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Decapping and Chip-Documentation - Howto

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Noopy:

--- Quote from: magic on October 07, 2021, 06:09:43 pm ---
--- Quote from: Noopy on October 07, 2021, 08:30:21 am ---Unfortunately on this die the layers don´t show the nice colors we have seen with other dies.

--- End quote ---
Yep, because it was the glass :)

--- End quote ---

I had the hope there is still some ... ... resonance ... ... refraction ... ... whatever.  ;D

RoGeorge:
AFAIK the color is given by the nanostructures being (multiple of) half wavelength, and the incident and reflected wave interfering with each other, somewhere in the middle of this video it is explained with a few more details:



Assuming the refraction index is the same, and the metal or semiconductor layers are glossy (no nano "bumps" on the surface to turn them into a metamaterial), I guess it should be possible to calculate the glass thickness by measuring the reflected spectrum.

Noopy:
I agree with you.  :-+
Nevertheless I had the hope...  ;D

XantheFIN:

--- Quote from: magic on August 19, 2021, 06:52:21 am ---If anyone ever wondered what a SO8 package looks like inside, I found some old pictures from my experiments with blueskull's acid + saltpeter formula.

I'm not sure if I was supposed to make a saturated solution of saltpeter in acid or mix a saturated solution of saltpeter in water with acid; maybe the latter would have eliminated crystallization of salts on the chip and sped up the process, but dunno about corrosion OTOH.

Anyway, the junk covering the die on the first picture is just some salt from the process, nothing that came from the factory ;)
The next two pictures were taken after cleanup and some mechanical separation.

--- End quote ---
Hi what is this formula you used in process? "blueskull's acid + saltpeter formula"?

magic:
You can find it quoted here, the guy who posted it quit the forum and nuked most of his content.
https://www.eevblog.com/forum/projects/decapping-and-chip-documentation-howto/msg2875340/#msg2875340

It's a messy process and I'm not sure if I have done it the same way blueskull did or differently. At any rate:
- I now know that nitric acid evaporates from mixtures with concentrated H₂SO₄ quickly starting at ~80°C (this technique is used for distilling anhydrous HNO₃) so the whole process seems somewhat inefficient/wasteful
- I needed high temperature for anything to happen, it fumed quite a lot, I recirculated some vapor by putting a cap on top so it condensed (but don't pressurize the test tube)
- it took a few hours
- those HNO₃ and NO₂ fumes are toxic, just so you know
- maybe I was supposed to add water to the reaction (use a solution of KNO₃ instead of dropping dry salt into H₂SO₄) but not sure
- too much water means corrosion of bonding pads and/or bond wires

Generally, you should only bother with that if you want to preserve everything intact, including wires and pads.
For just a bare die, it's much easier to use:
- ordinary 65% nitric acid ~120°C in 5ml beaker with watch glass cover (don't sniff the fumes)
- 2ml sulphuric acid at 200~250°C - less toxic, more danger of burns, it bubbles, eye protection advised
- electric heater 400~600°C (needs a few tries to get it right)
- fire (Russian roulette)
- boiling rosin at who know what °C - some people say it works, I never succeeded

This source claims that pure concentrated sulphuric acid may work without corrosion, but it didn't work like that for me. Maybe I haven't used enough and the concentration dropped as water was produced in reactions.
http://www.stockly.com/forums/showthread.php?p=2239

See also
http://siliconpr0n.org/wiki/doku.php?id=decap:epoxy_acid

Have fun ;D

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