Decapping and Chip-Documentation - Howto

[Noopy]

The chip itself is produced at pretty high temperatures. The wafers are yellow 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.

You are right but a torch can ruin the metal layer:

[iMo]

It could be the metallization layers get ruined by the gases streaming off the epoxy package penetrating the glass passivation layer, when put into torch (the epoxy package contains up to 8% of water and 17% of epoxy resin).
Nice pictures!

[GeorgeOfTheJungle]

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.

I think the idea is not to go further than 600˚C or so maximum (aluminium melts at 660). 400˚C in noopy's oven seems to work fine: https://www.richis-lab.de/decap-ofen.htm

[GeorgeOfTheJungle]

Thanks! 

One of my favourites:

Yep, that's even better! 

What's a MEMS-Sensor, a solid state microphone?

[Noopy]

It could be the metallization layers get ruined by the gases streaming off the epoxy package penetrating the glass passivation layer, when put into torch (the epoxy package contains up to 8% of water and 17% of epoxy resin).
Nice pictures!

Sounds possible...

Thanks! 

I think the idea is not to go further than 600˚C or so maximum (aluminium melts at 660). 400˚C in noopy's oven seems to work fine: https://www.richis-lab.de/decap-ofen.htm

That´s the idea. Don´t risk more than neccesary. 

What's a MEMS-Sensor, a solid state microphone?

"Small, Low Power, 2-Axis ±3 g i MEMS® Accelerometer"
https://www.analog.com/media/en/technical-documentation/data-sheets/ADXL323.pdf
And it looks really nice! 

[iMo]

I think the idea is not to go further than 600˚C or so maximum (aluminium melts at 660). 400˚C in noopy's oven seems to work fine: https://www.richis-lab.de/decap-ofen.htm

Yea, I got the package in the same shape as on the last picture in the link
The biggest issue was to find the chip in the dirty mess
Sure, the gas oven or torch is not easy to regulate.

[magic]

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.

Epoxy package doesn't protect from humidity. Quite the contrary, it soaks up like a sponge. Sensitivity to humidity is a well known problem with plastic-encapsulated voltage references, for example.

I'm pretty sure that oxygen diffuses right through it as well for that matter, and sodium hydroxide (the thing that sodium ultimately turns into in contact with humidity) probably too. Though I'm not sure if Na/Na₂O/NaOH seriously exists in the air in any serious quantities?

NaOH is a chip killer. It can dissolve every part except epoxy and copper. You could actually drop a chip in NaOH solution for a few years and see if epoxy will protect it

It could be the metallization layers get ruined by the gases streaming off the epoxy package penetrating the glass passivation layer, when put into torch (the epoxy package contains up to 8% of water and 17% of epoxy resin).
Nice pictures!

I have a simpler theory: the melting point of aluminium is only 660°C
I suppose it just melts, gathers in blobs and then solidifies again, displaced.

At any rate, as I said, 10 minutes at 450°C and the opamp I tested was totally dead and unreactive to anything.

[iMo]

Though I'm not sure if Na/Na₂O/NaOH seriously exists in the air in any serious quantities?

I was reading (or it was youtube?) some interesting stuff on history of chip making in Japan. They were coping with Na in air as they were located near the sea shore.

[GeorgeOfTheJungle]

Yep, it's salt, chlorine and sodium ions, both things are bad for the chips, near the sea there's lots of that in the moist air.

[GeorgeOfTheJungle]

Epoxy package doesn't protect from humidity. Quite the contrary, it soaks up like a sponge.

"Like a sponge"? Hyperbole for the win

[GeorgeOfTheJungle]

What's a MEMS-Sensor, a solid state microphone?

"Small, Low Power, 2-Axis ±3 g i MEMS® Accelerometer"
https://www.analog.com/media/en/technical-documentation/data-sheets/ADXL323.pdf
And it looks really nice! 

[TheUnnamedNewbie]

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.

All those high temperatures are done in the FEOL. Once you do metalization in the BEOL I don't think you see those temperatures anymore.

I believe that more modern technologies don't use glass passivation anymore but some polymers? I know colleagues at the lab complain about it a lot since it is a lot less robust and easy to accidentally probe through.

[magic]

Why would they do that? Isn't SiO₂ still the basic insulator used all over the die anyway? Something to do with high-k CMOS?

[Noopy]

Thanks for the link, looks very interesting! 

Why would they do that? Isn't SiO₂ still the basic insulator used all over the die anyway? Something to do with high-k CMOS?

Something with CTE mismatch. Having a low modulus layer like polyimide helps mitigate the stress. Even some power devices do this. Cree SiC MOSFETs all have this.

I know only one use of polyimide: It is used considerable time for memory as a additional layer. The reason is that in the mold compound there are always some radioactive particels which can change the logic level of small memory cells.
Interesting that it´s also used for SiC MOSFETs.

[GeorgeOfTheJungle]

Epoxy package doesn't protect from humidity. Quite the contrary, it soaks up like a sponge.

