Today, smartphones are more than 6 mm thick and pacemakers are smaller than a button, and cutting-edge substrates called HDI (high-density interconnect) boards support these electronic wonders. Compared with traditional PCBs (printed circuit boards), HDI (High Density Interconnector)technology is reshaping the physical limits of the electronics industry. Spatial reconstruction, signal revolution, and manufacturing transformation drive this fundamental difference.

Spatial Density:

Ordinary PCBs function like multi-story apartment buildings, using ‘stairwells’ (mechanically drilled through holes) that penetrate layer stacks to interconnect circuit levels.These holes, which are usually larger than 0.2mm in diameter, not only take up valuable board space, but also force the wires to take detours, resulting in limited wiring density – line width/spacing is mostly above 100μm.

HDI boards are like precise three-dimensional transportation hubs: laser ablation technology is used to create micro-holes (<0.1mm) as thin as a hair, and a composite structure of blind holes (from the surface to the inner layer) and buried holes (between the inner layers) is used. Ultra-fine wiring with sub-75μm copper traces enables a 2-3X increase in circuit complexity within the same area.For example, the motherboard of a flagship mobile phone is only the size of a fingernail, but it can accommodate the interconnection needs of 1 billion transistor chips.

Signal Transmission：

The signal transmission of traditional PCB is like a vehicle detouring a multi-layer roundabout. The long-distance through-hole path causes signal delay and attenuation, and is susceptible to electromagnetic interference in high-frequency scenarios, which restricts the performance breakthrough of 5G/6G communication equipment.
The HDI board’s micro-hole interconnection architecture actively shortens signal transmission distance by over 60%, and its any-layer stacking technology (Any-layer HDI) enables point-to-point direct connections across all board layers This “zero detour” topology greatly improves signal integrity and can stably transmit millimeter waves above 40GHz, becoming the core carrier of autonomous driving radar and space satellite payloads.

Manufacturing Paradigm:

Ordinary PCBs rely on mechanical drills for drilling and etching processes, with an error tolerance of ±50μm, and the yield rate drops significantly above 8 layers. Its advantage is that the cost of a single board is low, and it is suitable for low-complexity products such as power adapters.
The HDI production line is a nano-scale “photon operating room”: the ultraviolet laser ablates the channel with microsecond pulses, with an accuracy of ±5μm; semi-additive copper plating technology (mSAP) is used to directly “grow” ultra-fine lines on an insulating substrate. Although the initial R&D cost is 30%-50% higher, its system-level integration advantage brings higher cost effectiveness in space-constrained scenarios such as smart watches and capsule endoscopes.

Summary of core differences:

Physical structure: HDI uses laser microvias instead of mechanical through-holes to achieve three-dimensional high-density wiring
Electrical performance: Microvia short paths ensure high-frequency signal integrity and reduce latency by 40%
Manufacturing process: Ordinary PCBs are suitable for etching/drilling, while HDI relies on laser direct writing and precision electroplating
Evolutionary logic: Functional electronics → ordinary PCB | Smart hardware → HDI board