Applying solder paste

Soldering iron tips? Yeah, get a fine tip one.

I've done lots of SMT parts, from 0201 to QFN. I just use a fine tip iron, fine solder, flux and a stereoscope. I don't mess with paste. Waste of time.

I've just twigged: I should've bought some needles to screw into the end of the syringe. Funny how posting dumb questions to SED brings the answer sometimes.

Is that a great straight line or what! Yup, you can get the proper tips from (among other places)

The plastic cap is only that.

There's a section at Sparkfun's tutorials that covers using paste with a stencil.

You can probably also successfully apply it with the syringe and use the electric skillet method. Some practice may be needed to get the amount of paste and the time and temperature in harmony.

I've got a very fine tip, flux and microscope; but the finest solder I could get was 0.56mm. I can't apply this to 0.5mm-spaced pins directly. Is that how you do it? What gauge do you use?

Always ;-)

...Jim Thompson

Hm. I have .25mm (10 mils) solder. I think the technique changes in each case. Sometimes I apply solder to the pads first, then I stick the chip on. Other times, I apply solder to the package, esp the QFN/MLF packages where the pins are flush to the part. Very important too is a *clean* tip. Some fluxes like the no-clean stuff leave a black residue impeding heat flow. You should also get a little jar of tip tinner/cleaner. It glues to the soldering station.

Another fine tip:

I have bought 0.23 mm tin locally in a shop in Berlin (Segor), article LZ 0.23-100 Sn60Pb38Cu2 DIN EN 29453 FSW-26

It flows really good, but contains lead. So what? A 100 gr. reel is Euro 23.90. Should be enough for the foreseeable future.

They also deliver by mail.

Enter "Lötzinn" into the search field under "Artikelschnellsuche". Use copy & paste if you cannot find the ö on your keyboard :-) It is the 3rd item listed.

regards, Gerhard

Well, a better tip is just what you want!

I believe that applicator tips (i.e. needles) for these syringes are sold separately. You screw off the sealing cap (which is there to preserve the paste prior to use) and then screw in a tip which has the diameter appropriate for the application for the application (sorry :-).

I believe that for the finest-pitch parts, the paste is usually applied via a silk-screening process (for reflow).

For hand assembly of the finer parts, you may find it easier to not worry about the solder/paste slop during the initial application. Get the part soldered in, and then re-flux the row of pins and use some fine-gauge solder-wick to slurp off the excess from between the pins.

Didn't it come with any instructions? Before cutting anything, I'd unscrew the little red cap, and see what's under it - maybe that's the needle. If so, then just squirt the paste where you need it; you probably won't need very much.

Good Luck! Rich

The only two times time I use paste are :

Other times I use suitably fine solder wire - put solder one one pad of all footprints on PCB, place part while melting solder, then solder other pad.

You can never have too much (fresh) flux.

We were comically trolled. Or commically .

Thanks. I've ordered a reel.

For prototyping you WANT the lead - it reduces melting point and flows better. You also want solder with 2% silver if possible, as this further reduces melting point

It does not matter how you apply it, or what solder you use. The key is to have lots of flux. I can use a gas fired soldering iron on fine pitch semi's with success. The flux will help the solder to flow onto the pads and prevent it from shorting across pads. Maybe someone needs to do a vid of this. I might have a look on youtube and if nothing is there I will try fire up the old ersascope at work and take a vid.