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Comment by Hasz | Hacker News Reader

I have done this a bunch of different times, mostly to resolve sourcing disputes. Dissolving in boiling sulphuric acid/nitric acid will make quick work of most epoxy packaging

IMO, I have mostly seen mislabeling, rebinning, and passing off obvious QC rejects.

example from many years ago: https://www.youtube.com/watch?v=e6DfBuPwAAA

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> Dissolving in boiling sulphuric acid/nitric acid will make quick work of most epoxy packaging

That's the better method of course (results wise), but it's not nearly as accessible, hence my recent evangelism of the virtues of 2000 grit sandpaper.

I like it. I've used sandpaper to solve some interesting problems in the past as well with great success. I suspect we are only seeing the beginnings here in a trend of high-tech applications of fine grit paper.

I expect it's much easier to acquire fine sandpaper, yet my inner child yearns for laser decapping. (Or I suppose more than "decapping", depending on the depth.)

High power lasers are becoming more and more affordable. Laser ablation is definitely an option but you really want to have some proper fume extraction around that.

Laser decapping will destroy the die, except if you have a rare package that does not mix glass in the epoxy.

You could still compare the internal structure of the package and bonding, but the die itself is mostly destroyed.

I'm off to build an MCP so AI can control the sandpaper

You may as well start off with one of these then:

https://phillipscorp.com/india/phillipsgrinding/phillips-sur...

All you need is a serial port and some G-codes.

Surface grinders generally don’t use CNC, they are a simple machine.

This is a fun playlist of a conversion of a manual machine to CNC:

https://www.youtube.com/playlist?list=PLDlWKv7KIIr9rlCwZ9K43...

In the 1950's, yes. But these days they definitely are CNC based.

https://www.rooy.nl/en/areas-of-expertise/surface-grinding/

I prefer Japanese sharpening stones or those DMT diamond whetstones. It’s relative easy to 3d print a jig that converts a woodworking honing guide into an IC holder and you get a feel for how many passes to do very quickly before slowing down and checking each pass.

That's a super interesting idea! I'll also have to try that.

There was a sandpaper expert in that company associated with sour-tasting fruit which shall not be named. I believe you guys have met, though I think by that time he already pivoted to making the perfect cheesecake.

I've heard that boiling epoxy in molten colophony for a few hours, like a long-cooked version of rosin potatoes, will also dissolve it. I haven't tried it myself. Colophony is much more expensive than sulfuric or nitric acid, but safer to handle (when not molten) and often easier to get.

I did not know that. Pine rosin is such lovely and versatile stuff. And sure enough:

https://m.youtube.com/watch?v=pIpxawdUb4I&t=30m18s

…plus it smells much better; and, as you mention, it’s useful for potatoes too!

https://bittersoutherner.com/feature/2022/the-elusive-roots-...

These slides from the talk say it only takes 5–20 minutes. I'm not sure it will smell better when you heat epoxy to the specified 320–360°. I'm interested in hearing whether anyone else has tried this.

I appreciate the effort, but the bar is already very high when you recommend a SEM in the same breath.

The SEM was cheaper than an optical microscope or a fume hood though :).

(also I don't recommend a SEM in the first post, a cheapo USB 'microscope' will do, I just happen to have had SEM images on hand)

<NileRed voice> …I wanted to look at this chip… so first I put it in a jar of hot nitric acid.

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