The Price Step between Four Layers and Six
Moving from four to six layers adds 30 to 55 percent to bare board cost through double core usage, lamination press overhead, and tighter registration yields.
Tooling Holes
Panel Registration
Mechanical reference features drilled into bare circuit board margins provide physical anchoring for pick and place machinery during surface mount assembly. Unplated circular apertures allow automated placement heads to align optical fiducials and mechanical pins simultaneously without touching active copper traces. Edge routing routines mill these positioning locations during board fabrication to maintain tight positional tolerances against inner layer artwork.
Drilling inaccuracies during panelization propagate directly into component placement offsets during downstream component soldering.
Fiducial Clearance
Automated optical inspection systems verify that minimum distances remain clear between placement guides and active components to prevent optical masking errors. Copper planes withdraw from locating perimeters according to fabrication drawings to eliminate shorts during wave soldering processes. Mechanical stress accumulates around locating apertures when panel clamps apply excessive pressure during conveyor transport through reflow ovens.
Fixture Alignment
Vacuum tables secure printed circuit boards against warping by drawing negative pressure through specialized evacuation openings located across the production pallet. Steel pins engage locating features on panel margins to restrain lateral movement during high speed placement cycles. Thermal expansion mismatch between copper traces and FR4 substrates during high temperature processing demands floating pin designs to accommodate dimensional changes without distorting finished circuit boards.