What is PCB Via and Which Type Should You Choose?

Printed Circuit Board (PCB) design is a critical aspect of electronic product development. PCBs provide an organized and compact layout for electronic components, enabling efficient signal transmission and minimizing the risk of electrical interference. One essential element of PCB design is the via, a small hole drilled into the board that allows electrical connections between the different layers of the board.

In this article, we will provide a comprehensive overview of PCB via, including its types, design considerations, and applications. We will also discuss the importance of choosing the right type of via for your PCB design and how it can impact your product's performance and reliability.

What is a Via?

A via is a small hole drilled into a PCB that connects the different layers of the board. The via is lined with a conductive material, such as copper, that allows current to flow through the hole and establish a connection between the layers. Vias are essential in multilayer PCB designs as they provide a means for electrical and thermal connections between the different layers of the board.

Vias can be drilled through the entire thickness of the board, connecting all the layers, or they can be drilled partially through the board, connecting only a few layers. The size and shape of the via depend on the specific application and design requirements. Vias can be circular or non-circular, and their diameter can range from a few mils to several hundred mils.

The placement of vias is also critical in PCB design. Vias are typically placed in areas where there are no critical components or traces, as they can interfere with the signal or cause electrical noise. In addition, the location of vias can impact the board's thermal performance, making it important to consider the thermal requirements of the design when placing vias.

Types of Via in PCB

There   are several types of vias in PCB design, each with its unique characteristics and applications. The following are some of the most common types of vias in PCB design:

1. Through-hole Via:

The through-hole via is the most common type of via in PCB design. It is a hole that extends through the entire thickness of the board and connects all the layers. Through-hole vias are typically used for high-current connections or for providing mechanical support to the board. They are also useful in applications where there is a need for a solid, continuous connection between the layers.

2. Blind Via:

A blind via is a hole that connects the outermost layer of the board to one or more inner layers, but it does not extend through the entire thickness of the board. Blind vias are typically used in high-density PCB designs where space is limited. They allow for connections between the outer layers of the board and the inner layers, without the need for a through-hole via that takes up valuable board space.

3. Buried Via:

A buried via is a hole that connects two or more inner layers of the board, but it does not extend to the outermost layer of the board. Buried vias are useful in high-density PCB designs where there is a need for a large number of connections between the inner layers of the board. They offer a space-saving solution that allows for more connections without increasing the board's size.

4. Via-in-pad:

A via-in-pad is a hole that is located directly under a component's pad. Via-in-pad technology is useful in high-density PCB designs where space is at a premium. The via-in-pad allows for a more direct connection between the component and the board, reducing the length of the trace and improving the signal quality. It also reduces the risk of solder bridging, as the via is filled with conductive material during the assembly process.

5. Micro Via:

A micro via is a small diameter via that is typically less than 6 mils. Micro vias are useful in high-density PCB designs where space is limited, and there is a need for a large number of connections. They are also useful in high-frequency applications where signal integrity is critical.

6. Stacked Via:

A stacked via is a via that is created by drilling two or more holes that are stacked on top of each other. Stacked vias are useful in high-density PCB designs where there is a need for a large number of connections between the layers. They offer a space-saving solution that allows for more connections without increasing the board's size.

7. Via Tenting:

Via tenting is a process where the via is covered with a non-conductive material, such as a solder mask or epoxy, to prevent the ingress of contaminants or moisture. Via tenting is useful in harsh environments where there is a risk of corrosion or damage to the board. It also improves the board's appearance and reduces the risk of accidental short circuits.

Design Considerations for Via in PCB

When designing a PCB, it is essential to consider the via's design and placement. A poorly designed or placed via can impact the board's performance and reliability. The following are some of the critical design considerations for via in PCB:

1. Via Aspect Ratio Calculator:

The aspect ratio of a via is the ratio of the via's depth to its diameter. The aspect ratio affects the via's ability to conduct current and the plating thickness. A high aspect ratio via may require a more extended plating cycle, resulting in a thicker plating layer. A low aspect ratio via may have a thinner plating layer, which can affect the via's conductivity. A via aspect ratio calculator can help determine the optimal aspect ratio for a specific design.

