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High-Density PCBs

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • Any printed circuit board that offers dense placement of components and denser interconnections can be regarded as a high-density PCB or high-density interconnect (HDI) PCB. 

  • High-density PCBs consist of features such as blind and buried vias, layers with through vias, coreless construction with pairs of layers, alternative coreless construction with layer pairs, and passive substrate construction with no electrical connection.

  • There are fewer signal integrity issues in HDI boards and a significant decrease in crossing delays, signal losses, etc.

High-Density PCB

Instead of through holes in standard PCBs, HDI PCBs utilize micro via technology

Miniaturized electronic circuit boards are used in various industries: consumer electronics, communication systems, the automotive and aerospace industry, the healthcare sector, etc. In all these industries, high-density PCBs, otherwise called high-density interconnects (HDI PCBs), are of critical importance. HDI technology enables smaller-footprint devices to be produced at a competitive cost without compromising quality, performance, or board reliability. 

High-Density PCBs

Any printed circuit board that offers dense placement of components and denser interconnections can be regarded as a high-density PCB or high-density interconnect (HDI) PCB. These PCBs offer higher wiring density per unit area compared to traditional PCBs.

High-density PCBs consist of:

  1. Microvias
  2. Blind and buried vias
  3. Layers with through vias
  4. Coreless construction with pairs of layers
  5. Alternative coreless construction with layer pairs
  6. Passive substrate construction with no electrical connections
  7. A higher number of interconnections

With these features, high-density boards are compact and establish smaller dimension boards with smaller pads, vias, spaces, and traces. The high wiring density in HDI boards makes them lightweight, miniaturized circuits with a lower number of layers. With all these features, it is worth replacing a few PCBs on a product with a single HDI board.

IPC 2226 Defined Structures of HDI Boards

According to IPC 2226, HDI PCBs are boards with:

Lines and spaces 100μm

Smaller vias <150μm

Capture pads <400μm

Connection pad density ＞20 pads/cm2

Type

Feature

Type 1

Single micro via layer on at least one side of the core. Interconnections are established using PTH and plated micro via technology. No buried vias present, but blind vias are present.

Type 2

Single micro via layer on at least one side of the core. Interconnections are made through PTH and plated micro via technology. Both blind and buried vias are present.

Type 3

At least two layers of micro vias on single or both sides of the core. Interconnections made through PTH and plated micro via connections. Both blind and buried vias are present.

IPC 2226 HDI board structures

Advantages of HDI PCBs

High-density PCBs are extensively used in consumer electronics such as touch screens, mobile phones, tablets, computers, digital cameras, laptops, etc. HDI boards are smaller than traditional boards, without compromising on performance.  The advantages of HDI PCBs are:

  1. Lightweight and compact sizing - Populating more components on either side of HDI PCBs leads to smaller footprints and lightweight boards with improved functionality.
  2. Low-cost boards - With HDI technology, it is possible to reduce the raw material quantity, number of layers, and even the number of boards, which leads to an overall reduction in cost.  
  3. Improved performance and reliability - As components become closer and the number of transistors per unit area is higher, it is clear that the performance is improved in HDI boards. There are fewer signal integrity issues in HDI boards and a significant decrease in crossing delays, signal losses, etc. The use of micro vias over through holes has a remarkable impact on the reliability of the HDI board due to the former’s smaller aspect ratio and high-quality construction.
  4. Shorter time-to-market - The HDI PCB production process exhibits outstanding design efficiencies and shortens the time to market. With HDI boards, design and testing also speed up.

Comparing HDI PCBs and Traditional PCBs

Here are some other differences between HDI PCBs and standard PCBs.

Parameter

Standard PCB

HDI PCB

Size and weight

Large and heavy

Small and light

Component desnity

Lower

Higher

Via technology

Through hole, blind, and buried vias

Blind, buried, and micro vias

Aspect ratio

Higher

Lower

Compatible to high pin count devices

May or may not

Yes

Compatible to small pitch devices

May or may not

Yes

Number of layers

More

Less

Drilling technology

Laser drilling

Mechanical drilling

 High-density PCB designs will continue to replace standard PCB designs due to their advantageous features, and the technology of high-density PCBs will continue to evolve to improve the degree of compactness and miniaturization. Cadence OrCAD PCB Designer software offers comprehensive PCB solutions for designing HDI boards with advanced routing and component placement technology.

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