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Differences between different types of flux in solder?

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exe:

--- Quote from: tooki on July 17, 2018, 08:48:43 am ---
--- Quote from: exe on July 17, 2018, 07:46:36 am ---No-clean doesn't mean cleaning is not required. It can only be left on the pcb if fully activated, i.e., you follow the process described in datasheet. Many fluxes remain active if not heated. Such fluxes are for reflow and not suitable for hand soldering. Flux can also be highly conductive if not fully activated.

--- End quote ---
Can you elaborate on the differences between no-clean and RMA? Because in the ordinary sales materials, both no-clean and RMA are described as being safe to leave in most situations. I’ve struggled to find a good analysis and description of their differences in actual use.

--- End quote ---

They need to describe these "situations". Too bad most fluxes I have do not define this. So, I do my own evaluation before using any flux.

So, concerning your question about the difference between no-clean and RMA. I don't know and I don't care because these terms do not reflect the real performance.

If I don't forget, I'll post in the evening a photo of how different fluxes behave with and without activation over time.

exe:
I attached two pictures: one is after one month, and one after like 9 months (I'm too lazy to label fluxes on the first picture, sorry). All of these fluxes except two or three are "no clean". Each flux I tested in two ways: 1) I just applied it 2) I heated it with a heatgun for a while. These are laying on my bench for more than 7 months.

I didn't try to reproduce reflow process, so by no means my experiment represents quality of fluxes in production environment. But it is close-enough to how I normally use them. So, some fluxes are corrosive only when cold, some corrosive only after heating. Besides that, I did conductivity tests, but that's another story.

My personal conclusion: do not waste time trying to find "the best" flux as these are just too active and require cleaning for my use cases. I stick with rosin-based fluxes that are truly no-clean. Their performance is not great, but most of my parts are new and shiny, so they solder well even without any added flux (my solder wire has flux).

When I was a beginner, I wanted to have best tools, best flux, etc. But it was a waste of time and money. Now I'm trying to get things done. And 99% of time my cheap tools more than enough. Expensive fluxes like fl-22 or amtech won't make me more productive. Although, there are situation when you might want a special flux. E.g., reworking BGA stuff, it needs non-boiling no-clean flux. Or, I have a high-temperature flux I used to solder enamel wires.

Teledog:
I concur with Exe.
Plain rosin is best.
Made my own liquid rosin for years..with finely ground instrument bow rosin  & 99% IPA.
Coat boards with it  & no corrosion ..even years later.
It IS hygroscopic, so if you do use it on a board, bag it for archive/storage or wash it with IPA/flux cleaner after soldering.
 :-+

GigaJoe:
I don't know ...   I left a flux couple time, then a circuit started to oscillate in Mhz range,  20-50 mV  ...   now I use acetone to clean it, rather pulling hairs ..

exe:

--- Quote from: GigaJoe on July 18, 2018, 03:48:45 am ---I don't know ...   I left a flux couple time, then a circuit started to oscillate in Mhz range,  20-50 mV  ...   now I use acetone to clean it, rather pulling hairs ..

--- End quote ---

Yep, a typical flux story :). Cleaning the flux is always a safe bet (except when there are components sensitive to cleaning agent). Also, precise analog circuits may be sensitive to leakage currents (esp. high-impedance inputs).

There is another catch: rosin solution in spirit is conductive until it dries. So, the circuit may not work properly immediately after soldering (never had problems with this myself, but noticed this behavior while experimenting with fluxes).

I have to do a series of (unprofessional) videos on fluxes in a month or so.

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