Now that I have a proper (homebrewed) fume hood decapping is a lot easier and safer. No fumes to breathe, and a nice thick sash between me and the beaker of hot acid if something goes wrong. That said, I still wear goggles, gloves, and a lab coat as per SOP.
For the new process I am using sulfuric acid as it's much cheaper than nitric. (Concentrated sulfuric of an acceptable quality can be purchased as a drain cleaner, while nitric must be mail-ordered with special hazmat shipping fees). The downside is that sulfuric cannot be used for live decapsulation (at least not easily) since it takes so long. For bare-die decaps it's by far the most cost-effective option, though.
The first step, as is usual for bare-die decaps, is to put them in a beaker of acid, cover with a watch glass or petri dish to slow down evaporation losses. and heat.
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| View through the sash of my fume hood as the acid warms up |
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| Close up of beaker on the hot plate |
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| Later in the decap |
At this point all that has to be done is to leave the chips to cook for a while. I was running at only around 100C (150-200 is more common) so it took an hour or two.
Before I get to the results, a warning as to what you're dealing with here. While pouring the used acid off into another beaker to pull the dies out with tweezers, I spilled a drop on a kimwipe I had in the hood. This was the result:
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| H2SO4 + organics = bad |
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| Top metal of FT232RL |
Wiki page: http://siliconpr0n.org/archive/doku.php?id=ftdi_ft232rl