Coplanarity

Coplanarity is the degree to which package leads or contact surfaces lie in the same geometric plane - it is a critical parameter for reliable solder-joint formation during board assembly.

What Is Coplanarity?

• Definition: Measured as the maximum height deviation among leads or terminals from a reference plane.
• Affected Stages: Molding warpage, trim-form, and handling can all influence coplanarity.
• Assembly Impact: Poor coplanarity causes uneven solder wetting and open-joint risk.
• Inspection: Assessed with optical metrology and fixture-based lead-planarity systems.

Why Coplanarity Matters

• Solder Reliability: Coplanarity defects are a major source of board-level connectivity failures.
• Yield: Out-of-spec leads can increase placement fallout and rework rates.
• Process Integration: Coplanarity links package process capability to PCB assembly robustness.
• Customer Requirements: Strict coplanarity limits are common in high-reliability applications.
• Trend Sensitivity: Gradual drift can occur from tool wear and thermal-process changes.

How It Is Used in Practice

• Inline Measurement: Monitor coplanarity per lot with defined reaction limits.
• Root-Cause Mapping: Correlate deviations to mold warpage and trim-form settings.
• Tool Maintenance: Maintain form-tool alignment and flatness to sustain planarity control.

Coplanarity is a board-assembly-critical geometric quality metric - coplanarity control requires coordinated molding, forming, and metrology discipline across the package flow.