Edsyn FL 112 flux performs badly

[irdc]

Hi,

I recently bought some Edsyn FL 112 flux as part of stocking up for an SMD project (I cannot find much information about this flux online, so I cannot link to that). Sadly, this flux appears to perform really badly with my SAC305-solder (Felder iso-core ultra-clear): lots of solder bridges that won't resolve and it just doesn't flow nicely.

When in sheer desperation I grabbed a Kester #951 flux pen that was 15 years (!) out of date all my problems suddenly melted away: nice wetting, shiny joints (well, as much as SAC305 lets you) and easy removal of solder bridges (I mean, they're TSSOPs, of course there's going to be solder bridging).

I've already approached the seller about this issue, but I'm wondering: anyone else having this problem? Is there something I'm doing wrong; too much flux maybe? Is my soldering iron too hot (I'm using 370 °C / 698 °F)? I'm admittedly a bit of a beginner, so I'm not totally discounting user error here.

[m98]

370 °C is a bit too hot. The flux will decompose and evaporate too quickly at this temperature. You might want to try a flux paste (Edsyn FL22, for example), works much better for rework as it won't fully evaporate while you work on the joint.
Which soldering iron and tip are you currently using?
Make sure the tip "fits" your soldering joint to facilitate good heat transfer. So no round or "micro-soldering"-tips, unless you absolutely need one. If you find yourself needing to crack up the temperature too high, chances are, you're either not making good contact, or the heat capacity of the tip isn't enough to keep up the temperature.

[irdc]

370 °C is a bit too hot. The flux will decompose and evaporate too quickly at this temperature.

I was figuring as much. Either that or too cold (I mean, it is a flux intended for lead-free solder). I'll try some lower temperatures; maybe 320 °C or 300 °C.

I'm still left wondering why the Kester worked as well as it did then…if anything, the Kester evaporated a whole lot more than the Edsyn. Maybe it's the ageing? 😉

Which soldering iron and tip are you currently using?

I'm using what is marked as a SkyTronic 703.050 but is also sold as the Velleman VTSSC30N, together with a BITC10N3 3mm slanted tip. Temperature transfer appears to be fine (as I said: soldering goes really well with the Kester).

You might want to try a flux paste (Edsyn FL22, for example), works much better for rework as it won't fully evaporate while you work on the joint.

I'll probably eventually do that; I had already been considering switching to the CIF F42202 flux paste. Well, it's all learning by doing I guess 😊

[wraper]

370 °C is completely fine for Lead-free soldering if you do the job fast.