An Introduction to HDI High Density Interconnector PCBS by RAYPCB

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What are HDI PCBs?

HDI (High Density Interconnector) PCBs are printed circuit boards that feature a higher wiring density per unit area than conventional PCBs. This is achieved through the use of smaller vias, finer trace widths and spaces, and Microvias that are laser-drilled and allow for layer-to-layer connections within the PCB.

HDI PCBs enable the design of compact, high-performance electronic devices by allowing more components to be packed into a smaller area. They are widely used in applications such as smartphones, tablets, wearables, and other consumer electronics where space is at a premium.

Key Features of HDI PCBs

  1. High wiring density: HDI PCBs can accommodate more traces and components per unit area compared to traditional PCBs.
  2. Smaller vias and microvias: HDI PCBs use smaller vias (0.006″ to 0.004″) and microvias (0.004″ to 0.002″) to create interconnections between layers.
  3. Finer trace widths and spaces: HDI PCBs feature trace widths and spaces as small as 0.003″, allowing for more routing channels.
  4. Multilayer structures: HDI PCBs often have multiple layers (8 or more) to accommodate the high density of interconnections.
  5. Laser-drilled microvias: Microvias in HDI PCBs are typically laser-drilled, enabling precise and reliable layer-to-layer connections.

Benefits of HDI PCBs

HDI PCBs offer several advantages over traditional PCBs:

  1. Miniaturization: HDI PCBs allow for smaller, more compact electronic devices by accommodating more components in a smaller area.
  2. Improved performance: The high wiring density and smaller features of HDI PCBs result in shorter signal paths, reducing signal loss and improving overall performance.
  3. Increased functionality: With more space for components and interconnections, HDI PCBs enable the integration of more features and functions into a single device.
  4. Reduced cost: Although HDI PCBs may have a higher initial cost, they can lead to overall cost savings by reducing the size and weight of the final product and simplifying the assembly process.

HDI PCB Design Considerations

When designing HDI PCBs, several factors must be considered to ensure optimal performance and manufacturability:

Stack-up Design

The stack-up of an HDI PCB refers to the arrangement of copper layers and dielectric materials. A typical HDI PCB stack-up may include:

  • Core layers: Thicker dielectric layers that provide mechanical stability and support for the PCB.
  • Buildup layers: Thinner dielectric layers that are added to the core layers to accommodate the high density of interconnections.
  • Microvia layers: Layers that contain laser-drilled microvias for layer-to-layer connections.

The stack-up design should be optimized for signal integrity, impedance control, and manufacturability.

Via Types and Sizes

HDI PCBs use various types of vias, including:

  • Through-hole vias: Traditional vias that go through all layers of the PCB.
  • Blind vias: Vias that start at an outer layer and terminate at an inner layer.
  • Buried vias: Vias that connect inner layers without reaching the outer layers.
  • Microvias: Laser-drilled vias with diameters ranging from 0.002″ to 0.004″, used for layer-to-layer connections in HDI PCBs.

The choice of via types and sizes depends on the specific design requirements and the capabilities of the PCB manufacturer.

Trace Width and Spacing

HDI PCBs feature finer trace widths and spaces compared to traditional PCBs. Typical trace widths and spaces in HDI PCBs range from 0.003″ to 0.005″, depending on the specific design requirements and the PCB fabricator’s capabilities.

When designing traces for HDI PCBs, it is essential to consider factors such as signal integrity, crosstalk, and manufacturing tolerances. Impedance control is also critical, especially for high-speed signals.

Component Selection and Placement

Selecting the appropriate components and placing them optimally on the HDI PCB is crucial for achieving the desired performance and manufacturability. Some considerations include:

  • Using components with smaller footprints, such as chip-scale packages (CSPs) and ball grid arrays (BGAs).
  • Placing components to minimize signal path lengths and reduce crosstalk.
  • Ensuring adequate spacing between components for manufacturing and assembly processes.
  • Optimizing Component orientation for signal integrity and thermal management.

