Effective Qualification of Soldering Iron Performance Criteria

This article is based on an original publication by Metcal.

Commonly tasked with hand soldering process responsibility, quality managers and line supervisors routinely look to common verification methods - such as measuring the idle tip temperature of a soldering station and using this as a point of reference for system compliance. However, this popular method is now being called irrelevant by some industry professionals when it comes to true system process control. Read on to discover the important factors of hand soldering and to learn more about simple, repeatable and effective qualification.

1.) Understand the conduction soldering process
A solid understanding of the hand soldering process is necessary before exploring alternative methods. The following factors are generally of concern:

  • Soldering joint connection quality
    An excess of thermal energy delivered into the solder joint can result in too high a temperature, potentially causing damage to the PCB laminate. Alternatively, low thermal energy could result in unsoldered joints or other faults.
  • Throughput
    To ensure maximum productivity, hand soldering should be performed at a speed to facilitate fast solder joint formation without quality compromise.
  • Process consistency (or repeatability)
    The soidering station should successfully yield consistent, high-quality connections throughout its lifetime as well as the lifetime of the tips.

In short, each of these concerns relies upon proper transfer of thermal energy. Control is the crucial component of this process, as too much or too little thermal energy delivery will result in a negative impact on quality and production.

2.) Thermal energy delivery
Size of the thermal mass, or combined size of the tip and the heating element, is the main contributor to proper transfer of thermal energy. Because it both stores and transfers thermal energy from the heater to the tip, when both ends of the thermal mass are of equal temperature energy is stored and ceases to flow. Alternatively, if thermal mass of one end exceeds temperature at the other end, thermal energy will flow - but the process takes time. Management of thermal time constants is critical to maintaining an efficient soldering process.

3.) Solder station qualification using power measurement
Tip temperature is usually the result of technique, including tip cleanliness, positioning and seating of the tip in relation to the instrument sensor. Actual tip temperature will often differ from heater temperature by a degree dependent on sensor mass and tip geometry, with longer or thinner geometries contributing to more potential errors.


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