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Cosmetically "Perfect Soldering"
May be Defective

Don't be Fooled by Heat-Induced "Soldering"

Is Your Training Causing Touchup and Rework?

If a manually soldered connection meets the cosmetic reliability requirements of A-610 and J-STD-001, is it, in fact, reliable? The answer is: not necessarily.

An “acceptable” connection made with a soldering iron may not actually be reliable. Indeed, it may not even be soldered. At the elevated temperatures of soldering irons (roughly 700°F/370°C or more), solder will stick to metal oxides and create the erroneous impression of wetting.

This can be proven with the following experiment.


  1. Insert a copper wire without flux into a solder pot at 450°F/232°C. Since no flux was used, the wire has not been deoxidized. As expected, there is no solder coverage (Fig. 1). Label this Sample 1.
  2. Apply flux capable of deoxidizing copper to an identical copper wire and insert the wire into the 450°F/232°C solder. The result is  complete coating of solder (Fig. 2). Label this Sample 2.
  3. Increase the solder temperature to 680°F/360°C (a typical soldering iron temperature). Then, insert an identical copper wire without flux into the hot solder. Solder completely covers the wire (Fig. 3) and meets the visual acceptance requirements of J-STD-002. This is Sample 3.
  4. Compare the visual results of Sample 2 and Sample 3. They appear identical. But are they?
The wire looks soldered but the coating is just a shell


To determine whether Samples 2 and 3 are truly identical, cross-section the two wires and examine the solder with a scanning electron microscope (SEM)

Fig. 4 is the SEM cross–section of Sample 2 (reliably soldered at low temperature with flux).  Fig. 5 is the SEM cross–section of Sample 3 (high solder temperature, no flux).

Although without magnification both samples appeared soldered, the magnified cross-section shows that the results are actually very different. The solder on Sample 2 (Figure 4) shows a clear intermetallic layer where the solder meets the copper and the solder coating is thick and free of porosity. The solder on Sample 3 (Figure 5), on the other hand, is very thin and porous. There is no intermetallic bond. In other words, the wire is not actually soldered; there is only a shell of solder coating the oxidized copper.

Solder training that focuses on memorizing visual requirements does not provide students with the process knowledge needed to meet the requirements without touchup and rework. Worse still, the students end up believing that appearance is all that matters. Inevitably, they end up relying on soldering iron heat to achieve connections that meet the cosmetic requirements. That doesn't happen with Science of Soldering©.

Science of Soldering© is different from all other solder training. Our students learn the process management systems that exceed the most rigorous workmanship requirements without touchup or rework. Defects disappear. Failures plummet. And efficiency soars.

Make the most of your training budget. Put Science of Soldering© to work for you.

What Our Clients Say

Science of Soldering© was everything I hoped it would be and then some. It was well planned out and presented in a logical way that really made the participants think about the proper recipe for soldering.

Other training I have had regarding soldering mainly focused on end results and was presented in a way to simply pass a certification test. Science of Science goes above and beyond what J-STD-001 and A-610 training has to offer. I highly recommend this training for individuals from beginning operators to experienced engineers. It was a real pleasure for myself and the other participants.

Brian Strodtbeck

Process Engineer – Electronics

Electrical Power Systems

Goodrich Corporation

Twinsburg, OH 44087

Solder completely covers the wire and a thin intermetallic is visible between the wire and the solder
Solder has not bonded to the wire. There is no intermetallic and the solder is thin and porous with cracks


This experiment shows that surfaces "soldered" at common soldering iron temperatures may not actually be soldered. When a soldering iron has been used either in making the original connection or in touchup/rework, acceptable appearance does not prove reliability. Only the person who actually made the connection and knew how to interpret the motion of the solder during application can know whether the connection is, in fact, reliable.

Visual standards have a role (a connection that doesn't meet the cosmetic requirements is likely not reliable) but meeting the visual requirements does not guarantee reliability. Contract manufacturers often use touchup and rework to fool customers who do not understand the limitations of the standards. And the massive rework that is common among Class 3 manufacturers often makes the concept of "high reliability" a sad joke.

See more client comments here

Science of Soldering© teaches more than how to perform and visually inspect high reliability soldering. It provides thorough soldering process knowledge that will consistently yield the desired results. With this knowledge our personnel now understand the best way to perform their job and don’t just try to make a pretty looking connection.

Jeff Gray

Director Product Quality Assurance and Conformance

Esterline | Power Systems

Buena Park, CA 90620

Science of Soldering© is the best value for the dollar I have encountered in the last thirty years.

Robert Khaleel

Lockheed Martin

Orem, UT