Afterthought on Lead-Free Solder

In this posting, I had written about lead-free solder and its similarity to the older idea of silver-tin-copper mixture. What I had written was my earlier assumption, that a fourth element had been added to the mixture to bring its melting-point down a bit.

From what I have read, what is in fact used is Sn96.5/Ag3.0/Cu0.5 with a melting-point of 217°C, as opposed to the melting-point of 189°C which the old-fashioned solder has. What this means, is that the modern, lead-free solder, is in fact silver-sod, and not a silver-sod-like solder.

Also, I had run into a problem in my use of this solder-type, which was the formation of a resin-droplet on the soldering joint. To my naked eye, this tiny spot of brown looked a bit like copper-wire that might not have been whet by the solder, but two inspections with the magnifying lens revealed that it was a translucent droplet on the surface of the soldering joint.

The silver-sod in wire-form which I had bought, had a rosin core. This is a type of electrical flux, where several types are possible. But apparently, other references exist, of resin-droplets being left on the soldering joints. As I had imagined, such deposits are likely to be hardened, and require a wire-brush to scrape off. I was avoiding the use of such force, to avoid possibly compromising the soldering joint I had just made.

Contrarily to the example I just cited, mine was a brown deposit and not black.

But my afterthought would be, that it was probably a mistake of mine, not to get out the wire-brush and clean the joint. Yet, since mine was an example of rosin resin, I also do not fear much that damage will result from having left a droplet of it on the tin.

Dirk

(Edit 12/01/2016 : ) Rereading the above article had made me so unsure of my first soldering joint, that I just decided this evening to redo it.

The key point: Residues of flux can cause oxidation, and can thus lead to a failure of the connection later down the road.

I removed the electrical tape and re-inspected. The old droplet of brown, had turned green.

So this time around, I re-soldered the same connection, and after that, used a wire-brush to remove any excess residue. Also, this time I took extra care, to use ample solder.

 

First Stage of my Project Reached

Often it can happen that before we open up some technical work that was performed by somebody else, we have one idea about what to find, but that after we do so, we find something quite different. Today, while working on my project, this was the case.

When Electricians connect two leads to a single-pole, single-throw switch, what they are supposed to do is remove the insulation a certain distance from the free end of each lead, loop the bare wires around each terminal of the switch, and tighten the screws of the terminals.

When the switch is ‘open’, no current can flow, and when the switch is ‘closed’, current flows with minimum series resistance.

If one wire is black and the other red, which are both codes for phase-wire, past experience tells me that they have never been connected to supply, 180° out of phase with each other, because the first time the circuit was closed, there would have been fireworks. In this case, the supply-wire was black, and the load-wire to be fed was red.

But this is how the previous design was screwed up: Instead of having a free end of supply (black) wire, the previous Electrician had de-insulated a segment about 1.5cm long along this wire, leaving the rest of the wire insulated. Hence, the black wire came from out of the wall, looped through one of the switch-terminals where it was de-insulated, and went back into the wall in one continuous path, to feed circuits elsewhere, which that switch was not supposed to be able to turn off.

But, the load (red) wire was passed in as one free end, and lodged in so tightly that even after I had completely removed the screw of the terminal, I could not remove this red wire. My only solution was actually to cut the red wire, and to leave some length of it in the terminal, rendering the rest of the switch useless, even if it was to be reassembled – ever.

What this meant, was that the plastic screw-on caps, with the little springs inside, that are normally excellent for this sort of thing, were useless to me, because nowhere did I obtain 3 free leads facing in one direction, to twist together mechanically. All I could do, was to entwine the red (load) wire with the bare section of the black (supply) wire a little bit, and then rely on my soldering job 100% to hold everything together.

Then, I had to apply several layers of professional-grade electrical tape, to prevent this blob of metal from shorting against the inside switch housing.

When we apply any soldering job, a detail which most inexperienced people may not know, is that we never really apply the solder to the tip of the soldering iron or gun. We always use the soldering tip, to heat up the copper wires or terminal, until the copper itself becomes hot enough to melt the solder. If we neglect to do that, liquid solder will fail to bond to the colder parts of the copper, will bead instead, and will yield a faulty connection which we will hear bad news from…

It comes as a secondary fact, that we actually cannot avoid the liquid solder additionally touching the tip of the soldering iron or gun.

Continue reading First Stage of my Project Reached

Modern Lead-Free Solder

It was a traditional show, that lead, tin, arsenic. antimony and ultimately bismuth could be combined into a metallic mixture, that would melt in your hand. Further, without the antimony or bismuth, traditional solder was formed.

Dumping waste lead into the environment is now frowned upon, so that alternatives to this have been sought for some time.

For a long time, a type of alloy was known, by the name of silversod, or in German, “Kaltlot”. This was a Silver-Tin-Copper mixture which household soldering irons were not hot enough to liquefy. For the same reason – a significantly higher melting point – silversod was not used in electronics, because higher temperatures can easily damage them.

But the quest continued. From what I can tell, a lead-free solder is available commonly today, which does contain silver. But because this solder contains a fourth element – which I do not know – it has a lower melting point than, and cannot be named silversod.

(Edit 12/02/2016 : ) It has come to my attention, that modern solder only contains tin and lead, not a third element, the latter of which would bring down the eutectic point further.

Similarly, since we live in a society that likes to simplify, the possibility exists that the silversod I was used to as a child, which my soldering iron could not liquefy, merely consisted of tin and silver – no copper.


When we use a soldering gun, this is already unsuitable for delicate electronics. One reason is the fact that the tip of a soldering gun produces a strong magnetic field, which will induce currents in circuit-boards, strong enough to damage transistors and chips. Thus, soldering guns are mainly meant for heavier, less-sensitive soldering. Here, the lead-free solder is used.

If you ever need to solder a modern circuit board, first of all, may God Help You. The chips today are mainly SMD packages that need to be soldered by a robot. Yet, there might still be discreet components, with leads that pass all the way through the PC board, the old-fashioned way. And here, the use of a 25-35 Watt soldering iron is applicable, although even-lower wattages, that are harder for amateurs to use, are also available in soldering pencils.

For electronics, the old, lead-bearing solder is still used, precisely because even the latest lead-free mixture has a slightly higher melting point yet, that can damage chips and transistors.

For the project I just started, I plan to use a soldering gun, and therefore also the lead-free, silver-bearing solder.

Dirk

Continue reading Modern Lead-Free Solder