Via in Pad Impact the Thermal Performance of a PCB

Via in pad is a useful tool to reduce component size, improve PCB space utilization and increase signal conductivity. It is particularly valuable for high-speed and high-frequency designs that must maintain signal integrity. However, it does add manufacturing complexity and cost. For these reasons, it is critical that designers perform a comprehensive cost-benefit analysis to determine whether or not this technology is appropriate for their projects.

One important consideration is that via in pad has a very significant impact on the thermal performance of a circuit board. The presence of a thermal via causes the difference in temperature (DT) between the pad and any copper surface to drop dramatically. This lowers the pad temperature and raises the copper surface, making it harder to maintain a consistent, controlled temperature at the pads.

In fact, adding a single thermal via can actually decrease the overall temperature of a pad by up to 10oC. This is because the via acts as a thermal radiator that cools down the entire pad area by the thermal effect of convection and radiation. Similarly, multiple thermal vias can cancel out the benefits of one another because they have a similar effect on the pad temperature.

Does a Via in Pad Impact the Thermal Performance of a PCB?

For this reason, thermal vias should only be placed in areas of the board where they will benefit the overall design. Often, this will mean placing them in the power/ground plane and on the far side of the board so they can benefit from the greater surface area. However, it is important to keep in mind that the additional copper area created by a thermal via will also be exposed to the environment and may cause problems if not properly treated and maintained.

Using a via-in-pad technique also requires the use of specialized drilling equipment capable of creating small-diameter vias with precision. In addition, proper filling and plating techniques are needed to ensure reliable conductive paths within the vias. Lastly, careful solder mask selection is necessary to prevent trapped air from outgassing during assembly.

A common way to mitigate these risks is to implement an alternative DFM/DFA solution such as the widely used Dog-Bone Fanout instead of a traditional via in pad. This can help improve signal integrity and reduce parasitic inductance while maintaining the same level of thermal conductivity as a via in pad.

Another common concern is that the extra steps required to cap and fill the vias can add significant time and cost to the manufacturing process. This is especially true if the board uses multiple types of plated vias (e.g., blind vs. buried).

It is important to keep in mind that the additional cost of using via-in-pad is typically more than offset by the benefits. In addition to reducing the overall footprint of the circuit board, via-in-pad can lead to improved signal integrity, reduced heat generation and increased land for routing. In the end, it is up to the designer to evaluate each project and decide if the extra cost of using a via-in-pad is worth the added performance of the circuit board.