Electronic – using plumber’s copper solder as a “solder paste” for SMD components


Can I ? 😀

It is what I currently have plenty of lying around and, well… it says S-Sn97-Cu3 at composition

If not, could I use regular solder wire, coat the SMT pads with it, apply flux afterwards, place the SMD part and hold it into place, then gradually apply hot air to it ?

edit The package I am looking to solder in this way is a no leads type. Sorry, forgot to mention.

edit2 Found this paste over here. It has the same binder and the same flux/binder ratio as the one that I have. So it would appear that all that remains is the flux. I do not know what it is, but on my flask it says it contains zinc chloride, it thoroughly warns against inhaling, ingesting, eye and skin contact. Also there are some writings:
S 1-2/S 20/S 26/S 36-39

Charge: FD

AT 2247

I wonder if the regular electronic parts solder paste has any warnings against skin/eye contact, inhaling and ingesting.

Best Answer

The "no-clean" rosin flux used in most electronics solder has two interesting properties:

  • The junk it leaves on the board is a pretty good insulator (not perfect, but unless you do very high impedance sensitive analog stuff, it's fine to leave it on).

  • It doesn't corrode the copper, the pins, etc...

However, other types of flux, like some water-soluble ones that are easy to clean are actually conductive (ions... in water...) and corrosive (will eat your copper!)

So you must clean them (preferably with an ultrasonic cleaner), which is kind of annoying. Good luck getting it out from under a QFN.

Now, you got... Zinc Chloride!

It is very hygroscopic, which means it will suck up any moisture in the air, and then it will be conductive (water+ions) and your board will get electrolyzed and destroyed pretty quick.

It's also very good at corroding metals...

Wikipedia says:

Because of its corrosive nature, this flux is not suitable for situations where any residue cannot be cleaned away, such as electronic work.

So... nope. Get a solder specified for electronics, preferably with lead, it melts at a lower temp.