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What is a PCB Via? A Complete Guide!

Vias in a PCB Board

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PCB has various components placed on it and every component is connected through conducting paths. It’s a challenging task to connect every component in the circuit board minimizing interference, distortion, and noise. In multilayer PCB, connecting the layers is even more difficult. Thus, vias are there to solve this challenge of connecting the various layers through conducting paths.

What are Vias in PCB Design?

Vertical Interconnect Access (Vias) are the small holes that are drilled through the board that allow the electrical connections in between the various layers of PCB. It helps with proper electrical connection to travel between the layers. Multilayer PCB has independent layers, thus the vias work as a bridge to establish connections.

Friends who have played Mario will probably understand the principle of connecting water pipes. The difference is that water pipes are to allow water to flow, while the purpose of connecting circuit boards is to conduct electricity, so they are called “conductive holes.” In order to conduct electricity, a layer of conductive material (usually copper) must be electroplated on the drilled surface. This allows electrons to move between the different layers of copper foil, since the surface of the original drilled hole is only the resin, which is not conductive.

Vias allow designers to optimize the PCB layout, minimize signal interference, and maximize spatial efficiency. Vias play a crucial role in maintaining the accuracy of the transmitted signal, in high-speed digital circuits, where signal integrity matters the most. Vias maintains the performance and reliability of the electronic system by routing signals through multiple layers on the circuit board.

Importance of Vias in PCB Design

The importance of Vias in PCB design is crucial. Some of the major key aspects of Vias include:

Signal Routing

Vias enables electrical signal routing between various layers of PCB. Vias provides the necessary pathways for signals allowing optimized signal paths and minimizing signal degradation.

Power Distribution

Vias facilitate the power distribution throughout the PCB. They help to route the power between various layers and ensure all components receive the required power supply for operations. It is important in devices with high power requirements like high-performance integrated circuits and microprocessors.

Space Optimization

It helps to optimize the space on the PCB. It allows the signal and power to be routed through multiple layers. Vias helps the designers to create a more compact, and densely packed circuit board. It benefits when there is limited space like wearable devices, smartphones, tables, and more.

Signal Integrity

Maintaining signal integrity is crucial for reliable data transmission, especially in high-speed digital circuits. Vias help to maintain signal integrity by reducing noise and interference, signal distortion occurring through signal propagation.

Manufacturability

Vias help to maintain the manufacturability of multilayer PCBs. It helps to create interconnections between various layers. The advancements in Via technologies like blind and buried vias have expanded the design possibilities and capabilities of PCB manufacturers.

Types of Vias in PCB Design

Vias, also called metallized holes, is one of the important elements of PCB design. In double-sided and multi-layer PCB boards, in order to connect the printed wires between each layer, a common hole, that is, a via hole, is drilled at the intersection of the wires that need to be connected in each layer. Commonly vias are divided into five categories, namely blind vias, buried vias,  through hole vias, microvias and via in pad. Let’s see a picture of some vias in a multilayer PCB.

All types of vias in pcb design

Blind Vias

A Blind via PCB is drilled from one side and connects the inner layer of the circuit board. It doesn’t pass through the whole circuit board. They are visible from one side only. It helps to make use of extra space on the PCB by enabling the connections between the layers. They are commonly used in BGA assembly.

Buried Vias

Buried Vias connect the inner layers of the circuit board without penetrating the outer layers. It maximizes the space utilization. Buried vias are crucial for high-density PCBs. It enhances the routing flexibility without sacrificing the surface area. It is useful for PCBs with dense routing. Buried vias offer greater space savings as compared to blind vias. They don’t cover any surface area on the outer layers.They are commonly used on high-density PCB designs where maximizing the signal layers is important to route the complex circuits.

Through Hole Vias

This is the most common type of vias. Such vias are also relatively cheap, but sometimes the layers do not need to connect these vias. For example, we have a six-story house, and I bought the third and fourth floors. I want to design an internal staircase to only connect the third and fourth floors. To me, the space on the fourth floor is used up by the original stairs on the first and sixth floors. So although through hole vias are cheap, they will use up more PCB space.

Through-hole PCB vias extend through all layers of PCB and connect the traces on various layers. It is bigger than the blind and buried vias. They are easier to observe from the naked eye as they have larger dimensions than other vias. They are simple to make and the process can be continued starting from the top layer to the bottom layer. It means it doesn’t need to stop the drilling process at the desired points. Through-hole vias provide strong mechanical support. They provide suitable applications where mechanical strength and reliability are essential, such as in industrial electronics and automotive electronics.

Microvias

Microvias are very small vias that are used to connect different layers of a multilayer PCB. They have a diameter of less than 0.15 mm and a depth-to-diameter ratio of 1:1 or less, and the maximum depth of the start and stop layers does not exceed 0.25mm. They are typically formed by laser drilling or photoimaging. They enable high-density and complex PCB designs, especially for applications that require miniaturization, such as smartphones, wearables, or IoT devices.

