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PCB Via Types: Through-Hole, Blind, Buried & Microvias
PCB via types determine how electrical connections are made between different layers of a printed circuit board. From standard through-hole vias to high-density microvias, each structure provides different levels of routing density, board complexity, and manufacturing requirements. Understanding the differences helps engineers select the right via structure for multilayer and HDI PCB designs.
What Is a PCB Via?
A PCB via is a plated conductive structure that connects copper features on different layers of a printed circuit board. Vias allow signals, power, and ground connections to move vertically through a multilayer PCB.
The main difference between via types is where the via starts and ends within the board stackup. Through-hole vias span the full board thickness, while blind and buried vias connect selected layers. Microvias use a smaller, typically laser-formed structure for high-density interconnect applications.
Common Types of PCB Vias
Through-Hole Vias
A through-hole via extends from one outer surface of the PCB to the opposite surface. It passes through the complete board thickness and can connect selected copper layers along its path.
Through-hole vias are widely used because they offer a relatively straightforward and cost-effective solution for standard multilayer PCB designs. They are suitable for general signal routing, power and ground connections, and many conventional PCB applications.
The main limitation is that the via and its clearance area occupy routing space across multiple layers, which can become a constraint as board density increases.
Blind Vias
A blind via connects an outer layer of the PCB to one or more inner layers without passing through the entire board. Because the via is accessible from only one surface, it can provide more routing space on the inner layers and opposite outer layer.
Blind vias are commonly used when conventional through-hole vias cannot provide enough routing density, particularly around fine-pitch components and HDI structures.
Depending on the stackup and manufacturing process, blind vias can be formed using mechanical drilling or laser drilling.
Buried Vias
A buried via connects two or more internal PCB layers without reaching either outer surface. After the PCB is laminated, the via is completely enclosed within the board structure.
Buried vias allow designers to create layer-to-layer connections while keeping the outer surfaces available for components and routing. They are generally used in higher-density multilayer PCB designs where routing space is limited.
Because buried vias require additional fabrication steps and must be defined within the internal layer structure, their use should be coordinated with the PCB manufacturer’s manufacturing capabilities.
Microvias
Microvias are small vias primarily used in HDI PCB designs. They are typically formed using laser drilling and generally connect adjacent layers within a build-up structure.
Compared with conventional mechanically drilled vias, microvias occupy less board area and allow tighter routing around fine-pitch components. They are particularly useful for BGA fan-out, compact electronics, and high-density interconnect applications.
Microvias can also be arranged as stacked or staggered structures when connections need to extend across multiple build-up layers.
Advanced PCB Via Structures
Stacked Microvias
Stacked microvias are vertically aligned microvias placed directly above one another across multiple layers. This structure provides a compact vertical connection and minimizes the horizontal area required for multi-layer routing.
Stacked microvias are commonly used in advanced HDI designs where routing density is a primary concern. Because the interfaces between stacked structures require careful fabrication control, the stackup and via construction should be considered together with the PCB manufacturer’s capabilities.
Staggered Microvias
Staggered microvias are offset from one another rather than positioned directly on the same vertical axis. The offset creates a step-like connection between different layers.
This structure requires slightly more board area than stacked microvias but can simplify the interconnection between build-up layers and reduce some of the fabrication challenges associated with directly stacked structures.
Staggered microvias are widely used in HDI PCB designs where a balance between routing density and manufacturability is required.
Skip Vias
A skip via is a microvia structure that extends across more than one adjacent layer while bypassing an intermediate layer. It allows a connection to reach a deeper layer without creating a separate via connection on every intermediate layer.
Skip vias can be useful in high-density HDI routing when the stackup and routing requirements allow selected layers to be bypassed.
PCB Via Filling and Covering Methods
Via construction can also be classified by how the via opening is treated after drilling and plating. The appropriate method depends on the PCB structure, assembly requirements, and intended application.
| Method | Main Purpose |
|---|---|
| Open Via | Standard exposed via connection |
| Tented Via | Covers the via opening with solder mask |
| Resin-Filled Via | Fills the via with resin for structural and assembly requirements |
| Copper-Filled Via | Fills the via with copper for electrical and thermal performance |
Open vias are commonly used in standard PCB designs. Tented vias can help protect the opening and prevent unwanted solder or contamination from entering the via. Resin-filled and copper-filled vias are used when additional requirements such as via-in-pad structures, thermal transfer, or advanced HDI construction need to be addressed.
PCB Via Types Comparison
| Via Type | Layer Connection | Routing Density | Typical Application |
|---|---|---|---|
| Through-Hole Via | Top to Bottom | Low | Standard multilayer PCBs |
| Blind Via | Outer Layer to Inner Layer | High | HDI and dense routing |
| Buried Via | Inner Layer to Inner Layer | High | High-density multilayer PCBs |
| Microvia | Typically Adjacent Layers | Very High | HDI and fine-pitch components |
| Stacked Microvia | Multiple vertically aligned layers | Very High | Advanced HDI designs |
| Staggered Microvia | Multiple offset layers | Very High | HDI designs requiring improved manufacturability |
| Skip Via | Selected non-adjacent layers | High | Advanced HDI routing |
How to Choose the Right PCB Via
The right via structure depends on the PCB layer count, routing density, component pitch, stackup, and manufacturing requirements.
| Design Requirement | Recommended Via |
|---|---|
| Standard multilayer PCB | Through-Hole Via |
| Dense multilayer routing | Blind or Buried Via |
| HDI PCB | Microvia |
| Maximum routing density | Stacked Microvia |
| HDI with offset layer connections | Staggered Microvia |
| Selected-layer HDI routing | Skip Via |
For standard boards, through-hole vias are often sufficient. As routing density increases, blind, buried, and microvia structures provide greater flexibility. Advanced HDI designs may require stacked, staggered, or skip microvias to achieve the required layer-to-layer connections.
SLLPCB PCB Via Capabilities
SLLPCB supports a range of PCB via structures for conventional multilayer and high-density PCB applications.
| Via Capability | SLLPCB |
|---|---|
| Through-Hole Vias | ✓ |
| Blind Vias | ✓ |
| Buried Vias | ✓ |
| Microvias | ✓ |
| Stacked Microvias | ✓ |
| Staggered Microvias | ✓ |
| Skip Vias | ✓ |
| Resin-Filled Vias | ✓ |
| Copper-Filled Vias | ✓ |
Our engineering team can evaluate the required via structure together with the PCB stackup, routing requirements, component density, and manufacturing conditions to determine a practical solution for production.
PCB Via FAQs
What are the main types of PCB vias?
The main PCB via types include through-hole vias, blind vias, buried vias, and microvias. Advanced structures include stacked, staggered, and skip microvias, which are mainly used for high-density and HDI PCB designs.
What is the difference between blind and buried vias?
A blind via connects an outer PCB layer to an inner layer without passing through the entire board. A buried via connects internal layers only and does not reach either outer surface.
What is a microvia used for?
Microvias are mainly used in HDI PCB designs where conventional vias take up too much routing space. Their small size allows dense routing around fine-pitch components and high-I/O packages.
