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Via-In-Pad PCB Design

Via-in-pad is the design practice of placing a via in the copper landing pad of a component. Compared to standard PCB via routing, via-in-pad allows a design to use smaller component pitch sizes and further reduce the PCBs overall size. With component manufacturers pushing smaller parts every year and the demand from consumers for smaller devices, the usage of via-in-pad practices by hardware engineers has become more commonplace. In this article, we will discuss the differences between via-in-pad and traditional vias, when should you use via-in-pad, and how to design for it.

What are the different types of vias?

As a refresher, vias can be divided into three types: through-hole vias, blind vias, and buried vias, each of which implements different properties and functions and helps the overall best performance of the PCB and even electronics.

Through-Hole Via

This is the most common via type and is a hole drilled through all layers of a PCB. It is the simplest via type and is most cost-effective. It however takes up more space on your PCB, reducing the space required for components.

Blind Via

This via connects the external layers with the internal layers of the PCB without going through the whole PCB.

Buried Via

Buried vias connect internal layers of the PCB, are more complex to create, and come at a higher cost. These holes originate and end in the internal layers of the PCB and are not visible from the exterior.

For the increasing applications in small electronic products and finer pitch devices, vias in pad become very popular because they are a practical solution responsible for the electrical connection between traces in different layers. And many PCB designers like to use via-in-pad to increase PCB component density and save board space.

What is Via-in-Pad?

A via-in-pad is when a via is positioned directly on a surface-mounted component pad and plated with copper. In a traditional via, the trace carrying the signal is routed away from the pad (dog-bone style) and to the via.

The function of a via-in-pad is to reduce the form factor of the board, minimizing the space required for trace routing. VIPs find their application in BGA components with pitches of 0.5mm or lesser.

Why Was Via-In-Pad Developed?

The short answer: Space. As PCB designers increased the functionality, the number of layers used within the design increased. Even with the components placed on both sides, blind vias and buried vias still did not allow for enough surface space for all of the components to be placed.

What are the advantages of Via-in-Pad?

  • Fine pitch BGA higher pin counts trace connections are routed efficiently due to ultrasmall size of micro-via via-in-pad
  • High-Density Interconnect PCBs are not possible without via-in-pad
  • Components placement require less board area
  • Increase the performance and reliability of pcb board
  • Signal Integrity and quality is improved
  • Thermal management of PCB is improved by implementing via-in-pad
  • Via in pads are highly suitable for high-speed circuit design
  • Reduce the inductance and parasitic capacitance and loading

Conclusion

With electronic components ever-shrinking smaller, hardware engineers will need to utilize and learn new tools and techniques to implement these components in a reliable and scalable way. Via in pad allows the smallest component fan out possible with current PCB construction techniques. When looking at using via-in-pad techniques, consider the extra manufacturing cost and time that places on your product’s bill of materials. Make sure to work closely with your contract PCBA manufacturer as they will be able to give suggestions in regards to how via-in-pad can change the manufacturing process.