Microvias can improve the PCB performance and functionality by reducing the space and routing disruptions caused by traditional through-hole vias. They can also enhance the thermal and electrical properties of the PCB by providing better heat dissipation and signal integrity.

What is a microvia hole?

Via-in-Pad (VIP)

Via in pad is a technique that places a via directly in the metal pad of a surface-mount component. This technique can save space and reduce the trace length, which can improve the signal integrity and thermal management of the PCB. However, it also poses some challenges, such as soldering difficulties and potential reliability issues.

VIP technology reduces the overall size of the PCB by eliminating the need for additional vias and simplifying the routing of critical signals. It is suitable for high-speed and high-reliability applications such as high-frequency RF circuits and fine-pitch BGAs (Ball Grid Arrays).

what is via in pad - a diagram of via in pad

How is Via Manufactured?

The manufacturing process of vias includes various factors like:

  • Drilling: At first, small holes are drilled through the PCB layers to the precise locations. This is carried out based on design requirements. These holes serve as a pathway for the vias.After drilling, the PCB is cleaned to remove any kinds of residue and debris left from the initial drilling process. The contamination could affect the conductivity of the It ensures the vias are free from the contaminations.
  • Plating: With conductive materials like copper, the drilled holes are plated. This plating is important for establishing the continuous electrical connection between the PCB layers. It prevents the vias from oxidations and also strengthens the vias.
  • Etching: The excess copper is etched away for the surface of the PCB. It leaves only the vias and traces behind. It helps to define the desired circuitry and also ensures the vias are properly integrated into the PCB layout.
  • Surface Finish: Finally, the PCB may undergo surface finishing processes to improve its solderability and protect it from environmental factors such as oxidation. This step helps ensure the long-term reliability of the vias and the overall integrity of the PCB.

The plating process can vary depending on the type and size of the via.

Considerations for Vias in PCB Design

Aspect Ratio:This refers to the ratio of the depth of the via hole to its diameter. A higher aspect ratio indicates a deeper hole relative to its width. Designing vias with appropriate aspect ratios is crucial to ensure proper plating and reliability during fabrication. 0.75:1 is the ideal aspect ratio for the micro via and 10:1 is the ideal aspect for through-hole vias.

Size and Diameter: The size and diameter of vias depend on the specific application and the manufacturing capabilities. Smaller vias like micro vias are suitable for high-density PCB designs. On the other hand, larger vias are required for high-current applications.

Placement and Spacing: Vias should be strategically placed and spaced to optimize the signal routing. It should minimize signal integration and also ensure proper manufacturability. The proper placement and spacing help to maintain the signal integrity and also prevent electrical noise.

Thermal Considerations: In designs like high-power components, vias can affect the thermal performance of a PCB. Proper thermal management consists of size considerations and vias density. It helps to properly dissipate the heat effectively and thus prevents them from thermal issues like hot spots.

Signal Integrity: Vias can introduce impedance discontinuities or signal reflections impacting the signal integrity. Designing the vias with proper sizes, spacing, and configurations helps to minimize signal degradation. It maintains the signal integrity throughout the PCB.

Annular Ring: The annular ring is the pad area surrounding the drilled via hole. It plays a crucial role in ensuring proper soldering and electrical connectivity. Designing vias with sufficient annular ring size helps prevent issues such as solder voids and poor solder joints.

Standard Via Size in Mils: The standard size of vias is often expressed in mils (1 mil = 0.001 inches). The specific size of vias varies depending on the application, PCB design requirements, and manufacturing capabilities. Standard via sizes typically range from a few mils to several tens of mils in diameter, with smaller vias being common in modern high-density PCB designs.

Conclusion

Vias play a crucial role in PCB design. Vias in PCBs are microscopic bridges that allow electricity to travel between different layers of the circuit board. They are extremely important because they ensure that signals, electricity, and heat travel around efficiently while also saving space and keeping everything running properly. PCB designers and manufacturers must consider factors such as size, placement, and material. Getting these elements helps ensure that the PCB functions properly and lasts a long time.

For all your PCB design and manufacturing needs, trust ElePCB. Our expert team ensures high-quality, reliable PCBs tailored to your specifications. Contact us today to bring your designs to life!

Q1: What are vias in PCB used for?

A1: It helps to establish the electrical connections between the various layers of the board. Besides, it also enables signal routing, also enabled power, and ground planes throughout the circuit.

Q2: Which materials are used to make Vias?

A2: Vias are typically made with conductive materials like copper for plating. For the substrate, manufacturers use non-conductive materials like epoxy resin. The combination of materials helps to create the electrical pathways in between the various layers of PCB providing the proper structural and insulation support.

Q3: Do Vias only exist in multilayer PCB boards?

A3: No. The use of Vias is more common in multilayer boards, which have multiple copper layers that require connections between these layers by Vias. In double-sided PCBs, vias are usually used to connect the top and bottom circuits for signal transmission or component connection. In single-sided PCBs, vias are used relatively rarely and are usually only used to connect the component leads on the circuit board to the pads on the bottom layer.

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Irene Shi
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