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I read a post on this sub-stack from seven years ago, which detailed exactly what I need to do. I will be soldering some components on a laptop PCB, and I'll be using rosin flux. Therefore, I'll be cleaning it w/ 99 percent isopropyl alcohol, which apparently, when it dries, leaves a residue behind. Thus, I'll be using the DI water to remove that residue. The only thing the post didn't mention was the type of DI water.

I looked elsewhere online, and remarkably, I couldn't find an answer. I'm assuming that I'll need to use either Type I or Type II DI water, but I thought it wise to inquire. Does the type make a difference, and is there a specific brand anyone recommends for this type of work? Any help would be greatly appreciated. Thank you.

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  • \$\begingroup\$ Ethanol does not leave residual. For PCB it is not important but to clean connectors it is. \$\endgroup\$
    – user263983
    Commented Apr 1, 2021 at 11:06

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There is no need to wipe/clean the residue of the isopropyl alcohol. Its residue is a white-like stain, mainly around components. Maybe that is why you cannot find any references.

Many times you might as well see in other products this white stain, like here, where someone asks what are those white stains:

enter image description here

And the accepter answer:

It looks like residue from cleaning more than corrosion so gently cleaning with some isopropyl alcohol should remove it, use a coffe filter but not a tissue as that can leave fibers in the board. If it is only a leftover residue it should not impact the performance of the card.

Is it working as expected? Being an older GPU corrosion is possible if it was in a humid enviorment for a time but as it is a used card it is a case of you pay your money and take your chance.

Make sure though it is DRY after cleaning before you power it up !!!

Hope it works out for you

Cheers

He recommends re-cleaning the board with isopropanol, but there is no need, since the white stains will be created once again.

EDIT: Ok I just read here That the white stain is not a product from isopropanol, but flux residue as you mentioned. I guess you learn things everyday. So yes, try to remove it again with isopropanol.

White residue is generally a symptom of ineffective PCB cleaning. Common conductive flux residues from the soldering process can include various unreacted activators, binders, rheology components, and saponifiers. Among these are numerous iterations of acids (abietic, adipic, succinic among others), highly basic ingredients (amino compounds), and even constituents found in “soaps” such as phosphate and sulfate ions. When a cleaner does not fully dissolve all the constituents, or the cleaner is not allowed to flow off the PCB, the remaining solvent can evaporate off and leave behind residue that is either white or like water spots.

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The type is not important, and you don't need ultra pure lab quality water, any deionized water you can get from nearest store will work just fine.

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