While both are circuit boards, HDI (High-Density Interconnect) boards differ significantly from regular PCBs. High-end smartphones and tablets all use HDI boards.
 
1. Different Design Density: Regular PCBs have relatively thick circuits and fewer layers. In contrast, HDI boards feature thinner traces and smaller vias, allowing more components to be placed in a limited space.
2. Different Process Difficulty: Regular PCBs mostly use through-holes, whereas HDI boards require blind vias, buried vias, and microvias, with extremely high precision requirements for the manufacturing process.
3. Different Application Scenarios: Regular PCBs are commonly used in conventional products such as home appliances and lighting power supplies. HDI boards, on the other hand, are widely applied in high-end miniaturized electronic products like smartphones, tablets, and wearable devices.