Capability Index
Statistical analysis represents a standard method for evaluating the capability of a manufacturing line to produce boards within specified tolerance limits. Implementing cpk process control allows assembly houses to measure both the centering and the spread of critical deposition or placement distributions. The value is calculated by comparing the distance from the process average to the nearest specification limit against the three-sigma spread of the process.
A result below 1.33 suggests that the distribution is too wide or too far off-center, increasing the probability of defects. This metric guides the adjustment of print and placement parameters.
Production Application
Solder paste inspection systems generate the real-time volume dataset required for these calculations. By tracking cpk process control across hundreds of prints, manufacturing engineers can identify gradual tool wear or squeegee deformation before the print quality degrades below acceptable levels. The evaluation applies primarily to steady-state operations.
Fluctuations in ambient temperature or paste viscosity can cause the distribution to shift, triggering immediate alarm limits.
Defect Prevention
Preventing stencil bridging and insufficient volume defects relies on maintaining a stable process distribution. When cpk process control drops, the risk of assembly failures on fine-pitch components increases dramatically. Restoring control often involves cleaning the stencil or adjusting the print speed.
This metric provides a mathematical boundary that separates normal process variation from actionable machine drift.
