Decapping and Chip-Documentation - Howto

[iMo]

..
Without further experiments I can't say with certainty what really helped, but it appears that the key to success is high temperature and reflux.
..

The colophony contains acids. Under ambient temp the acids are not active. With higher temp they activate.
Therefore colophony has been used as the soldering flux since ever (there are many varieties of the colophony too)..

[magic]

But you can't go too hot either, or you end up with carbonized mess like on my first attempt 4 years ago:


Further experiments will be needed to find the best temperature. Here Sacodepatatas says that it should only take a few minutes, so maybe I still didn't heat it enough. Experiments will also be needed to see if this works on anything other than AliExpress junk, because the chip I decapped was a Chinese MC34063.

It's not clear what the exact mechanism is. Maybe there is a reaction with resin acids and temperature speeds it up, maybe at 380°C epoxy pyrolyzes by itself and colophony only acts as a solvent for the resulting products. Maybe the resin acids turn into something else, more aggressive towards epoxy.

One thing I can say is that boiling for many minutes at 340°C does nothing, but at 380°C or so something starts to happen, the solution turns brown-green and loses transparency, and the chip disappears.

[RoGeorge]

But you can't go too hot either, or you end up with carbonized mess

Maybe use a cheap soldering iron, or an already corroded tip (cardridge-type, the ones that have the thermocouple inside the tip, like T12 for example), and put it inside the vial, so to boil the colophony rosin at a constant temperature fixed from the soldering station.

There are also ready made thermostated pots/tin bays, for tinning wires.

[iMo]

I put a chip (LT1021) into the flame of an ordinary gas oven in my kitchen till the epoxy became fragile (was almost red), the chip simply dropped off the crust after I pressed it with pliers a bit..

[magic]

I decapped another one, a Fairchild TL431, so this can work on brand name chips as well. Took half an hour, probably because TO92 is thicker than SO8.

Temperature is stabilized by the boiling liquid, which absorbs excess heat and vaporizes. You just need not to go too crazy with heat input so that the vapor has a chance to recondense before escaping into the air. Watch the test tube and make sure that there isn't too much foam and that the white mist above the liquid isn't rising too high. Pretty simple. Below you can see what it looks like - the green stuff is the overheated colophony (little of it left at this point), yellow is foam, white is the condensing mist which is supposed to be falling down back into the liquid.

I put a chip (LT1021) into the flame of an ordinary gas oven in my kitchen till the epoxy became fragile (was almost red), the chip simply dropped off the crust after I pressed it with pliers a bit..

You can, but anything that produces cleaner, more repeatable results with less risk of overheating the die or losing it inside a chunk of epoxy falling on the floor is welcome. Unfortunately, the chips aren't coming entirely clean form this and the colophony gunk isn't the easiest thing in the world to remove and I ended up scratching this die a little. Acids are cleaner, particularly HNO₃.

I wanted to say that one could use colophony to decap chips with the package leadframe and bondwires intact, but the damn die fell off during the boil. Well, at least I have a picture of the package

[T3sl4co1l]

Imagine future paleontologists' surprise when they find a glass vessel, containing solid amber, with a "dead bug" trapped within.

Tim

[magic]

I wanted to see if there is something special about colophony or if it's just a matter of temperature and time. I repeated the experiment with an identical MC34063 in paraffin wax instead of colophony. I managed to tweak the flame just right to get stable 380±5°C and it stayed this way for 30 minutes - I checked every 5 minutes.

The paraffin was boiling gently, smoking a little and turning dark, but nothing happened to the chip besides minor surface damage. Laser markings are mostly gone. No significant charring occurred, the chip is still hard and can't be cracked by hand, so it looks like temperature in excess of 400°C is required to effectively char epoxy.

A word of caution: heating flammable liquids with open flame has obvious potential to create extra mess if an "oopsie" happens. Molten wax is flammable, colophony is too. I place the whole setup in a steel bowl to contain any fire that might occur.


