Lead-Free Soldering of Strain Gauges

Watch the video for a quick overview of the different soldering steps:

1. Removing the oxide layer on the solder pad (using an eraser pencil)
2. Cleaning the solder pad to remove eraser residue and other dirt (with RMS)
3. Pre-tinning of the solder pads
4. Pre-tinning of the wire
5. Soldering the wire to the solder pad
    

• There are a lot of different things to consider when soldering a wire with an electrical strain gauge, such as the solder tip geometry. They must have a suitable thermal capacity, which means that narrow, or spiked, soldering tips are typically unsuitable. Chisel-shaped, rounded, or broader soldering tips are better-suited to lead-free strain gauge soldering.
• Additionally to ensure a correct processing of the solder the temperature of the soldering tip needs to be in a specified range.
• If the temperature of the soldering iron rises above the upper use limit, it could prematurely vaporize the fluxing agent used to prepare the substrate material. This could result in a significantly weakened solder joint. It could also delaminate the strain gauge solder terminal, reducing the adhesion of the components. Conversely, if the temperature is too low the solder may not wet correctly. This necessitates longer soldering times, which can damage the strain gauge soldering terminal and reduce the efficacy of the test equipment. Temperature is also a critical factor in the maintenance of the soldering iron itself. Prolonged use can accelerate the oxidation of the soldering tip, so it is advisable to lower the temperature or switch off the instrument entirely during pauses. Ideally, the soldering time should be as brief as possible, and the solder tip should be re-tinned between uses to prevent surface oxidation.