What is HDI PCB?
HDI stands for High-Density Interconnect, which refers to circuit boards with higher wiring density per unit area compared to traditional circuit boards. Printed circuit board technology has been evolving to meet the demands of smaller and faster products.HDI boards are more compact and feature smaller vias, pads, copper traces, and spaces. As a result, HDI allows for denser routing, making the PCB lighter, more compact, and with fewer layers. A single HDI board can accommodate the functionalities of multiple boards previously used in a device. HDI PCBs are a preferred choice for high-layer and expensive laminated boards.
Structures of Different HDI PCB
There are two basic HDI standard structures known as Sequential Build-Up and Every Layer Interconnect (ELIC). Among these two structures, the Sequential Build-Up structure is the most commonly used. In this structure, firstly, the core is constructed and laminated. Then, drilling, plating, and filling processes are carried out. This layer is then laminated together with other layers, followed by repeating the drilling, plating, and filling processes. ELIC is employed for applications with high interconnectivity requirements, where all microvia layers can be freely interconnected. The number of layers is one of the crucial factors in designing HDI boards. This decision is based on the type of stack-up used in the PCB design.
Based on the design requirements, HDI printed circuit boards can employ different layering techniques to achieve the desired performance.
The Advantages of HDI PCB
- Improved Reliability: Due to their smaller aspect ratio, microvias offer better reliability compared to typical through-hole vias. They are more robust than through-holes and employ superior materials and components, resulting in excellent performance for HDI (High-Density Interconnect) technology.
- Enhanced Signal Integrity: HDI technology incorporates via-in-pad and blind-via techniques. These techniques help bring components closer to each other, reducing the length of signal paths. HDI technology eliminates stubs caused by through-holes, reducing signal reflection and improving signal quality. Therefore, shorter signal paths significantly enhance signal integrity.
- Cost-effectiveness: With proper planning, HDI technology can reduce overall costs compared to standard PCBs. This is due to the requirement of fewer layers, smaller dimensions, and fewer PCBs needed.
- Compact Design: The combination of blind and buried vias reduces the space requirements of the circuit board.
| Serial No | Item | Technical Parameters |
| 1 | Base Material | FR-4｜High Tg｜Halogen-free｜PTFE｜ Ceramic PCB｜ Polyimide |
| 2 | Board Type | PCB｜FPC｜R-FPC｜HDI |
| 3 | Hignest Layer | 64 Layer |
| 4 | Minimum base copper thickness | 1/3 OZ (12um) |
| 5 | Maximum finished copper thickness | 8 OZ |
| 6 | Minimum trace / gap (Inner layer) | 2/2mil (H/H OZ base copper) |
| 7 | Maximum produce size | 609*889mm |
| 8 | Minimum trace / gap (Outer layer) | 2/2mil (1/3 OZ base copper) |
| 9 | Minimum distance from hole to inner conductor | 6mil |
| 10 | Minimum distance from hole to outer conductor | 6mil |
| 11 | Minimum over-hole solder ring | 3mil |
| 12 | Minimum component solder ring | 5mil |
| 13 | Minimum BGA pads | 8mil |
| 14 | Minimum BGA Pitch | 0.4mm |
| 15 | Minimum Finished Hole Diameter | 0.15mm(CNC)｜0.1mm(Laser) |
| 16 | Maximum board thickness to hole diameter ratio | 20:1 |
| 17 | Minimum solder resist bridge width | 3mil |
| 18 | Soldermask / circuit processing method | Film｜Laser Direct Imaging |
| 19 | Minimum insulation layer thickness | 2mil |
| 20 | HDI & Specialty Boards | HDI(1-7 steps)｜R-FPC(2-16 layers)｜High frequency mix-pressing(2-20 layers) |
| 21 | Surface Finish Type | Immersion gold(ENIG), HASL lead free, Immersion tin, Immersion silver, OSP, Full board gold plating, Immersion gold + OSP |
