No Stupid Questions

We don't really have electronics stores here anymore. The highest I've seen locally is 91%, and while it does kind of clean it off, denatured alcohol has always worked a lot better for me so it's disappointing to see that it's gone. I'll probably just order some online. But still, I'd be interested in knowing why.

I don't... sounds like something I should have had many years ago though.

Not that this comment is all that relevant to you, but here's a wall of text for context:

The devil is probably in the details here. My assumption is that your denatured alcohol is referring to ethanol mixed with other toxic alcohols (such as methanol).

This can't be 100% pure ethanol because it MUST contain denaturants to discourage drinking, otherwise it would not be denatured and would legally require an additional excise tax. In that case, you might find it as Everclear (190 proof or 95% or ethanol by volume at highest concentration). It can be close to 100% alcohol, of course, because methanol is an alcohol.

I HAVE seen (at least in the US) food grade USP purity ethanol for sale (with additional cost due to excise tax inclusion) that's at least 99.5% pure. I have also seen 99% purity isopropyl alcohol (IPA). My point in the reply to the original content is that it's not accurate. Distillation of binary mixtures results in azeotropes that prevent purity of more than 91% IPA (by volume) and ~95% ethanol. But there's ways around it such as adding a third solvent for a ternary mixture, salting out (shown in some chemistry demonstrations), changing the pressure of distillation, or using molecular sieves to remove water content. Alternatively, you could use freeze distillation, or even zone melting if you chose to freeze the mixture instead of boiling it. In fact, once you PASS the azeotrope, you can actually distill at standard pressure albeit what you want and don't want in the column would switch places.

Getting the last few percent of water out of it definitely costs more, but it's not something so hard that you can't find commercially available alcohol solvents at purities above the azeotropic point. I know this is the case since I've acquired them for home use and have used them in multiple lab settings before. The annoying part for those who REALLY don't want much water in the solvents is that at that point your solvents are hygroscopic and unless sealed properly or kept in a desiccated environment they're gonna tend to absorb water back toward the azeotropic point.

Ethanol is similar to IPA in solvent properties but they won't be the same. I don't have enough wet lab experience to give a good answer in this regard though. If you're able to take things apart, I've cleaned PCBs the Louis Rossmann way, which is with Branson EC solution and sonication. Drying is really the most important step there ;)