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bonding:removal

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bonding:removal [2016/10/18 00:41] – mcmasterbonding:removal [2020/10/25 06:06] (current) – mcmaster
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 +{{:bond:bond_tangle.jpg?300}}
 +
 It is often desirable to remove bond wires. Common reasons include: It is often desirable to remove bond wires. Common reasons include:
   * Leaving a clean surface to re-bond the die into a new package   * Leaving a clean surface to re-bond the die into a new package
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   * Providing a clear view of the die surface for imaging   * Providing a clear view of the die surface for imaging
  
-{{:bond:bond_tangle.jpg?300}}+Bare die TLDR 2020-04-30: 
 +  * Gold wire: use 60/40 solder with a PTFE watch glass, temp controlled heatgun, and carbon fiber tweezers 
 +  * Aluminum pad: briefly sonicate in a corrosive solution 
 +  * 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."
  
-FIXME: Gold is soluble in molten Sn, will a Sn-based alloy work? 
  
-==== Lead ====+===== 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 
 + 
 +Notes 
 +  * teflon melting point 620F (327C) 
 +  * 770F heatgun => 415F blob? 
 +  * 2020-05-04: 770F => 441F measured 
 +  * 60/40 melts around 190C => 374F 
 + 
 +===== 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:bond:amalgam:removed_2.jpg?300}} {{:mcmaster:bond:amalgam:removed_2.jpg?300}}
  
-=== JM procedure 10/27/2016 ===+ 
 +==== mcmaster solder pot ==== 
 + 
 +^ Watt ^ Dial ^ Temp C ^ Note ^ 
 +| 37 |  | 244 | Sludgy. Too cold | 
 +| 41 |  | (260 est) | Probably ideal target | 
 +| 45 |  | 275 | Okay, maybe slightly cooler | 
 +| 85 |  | 300+ | Too hot | 
 + 
 +Model: [[https://www.amazon.com/gp/product/B074K3GVQM/|KD-350 150W]] 
 +  * 150W 
 +  * 480C max (60/40 melts at 188C) 
 + 
 +Thermometer: [[https://www.amazon.com/gp/product/B0749NPRQW/|GDEALER DT8]] 
 +  * Measurement range:58℉ to 572℉(-50-300℃) 
 +  * Accuracy: ±1℃（±2℉) between -50~200℃(-58℉~392℉),±2℃/℉ more than 200℃/392℉ 
 + 
 +Watt meter: [[https://www.amazon.com/gp/product/B000RGF29Q/|P3 International P4460 Kill A Watt]] 
 + 
 +Flux: [[https://www.amazon.com/gp/product/B005T8KZ0I/|MG Chemicals 835-100ML]] 
 + 
 +Handle: something like [[https://www.amazon.com/Quantity-Spudger-Scraper-Removal-Wholesale/dp/B012P07V0E/|this]] 
 +  * Bent at a 90 degree angle 
 + 
 +Amazon notes: 
 + 
 +<code> 
 +The Twinkle Bay Lead Free Solder Pot is ideal for tinning the ends of stranded wire leads, pre-tinning small electrical parts, re-tinning soldering iron tips and dip soldering small circuit boards. 
 + 
 +Pot solder capacity: 500g / 17.6oz 
 +Item weight: 455g / 16oz 
 +Package weight: 515g / 18.2oz 
 +Pot solder Diameter: 50mm / 1.97in 
 +Item Size(L x W x H): 150 x 90 x 65mm / 5.9 x 3.5 x 2.2in 
 +Rated voltage: 110V  
 +Rated power: 150W 
 +Min approx temperature: 200°c 
 +Max approx temperature: 480°c 
 + 
 +Note: The grounding/earth wire must be connected before used in order to protect the circuit from static electricity. 
 +It's normal to appear a little smoke from the electric core at the first time to use. 
 +Reasonable operating temperature 300-350°c (Stalls about 4-9) can prevent man-made aging of tin stoves. 
 +Must turned off the power when you left in order to keep the safe. 
 +</code> 
 + 
 + 
 +==== mcmaster procedure 10/27/2016 ====
  
 {{:mcmaster:bonding:removal:ladel.jpg?300|}} {{:mcmaster:bonding:removal:ladel.jpg?300|}}
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   * Dip ladle into solder   * Dip ladle into solder
   * Let sit for 30 seconds   * Let sit for 30 seconds
-  * Inspect die under microscope, cleaning first if you desire+  * Remove ladle 
 +  * Clean die in acetone (leave it on the ladle) 
 +  * Inspect die under microscope.  Clean and repeat if not fully dissolved 
 +  * Sonicate in cold WFNA for 1 minute 
 +    * Acetone removes most but not all flux 
 +  * Clean in acetone
  
 This technique has very quick turnaround time (other than solder warming up) and is gentle on the die This technique has very quick turnaround time (other than solder warming up) and is gentle on the die
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 I made my ladle from a scrapped aluminum case.  Then put a few layers of heat shrink on the handle and reduced the handle diameter to reduce conductivity.  Still, it can only comfortably be held for short periods of time and usually requires insulating gloves. (more than the white ones shown) I made my ladle from a scrapped aluminum case.  Then put a few layers of heat shrink on the handle and reduced the handle diameter to reduce conductivity.  Still, it can only comfortably be held for short periods of time and usually requires insulating gloves. (more than the white ones shown)
  
 +Old flush is more difficult to clean off.  Therefore, change / clean beaker if its getting dirty.
  
-=== JM 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|}}
  
 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
 +
 +===== Gold field's metal =====
 +
 +McMaster has some to try
  
  
-==== Field's metal ====+===== Gold galinstan =====
  
-JM has some on order to try+Strongly wetted die. Didn't try flux, but not sure it would have released
  
bonding/removal.1476751291.txt.gz · Last modified: 2016/10/18 00:41 by mcmaster