Buildup HDI Stackup Design and Layer Thickness Control
Stackup thickness control requires calculating pressed prepreg heights over local copper patterns to hold impedance and microvia drilling tolerances.
Layer Thickness Control
Dimension Management
Precision monitoring of the distance between copper planes ensures that the electrical properties of a circuit board remain stable. The layer thickness control involves adjusting the lamination pressure and the amount of resin in the prepreg to hit a target height. This process is essential for maintaining the impedance of high speed signals and the overall thickness of the final product.
Tolerance Monitoring
Manufacturers use sensors and manual measurements to verify that each layer of the board stays within the specified range. A layer thickness control is managed by the production team during the layup phase where different materials are combined in the press. If the dielectric is too thin, the capacitance increases and the signal speed changes, which can cause timing errors in the circuit.
If it is too thick, the board might not fit into its housing or connector. This balancing act requires a deep understanding of how resin flows under pressure.
Impedance Stability
Computer models predict how the thickness of the insulation will affect the resistance of the electrical paths across the board. The layer thickness control allows the fabricator to compensate for variations in the raw materials provided by different suppliers. Consistent dimensions are the only way to ensure that the performance of the prototype matches the performance of the mass produced boards.