Product Overview
UGPCB introduces the 6‑layer 2+N+2 HDI PCB (Model: 6L 2+N+2 HDI PCB). This high‑density interconnect printed circuit board is engineered specifically for communication equipment. It uses ITEQ IT150 high‑performance laminate, combined with a second‑order HDI build‑up architecture, 2.5mil/2.5mil fine‑line trace and space, and 0.1mm laser microvias. These features deliver reliable interconnections for 5G base stations, high‑speed network switches, optical modules, and similar applications.
In the PCB industry, HDI (High Density Interconnect) technology is the core enabler for shrinking component pitches and rising signal speeds. The 2+N+2 HDI PCB architecture represents the second‑order HDI category. It achieves an optimal balance among routing density, signal integrity, and manufacturing cost.
What Is a 2+N+2 HDI PCB?
Definition and Nomenclature
“2+N+2” is a standardized naming convention for HDI stack‑up structures. It is defined in the IPC‑2226 standard and is classified as Type III within that system.
Breaking down the term:
- The first “2” means two sequential build‑up layers above the core.
- “N” stands for the number of core layers (here N=2, i.e., two inner core layers).
- The second “2” means two sequential build‑up layers below the core.
Thus, a 2+N+2 structure adds two build‑up layers on each side of the conventional core. These are constructed through two sequential lamination cycles. This 6‑layer board therefore comprises: 2 outer build‑up layers + 2 inner core layers + 2 outer build‑up layers.
HDI Classification per IPC‑2226
The IPC‑2226 standard defines several HDI types based on microvia structures and build‑up layer counts:
| HDI Type | Structure | Build‑up Layers (per side) | Minimum BGA Pitch | Typical Applications |
|---|---|---|---|---|
| Type I | 1+N+1 | 1 layer | 0.5mm | Smartphones, mid‑density designs |
| Type II/III | 2+N+2 | 2 layers | 0.4mm | Networking equipment, high‑performance computing |
| Type III / ELIC | 3+N+3 and above | 3+ layers | 0.3mm and below | Flagship smartphones, AI modules |
This product falls into the 2+N+2 category. It features two build‑up layers per side, with microvias that can be arranged in either stacked or staggered configurations.
Core Technical Specifications
| Parameter | Specification |
|---|---|
| Model | 6L 2+N+2 HDI PCB |
| Material | ITEQ IT150 |
| Layer Count | 6 layers (2+N+2 second‑order HDI) |
| Solder Mask Color | Black or White (optional) |
| Finished Board Thickness | 1.0mm |
| Inner Layer Copper Thickness | 1 OZ (~35μm) |
| Outer Layer Copper Thickness | 0.5 OZ (~17.5μm) |
| Minimum Trace / Spacing | 2.5mil / 2.5mil (~63.5μm / ~63.5μm) |
| Minimum Mechanical Drill | 0.2mm |
| Minimum Laser Drill | 0.1mm |
| Surface Finish | Immersion Gold + OSP |
| Primary Application | Communication equipment |
Material Deep Dive: ITEQ IT150
Material Positioning
ITEQ IT150 is a medium‑Tg, halogen‑free, multifunctional epoxy laminate. It sits between standard FR‑4 and high‑performance low‑loss materials. It delivers lead‑free process compatibility, good manufacturability, and cost‑effectiveness.
The IT150GS variant (within the IT150 family) is a medium‑Tg (Tg >150°C by DSC), halogen‑free, middle‑loss material. It offers high thermal reliability and excellent CAF resistance. It is specifically designed for server, storage, and networking applications.
Key Performance Parameters
Based on ITEQ official datasheets and IPC‑TM‑650 test methods:
| Property | Test Method | Typical Value | Unit |
|---|---|---|---|
| Glass Transition Temperature (Tg) | DSC (IPC‑2.4.25) | 155 | °C |
| Decomposition Temperature (Td, 5% wt loss) | TGA (IPC‑2.4.24.6) | 365 | °C |
| Z‑axis CTE (α1, below Tg) | IPC‑2.4.24 | 35–40 | ppm/°C |
| Z‑axis CTE (α2, above Tg) | IPC‑2.4.24 | 220–240 | ppm/°C |
| X/Y‑axis CTE (40–125°C) | IPC‑2.4.41 | 11/13 | ppm/°C |
| Dielectric Constant (Dk) @ 1GHz | IPC‑2.5.5.13 | 4.2–4.5 | — |
| Dissipation Factor (Df) @ 1GHz | IPC‑2.5.5.13 | 0.010–0.018 | — |
| T288 Thermal Stress | IPC‑TM‑650 | >60 | Minutes |
| Moisture Absorption | IPC‑2.6.2.1 | 0.12 | % |
| Flammability Rating | UL94 | V‑0 | Rating |
| UL MOT (Max Operating Temp) | — | 130 | °C |
Material Advantages
1. Lead‑Free Process Compatibility
Standard FR‑4 typically has a Tg around 130°C. ITEQ IT150 delivers 155°C. Under lead‑free reflow peaks of 260°C, this higher Tg provides superior dimensional stability. The material resists excessive Z‑axis expansion, which significantly reduces the risk of via barrel cracking and pad lifting during assembly.
