Should You Make An Investment In A Resistance Soldering Iron?

Posted by Katarzyna Swiatek on

Should You Make An Investment In A Resistance Soldering Iron?

Resistance soldering irons have a wide range of applicability.  This discussion is limited to small project applications that require a certain amount of precision.

More specifically we will focus on jewelry, electronics, thin copper- based metal, fine wiring and photo-etched parts and similar projects.

And we will show you why we think you should probably have one of each.

The Traditional Approach To Soldering

For convenience, we define traditional as non-resistance.

Traditional soldering irons come in different forms. Most hobby modelers use simple electric temperature controlled units, others hot air guns and a few gas torches.

Traditional soldering involves using the soldering iron to melt a filler metal (solder) which flows into the joint between two metal pieces. The filler metal then cools and solidifies, creating a strong and permanent bond between the two metals.

It is a general purpose soldering method.

What is Resistance Soldering?

resistance soldering ironResistance soldering is a specialized type of soldering that involves passing an electrical current through the metal to be joined. The current is passed through a special tip that is placed in contact with the metal. The resistance of the metal to current flow causes heat to be generated at the point of contact.

Differences between Traditional Soldering and Resistance Soldering

Traditional soldering involves heating a fair area of metal piece while resistance soldering heats only the point of contact between the metal and the solder. Heating an area around the place a joint is to be made will cause solder in adjacent joints to melt.  Heating only at the point of contact does not affect adjacent joints.

The temperature at the tip of a traditional iron depends on the power setting of the iron.  A joint can be made simply by touching the tip to the work. Tap and join soldering is important when working with smd components and LEDs.

Resistance solderers, however, because they use current flow through the contact paint to generate heat, require a positive voltage on the tip and a negative voltage on the metal. A definite contact and hold period is required.

How They Are Used.

Some soldering jobs dictate the use of a traditional soldering iron.  Examples include attaching wires to LEDs, adding components to PCB boards, joining fine wires and similar jobs.

In each of the above examples the joints can be made by simply taping the joint with a fine hot tip. And perhaps more significantly, setting up these projects to have a negative ground on them is not at all practicable.

So, if you solder any of the projects mentioned above, you need a traditional soldering iron.

We Now Move Into The Realm Of Quality.

Heating thin brass can cause the metal to warp.

And heating causes oxidation,

When using a traditional soldering iron, the parts to be joined are most often tinned. Tinning, particularly when using photo-etched parts, often results in warping the metal.

And when tinned parts are joined, one most often sees excess solder at the edges of the joints.

One can, of course, live with this.

But you do run into difficulties with traditional soldering irons when trying to make closely spaced joints.  And that is because heat from a traditional soldering iron is not localized. As the metal is heated to the solder melting point, it radiates out from the point of contact.

brass projectHeat generated by a resistance soldering iron is generated instantly with pinpoint accuracy using controlled, but powerful, bursts of current. This pinpoint accuracy allows you to do some extremely fine work that you could not do with a traditional iron.



But even more noteworthy, when it comes to resistance soldering irons, is that you can avoid tinning, avoid excess solder at joint edges and avoid warping your work.

There is no magic in this. Small dots of soldering paste make fast, pinpoint, solid joints.

By way of example, this is a comment by a user of a resistance soldering iron made with the kit that you find here.

“Followed the instructions to make it. And it works great. I am working on etched parts and using solder paste. No warping and no need to clean up excess solder. I like the idea that I don't have to tin anything.

As an aside, a resistance soldering iron is a heat on demand unit.  The tip heats almost instantly and cools extremely fast. Aside from not wasting power, your risk, or an interloper such as a child, of getting burned by a traditional soldering iron that sits on your worktable with a hot tip, continuously consuming power, is eliminated.


Summary Of Advantages Of Resistance Soldering

Working With Photo-etched Parts And Other Thin Metals – You can use small dots of solder paste placed exactly where you need them.  A short burst of power quickly makes the joint.

Solder paste consists of solder suspended in flux. It joins metals rapidly without the need for tinning. 

Soldering Jewelry – Using solder paste and a resistance soldering iron eliminates fire scaling.  And once again, the paste can be accurately placed so that there is no excess solder around the joint.

Close Proximity Soldering – There is no match for the ability of a resistance solderer to make joints without affecting those around the soldering probe tip.


Fine And Small Piece Soldering – Lattice work, fine rings, adding minute decorative pieces and bands and the like are done quickly and cleanly.

Solder Paste Friendly – Solder paste takes a finite time to melt the flux and then the solder.  With the pinpoint application of a burst of current, a joint can be made near instantaneously. Even at a lower current setting, the results are better than those achieved with a traditional soldering iron.

Heat On Demand – Two definite steps must take place before any heat is generated.  A connection must be made between the positive probe and the grounded work piece. Then power must be applied

Soldering temperature is reached near instantaneously. And because only a small area was heated, when power is removed, cooling is rapid – as one person said, “a little longer than instantaneously.”

A traditional soldering iron takes time to reach temperature.  And then sits on a workbench at high temperature continuously consuming power.  It is a continuous burn hazard.

A dormant resistant soldering iron neither consumes power nor does it constitute a burn hazard.  It is big (meaning adult) and little kids burn safe.

Soldering To Mild Steel – The need to solder small steel washers or steel wire is easily satisfied by a resistance soldering iron.

Overall Improvement In Quality Of Projects – This is the hallmark a resistance soldering iron.  And it is the reason that people are willing to spend as much as $500 to buy commercial units.

You don’t have to spend that much.  But you should note that they sell at such high prices is an indication of their outstanding performance.


The Cost Of The Investment?

The cost of factory built resistance soldering irons is the main reason that modelers shy away from resistance soldering irons.

Some go forward with making their own.  Most of the tutorials on how to do this involve hacking transformers - a practice that is at best unsafe.

But one can use transformers that are specially designed for resistance soldering irons. One, for example is here. And there is a complete guide to making your own resistance soldering iron with a safe transformer is here.

In the final analysis, if you make your own, cost should not deter you from being able to make projects better than you ever thought you could.


So, Should You Invest Or Not?

It is important to note that a resistance soldering iron is not a replacement for a traditional iron. It is a value add item

If you:

  • work on photo-etched parts,
  •   want to eliminate warping,
  •   want to eliminate tinning,
  •  want to eliminate having to remove   
  •  excess solder from edges of joints,
  •  want to solder pieces in close    
  •  proximity to each other,
  • want to join mild steel and brass,
  • want to make high quality finely detailed pieces,
  • want to eliminate a hot soldering iron on your workbench,
  • want to produce high quality projects,

then you should consider making the investment.


In our experience, we have never found anyone who has invested in a resistance soldering regretting it.  They love them.