High density interconnect (HDI) is a technology that is rapidly becoming prevalent in PCB design and integration into electronic products of all kinds. HDI is a technology that provides for a much denser construction on a board by the ability to place increasingly smaller components in closer proximity, which also results in shorter paths between components.
HDI PCBs are finding their way into a growing number of products:
- Military communications devices and other strategic equipment
- Aerospace – smaller space requirements and light weight are ideal for such applications
- Computers and smartphones – phones and computers are taking full advantage of smaller profiles, reduced weight, and increased functionality, made possible through the integration of HDI circuits.
- Medical equipment – diagnostic and monitoring equipment has become more reliable and expanded with technical features that aid medical teams with patient treatment, powered by HDI PCBs and advanced software.
Benefits of HDI
HDI boards utilize buried or blind vias, or a combination, and may also incorporate microvias with an incredibly small diameter. This facilitates the incorporation of more technology in less space, with fewer layers. Multi-layer HDI boards are also in common use, with many layers being accommodated through various construction methods utilizing blind, buried, stacked, and staggered vias.
With smaller components and blind via and via in pad technology, components may be placed closer together, resulting in faster signal transmission rates while also reducing crossing delays and signal loss. These are key considerations that generate improved performance of HDI PCBs.
HDI boards are preferred for applications where space, performance, reliability, and weight are concerns. This makes them more suitable for nearly every application related to electronics, consumer products, computers, and aeronautics.
Multi-layer HDI boards can provide strong interconnection of stacked vias, resulting in high levels of reliability, even in more extreme environments.
HDI Drawbacks and Considerations
Although the benefits of HDI are considerable, there are drawbacks to the technology, as well.
Specialized processing and equipment required to manufacture HDI boards is expensive. Such equipment includes laser drills, laser direct imaging processes, and other specialized fabrication equipment and materials. This need for specialized equipment and operator training is partially accountable for the higher cost of HDI fabrication.
Attention to detail is critical in the design and manufacturing of HDI printed circuit boards. This requires expertise and experience.
Many fabricators have not made the investment or transition to laser direct imaging (LDI) for board fabrication. In the case of HDI boards, the tight tolerances for finer lines and tighter spacing make LDI an important consideration in quality results. While contact imaging is still widely used in PCB manufacturing, LDI is much more preferable for HDI boards, although the expense for the equipment can be considerable.
Designing and Manufacturing HDI PCBs
Designing PCBs for HDI applications requires specific tools, as does the manufacturing process. Utilizing computer aided design (CAD) software for design and computer aided manufacturing (CAM) tools is considered mandatory in utilizing HDI technology for PCB creation.
Training for design engineers is also a time-consuming effort as HDI becomes more and more prevalent in the market, but the payback in efficiency and reduction in rework and manufacturing delays is worth the investment.