2. Excellent CAF Resistance
CAF (Conductive Anodic Filament) is a primary failure mode in PCBs. It occurs when electrochemical migration creates short circuits under humid and hot conditions. ITEQ IT150 offers high CAF resistance (18L / less than 100mil). This makes it especially suitable for long‑term outdoor deployment in communication infrastructure.
3. Halogen‑Free Compliance
ITEQ IT150 meets JPCA‑ES‑01‑2003 halogen‑free standards. Chlorine (Cl) and bromine (Br) content are each below 0.09% by weight. Total Cl+Br is below 0.15% (1500ppm).
Design Guidelines
Stack‑Up Architecture
The 2+N+2 HDI PCB is manufactured through sequential lamination:
- Core fabrication – Start with a double‑sided copper‑clad laminate. Etch inner layer circuits, perform mechanical drilling (0.2mm), and plate to create buried via connections.
- First build‑up – Apply prepreg and copper foil (or RCC) to both sides of the core. Execute the first lamination cycle.
- First laser drilling – Drill first‑order blind vias (laser holes at 0.1mm) and fill them with copper.
- Second build‑up – Apply additional dielectric layers and copper foil. Execute the second lamination cycle.
- Second laser drilling – Drill second‑order blind vias (0.1mm) and fill with copper.
- Outer layer circuits – Form outer layer circuits (trace/space 2.5mil) and apply the surface finish.
This two‑sequential‑lamination process is precisely what the “2” in 2+N+2 signifies.
Fine‑Line Circuit Design
This product achieves 2.5mil/2.5mil (~63.5μm/63.5μm) trace width and spacing. This exceeds the HDI Design Level C (60‑99μm) defined in IPC‑2226. This fine‑line capability enables:
- 0.4mm pitch BGA breakout with ample routing channels.
- Flexible signal routing for high‑density component placement.
- Reduced layer count, which lowers overall PCB cost.
Microvia Technology
This product uses a hybrid drilling approach:
- Mechanical drilling – Minimum diameter 0.2mm, used for through‑holes and buried vias in the core.
- Laser drilling – Minimum diameter 0.1mm (4mil) , used for blind vias in build‑up layers.
The 0.1mm laser microvia reduces via area by 75% compared to a 0.2mm mechanical hole. This significantly frees up routing space. It is fundamental to achieving high‑density interconnect and enabling via‑in‑pad designs for fine‑pitch BGAs.
Operating Principle
The 2+N+2 HDI PCB works through a multi‑layer interconnect architecture:
- Core‑layer interconnection – Buried vias, formed by mechanical drilling + plating, connect signals between core layers.
- Build‑up interconnection – Blind vias, formed by laser drilling + plating, connect outer signal layers to inner layers.
- Full‑board through‑holes – After stack‑up completion, mechanical drilling penetrates all layers to create through‑holes.
- Signal transmission path – High‑speed signals travel from surface BGA pads → through laser blind vias into inner layers → across buried vias through the core → through laser blind vias on the opposite side to the bottom layer.
This stepped interconnect structure shortens signal paths and reduces parasitic via effects. As a result, it preserves high‑speed signal integrity.
Performance Advantages
Thermal Reliability
ITEQ IT150’s Td (decomposition temperature) reaches 365°C, which is well above the lead‑free reflow peak of 260°C. T288 thermal stress testing exceeds 60 minutes without delamination. This ensures material integrity through multiple reflow cycles.
