Sometimes when soldering, it sorta "pops" and leaves tiny droplets of clear, hard substance on my PCB. It seems to be able to melt away with a brush of my iron, and isn't too bad. I'm ironing at about 260 degrees C (510 F) with "44" rosin core .80mm.
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3 Answers
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As the other answerers have said, the clear, hard substance is the rosin from the solder.
There are a number of things which can cause what you describe.
- Voids in the rosin core:
As the solder heats up, the gas in the void becomes pressurized. Once the solder is sufficiently molten that the gas in the void can escape, it does so. Violently. - Some rosin is hygroscopic:
The composition of some rosin cores can cause it to absorb moisture from the air. Once the rosin is heated to a certain point, it releases the absorbed moisture in the form of steam. Sometimes rather violently. - Hot-Spots on your soldering iron:
If you are using a low-quality soldering iron, the tip may not be very thermally conductive. Therefore, if you apply a lot of solder to the tip, it can cool fairly dramatically. If the applied solder then runs along the surface of the iron (due to surface tension) to a section which is much hotter, it can cause the rosin to boil off suddenly.
Overall, the little rosin balls are generally fairly harmless. If you want your boards to look really nice, you can wash your assembled PCB once you are done putting it together.
Look up your flux's datasheet. It will tell you what you should clean it with. There are water soluble fluxes, as well as more aggressive fluxes which require solvents.
From your post, ("44"), I assume you are using Kester #44 solder. You can find it's datasheet here.
It states:
Cleaning:
Kester 44 possesses excellent fluxing ability, the flux residue is non-corrosive and non-conductive under normal conditions of use. When exposed to an elevated temperature and humidity environment (38°C, 94% RH) for 72 hours, there is no evidence of corrosion caused by the flux residue. Throughout its many years of wide usage, 44 Rosin Flux has produced many billions of soldered connections. In all these billions of solder joints, involving the most delicate and critical of electrical and electronic components, there has never been an authentic instance of corrosion by the flux residue under normal conditions of use. This mild property of the residue permits leaving the flux on the assembly for many applications.
It's worth noting that more aggressive fluxes can be harmful to leave on your PCB. Such fluxes can actually eat away at the plating on the device pins over time.
As a last note, one area where cleaning the flux off the PCB is critical is very high impedance applications.
While the flux residue is a good insulator, it is significantly worse then the PCB alone. Therefore, you can have considerable leakage through the flux (~1MΩ between SMD pins). While it is not much current, if you are trying to measure nanoamperes, it can be a significant issue.
answered Oct 31, 2011 at 10:02
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2\$\begingroup\$ Something that people can forget is when using something that is going to operate at radio frequencies with matched impedance circuits you need to ensure your flux does not cause issues with impedance matching, it actually formed the issue of a product I worked on long ago. The newer technician had waited a while before implementing her own methods and when she did we suddenly would have random boards with impedance problems. Acetone was required for the flux being used to be removed, even the thin layer caused major issues. \$\endgroup\$– KortukCommented Oct 31, 2011 at 13:48
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\$\begingroup\$ Awesome answers! Thanks. I didn't know that stuff was even called flux. \$\endgroup\$ Commented Nov 2, 2011 at 21:25
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Moisture absorbed by the PCB can cause that, if the boards aren't assembled soon after manufacture. It can be avoided by baking the boards for a couple of hours.
answered Oct 31, 2011 at 0:32
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That's the rosin core, it has a tendency to sprinkle around especially with the larger diameter solder wire. It is no problem just to leave it there.
