For years I've been soldering with normal Sn60Pb40 solder wire. But now I try to switch to lead free solder. In many forums over the internet I found the Amasan BF32-3 solder wire. It's a Sn95Ag4Cu solder wire with 3.5% flux.

So I tried it and was very disappointed. Nearly every solder joint was looking different. Some of them were (partially) shiny; some (the most) of them were dull. And the worst thing was, that even with additional flux, the solder didn't flow like the leaded. So there is no way, I could solder fine pith SMD stuff with it.

I’m using a JBC soldering iron station with a C245-907 2.2mm chisel tip and tried different temperatures starting with 290°C to 360°C. The best results I get with about 315°C, with 350°C I got the worst results. I used the Amtech NC-559 Flux – the original, not the fake from china.

Some other guys told me, that maybe the solder wire is not the best. That's why I'm looking for other soldering wires. But there are so many on market. Some with copper, some are Sn96.5Ag3.5 like the Amtech ASN96A3.5-0.50.

So can someone tell me, with what type of solder wire or what product I can get nice shiny solder joints. And yes, I now that dull joints were not a sign for a bad or even cold joint.

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    \$\begingroup\$ It's not that you can't solder fine pitch SMD well with this type solder alloy, but that you will either need to have extremely clean surfaces, or use additional flux beyond that in the wire core. \$\endgroup\$ – Chris Stratton Mar 21 '14 at 20:12
  • \$\begingroup\$ Why do you want 'nice shiny solder joints', knowing 'that dull joints were not a sign for a bad or even cold joint'? \$\endgroup\$ – jippie Mar 21 '14 at 20:59
  • \$\begingroup\$ Well, I want shiny solder joints, because the shiny ones just look great. Well, on my Lab Desk I have a 5$ vacuum cleaner with a hand soldered through-hole switch. It just looks great. The joint is not shiny like my leaded ones, but the joints are evenly shiny. But my joints…. Well, some of them are shiny with some very dull spots on the whole surface, some other are shiny with dull spots. It just looks some kind of wrong. And – for me – it’s hard to work with it. Well, as I said, I even used additional flux for the surface, and still got some solder spikes. \$\endgroup\$ – user39063 Mar 21 '14 at 21:40
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    \$\begingroup\$ A fresh, clean, well-made defluxed lead-free joint can start out pretty shiny, though it may darken fairly quickly. Your dark spots sound like residual burned flux or the oxides it tried to carry away. \$\endgroup\$ – Chris Stratton Mar 21 '14 at 22:02
  • \$\begingroup\$ Chris, I don't talk about burned flux or something like that. Take a look on this high res picture, take a very close look. You can see, that some of the joints have a smooth surface. But others are uneven. Like cellulite ;) I tried to solder using my microscope. I saw, that my joints were ok, when the solder was hot. But then it got cold, the joints started to look like this. ssl.port29.net/Files/IMG_7769.jpg \$\endgroup\$ – user39063 Mar 21 '14 at 22:29

For things that require RoHS, I've been using a version of lead-free popular with assembly houses- Sn99.3/Cu0.7 2% flux, which seems to work okay.

The joints are not quite as shiny as the beloved Sn63/Pb37 with RMA flux, but quite acceptable.

enter image description here

Left two joints are lead-free, right joint is Sn63/Pb37.

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  • \$\begingroup\$ Doesn't Sn99.3/Cu0.7 have a high risk of generating tin whiskers? Do you do anything to mitigate that? \$\endgroup\$ – sampablokuper Feb 24 '19 at 18:56

The simple answer is get good old lead based solder wire and some flux and most chances it will be easy to get shiny looking solder joints. I have worked with many lead free solder wires at work and although they are all different, the end result is always a dull looking solder joint. Having that said - a shiny solder joint is on itself not an indication of a good bond. The shape of the solder in respect with the hole size and other geometrical parameters is (look up NASA soldering standards). The appearance of your solder joints also got to do with the cooling of the joint, how fast it cools etc. This will cause different looks and textures, not indicating anything about the electrical properties of the bond.

If you absolutely must have shiny joints try looking into solder pasts.

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  • \$\begingroup\$ I took a high res shot of my results. As you can see, the joints are shapeless with "cellulite" on surface. ssl.port29.net/Files/IMG_7769.jpg \$\endgroup\$ – user39063 Mar 21 '14 at 22:24
  • \$\begingroup\$ @user39063 - most of the solder joints seem to be pretty good. This is not satisfactory? \$\endgroup\$ – user34920 Mar 22 '14 at 21:15

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