HDI circuit board FR4 TG170 substrate ENIG 2u' 10 Layer PCB

• Definition of a High-Density Interconnect (HDI) Printed Circuit Board

High-density interconnect, or HDI, circuit boards are printed circuit boards with a higher wiring density per unit area than traditional printed circuit boards. In general, HDI PCBs are defined as PCBs with one or all of the following: microvias; blind and buried vias; built-up laminations and high signal performance considerations. Printed circuit board technology has been evolving with changing technology that calls for smaller and faster products. HDI boards are more compact and have smaller vias, pads, copper traces and spaces. As a result, HDIs have denser wiring resulting in lighter weight, more compact, lower layer count PCBs. Rather than using a few PCBs in a device, one HDI board can house the functionality of the previous boards used.

• Benefits of HDI Printed Circuit Boards

The primary benefit of HDI printed circuit boards is the capability to “do more with less”; with copper-etching technology continuously refined for better precision, it became possible to combine functionalities of multiple PCBs into one HDI PCB.

Shortening the distance between devices and trace spaces, HDI PCBs allow for deployment of a large number of transistors for better performance in electronics while lowering power consumption. Signal integrity is also improved due to the shorter distance connections and lower power requirements. Other performance improvements over conventional PCBs include stable voltage rail, minimal stubs, lower RFI/EMI, and closer ground planes and distributed capacitance.

Additionally, consider using a HDI printed circuit board for the following benefits:

• Cost-effectiveness: when properly planned out, overall costs are reduced due to the lower number of necessary layers and smaller sizes/fewer number of needed boards when compared to standard PCBs.
• Faster time-to-market: Design efficiencies in HDI PCB production mean faster time-to-market. Because of the easy placement of components and vias and electrical performance, it takes a shorter amount of time to go through the design and testing process for HDI PCBs.
• Better reliability: Microvias have much better reliability than typical through holes due to the use of a smaller aspect ratio; they are more dependable than through holes, granting HDIs outstanding performance with better materials and parts.

• High-Density Interconnect Printed Circuit Board Structures

Depending on the design requirements, HDI Printed Circuit Boards can utilize different layering methods to achieve the desired performance.

• This structure of HDI PCB contains 1 “build-up” of high-density interconnection layers, suitable for BGA with lower I/O counts.
• It has fine lines, microvia and registration technologies capable of 0.4 mm ball pitch, excellent mounting stability and reliability, and may contain copper filled via.
• Applications: Cell phone, MP3 Player, GPS, Memory Card.

Fig.1: HDI PCB (1+N+1)

Fig.2: HDI PCB (2+N+2)

Fig.3: ELIC (Every Layer Interconnection)