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Many types of solder are available today, such as acid-core, silver, rosin-core and aluminum solder. What kind should I use for building antennas and radio equipment? Why?

From test question: T7D08

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First of all, acid-core solder is never used for electronics any more, that just isn't what it's for. I think it's still used for plumbing or other soldering where there aren't sensitive components involved.

Second, aluminum solder isn't a thing. The best I can find is that there's some solder specifically for soldering aluminum to other stuff, but you shouldn't use that for electronics soldering either.

By silver solder, I can only assume you mean lead-free solder, which also contains silver. That's fine, as is standard lead-tin solder. Rosin-core solder can be either tin-lead or lead-free, it just has a core of flux which helps to remove the oxidization on the surface of components for better soldering.

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  • $\begingroup$ Not all lead-free solder contains silver. But SnCuAg solder has several advantages, such as a lower melting temperature and freedom from the tin whiskers issue. $\endgroup$
    – Mike Waters
    Mar 1, 2019 at 22:19
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    $\begingroup$ @MikeWaters followed your link and found this: nepp.nasa.gov/whisker/other_whisker/SAC/index.htm $\endgroup$
    – Pete
    Aug 28, 2020 at 5:56
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The OP question is copied directly from the the FCC amateur Technician test question pool. The answer is rosin core solder.

The question and its answer mostly sidesteps the question of solder composition. Rosin core lead-tin (63/37%) is the easiest to work with in radio and electronics use. Whether it is "best" is a matter for argument.

International regulations for electronics manufacture have mostly prohibited solder containing lead; therefore there is now a range of lead-free substitutes, some even containing silver.

Another distractor option is "Aluminum solder," an oblique reference to aluminum brazing rod, which might be used to fabricate an antenna, but not in circuitry.

Acid core, used for plumbing, is never used in electronic work. That industry also switched to lead-free.

FWIW, bootleggers discovered long ago that assembling a liquor still with lead solder resulted in "poor man's poison" (lead poisoning). They switched to silver solder.

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I know this is an old thread but I thought I'd chime in anyway.

Lead-free solder is used for plumbing since the early eighties, because you don't want lead on contact with potable water.

For electronics, the danger from soldering is from inhaling the flux smoke. The temperatures used aren't high enough to vaporize the lead, so there is minimal lead exposure from soldering.

So, for electronics leaded solder is my preference unless I want to build something that is sold into the EU, where it is prohibited.

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  • $\begingroup$ I strongly disagree with "there is minimal lead exposure from soldering." Lead-tin solder melts at about 188 °C (370 °F), and lead boils at 1749 °C (3180 °F), so you're right that solder smoke isn't a significant lead risk. However, lead solder is very soft, and handling it can deposit tiny particles on the skin. Tiny amounts of ingested lead can lead to medical problems, so people soldering with lead-tin solder should be careful to wash their hands before eating, smoking, touching door knobs, etc. $\endgroup$
    – rclocher3
    Dec 20, 2021 at 17:37
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The best solder for Amateur and hobby use is eutectic solder, which solidifies without crystallizing regardless of the speed of cooling down. This eliminates so-called cold solder joints, which can sometimes appear to be solid, but may make poor electrical connection.

Traditionally, eutectic solder was made of 63% tin and 37% lead, and is easy to use because it has a very low melting point, but laws are tightening to eliminate lead, which is poisonous, from all electronics. An example replacement is made of Tin-Silver-Copper alloy.

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  • $\begingroup$ Hello David, and welcome to this site! I mostly use 63/37 for electronics work, but I am also a fan of a certain brand and alloy of lead-free Sn-Cu-Ag solder (2.5% silver). I started using it on a product that we manufacture, but I also use it sometimes on the ham workbench when I need extra strength or resistance to cold-flow. $\endgroup$
    – Mike Waters
    Mar 2, 2019 at 17:12
  • $\begingroup$ The European Union's RoHS (Reduction of Hazardous Substances) laws specifically exempt hobbyists. $\endgroup$
    – rclocher3
    Dec 20, 2021 at 17:38
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The answer to the test question that the OP wanted to be answered is "rosin-core solder".

Traditionally hams have used lead-tin solder with a flux core. I used it for years. In my opinion, we hams should follow the electronics industry and move on from solder containing lead to lead-free solder. Everything that we solder will end up in landfills, and lead is an insidious poison, especially in ground water. There is a risk that leaded solder we use today will contaminate ground water in the future. In my opinion, the convenience of lead-free solder doesn't justify the environmental risk, now that acceptable lead-free solder exists.

Lead-free solder is harder to work with, but not tremendously so. The flux in flux-core solder usually isn't enough with lead-free solder, so I keep a syringe of paste flux on hand; a little dab of flux on the joint I want to solder makes the solder flow freely. Soldering iron tips wear out faster, but modern microprocessor-controlled irons lower the tip temperature when the iron is idle, which helps, and keeping a blob of solder on the tip helps also. Replacement tips aren't expensive.

Lead-free solder would be more difficult to use when soldering a PL-259 plug, but there are PL-259 versions that are designed to be crimped, and in my opinion they work better. A crimping tool costs more than a soldering gun, but in my opinion the expense is worthwhile.

I've heard that tin "whiskers" can grow from lead-free solder and short electronics, but in nearly 20 years of experience with lead-free solder, I've never seen such a whisker, or seen a short caused by one.

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