As electronic devices continue to shrink in size while increasing in complexity, traditional PCB designs often fall short. That’s where microvia PCBs come in. Microvias enable engineers to create high-density interconnects (HDI), reduce board size, and improve electrical performance. Understanding the microvia PCB layer structure is crucial for developing compact and reliable products.
In this microvia PCB layer structure guide, we’ll explain how microvias work, how they’re integrated into multilayer boards, and how manufacturers like Viasion ensure performance and reliability in every design.
What Is a Microvia?
A microvia is a very small via, typically with a diameter of 150 microns (0.15 mm) or less, that connects one layer of a PCB to the next. Unlike traditional through-hole vias that span the entire board, microvias are drilled using lasers and are used only between adjacent layers. This makes them ideal for use in HDI PCBs, which require more connections in less space.
Microvias are classified into three main types:
- Blind vias: Connect an outer layer to an inner layer but don’t go through the entire board.
- Buried vias: Connect two inner layers and are not visible from the surface.
- Stacked microvias: Multiple microvias stacked directly above one another to connect more than two layers.
- Staggered microvias: Multiple microvias offset between layers to reduce stress and improve reliability.
Importance of Microvia Layer Structures
The structure of a microvia PCB refers to how the microvias are integrated within the multilayer stack-up. This structure is essential for:
- Signal integrity: Ensuring minimal resistance and signal loss in high-speed circuits.
- Space efficiency: Reducing board size by utilizing vertical connections.
- Thermal management: Offering better heat dissipation paths through tighter layouts.
- Mechanical strength: Preventing via collapse or cracking under thermal and mechanical stress.
As the number of layers increases in HDI PCBs, the correct microvia strategy becomes even more critical.
Typical Microvia PCB Layer Structures
Here’s an overview of common layer structures used in microvia PCBs:
- 1+N+1 HDI
This is the most basic microvia structure, with one build-up layer on each side of a central core (N layers). It uses blind microvias from the surface to the adjacent inner layer.
- 2+N+2 HDI
This structure has two build-up layers on each side of the core, often using stacked or staggered microvias. It’s suitable for more complex routing and higher component density.
- Any-Layer HDI
In this configuration, microvias can be used between any two layers of the PCB. It allows full routing flexibility and is commonly used in advanced smartphones, tablets, and medical devices.
Each of these structures must be carefully designed to balance electrical, thermal, and mechanical demands, particularly in high-frequency and high-density applications.
Microvia Filling and Plating
Once microvias are laser-drilled, they are filled and plated. Two common filling methods include:
- Copper-filled microvias: Offer better current handling and structural support, often used in stacked microvia designs.
- Non-conductive resin-filled: Used when mechanical support is needed but current flow is not required.
At Viasion, engineers precisely control this process to ensure reliability, even in boards with dozens of layers and tight tolerances.
Challenges in Microvia PCB Design
Despite their benefits, microvias come with their own set of challenges:
- Via cracking: If not properly filled or plated, microvias can crack under thermal cycling.
- Registration accuracy: Laser drilling and layer alignment must be extremely precise, especially for stacked vias.
- Cost: The materials and processes involved in fabricating microvia PCBs are more advanced and costly than traditional boards.
This is where the experience of your manufacturing partner becomes invaluable.
Quality Assurance at Viasion
At Viasion, a reliable and experienced PCB manufacturer, microvia PCBs are fabricated using state-of-the-art HDI processes and laser drilling equipment. The following practices ensure robust and reliable microvia layer structures:
Advanced Laser Drilling
Viasion uses precise CO₂ and UV laser drilling systems capable of producing microvias with clean walls and tight diameters. This ensures strong interconnections and minimal signal loss.
Automated Layer Alignment
Misaligned microvias can lead to circuit failure. Viasion’s advanced registration systems ensure accurate alignment between layers during lamination and drilling.
Controlled Plating and Filling
Whether it’s copper-filled for electrical connectivity or resin-filled for structural strength, Viasion uses highly controlled electroplating and filling processes for consistent results.
Reliability Testing
To meet IPC-6012 and other international standards, microvia boards at Viasion are tested through thermal cycling, cross-sectioning, and microvia integrity analysis.
Applications of Microvia PCBs
Microvia PCBs are ideal for:
- Smartphones and tablets: For compact layout and high-speed signals.
- Wearable electronics: Where space and performance must be balanced.
- Medical devices: Offering reliable connections in compact packages.
- Automotive electronics: Particularly in infotainment and advanced driver-assistance systems (ADAS).
- Telecommunication equipment: Where signal integrity is paramount.
If you’re developing a device that requires miniaturization and multi-layer routing, microvia PCB designs are likely the best solution.
Final Thoughts
Understanding the microvia PCB layer structure is essential for building compact, powerful, and reliable electronics. Microvias enable the next generation of electronic products by allowing higher component densities, improved thermal performance, and better signal integrity.
At Viasion, you gain access to a team of experts with deep knowledge in HDI and microvia PCB fabrication. Whether you’re building a prototype or scaling up production, Viasion’s capabilities ensure your project is delivered with precision, performance, and durability.
When you’re ready to explore microvia PCBs, Viasion is ready to help you design and manufacture boards that meet your exact specifications.