2. Standard Via Sizes in Mils:

Standard via sizes are typically measured in mils, and they vary depending on the PCB's thickness and the manufacturer's capabilities. The standard via sizes can impact the board's manufacturing cost, yield, and reliability. It is essential to consider the manufacturer's capabilities when selecting the via size and to ensure that the via size is appropriate for the design requirements.

3. PCB Annular Ring Calculator:

The annular ring is the copper ring that surrounds the via. The annular ring's size is critical in determining the via's reliability and performance. A small annular ring can lead to a weak connection between the via and the copper pad, resulting in poor conductivity and reliability. A larger annular ring can increase the manufacturing cost and reduce the board's density. A PCB annular ring calculator can help determine the optimal annular ring size for a specific design.

4. Via Plating Thickness:

The via's plating thickness affects the via's conductivity and reliability. A thicker plating layer can improve the via's conductivity but can also increase the manufacturing cost and reduce the board's density. A thinner plating layer can reduce the manufacturing cost and increase the board's density, but it may affect the via's conductivity and reliability. It is essential to consider the plating thickness when designing the via and to ensure that it is appropriate for the application.

5. What is a Stub in PCB Layout:

A stub is an extra length of trace that connects to the via. Stubs can cause signal reflection and interfere with signal integrity, leading to poor performance and reliability. It is essential to minimize the length of the stub and to ensure that it is as short as possible. It is also critical to consider the impedance of the stub and to ensure that it matches the impedance of the trace.

What is Via-in-pad Design?

Via-in-pad technology is becoming increasingly popular in high-density PCB designs. In via-in-pad technology, the via is located directly under the component's pad, allowing for a more direct connection between the component and the board. This technology offers several advantages, including improved signal quality, reduced trace length, and reduced risk of solder bridging.

What is JLCPCB via-in-pad?

JLCPCB via-in-pad on 6- 20 layer PCBs are upgraded to POFV (Plated Over Filled Via) for free and will continue to be the free default for all upcoming high layer count boards. This means its costs will no longer be added to the total price whether it’s a sample or batch order, allowing everyone to truly enjoy the benefits of JLCPCB’s advanced fabrication.

The Advantages of Via-in-pad

Via-in-pad technology involves drilling a small hole in the pad and filling it with conductive material during the manufacturing process. This process eliminates the need for a separate via, reducing the board's size and improving its density. Via-in-pad technology also reduces the length of the trace, improving the signal quality and reducing the risk of interference and noise. Additionally, via-in-pad technology reduces the risk of solder bridging, as the via is filled with conductive material during the manufacturing process.

JLCPCB is a popular PCB manufacturer that offers free via-in-pad technology for high-density PCB designs.

Considerations for JLCPCB Via in Pad:

When using JLCPCB's via-in-pad technology, there are several considerations to keep in mind.

A. Minimum Via Size:

JLCPCB recommends a minimum via size of 0.2mm for via-in-pad technology. This size ensures that the via does not interfere with the component's soldering process and provides sufficient conductivity.

B. Minimum Annular Ring Size:

JLCPCB recommends a minimum annular ring size of 0.1mm for via-in-pad technology. This size ensures that the via has sufficient copper coverage, providing good conductivity and reliability.

C. Via Filling:

JLCPCB uses a conductive paste to fill the via during the manufacturing process. The conductive paste is carefully selected to ensure that it provides good conductivity and does not cause any adverse effects on the component or the board.

D. Component Clearance:

When using via-in-pad technology, it is essential to consider the component clearance to ensure that the via does not interfere with the component's placement or operation. JLCPCB recommends a minimum clearance of 0.1mm between the via and the component's pad.

E. Solder Mask:

JLCPCB recommends that the solder mask opening be slightly larger than the component's pad to ensure that the paste does not overflow onto the adjacent pads.

F. Via-in-pad Limitations:

JLCPCB's via-in-pad technology has some limitations. It is not suitable for components with large pads or for components that require a large amount of solder paste. In addition, via-in-pad technology may not be suitable for applications that require high reliability or high current.

Conclusion:

Choosing the right via for your PCB design is a critical decision that can impact the board's performance, reliability, and manufacturing cost. When selecting a via, it is essential to consider the specific requirements of the application, the PCB manufacturer's capabilities, and industry standards and best practices.

Working closely with the PCB manufacturer and following best practices and industry standards can help ensure that the selected via is optimized for the specific application and provides reliable operation.