HDI PCB Manufacturing Process

The manufacturing process for HDI PCBs involves several steps:

  1. Core layer fabrication: The core layers are manufactured using traditional PCB fabrication techniques, such as etching and lamination.
  2. Buildup layer fabrication: The buildup layers are added to the core layers using a sequential lamination process. Each buildup layer is etched to create the necessary traces and pads.
  3. Laser drilling: Microvias are laser-drilled in the buildup layers to create layer-to-layer connections.
  4. Plating: The microvias and other features are plated with copper to establish electrical connections.
  5. Solder mask application: A solder mask is applied to protect the traces and pads from damage during the assembly process.
  6. Surface finish: A surface finish, such as ENIG (Electroless Nickel Immersion Gold) or OSP (Organic Solderability Preservative), is applied to the exposed pads to enhance solderability and protect the copper from oxidation.

RAYPCB’s HDI PCB Capabilities

RAYPCB is a leading PCB manufacturer specializing in HDI PCBs. With state-of-the-art facilities and a team of experienced engineers, RAYPCB offers a range of HDI PCB solutions to meet the unique needs of its customers.

HDI PCB Stack-up Options

RAYPCB offers various HDI PCB stack-up options, including:

Stack-up Type Layers Core Thickness Prepreg Thickness Microvia Diameter
1+N+1 4-6 0.20-0.40mm 0.08-0.15mm 0.10-0.15mm
2+N+2 6-10 0.30-0.50mm 0.08-0.15mm 0.10-0.15mm
3+N+3 8-14 0.40-0.70mm 0.08-0.15mm 0.10-0.15mm

HDI PCB Design Support

RAYPCB’s team of experienced engineers provides comprehensive HDI PCB design support, including:

  • Stack-up design optimization
  • Signal integrity analysis
  • Impedance control
  • Design for manufacturability (DFM) review

HDI PCB Prototyping and Manufacturing

RAYPCB offers rapid prototyping and volume production services for HDI PCBs. With advanced manufacturing equipment and strict quality control processes, RAYPCB ensures the highest quality and reliability for its HDI PCB products.


HDI PCBs are essential for the development of compact, high-performance electronic devices. By understanding the key features, benefits, and design considerations of HDI PCBs, engineers can create innovative products that meet the demands of today’s market.

RAYPCB, with its expertise in HDI PCB manufacturing and design support, is well-positioned to help customers bring their HDI PCB designs to life. From prototyping to volume production, RAYPCB delivers high-quality HDI PCBs that meet the most stringent requirements.

Frequently Asked Questions (FAQ)

  1. What is the minimum trace width and spacing for HDI PCBs at RAYPCB?
  2. RAYPCB can manufacture HDI PCBs with trace widths and spaces as small as 0.003″ (0.075mm), depending on the specific design requirements and the chosen stack-up.

  3. How many layers can an HDI PCB have?

  4. HDI PCBs can have various numbers of layers, typically ranging from 4 to 14 layers or more. The number of layers depends on the complexity of the design and the specific application requirements.

  5. What is the minimum microvia diameter for HDI PCBs at RAYPCB?

  6. RAYPCB can manufacture microvias with diameters as small as 0.004″ (0.10mm) for HDI PCBs. The specific microvia diameter depends on the chosen stack-up and the design requirements.

  7. What surface finishes are available for HDI PCBs at RAYPCB?

  8. RAYPCB offers various surface finishes for HDI PCBs, including ENIG (Electroless Nickel Immersion Gold), OSP (Organic Solderability Preservative), and Immersion Silver. The choice of surface finish depends on the specific application and the customer’s preferences.

  9. How long does it take to manufacture HDI PCBs at RAYPCB?

  10. The lead time for HDI PCB manufacturing at RAYPCB depends on the complexity of the design, the chosen stack-up, and the order quantity. Typical lead times range from 2-3 weeks for prototypes to 4-6 weeks for volume production. However, RAYPCB also offers expedited services for urgent projects.