What is a Blind Via PCB? A Complete Guide

As electronic circuits become smaller, the demand for high-density PCBs keeps soaring. One of them is the blind via PCB. This board optimizes routing options, allowing more components and connections without sacrificing space. As you’ll also learn below, it has numerous applications in modern electronics despite costing more to create.

What is a Blind Via in PCB?

A PCB blind via is a tiny layer-interconnect hole that starts on an outer layer and terminates inside the board. In other words, it doesn’t go through the PCB. Unlike through holes, the blind via is only visible on one side.

Vias, or “vertical interconnect access,” holes are drilled in PCBs mechanically or using laser technology. It connects desired layers electrically. They reduce the need to crowd the board surface with numerous traces and connections.

The blind via hole goes a step further. It saves space, optimizes signal quality by reducing stubs, and several other benefits. These properties make it suitable for high-density, compact circuits.

Difference between a Buried and Blind Via PCB

The difference between a buried via and a blind via is their placement. A buried via exists inside the board, connecting the inner layers. As such, it remains hidden. A blind type comes out on one side.

A buried via is also more challenging to make than a blind type, given its position. It requires detailed design considerations and unique board fabricating steps. It also makes the board more expensive to manufacture.

How are Blind Vias Made

PCB manufacturers use various methods to create blind vias depending on the required results and cost calculations. That’s because each technique, whether contact or non-contact, like laser drilling, has its benefits and limitations, as explained below.

Photo-Defined Vias

These are created by etching a resin-covered laminate. The fabricator bonds a photopolymer to the substrate and covers it with a pattern indicating the “via” locations. Exposing the photoresist to UV light hardens the material, leaving the “vias” soft.

Immersing the exposed board in an etching solution selectively removes material, creating the vias. Photo-defined holes are best for BGA packages and similar parts. They’re more cost-effective, especially when only a few holes are required.

Controlled Depth Vias

They use a procedure similar to creating through holes, with the difference being the need for depth control. Mechanical bits positioned above pads drill the vias to a predetermined level, taking care not to cause damage.

Mechanical drilling is the cheapest hole-creation method, even when it involves partial drilling. However, it has its limitations. For instance, you can only use it if the diameter is too small, such as when making micro-vias. In such cases, laser drilling is the better technology.

Sequential Lamination Vias

Sequential lamination involves drilling and etching thin laminates, one at a time. The first laminate only has one side processed while the other remains untouched. This first board will form layer one, with the untouched side facing out.

Another layer goes through the same process, and so on, until the fabricator achieves the required number of laminations. Bonding the boards together creates the desired multilayer PCB with blind holes.

Laser Drilled Vias

The PCB maker may also use the extreme heat of lasers to vaporize laminate material and create partial holes. Laser drilling makes the smallest openings. It’s also the fastest of the methods discussed here.

There are two leading laser-drilling technologies: Excimer and CO2. The Excimer laser is more powerful and used to drill laminates layered with copper foil. A CO2 laser cannot drill copper. It’s, therefore, best used before plating the core.

PCB Blind Via Fabrication Process

The steps for blind via PCB fabrication depend on the method used to create the holes. The following sequence describes the various stages from when the board is sized to when it undergoes the coating procedure to protect it.

• Pieces of laminates, such as FR4, are sized and, using photolithography, patterned with traces
  
• Several laminates are bonded together under intense pressure to create multilayer boards
  
• The boards go through a drilling process using one of the methods discussed earlier
  
• The resulting via holes are plated to make them conductive and connect the layers
  
• The boards are then covered with photoresist and etched to produce the outer traces
  
• The next step involves applying a solder mask to protect the conductive paths
  
• The fabricated PCBs are coated with a protective finish and silk screen layer
  
• In the final step, the boards are given the final touches that include profiling
  
• They are then checked and tested before packing them as bare boards
  
• The manufacturer may also assemble the PCBs with components
  

What are the Benefits of Blind Via PCB?

Printed circuit boards with blind vias are valuable when creating boards for complex electronic devices and systems today. They offer benefits that range from space savings to improved performance and routing simplicity. These benefits are discussed in detail below.

Space Optimization

The vias only appear on one side, unlike through holes. This construction saves board space and packs more components. It enables the creation of circuits that cater to the needs of modern electronics, such as portable devices.

Enhanced Electrical Performance

Partial holes control impedance, ensuring efficient energy delivery and distribution across the board and between power planes. This benefit improves the circuit board’s overall electrical performance, making it more reliable.

Routing Efficiency

It simplifies routing. Unlike through holes, blind vias only go through layers they connect to, making routing more effective. It reduces routing inefficiencies and makes connecting parts easier.

Improved Signal Quality

The shorter hole length and size reduce parasitic capacitance. That, in turn, improves signal strength and quality by minimizing degradation and reflections. It makes these board types fit high-speed signal applications or data rate circuits.

Blind Via PCB Disadvantages

The use of blind vias has a few disadvantages you must know of. They include the challenges fabricators face when creating the board and the increased manufacturing costs that make it a more expensive PCB type.

Manufacturing Complexity

They are more challenging to produce, requiring additional manufacturing steps than standard boards using through holes. The holes are more difficult to plate, given their depth and size. They may also trap air and cause soldering problems, such as opens.

Increased Cost

The complexity of blind via circuit boards increases manufacturing costs, making them more expensive than other boards. That said, selecting a less expensive drilling technology can help reduce the high blind via cost.

Blind Via PCB Applications

Blind via PCBs are high-density-interconnect (HDI) boards with many components and signal lines packed in small spaces. They mount complex components, such as integrated circuit chips (ICs), allowing manufacturers to produce more compact circuit boards.

This construction makes them usable in compact electronic gadgets like smartphones, tablets, laptops, cameras, etc. They are also critical parts of medical devices, industrial automation systems, robots, and telecommunications.

Other industries that need this PCB type include automotive, aerospace, and military. Generally, the board is valuable in any application that requires increased connections in a smaller space.

Conclusion

The blind via PCB is becoming increasingly popular as the world moves into smaller electronic devices and systems. These electronic circuits are also more complex. Although a more expensive type than a through-hole board, it has various advantages, such as space savings, better signal quality, and other benefits.