This standard specifies the principles, procedures, data processing, and precision requirements for the gravimetric determination of non-volatile matter content in soft soldering fluxes, applicable to specific types of liquid and paste soft soldering fluxes. Its core principle involves removing volatile substances from the sample through heating in a boiling water bath and drying in an oven, calculating the percentage of non-volatile matter based on the mass difference before and after heating. The relevant testing instruments include thin-section glass culture dishes with a nominal diameter of 100 mm, 20 mL to 25 mL weighing pipettes, a drying oven capable of maintaining a constant temperature of 110°C ± 2°C, a desiccator containing silica gel desiccant, and an analytical balance with an accuracy of 0.001 g, ensuring accurate and reliable test results.