Plumbers Solder Paste

So I saw some solder paste at the hardware store in the plumbing section. Something like this:

[www.solder-it.com]

I bought it on a whim doubting its usefulness. It was cheap though.

I finally got around to trying it yesterday with my first attempt at SMT soldering. It came out of a somewhat fine nozzle ~2mm I then slid it around to the pads. It had the consistency of wet sand so wasn't the easiest thing to work with but was doable. I got everything in position and heated it up. I used a baking tray that wasn't completely flat so didn't have much success... melting a corner of the board and not melting the solder on other parts. I then went and used a soldering iron and the paste did seem to melt properly and looked normal.

I imagine the proper stuff is much finer and easier to work with but this paste was easy to find and cheap. Does the proper stuff get gritty when it dries out or is this just cause this paste is for copper pipe and is thus not as fine?

Oh and I did an initial test of the board and power works and the lights turn on when I turn the stepper. I haven't gotten it fully hooked up yet.

Mike

Edited 2 time(s). Last edit at 01/14/2010 02:54AM by mikefazz.

All of the plumber's solder pastes that I have used were lead free, which means a higher temperature (than lead based solder) is needed. When doing plumbing repair it melts like regular solder - but I'm usually using an acetylene torch which is considerably hotter than pcb toaster oven or soldering iron.

My guess on the grittiness (is that a word) is that you didn't get it hot
enough to melt all of the solder.

Plumber's paste is often packed in an oil based grease as well, which can
be a pain to remove from the boards afterwards.

Thanks for the info it did seem like it melted at too high a temperature. A soldering iron did the job though. Not sure about the oil... if paste does dry out if not used right away I definitely left it for a month or so before using.

So if you have no other way to get paste this can be an option though not ideal.

... some time ago i mixed a gold-soldering-paste from eutectic gold-tin-spheres (30 microns diameter and 80%gold+20%tin, first time melting at 380°C), gold-dust around 1 micron in particles-size and dexpanthenol + a droplet H2O dest. as 'solvent'.

Maybe you can use dexpanthenol + water (water-basis) or lanolinum + oil (oil-basis) for remixing/reactivating old solder-pastes ...

Viktor

Dear Mr. Viktor,
I am interested to develop eutectic AuSn (80-20 ) solder paste.
Pl. guide me for preparing the same and vehical for the same.
Thanks,


Hasmukh Prajapati.

Hello Hasmukh Prajapati,

... i bought the AuSn8020 from a goldsmith-shop (didn't remember name and adress ), it was intented to fuse gold together at lowtemp - first melting-temp was below 400°C, second time you have to heat above 700°C to melt it again.

The spheres were relative uniform with diameters around 30 microns.

For better handling i mixed them with gold-dust - the dust particles were around 1 micron in diameter, i've got the dust from Heraeus.

Paste-basis was dexpanthenol (what's an extreme viscous alcohol) and a droplet of H2O-dest. - the proportions could be something around 70% AuSn, 18% gold-dust, 10% dexpanthenol, 2% H2O ...

---

Viktor
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You can buy solder paste very cheap from these guys:
[www.smtsolderpaste.com]

Plumbers solder paste is no good because it uses acid flux. This is very unfriendly to SMT parts and boards.

Seconded the don't use it because it's acid flux. The acid eats anything electronics for lunch. Some people at work were using it on boards and after a few months their solder joints turned green with corrosion!