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I.​What is HDI PCB?

HDI is short for High Density Interconnector. It is a production technology of printed circuit board. It is a kind of circuit board with high circuit distribution density using micro-blind buried hole technology. HDI board has inner circuit and outer circuit, using drilling, hole metallization and other processes, so that each layer of circuit internal connection.


  • The differences between HDI PCB and Ordinary PCB

HDI board is generally made by stacking, the more times the stacking, the higher the technical level of the board.

Ordinary HDI board is basically one stacking. The high level HDI uses two or more laminar structure of technology. At the same time, the use of stacking holes, electroplating hole filling, laser direct drilling and other advanced PCB technology. When PCB density increases beyond eight layers, the cost of manufacturing with HDI is lower than that of traditional complex laminating processes.

The electrical performance and signal accuracy of HDI board are higher than traditional PCB. In addition, HDI board for radio frequency interference, electromagnetic interference, electrostatic release, heat conduction and other better improvement. High density integration (HDI) technology enables end product designs to be miniaturized while meeting higher standards of electronic performance and efficiency.


II.Why we need the HDI board?

As electronic products tend to be multifunctional and complex, the contact distance of integrated circuit components decreases and the speed of signal transmission increases.With the increase in the number of connections and the shortening of the local length of interpoint circuit. We need the application of high-density line configuration and microhole technology is required to achieve the goal. HDI PCB has many technical advantages.

  • Design flexibility. HDI boards offer designers more design flexibility. Designers can take advantage of high component density, which facilitates faster signal processing.
  • Save space. Due to its advanced technical features, HDI board can easily accommodate more connections on the same board with fewer layers.
  • Suitable for intensive and complex packages. HDI is a good choice for intensive and complex packages involving high pin count and low spacing.
  • HDI boards meet the growing demand for smaller PCBS. non-HDI boards require more space and weight, making them difficult to use in many cases. Similarly, multiple PCBS can be integrated into a single HDI.
  • Signal integrity. The advanced technical features of this kind of PCB can help improve signal integrity and electrical performance.


III.Application of HDI circuit board

HDI PCB is suitable for a variety of industries. As mentioned above, you'll find them in all types of digital devices like smartphones and tablets, and miniaturization is key to the effective use of products. You can also find it in cars, planes and other vehicles that rely on electronics.

One of the most critical areas where high-density PCBS are making great progress is in the medical field. Medical devices often require small packages with high transmission rates that only HDI PCBS can provide. For example, the implant needs to be small enough to fit the human body, but any electronics involved in the implant absolutely must efficiently allow high-speed signal transmission. In addition, other medical devices, such as emergency room monitors, CT scans, etc., are also available on HDI PCB.


IV.​HDI circuit board laminated structure

  • Simple one-laminated HDI

The inner multi-layer board has no buried hole. And the pressing is completed in one time. Although it is a laminated board, its manufacturing is very similar to the conventional lamination of the lamination board. But the subsequent lamination is different from the need for laser drilling blind holes and other processes. Because this lamination structure has no buried hole, so in the production, the second layer and the third layer can be a core plate, the fourth layer and the fifth layer as another core plate, the outer layer plus the medium layer and copper foil, plus the medium layer after a press.

  • Conventional one-laminated HDI

The structure of this type of HDI is (1+N+1), (N≥2). This structure is the mainstream design of the industry at present, the inner multilayer plate has buried holes, need two pressing to complete. This type of primary laminate, in addition to the blind hole, there are buried holes.

  • Conventional 2 laminated HDI

The structure of this kind of HDI is (1+1+N+1+1), (N≥2). This structure is the mainstream design of secondary layer in the industry at present. The inner multi-layer has buried holes and needs three times of pressing to complete. The main reason is that there is no overlapping hole design, so the production difficulty is normal. If the optimization of buried hole of (3-6) layer can be changed to that of (2-7) layer as mentioned above, the one-time pressing can be reduced, and the process can be optimized to achieve the effect of cost reduction.

  • Blind holes stacking design of 2 laminated HDI

The structure of this type of HDI is (1+1+N+1+1), (N≥2). This structure is part of the industry's secondary laminated plate has such a design, the inner multi-layer has buried holes, need to complete the secondary pressing. The main features of this design are overlapping hole design and cross-layer blind hole design. The main features of this design are also overlapping blind hole above (2-7) buried hole, which increases the production difficulty. The buried hole design is in (2-7) layer, which can reduce the first lamination, optimize the process and achieve the effect of cost reduction.

  • Cross-layers blind hole design of 2 laminated HDI

The structure is (1+1+N+1+1), (N≥2). This structure is the industry has a certain difficulty in the production of the second layer of the board, such a design, the inner multi-layer board has buried holes in the (3-6) layer, need three times of pressing to complete. Mainly because of the cross-layer blind hole design, it is difficult to make, and it is difficult for HDI PCB manufacturers without certain technical ability to make it.


V.​What should we pay attention when design the HDI PCB?

Like any other PCB technology, HDI PCB also requires some specific concerns.

  • Materials. HDI PCB still takes them seriously because of some manufacturing limitations. The electrical properties of signal wiring will depend on the type of material chosen. The choice of materials is also a major factor in determining the cost.
  • ELIC. The construction of smart phones use this technology widely. It helps reduce mechanical holes and creates smaller spacing inside the board.
  • Track uniformity and minimum line width. These are important considerations to avoid short circuits or disconnections.
  • Component layout. HDI technology emphasizes accurate component placement. This placement helps ensure the feasibility of installing, welding and maintaining the board.
  • Distribution of blind holes and blind holes. An asymmetrical stack design may create unnecessary pressure, which can cause the board to warp.