First Impressions of the FNIRSI SAG-55 (Pro)

RE: First Impressions of the FNIRSI SAG-55 (Pro)

Jan Cumps — Fri, 08 Aug 2025 17:21:19 GMT

> I did manage to lift one pad while I was removing excess solder with my iron and solder wick

More heat! This usually happens when your iron has a too low temperature, or not enough capacity to keep pad and wick hot enough.

Often, "just not enough" heat does more damage than too much. Because you melt part of the solder, the wick gets in, it solidifies, and you rip off the pad.

RE: First Impressions of the FNIRSI SAG-55 (Pro)

shabaz — Fri, 08 Aug 2025 15:33:42 GMT

Hi Gene,

I always feel uncomfortable soldering SMD LEDs, to me they are always more difficult than other SMD components!

The solder you're using is a very low temperature Bismuth mix, which doesn't have the same feel as normal solder when reflowing. It's more useful for removing parts, because it can be used to mix with the existing solder, to lower the melting point. Also, that Bismuth solder seems to take a lot longer to solidify, than (say) normal eutectic solder.

I use no-clean Sn62Pb36Ag2 solder paste (called Qualitek 818, but there will be many other brands with similar mix), which is still quite a low temperature (about 182 degrees C I believe) but solidifies quickly. As you say, pre-heater will help, I never reflow without that (and worth getting a little thermocouple meter, to see what temperature your board is at, so you can more easily replicate in future). For instance, I will heat the board to about 80-90 degrees C, and I can keep the board at that temperature indefinitely while I take care to place the part that needs reflowing, so I'm in no hurry. Sometimes I'll squirt on a tiny bit of flux paste from a metal-nozzle syringe (it will instantly dissolve to a liquid when the board is warm). I use the hot air to gently ramp up from a distance (i.e. just slowly bring in the hot air rather than adjust the temperature of the hot air tool) and then when it's visibly reflowed, I'll keep it there (just moving the nozzle in a circular motion to make sure the heat is on all the pads) until I'm certain all has reflowed then slowly move it away. I don't have a proper scientific process, but I've just learned what works for me, and it's reasonably repeatable.

RE: First Impressions of the FNIRSI SAG-55 (Pro)

BigG — Fri, 08 Aug 2025 12:16:19 GMT

Great post.

I discovered this small hot plate early last year and love using it for this sort of work. I first warm up the board using this hot plate and then finish off with a hot air gun. Works a treat.

https://www.adafruit.com/product/5903

RE: First Impressions of the FNIRSI SAG-55 (Pro)

rsjawale24 — Fri, 08 Aug 2025 11:32:44 GMT

Great post.
FNIRSI has good soldering stations as well. I'm not sure if anyone has tried them yet. I'm planning to buy the one with C245 or C115 tips.

RE: First Impressions of the FNIRSI SAG-55 (Pro)

dougw — Thu, 07 Aug 2025 21:07:06 GMT

"No Clean" solder flux should be called "Not Clean" [emoticon:fbd079a1c4f748c5a234faee215de9cc]

No clean flux always leaves a residue. [emoticon:83bbb1525ffc44c294fc5d238d2a33f7] We have had big issues with no clean flux residue.

RE: First Impressions of the FNIRSI SAG-55 (Pro)

DAB — Thu, 07 Aug 2025 19:20:42 GMT

Very good post.