This post is a follow-up to a blog I published earlier this year on how to avoid flux charring during the soldering process.
In that post, I noted that the two main catalysts for flux charring are dwell time and soldering iron tip temperature settings (>415˚C). As we continue to expand our application knowledge of robotic soldering, the need for increased focus on these two aspects of the soldering process is becoming more and more apparent. I’ll focus on tip temperature here.
There is a misconception that increasing the soldering iron’s tip temperature will increase soldering speed, thus decreasing the cycle times of robotic soldering operations. However, that is not always the case, because not every formula is designed to be exposed to high tip temperatures and, without the proper settings adjustments, many things can go awry. A smooth solder joint appearance requires the correct amount of temperature and time, and fine-tuning the process parameters may be required to achieve the best possible outcome. When the tip temperature is too high, the flux is exhausted before reaching the intended soldering area, and the charred wire end withholds the needed cleaning power that the flux provides. The resulting joint will likely be rejected upon inspection.
It is vital that the tip temperature be only high enough to melt the solder and activate the flux during robotic soldering applications. Again, each flux formula is different, and the settings that worked well for one formula will not always provide similar soldering results with a different formula. To find the optimal settings, I suggest starting on the lower end of the temperature scale when introducing a new cored wire formula to the process - somewhere around 290 - 300˚C for most common alloys. If the solder does not melt, increase the temperature incrementally (+/- 10˚C) until it does. Add 20˚C or so to that and you will likely have an excellent setting for soldering because, at this temperature, the solder should now melt quickly, but the flux core will not be exhausted too fast.
Another result of higher tip temperatures is reduced tip longevity, which will result in more frequent purchases of iron tips and increased expenses. Tip longevity is reduced because the increasing temperatures accelerate the oxidation of the tip as well as how the solder (and the flux if the solder is flux-cored) interacts with the tip’s iron plating. There is also added thermal stress placed onto the metal as a result of increased heat to the tip. To avoid the occurrence of these soldering iron issues, it is best to use a lower tip temperature and only incrementally add heat as needed.
To summarize:
- Hotter & faster settings do not always equal better soldering. Instead, it can result in charring and reduced iron tip longevity.
- When introducing a new soldering wire, start at a lower tip temperature and work your way up to find the proper temperature for the material being used.
To borrow an adage from the US Navy SEALs: SLOW IS SMOOTH. SMOOTH IS FAST.