In HDI PCB manufacturing, 1+N+1 and 2+N+2 are the two most common types of structures. Although both of them adopt the micro via-hole technology, there are obvious differences in the lamination mode, manufacturing difficulty, cost, reliability and application field.
This guide will analyze HDI PCB 1+N+1 vs. 2+N+2 from the aspects of HDI micropore structure, manufacturing process, cost, design advantages, application scenarios and selection methods, so as to provide professional reference for PCB engineers, electronic product R&D personnel and procurement personnel.
1. What Is HDI PCB Microvia Technology?
With the continuous development of smartphones, automotive electronics, medical devices, and high-performance communication equipment, traditional multilayer PCBs are facing increasing challenges in miniaturization, signal integrity, and component density.
HDI PCB (High Density Interconnect PCB) is an advanced PCB technology that uses microvia interconnection technology to achieve higher wiring density within limited board space.
Unlike conventional mechanical vias, HDI microvias are typically created through laser drilling and have:
- Smaller via diameter (usually 50–150 μm)
- Higher wiring density
- Shorter signal transmission paths
- Improved electrical performance
- Better support for fine-pitch components
The HDI structure is commonly expressed as: 1+N+1, 2+N+2, 3+N+3
where:
- The first number represents the number of HDI buildup layers on the top side
- N represents the core multilayer PCB layers
- The last number represents the bottom-side HDI buildup layers
For example:
- 1+N+1: One HDI buildup layer on each side
- 2+N+2: Two HDI buildup layers on each side
2. Understanding HDI PCB Layer Structures
HDI PCB manufacturing uses a sequential buildup process (SBU), where dielectric layers and copper foils are added layer by layer outside the core PCB.
A typical HDI PCB structure includes:
- Core layer
- Inner copper layers
- Prepreg dielectric layers
- Microvias
- Copper-filled vias
- Outer circuit layers
The microvia connection method determines the performance and complexity of the HDI PCB.
Common HDI via structures include:
Blind Microvia
A microvia connects an outer layer to an internal layer but does not pass through the entire PCB.
Buried Via
A buried via connects internal layers without reaching the surface.
Stacked Microvia
Multiple microvias are placed vertically on top of each other.
Staggered Microvia
Microvias are offset between different layers to improve reliability.
3. What Does 1+N+1 Mean in HDI PCB?
Definition of 1+N+1 HDI Structure
A 1+N+1 HDI PCB contains:
- One buildup layer on the top side
- N-layer core structure
- One buildup layer on the bottom side
Example:
A 6-layer 1+N+1 HDI PCB may consist of:
- Top microvia layer
- 4-layer core
- Bottom microvia layer
The microvia only connects the outer layer to the first inner layer.
Structure:
Top Layer
↓
Microvia Layer
↓
Core Layers (N)
↓
Microvia Layer
↓
Bottom Layer
Advantages of 1+N+1 HDI PCB
3.1 Lower Manufacturing Cost
Because it requires fewer buildup cycles, 1+N+1 HDI is more affordable than advanced HDI structures.
Typical prototype pricing:
- Small quantity HDI PCB prototype: Approximately $100–$500 per design setup
- Production orders: Around $5–$50 per PCB depending on size, layer count, and volume
3.2 Shorter Production Lead Time
The simpler structure reduces:
- Laser drilling processes
- Copper plating cycles
- Lamination steps
Typical lead time:
- Prototype: 7–15 working days
- Mass production: 3–5 weeks
3.3 Good Balance Between Performance and Cost
1+N+1 HDI provides:
- Higher routing density than standard multilayer PCB
- Better signal performance
- Lower manufacturing complexity
It is suitable for many consumer electronics applications.
4. What Does 2+N+2 Mean in HDI PCB?
Definition of 2+N+2 HDI Structure
A 2+N+2 HDI PCB contains:
- Two HDI buildup layers on the top side
- N-layer core
- Two HDI buildup layers on the bottom side
Structure:
Top Layer
↓
Microvia Layer 2
↓
Microvia Layer 1
↓
Core Layers (N)
↓
Microvia Layer 1
↓
Microvia Layer 2
↓
Bottom Layer
This structure allows more complex interconnection designs.
Microvia Technology Used in 2+N+2 HDI
2+N+2 usually requires:
Stacked Microvias
Example: Layer 1 → Layer 2 → Layer 3
Microvias are stacked vertically.
