Gold-plated PCB soldering is not simply a matter of Printing Solder Paste and running it through a reflow oven; it requires simultaneous consideration of the structural characteristics of ENIG-processed gold-plated PCB pads, where the gold layer thickness is typically 0.05–0.1 μm and the nickel layer thickness is 3–5 μm. If the Flux activity in the Solder Paste is too weak, it cannot fully wet the gold surface; if the activity is too strong, it will accelerate the dissolution of gold into the molten solder, leading to frequent solder joint embrittlement and black pad phenomena.

We have verified on the production line that the SN96.5AG3.0CU0.5 lead-free solder paste provided by JiajinYuan, paired with its dedicated rosin-based no-clean flux, under reflow conditions with a peak temperature of 235°C and a time above liquidus of 65 seconds, stably controls the wetting angle on 0.075 μm gold-thickness pads to within 22°, and X-ray inspection shows that the internal void rate of solder joints is below 1.8%, which reduces the void rate by approximately 40% compared to conventional solder paste under the same parameters.

Before SMT Soldering, it must be confirmed that the PCB storage time does not exceed six months and the ambient humidity is maintained between 30% and 60% RH; otherwise, thickening of the oxide film on the nickel layer surface will significantly weaken the solderability of the gold layer. The nitrogen reflow oven supporting JiajinYuan's gold-plated PCB soldering solution has a measured oxygen content stably maintained in the 85–95 ppm range over the long term, which improves the surface finish of solder joints while reducing the risk of abnormal thickening of the copper/nickel interface IMC.

Stencil apertures must be designed at a 1:1 ratio according to pad dimensions with an additional 5% area compensation; the squeegee pressure is set in the 2.8–3.2 kgf range and the printing speed is controlled at approximately 35 mm/s. This ensures complete solder paste release without causing local wear of the gold layer due to extrusion. We once found that after continuously printing 32 PCBs from a certain batch, the gold layer at the pad edge of the 33rd board peeled off; the root cause was that the squeegee angle deviated from the standard value by 0.5 degrees and was not calibrated in time.

AOI inspection cannot only check whether the solder paste coverage area meets the standard; it must also focus on whether there are microcracks or shrinkage depressions at the solder paste edges. Such defects are highly likely to evolve into solder joint cracking or head-in-pillow effects after reflow. JiajinYuan's gold-plated PCB soldering solution requires setting the AOI recognition threshold to ±8% solder paste volume deviation and ±12 μm height fluctuation, paired with an SPI sampling frequency of one board every ten boards, to effectively intercept early-stage risks.

During repair and rework, it is strictly prohibited to use a ordinary soldering iron to directly heat gold-plated pads; a hot air gun must be used with a nitrogen nozzle, the temperature set at 320°C, and the single-point blowing time must not exceed 8 seconds. Otherwise, the nickel layer will undergo lattice distortion due to local overheating, resulting in poor wetting or solder joint spikes during subsequent secondary soldering. We have statistically found that the failure rate of pads reworked more than three times reaches 67%, of which 82% stems from nickel layer thermal damage rather than gold layer consumption.