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What do you know about HDI Board

  HDI board refers to High-Density Interconnect, namely High-Density Interconnect board. It is a relatively new technology developed by the PCB industry at the end of the 20th century. When the drilling hole size of the traditional PCB reaches 0.15mm, the cost is very high and it is difficult to improve it again because of the affection by the drilling tool. The drilling of HDI board no longer relies on traditional mechanical drilling but uses the laser drilling technology so that it's sometimes called a laser plate. The hole diameter of the HDI board is generally 3-5mil (0.076mm-0.127mm) and the width of circuits is generally 3-4mil (0. 076mm-0.10mm). The size of the pad can be greatly reduced, so more circuits can be distributed within the unit area, resulting in higher density. The emergence of HDI technology adapts and advances the development of PCB industry, making it possible to arrange the more concentrated BGA, QFP and so on in the HDI board. At present, HDI technology has been widely used, among which the level 1 HDI has been widely used in the PCB production of BGA with 0.8 pitch.

  Under the premise that the electronic products tend to be more complicated, the contact distance of the integrated circuit components is reduced, and the speed of signal transmission is relatively increased, which is followed by an increase in the number of wires and a locality of the length of the wires between the points. Shortening, these require the use of high-density line configuration and micro-hole technology to achieve the goal. Wiring and bridging basically have difficulties for single and double panels, so the circuit board will be multi-layered, and as the signal lines continue to increase, more power layers and ground planes are necessary means of design. These have prompted the Multilayer Printed Circuit Board to become more common.

  For the electrical requirements of high-speed signals, the board must provide impedance control with AC characteristics, high-frequency transmission capability, and reduce unnecessary radiation (EMI). With the structure of Stripline and Microstrip, multi-layering becomes a necessary design. In order to reduce the quality of signal transmission, an insulating material with a low dielectric constant and a low attenuation rate is used. In order to meet the miniaturization an array of electronic components, the circuit board also continuously increases the density to meet the demand. The emergence of assembly methods such as BGA (Ball Grid Array), CSP (Chip Scale Package), and DCA (Direct Chip Attachment) has pushed printed circuit boards to an unprecedented high-density state.

  Where the hole diameter less than 150um is known in the industry as Microvia, the circuit made by the micro-hole geometry technology can improve the efficiency of assembly, space utilization, etc., and also for the miniaturization of electronic products. It's a necessity.

  For circuit board products of this type, there have been many different names in the industry to call such boards. For example, European and American operators used the sequential construction method because they made the program. Therefore, this kind of product is called SBU (Sequence Build Up Process), and is generally translated as "sequential layering method". As for the Japanese manufacturer, the hole structure made by this kind of product is much smaller than the previous hole. Therefore, the production technology of this kind of product is called MVP (Micro Via Process), which is generally translated as "microporous process". Some people also call the MUM (Build Up Multilayer Board) because the traditional multi-layer board is called MLB (Multilayer Board), which is generally translated as "layered multi-layer board".

  HDI circuit advantages

1. Reduce PCB cost: When the density of PCB increases beyond the eight-layer board, it will be manufactured in HDI, and its cost will be lower than that of the traditional complicated pressing process.

2. Increase line density: the interconnection of traditional boards and parts

3. Conducive to the use of advanced packaging technology

4. Have better electrical performance and signal correctness

5. Better reliability

6. Can improve thermal properties

7. Can improve RF interference / electromagnetic interference / electrostatic discharge (RFI / EMI / ESD)

8. Increase design efficiency

HDI application

  Electronic design is also trying to reduce its size while continuously improving the performance of the whole machine. From small mobile phones to smart portable products, "small" is a constant pursuit. High-density integration (HDI) technology enables the end-product design to be more compact while meeting higher standards of electronic performance and efficiency. HDI is currently widely used in mobile phones, digital (camera) cameras, MP3, MP4, notebook computers, automotive electronics, and other digital products, among which mobile phones are the most widely used. HDI boards are generally manufactured using a build-up method. The more times the layers are stacked, the higher the technical grade of the board. Ordinary HDI boards are basically one-time laminate, high-order HDI uses two or more layers of technology, and adopts advanced PCB technology such as stacking holes, plating holes, and laser direct drilling. High-end HDI boards are mainly used in 3G mobile phones, advanced digital video cameras, and IC carrier boards.

How to distinguish between first-order and second-order and third-order of HDI PCB

  The first order is relatively simple, and the process and process are well controlled.

  The second order began to be troublesome, one is the alignment problem, one punching and copper plating problem. There are a variety of second-order designs. One is the staggered position of each step. When connecting the sub-adjacent layers, the wires are connected in the middle layer. This is equivalent to two first-order HDIs.

  The second is that the two first-order holes overlap, and the second-order is realized by superposition. The processing is similar to the two first-order, but there are many technical points to be specially controlled, that is, the above.

  The third type is to directly punch from the outer layer to the third layer (or the N-2 layer). The process is much different from the front, and the punching is more difficult.

The difference between the HDI board and  PCB

 PCB boards are mainly FR-4, which is made of epoxy resin and electronic grade glass cloth. Generally, the traditional HDI, the outermost use of adhesive copper foil, because of laser drilling, cannot open the glass cloth, so generally, use glass fiber-free adhesive copper foil, but now high-energy laser drill can already penetrate 1180 glass cloth. This is no different from ordinary materials.

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