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What is a HDI PCB, and what differentiates it from standard printed circuit boards? In this blog, we cover the basics and benefits of HDI printed circuit boards.
What is HDI PCB?
A high-density interconnector (HDI) PCB is a circuit board with a higher wiring density per unit area compared to more conventional boards. They are constructed out of a number of layers of conducting materials that are separated by a dielectric material, which are glued together by adhesives and linked by microvias. By definition, these constitute any printed circuit board with an average of 120-160 pins per square inch.
HDI PCBs have finer spaces between lines, higher connection pad density, and more parts assembled onto a smaller surface. They rely on microvias in order to function. With many layers that must communicate with each other in order to properly function, the condensation of parts relies on extremely small parts delivering electrical signals from one layer to another. Microvias are a specialized type of via with a hole diameter of 150 microns or less that allow this kind of printed circuit board to function.
Different kinds of Vias in HDI PCB
Vias are a tiny conductive hole that connects multiple layers in a HDI PCB and allows signals to flow through them easily. Depending on the functionality of a PCB, four different types of vias are drilled into a HDI PCB, namely: Through Hole vias, Blind Vias, Buried Vias and Microvias.1. Blind Vias – A type of via where a hole is pierced using a drill or laser to connect the external layer of multi-layer HDI PCB to the internal layer. Since the hole is visible only on one side of the PCB board, it is called Blind via. This type of via is difficult to construct and are expensive.
2. Through-Hole Vias – It is a hole pierced using a drill or laser through the PCB from top to bottom connecting all the layers of the multi-layer PCB. The Through-hole PCB is easy to construct and are the most cost-effective type of vias. The Through holes are further divided into Plated Through (with copper pads) Holes and Non-Plated Through Holes (without copper pads).
3. Microvias – It is the smallest vias or holes with a diameter less than 150 microns, drilled using a laser. Microvias are most commonly implemented in HDI PCBs, usually to connect one layer of the PCB to its adjacent layer and have a very small diameter in comparison to the mechanically drilled vias such as through-hole. Due to their size and ability to connect one layer to an adjacent layer, they enable denser printed circuit boards with more complex designs.
4. Buried Vias – A via that connects two internal layers of multi-layer HDI PCB. This via is always inside the printed circuit board and are not visible from the outside. Therefore, it is called buried via. The buried via is also an electroplated hole that needs a separate drill file. The layer count in a buried via is even in number i.e., 2, 4, 6, and on.
Advantages of HDI PCB
• HDI PCB provides designers with the freedom to design and place more components on both sides of the PCB. This is due to the higher wiring density with finer track arrangements on PCBs.• With the use of microvias and via-in-pad technology, the components in an HDI PCB are densely packed with versatile routing which results in faster transmission of the signal and better signal quality.
• The HDI PCB boards allow you to pack all functions in one board rather than using several boards as in standard PCBs. This results in reducing the size and overall costs compared to the traditional PCBs.
• The HDI PCB boards are highly reliable due to the implementation of stacked vias which make these boards a super shield against extreme environmental conditions. Hence the boards are highly reliable.
• Laser drilling produces smaller holes and improves the thermal properties of the board.
Applications
• Healthcare industry – HDI PCB have shown tremendous possibilities in the healthcare and medical fields. For example, tiny, implanted devices such as pacemakers, portable X-Rays and external devices such as hearing aids use the HDI technology.• Consumer devices – Due to the compact nature, the HDI PCBs are used in most consumer products such as smartphones, tablets, laptop computers, touch screen products and home appliances.
• Aerospace – HDI PCBs can withstand extreme environmental conditions making it feasible to be utilized in electronics design for missile systems, aircraft, and defense applications.
• Wearables – Due to the size of HDI PCBs, they are widely used in wearable technologies. F0r example, VR headsets, smartwatches, smart clothing, and more.
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