Decapping and Chip-Documentation - Howto

[Noopy]

Hi all,


today I can show you a Howto regarding an easy way of decapping and documentating Chips:

https://www.richis-lab.de/Howto.htm





I´ve structured the topic in different articles:

1. Decapping
https://www.richis-lab.de/Howto_Decap.htm

2. Optics
https://www.richis-lab.de/Howto_Optik.htm

3. Positioning and ligths
https://www.richis-lab.de/Howto_Licht.htm

4. Picture tuning
https://www.richis-lab.de/Howto_Tuning.htm


As usual text on my homepage is german but I will answer every question you have regarding the topic.


Have fun! 



Best regards,


Richard

[magic]

1. Decapping
https://www.richis-lab.de/Howto_Decap.htm

It seems that you got fire to work. I had problems with it and ruined many dies by overheating so I switched to a Chinese 936 iron



Normal soldering temperatures aren't sufficient, I drive the heater manually from 24V DC. Temperature is monitored by connecting the thermocouple sense pins to a TM-902C type thermometer.
About 600~650°C at the heater is sufficient. Aluminum melts at 660°C and the die is cooler than the heater so it should be safe; I have opened a dozen chips that way and never overheated a single one.
Plenty of magic smoke is emitted but there are no flames. Do it outside or under ventilation.

Alternatively, 65% nitric acid at boiling temperature (130°C or so IIRC) does a great job in a few minutes with zero risk to the die except for eating aluminum bonding pads. Disadvantages are fumes (do it outside) and lack of general availability in this EU shithole (find somebody who has access to it professionally).

I'm planning to try 95% or 98% sulfuric next time because I've seen reports that it doesn't attack aluminum. OTOH, sulfuric is said to require higher temperature, something like 200°C or more.

It is beneficial to "preprocess" the chip by cutting excess epoxy with tin snips, particularly for chemical methods.

2. Optics
https://www.richis-lab.de/Howto_Optik.htm

3. Positioning and ligths
https://www.richis-lab.de/Howto_Licht.htm

I haven't done any imaging yet myself.

I found this interesting blog, they show some decent pictures and talk a bit about their methodology. They used microscope lenses, though.
https://resnicklab.wordpress.com/2012/09/26/microscopes-and-imaging/

The general conclusion appears to be that best results are obtained with long focal length and long distance. Of course diffraction and aberrations still set a limit on practical magnification.
They also say that silicon is partly transparent and that this is the reason why you get nice colorful images with back illumination. I'm not sure if it's true.

It is 100% definitely not true and it was somebody else who said this nonsense. Light penetrates silicon to the depth of no more than a few microns. Nice colorful images are product of iridescence / thin film interference occurring in a layer of silicon dioxide covering the chip with varying thickness, partly left over from the fabrication process and partly added deliberately to protect the insides ("passivation").

[Noopy]

I didn´t have much problems with die damage due to the heating. Sometimes there was some kind of blistering but not bad.
I try to heat the package very quickly with a hot blue flame and only as long as necessary.
With my proceeding real damage comes only when you use the hot flame directly on last package parts on the die.

Interesting you use only "electric heat" to open the packages. Perhaps some time I´ll try that too.

Surely acids are the best way to get nice clean dies but I didn´t want to work with such dangerous chemicals.


Regarding the imaging I was proud having found a cheap method of taking photos with good magnification factors (as long as you already have a DSLR).
Surely there are special microscopes with special optics but you have to spend a lot of money for such a tool.

On the page you linked I couldn´t find a clue which resolution they really acchieve and how the final setup looks like. 
I think I have to study the page in more detail... 

[Noopy]

Hi all!


News on my page (yes, german...  ):
https://richis-lab.de/decap-ofen.htm


I have built an ofen for the decapping:




Works quite fine and reproducible! 




Something around 400°C for 2-5 minutes and you are inside the package. 


 

[magic]

That's seriously cool and much better than anything I have ever done

BTW, I actually like that smell

[Noopy]

That's seriously cool and much better than anything I have ever done

BTW, I actually like that smell

Thanks! 

Well, the smell reminds somehow of the youth but with time (and chips) it becomes too much... 
Thank god I have a porch! 

[GeorgeOfTheJungle]

  =>

[magic]

98% sulfuric, oleum or fuming nitric?

I tried  less concentrated acid once and bonding pads went away with the package

[GeorgeOfTheJungle]

That's seriously cool and much better than anything I have ever done

BTW, I actually like that smell

Thanks! 

Well, the smell reminds somehow of the youth but with time (and chips) it becomes too much... 
Thank god I have a porch! 

İt's the smell of magic smoke, isn't it?

[Noopy]

That's seriously cool and much better than anything I have ever done

BTW, I actually like that smell

Thanks! 

Well, the smell reminds somehow of the youth but with time (and chips) it becomes too much... 
Thank god I have a porch! 

