Printed Circuit Boards (PCBs) form the backbone of modern electronic devices, providing the physical platform for mounting and interconnecting electronic components. Among the essential elements in PCB design are vias—small holes that allow electrical connections between different layers of the board. Vias play a role in ensuring efficient routing of electrical signals, managing thermal performance, and optimizing space within complex multi-layer boards. This white paper delves into the various types of PCB via holes, including through-holes, blind vias, buried vias, and more, highlighting their applications, advantages, and considerations in PCB manufacturing and design.
Image 1 & 2 - Blind & Buried Vias and Through-Holes
“The primary purpose of vias is to facilitate the routing of
electrical signals between layers, allowing for more compact
and complex circuit designs." - Ryon Hu
1. Introduction to PCB Vias
Vias are conductive pathways that connect different layers in a 2-layer and multi-layer PCB. They are created by drilling holes through the PCB substrate and plating them with conductive materials, typically copper. The primary purpose of vias is to facilitate the routing of electrical signals between layers, allowing for more compact and complex circuit designs.
1.1 Importance of Vias in PCB Design
Signal Routing:
Vias enable the interconnection of components on different layers, optimizing the layout.
Thermal Management:
Thermal vias help dissipate heat from high- power components.
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Image 3 - Thermal Vias
Mechanical Support:
In some cases, vias contribute to the structural integrity of the PCB.
Image 4 - Via Mechanical Support
2. Types of PCB Via Holes
2.1 Through-Hole Vias
Through-hole vias are the most common type, extending from the top layer to the bottom layer of the PCB. These vias are drilled entirely through the board and plated to create a conductive path.
Image 5 - Through-Hole Via
Applications:
Widely used in both single-layer and multi- layer PCBs for general signal routing and component mounting.
Advantages:
• Simple to manufacture and cost-effective
• Strong mechanical connection, ideal for components subject to mechanical stress
Considerations:
• Occupy more space and limit routing on internal layers.
• May affect signal integrity in high- frequency applications due to increased inductance.
2.2 Blind Vias
Blind vias connect an external layer to one or more internal layers without passing through the entire PCB. These vias are drilled from the surface and stop at a predefined internal layer.
Image 6 - Through-Hole Via & Blind Via
Applications:
Used in high-density interconnect (HDI) PCBs where space optimization is critical.
Advantages:
• Maximizes routing space on internal layers
• Reduces board thickness and weight
Considerations:
• More complex and expensive to manufacture
• Requires precise drilling and alignment
2.3 Buried Vias
Buried vias are located entirely within the internal layers of the PCB and are not visible from the outer layers. These vias connect internal layers without affecting the external layers.
Image 7 - Through-Hole Via, Blind Via, and Buried Via
Applications:
Essential in HDI PCBs and complex multi- layer designs.
Advantages:
• Frees up space on the surface layers for additional routing or components
• Enhances signal integrity by reducing layer transitions
Considerations:
• Increases manufacturing complexity and cost
• Requires careful planning during the design phase
3. Specialized Via Types
3.1 Microvias
Microvias are extremely small vias, typically less than 150 microns in diameter. They
are often used in HDI PCBs to connect adjacent layers.
Image 8 - DR L2-7
Applications:
Smartphones, tablets, and other compact electronic devices.
Advantages:
• Allows for higher component density and miniaturization
• Reduces parasitic capacitance and inductance, improving signal integrity
Considerations:
• Requires advanced manufacturing techniques such as laser drilling
• Higher production costs compared to traditional vias
3.2 Via-in-Pad (VIP)
Via-in-pad involves placing vias directly beneath surface mount device (SMD) pads. This technique is commonly used in high- frequency and high-speed designs.
Image 9 - VIA-in-Pad (VIP)
Applications:
RF circuits, BGAs (Ball Grid Arrays), and fine-pitch components.
Advantages:
• Reduces inductive and capacitive effects, enhancing performance
• Saves board space and allows for more compact designs
Considerations:
• Requires filling and planarization to ensure a flat surface for soldering
• Increases manufacturing complexity and cost
This blog is an excerpt from the white paper Understanding PCB Via Holes: Through-Holes, Blind Vias, Buried Vias, and More. The full white paper includes two additional sections: Manufacturing Considerations and Design Guidelines & Best Practices.
Download the complete white paper today!
PCB via holes are fundamental to the functionality and performance of modern electronic devices. Understanding the different types of vias—through-holes, blind vias, buried vias, microvias, and via-in-pad—enables designers to make informed decisions that optimize electrical performance, mechanical strength, and manufacturing efficiency. As technology advances, the demand for more compact, high-speed, and reliable PCBs continues to grow, making the role of vias even more critical in the evolution of electronic design.
By considering the applications, advantages, and challenges of each via type, designers and manufacturers can create more efficient, durable, and high-performance PCBs tailored to the specific needs of their projects.