The components of flux are classified as: protective film, activator, diffusant, and organic solvent.

Among the inspection items for metallic materials, the examination of welding flux is an important method for evaluating the performance of electric arc welding and for assessing the quality of the flux. Next, we will first determine the specific inspection procedures based on the characteristics of the welding flux, as well as its relevant testing standards and properties.

Soldering flux components are classified as follows: a protective film, an activator, a diffusant, and an organic solvent. The respective functions of these four experimental reagents are as follows: during soldering operations, the protective film prevents oxidation and reduction reactions of the soldering materials, thereby enhancing their welding performance; the activator facilitates the wetting and spreading of the flux, ensuring smooth spot welding; the diffusant dissolves the preceding three chemical substances; and finally, the solvent enables the formulation of the soldering flux.

In the flux test report, the performance of the flux is comprehensively evaluated based on a series of tests, including appearance, physical stability, non-volatile matter content, flux viscosity and specific gravity, water-soluble resistance, halogen content, flux spread ratio, and bronze mirror corrosion testing.

During visual inspection of the flux, we generally examine whether delamination has occurred and whether there are any sediments or contaminants.

From the perspective of physical stability, common methods such as vibration or mixing are employed to specifically assess the physical stability performance of raw materials.

To determine the non-volatile matter content, the water-soluble flux is dried by either heated water bath or natural convection drying. Approximately 6 g of flux is accurately weighed (placed in a pre-weighed, flat-bottomed weighing dish with a diameter of 50 mm) to an accuracy of ±0.002 g (M1), then subjected to a heated water bath to evaporate most of the organic solvents. Subsequently, the sample is transferred to a convection oven maintained at 110°C ± 2°C (IPC: 85°C) and dried for 4 hours. After removal, the sample is allowed to cool to room temperature in a desiccator and then reweighed. This drying and weighing procedure is repeated until the weight difference between successive determinations remains within ±0.05 g, indicating that the sample has reached constant weight; at this point, the sample mass is M2. The non-volatile matter content of the flux is then calculated using the following formula: Non-volatile matter content (%) = (M2/M1) × 100.

Measure the resistance of the aqueous extract by first thoroughly cleaning the measurement electrodes with twice-distilled water, then immersing them in a beaker containing only flux, measuring the resistance, and recording the reading.

Viscosity and hardness: At 5°C, insert a medical burette into the solder flux and sequentially draw the flux into the burette to determine the relative height difference; this will allow an estimation of whether the flux can rapidly achieve such extreme consistency. Alternatively, use a viscometer to measure its viscosity in real time (in Pa·s). At an ambient temperature of 23±1°C, determine its specific gravity according to the instructions in the densitometer’s user manual.

The copper-coin corrosion test showed no significant etching when compared with the standard bronze mirror.

The application of solder paste is indispensable in the manufacturing processes of SMT assembly plants. Solder paste is a paste-like or putty-like material formed by uniformly mixing alloy solder powder with a viscous flux. As an essential soldering material in SMT processes, solder paste is widely used in reflow soldering and is one of the most important electronic auxiliary materials in the electronics industry.