Paste vs solder --- silver?

Sn63Pb solder paste makes shiny joints. Good Pb-free joints look a lot like bad SnPb joints.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

one paste I'm trying is sn63/pb37 380 degree melt the other which I like better is low temp sn42/b57/ag1 ? and it looks very gray but goes on easier and is 271 degrees

joint is strong though and VOM says it's ok -- I'm so old school it looks like a cold joint

Phil Hobbs wrote in news: snipped-for-privacy@electrooptical.net:

Exactly.

63/37 is a formulation that took a bit of time to get to, but is great! Lead free looks grainy and like the microcrystalline structure is fractured. On every joint.

I want 63/37 back. Metallic form lead poses no problem.

an oven. Using 2 types of paste. My question is --

red joint? (Less silverish?),

e of a hand soldered joint. The connection is good -- vom says so etc.

r is low temp 42/57. But again, does paste have a lower "sheen" (generally ?)

thanks Phil -- gives me peace of mind. so the 2nd one I mentioned is lead f ree I'm gueesing (no pb) and I rather like it -- seems easier to apply for somereason but may be newer than the other. aging I guess makes the paste l ess fluid? yes -- the joint looks like crap but as long as it works and wi ll stay that way for years, guess I don't care what it looks like.

must be all that point to point wiring I did in 1968.

mkr5000 wrote in news: snipped-for-privacy@googlegroups.com:

Lead free slumps as it solidifies. 63/37 makes nice joints because of its surface tension and the alloy plays nice with fluxes. It is a good tight alloy too. The high tin alloys are like doped silicon. Only one atom of the dopant every now and then. And with solders it upsets the way the Tin wants to solidify.

For lead free, I would put small dabs of SMT paste on the joint and then reflow it with the solder iron tip.

The rework world still uses 63/37 for repair. For one thing, the higher solder temp of lead free makes rework on a cold PCB more difficult. So the world gave a pass on the repair channel... at least over here in the US.

I'm not using it for rework -- soldering some new bards.

On Saturday, February 15, 2020 at 5:44:48 PM UTC-5,

The term you're dancing around is "eutectic solder", which is an alloy that melts and freezes at the same temperature. 63/37 alloy solder is eutectic at 183 degrees C.

Personally, I find it is much easier to hand-solder with 63/37. With the correct temperature-controlled soldering iron setup (and tip), you can make perfect joints every time. I am not a fan of lead-free solders.

mpm wrote in news: snipped-for-privacy@googlegroups.com:

No. I was not "dancing around a term".

The fact is that performing a repair on a cold board takes skill, especially for through hole with high layer counts. That is why some folks preheat the entire assembly so that the heat soak of a repair event can be done more easily and with better assurance of no damage being imparted on the board. The higher melt point of lead free solders makes that job even more difficult.

So it has nothing to do with whether either is eutectic or not. It has to do with the whole process (hole process) being hotter and more damage prone.

Much colder than lead free. (cold is a relative term). I like it the most as well. Pure lead on stained glass is funn too.

Yes, and with lead free too. It is just that most rework stations do not use lead free because of the heat difference.

Me needer.

The opposite is true in UK/Europe... mostly lead free, except military stuff etc.

whenpaste starts to go bad does it harden up? do you know whn it's at the end of it's life that it doesn't stick to the board well? (having that problem with 1 of the pastes I'm trying)(pretty old)

is there some sort of trick to "reconstitute" it? --thanks

n an oven. Using 2 types of paste. My question is --

dered joint? (Less silverish?),

ine of a hand soldered joint. The connection is good -- vom says so etc.

her is low temp 42/57. But again, does paste have a lower "sheen" (general ly?)

end of it's life that it doesn't stick to the board well? (having that pro blem with 1 of the pastes I'm trying)(pretty old)

What kind of flux? Years ago I was told my a Manufacturing Engineer who ove rsaw our PCB department that a tiny amount of additional flux could be stir red into the paste, but if it is rosin based you could add a few drops of h igh purity Isopropyl Alcohol to thin the flux that is drying out to see if it spreads better on your stencil. It has to be well mixed, and one design engineer said that he had seen that mentioned in some trade journal for the PCB industry. Only for hand stenciling, not by a machine process.

How old is the finish on the board you're trying to use. That can make a difference too. (Obviously.) Some finishes have a pretty short shelf life one the pack of PCB's is opened.

Michael Terrell wrote in news: snipped-for-privacy@googlegroups.com:

Old paste is good for rework or hand application to a board for hand pick and place, but I would not thin a paste and then try to use it with a stencil. Not unless you wipe it with the squeegie very lightly. You do not want to hydraulically force solder under the stencil from it being too thin and you squeegie actually forcing tiny solder balls under the stencil between the nodes.