BTW, does any recognize this logo? I strongly suspect it's some Chinese manufacturer because these chips were sourced from a known importer of chinesium and the die has overall appearance similar to those ultra-cheap opamps from AliExpress. Maybe these chips can be bought more legitimately from LCSC? Thankfully, at least they don't pretend to be TI this time...

[Noopy]

Nice! Thanks for clarification! 


In the meantime I had another idea for decapping:
Perhaps one could at least weaken epoxy with potassium permaganate? It is used for desmear, for cleaning the drilled holes in PCBs before putting copper into these holes. The permaganate definitely removes the resin residues in the holes. Perhaps it is powerful enough so weaken an epoxy package. Perhaps with some more time...
Unfortunately it seems potassium permaganate can also be used in drug business. It seems you can still buy it in the EU but not online and you have to explain why you need it. 

[T3sl4co1l]

Don't think permanganate will do much by itself, you'd need acid to get it cooking.  But that's either going to decompose quickly, or make a lot of nasty gas (8 HCl + KMnO4 --> MnCl2 + KCl + 2.5 Cl2 + 4 H2O), or something altogether hideous (H2SO4 makes the explosive Mn2O7).

So I mean... "yes BUT"

HNO3 has the middle ground of emitting toxic gas just aggressively enough to devour packaging without getting explosive.  Or H2SO4 somewhat less toxic (SO2 vs. NO2 gas) but much slower and hotter.

Sulfuric can be accelerated with peroxide (or chromic acid, if you don't mind a potent carcinogen..), but that's probably expensive enough not to bother with.

Anything Cl based I think is more prone to chlorinating rather than digesting.  And even with aggressive enough Cl (radicals, I guess?), you might be inviting chlorophenols from the aromatic resin (possible persistent/toxic nasties?).  Maaaybe molten chlorate, but that's on the hot side (into resin decomposition range?), and very aggressive besides (the melt is literally bubbling with oxygen..).  I wonder if maybe it can be tamed by blending with KNO3 (to lower MP), maybe something somewhat inert to help "cool it off" (and further lower MP), say Na2SO4, NaCl/KCl...

Tim

[Noopy]

Oh, thank you for the clarification! I think I won't give it a try... 

[iMo]

I wanted to see if there is something special about colophony or if it's just a matter of temperature and time..

..
Without further experiments I can't say with certainty what really helped, but it appears that the key to success is high temperature and reflux.
..

The colophony contains acids. Under ambient temp the acids are not active. With higher temp they activate.
Therefore colophony has been used as the soldering flux since ever (there are many varieties of the colophony too)..

https://en.wikipedia.org/wiki/Abietic_acid

In 2005, as an infestation of the Mountain pine beetle (Dendroctonus ponderosae) and blue stain fungus devastated the Lodgepole Pine forests of northern interior British Columbia, Canada, resin acid levels three to four times greater than normal were detected in infected trees, prior to death. These increased levels show that a tree uses the resins as a defense.

Thus no epoxy chips would ever hang on the pine trees (the colophony aka "soldering resin/flux" is made from those trees)..

[magic]

Actually, I'm starting to suspect it's not abietic acid but rather products of thermal decomposition of colophony, i.e. the disgusting sticky tar which it turns into when heated above 360°C or so. I plan to do more experiments to find out.

By the way, I looked for procedures for extracting abietic acid from colophony and found a relatively simple one in US patent 2296503. Maybe I will try it some day if I'm really bored...

In the meantime I had another idea for decapping:
Perhaps one could at least weaken epoxy with potassium permaganate? It is used for desmear, for cleaning the drilled holes in PCBs before putting copper into these holes. The permaganate definitely removes the resin residues in the holes.

You could try if you have permanganate. But PCB material is not the same as chips, which is not the same as potting compounds for PCB-based modules, which is not the same as DIY casting resins, which is not the same as...

A few years ago I wasted many hours looking up methods for dissolving various epoxies, only to find out that they don't work on other epoxies. I tried dichloromethane, vinegar, glacial acetic acid, concentrated formic acid and considered also buying some phenols, DMF, NMP and whatnot, but I gave up. I figure the industry would already be using simpler methods if they worked.

