PCB HDI (High Density Interconnector) products are an important part of the modern electronic manufacturing industry. They achieve higher circuit density and shorter electrical connection paths through advanced micro-hole technology and multi-layer structure design. So what is the difference between HDI products and ordinary multi-layer board products+ We use 4-layer through-hole vs 4-layer 1-step 1-press HDI products as an example to introduce PCB HDI products from four aspects: process, stacking, product characteristics and product requirements:
1. Process
HDI and Through-Hole PCB Process Comparison
The colors in the figure above indicate the differences between HDI products and ordinary products. The following is a brief description
1.HDI pre-press drilling: The drilling here is no different from the ordinary double-sided board drilling. Its purpose is to drill the buried via in the HDI inner layer stacking structure. Generally, the size of the buried via is small, usually no larger than 10mil (0.25mm).
2. HDI plating before lamination: The plating here is the same as that of ordinary double-sided boards, but the hole copper is relatively thin, only 12um according to IPC. The circuit after electroplating is actually the circuit process of the outer layer (dry film, not wet film).
3. HDI laser drilling: This is the main difference between ordinary products and HDI products. It uses the high energy density of CO2 laser to locally heat the material, melt the material or even vaporize it, so as to realize the processing of holes. Since this processing depends on the size of laser energy, there are restrictions on the hole diameter, hole depth and pre-processing. I will not expand on this here. In the next issue, I will talk about how Laser drilling is made.
4. HDI electroplating: HDI electroplating is much more complicated and difficult than ordinary multilayer boards, mainly reflected in the differences in sub-processes, chemicals, and control priorities.
For example: HDI copper plating generally requires horizontal copper wire, while ordinary multilayer boards are not so picky; for another example, VCP and special electroplating agents are needed for blind via copper plating…
After talking about Laser, we can open another issue to talk about HDI electroplating, so that the knowledge sharing of HDI can be made into a series~ Very good~
2. Stacking
The stacking structure of PCB HDI board usually includes multiple inner and outer layers, and the electrical connection between each layer is achieved through blind buried vias and electroplating technology. According to different application scenarios and design requirements, the number and arrangement of inner layers can be flexibly adjusted. At the same time, in order to increase signal transmission speed and reduce crosstalk, HDI board may also adopt special wiring strategies and impedance control technology.
3. Product Features
1. High-density wiring: Through blind buried hole technology and multi-layer structure design, PCB HDI boards can achieve higher circuit density and shorter electrical connection paths. This is why HDI products can achieve 3mil or even 2mil lines.
2. Excellent electrical performance: The use of high-quality substrates and conductive materials, as well as precise manufacturing processes, ensures that PCB HDI boards have good electrical properties, such as low impedance, low crosstalk, etc. Especially now, communication products are all designed with HDI, such as mobile phones, walkie-talkies, audio and video systems, etc.
In summary, PCB HDI products occupy an important position in the modern electronic manufacturing industry with their high-density wiring and excellent electrical performance. At the same time, their strict manufacturing process and quality control also ensure the high performance and stability of the products. With the continuous advancement of technology and the continuous expansion of application fields, PCB HDI products will have a broader development prospect.
