Navigating the Challenges of High-Density Interconnect (HDI) PCB Design

Across countless industries around the world, the demand for high-density interconnect (HDI) PCBs is expanding exponentially since traditional PCBs simply are not cutting it with today’s trends catering to shrinking devices and increased performance expectations.

These advanced circuit boards enable the packing into a smaller footprint by using finer lines, smaller vias, and more densely layered designs. They are in nearly every device where portability and high performance are essential, ranging from tablets and smartphones to complex medical and aerospace equipment.

The best aspect of HDI technology is how efficiently these PCBs utilize the available space without sacrificing speed or functionality. Stacking layers, blind and buried vias, and microvias are standard features that enable shorter signal paths and improved electrical performance, reducing interference and signal loss and thereby overall device reliability.

As electronic devices continue to shrink in size while also becoming increasingly powerful, HDI PCBs have become essential.

What are some of the biggest challenges in HDI PCB design, and how can these obstacles be overcome?

As high-density interconnect (HDI) PCBs play an increasingly significant role in the evolution of modern electronics, understanding the intricacies of HDI PCB design is a growing necessity. Due to a variety of factors, including the complexity of microvias and the need for optimal signal integrity, manufacturing these types of PCBs presents significant challenges.

Yet, with the right approach, these challenges can be surpassed. The following are some of the biggest challenges in HDI PCB design and explanations for how these obstacles can be overcome:

1. Routing Congestion Caused by High Component Density

Finding ways to create adequate space for routing can be complicated when placing components on an HDI PCB, and the density of your component layout can lead to various issues. Since you must fit a variety of components into a limited space, routing congestion is nearly impossible to avoid.

Despite this limitation, you must still be cautious about placing components strategically to avoid issues that will impact the device’s signal integrity. For instance, if you put sensitive components near sources of heat, close to the edge of the board, or too close to other elements, you may encounter various issues, such as crosstalk, EMI, and impedance mismatches.

You must consider the concentration of heat and proper thermal dissipation when placing your components; therefore, it is advisable to avoid routing critical lines, such as clock signals, grounds, or buses, through hotspots. Improper component placement can also lead to manufacturing defects, resulting in problems during the soldering and assembly stages of production.

To counter these issues, you can keep in mind the following guidelines relating to component placement:

• Group components together that have the same function and that connect to the same signal or have the same electrical characteristics.
• Keep 4 to 8 mil of spacing between traces and nearby components.
• Stay on top of clearance and space restraint violations with design rule-checking tools.
• Utilize integrated components, like COBs, SMDs, and BGAs.
• Keep noise-sensitive components away from noisy components.
• Place high-current components closer to the power plane.

2. Signal Integrity Issues Caused by Trace Impedance Mismatch

Signal integrity issues in PCBs are caused by faster signal rise times, and this challenge becomes increasingly common as the frequency increases. One of the most common problems related to HDI PCB design is unregulated line impedance, as impedance mismatches and signal reflections can occur at vias and connectors when high-speed signals are present or when trace widths change.

Another relatively common issue in densely routed boards is the coupling of adjacent traces, which leads to crosstalk, distorting signals, and negatively impacting overall performance.

Uneven line impedance can also result in high-speed signals facing skew when travelling across various trace lengths, which also leads to timing misalignment and synchronization problems during data transmission.

To tackle issues on signal integrity when you are working with high-density boards, you can employ the following strategies:

• Increase the spacing between high-speed signal traces.
• Use 3W as a minimum separation between adjacent differential pairs, and maintain a 30-mil keep-out zone from other signals or a 50-mil keep-out zone for clocks or periodic signals.
• Within a differential pair, keep the spacing between the traces to less than twice the width of a single trace.
• Keep traces that tend to be prone to crosstalk at right angles to one another.
• Keep serpentine traces a distance of at least four times their width away from adjacent copper.
• Surround sensitive traces with guard or ground traces.

3. Heat Dissipation Problems Caused by Inadequate Thermal Pathways

If your HDI PCB design features traces and components that are closely packed together, you must be aware of the potential for heat dissipation problems. Without sufficient thermal pathways, you may face elevated temperatures, localized hotspots, and thermal-related issues. Most PCB substrates have a low thermal conductivity of 0.3 to 0.6 W/M-°C, making them ineffective at conducting heat away from components.

Depending on how the layers are arranged in your high-density interconnect circuit board, this can impact the way heat is conducted, distributed, and dissipated, particularly with regard to power and ground planes. If there is an uneven distribution of layers, the thermal performance of the circuitry and its overall reliability will be negatively affected.

To ensure that your HDI PCB design prevents heat dissipation issues, take the following steps during your design process:

• Transfer heat between different layers using thermal vias.
• Use cooling fans to increase the airflow.
• Add heat sinks to components that generate heat, like switching devices.
• Distribute heat-generating components across your board rather than clustering them together.
• Keep the length of traces carrying high-power or high-current signals to a minimum.
• Adhere to IPC-2141 and IPC-4562 standards when selecting trace widths.
• For power and ground planes, use thicker copper.

How Circuits Central Can Help Simplify HDI PCB Design with Tailored Solutions

Although there are various potential challenges you may face during the HDI PCB design process, Circuits Central can help you overcome these issues with ease, simplifying the process with tailored solutions that result in high-performing HDI PCBs.

As a world-class PCB and electronics manufacturer with over 25 years of experience, we possess the knowledge, expertise, tools, and facilities to design and assemble even the most complex circuit boards. We can work closely with you to ensure that the particular needs of your boards are met.

Our engineers take an innovative approach to design, and we have helped clients from various industries to produce top-tier PCBs.

In addition to being the best source of help with your PCB design process, we can also handle PCB prototyping, PCB assembly, and post-manufacturing PCB testing. You can count on us to make the entire process, from start to finish, easy and efficient, ensuring you get the high-performing PCBs you need on time and without issues.

For more information about how we can help with HDI PCB design or to learn more about our PCB production facility, call Circuits Central at 1-888-602-7264 or contact us here.