Microvia aspect ratio compares the connection depth with an agreed hole diameter. The arithmetic is simple: aspect ratio equals depth divided by diameter, using the same units. The engineering decision is more involved because the measurement convention, absolute size, material and copper process all affect manufacturability.
Make the denominator explicit
Laser-formed holes can taper. Entry diameter, target-side diameter and a finished-hole measurement may produce different numerical ratios. State which convention is used in the drawing and supplier review. A ratio reported without that definition is difficult to compare meaningfully.
As an arithmetic example, a 60 micrometer depth divided by an 80 micrometer diameter gives 0.75. This example demonstrates the calculation only. It is not a recommended geometry, a process limit or evidence that the construction is available from this site's operator.
Inputs to record with the calculation
| Input | Why it belongs in the review |
|---|---|
| Depth and units | Prevents mixing dielectric thickness with total board thickness |
| Diameter convention | Makes tapered features and supplier data comparable |
| Pad and target geometry | Adds the landing and registration context missing from the ratio |
| Material and process | Connects the geometry with the actual manufacturing route |
Do not approve a feature from one number
Two holes can share the same ratio while differing in absolute dimensions and processing difficulty. Copper filling, surface preparation and geometry tolerances remain relevant. Compare the proposed feature with the supplier's supported construction and agreed acceptance evidence.
If a supplier recommends changing dielectric thickness to improve the geometry, review the electrical consequences. A thinner dielectric can alter impedance and coupling, while a larger pad or hole can reduce routing space. Accept the revised construction as a coordinated change.
Use the checker as a handoff tool
Enter the depth and diameter in the browser-local checker, retain the input convention and carry the result into the quote request. Review the associated via-in-pad requirements separately when the connection lies under a solder land. A favorable screening result is not fabrication approval.
The final drawing should identify the accepted dimensions and tolerances, not merely the calculated ratio. Keep the supplier's written response with the stackup revision so later material or geometry substitutions can be evaluated consistently. Minimum supported dimensions and approved aspect-ratio limits remain [NEEDS CLIENT INPUT].
Continue the engineering review
- PCB microvia design fundamentals
- Laser drilling for HDI PCBs
- Microvia capture pads and registration
- HDI PCB engineering hub
Open the related planning tool. Review its assumptions before using an estimate in a design decision.
Review your HDI requirements
Share the board revision, proposed stackup, quantity and open questions. Include the requirements discussed in this guide so the project review starts with the same assumptions.