Layer Interconnection
High-density printed circuit board architectures utilize micro-drilled vertical conductive pathways to bridge adjacent signal layers across thin dielectric substrates. A microvia interconnect provides high-density signal routing through laser-ablated microvias filled with electrodeposited copper. Compact geometrical dimensions permit fine-pitch ball grid array placement without land pattern overcrowding.
Automated optical inspection verifies pad centering prior to laser ablation.
Plating Mechanics
Specialized acid copper electroplating baths deposit copper inside blind via structures using organic additives to achieve bottom-up superfilling. When plating parameters diverge, a microvia interconnect develops target-pad separation or voiding inside the copper pillar during reflow thermal excursions. Thermal stress testing subjects cross-sectioned test coupons to multiple simulated assembly passes at 260 degrees Celsius.
Micro-sectioning and micro-hardness testing evaluate copper grain morphology within the filled structure. Plating thickness variations alter local current density distribution during high-frequency signal transmission. Incomplete cleaning of laser residues causes interface separation between capture pads and plated copper walls.
Reliability Assessment
Interconnect stress testing applies rapid thermal cycles to dedicated coupon structures, monitoring net resistance continuously. Failures in a microvia interconnect manifest as abrupt resistance steps during thermal expansion of dielectric resins. Acceptance criteria enforce zero target-pad separations under standard IPC-6012 HDI qualification protocols.