Advantages:
- Maximum routing density
- Suitable for advanced IC packages
- Supports smaller BGA pitch
However, stacked microvias require:
- Better laser drilling control
- Advanced copper filling technology
- Higher manufacturing precision
5. HDI PCB 1+N+1 vs 2+N+2 Comparison
Structure Complexity
1+N+1
- Single buildup layer
- Simple microvia connection
- Lower process difficulty
2+N+2
- Double buildup layer
- Multiple microvia connections
- Higher process complexity
Routing Capability
1+N+1
Suitable for:
- 0.5 mm pitch BGA
- Moderate component density
- Standard high-density applications
2+N+2
Suitable for:
- 0.4 mm pitch BGA
- 0.35 mm pitch components
- Advanced processors and chipsets
Reliability Comparison
1+N+1 HDI:
Advantages:
- Lower manufacturing risk
- Excellent reliability
- Easier inspection
2+N+2 HDI:
Advantages:
- Higher performance
- Better miniaturization capability
Challenges:
- More complex via structures
- Higher requirements for copper filling
- More strict impedance control
6. Manufacturing Process Differences
1+N+1 HDI Manufacturing Process
Typical process:
- Inner layer fabrication
- Lamination
- Laser microvia drilling
- Desmear treatment
- Copper plating
- Outer layer imaging
- Surface finishing
2+N+2 HDI Manufacturing Process
Additional steps:
- First buildup lamination
- First laser drilling
- Microvia filling
- Second buildup lamination
- Second laser drilling
- Sequential copper plating
The additional buildup cycles increase:
- Equipment requirements
- Process control difficulty
- Manufacturing cost
7. Cost Comparison of 1+N+1 and 2+N+2 HDI PCBs
Generally:
1+N+1 HDI PCB Cost
Approximate price:
- Prototype: $150–$800 per design
- Medium volume: $10–$80 per board
Factors affecting cost:
- Layer count
- PCB size
- Material selection
- Surface finish
- Quantity
2+N+2 HDI PCB Cost
Approximate price:
- Prototype: $300–$1500 per design
- Production: $30–$150 per board
The higher cost comes from:
- More lamination cycles
- Additional laser drilling
- Advanced via filling requirements
8. Design Advantages and Limitations
1+N+1 HDI Advantages
- Cost-effective
- Faster manufacturing
- Good reliability
- Suitable for most compact electronics
Limitations:
- Limited routing space
- Not ideal for extremely fine pitch devices
2+N+2 HDI Advantages
- Maximum wiring density
- Supports advanced semiconductor packages
- Better signal performance
- Enables thinner devices
Limitations:
- Higher cost
- Longer production cycle
- Requires experienced HDI manufacturers
9. Applications of Different HDI Structures
1+N+1 HDI PCB Applications
Common applications:
- Smartphones
- Tablets
- Smart wearable devices
- Consumer electronics
- IoT products
- Digital cameras
2+N+2 HDI PCB Applications
Common applications:
- High-end smartphones
- 5G communication equipment
- Automotive ADAS systems
- AI hardware
- Medical imaging equipment
- High-performance computing devices
10. How to Choose Between 1+N+1 and 2+N+2 HDI PCB?
Choosing the right HDI structure depends on:
1. Component Density
If your PCB contains:
- Large BGA packages
- High pin-count ICs
- Fine-pitch components
2+N+2 may be required.
2. Product Cost Target
For cost-sensitive products:
1+N+1 is usually the better choice.
3. Electrical Requirements
Applications requiring:
- High-speed signals
- Low signal loss
- Controlled impedance
may benefit from 2+N+2 HDI.
4. Production Volume
For mass production consumer electronics: 1+N+1 offers better cost efficiency.
For premium products: 2+N+2 provides higher performance.
11. HDI PCB Manufacturing Capability at KingSunPCB
As an experienced PCB manufacturer, KingSunPCB provides advanced HDI PCB manufacturing solutions for global customers.
Our HDI PCB capabilities include:
- 1+N+1 HDI PCB fabrication
- 2+N+2 HDI PCB manufacturing
- Laser microvia drilling
- Copper-filled microvia technology
- Fine-line HDI PCB production
- High-layer-count HDI boards
- Prototype and mass production services
KingSunPCB supports industries including:
- Automotive electronics
- Consumer electronics
- Industrial control
- Medical equipment
- Communication systems
With strict quality management systems, including ISO-certified manufacturing processes, KingSunPCB helps customers achieve reliable high-density PCB solutions.
12. Frequently Asked Questions (FAQ)
Q1: What is the difference between 1+N+1 and 2+N+2 HDI PCB?
The main difference is the number of buildup layers. 1+N+1 has one HDI layer on each side, while 2+N+2 has two buildup layers on each side, providing higher routing density.
Q2: Is 2+N+2 HDI PCB better than 1+N+1?
Not always. 2+N+2 provides better performance and miniaturization capability, but 1+N+1 is more cost-effective for many applications.
Q3: How much does HDI PCB manufacturing cost?
HDI PCB prices typically range from $10 to $150 per board depending on structure, layer count, materials, quantity, and complexity.
Q4: Which HDI structure is used for smartphones?
Both structures are used. Standard smartphones often use 1+N+1 HDI, while flagship smartphones with advanced processors may use 2+N+2 or higher-level HDI technology.
Q5: Why are microvias important in HDI PCB?
Microvias enable higher wiring density, smaller PCB size, improved signal integrity, and support for advanced electronic components.
13. Conclusion
The choice between HDI PCB 1+N+1 and 2+N+2 microvia structures depends on product requirements, cost targets, component density, and electrical performance.
For cost-efficient high-density applications, 1+N+1 HDI PCB provides an excellent balance between performance and manufacturing complexity.
For advanced electronics requiring maximum miniaturization and signal performance, 2+N+2 HDI PCB technology offers superior capability.
By selecting an experienced HDI PCB manufacturer such as KingSunPCB, engineers can achieve reliable microvia interconnection solutions for next-generation electronic products.