I remember from my experiments that soaking PCB material in some of the stuff I had (DCM or formic acid IIRC) for a week destroyed it. Meanwhile chips were completely unaffected. Even vinegar destroyed some of the weaker resins, but not PCB or chips.

[iMo]

At 30:50 they show how to use the colophony for epoxy chips decapping (the same way as you did)..

[iMo]

Epoxy resin can dissolve in hot colophony (also known as rosin) due to several reasons related to their chemical composition and properties:

    Solubility and Chemical Affinity: Both epoxy resin and colophony contain organic compounds with similar chemical characteristics, which can lead to mutual solubility. Colophony is mainly composed of resin acids, such as abietic acid, which are hydrophobic and can interact with the non-polar parts of the epoxy resin. This chemical affinity allows the epoxy resin to dissolve in the colophony, especially when the latter is in a molten state.

    Temperature Effects: Heating colophony reduces its viscosity and increases the kinetic energy of the molecules, allowing them to interact more freely with the epoxy resin. The heat can also soften the epoxy resin, making it more amenable to mixing and dissolving into the colophony.

    Plasticizing Effect: Colophony can act as a plasticizer for the epoxy resin. Plasticizers are substances added to materials to increase their flexibility and decrease their brittleness by reducing intermolecular forces. When hot colophony is mixed with epoxy resin, it can penetrate the resin's network, reducing intermolecular forces and leading to the dissolution of the resin.

    Polar Interactions: Both colophony and epoxy resins contain polar groups, such as hydroxyl and carboxyl groups. These polar groups can interact, leading to the disruption of the epoxy resin's structure and facilitating its dissolution in the colophony.

In summary, the dissolution of epoxy resin in hot colophony is due to the combination of chemical affinity, temperature effects, plasticizing action, and polar interactions. The heat facilitates these processes, leading to a homogeneous mixture.

[T3sl4co1l]

What is this quoting from?

[magic]

Prolly from the You Tube Dude, who is neither a chemist nor has conducted any experiments to understand the process, and speculates wildly?

Meanwhile others say that cured epoxy resins are so highly cross-linked that they essentially form a single molecule (there's a chain of carbons connecting any two atoms anywhere, likely more than one) and there is no "dissolving" them, you can only destroy the stuff by breaking it back into smaller pieces. If this is true, and it very well may be considering how those polymers are formed, then this quote looks like basically word salad.

[iMo]

What is this quoting from?

I cannot say as some members here may get a stroke..

Btw., the epoxy package contains a lot of water, people say up to 5% of the volume. So that may play a role with some chemical interactions as well.. Anyhow, the chemical composition of colophony plays a role with the desintegration of the epoxy package, indeed..

[T3sl4co1l]

I was thinking GPT... and now I'm triply thinking so.  It's factually incorrect enough.

Unsourced quotations are largely disregardable anyway, which this only further supports.

Tim

[Conrad Hoffman]

Here at work we use hot NMP to disassemble epoxy joints. The stuff was easy to get until they banned it from paint removers, but I see it on Amazon here and there. I think we use it at about 100C in a small covered beaker in an oven we keep in the garage and it takes 24 hours or so for tough or hard to access joints to break down. Don't know if it would break down an IC, but worth a try. One of the epoxy makers sells an epoxy solvent with an obscene price, but the MSDS shows it as just NMP.

[ckocagil]

Here's my experience decapping over a dozen chips:

Method 1: Nitric acid in test tube over bunsen burner. My advice: don't bother with method 1, go to method 2. Watch out for the nitric acid exploding, i.e literally shooting out the tube as if it were a barrel. Hot nitric acid is no joke. I haven't been hurt so far, but it could have easily blinded me. Okay, if you're going this route, don't just chuck your entire packaged IC in the tube. Grab some pliers and break off the epoxy to the sides of the chip. Small starting piece => the faster, safer, and easier the process will be. If it's DIP, hold tightly the bottom half of the chip in a vice and pull off the top with pliers. This will de-sandwich your DIP chip.

