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Salvaging and "renew" an IC
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Rat_Patrol:
I have several hundred (could get into thousands, maybe) SOIC-16 chips that I need to salvage and then re-use. They will be placed by a PnP machine, and regular reflow. Basically, once removed and "prepped", used like a new chip would be. These chips are obsolete & unobtainable, can't just buy new.

Here is the situation:
They are covered in a mix of silicone and urethane conformal coatings. I cannot see through the silicone conformal coating as it is very thick and appears colored, and causes mounting/reflow issues. This coating needs to come off. I've used some spray on conformal coating remover "for silicone" with zero results.

Sometimes the pads from the old PCBs come with and get stuck onto the chip. I am using IR heat from the bottom of the board to remove these chips (the PCBs are shot, not reused), and sometimes form solder bridges during removal, somehow.

My goals:
Need to remove the silicone conformal coating. The urethane coating can stay on.
Need to clean the contacts of the ICs. Open to ideas on this one. I have been doing it by hand so far, and it is slow and tedious.

Basically, how do the "new" used chips from China et al appear new? What methods do they use, and can they be utilized in a smaller operation?
Tomorokoshi:
Have you tried anything like these:

https://www.dow.com/en-us/pdp.dowsil-ds-2025-silicone-cleaning-solvent.04089120h.html

https://siliconesolutions.com/silicone-remover.html

As suggested in the datasheets for these before using a chemical method it may be best to consult with the manufacturer. Test against other SOIC parts to see what happens to the plating, package, labeling, and leftover acrylic coating.

Silicone conformal coatings are likely one of these:

https://www.dow.com/en-us/search.html?x11=category&q11=products&x54=industry&q54=Electronics&step=industry&q=conformal%20coating&t_s=1597006782079&tab=products

There may be guidance in some of the documents for how to remove the cured material.

For the cost and the amount of work going into reclaiming the parts, it may be best to skip the PnP machine and install them by hand. The alignment of the pins, plating issues, etc. may require some careful attention anyway.
Rat_Patrol:

--- Quote from: Tomorokoshi on August 09, 2020, 09:14:51 pm ---Have you tried anything like these:

https://www.dow.com/en-us/pdp.dowsil-ds-2025-silicone-cleaning-solvent.04089120h.html

https://siliconesolutions.com/silicone-remover.html

As suggested in the datasheets for these before using a chemical method it may be best to consult with the manufacturer. Test against other SOIC parts to see what happens to the plating, package, labeling, and leftover acrylic coating.

Silicone conformal coatings are likely one of these:

https://www.dow.com/en-us/search.html?x11=category&q11=products&x54=industry&q54=Electronics&step=industry&q=conformal%20coating&t_s=1597006782079&tab=products

There may be guidance in some of the documents for how to remove the cured material.

For the cost and the amount of work going into reclaiming the parts, it may be best to skip the PnP machine and install them by hand. The alignment of the pins, plating issues, etc. may require some careful attention anyway.

--- End quote ---

Ordered up some of the Dow silicone remover, see how that does.

I'm REALLY hoping to not have to solder by hand. Even if I have to hand place them (what I am doing now), I REALLY don't want to take the time to hand solder.

I think I'll try attacking the silicone with a brass brush before the ICs are removed. Still doesn't solve the issue of pads lifting, but one problem at a time I guess...

Need something akin to a desktop HASL machien. That should clean up the contacts wonderfully.
coppercone2:
build a special small fixture so you can put the chips on it one by one and carefully scrape them at convenient angles (ball joint micro vise).

You might want to get a micro chisel or carefully cut a exacto chisel blade to the right size and shape.
KL27x:
^+1. Step 1. mechanical removal of bulk material

Then you do the solvents plus brushing.

Finish with solvents and something to absorb/adhere/collect any undissolved particulates. Sawdust, paper towels, something.

Then rinse and blot dry.
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