Measuring Soldering Tip Temperature Accuracy
This article is based on an original publication by James R. Hagan, Sr. Product Designer, Weller.
The Importance of Tip Temperature Accuracy
Tip temperature accuracy is a key performance factor for soldering stations, as inaccurate or ambiguous readings can lead to a range of issues. Overheating and temperature deficits can both negatively affect the soldering process.
- Overheating can promote trace lifting, poor solder joints, and damage to components or the circuit board. It can also result in oxidation or erosion of tip surface plating. Fluxes, which degrade at a higher rate with increased temperatures, may carbonize on the tip surface, forming black residues.
- Temperatures that are too low may cause poor heat transfer or longer dwell periods, leading to decreased productivity or poor solder connections.
Measuring Tip Temperature Accuracy
Soldering tip temperature can be measured with accuracy and ease using either the thermocouple or the contact pyrometer method. The Weller WA2000 Soldering Analyzer has the capacity for both methods, as well as tip to ground resistance and millivolt potential measurement.
Thermocouple measurements are taken when two dissimilar metals are joined, creating a specific DC voltage, or millivolt, reading at an absolute temperature. Many types of thermocouples are available for temperature measurement; Weller uses a Type K thermocouple, which is constructed of dissimilar metals Alumel and Chromel with a temperature range of -200°C to 1350°C/-328°F to 2462°F.
Years of soldering tip measurement research has determined that a thermocouple bead welded to the tip surface provides the most accurate reading of soldering tip temperature. In this arrangement, two dissimilar metals are joined, creating a sensing junction by bead-welding the wires together. The thermocouple is then welded to the working surface of the soldering tip to offer the most accurate possible measurement, leaving an error range of just 1.1°C/1.9°F or 4%, whichever is greater.
The preferred method for tip temperature measurement used by Weller is achieved by attaching a thermocouple to the working area of the tip. Welding a 30 gauge Type K tip to the working surface ensures precise measurement at the contact point of the soldering tip.
Generally designed to measure tip temperature stability rather than tip temperature accuracy, actual temperature readings using this method will likely appear 30-60°F below operating temperature. This method is not intended to offer precise temperature measurement and its accuracy depends on many factors including cleanliness of the tip, angle of contact, operator pressure and more.