PCB Via Types: Through-Hole, Blind, Buried, and Micro Via Explained

Vias are the vertical interconnects that carry signals and power between copper layers in a multilayer PCB. Choosing the right via type affects board density, signal integrity, manufacturing cost, and reliability. This guide covers every common via type and explains when each one is appropriate.

Through-Hole Via

The through-hole via is the most common and least expensive type. A drill bit penetrates all layers of the board, and the hole is plated with copper to connect the relevant layers. Through-hole vias are visible from both sides of the finished board.

• Standard size: 0.3mm finished hole / 0.6mm pad (12mil / 24mil)
• Minimum practical size: 0.2mm hole / 0.45mm pad (mechanical drill)
• Cost impact: None — included in base manufacturing cost
• Limitation: Consumes space on every layer, even if connection is only between two adjacent layers

Blind Via

A blind via connects an outer layer to one or more inner layers but does not pass through the entire board. It is visible from only one side. Blind vias save routing space on inner layers and are essential for high-density designs.

• Typical use: BGA fanout on 4+ layer boards where routing density is critical
• Manufacturing: Controlled-depth drilling or sequential lamination
• Cost impact: Adds 20–40% to board cost depending on quantity
• Minimum size: 0.1mm (laser) to 0.2mm (mechanical)

Buried Via

A buried via connects two or more inner layers without reaching either surface. It is invisible on the finished board. Buried vias maximize routing space on both outer layers but significantly increase manufacturing complexity.

• Typical use: High-density interconnect (HDI) boards, smartphones, tablets
• Manufacturing: Requires sequential lamination — inner layers are drilled, plated, and laminated before outer layers are added
• Cost impact: Significant — adds 50–100% to board cost

Micro Via

Micro vias are laser-drilled vias with a diameter of 0.1mm (4mil) or less. They typically connect only two adjacent layers and are the building block of HDI construction. Micro vias can be stacked (directly on top of each other) or staggered (offset between layers).

• Typical size: 0.075–0.1mm (3–4mil)
• Depth: Usually one layer pair (aspect ratio ≤ 1:1)
• Manufacturing: Laser drilling, typically CO2 or UV laser
• Cost impact: High — requires HDI manufacturing capability

Stacked vs Staggered Micro Vias

Stacked micro vias are aligned vertically and connected by copper filling, allowing connection across multiple layers in a small footprint. They offer the highest density but require copper fill and planarization at each via level. Staggered micro vias are offset, which is easier to manufacture but requires more routing space.

Via-in-Pad

Via-in-pad places a via directly within a component pad, typically for BGA fanout. The via must be filled with epoxy or copper and capped (planarized) to prevent solder wicking. This technique is essential for fine-pitch BGAs (0.5mm and below) where routing space between pads is insufficient for traditional fanout.

Choosing the Right Via Strategy

For 2-layer and simple 4-layer boards, through-hole vias are sufficient. For BGA designs with 0.8mm+ pitch, through-hole vias with fanout traces work well. Below 0.8mm pitch, blind vias or via-in-pad become necessary. Micro vias and buried vias are reserved for HDI designs where density demands them. Always confirm your via requirements with your manufacturer before finalizing your layout.