Of course, both 44 paste and 1544 would fail shapirus’s requirement to be non-conductive before heating. I don’t think he understands that flux specs refer to the conductivity of the post-soldering residues.
Not that I don't understand, but I don't care. I test the fluxes I get my hands on for my specific requirements, which is hand soldering of both THT and SMD parts. And I believe this specific use case is of interest to many electronics hobbyists that can read this, too. Another way of looking at it is worst case scenario testing.
That’s fair.
My main concern was you trying to get a refund for flux because of it not meeting the claimed conductivity specs, even though you hadn’t reflowed it. That’s not fair unless they specifically said it was nonconductive in a non-reflowed state.
Of course, both 44 paste and 1544 would fail shapirus’s requirement to be non-conductive before heating. I don’t think he understands that flux specs refer to the conductivity of the post-soldering residues.
Not that I don't understand, but I don't care. I test the fluxes I get my hands on for my specific requirements, which is hand soldering of both THT and SMD parts. And I believe this specific use case is of interest to many electronics hobbyists that can read this, too. Another way of looking at it is worst case scenario testing.
Besides, the two fluxes from my last post are specifically advertised for BGA rework and general repair, which does not guarantee full heating, either (I believe even when using a hot air gun). And hey, they are 500-1000 times (!) more conductive than the other fluxes I tested.
Hot air alone is not adequate to achieve full heating. It heats locally, but also blows barely-molten flux all over the place. However, BGA rework is usually done with both preheating from below and hot air (or infrared) from above. And above all, if the balls reach reflow temperature, then the flux between them will also have reached that temperature. It’s only whatever flux has flowed far away that is of concern.
It would also be interesting to test conductivity after full heating, but that would require having a reflow oven, which I don't have, and the motivation to do it, which I also don't have, since I don't do that kind of soldering.
You should reconsider. Reflow in an oven is exceedingly efficient. (And practically mandatory for many modern packages.) A simple $50 toaster oven is enough for basic use.
...but I might try something, just for a quick test: for example, set the hot air gun to what, say, 280 °C, heat the PCB with the flux on top from below (to avoid direct blowing on the flux so that more of it stays in place) for, say, 30 seconds, then let it cool and measure what remains. Just to see if the "it must be heated to stop conducting" claims are substantiated, and to what extent, if they are.
You make it sound as though that’s some crackpot theory… No, it’s how no-clean fluxes are designed to work.
However, I would be leery of your proposed methodology, because it’s quite possible that it wouldn’t heat it evenly enough to draw any conclusions. If you do this, you’d want to do it with a custom test PCB that has solder pads that you can apply solder paste to, so that you can actuate whether it reached reflow temperatures.
Remember: there are TWO temperature thresholds to reach. The first (lower) one activates the flux, the second (higher) one neutralizes it again. If you heat to a temperature that reaches the activation temperature, but not the neutralization temperature, it may be left in a more conductive, more corrosive condition than the unheated state! So the only fair test of this “claim” is to actually get it hot enough to melt solder, since that’s what it was designed for.