At JBPCB, 8-layer HDI PCBs have become a core component that bridges the gap between complex circuit designs and compact device form factors. As a cutting-edge solution in the HDI (High Density Interconnect) field, they enable higher component density, shorter signal paths, and stronger electrical performance, making them an indispensable part of modern smart devices, industrial equipment, and medical instruments.

What materials are used to make HDI PCBs?

Substrate Materials: FR-4 (Flame Retardant Grade 4), High-Tg FR-4, and Rogers series. Serves as the bottom layer; High-Tg FR-4 resists deformation at high temperatures (critical for an 8-layer stack).

Conductive Materials: Electrolytic copper foil (1oz-3oz), rolled copper foil. Forms signal traces; rolled copper ensures lower signal loss in high-frequency applications.

Dielectric Materials: Prepreg (resin-impregnated glass cloth), Dry film. Insulates copper layers and ensures stable impedance control in an 8-layer structure.

Solder Mask: Liquid solder mask and dry film solder mask. Protects copper traces from oxidation and shorts, enhancing board durability.

1: Substrate Material: FR-4 (flame retardant grade 4), high-Tg FR-4 series as the bottom layer; high-Tg FR-4 resists deformation at high temperatures (critical for the 8-layer stack).

2: Conductive Material: Electrolytic copper foil (1oz-3oz) and rolled copper foil for signal traces; rolled copper ensures low signal loss in high-frequency applications.

3: Dielectric Material: Prepreg (impregnated glass cloth) and dry film insulation between copper layers ensure stable impedance control throughout the 8-layer structure.

4: Soldermask: Liquid and dry film soldermask protect the copper traces from oxidation and shorts, thereby enhancing the durability of the board.

The production of 8-layer HDI PCBs is a sophisticated, multi-stage process requiring advanced equipment and strict quality control. Unlike standard PCBs, it relies on microvias (≤0.15mm in diameter) to connect the layers, reducing board thickness and increasing density. The core steps are as follows:

1. Substrate Cutting and Cleaning: FR-4 or high-Tg substrates are cut to standard sizes and then cleaned to remove oil and dust (to prevent bonding problems in subsequent steps).

2. Inner Layer Patterning: The circuit pattern is printed on the inner copper layer using photolithography, and then excess copper is etched away.

3. Lamination: Eight layers (including inner layers, prepreg, and outer copper foil) are stacked in a specific order and then pressed together under high temperature (180-200°C) and pressure to form a single board.

4. Microvia Drilling: Laser drilling is used to create microvias (blind vias for inner-outer layer connections and buried vias for inner-outer layer connections)—a critical step in achieving the density of 8-layer boards.

5. Electroplating: Copper is plated into the microvias and onto the board surface to ensure interlayer conductivity.

6. Outer Layer Patterning and Solder Mask Application: The outer layer patterning is repeated, followed by solder mask application and silkscreen printing (for component labeling and logos).

7. Testing and Inspection: Electrical testing (opens/shorts, impedance) and visual inspection (microvia quality, layer alignment) are performed to meet IPC-A-600 standards.

HDI PCB process capabilities:

HDI PCB laminate structure diagram：

Applications for HDI PCBs:

Consumer Electronics: Smartphones (such as flagship models with 5G and multiple cameras), tablets, and wearable devices (smartwatches, fitness trackers)—areas where space is at a premium.

Telecommunications: 5G base station modules, RF transceivers, and IoT gateways—require low signal loss and high-frequency compatibility.

Medical Devices: Portable diagnostic equipment (glucose meters), ultrasound machines, and medical wearables—demand stable performance and miniaturization.

Industrial Electronics: Industrial controllers, robotics, and automation sensors—operate in harsh environments (high temperature, vibration), requiring extremely high reliability.

Automotive Electronics: Advanced Driver Assistance Systems (ADAS), in-vehicle infotainment systems, and electric vehicle battery management systems—require extremely high thermal stability and interference immunity.

Frequently Asked Questions (FAQs) About 8-Layer HDI PCBs

Q1: What is the difference between an 8-layer HDI PCB and a standard 8-layer PCB?

A1: The key difference is that 8-layer HDI PCBs use microvias, enabling higher component density and thinner board thickness. Standard 8-layer PCBs use through-holes (with larger diameters), which limits component density and increases board thickness.

Q2: Why choose an 8-layer HDI PCB over a 4- or 6-layer HDI PCB?

A2: 8-layer HDI PCBs offer more signal, power, and ground layers, supporting complex circuits (such as multi-core processors) that 4- or 6-layer HDI PCBs cannot accommodate. They are ideal for high-performance devices with strict space and performance requirements.

Q3: What quality standards should 8-layer HDI PCBs meet?

A3: They typically comply with IPC-A-600 (PCB acceptance criteria) and IPC-6012 (HDI-specific standards). For automotive or medical applications, additional certifications such as IATF 16949 (automotive) or ISO 13485 (medical) may be required.

Q4: How can the production cost of 8-layer HDI PCBs be reduced?

A4: Optimize microvia design (reduce blind/buried via types), use standard substrates in non-high-frequency applications (for example, use FR-4 instead of Rogers), and increase order quantity to reduce unit cost.