Vertical Alignment
Alignment of internal circuit layers, drilling depth, and vertical connections in a multi-layer board ensures the reliability of microvias and blind vias. Achieving precise z-axis registration prevents the drill from penetrating too deeply or stopping short of the intended internal target pad. This vertical accuracy relies on controlled lamination thickness and accurate drill calibration.
Misalignment in this direction leads to open circuits or weak connections. Fabricators measure this parameter using cross-sectional analysis.
Drilling Accuracy
As electronic packages shrink, microvias require precise depth control to connect the outer layer to the first internal layer without damaging the underlying circuit layers. If the laser or mechanical drill cuts too deep, it breaks through the thin copper capture pad, destroying the electrical path. Conversely, if the drill does not go deep enough, the subsequent copper plating cannot establish a connection, resulting in an open circuit.
Variations in prepreg thickness and resin squeeze-out alter the height of internal layers, making accurate depth control difficult to maintain without dynamic sensor feedback. Modern drilling machines use conductive contact sensing to detect the surface before drilling.
Reliability Outcome
Inspection of test coupons at the board edge reveals the vertical alignment of the drilled features. When the depth variance stays within the specified tolerance band, the resulting joints are durable enough to survive thermal stress testing. Consistent depth control avoids connection failures during operational life.
Durable connections are the standard for high-density circuits.
