vltra High Density Interconnects (UHDI) PCB takes HDI technology a step further creating an
even more dense version of a printed circuit board
where the components are placed closer to each other allowing the overall board size to be smaller.
UHDI pushes the limits of fabrication capabilities
for PCBs and semiconductor devices and represents an advancement in miniaturization and integration that allows
for the creation of electronic components and systems with extremely high levels of functionality in a smaller footprint.
UHDI technology enables finer lines and smaller vias/microvias while significantly increasing interconnectivity,
hence resulting in higher signal integrity and less power consumption by PCBs. UHDIs are sub-1-mil (0.001")
line widths and spaces, necessitating the change in the unit of measurement from mils to microns.
A 1-mil trace is 25 microns, hence, UHDI refers to traces and spaces on a printed circuit board that are sub-25 microns.
According to an established workgroup by IPC, UHDI is described as a PCB that has:
Conductor/trace width and isolation distance below 50 µm
Dielectric thickness below 50 µm
Microvia diameter below 75 µm
Product characteristics that exceed the existing IPC 2226 level C standard
UHDI PCB Design
UHDI PCBs can be either rigid or flexible and are often multilayered to handle the density of interconnects. As electronics continue to shrink,
so does the printed circuit board, not only in the X-axis but also the Y-axis. Although multilayering is essential to maintaining signal integrity and minimizing electromagnetic interference
in UHDI PCBs, PCB designers use fine-line routing that enables consolidation of traces into smaller layer count, which reduces the number
of HDI buildup layers. Eliminating HDI buildup layers can greatly reduce the costs required to fabricate the PCB,
which further enables offsetting some of the additional costs required to access ultra-HDI fabrication capabilities.
High-performance substrates like Ajinomoto build-up film (ABF), BT epoxy-based materials, thin liquid crystal polymer
(e.g., UltraLam) and resin-coated copper films (metalized polyimide, pure polyimide, cast polyimide) are used as alternatives to laser-drillable materials and thin reinforced FR4.
These may be used in combinations to create an ultra-HDI build. One such combination is the use of BT epoxy-based laminates as a core with conventional buried
vias and ABF as the outer buildup layers that support fine-line routing. This buildup style is used as an organic substrate in BGA packaging, but the same approach can be used for an ultra-HDI PCB.
Challenges for UHDI PCB Fabrication
With every major advancement in technology comes manufacturing challenges. UHDI is not just a major change,
it is a quantum leap in technology. It represents a change in the fundamental method of manufacturing printed circuit boards, moving from the traditional subtractive process to additive ones.
It also requires not only new manufacturing methods but also new manufacturing equipment, chemistry, materials, and inspection capabilities.
UHDI PCB manufacturing capability was typically only cost-effective when volumes were very high, which is why it has been only used for some high-compute consumer products and
IC production with higher I/O counts. Now that global access to these advanced capabilities is broadening, more designers can access
these capabilities at lower volume, and even during prototyping. This also means more of the advanced components found in high-volume produced consumer devices can be used at lower volume.
Thus, UHDI capability is now becoming more accessible with lower volume fabricators.
PCB manufacturers that produce ultra HDI boards need to meet more stringent requirements with regard to equipment and their manufacturing environment.
To enable factories to manufacture Ultra HDI boards, a great deal of updating needs to be done. Investments have to be made at the manufacturing
stage in both equipment and processes. Updates required for manufacturing
Ultra HDI circuit boards include:
State-of-the-art laser direct imaging (LDI) equipment
Extremely clean environment
More thorough testing
Latest automatic optical inspection equipment
The latest equipment and chemistry for copper plating
New methods such as mSAP (modified Semi-Additive Process)
New, cleaner and more homogeneous materials
Advantages of UHDI PCBs
UHDI PCBs offer significant advantages, particularly in reducing the weight and size of electronic devices while maintaining high performance.
Their ability to accommodate a higher number of components within a compact space enhances component density,
making them ideal for advanced electronic applications. Additionally, UHDI PCBs improve electrical performance
by minimizing distances between components and shortening electrical paths, which reduces signal loss, parasitic
capacitance, and inductance. This results in better signal integrity and faster signal transmission. Furthermore, their multi-layer structure and
complex routing capabilities provide greater design flexibility, enabling the development of more innovative and sophisticated electronic products.
Applications of UHDI PCBs
UHDI is revolutionizing a wide range of industries through miniaturization without impacting performance. Key application areas include:
Consumer Electronics: Smartphones, tablets, and wearable devices take benefits from the compact design for high performance through UHDI.
Automotive Electronics: ADAS and EV power electronics and infotainment systems are made possible with UHDI to improve reliability and efficiency.
Medical Devices: UHDI enables the development of highly compact and precise medical electronics, such as imaging systems and implantable devices.
Aerospace and Defense: The performance and reliability in mission-critical applications such as radar systems, avionics, and satellite communications are enhanced by UHDI technology.
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