Originally published at: https://www.protoexpress.com/blog/hdi-pcb-routing-challenges/
HDI designs pose complex routing challenges due to their tight spacing between components and traces. The use of DRC settings in advanced design tools, opting for smaller packages, implementing thermal management strategies, and early collaboration with manufacturers can help you navigate through these challenges. Highlights: Route adjacent differential signal pairs with a 3W separation to minimize cross-coupling effects. Prefer integrated components such as SMDs, BGAs, and chip-on-board to minimize space usage. Consider advanced dielectric materials with higher thermal conductivity, like Isola I-Tera MT40, for power and ground planes for improved thermal performance. 5 HDI PCB routing challenges with solutions 1.…
Given the potential for increased heat generation in 5G devices, how do you address thermal management in HDI designs, and what impact does it have on routing configurations?
What are the key considerations when routing microstrip and stripline traces in HDI boards for RF applications?
To address increased heat generation in 5G devices, especially in HDI designs with smaller BGA sizes and higher processing power, large Cu surfaces and air gaps are utilized to efficiently transfer and dissipate heat. A few strategies, such as using low-height components surrounding the BGA, keeping a few solder masks open at the bottom of the BGA’s, utilizing ground planes as heat sinks, implementing thermal vias for QFN ICs, transferring heat to metal chassis, and using untented vias can aid in effective heat dissipation. Further, increasing the number of vias on the power plane helps mitigate hotspots. These strategies can influence the spatial arrangement of components and how they are connected. Additionally, thermal considerations often lead to adjustments in trace widths and spacing to disperse heat effectively while maintaining optimal signal integrity.
Striplines are generally avoided for SMA connections in RF applications, and microstrip configurations are preferred. It has to follow a co-planar structure where vias are added at a regular interval on the boundary of the two Cu ground pours with a spacing less than λ/10, where λ is the wavelength of the highest frequency content in the signal. Typically, we maintain a spacing of 20-30 mils for vias to ensure optimized routing space in internal layers. In cases of through-hole SMA connectors, it’s crucial to avoid unintended stubs. If stubs are unavoidable, their length must be carefully managed based on the signal frequency requirements. The length of the trace should be as short as possible. Additionally, incorporating reference planes on adjacent layers is essential for optimal performance.