Pre-welding preparation determines 80% of welding success or failure

Before each operation, the PCB pads and component pins must be wiped with absolute ethanol and an anti-static cloth, while confirming that the JIAJINYUAN HAKKO 936 series soldering tip has been fully preheated to 320°C and tinned. If the soldering tip is found to be oxidized and blackened, a new tip must be replaced, because the oxide layer will seriously hinder heat conduction, which in turn leads to poor solder wetting and an increase in solder joint void rate.

Soldering iron temperature and contact time must be controlled in coordination

When performing Manual Soldering on 0402 to 1206 resistors and capacitors, the soldering iron temperature should be fixed between 300°C and 320°C, and the single contact time of the solder joint should be strictly controlled within 2 seconds. Once it exceeds 2.5 seconds, it will cause PCB pad copper foil peeling, excessive solder oxidation and Flux carbonization. At this time, not only is it easy to form sharp peaks, but also micro-cracks that are difficult to distinguish with the naked eye will be left at the root of the solder joint.

The solder supply method directly affects the solder joint forming quality

The wire feeding action must be carried out synchronously 1 second after the soldering tip contacts the solder joint, and the diameter of the Solder Wire needs to match the thickness of the pin. For example, a 0.3mm pin corresponds to a 0.5mm Solder Wire. If a 0.8mm Solder Wire is used, it is extremely easy to cause solder accumulation, bridging and sharp peaks. However, feeding the wire in advance will cause the flux to volatilize at high temperature before it is fully activated, thereby reducing the fluidity of the solder and increasing the risk of cold solder joints.

The essential difference between cold solder joints and sharp peaks lies in different thermodynamic paths

Cold solder joints mostly occur when the soldering tip does not completely cover the joint surface of the pad and the pin. At this time, insufficient local temperature causes the solder to fail to fully wet the metal surface. Sharp peaks, on the other hand, originate from the imbalance of solder surface tension when the soldering tip is withdrawn, which is common when the tilt angle of the soldering tip is greater than 30 degrees, the withdrawal speed is too slow, or the solder joint is subjected to vibration interference during cooling. These two types of defects are both classified as Class II defects in JIAJINYUAN AOI inspection, but the rework strategies are completely different.

Daily maintenance is more effective than parameter adjustment in preventing batch defects

Before starting work every day, the soldering tip must be cleaned with a wet sponge more than three times, and re-tinned for protection before shutting down. Otherwise, the residual flux residue will carbonize into hard particles at high temperature. These particles will be embedded in the solder joint during subsequent soldering to form inclusion pores, and at the same time accelerate the aging of the soldering tip thermocouple, eventually leading to temperature control drift exceeding ±5°C. This is the fundamental reason why new production line operators suddenly experience concentrated sharp peaks after two hours of continuous operation.