Signal Integrity
At 1GHz, ITEQ IT150 exhibits a dielectric constant Dk of approximately 4.2–4.5 and a dissipation factor Df of 0.010–0.018. As a “standard‑to‑mid‑loss” material, IT150 provides a compelling price‑performance ratio compared to ultra‑low‑loss materials. This makes it ideal for production‑ready communication equipment.
Mechanical Strength
ITEQ IT150 delivers flexural strength of 470–500 N/mm² in the warp direction and 400–430 N/mm² in the fill direction. This ensures structural integrity throughout assembly and field deployment.
Product Classification
This product is classified across multiple dimensions:
| Classification System | Category |
|---|---|
| IPC‑2226 HDI Type | Type II/III (2+N+2, double build‑up per side) |
| HDI Order | Second‑order (2 laser drilling cycles + 2 lamination cycles) |
| Rigid/Flexible | Rigid PCB |
| Layer Count | 6‑layer multilayer board |
| Material System | Medium‑Tg, halogen‑free, FR‑4‑compatible epoxy |
| Surface Finish | Immersion Gold + OSP hybrid finish |
| Application Domain | Communication‑grade PCB |
Manufacturing Process Flow
UGPCB follows this production sequence for the 6‑layer 2+N+2 HDI PCB:
Step 1: Core Layer Fabrication
Material cutting → Inner layer dry film → Etching → AOI inspection → Brown oxide treatment
Step 2: First Build‑Up
Lamination (core + prepreg + copper foil) → First lamination → First‑order laser drilling (0.1mm) → Desmear → Electroless copper + plating → Circuit patterning
Step 3: Second Build‑Up
Second lamination → Second lamination → Second‑order laser drilling (0.1mm) → Desmear → Electroless copper + plating → Circuit patterning
Step 4: Outer Layer and Finishing
Mechanical drilling (0.2mm through‑holes) → Electroless copper + plating → Outer layer circuits (2.5mil/2.5mil) → Solder mask → Immersion Gold + OSP surface finish → Electrical testing → Final inspection → Packaging and shipment
The entire process involves two lamination cycles and two laser drilling operations. This demands exceptional process control and precision.
Application Scenarios
This product is primarily designed for communication equipment:
5G Communication Infrastructure
- 5G base stations (gNB) – RF front‑end and baseband processing units.
- High‑speed backplane interconnects for 5G network equipment.
- Enterprise‑grade routers and core switches.
High‑Speed Data Transmission
- 400G/800G optical modules – control and signal processing boards.
- High‑speed fiber‑optic switches.
- Optical transceivers.
Other High‑End Applications
- High‑performance servers and storage devices.
- AI inference/training accelerator cards.
- Advanced medical imaging equipment.
The 2+N+2 HDI structure is particularly well‑suited for moderate pin‑count, high‑density BGA routing. It enables complex signal interconnects within limited board space.
Why Choose UGPCB?
UGPCB brings deep manufacturing expertise to HDI PCB production:
- Fine‑line capability – 2.5mil/2.5mil trace/space in volume production, meeting advanced HDI design requirements.
- Mature microvia process – 0.1mm laser via + 0.2mm mechanical drill hybrid solution with stable yield.
- Comprehensive material certification – Full qualification on ITEQ IT150 and other mainstream material systems.
- End‑to‑end process control – Every step from cutting to electrical testing strictly follows IPC‑6012 rigid PCB qualification and performance specifications.
- Communication industry track record – Extensive experience in 5G base station, optical module, and network equipment PCB manufacturing.
Request a Quote Today
Whether you are designing high‑speed backplanes for 5G base stations or developing next‑generation optical modules, UGPCB’s 6‑layer 2+N+2 HDI PCB provides the reliable interconnect foundation your project deserves.
Data Source Declaration
The technical data cited in this document comes from the following authoritative standards and sources:
- IPC‑2226 – Sectional Design Standard for High Density Interconnect (HDI) Printed Boards
- IPC‑6012E/F – Qualification and Performance Specification for Rigid Printed Boards
- IPC/JPCA‑2315 – Design Guide for High Density Interconnect Structures and Microvias
- ITEQ IT‑150 / IT‑150GS Official Datasheets and Material Specifications
- IPC‑TM‑650 – Test Methods Manual (including methods 2.4.4, 2.4.24, 2.4.24.6, 2.4.25, 2.5.5.13, 2.6.2.1, and others)
- JPCA‑ES‑01‑2003 – Halogen‑Free Copper‑Clad Laminate Standard
- UL94 – Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances
