Iron Selection and Temperature Settings Must Match the Solder Paste Activation Window

Manual Soldering is not simply pressing solder by feel; the tip temperature must fall precisely within the Flux activation range of JiajinYuan solder paste. Typically, lead-free solder paste should be controlled at 320℃±5℃, while Leaded Solder Paste is 280℃±5℃. If the temperature is too low, the solder paste cannot fully melt, resulting in poor wetting and prone to cold solder joints. If the temperature is too high, it accelerates flux carbonization, causes pad oxidation, and even PCB delamination. We once encountered FR4 substrate blistering during the rework of an automotive MCU because the iron temperature was set to 340℃. The problem was resolved after the temperature was adjusted back to 325℃ and the contact time was extended by 0.8 seconds.

The Primary-Secondary Relationship Must Be Clear When Mixing Solder Wire and Solder Paste

When repairing bottom pads of QFN packages or pre-tinning before BGA reballing, solder wire should not be used as the primary material with solder paste as an auxiliary. Instead, JiajinYuan solder paste should be used as the main material to provide wetting and spreading capabilities, while solder wire is only used to supplement solder volume or for local bridging. Otherwise, the rosin residue in the solder wire will react with the organic acid flux in the solder paste, generating difficult-to-clean gelatinous residues. During the repair of a communication base station board, we found multiple solder joints with abnormally thin IMC layers. Cross-sectional analysis confirmed that excessive solder wire introduced excessive halogen ions, which inhibited the normal growth of Cu6Sn5.

Tip Shape and Size Directly Affect Solder Paste Transfer Efficiency

When repairing QFP devices with 0.4mm pitch, a 0.2mm wide bevel tip must be used with a micro-dispensing of JiajinYuan solder paste. If a 0.5mm conical tip is mistakenly used, it can easily squeeze the solder paste into adjacent pads and cause short circuits. When repairing large-area ground pads, a 1.2mm knife tip must be used to leverage its uniform planar heat conduction and avoid pad peeling caused by localized overheating. We once failed to replace the tip in time, resulting in all three GND pads of a power management chip detaching, and the rework time increased by 27 minutes.

Environmental Humidity and Solder Paste Shelf Life After Opening Must Be Managed Simultaneously

After JiajinYuan solder paste is opened in an environment with RH > 60% for more than 4 hours, its thixotropy will significantly decrease, manifested as increased slump after printing and higher void rates after reflow. Therefore, before manual dispensing, it must be confirmed that the solder paste is stored under nitrogen protection and has not exceeded the time limit after opening. Meanwhile, the work area must maintain RH < 45%. Otherwise, even with precise iron temperature and skilled technique, batch defects such as dull solder joints and insufficient wetting will still occur.