Deflection Behaviour
Entry material hardness, spindle speed and mechanical drill bit flexure collectively govern hole positioning accuracy relative to programmed numerical control coordinate locations. Deviation from intended entry coordinates, known as drill bit wandering, introduces severe positional misregistration across multilayer panel stackups. The physical displacement occurs when rotating drill flutes bend upon contacting uneven surface foil textures or dense glass weave bundles.
Target Deviation
High aspect ratio drilling exacerbates mechanical tool deflection as drill bits penetrate deeper into thick panel materials. Cutting tip geometry experiences asymmetric lateral forces when encountering variations in glass fabric weave densities, driving the drill tip away from the spindle center axis. Fabricators minimize initial tip deflection by placing aluminum entry sheets on top of the production panel stack.
Hard entry materials provide a flat surface that stabilizes drill tips prior to penetrating glass-reinforced laminate layers.
Breakout Risk
Severe positional drift forces drill entry points outside intended capture pad perimeters on internal signal layers. As lateral offset increases, drilled holes sever copper traces or breach minimum dielectric clearance distances to adjacent isolated copper features. Automated X-ray inspection systems verify exit hole locations across lower panel layers to measure total drill bit wandering before copper electroplating processes begin.
Exceeding alignment tolerances leads to breakout defects, causing irreversible open circuits or short circuits after lamination. Replacing worn solid carbide tools and reducing panel stack height prevent drill deflection from compromising board interconnections.
