Table of Contents
1、 Definition and Core Features of HDI PCB
HDI PCB (High Density Interconnect Board) is a circuit board that achieves high-density wiring through micro blind buried hole technology. Its core features include:
1. Micro aperture: Using laser drilling technology, the aperture is only 3-6mil (0.076-0.152mm), much smaller than the 0.3mm or more of ordinary PCBs.
2. High line density: The line width/spacing can reach 3mil/3mil (0.076mm/0.076mm), increasing the number of lines per unit area by more than 30%.
3. Multi layer structure: Multi order interconnection is achieved through the Build Up method. Ordinary HDI is a first-order layer, while high-order HDI can reach more than 5 orders.
2、 Core differences between HDI PCB and regular PCB
| Comparing dimensions | HDI PCB | 普通PCB |
| Wiring density | Line width/spacing ≤ 3mil, supports BGA/CSP packaging | Line width/line spacing ≥ 8mil, suitable for traditional packaging |
| Aperture technology | Laser drilling (micro blind hole/buried hole) | Mechanical drilling (mainly through holes) |
| Layers and thickness | Multi layer (more than 10 layers), thinner thickness (0.6-1.6mm) | Mostly 4-6 layers, with a relatively large thickness (1.6-2.4mm) |
| Signal performance | Reduce crosstalk and EMI, support high-speed signal transmission | The signal path is long and susceptible to interference |
| Application scenarios | Mobile phones, 5G devices, medical instruments | Home appliances and industrial control equipment |
3、 Difficulties in HDI PCB design and manufacturing
1. Design Challenge
-Micro blind hole layout: To avoid stress concentration caused by stacking blind holes, it is recommended to use a staggered via structure.
-Signal integrity: Fine pitch wiring (such as 50 μ m/50 μ m) requires impedance tolerance control (± 10%) and optimization of differential pair length.
-Heat dissipation management: dispersing the heat of high-power devices through metal filled blind holes or thermal vias.
2. Manufacturing difficulties
-Laser drilling accuracy: The aperture error should be controlled within ± 25 μ m to avoid the influence of hole wall roughness on reliability.
-Electroplating hole filling: Adopting reverse pulse electroplating technology to ensure the uniformity of copper thickness on the hole wall and prevent void defects.
-Material selection: Use high Tg FR-4 or polyimide substrate to cope with high-frequency signal loss and high temperature environment.
3. Testing and Verification
-Reliability testing: including thermal cycling (-55 ℃~125 ℃), mechanical impact, etc., to verify the strength of solder joints and micro hole connections.
-Signal integrity testing: Use a Vector Network Analyzer (VNA) to detect high-frequency signal loss.
4、 Future Development Trends
With the popularization of AI and 5G technology, HDI PCB design is evolving towards higher density (line width<20 μ m), higher layers (>20 layers), and 3D integration. For example, the AI server adopts a 10+layer HDI design to support 112G SerDes signal transmission.
