When sourcing mobile phone PCBs, you must prioritize High-Density Interconnect (HDI) technology, typically requiring Level 3 or higher to accommodate the compact nature of smartphones. Key specs include minimum trace width/spacing (often ≤0.05mm), blind and buried via configurations, and the use of high-frequency base materials (like Rogers or high-Tg FR-4) to ensure signal integrity for 5G connectivity. Additionally, verify the surface finish, such as ENIG (Electroless Nickel Immersion Gold), which is essential for the fine-pitch soldering required in mobile components.