What is HDI (High Density Interconnects) wiring? HDI (High Density Interconnects) wiring refers to the use of the latest design strategies and manufacturing technologies to achieve more dense designs without affecting circuit functionality. In other words, HDI involves the use of multiple wiring layers, smaller wiring, vias, solder pads, and thinner substrates to install complex and usually high-speed circuits within previously impossible footprint areas. With the development of manufacturing technology, HDI wiring has begun to be seen in many designs, such as motherboards, graphics controllers, smartphones, and other space limited devices. If implemented properly, HDI wiring can not only greatly reduce design space, but also reduce EMI issues on PCBs. Reducing costs is an important goal for the company, and HDI cabling can precisely achieve this. It is important to understand that HDI wiring and micro vias are more complex than typical multi-layer wiring strategies. We may have designed 8-layer or 16-layer PCBs, but we still need to learn some new concepts involved in HDI wiring. In typical PCB design, the actual printed circuit board is viewed as a single entity and divided into multiple layers. However, HDI wiring requires design engineers to think from the perspective of integrating multiple ultra-thin layers of a PCB into a single functional PCB.

It can be said that the key driving force for achieving HDI wiring is the development of via technology. Through holes are no longer copper plated holes drilled on various layers of PCBs. The traditional via mechanism reduces the wiring area in PCB layers that are not used by signal wires. Traditional via holes have no place in HDI wiring. In HDI wiring, micro via is the focal point that plays a driving role, responsible for integrating multi-layer dense wiring together. For ease of understanding, it can be considered that micro vias are composed of blind or buried holes, but have different structural methods. Traditional through holes are drilled using a drill bit after combining the layers together. However, micro vias are drilled by laser on each layer before stacking. Laser drilled micro vias allow interconnection between layers with the smallest aperture and pad size. This is beneficial for achieving a fanout layout of BGA components, where the pins are arranged in a grid format.