Introduction

In the ever-evolving world of printed circuit board (PCB) manufacturing, advancements in design and technology continue to drive the development of more complex and efficient electronic devices. A key aspect of PCB manufacturing is the creation of vias — the electrical paths that connect different layers of a PCB. Two primary types of vias used in modern PCBs are Plated through-hole and  Hidden vias . These components play a critical role in ensuring that multi-layer PCBs can function correctly, and choosing the right via type can significantly impact both the performance and manufacturability of a circuit board.

In this blog, we will dive deep into the differences, advantages, applications, and manufacturing processes of Plated through-hole and Hidden vias. By the end, you will have a better understanding of how these technologies impact PCB designs and help engineers select the right type for their specific applications.

Through-Hole and Blind-Via

What Are Through-Hole Vias?

A through-hole via (also called a through-hole plated via) is the most common type of via used in traditional PCB manufacturing. This type of via creates an electrical connection between all layers of a multi-layer PCB by drilling a hole through the entire thickness of the PCB board. The hole is then plated with copper to establish the electrical path.

Manufacturing Process of Plated through-hole

The process of creating Plated through-hole involves several steps:

1. Drilling: A hole is drilled through the entire thickness of the PCB, from the top layer to the bottom layer. The size of the hole depends on the requirements of the circuit design and the components to be used.

2. Copper Plating: After drilling, the hole is plated with copper, either through an electroplating process or using a chemical method, to form the conductive pathway.

3. Etching and Cleaning: After the vias are plated, excess copper is removed by an etching process to ensure that only the required connections remain.

4. Final Testing: The board is tested to ensure that all vias have proper conductivity and that there are no shorts or defects in the electrical connections.

Advantages of Plated through-hole 

• Reliability: Through-hole vias are widely considered highly reliable for providing robust electrical connections in multi-layer boards. The connection spans the entire thickness of the PCB, which makes it highly stable.

• Cost-Effective: Plated through-hole are generally less expensive to manufacture than other types of vias, especially for less complex PCBs.

• Mechanical Support: The solid copper structure of through-hole vias can provide additional mechanical support to certain components, such as connectors, resistors, and capacitors, which are often placed in through-hole locations for durability.

Disadvantages of Plated through-hole

• Space Consumption: Because the via passes through the entire PCB, it occupies significant real estate on the board, which can be problematic in high-density designs. This space could be better utilized for routing traces or placing components.

• Increased Board Thickness: Plated through-hole require the drilling of large holes through multiple layers, which can increase the thickness of the PCB.

• Potential for Damage: The drilling process can cause mechanical stress on the PCB, which may lead to delamination or other forms of damage if not properly managed.

What Are Hidden vias ?

Hidden vias are a type of via that only extends through some of the PCB layers but does not go all the way through the board. Hidden vias are typically used in multi-layer PCBs, where they connect an outer layer to one or more inner layers, without extending to the opposite outer layer.

Manufacturing Process of Hidden vias

The process of creating Hidden vias is more complex than Plated through-hole, as it requires additional steps to ensure that the via does not break through the board completely. Here’s a breakdown of the blind via process:

1. Layer Stacking: The PCB is manufactured in layers. The outer layers are stacked first, and the inner layers are laminated to them.

2. Drilling: A hole is drilled to a specified depth, connecting the outer layer to one or more inner layers. The drill stops at a predetermined depth to prevent the hole from reaching the opposite outer layer.

3. Plating: The drilled hole is then plated with copper, just as in the through-hole process, but only the part of the hole that connects the inner layers will be plated.

4. Etching and Final Testing: As with through-hole vias, the excess copper is etched off, and the board undergoes testing to ensure the electrical connections are correct and there are no faults.

Advantages of Hidden vias

• Space Saving: Hidden vias occupy less space than Plated through-hole because they don’t go all the way through the board. This allows for more efficient use of PCB space, especially in high-density designs.

• Reduced PCB Thickness: Hidden vias can reduce the overall thickness of a PCB since they do not pass through the entire board, which can be beneficial in designs where thinness is critical.

• Improved Signal Integrity: Hidden vias are often used in high-speed and high-frequency circuits to reduce signal degradation. They are less likely to cause impedance mismatches compared to Plated through-hole, as the vias are generally shorter.

• Better Layer-to-Layer Connectivity: Hidden vias can offer better routing between layers, allowing designers to achieve more complex interconnections with fewer design constraints.

Disadvantages of Hidden vias

• Complexity and Cost: The process of manufacturing Hidden vias is more complex than that of Plated through-hole, often requiring more sophisticated drilling and plating techniques. This increases the cost of production.

• Limited Use in High-Density Designs: While blind-vias save space, they are generally not suitable for very high-density designs, where multiple vias may be required to interconnect numerous layers. In these cases, more advanced via technologies such as  Hidden vias  or microvias may be more appropriate.

• Potential for Yield Issues: The additional steps required to manufacture Hidden vias increase the risk of defects and reduced yield rates, as any drilling or plating errors could compromise the integrity of the via.

Plated through-hole vs. Hidden vias : When to Use Each

Both Plated through-hole and Hidden vias have their unique advantages and challenges. Choosing the right via type depends largely on the specific requirements of the PCB design and the application it is intended for.

