A PCB microvia is a short interlayer connection used in dense routing structures, commonly formed by laser drilling through a thin dielectric. Its usefulness comes from the complete pad-and-hole geometry and selected layer span. Calling a hole a microvia does not establish that it is filled, suitable for a solder pad or qualified for a particular thermal exposure.
Define the geometry before comparing options
Identify the start layer, target layer, dielectric depth and the diameter measurement used for acceptance. A laser-formed hole can be tapered, so an entry diameter and a target-side diameter are not interchangeable. Record capture and target pad dimensions separately from the hole dimension.
The aspect ratio calculation is depth divided by the specified diameter. It is a screening input, not a universal process approval. The same numerical ratio can occur in constructions with different absolute dimensions, materials, plating access and process margins.
Microvia terminology in a release drawing
| Term | What the drawing should identify |
|---|---|
| Start and target layers | The exact copper layers connected by the feature |
| Depth | The dielectric distance for the stated measurement convention |
| Hole diameter | Whether entry, target or another agreed dimension is intended |
| Fill and cap | The required finished structure and applicable acceptance criteria |
Plan the connection beyond the first layer
A surface microvia only solves the first transition. Follow the net to its destination and check each subsequent connection. If another microvia continues the path, specify whether it is offset or stacked. If a buried via is involved, show how the structures meet.
Also inspect surrounding clearances. A hole may fit while its pad, antipad or required copper separation prevents a neighboring signal from routing. Use the complete feature geometry in the layout rules and keep it aligned with the fabricator's reviewed proposal.
Inspection and design approval
Ask how the selected connection is represented in coupons and how the acceptance plan relates to the product's assembly exposure. Dimensional inspection and electrical continuity answer different questions; neither should be used as shorthand for every form of reliability evidence.
An illustrative prototype should include the most demanding microvia path actually used in the board, not merely an easy surface connection. Record the stackup, material and processing revision associated with the test results. For a supplier change, compare those features before deciding whether previous evidence remains applicable. Minimum laser-hole diameter and qualified structures for this site's operator are [NEEDS CLIENT INPUT].
Continue the engineering review
- Microvia aspect ratio design tradeoffs
- Microvia capture pads and registration
- Microvia reliability and thermal exposure
- HDI PCB engineering hub
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.