2.2 Surface Finishes & Panelization Strategy

The interface between the component and the board determines the integrity of the solder joint and the efficiency of the assembly line. Surface finish selection is a strategic trade-off between shelf life, planarity, and cost, while panelization dictates the mechanical throughput of the SMT machinery.

Surface Finish Matrix

The finish must be matched to the component pitch and assembly lifecycle.

• ENIG (IPC-4552): Electroless Nickel Immersion Gold. The default standard for Fine Pitch (< 0.5 mm) and BGA components. Provides excellent planarity and long shelf life (12 months).
• OSP (IPC-4553): Organic Solderability Preservative. Acceptable for cost-sensitive, single-reflow assemblies. Prohibited for boards requiring multiple thermal cycles or aggressive wash processes. Shelf life is limited to 6 months.
• Immersion Silver (IPC-4553): Excellent for RF applications due to lack of nickel skin effect. Sensitive to handling and sulfur (tarnish).
• HASL (Lead-Free): Hot Air Solder Leveling. Prohibited for fine-pitch components due to poor planarity (solder meniscus).

Panelization and Breakaway

Single boards must be arrayed into a panel (pallet) to maximize machine utilization and ensure transport stability.

• Tooling Rails: Panels must have 5.0 mm to 7.0 mm breakaway rails on the long edges for conveyor transport.
• V-Score: Linear grooves for rigid separation. The web thickness must be 1/3 of the board thickness. Keep-out Rule: No ceramic capacitors (MLCC) or sensitive ICs within 5.0 mm of a V-Score line to prevent flex-cracking during depanelization.
• Tab-Route: For irregular shapes. Mouse-bites (perforated tabs) must use 0.5 mm holes spaced 1.0 mm apart. Tabs must be located away from stress-sensitive components.

Final Checklist