Andrew Zonenberg on Nostr: Here's the die before final cleaning. Copper bond wires are challenging to preserve ...

Here's the die before final cleaning.

Copper bond wires are challenging to preserve without access to ultra high purity nitric acid (WFNA/RFNA). I've developed some techniques using mixtures of nitric and sulfuric that are decent at preserving some of them, as seen here (70% nitric without any additives would have obliterated all of the wires), but there's still quite a few damaged ones.

I might have had better luck if I etched less long, it looks like the top left etched a lot deeper (to the point of hitting the copper die attach paddle) than the right and bottom. Not sure why that happened.