Via Profile
Electroplating processes deposit solid copper within blind laser-drilled structures to create planar conductive pathways between adjacent printed circuit board layers. High density interconnect fabrication relies on blind microvia filling to achieve void-free metallization that supports subsequent microvia stacking. Standard copper plating chemistries utilize specific organic additives to accelerate deposition at the via bottom while suppressing growth on the outer capture pad.
Plating Mechanism
Chemical additives in the acid copper bath govern the localized plating rate through differential mass transport within the narrow hole geometry. Suppressors and levelers adsorb heavily on the top surface pad, reducing local current efficiency, while accelerators accumulate at the bottom tip to drive preferential bottom-up growth. Successful blind microvia filling demands strict concentration control of brighteners and chloride ions to prevent premature top closure.
When bath flow or additive ratios deviate from target limits, central fluid stagnation generates trapped voids or internal seams along the central axis of the structure. Microsection analysis under high magnification verifies structural integrity and measures dimple depth across production coupons.
Acceptance Boundary
Insufficient copper deposition leaves top surface depressions that impair automated component placement during surface mount assembly. Dimple depth limits specified in IPC-6012 dictate acceptable surface planarity for thermal and electrical performance. Excessive dimple formation leads to solder voiding during reflow when surface mount pads coincide with underlying via structures.
Microsection inspection confirms whether target plating thickness and planarity criteria meet class standards across fabricated boards.
