After OSP-coated PCBs are stored in high-temperature, high-humidity environments for over 72 hours, jagged, intermittent edges and Solder Paste tailing at stencil apertures are clearly observed during solder paste printing. The root cause is moisture-induced decomposition of the OSP organic film and localized oxidation of the copper surface, which causes a sharp drop in solder paste wettability. In this case, immediately stop using this batch of PCBs, isolate the storage area to control temperature and humidity, transfer unused boards to nitrogen cabinets for temporary storage, wipe the surface with a 2% citric acid aqueous solution before line loading, then bake at 60°C for 30 minutes. Future procurement must explicitly require suppliers to provide factory inspection reports for OSP film thickness of 0.2~0.5μm, with attached temperature and humidity sensitivity level labels.

ENIG-coated boards exhibit widespread black pad defects after Reflow Soldering. Under a microscope, a gray-black, discontinuous interfacial layer is visible at the solder joint root. This is not caused by excessive gold thickness, but by nickel corrosion triggered by either nickel layer phosphorus content below 7% or overly long immersion gold time during the plating process. Remedial measures include suspending use of ENIG boards from the current supplier, pre-baking already assembled but un-reflowed PCBs at 150°C for 30 minutes before entering the reflow oven, while reducing the reflow peak temperature from 235°C to 228°C and controlling the time above liquidus to 60±5 seconds. Long-term countermeasures require suppliers to provide SPC control data for nickel layer phosphorus content of 7.5±0.5% and gold thickness of 0.05~0.1μm.

Immersion silver boards frequently experience silver migration leading to adjacent pad short circuits after SMT placement, especially in dense 0201 resistor areas. Symptoms include elevated AOI false alarm rates and some solder joints appearing dull without metallic luster. The root cause is uneven silver layer thickness (local <0.3μm) combined with residual halogen activators in the solder paste, which forms ion migration channels under powered conditions. On-site treatment requires wiping the pad area with a mixture of isopropanol + 0.5% ethylenediamine, then baking at 120°C for 15 minutes. Key prevention measures include limiting solder paste halogen content to ≤500ppm, completing reflow within 48 hours after immersion silver plating, and requiring 100% ionic contamination testing (≤1.56μg/cm² NaCl equivalent) for all immersion silver boards.

HASL boards are prone to pad peeling and solder ball splattering during secondary reflow. Macroscopically, spherical solder particles with diameters of 50~100μm are scattered around solder joints. The essence is that repeated thermal shock causes the copper-tin intermetallic compound layer to embrittle and spall, which in turn triggers localized solder paste agglomeration. Emergency solutions include reducing the second reflow peak temperature to 220°C and increasing cooling zone wind speed to 5.5m/s to accelerate solidification. Process rules must prohibit full-area reflow of the same board twice; if rework is required, only localized hot air gun spot soldering is allowed, with temperature not exceeding 300°C and time ≤5 seconds.

The same model of solder paste exhibits a wetting angle difference of over 12° between OSP and ENIG boards. Typical manifestations are that solder joint climb height on OSP boards is less than 40% of pad width, while on ENIG boards it reaches 75%. This is not a problem with the solder paste itself, but is caused by the OSP film having poorer thermal stability below 200°C, while the ENIG nickel layer provides a stable diffusion channel. The verification method is to print the same batch of solder paste on both types of boards, and use the same SPI device to measure volume ratio deviation; if it exceeds 8%, the coating compatibility is judged to be abnormal. Adjustment strategies include switching OSP boards to low-activity ROL0 grade solder paste, while ENIG boards can maintain ROL1 grade, but the stencil aperture ratio must be changed from 1:1 to 0.95:1 to avoid excessive solder volume accumulation.