Solder Paste is the lifeblood of SMT production lines. It must be accurately transferred to the pads during the stencil printing process, meeting both the shear-thinning property when pushed by the squeegee and maintaining sufficient viscosity after component placement to prevent component displacement. JJY JG-818A solder paste maintains a viscosity in the range of 750±50 Pa·s at 25°C. When used with a 0.12 mm thick laser stencil and a 45° squeegee angle, it can achieve a pad coverage rate of over 95%. If Solder Wire is mistakenly melted and applied as a substitute for solder paste, the Flux gas cannot escape in time during reflow, resulting in dense micropores and causing the void rate of BGA solder joints to exceed the standard.

Manual Soldering and rework must use solder wire instead of solder paste. This is because when a hot air gun applies localized heat, the rosin-based flux in the solder paste will carbonize and turn black, encapsulating the solder balls. JJY JG-63B solder wire contains a 0.5% active halogen flux core, which can penetrate the oxide film instantly upon contact with a 320°C soldering tip. However, if a solder wire with a diameter of 0.8 mm or larger is used to solder 0201 resistors, the uncontrolled amount of molten solder can easily cause bridging between adjacent pads. In such cases, it is necessary to switch to a 0.3 mm thin-diameter solder wire and control the wire feeding rhythm, allowing the solder to naturally spread along the pad edges rather than pile up.

PCB pre-tinning before wave soldering or tinning thick copper layer heat sinks must use Solder Bars, as they have a stable melting point of 183°C and excellent fluidity. JJY JG-99.3 solder bars maintain a surface tension fluctuation of less than 8 mN/m when continuously fed into a 260°C solder bath, enabling uniform coverage of large-area copper foils. However, if solder bars are mistakenly placed into a reflow oven, the uncrushed blocky residues of the bars at high temperatures will clog the nitrogen nozzles, causing a sudden rise in oxygen content inside the oven and resulting in a dull gray oxide layer on the surface of lead-free solder joints. This oxide layer is often misjudged as insufficient solder during AOI inspection, triggering false alarms.

During production line changeovers, batch management of solder paste and solder wire is most prone to confusion. For example, in one instance, JJY JG-818A solder paste was mistakenly issued to the repair station as JG-63B solder wire. The operator directly squeezed the solder paste from a syringe onto the soldering tip for heating. As a result, the 20 μm alloy powder in the solder paste segregated under non-uniform heating. After cooling, the solder joint cross-section showed a layered structure of a silver-white tin-rich phase and a gray-black lead-rich phase. X-ray inspection revealed that the thrust value was 30% below the standard lower limit. This type of failure often manifests with a delay in mass production, and the root cause of mixed solder materials is only traced back when customer complaints arise.

All solder storage must strictly differentiate temperature and humidity requirements. Solder paste must be refrigerated at 0–10°C and allowed to warm up for 4 hours before use. Solder wires and bars must be stored in a dry cabinet with RH < 60%. If solder paste freshly taken out of the refrigerator is directly put on the machine for printing without warming up, condensed water mixed into the paste will burst into pinholes during the reflow stage. When damp solder wire is used for soldering with a soldering iron, it will emit a distinct "crackling" sound accompanied by splattering. In such cases, the damp front section must be cut off before use; forced heating for drying is absolutely prohibited.