Author Topic: Decapping and Chip-Documentation - Howto  (Read 4632 times)

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Offline Noopy

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Decapping and Chip-Documentation - Howto
« on: September 03, 2019, 10:09:03 pm »

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!  :popcorn:



Best regards,


Richard


Offline magic

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Re: Decapping and Chip-Documentation - Howto
« Reply #1 on: September 04, 2019, 08:21:18 am »
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 :)
[attachimg=1]
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.
« Last Edit: September 04, 2019, 08:49:09 am by magic »
 
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Offline Noopy

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Re: Decapping and Chip-Documentation - Howto
« Reply #2 on: September 05, 2019, 03:43:21 am »
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...  :popcorn:

Offline Noopy

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Re: Decapping and Chip-Documentation - Howto
« Reply #3 on: January 09, 2020, 10:48:06 pm »
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.  :-+


 :popcorn:

 
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Offline magic

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Re: Decapping and Chip-Documentation - Howto
« Reply #4 on: January 09, 2020, 11:10:39 pm »
That's seriously cool and much better than anything I have ever done :-+

BTW, I actually like that smell ;D
 

Offline Noopy

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Re: Decapping and Chip-Documentation - Howto
« Reply #5 on: January 09, 2020, 11:14:29 pm »
That's seriously cool and much better than anything I have ever done :-+

BTW, I actually like that smell ;D

Thanks!  8)

Well, the smell reminds somehow of the youth but with time (and chips) it becomes too much...  >:D
Thank god I have a porch!  8)

Offline GeorgeOfTheJungle

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Re: Decapping and Chip-Documentation - Howto
« Reply #6 on: January 17, 2020, 12:37:30 pm »
:clap:  :-+ => :popcorn:
The further a society drifts from truth, the more it will hate those who speak it.
 
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Online blueskull

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Re: Decapping and Chip-Documentation - Howto
« Reply #7 on: January 17, 2020, 01:11:23 pm »
Been there, done that. But I did the acid solution method and IT WAS NASTY!
I decapped a few packaged MOSFETs and extracted the dies to use in a project (good luck buying bare dies in small quantity). It's challenging to decap those, harder to keep them intact.
 

Offline magic

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Re: Decapping and Chip-Documentation - Howto
« Reply #8 on: January 17, 2020, 01:32:55 pm »
98% sulfuric, oleum or fuming nitric? ;)

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

Offline GeorgeOfTheJungle

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Re: Decapping and Chip-Documentation - Howto
« Reply #9 on: January 17, 2020, 01:56:56 pm »
That's seriously cool and much better than anything I have ever done :-+

BTW, I actually like that smell ;D

Thanks!  8)

Well, the smell reminds somehow of the youth but with time (and chips) it becomes too much...  >:D
Thank god I have a porch!  8)

İt's the smell of magic smoke, isn't it?
The further a society drifts from truth, the more it will hate those who speak it.
 

Online blueskull

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Re: Decapping and Chip-Documentation - Howto
« Reply #10 on: January 17, 2020, 02:20:10 pm »
98% sulfuric, oleum or fuming nitric? ;)

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

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.
 

Offline Noopy

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Re: Decapping and Chip-Documentation - Howto
« Reply #11 on: January 17, 2020, 02:32:03 pm »
That's seriously cool and much better than anything I have ever done :-+

BTW, I actually like that smell ;D

Thanks!  8)

Well, the smell reminds somehow of the youth but with time (and chips) it becomes too much...  >:D
Thank god I have a porch!  8)

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.  ;D
 
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Offline magic

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Re: Decapping and Chip-Documentation - Howto
« Reply #12 on: January 17, 2020, 03:25:17 pm »
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 :)
 

Online blueskull

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Re: Decapping and Chip-Documentation - Howto
« Reply #13 on: January 17, 2020, 03:37:33 pm »
Did you try without the nitrate?

Yes, but my hot plate doesn't go nearly to the temp needed for it to work, and I'm not nearly willing to risk losing a piece of skin.
 

Offline GeorgeOfTheJungle

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Re: Decapping and Chip-Documentation - Howto
« Reply #14 on: January 17, 2020, 03:38:19 pm »
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?
The further a society drifts from truth, the more it will hate those who speak it.
 

Online blueskull

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Re: Decapping and Chip-Documentation - Howto
« Reply #15 on: January 17, 2020, 03:48:15 pm »
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?

CTE mismatch can cause failures within the die, also plastic can pop if being heated too quickly, plus dopant diffusion can happen if you heat silicon too much.
Also, chips may have organic kapton passivation, which can be damaged by heat. Acid can attack epoxy much faster than kapton, but heat attacks kapton faster than epoxy.
 

Offline GeorgeOfTheJungle

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Re: Decapping and Chip-Documentation - Howto
« Reply #16 on: January 17, 2020, 03:55:30 pm »
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?
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Online blueskull

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Re: Decapping and Chip-Documentation - Howto
« Reply #17 on: January 17, 2020, 04:03:45 pm »
I mean, once decapped, the chip exposed to the air won't work for much longer, right?

Who told you that?
 

Offline GeorgeOfTheJungle

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Re: Decapping and Chip-Documentation - Howto
« Reply #18 on: January 17, 2020, 04:22:56 pm »
I've read it in the book "Microchip Fabrication" (Peter Van Zant)  :-//
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Online blueskull

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Re: Decapping and Chip-Documentation - Howto
« Reply #19 on: January 17, 2020, 04:27:28 pm »
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.
 

Offline magic

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Re: Decapping and Chip-Documentation - Howto
« Reply #20 on: January 17, 2020, 04:36:01 pm »
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.
 

Offline MagicSmoker

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Re: Decapping and Chip-Documentation - Howto
« Reply #21 on: January 17, 2020, 04:57:42 pm »
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).

 

Offline magic

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Re: Decapping and Chip-Documentation - Howto
« Reply #22 on: January 17, 2020, 05:05:01 pm »
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.
 

Online blueskull

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Re: Decapping and Chip-Documentation - Howto
« Reply #23 on: January 17, 2020, 05:08:04 pm »
Pure nitric is the standard chemical in failure analysis labs. But it's expensive and rarely available to individuals.

Adding to that, commonly available 68% is not good enough (will still work, but will damage aluminum bonding pads). You need at least RFNA or even WFNA to decap safely, but due to their potential of making explosives and narcotics, they are banned in many countries to individuals.

H2SO4 can be had in forms of drain cleaner or toilet tile cleaner, and the additives won't change its property decapping chips.
 

Offline GeorgeOfTheJungle

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Re: Decapping and Chip-Documentation - Howto
« Reply #24 on: January 17, 2020, 05:35:27 pm »
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.
The further a society drifts from truth, the more it will hate those who speak it.
 


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