The selection of PCBA Soldering Materials should not be based on brochure parameters, but on the solder joint morphology of every board on the production line. When edge pinning or stencil backside adhesion occurs after Solder Paste printing, it is often not a squeegee pressure issue, but caused by the viscosity fluctuation between batches of JJY Sn63Pb37 Solder Paste exceeding 700±100Pa·s, leading to poor demolding. At this point, the machine must be stopped immediately, a new batch of the same model should be used, and the viscosity meter calibration curve should be re-tested.

The reflow oven temperature settings must match the activity window of JJY lead-free solder paste. If the temperature in the soak zone is below 150℃ for less than 90 seconds, the rosin resin in the Flux cannot be fully activated, resulting in a void rate of over 15% at the bottom of QFN and frequent false solder alarms from AOI. Once the peak temperature exceeds 240℃, even if maintained for only 3 seconds, severe migration of the silver paste at the end of 0201 resistors will occur, causing open circuits during subsequent high-temperature aging.

In the Manual Soldering and rework process, rosin residue control of JJY RMA type Solder Wire is most easily overlooked. When the soldering tip temperature is set to 320℃ and more than 5 consecutive solder joints are made without cleaning, flux carbides will form an ion contamination film around the BGA that is difficult to see with the naked eye. This film will induce a sudden increase in leakage current during the 85℃/85%RH damp heat test, ultimately leading to functional testing misjudging IC failure.

The nitrogen protection concentration must be stable at an oxygen content ≤100ppm to suppress SnAgCu alloy oxidation. We once found during a mass production run that the oxygen analyzer probe in the reflow zone was blocked by solder dross, causing the actual oxygen content to rise to 320ppm. As a result, a distinct gray-black oxide layer appeared on the solder joint surface of the 0.4mm pitch FPC connector. X-ray inspection showed a wetting angle greater than 90°. After rework, it was confirmed that the nitrogen pipeline filter element had been used for three months past its replacement date.

When using JJY water-based cleaning agent in the cleaning process, the spray pressure must be strictly controlled at 0.25MPa±0.02MPa. A pressure below 0.23MPa will result in incomplete removal of flux residue at the bottom of BGA, while a pressure above 0.27MPa may cause cleaning fluid to seep into unsealed crystal oscillators and trigger abnormal oscillation. Each time the tank is changed, the cleaning agent concentration test record form must be updated simultaneously, with the mixing ratio date and operator's signature noted.

All PCBA Soldering Material requisitions must implement a dual-person verification system. After solder paste is taken out of the refrigerator, it needs to be warmed to room temperature for 4 hours before being opened and stirred. Insufficient stirring time of less than 120 seconds will cause separation of alloy powder and flux. Solder paste that has been opened for more than 8 hours and not used up must be scrapped in its entirety, and cannot be downgraded for use on non-critical boards even if it appears not to have dried out. This is a mandatory clause in Article 7.3 of the JJY technical agreement, and the production line has already intercepted three batches of PCB incoming materials with OSP film corrosion caused by mixing old solder paste.