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Is anyone using solder paste?  There seems to be a lot of uses from surface mount soldering, soldering wires to rails to fixing jewelry and I'm sure many others.  There are low temp versions which seem useful.  If you are using do you use hot air or your soldering iron?  What solder paste would you recommend?  Any other suggestions or tips?

Chris

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Got some of this 'No Clean Tacky Soldering Flux 5 Grams' from Amazon a while back. Wanted to try it to help hold surface mount components in place while soldering, had never used it before. Hands aren't as steady as they were when I was younger and I kept knocking things out of alignment before I got them tacked in place. It's worked pretty well for me so far.

I seldom use any flux on thru-hole components, but I do sometimes use a rosin core paste flux (very old, small can from Radio Shack) when removing components, de-soldering, re-soldering, cleaning tips, etc.

If you can find 63-37 ratio solder paste I would use that.  If you can't locate any then you might have to use SAC 305 paste which should plentiful.  The no clean fluxes work best if you have very clean surfaces to solder.  Otherwise you will need paste with a more active Flux to get the more oxidized surfaces to solder.   For smaller components you may need to glue them down prior to using the hot air or an iron.  They will tend to wick up to the heat source or tombstone on you.  You can also reflow solder on your pads and hold the comp in place with tweezers while you reflow each pad with a heat source.  A microscope or a mag lens on headgear is very helpful.   Harbor freight has some fir 5.00 I think.

@Lehigh74 posted:

chipquik

Thanks for the ChipQuick 63/37 solder paste reference.  I ordered 250g amount.  Roughly 1/2 pound .  It has eliminated solder blobs, reduced the total amount of solder used per connection and freed up my hands for quick and effective soldering.   Average time to get a great solder connection with minimal solder use 2-3 seconds.    I think this amount will last for a few years of repairs and tinkering.

I'm getting ready to try Chip Quik SMD291AX this week.  I found the low temperature solder paste to be to brittle.  I use a hot air gun (since my reflow oven is not yet operational) that has been calibrated with a thermocouple.  I find the reported temperature of the hot air guns to be off (albeit linearly off).  I make my own stencils (which is what I'm working on now).  Generally, the shelf life of solder paste is limited and I store mine in the fridge.

Anthony

@Craftech posted:

Soldering paste for things like wire to metal (track, etc).  Rosin core for sensitive electronics with no paste.

If you look at the instructions from (for example) decoder manufacturers (like TCS) they specifically state not to use a flux on motherboards and decoders so I assume that carries over to any electronics or PCB.

I think you're thinking of a different kind of soldering "paste".  The solder paste used for SMT as mentioned in the OP's post is certainly used on PCB's, it's how components are positioned and soldered!

You seem to be talking about soldering flux in a can, if it's acid based, it's certainly not for electronics!  It would be correct to never use that on your PCB's.

I think you're thinking of a different kind of soldering "paste".  The solder paste used for SMT as mentioned in the OP's post is certainly used on PCB's, it's how components are positioned and soldered!

You seem to be talking about soldering flux in a can, if it's acid based, it's certainly not for electronics!  It would be correct to never use that on your PCB's.

I think you are right.  I looked again at what TCS says about using "paste".  It sounds like they are referring to acid based flux which I assumed no one would ever think of soldering electronics with in the first place.

Important Soldering Tip

Please do not use any flux either liquid or paste on the mother board. Over time, the acidic properties of liquid or paste flux will begin eating away at the fiberglass PCB and will damage it. Use only Rosin-core solder or no-clean flux approved for electronics use.

TCS recommends the use of Kester "44" Sn63 Pb37, .015" diameter Rosin-core solder. Kester part number 24-6337-0007.

You can order this solder from the following retailers:
Digikey - PN:KE1110-ND
Techni-Tool - PN:488SO6775

Then I looked at the soldering flux I have and it is in fact CAIG Brand Rosin Soldering Flux (No-Clean) so I guess it can be used on PCBs after all.

John

In case any posters are wondering, 63/37 solder refers to the combination of alloys used in the solder.  This is 63% tin, 37% lead, and almost always a small amount of silver and a few other very minor amounts of other metals and flux.  This is call a eutectic solder.  This combination of alloys is the LOWEST melting point of tin/lead alloys.  Any combination of metals has it's own eutectic point.  This solder has no semi solid state.  It is either liquid or solid, with no plastic state, a frequent cause of cold solder joints. It melts AND freezes at 183 degrees C.  This temperature is ACTUALLY lower than either tin or lead's normal melting points!  MAGIC!   Not really, but it is the eutectic combination of alloys at work.

I would only use old tin can based rosin flux when soldering connections to track.  If trying to solder or desolder surface mount components, look for a special flux designed for that purpose.  Mostly, for repair, a product that is a combination of rosin core flux and tiny alloy solder balls is used.

Let's reinforce NEVER use ACID based flux on ANY electronics, even 100 year old stuff!

@Mike CT posted:

Acid base flux, used in plumbing, works well with larger wire attachments to galvanized rail, Gargraves or Ross.  Usually requires more heat, a propane, or map gas torch.  Also works for a  miserable attachment, copper to steel.  IMO.

FWIW, I've never had to resort to acid based flux for any of my model train work, I use my 140W gun and plain rosin core solder.  If I feel the need for more flux, I just use my tub of Deoxit Rosin Soldering Paste.

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