What Are High Density Interconnect PCBs?

High Density Interconnect

High Density Interconnect PCBs are the latest advancement in printed circuit board (PCB) technology. They allow for more components to be crammed into smaller spaces by providing higher wiring density. They also reduce the size of the PCB, making it more suitable for smaller and lighter devices.

These features make high density interconnect PCBs ideal for applications that require high performance, reliability, and quality in a small form factor. They are a common choice for consumer electronics such as smartphones, tablets, wearables, and cameras. Additionally, they are increasingly used in automotive applications such as infotainment systems, advanced driver assistance systems (ADAS), and vehicle control units.

The main advantage of HDI PCBs is their superior electrical performance and lower power consumption. They also offer increased reliability, thanks to the use of blind and buried vias that reduce the distance between components. They can also be more cost-effective than conventional PCBs, as they can be made from fewer layers and materials.

What Are High Density Interconnect PCBs?

There are several types of HDI PCBs. The most basic is a 1+N+1 design, with one signal layer on both the top and bottom of the stackup, sandwiching N number of sequential build up layers of alternating dielectric and copper in between. Other options include 2+N+2 and 3+N+3 HDI. Each type has a different number of sequential laminations, and each type has its own specific structure of blind and buried vias.

The most complex types of HDI PCBs are Any Layer designs, which have high-density interconnect layers on every layer of the stackup, allowing for maximum routing flexibility. They utilize copper filled stacked microvias structures on all layers, which provide more reliable connections for large pin-count devices. These types of HDI PCBs are often used in mobile / cellular phones, tablet computers, ultra-mobile PCs, MP3 players, GPS, memory cards and other small electronic devices.

Another benefit of HDI PCBs is their ability to support multiple power and ground planes in the same location. This allows for the separation of power and signal lines from each other, which in turn improves thermal management and reduces interference between signals. Finally, HDI PCBs have a higher surface density than traditional PCBs, which reduces the overall weight of the device and allows for thinner designs.

The production process for HDI PCBs is a bit more complicated than for standard PCBs. The boards are first etched before being separated by partially cured laminates and then layered together like a book. The layers are then heated and pressed to liquify the prepreg, which sticks the layers together. The etching process is then repeated, and the prepreg is sprayed with metal to add the required conductors.

The final step in the manufacturing process is the laser drilling of the microvias. Using this method ensures very precise hole locations. This can be challenging when utilizing staggered and stacked microvias, but is essential for high-speed connections. When necessary, a near-pad technique can be used, which places a very small trace on the pad that is bonded to the microvia to complete the connection if drill wander creates a gap in the desired route.