1. What is a blind or buried via?

A blind or buried via is a through-hole in PCB design used to connect different layers without penetrating the entire board. A blind via connects outer layers to inner layers, whilst a buried via connects only inner layers. Altium Designer supports this type of advanced design.

2. Design Process

3. Stack-up configuration

Before commencing PCB design, the stack-up structure must be defined, specifying the material and thickness of each layer. Configure this via Design > Layer > Stack Manager, ensuring that sufficient internal layers are included
to support buried via requirements.

4. Defining via types

Set the via type to ‘Blind’ or ‘Buried’ in the PadVia properties. Altum distinguishes between blind vias (Top Layer to Mid-Layer 1) and buried vias (e.g. Mid-Layer 1 to Mid-Layer 2) using the ‘Start Layer’ and ‘End Layer’ properties.

5. Configure the design rules under Design > Rules to set the relevant rules for blind and buried vias:

• Routing > Routing Via Style: Define the diameter and hole size for vias between different layers.
• Manufacturing > Hole Size: Set a minimum hole size to ensure manufacturability.

6. Placing and Verifying Vias

When placing vias using the shortcut keys P+V, select the appropriate layer pair via the Properties panel. Once complete, run a Design Rule Check (DRC) to verify that the blind and buried vias comply with design rules and manufacturing requirements.

7. Manufacturing File Output
When generating Gerber files, tick all relevant layers (including inner layers) in the ‘Output Settings’ section, and annotate the drill positions and depths for blind and buried vias on the ‘DrillDrawing’ layer. Simultaneously,
generate an NC Drill file to enable the manufacturer to identify the via properties.

8. Points to Note

• Blind and buried vias increase manufacturing costs; it is necessary to confirm the manufacturer’s process capabilities (e.g. minimum hole diameter for laser drilling).
• In high-frequency designs, attention must be paid to impedance discontinuities caused by blind and buried vias; parameters can be optimised through simulation. Avoid excessive use of blind vias in the BGA area, as this may lead to stress concentration during soldering.

9. Example Parameters
Reference specifications for typical blind and buried via holes:
Laser drilling: diameter 0.1 mm to 0.2 mm
Mechanical drilling: diameter 0.2 mm to 0.3 mm
Recommended aspect ratio (hole depth to hole diameter): ≤1:1 (laser) or ≤10:1 (mechanical)