"Like a sponge"? Hyperbole for the win

"Microchip Fabrication, 3rd edition, p559"

Hermetic sealing results in a package that is impervious to the penetration of moisture and other gases. Hermetic seals are required for chips operating in harsh and demanding environments such as rockets or space satellites [..]
Nonhermetically sealed packages are adequate for most consumer applications [..] This sealing system provides good and adequate environmental protection of the chip, except in the most demanding situations. A better term for this type of enclosure sealing method would be "less hermetic". These packages are composed of epoxy resins or polymide materials and are generally referred to as "plastic packages".

[magic]

https://www.analog.com/en/analog-dialogue/articles/does-my-voltage-reference-design-hold-water.html

Does My Voltage Reference Design Hold Water? Methods of Managing Humidity and Performance in Precision Analog Systems

Seriously though, the question was if the plastic is critical for protecting the IC from "ambient" chemicals. To my limited knowledge, it's not.
Go ask blueskull how long his decapped transistors survived outside the package. I think his bewilderment suggests that it wasn't really a problem

[GeorgeOfTheJungle]

https://www.analog.com/en/analog-dialogue/articles/does-my-voltage-reference-design-hold-water.html

Does My Voltage Reference Design Hold Water? Methods of Managing Humidity and Performance in Precision Analog Systems

Meh, clickbait is everywhere these days 

Seriously though, the question was if the plastic is critical for protecting the IC from "ambient" chemicals. To my limited knowledge, it's not.

I've found this:

https://www.ti.com/lit/an/snoa300a/snoa300a.pdf

Current plastic packages use various molding compound formulations consisting of epoxy resin, silica
fillers, and other minor constituents. The epoxy resin is non-hermetic and absorbs a small percentage of
moisture through diffusion. Eventually, an equilibrium develops between the moisture content inside the
package and the ambient moisture and temperature conditions. If enough moisture is present in the
package during surface mounting, the intense reflow heat turns the moisture into saturated steam (1). This
extreme pressure, accompanied by a drop in flexural strength of the molding compound at temperatures
reaching up to 240°C, may cause the package to fracture allowing the steam to escape (2). Once the
fracture occurs and the steam has escaped, a greater threat now exists to the device. The fracture allows
moisture and ionic contaminants such as sodium, potassium, or chlorine to infiltrate the plastic package,
potentially causing corrosion, and eventually failure of the device. Therefore, moisture-induced cracking
must be prevented in order to maintain the long-term reliability of surface mount plastic packages.

Maybe Dave would like to investigate, sounds to me like a good theme for a cool for-nerds-only EEVBlog vidjeo: take some AVRs or something with the blinky sketch, decap them (cool die photos!) with noopy's oven system (Magic smoke!), let them run on a shelf 24/7 (boring), and see what happens: updates every Mailbag Monday.

[Noopy]

Maybe Dave would like to investigate, sounds to me like a good theme for a cool for-nerds-only EEVBlog vidjeo: take some AVRs or something with the blinky sketch, decap them (cool die photos!) with noopy's oven system (Magic smoke!), let them run on a shelf 24/7 (boring), and see what happens: updates every Mailbag Monday.

It would be a honor for me being mentioned in a Dave-Video! 
But I would have to bond new wires to a decapped die. That´s not possible for me... 
Opening a metal-can-package and let it run with high humidity would be possibility...

[magic]

Some people say that boiling chips in rosin gets the job done. Tried it today, here's the outcome:



There is some loss of volume, so it seems to work, but it certainly isn't fast. I boiled it for a good few minutes with no obvious effect so I cranked up temperature until it started to smoke. That was probably not a good idea

Or maybe it was? I don't even know if the attack occurred during those few minutes of slow boiling or due to the high heat at the end. Not sure if I want to do it again to find out.

I think I would rather simply drop the chip into an empty test tube and cook until it gives out the magic smoke.

[Noopy]

I have also heard from people trying rosin to decap chips.
In my view rosin doesn´t  really do the job. When people go to around 400°C they can destroy the epoxy but with this temperature you don´t Need rosin. 

[magic]

I actually wouldn't mind cooking it in some solvent which would cleanly strip all the decomposed epoxy in real time so that I don't need to do it manually. But it turns out that burning rosin is anything but clean

[iMo]

You would need a pretty strong acid for your cooking

[Noopy]

Heating a "wet" package sounds like a easy way to crack it. But my read is that there will only be one or more cracks. I´m afraid the epoxy will still be very hard to remove...

[cncjerry]

Imo,  loved your video.  That was something new for me.  Wondering what to do with them, maybe earrings if you have enough of them. ,pretty darn cool.

As far as  probing,  if you use your cnc mill with a probe in the chuck, it would make it much easier..

Thanks  for posting,

Jerry

[magic]

You would need a pretty strong acid for your cooking

I wouldn't; rosin is good enough, as I said. But it's slow as molasses and easily turns into a dirty mess.

Maybe there are other organic acids that could work. So far I found two possible candidates: benzoic and adipic. Both have high boiling points and are safe at room temperature. Their structure is also simpler than rosin acids, so hopefully pyrolysis products would be cleaner.