[sdiy] Transition to Lead-Free Hand Soldering

Tom Wiltshire tom at electricdruid.net
Thu Aug 19 22:08:34 CEST 2021


It’s very interesting to hear your experience, Mike. I haven’t tried this much beyond a few toe in the water experiments (found the water a bit cold and uninviting, to be honest).

One thing you don’t mention is why you’ve made this change. I can see for production it’s essential, and as you say, you can now get SMD assembly done at reasonable prices. But why not build the prototypes with leaded solder? What am I missing? (usually there’s something….)

Thanks,
Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================



> On 19 Aug 2021, at 20:45, Mike Beauchamp <list at mikebeauchamp.com> wrote:
> 
> I've recently started transitioning into Lead-Free solder for all of my projects. Now that surface-mount assembly is affordable in small quantities, it's very easy to get boards made using lead-free finishes and solders but the hand-soldering is a more difficult transition.
> 
> After a conversation with Kester on the telephone (it's amazing how helpful companies can be over the phone), they suggested a few products for me to try and I've now gone through a few rolls to give some opinions.
> 
> For Water-Soluble flux, I am using Kester Part # 24-9574-6403
> which is a .031" K100LD solder with the Organic 331 Flux.
> 
> For No-Clean solder, I am using Kester Part # 24-9574-7618
> which is a .031" K100LD solder with 3.3% Mildly Activated Rosin 275 Flux.
> 
> K100LD is described as "a eutectic Tin/Copper alloy with controlled metallic dopants  to control the grainstructure  within  the  solder joint,  and  to  minimize  the  dissolution  of  copper  into  the solder  pot.    K100LD virtually  eliminates  the  occurrence  of common  defects  such  as  icicling  and  bridging.    The  improved grainstructure also results in shinier solder joints than traditional lead-free alloy alternatives".
> 
> I'm not sure what all of that means, but it's a cheaper alternative to SAC305 at less than half the price for a roll and seems to be designed with hand-soldering thru-hole components in mind.
> 
> 
> In use, both solders are "OK". I increased my tip temperature to those recommended by Kester right away, but was still noticing that the lead-free solder remains "goopier" and doesn't wet and flow into gaps nearly as fast, or sometimes at all. As I continued to increase the tip temperature, this did change and the solder started acting more like the Lead I've used for 20 years.
> 
> I now have my Hakko 936 set to 800 degrees and things are mostly working, but not getting great flow on TH components that are being attached to the ground plane (even with thermal reliefs on the board). Also at this temperature both solders, especially the 275 Flux is spattering pretty crazy and eye protection is probably recommended. The flux residue from this solder has also completely gummed up my fume extraction tube as well, so that is also something to look out for and to be changing pre-filters often. I'm also noticing that soldering pins of cheap plastic IDC headers, it's very easy to melt the plastic with the 800F heat, so I don't dwell on them for long at all. Maybe better parts have higher heat tolerance?
> 
> These solders work good enough to get the job done the first time, but if you try to rework something or correct a mistake, the solders will suddenly change to sticky goo so I usually just suck the solder off completely and start with new solder.
> 
> 
> Kester has a good PDF to troubleshoot lead free hand soldering issues: https://www.kester.com/Portals/0/Documents/Knowledge%20Base/Lead-free-Handsoldering.Final_.4.19.06.pdf
> 
> 
> So there's definitely a compromise, but those two Kester parts are a good substitute for the leaded versions I was previously using (as suggested by Paul S. on here years ago). Next time I redesign my PCBS, I'm going to use a more aggressive thermal relief on ground plane thru-holes and I think the tip temperature should be adjusted based on the physical dimensions of the parts being soldered.
> 
> I'm not sure about the long-term reliability of Lead-Free solder. In my repair shop, I get a lot of music gear coming in with broken solders on PCB-mounted jacks, pots, tube sockets, etc and I can't help thinking that the lead-free solder is more brittle and prone to failure in these applications.
> 
> 
> Have you converted to lead-free in your hobby as well? I'm curious to hear others' suggestions and experiences.
> 
> Mike
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