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.
Copper Throwing Power
Electrolytic Distribution
Electrochemical measurements that quantify the ability of a plating solution to deposit metal uniformly across a surface with irregular geometry represent a fundamental metric in circuit board manufacturing. A high copper throwing power indicates that the plating thickness inside high aspect ratio holes closely matches the thickness on the surface of the panel. This property determines whether a fabricator can achieve the minimum hole wall thickness required by IPC Class 3 standards without over-plating the surface tracks.
Cathode Efficiency
Additives modify the local current density at the cathode surface. The cathode efficiency of the copper throwing power describes how electrical energy converts into metal thickness. Suppressors increase resistance at the high current density areas on the surface.
This forcing of current into the lower density areas inside the holes improves the uniformity of the final copper deposit.
Solution Chemistry
Temperature and acidity levels in the plating tank influence the mobility of ions as they move toward the board surface. The solution chemistry of the copper throwing power relies on a precise balance of copper sulfate and sulfuric acid to maintain high conductivity. Low copper concentrations combined with high acid levels generally yield better distribution into small vias.
Maintaining these parameters prevents thin spots at the center of through holes that could fail under thermal stress.