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I have recently been thinking about moving to a lead-free process for my production and though I've been reading up, I was hoping someone more knowledgable than me would be able to point me in the right direction. I have an option to choose between the following solder pastes and I was hoping to know which of these would be the easiest to transition to from a SnPb process that I currently have. I don't have any specialised equipment and my reflow equipment is a home-brewn oven that can reach a temp of about 245 deg C.

Solder pastes:

  1. Sn/Ag3/Cu0.5 (SAC305) NC Solder Paste
  2. Sn/Ag0.3/Cu0.7 (SAC0307) NC Solder Paste
  3. Sn/Ag3.0/Cu0.5/Ni0.06/Ge0.01 (SAC305+Ni+Ge) NC Solder Paste

Solder wires:

  1. Sn/Ag0.3/Cu0.7 (SAC0307) Solder Wire
  2. Sn99.3/Cu0.7 Solder Wire
  3. Sn/Ag3.0/Cu0.5/Ni0.06/Ge0.01 (SAC305) Solder Wire

Edit: I went ahead and bought the SAC0307 solder wire and paste. Both were really easy to use. The wire proved a little tough for my 25W iron but it was just as easy as leaded wire with a 50W iron. For the paste, I set the oven max temp to 240 deg C and that did a great job. Thank you again for all the great suggestions.

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    \$\begingroup\$ Is your market, or regulators, insisting you change? If not, don't. Lead free is hard work, especially with home brew equipment. Calibration of temperature profiles is much more critical than with lead based solders. You may find that putting your board assembly out is the best thing to do. But you might not be ready to hear that yet. Make some test boards, buy some solder, run through your oven, then ask the question again. \$\endgroup\$
    – Neil_UK
    Commented Aug 21, 2018 at 17:00
  • \$\begingroup\$ I agree with Neil_UK - if you don't have to change, then don't even consider it. Lead free is a far more finicky animal than regular lead solder. \$\endgroup\$
    – Norm
    Commented Aug 21, 2018 at 17:07
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    \$\begingroup\$ Anecdotal personal experience: reflow is fine with Pb free, hand and rework are a pain. For manual work, a bit of practice helps as it's quite different to leaded solder (visual cues are different, for example). \$\endgroup\$
    – awjlogan
    Commented Aug 21, 2018 at 21:03
  • \$\begingroup\$ Thank you. Unfortunately certain customers of mine are bound by local regulations and hence the move to lead free will be inevitable, if not now then soon enough. I think it’d be wise to atleast start preparing for it. Certainly I need to do some practice boards and see for myself what it’s like before moving any of my production boards to that. \$\endgroup\$
    – electrophile
    Commented Aug 22, 2018 at 2:32

1 Answer 1

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The challenges with lead free are these:

  • A higher melting point
  • Higher thermal EMF
  • Maybe less re-workability

With a higher melting point this can create problems, especially during rework. This can create problems for components, and for prototyping as that involves reworking and replacing parts. It can also create problems for mechanical components or components with large footprints or heatsinks as the temperature must be even higher than before.

enter image description here
Source: http://www.aimsolder.com/alloys

The other problem is a higher thermal EMF, which is the offset produced by the seebeck effect and usually in the uV. This can be noticeable if your working with signals on a uV level and gaining them up with analog electronics.

Another thing to keep in mind is switching solders can also mean switching fluxes and that can create problems. Read up on the flux or sample solder before buying to see if it will meet your needs. The flux can also contribute to how easy it is to rework the solder.

For me personally I'm a fan of SAC405, it's not what most of the assembly houses use so if your trying to match solders, that won't work because most use SAC305.

I got these from qualitek and I a pretty happy with them and the price. One is water soluble and one is no clean (can't remember which). DSP SAC405 - Type 863 or DSP SAC405 Type 798LF

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  • \$\begingroup\$ I'm always distracted... I'll fix that \$\endgroup\$
    – Voltage Spike ♦
    Commented Aug 21, 2018 at 22:16
  • \$\begingroup\$ @bitsmack meta.stackexchange.com/questions/126180/… \$\endgroup\$
    – Voltage Spike ♦
    Commented Aug 21, 2018 at 22:17
  • \$\begingroup\$ Thank you for that detailed answer. I’ve been reading up the aimsolder website as well. Unfortunately the only options I have available are the ones listed in my question. Anything specialized is going to be expensive enough to eat into my margins. What would you recommend from that list? One thing is certain - that I need to practice before I move my production boards to lead-free. \$\endgroup\$
    – electrophile
    Commented Aug 22, 2018 at 2:29
  • \$\begingroup\$ A 500g tube was 70$ for me \$\endgroup\$
    – Voltage Spike ♦
    Commented Aug 22, 2018 at 4:20
  • \$\begingroup\$ Many parts have a max temp of 205C for reflow soldering - how will you address that? \$\endgroup\$
    – CrossRoads
    Commented Aug 28, 2018 at 14:13

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