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I have read some discussions about the lead-free solders on the forum, but could not see what solder type is easier to use on hand soldering (for lead-free ones)?

As an example, I see only two RoHS compliant solder alloy options (e.g. on Mouser on this link)

  • SAC305
  • Sn96.5/Ag3/Cu0.5

as available type:

  • rosin activated
  • water soluble
  • no clean wire
  • spool solder
  • Glow core no-clean

Which properties would you recommend for the one that would melt on a lower temperature and convenient to use?

I have this lead-free solder that is not pleasant to use because of melting temperature.

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None of the options are particularly enjoyable. Most people I know who try it go back to lead. Prototypes rarely need to be RoHS compliant, so I use lead until manufacturing starts – Scott Seidman Jul 4 '14 at 14:47
You might find this answer useful:… IIRC, I raised the tip temperature by 100°F (56°C). – Spehro Pefhany Jul 4 '14 at 19:58
All the lead free solders I have used gave me splitting headaches due to the flux fumes generated at the higher temperatures. Switched back to leaded. The fumes of lead free are likely much worse for your health than the lead of leaded solder for the average hobbiest. – John Meacham Jul 4 '14 at 22:10
I totally agree with John and Scott - I use leaded solder. I did some research (online, if that counts) and the flux used in unleaded solder is, as far as I can see, appears much more unpleasant than the leaded flux. Both are bad for you so I'd always use a fan regardless. I also found unleaded hard enough to work and rework that I don't see why I should toture myself... – carveone Jul 9 '14 at 11:12

2 Answers 2

up vote 4 down vote accepted

Lead is a magic element that makes solder melt at a lower temperature and protects the tip of your iron against oxidization. Too bad it is a potent neurotoxin.

Unfortunately there is no such thing as "low-temperature" lead-free solder. Lead-free soldering will always be more difficult.

Without lead, and at higher temperatures, tip oxidization is your #1 problem. That means shutting off your iron immediately when you aren't using it. Don't let it bake. Some fancy lead-free irons have an auto-setback that reduces the tip temperature when it is placed in the cradle.

And stay away from "CLEAN" solder! Water-soluble flux is very aggressive but corrosive! It will eat vias and traces if it is not immediately cleaned off (should be called "MUST CLEAN"). It is only used by industrial processes that include an ultrasonic bath after soldering.

"NO CLEAN" solder is what you want and means the flux is not corrosive and does not need to be cleaned. Yes, the terminology is confusing.

FWIW I like Kester Sn96.5/Ag3/Cu0.5. The fumes are no worse than lead solder.

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"SAC305" and Sn96.5/Ag3/Cu0.5 are the same thing, SAC is just an acronym for Sn/Ag/Cu or Tin/Silver/Copper. The "305" refers to percentages of Ag and Cu (ie 3% and 0.5%). This is really on the only readily available lead free solder in widespread use. SAC105 is also available but offers no real advantage.

All the lead free solders are higher soldering temperature, SAC305 melts at 217C vs SnPb (37% Pb) lead solder at 183.

For hand soldering I prefer wire solder, but paste is possible too. The paste has a shelf life though, after a year it may be too thick to extrude from the syringe.

For fine pitch SMT parts you will want the finest gauge solder.

The key to a good lead free joint is plenty of flux. The fine gauge solder has so little flux in it I always add flux, either liquid from a dropper or "flux pen", or tacky paste which helps hold the parts in place while soldering.

Flux comes in 3 basic types:

  • No Clean: Requires no cleaning or solvents as the residue is inert. Note that this is invariably the least effective kind of flux in my experience. It is also very difficult to clean should you want to.

  • Water Soluble: Very strong and produces very irritating fumes when soldering. This must be washed with water to remove to avoid corroding the assembly. And then the assembly must be dried with something like a hair dryer. I avoid this type for hand soldering.

  • RMA or "Rosin, Mildly Activated" flux. This is the kind I prefer and gives good solder joints w/o noxious fumes. It should be clean off with Isopropyl Alchohol and a brush after.

I would recommend a fan to create a gentle air flow to push the fumes away in any case. Too much air will make it hard to solder due to cooling.

And lastly you need a soldering iron designed to reach the higher lead free temperatures. I always recommend a Metcal with interchangeable tips. They are expensive new, but are built like tanks and older quite functional units can usually be had for less than USD$200 on ebay.

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