İt's the smell of magic smoke, isn't it?

Quite right!
Thought about filling the smoke in tubes to refill the next failed IC. 

[magic]

I used saturated sodium nitrate dissolved in 98% hot (~100C) sulfuric acid. Don't use near boiling (337C) acid. It's gonna end up very bad if something happens.
Boiling H2SO4 burns basically anything organic instantly, while 100C ones give you a sec or two to wipe things off.

Did you try without the nitrate? I have heard of somebody using pure sulfuric acid to decap commercial parts for use in hybrid circuit prototypes, but I don't know if 98% is pure enough. And I think his temperature was higher.

There is certainly no point heating beyond 100~150°C if you add nitrate because all the nitric acid created in the reaction will evaporate or decompose. And yes, that's basically the nitrating mixture, except much hotter than usual, so it will burn/explode everything

[GeorgeOfTheJungle]

Silicon melts at 1414 ° C, gold at 1064, aluminium at 660, (what else can melt inside the chip?) if you can get the magic smoke at temps below that, why use nasty chemicals?

[GeorgeOfTheJungle]

But, do you expect the chip to work after decapping? What for? I mean, once decapped, the chip exposed to the air won't work for much longer, right?

[GeorgeOfTheJungle]

I've read it in the book "Microchip Fabrication" (Peter Van Zant) 

[magic]

I did an experiment once and heated a DIP8 opamp on the tip of soldering iron set to 450°C for ten minutes. It didn't work afterwards and the epoxy got a bit smelly but still too hard to break. So it seems you can't get working parts that way.

Plastics are permeable to air and moisture. If it's sold in plastic package it has to be chemically resistant. Chips are "passivated" with a layer of glass on top.

[MagicSmoker]

I used saturated sodium nitrate dissolved in 98% hot (~100C) sulfuric acid. Don't use near boiling (337C) acid. It's gonna end up very bad if something happens.
Boiling H2SO4 burns basically anything organic instantly, while 100C ones give you a sec or two to wipe things off.

Sounds like heaps of fun... and if I remember my inorganic chemistry correctly, this makes anhydrous nitric acid in situ, which is such a strong oxidizer it rapidly passivates most metals rather than dissolve them (I don't think aluminum bond wires will survive, however).

[magic]

Good enough that bare aluminum bonding pads survive

Pure nitric is the standard chemical in failure analysis labs. But it's expensive and rarely available to individuals.

[GeorgeOfTheJungle]

I've read it in the book "Microchip Fabrication" (Peter Van Zant) 

I've read the same in old soviet books. It doesn't hold anymore today.

Many modern chips are sold in solderable die form, called wlcsp or dsbga.

But are then put in a package of some sort before use, right? Even the cheapest COBs are.

[magic]

No. These are pretty much bare dies with solder blobs on them that you just put on your board upside down and reflow. Sometimes with interesting side effects.

https://www.raspberrypi.org/blog/xenon-death-flash-a-free-physics-lesson/

COBs are potted to protect their bonding wires from being torn. And maybe to stop light as well

[GeorgeOfTheJungle]

But it's been designed to be used like that, as the die of a CCD or a COG that can also be seen, which is not, I think, the same thing as if by removing the epoxy package it's been designed to be in and protected by, you had left it naked and exposed. Humidity and IIRC sodium are chip killers, and both can be in the air.

[iMo]

All chips are covered by few hundreds nm of glass passivation. The only openings are at the pads for the bond wires.
I wanted to see the die of the LT1021 Vref - I put the DIL8 epoxy into the direct flame of my kitchen stovetop, kept there for a couple of minutes (the package was yellow hot) and then I threw it into cold water. The epoxy package desintegrated while squeezed with fingers. No acids required.

[GeorgeOfTheJungle]

All chips are covered by few hundreds nm of glass passivation. The only openings are at the pads for the bond wires.
I wanted to see the die of the LT1021 Vref - I put the DIL8 epoxy into the direct flame of my kitchen stovetop, kept there for a couple of minutes (the package was yellow hot) and then I threw it into cold water. The epoxy package desintegrated while squeezed with fingers. No acids required.

Do me a favor: plug it in and let me know for how long it works

[GeorgeOfTheJungle]

Wow, this is a beautiful photo!


https://www.richis-lab.de/Howto_Licht.htm

[Noopy]

Thanks! 

One of my favourites:



Soon I´ll have a MEMS-Sensor... Really cool pictures… 

New pictures will be bigger. 700px are outdated.
One day I´ll update the old ones… 

[iMo]

The chip itself is produced at pretty high temperatures. The wafers are yellow/white hot during various diffusion processes (around 1000 degC). Thus to put a chip die into a kitchen stovetop flame is for the die the same fun as when you sit yourself into a steam sauna. The aluminum or copper metalisation layers will not desintegrate as they are hold together by the glass passivation layer. Of course, nobody would guarantee you the chip may work after such an exercise.