High Aspect Ratio Blind via Reliability Limits under Sequential Thermal Cycling and Z-Axis Stress
High aspect ratio blind vias require low Z-CTE filled laminates and pulse plating to prevent target pad separation during lead-free thermal cycling.
Reverse Pulse Plating
Deposition Waveform
Electroplating techniques that alternate between a long period of forward cathodic current and a short period of high intensity reverse anodic current improve the uniformity of copper thickness in complex board designs. Reverse pulse plating effectively manages the distribution of metal across high aspect ratio holes and blind vias. Such an approach differs from traditional constant current plating by actively stripping excess metal from high density areas during the reverse cycle.
It allows for faster plating rates while maintaining high quality standards.
Ion Replenishment
Pulses of reverse current remove copper from the edges and surfaces where current density is highest. The ion replenishment of the reverse pulse plating ensures that the diffusion layer at the board surface remains thin. This thin layer allows copper ions to reach the bottom of deep holes more efficiently.
Surface Distribution
Precise control over the timing and amplitude of the electrical pulses yields a more consistent surface finish. The surface distribution of the reverse pulse plating reduces the thickness of the copper at the corners of the holes. This prevents the dog boning effect where the plating is thicker at the hole entrance than in the center of the barrel.
Improved distribution saves money by reducing the amount of copper used and decreases the time required for subsequent etching steps. The process results in a grain structure that is more resistant to thermal cracking.