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.