Knowledge

Temperature: 23±3°C. Humidity: 40-60% RH. PCB baking required if ambient humidity >60% for >4 hours.

Use stencil step-down design (0.08mm thickness for center pad). Apply solder paste with ≥90% metal content. Set reflow peak temperature 5-10°C higher than peripheral pads.

CT is faster for high-volume production, while flying probe suits prototypes with frequent design changes.

Use vacuum fixtures to secure flexible PCBs during placement, and limit reflow peak temperature to 230°C.

Clean nozzles with IPA. Verify feeder alignment. Calibrate vision system.

SAC305 (3%Ag) has better thermal fatigue resistance, while SAC405 (4%Ag) improves wetting but costs 10% more.

Medical PCBs require water-clean flux (IPC Class 3), while no-clean flux suffices for consumer electronics.

3D SPI must monitor solder paste height (±15μm), volume (≥80% pad coverage), and area (no bridging).

Nitrogen reduces oxidation but increases cost by 15–20%. Recommended for BGA/QFN with voiding requirements <5%.

Asymmetric pad design (0.05mm larger on one side) and slow reflow ramp-up (<1°C/sec) reduce tombstoning risk.

For speeds >50mm/sec, maintain paste viscosity at 800–1,200 kcps. Too low causes bleeding, too high leads to skip printing.

Electropolished stencils provide smoother aperture walls for fine-pitch printing, while laser-cut stencils offer faster turnaround. Use electroplating for <0.4mm pitch components.