Processing Black IC's - The wet way.

[MicheleM]

Good morning/afternoon/ evening

I know that is a very old thread, but I noticed that nobody answered to GEO question (I am commenting right now for future readers and to discourage the hot wet ashing process because some absurd YouTube videos...) :
yes, for, glob tops (cob), N/S bridge and very thin IC chips you can do "cold" wet ashing without dangers
(Always wear googles, gloves and mask to open and pour H2SO4 in a glass that you can seal)
Leave the glass outside and be patient ( weeks). I want to thanks who commented here so I avoided any idea to boil the acid;
Even if I could do with the proper safety measures.
Thanks,
Regards,

M.

 

[patnor1011]

Incineration is much faster and in many cases, it can be cheaper than the acid method. While I never tried what you call cold ashing I do not think it will work. It is called ashing because acid pretty much burns all resin when concentrated and warm. If you leave it outside it becomes diluted and may not dissolve all of the material.

 

[MicheleM]

Good morning/afternoon/evening

Dear Patnor1011
thank for your reply, i have some comments about what you said:


"
Incineration is much faster and in many cases, it can be cheaper than the acid method.
"
my response:
yes sure, but i was not comparing these methods, i was only responding to a precise question: "Could concentrated sulphuric/sulfuric acid wet ash an IC chip at lower temperatures?".

"While I never tried what you call cold ashing I do not think it will work. It is called ashing because acid pretty much burns all resin when concentrated and warm. "

my response:
i called "cold" wet ashing , but it's simply room-temperature wet ashing.
theoretically the concept of temperature can be very complicated, (see for example https://arxiv.org/abs/1711.03770) in the present case the typical temperature scale involved in the process (from 290K( 17 Celsius. 63 Fahrenheit) to more or less 523 K (250 Celsius, 482 Fahrenheit ) governs the kinetic of the reaction , only marginally (but with my surprise the literature is not very good) phase-change (https://pubs.acs.org/doi/pdf/10.1021/ja01878a030 ; https://pubs.acs.org/doi/10.1021/je00059a022) or ionizations processes. Because you have concentrated (over 95 pct) acid. the dynamics is governed by a power law that depends from temperature. this simply means that, if the process works a temperatures in a specific phase, it works at almost any temperature in that phase. and (hotter = faster) with a power law.
Another important fact also depending by the temperature is the diffusion process, that improve the overall efficiency of the reaction.

experimentally: i tried successfully with Glob top embedded IC, N/S bridge IC and a single random chosen 5 mm^2 flat-packs.

"
If you leave it outside it becomes diluted and may not dissolve all of the material.
"
Yes, you have to close your system with a lid to avoid the H20 in the gas phase to enter. There are different ways equally safe to met this requirement, i prefer anyway to calculate the possible gas mole that could be emitted by the reactions , however it is sufficient to have enough space and use a resistant vessel/object, or if you prefer the gas to escape in any case, a plastic lid.


Regards,
M.