HDI PCB: Advantages and Disadvantages

This page covers the advantages and disadvantages of HDI (High Density Interconnection) PCBs. It outlines the benefits and drawbacks of utilizing this technology.

What is HDI PCB?

Introduction: PCB (Printed Circuit Board) technology has continually evolved, progressing from single-sided and double-sided boards to multilayer, flex, and rigid-flex designs.

HDI stands for High Density Interconnection. An HDI PCB refers to a circuit board featuring a higher wiring density per unit area. HDI PCBs incorporate finer lines and spaces, smaller vias and capture pads, and higher connection pad density.

HDI boards represent one of the fastest-growing PCB technologies. They often include blind and/or buried vias and frequently feature micro-vias, which measure 0.006 inches or less in diameter. Furthermore, HDI boards boast a higher circuit density compared to traditional circuit boards.

HDI technology facilitates space reduction, line reduction, via diameter reduction, BGA pitch reduction, pre-preg thickness reduction, and board thickness reduction. HDI PCBs typically support between 4 and 24 layers, with PCB thicknesses ranging from 0.4 to 2.8 mm. Minimum track/gap sizes of approximately 65/65 µm are generally supported.

Benefits or Advantages of HDI PCB

Here are the key benefits and advantages of using HDI PCBs:

• Increased Component Density: HDI PCBs allow for more components in smaller board areas, as they are populated on both sides. This results in denser trace routing.
• Reduced Power Consumption: HDI PCBs contribute to decreased power usage, leading to longer battery life in portable devices.
• Lightweight and Small Size: HDI PCBs offer the benefit of reduced weight and smaller overall size.
• Fast Signal Transmission: Enhanced signal quality and faster signal transmission speeds can be achieved using HDI PCBs.
• More Mounting Space: HDI PCBs provide more space to mount components compared to traditional PCBs.

Drawbacks or Disadvantages of HDI PCB

While HDI PCBs offer numerous advantages, they also come with certain limitations and disadvantages:

• Evolving Technologies: HDI PCB technologies are constantly evolving, which can make it challenging to stay current.
• Multiple Implementation Methods: There are various approaches to achieve similar technological results (e.g., copper filling, drilling).
• Lower Yield: The manufacturing process for HDI PCBs can result in lower production yields compared to traditional PCBs.
• Expensive Equipment: The production of HDI PCBs requires specialized and often expensive equipment.
• Reliability Concerns: Limitations are often linked to the reliability of plated holes, especially the aspect ratio of blind vias. The aspect ratio is the division of material thickness by the plated through-hole (PTH) diameter.
• Plating Process Challenges: The plating process is a critical factor. To ensure good hole plating integrity, the aspect ratio is often limited to 1:0.8 for blind vias, although advanced processes can achieve 1:1.
• Material Selection: Due to aspect ratio limitations, PCB manufacturers often select special, very thin pre-pregs that react appropriately to laser drilling.
• Material Compatibility: HDI multilayers must be constructed with compatible materials to ensure reliability.
• Laser Drilling Issues: Standard pre-pregs contain fiberglass, which is unsuitable for laser drilling. The glass content can change the laser direction, resulting in mediocre or incorrectly shaped laser via holes.
• Via Sensitivity: Via holes are sensitive and behave similarly to rivets used during assembly. RoHS (Restriction of Hazardous Substances) compliance can apply high thermal stress on vias, and material expansion in the z-axis can further stress them.
• Reliability vs. Miniaturization: The trend is to continuously reduce via diameter while simultaneously increasing reliability, which presents a significant challenge.

Definitions and Standards for HDI

• IPC-DD-135: Qualification Testing for Deposited Organic Interlayer Dielectric Materials for Multichip Modules (8/95)
• IPC-2226: Sectional Design Standard for High Density Interconnect (HDI) Boards (04/03)
• IPC/JPCA-2315: Design Guide for High Density Interconnects (HDI) and Microvia (06/00)
• IPC-6016: Qualification & Performance Specification for High Density Interconnect (HDI) Layers or Boards (05/99)
• IPC-4104: Specification for High Density Interconnect (HDI) and Microvia Materials (5/99)