {{:mcmaster:bonding:removal:ladel.jpg?300|}} {{:mcmaster:bonding:removal:ladel.jpg?300|}}
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 Old flush is more difficult to clean off.  Therefore, change / clean beaker if its getting dirty. Old flush is more difficult to clean off.  Therefore, change / clean beaker if its getting dirty.
  
-=== mcmaster procedure 04/29/2013 ===+==== mcmaster procedure 04/29/2013 ====
  
 Equipment Equipment
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     * Grabbing hot die will warp tweezers.  Use dedicated pair     * Grabbing hot die will warp tweezers.  Use dedicated pair
  
-=== Al foil ===+==== Al foil ====
  
 Idea was to encase die in paste and fold it into aluminum foil.  Then heat it strongly and remove the cleaned die.  However, the foil can scratch the die and does not give repeatable results.  Although this method is quicker, the beaker method above is more thorough and less prone to damage Idea was to encase die in paste and fold it into aluminum foil.  Then heat it strongly and remove the cleaned die.  However, the foil can scratch the die and does not give repeatable results.  Although this method is quicker, the beaker method above is more thorough and less prone to damage
  
-=== Soldering iron ===+==== Soldering iron ====
  
 NOTE: not recommended since its much more work and easily scratches die NOTE: not recommended since its much more work and easily scratches die
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     * Repeat until all gold is removed     * Repeat until all gold is removed
  
-==== Mercury ====+===== Gold mercury =====
  
 At least at room temperature (and even I (JM) dare not heat it) it performed much worse than the solder paste method.  Even after soaking die for an hour I could not completely remove all the gold.  I sonicated it in water which removed the liquid element but left behind a solid gold-mercury mixture. At least at room temperature (and even I (JM) dare not heat it) it performed much worse than the solder paste method.  Even after soaking die for an hour I could not completely remove all the gold.  I sonicated it in water which removed the liquid element but left behind a solid gold-mercury mixture.
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-==== Wood's metal ====+===== Gold wood's metal =====
  
 {{:mcmaster:bonding:removal:woods.jpeg?600|}} {{:mcmaster:bonding:removal:woods.jpeg?600|}}
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 Worked okay, but seems to slightly wet SiO2, leading to a lot of hard to remove metallic residue. Worked okay, but seems to slightly wet SiO2, leading to a lot of hard to remove metallic residue.
  
 +2020-04-23
 +  * https://twitter.com/lukeweston/status/1253256917457137664?s=20
 +  * Tried fluxing, much better. But not better than solder
 +  * Above older picture though looks like it might be more gentle, possibly ok for rebonding
  
-==== Field's metal ====+===== Gold field's metal =====
  
-JM has some on order to try+McMaster has some to try
  
  
-===== 2020-04-26 video =====+===== Gold galinstan =====
  
-https://www.youtube.com/watch?time_continue=108&v=AAKWzC3O00k&feature=emb_logo +Strongly wetted die. Didn't try flux, but not sure it would have released
- +
-Discusses misc metals to remove gold +
- +
-Discusses Wood's metal experiment. TLDR: works, but not any better than lead +
- +
-Move to PTFE watch glass + heatgun from solder pot+
  
bonding/removal.1588284013.txt.gz · Last modified: 2020/04/30 22:00 by mcmaster