High density interconnect (HDI) is the process of leveraging manufacturing capabilities and materials to create very small interconnect solutions. Small interconnects are required for some of the new applications and dense components on the market. It is the next generation of etched circuitry.
Benefits of HDI
- Higher density and smaller size
- Use of advanced component pacaging
- More design options and flexibility
- Improved electrical performance and signal integrity
- Improved thermal performance and reliability
Wearable technology is one of the new applications we are seeing where dense packaging is required. Imagine wearing a sensor device that can monitor all of your vitals and connect to the internet via Bluetooth so your doctor can monitor you remotely. The solution has to be bendable, stretchable, and dense. We will talk more about this in upcoming columns, but this is the type of application that drives density.
Gone are the days of plants with rooms full of noisy drilling equipment. HDI requires smaller holes and blind and buried vias that are best done with laser technology. Lasers provide a faster, more cost effective solution over drilling (after you get over the sticker shock cost of the equipment).
Very thin copper materials are essential to creating high density solutions. Nine-micron copper is what is used in many cases to create HDI solutions. Thinner materials are on the horizon. New higher speed materials—coverlays and adhesives—are being qualified on a daily basis to meet the challenges of higher speeds and impedance requirements.
HDI Lines, Spaces and Hole Sizes
Smaller lines and spaces are required for HDI. Today, 50-micron (2-mil) lines and spaces in production and 37.5 microns (1.75 mils) line and spaces are being provided in prototypes. The laser drill enables smaller hole diameter (50-micron hole diameters) and enables blind and buried vias for even denser packaging.
HDI requirements and equipment push flex vendors to invest in better educated human resources. The complexity of the circuits and the software for the equipment to make the circuits is driving circuit vendors towards a better educated work force.
Many industry flex circuit gurus discuss HDI with regard to the density of the package—the circuit itself. However, in addition to the package, an HDI flex requires HDI assembly—the need to place 1005 components and 12-mil pitch BGAs.
The flex circuit industry in North America is moving rather quickly. The packaging densities are moving to smaller and the electrical requirements much faster. In order to keep pace with the industry requirements of HDI, North American flex vendors need to invest in equipment, resources and R&D.