[sdiy] Transition to Lead-Free Hand Soldering

Tom Bugs admin at bugbrand.co.uk
Thu Aug 19 23:33:57 CEST 2021

I've have always used Lead Free (apart from a small supply of leaded for 
specific repairs). I guess RoHS was already in place over here & I 
didn't want any unnecessary dealings with lead. I barely remember any 
struggles with lead-free so am always a bit perplexed by such discussions!

I have used a Kester for where I need a water-soluble - no notes on the 
type at present but likely the same. I have to say that the fumes off 
this have appeared to present lung sensitivity for my assistant - she 
always uses fume extraction for any soldering, but now wears a face mask 
for the occasional times having to use this kester. So somewhat less 
than ideal.

Most of the time I/we entirely use Warton Metals SAC3 FastFlow Lead Free 
(22SWG) because it works so well & the fumes are no issue. It is not 
'cheap' but I have been entirely happy using it - unfortunately it is 
likely hard to find outside UK - not sure whether other SAC305 types may 
be similar or not

The only thing I would perhaps note is that tips maybe seem to wear out 
relatively quickly & can get gunked up with blackness - I only use brass 
wire cleaners, not sponges. I use Metcal irons so have a fixed tip 
It works well for me & I'm happy not to have to continue investigating 
for now!


On 19/08/2021 20:45, Mike Beauchamp 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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