This standard specifies the principles, procedures, data processing, and precision requirements for determining the non-volatile content in soft soldering fluxes using the boiling point method. It applies to specific types of liquid soft soldering fluxes containing highly volatile solvents with a non-volatile content of not less than 10%. The core principle involves heating the sample to completely evaporate the volatile components and calculating the non-volatile content based on the mass of the residue. Relevant testing instruments include a Martin boiling point apparatus with a spherical distillation flask, a temperature-controlled heater, a thermometer with a measurement range of 50°C to 150°C and a minimum scale of 0.5°C (or a corrosion-resistant thermocouple), and a laboratory balance with an accuracy of 0.001g, ensuring the precision of the test.