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I'm looking to start working with solder paste as I'll be making a batch of SMT boards. It seems that most people use lead-based solder paste that requires refrigeration. Vendors charge a hazardous materials fee that seems to be around $25 plus they will only ship overnight with a cold pack. So if I want just one or two syringes, the shipping can be double the product cost. Plus I have to keep it in a separate refrigerator or at least triple-bag it in my food refrigerator.

But I also see available lead-free synthetic solder paste (like Amtech's SynTECH-LF) that incurs none of the extra charges or special handling, although I'd refrigerate it anyway. I'll likely be using hot air soldering initially and then switch to stenciling and a toaster over. Does anyone have any experience with this synthetic solder paste? How difficult is it to work with?

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I've tried both on different projects and stick with lead solder for hand soldering SMT and through hole projects. I've found lead-free solder is very difficult to obtain consistent joints. Lead free soldering is successful in consumer electronics because the soldering environment can be precisely maintained compared to hand soldering on a bench. You also don't need solder paste for SMT work. I've been successful using very thin .025 solder.

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Long time since this been posted. :) Guess it's pretty hard to get replies on specific brands.

As far as solder paste in general goes, I've found the biggest issue to be shelf life. You need quite a batch of PCBs to use up a tube, even a small one. Synthetic seems to have an advantage in that.

On a different note, we've found that plumbing solder (!) works nice and costs little. It can be found in hardware stores, to solder copper and brass pipes. So if one just wanted to try out SMDs, I'd say forget that high-grade electronics stuff until it really matters. It's also good to cover ground planes. :D

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    \$\begingroup\$ -1 for suggesting plumbing solder. The problem with plumbing solder is that it has an acid-based flux. This is great for soldering pipes, but will over time dissolve the thin copper on PCB's. I've had to repair PCB's that were previously "repaired" with plumbing solder-- and it was nasty. \$\endgroup\$ – user3624 Dec 26 '11 at 18:33
  • \$\begingroup\$ @DavidKessner, doesn't the "acid-based flux" all vaporize / burn-off during the soldering process ? Also, isn't the regular flux used, a mild acid ? It has often been seen that pretty-much the same product gets packaged and marketed for a higher premium, to a different segment, that has a higher "perceived value" of the product. \$\endgroup\$ – icarus74 Jan 31 '12 at 7:05
  • \$\begingroup\$ @icarus74 My own anecdotal evidence would indicate that the acid is strong enough, and enough of it remains after soldering, to damage PCB's. This solder mfg web page backs up my claims that the solder/flux is different: cranesolder.com/faq.htm \$\endgroup\$ – user3624 Jan 31 '12 at 13:28
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I don't recommend lead-free solder, in any situation. The cause of the XBox's "Red Rings of Death" is the fact that they used lead-free solder for the BGAs.

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    \$\begingroup\$ -1: overgeneralizing \$\endgroup\$ – Jason S Dec 7 '11 at 19:57
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    \$\begingroup\$ -1 The overwhelming majority of consumer electronics made in the world today use lead-free solder without problems. I highly doubt that the solder itself was to blame-- rather it would be that the manufacturing process (oven temp, etc.) did not match the solder being used. In that case it's human error, not the solder itself, that is to blame. I will gladly change my -1 to a +1 if you show evidence to support your claim. \$\endgroup\$ – user3624 Dec 26 '11 at 18:30
  • \$\begingroup\$ @DavidKessner it's not an evidence, but an entire series of Acer laptops (Aspire 5520) has the same problem of desoldering chipset due to the fact that it's poorly soldered with lead-free paste. I have one and I had to (homemade) reflow it several times until it died. \$\endgroup\$ – clabacchio Feb 24 '12 at 21:05
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    \$\begingroup\$ @clabacchio You're right, it's not evidence until you put it into perspective of all the things made with lead-free solder that work perfectly fine. Also keep in mind that when BGAs were first introduced there were a lot of PCBs shipped with bad solder joints-- with leaded solder. Anytime there is something new, there are problems until everyone gets the process ironed out. \$\endgroup\$ – user3624 Feb 24 '12 at 21:15
  • \$\begingroup\$ @DavidKessner of course, I was just reporting my experience (really not beautiful nor recommendable) with problems due to bad use of lead-free solder paste; anyway, I think that unless you have to certificate a RoHS product, it's easier to solder the old-style lead paste... \$\endgroup\$ – clabacchio Feb 24 '12 at 22:34

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