When to Use Plated through-hole

Plated through-hole are ideal for:

• Low-Density Designs: For simpler PCBs with fewer layers, through-hole vias may be more appropriate, as they are cost-effective and easier to manufacture.

• Durability Needs: Through-hole vias are highly reliable and suitable for applications where mechanical strength and durability are critical, such as power supply boards or automotive electronics.

• Manufacturing Simplicity: Through-holes are often easier to manufacture compared to more complex via technologies. For low-cost or mass-produced boards, through-hole vias can be the best option.

When to Use Hidden vias

 Hidden vias are better suited for:

• High-Density Designs: When working with multi-layer PCBs that require complex interconnections, Hidden vias allow designers to save space and reduce the overall thickness of the board.

• High-Speed and High-Frequency Applications: Hidden vias are beneficial in applications where signal integrity is critical. Their shorter length and reduced risk of impedance mismatches make them ideal for high-speed digital circuits and RF applications.

• Advanced PCB Designs: Hidden vias are often used in more advanced PCB designs, such as those found in smartphones, tablets, and other compact, high-performance devices, where maximizing space is crucial.

Other Via Technologies: Microvias and Buried-Vias

While through-hole and blind vias are the most common types of vias, there are other more advanced via technologies that offer further improvements in performance and manufacturability. These include microvias and buried-vias.

Microvias

Microvias are small-diameter vias that are typically used in HDI (High-Density Interconnect) PCBs. These vias are generally made using laser drilling techniques and can be used to connect two or more layers in a PCB. They offer significant space savings and are well-suited for compact, high-performance designs. However, they can be more expensive and complex to manufacture than standard blind or through-hole vias.

 Hidden vias

 Hidden vias are similar to blind vias in that they do not go through the entire PCB. However, unlike blind-vias, Hidden vias are entirely contained within the inner layers of the PCB and do not reach the outer layers. This makes them ideal for complex, multi-layer designs, as they allow for dense interconnections without consuming precious space on the outer layers.

Conclusion

In conclusion, the decision between through-hole and Hidden vias comes down to the specific needs of a given PCB design. While through-hole vias remain a staple in traditional PCB manufacturing due to their cost-effectiveness, reliability, and mechanical strength, blind vias offer distinct advantages in high-density and high-performance designs, where space and signal integrity are paramount.

The growing demand for miniaturization, higher speeds, and increased functionality in electronic devices is pushing the limits of traditional PCB designs. As a result, technologies like microvias and Hidden vias are becoming more prevalent in advanced applications such as smartphones, wearable devices, medical electronics, and aerospace systems. These innovations allow designers to create ever more complex, compact, and powerful devices while maintaining signal quality and minimizing size.

It is also important to note that as PCB manufacturing techniques evolve, the choice of vias will likely become more interconnected with other aspects of PCB design, such as component placement, trace routing, and layer stacking. For example, HDI PCBs—which rely heavily on blind vias and microvias—are playing an increasingly important role in industries that require advanced technology, such as 5G communication, automotive electronics, and IoT (Internet of Things) applications.

Furthermore, manufacturers must balance performance requirements with cost considerations. While Hidden vias offer superior performance for high-speed and high-frequency applications, they come at a higher manufacturing cost due to the complexity of their production. As PCB technologies advance, however, costs may decrease, making blind and microvias more accessible for a broader range of applications.

For designers and manufacturers, keeping pace with these technological developments is critical. To succeed in an increasingly competitive and fast-moving market, PCB manufacturers must invest in the latest via technologies, refine their processes, and understand the trade-offs between cost, performance, and design complexity.

Finally, sustainability plays a crucial role in modern PCB manufacturing. As environmental regulations become stricter, manufacturers are turning to eco-friendly materials and processes to reduce waste and energy consumption. This shift to green manufacturing is not only essential for compliance but also enhances the reputation of companies committed to sustainable practices. By selecting the right via technology, manufacturers can improve both the performance and environmental footprint of their products.

In summary, choosing between through-hole and blind vias is just one aspect of the broader PCB design and manufacturing process. As technologies continue to evolve, PCB designers must leverage the right combinations of via technologies, materials, and processes to meet the demands of the next generation of electronics. By understanding the capabilities and limitations of different via types and staying informed about emerging trends, engineers can ensure that they are creating innovative, high-quality products that meet the needs of their customers and the market.

Plated through-hole and Hidden vias are two foundational technologies in PCB manufacturing, each with its own advantages and limitations. Through-hole vias offer reliability, mechanical support, and cost-effectiveness, making them suitable for simpler, low-density designs. Hidden vias , on the other hand, are better suited for high-density, high-speed applications where space-saving, reduced thickness, and signal integrity are priorities.

Understanding the characteristics of both types of vias, along with advanced technologies like microvias and buried-vias, allows PCB designers to make informed decisions and optimize their designs for performance, manufacturability, and cost-effectiveness. Ultimately, the right choice of via type will depend on the specific needs of the project, the complexity of the design, and the intended application of the PCB.

As technology continues to advance, the demand for more efficient, high-performance PCBs will only grow, making it essential for PCB manufacturers to continually explore and refine via technologies to meet the challenges of the future.

our linkedin sqpcb.com