Calculating Landed Cost Crossover between Flying Probe and Fixture Tooling
Landed cost crossover balances fixture NRE against probe runtime fees, shifting financial advantage to fixtures once batch volume savings offset tooling costs.
Target Pad Density
Spatial Allocation
Spatial design constraint defines the number of test access points or component land patterns located within a specific unit area of a printed circuit board. Managing target pad density requires balancing the number of test access points against the physical space of the circuit board. Metric values guide the selection of fabrication technologies such as microvias or fine-line traces.
Manufacturing Constraint
High levels of congestion require smaller annular rings and tighter solder mask clearances to prevent bridging during wave or reflow soldering. As the target pad density increases, the space available for test probes decreases, which might force a move to more expensive inspection methods. Designers balance this value against the electrical requirements for trace width and spacing.
Heat dissipation also becomes more difficult when components are packed closely together. Advanced routing techniques like via-in-pad can mitigate some of these physical constraints but often increase the fabrication cost.
Yield Correlation
Excessively high concentrations of pads lead to higher defect rates during the solder paste printing process. If the target pad density exceeds the capabilities of the assembly line, the risk of solder balls or insufficient fillets rises. Maintaining this value within the limits of the chosen manufacturing class ensures a predictable production yield.