The downside of mechanical manipulation is that it might crack or the die. Usually it happens at the corners where the die is weakest. So only do it if you have spares or don't care about an imperfect job.

Method 2: Get rid of the bunsen burner and nitric acid. Set your hot air station to 400-500 degrees C (I don't remember the exact temp). Use needle nose pliers or tweezers to heat the chip, then gently bend the chip which should break off pieces of the epoxy. Repeat until you have the bare die. With practice you get to decap chips very quickly. Clean the die surface by rubbing it against paper with some acetone. If you can't get it clean enough this way (which was rare) resort to tube+nitric+heat but only the bare die.

[magic]

Method 1: Nitric acid in test tube over bunsen burner. My advice: don't bother with method 1, go to method 2. Watch out for the nitric acid exploding, i.e literally shooting out the tube as if it were a barrel.

I have decapped a few SO8 chips in 65% HNO₃ with great success and no explosions, but I used a 5ml beaker filled to no more than 1~2ml, heated on a hot plate. Gentler heating and wide vessel appear to help.

I have seen a similar explosion (sudden boiling of superheated liquid) when trying to concentrate 10% H₂SO₄ in a test tube.

Method 2: Get rid of the bunsen burner and nitric acid. Set your hot air station to 400-500 degrees C (I don't remember the exact temp). Use needle nose pliers or tweezers to heat the chip, then gently bend the chip which should break off pieces of the epoxy.

Can you do it with a thick package like DIP or TO220? What if the die is very small, say 1mm² or less?

edit
Method 3: Get rid of the bunsen, heat the test tube with acid using a heat gun at low temperature (I'd start with 150°C and go up if necessary).

[ckocagil]

Can you do it with a thick package like DIP or TO220? What if the die is very small, say 1mm² or less?

I haven't done those with method 2. I'd first try pulling apart the top and bottom parts of the epoxy with a vice like I described above.

edit
Method 3: Get rid of the bunsen, heat the test tube with acid using a heat gun at low temperature (I'd start with 150°C and go up if necessary).

Good idea, temperature control should help a lot.

[magic]

Today I decapped more stuff with colophony: TL062, REF02, LM317L and BC560, so it looks like this should work on every epoxy chip. For some of them I used colophony from a different source, no problem with that either.

Heat appears to be the most important factor, with more flame I managed to reach 390~410°C and things were going faster. One TO92 package was almost completely dissolved after 20 minutes. Even if the chip doesn't fully disappear, remaining epoxy appears to be soaked with colophony and becomes quite soft, so it can be removed manually. By the way, the same happens to heat shrink tubes working in atmosphere of hot colohpony vapor - they soak up, soften and fall apart. It's possible that many plastics can be destroyed this way.

I have not succeeded in getting a fully preserved TO92 package. It looks like intense bubbling separates the die every time. All chips I decapped so far were either blown into pieces or still had some epoxy left, holding them together.

In fact, I wonder if this is even a chemical process at all, or purely mechanical - colophony penetrates into epoxy, vaporizes inside it and blows tiny fragments away. No idea...

My test tube is 8cm long and at 400°C it already works hard, condensing and returning a drop of colophony about every second, but that's not enough and plenty of fumes escape. I plan to buy longer tubes and see if it gets better. I have no idea how people are able to run this process in smaller containers without significant reflux. Maybe apply even more heat and pray that the chip is gone before the colophony?

At this temperature colophony starts to carbonize, leaving ugly black residue in the glass. In the last run today, I plugged the test tube with a ball of aluminium foil in hope of reducing evaporation loss. It didn't help much, pressure inside the tube pushed vapor outside, but it appears to have eliminated the carbonization problem - the test tube was clean, and even some crap left from the previous run got washed away. It looks like carbonization only occurs in presence of oxygen and plugging is a good idea.