Removing resin from an embedded circuit

sdowney717

Joined Jul 18, 2012
805
I stripped the gray epoxy coating off a mirror using orange citristrip.
I painted it on, then covered with plastic wrap.
After 2 days it was completely dissolved.

To get the glass clear of the metallic mirror, I used muriatic acid
 

GopherT

Joined Nov 23, 2012
8,009
Ok... just got back from the kitchen, where I placed a small chip of the material above the stove, and sure enough, it got really hot until it caught fire, but it didn't change its shape. It smoked a little bit, but I couldn't detect an odor (strange, isn't it?) Anyway, after about 1 minute the chip stopped smoking and flaming, but I kept it on the fire for one minute more. I let it cool for a couple of minutes after that, and after careful inspection I could tell that the material didn't change shape noticeably. So I pressed it a little bit using pliers, and the thing turned to dust! An "uncooked" chip is much harder to crack, and it turns into smaller chips, not into dust as this one did..... I love mysteries, but not when they're work related.... *the plot thickens*
Electronic components are so full of anti-oxidants and flame suppressants that I doubt you will see more than smoldering and graphitization as you heat it in the flame. It MAY still be organic. As JPANHALT mentioned there are some cement-like inorganic potting compounds. Alumina and zirconia will dissolve in caustic, calcium will dissolve in acid and silica in HF.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
8,783
So I've finally taken the part to an x-ray service supplier (it was actually gamma rays that they used) and snapped four different views of this little device's innards... and lo and behold! the thing is an electromagnet with a diamond-shaped winding in it, and two thee-thronged-fork-look-alike laminated cores. It does have a curious geometry inside, but now I know what I'm dealing with.
Anyway, this week I'm taking the part to a shop so they can mill it all the way down to the winding. That way I can count how many turns it has and what wire diameter it's made of.... then I'll start another thread asking for help on how to build a circuit to drive it.

@jpanhalt and @GopherT, you two were very kind and helpful in this little venture of mine. If you're exceedingly curious as to what material this stubborn part is made of, then I'll be more than happy to send you some of the chips resulting from the milling process so you can test them to your heart's desire, S&H included... just say the word.... thank you very, very much for all your help.
 

jpanhalt

Joined Jan 18, 2008
11,087
Thanks for the offer. I have been retired for almost 10 years and no longer have access to the tools to identify that material. Before that event, I would have been delighted to analyze it pro bono.

John
 

shortbus

Joined Sep 30, 2009
10,050
When I was working for Delphi/Packard electric, the R&D lab had a machine that did the milling on other manufactures parts, as kind of a reverse enginering type thing. It was a mill with a fly cutter and a digital camera. Took the potting off one thousandths of an inch at a time and took a camera shot after each pass of the mill. To try and capture the components and PCB traces to see what they were doing. Did it this way because the potting was so hard to dissolve.
 

RichardO

Joined May 4, 2013
2,270
When I was working for Delphi/Packard electric, the R&D lab had a machine that did the milling on other manufactures parts, as kind of a reverse enginering type thing. It was a mill with a fly cutter and a digital camera. Took the potting off one thousandths of an inch at a time and took a camera shot after each pass of the mill.
Connect the output of this machine to a 3D printer input and you are done. ;)
 

Thread Starter

cmartinez

Joined Jan 17, 2007
8,783
When I was working for Delphi/Packard electric, the R&D lab had a machine that did the milling on other manufactures parts, as kind of a reverse enginering type thing. It was a mill with a fly cutter and a digital camera. Took the potting off one thousandths of an inch at a time and took a camera shot after each pass of the mill. To try and capture the components and PCB traces to see what they were doing. Did it this way because the potting was so hard to dissolve.
Nah... the part's interior is rather simple and the x-rays have given me the perspective I needed, both geometrically and dimensionally. On the other hand, I'll mill the part deeply until I can clearly see a cross-section of the winding to get the information I need.
 
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