Inputs
- Board thickness
- Finished hole
- Drill allowance
- Pad diameter
- Registration tolerance
FPC / PCB Engineering Calculator
Via Aspect Ratio Calculator
Check finished hole aspect ratio, drill allowance and annular ring.
How to use the Via Aspect Ratio Calculator
Via aspect ratio checks drilling and copper plating feasibility. A thicker board with a smaller finished hole is more difficult to plate reliably.
Aspect ratio and annular ring
Formula: Aspect ratio = board thickness / finished hole diameter
- Board thickness: total board thickness through the plated hole.
- Finished hole: final hole diameter after plating.
- Annular ring: pad radius remaining around the drilled hole.
Formula Basis
- Formula basis: geometric via aspect ratio and annular-ring calculation.
- Engineering note: drilling, plating and annular-ring acceptance should be checked against manufacturer capability and applicable IPC design rules.
Example
0.8 mm board thickness with 0.2 mm finished hole gives an aspect ratio of 4:1.
Outputs
- Aspect ratio
- Drill size
- Annular ring
- Effective ring after registration
Engineering Notes
- Factory capability varies widely for mechanical drilling, laser drilling and microvia processes.
- Small finished holes need enough pad size to survive registration tolerance.
- High aspect ratio holes require more careful plating process control.
Validation Checks
- Drill capability
- Annular ring DFM
- Through-hole plating
- Hole-to-edge spacing
Related Manufacturing Process
- Drilling / Laser Via - Finished hole, drill compensation, annular ring, hole-to-edge distance
- Copper Plating - Current density, copper thickness, throwing power, plating area loading
Related Calculators
- Etching Compensation Calculator - Estimate artwork width from finished trace width, copper thickness and etch factor.
- Copper Plating Time Calculator - Estimate copper plating current, time and amp-hour loading.
- PCB Panelization / Panel Utilization Calculator - Calculate PCB panelization count, rotation option and material utilization.
- Coverlay Opening Calculator - Estimate coverlay opening size and bridge width from pad size, registration and adhesive allowance.
FAQ
What aspect ratio is safe?
It depends on factory capability and product class. This page flags conservative risk, but the final limit should come from your manufacturer.
Does this apply to laser vias?
The concept applies, but laser microvias need separate pad, depth and copper filling rules.