HDI Boards Affect PCB Design Complexity
The high-density PCB (HDI) trend allows electronic devices to shrink while maintaining performance and efficiency. However, the dense layouts of these advanced boards create unique design challenges that can impede production.
These challenges mainly center around signal and power integrity, caused by the close proximity of traces and components that must meet higher standards of electrical performance. Symptoms can include crosstalk, electromagnetic interference (EMI), reflections and other signal distortions that degrade the quality of data transmission.
To mitigate these issues, HDI designers need to use proper design for manufacturing (DFM) settings in their CAD tool, prioritize impedance-controlled routing and make sure the board meets all of its fabrication process requirements. They also need to optimize the layer count, implement thermal management strategies, and collaborate closely with fabricators throughout the design cycle.
With the tighter spacing of HDI traces, the type and amount of vias and the number of layers used, these designs require special expertise and equipment for manufacture. They also necessitate special materials, including thinner specialty dielectrics that are able to withstand the stresses of the high-speed signal paths.
How Do HDI Boards Affect PCB Design Complexity?
In order to keep the layer count as low as possible, some designers opt for a blind and buried via structure instead of the traditional through-hole. This reduces the overall PCB thickness and increases the routing density of the inner layers. However, it can increase the cost of the board, as these vias typically have to be capped and plated.
An additional option is to use a staggered via structure. While this option provides a lower overall layer count, it does not allow for the same level of routing density as a stacked via design. Another challenge with hdi board is the risk of signal loss and the need to ensure that return paths are as short as possible to minimize EMI susceptibility. These challenges are exacerbated by the fact that higher-speed signals must pass through more layers than lower-speed ones, and the signal-to-ground loop inductance must be minimized.
The density of an HDI board means that the designer must carefully construct the PCB stackup to provide adequate planes and a good return path for the signals. This is especially important for high-speed signals that may be impacted by noise, crosstalk, and line impedance mismatches. These issues can be reduced by placing the ground or power plane layer as close to the signal path as possible, using solid grounds below high-speed signals and making sure the signal and reference voltages are properly matched to prevent jitter.
EMI modeling is also useful for predicting and addressing these potential problems at the design stage. The right CAD tool can help with this by providing tools like impedance calculating, automated microvia placement and 3D visualization. This can be a big benefit for designers who must adhere to stricter signal integrity guidelines. Altium Designer offers all of these features and more.
