Via types (through-hole, blind, buried) in PCB Design - Full Explanation

Introduction

When designing printed circuit boards (PCBs), connecting different layers is essential for electrical signals to travel. Choosing the right type of via helps solve the problem of how to link these layers efficiently without wasting space or increasing manufacturing complexity.

Explanation

Through-hole vias

Through-hole vias are holes drilled all the way through the PCB from the top layer to the bottom layer. They connect every layer in between, allowing signals to pass through the entire board. These vias are the simplest and most common type, but they take up space on all layers they pass through.

Through-hole vias connect all layers by passing completely through the PCB.

Blind vias

Blind vias connect an outer layer of the PCB to one or more inner layers but do not go all the way through the board. They start on the surface and stop before reaching the opposite side. This saves space on the unused layers and helps keep the board compact.

Blind vias connect outer layers to inner layers without passing through the entire board.

Buried vias

Buried vias connect only inner layers inside the PCB and are not visible from the outside. They do not reach the outer surfaces, which helps maintain a clean board surface and allows for more complex layer connections inside. These vias require more advanced manufacturing steps.

Buried vias connect only inner layers and are hidden inside the PCB.

Real World Analogy

Imagine a multi-story building where people need to move between floors. Through-hole vias are like staircases that go from the ground floor all the way to the top floor. Blind vias are staircases that start on the ground floor but only go up a few floors, not reaching the top. Buried vias are hidden elevators inside the building that only connect middle floors without any doors on the ground or top floors.

Through-hole vias → Staircases going from the ground floor to the top floor, connecting all floors.

Blind vias → Staircases starting at the ground floor but stopping before the top floor.

Buried vias → Hidden elevators connecting only middle floors without access from outside.

Diagram

Diagram

┌───────────────┐
│ Top Layer     │
├───────────────┤
│ Inner Layer 1 │
├───────────────┤
│ Inner Layer 2 │
├───────────────┤
│ Bottom Layer  │
└───────────────┘

Through-hole via: │ drilled through all layers
Blind via:       │ drilled from top layer to inner layer 1
Buried via:      │ drilled between inner layer 1 and inner layer 2 only

A stack of PCB layers showing where through-hole, blind, and buried vias connect layers.

Key Facts

Through-hole via → A via that passes through all layers of the PCB from top to bottom.

Blind via → A via that connects an outer layer to one or more inner layers but does not go through the entire board.

Buried via → A via that connects only inner layers and is not visible from the outer surfaces.

PCB layer → A single conductive or insulating sheet within a multi-layer printed circuit board.

Via → A small hole in a PCB that allows electrical connection between different layers.

Common Confusions

Believing blind vias go through the entire PCB.

Believing blind vias go through the entire PCB. Blind vias only connect from an outer layer to inner layers and stop before reaching the opposite side.

Thinking buried vias are visible on the PCB surface.

Thinking buried vias are visible on the PCB surface. Buried vias are completely inside the PCB and do not appear on the outer layers.

Summary

Through-hole vias connect all layers by drilling through the entire PCB.

Blind vias connect outer layers to inner layers without passing through the whole board.

Buried vias connect only inner layers and remain hidden inside the PCB.