Is HDI Circuit Board Better Than Other PCBs?

What does HDI circuit board mean: HDI circuit board is HDI (high-density interconnection) PCB, which is a kind of (technology) for the production of PCBs, and a PCB with high circuit distribution density using micro-blind and buried via technology.

HDI circuit board blind and buried via PCB production process

With the development of the design of portable products in the direction of miniaturization and high density, the design of PCBs is becoming more and more difficult, which puts forward higher requirements for the PCB production process. At present, most of the portable products make the BGA package with a pitch of less than 0.65mm, and the blind and buried via design process is used, so what is the blind and buried via PCB?

Blind and buried PCBs, also known as “HDI boards”, are often used in the application of high-end products such as mobile phones, GPS navigation, etc.

PCB holes are divided into three types: blind vias, buried vias, and through vias, among which: blind vias are the type of vias that connect the inner traces of the PCB with the traces of the surface of the PCB, and this hole does not penetrate the entire board. Buried vias are only connected to the via type of the traces between the inner layers, so they are not visible from the surface of the PCB. A through hole is a hole that can be seen directly from the top layer to the bottom layer, which is called a “through hole”. Blind and buried via PCBs

Blind and buried via PCB

When it comes to blind/buried PCBs, the first thing that comes to mind is the high multi-layer board, which consists of an inner circuit and an outer circuit, and then uses drilling and the process of metallization in the hole to achieve the internal connection function of each layer of the circuit. However, due to the increase of line density and the continuous updating of the packaging method of the parts, in order to allow more and higher performance parts to be placed in the limited PCB area.

In addition to the finer line width, the aperture has also been reduced from 1 mm in the DIP hole diameter to 0.6 mm in the SMD, and further reduced to less than 0.4mm. However, it still occupies the surface area, so there are buried and blind vias, which are defined as follows:

1. Buried Via: The through holes between the inner layers cannot be seen after pressing, so it does not have to occupy the area of the outer layer
2. Blind Via is applied to the communication of the surface layer and one or more inner layers.
3. Buried hole design and production, the production process of buried hole is more complex than that of traditional multi-layer boards, and the cost is also higher.
4. Blind hole design and production, extremely high density, double-sided SMD design board, there will be upper and lower outer layers, I/O guide holes between each other interference, especially when there is VIP (Via-in-pad) design, it is a trouble. Blind vias can solve this problem. In addition, with the prevalence of radio communication, the design of the line must reach the range of RF (Radio frequency), more than 1GHz, and the blind via design can meet this demand.

There are three different ways to make a blind well plate, as described below:

1. Mechanical depth drilling, the traditional multi-layer board manufacturing process, to press, the drilling machine is used to set the Z-axis depth of drilling, but this method has several problems;
2. Only one piece of drilling can be drilled each time, and the output is very low;
3. The levelness of the drilling machine table is strict, and the drilling depth of each spindle should be consistent, otherwise it is difficult to control the depth of each hole;
   It is difficult to electroplating in the hole, especially if the depth is greater than the hole diameter, it is difficult to do the electroplating in the hole;

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