Vertical Offset
Maximum distance measured between the lowest pin terminal and the highest pin terminal of a surface-mount package establishes seating uniformity on printed circuit board pads. Flatness of component leads relative to a reference plane controls solder paste contact during surface-mount placement. Maintaining tight lead co-planarity prevents open solder joints and lifted leads on quad flat packages and small outline integrated circuits.
Automated optical inspection equipment measures vertical lead alignment prior to placement using laser triangulation or 3D vision systems. The dimensional measurement applies to surface mount leaded packages and does not apply to ball grid arrays or through-hole components.
Reflow Inspection
Excessive lead height variation leaves tall leads suspended above the solder paste deposit during reflow soldering. Surface tension of molten solder fails to bridge gaps exceeding zero point one millimeters on standard pitch components. Deviations in lead co-planarity lead to open circuits and weak solder fillets in finished circuit assemblies.
Component handling errors and improper tape packaging frequently bend outer leads out of plane. Automated re-alignment tools can rework deformed leads prior to board assembly.
Tolerancing Threshold
Standard IPC-A-610 criteria mandate maximum lead-to-plane separation thresholds based on lead pitch and component package type. Fine-pitch packages below zero point five millimeter pitch enforce maximum co-planarity limits of zero point zero seven five millimeters.
