PCB Blog - Application and Processing Technology of HDI Board

HDI PCB board, namely high-density interconnection board, is a kind of printed circuit board with high circuit distribution density using micro blind buried hole technology. It is a manufacturing process that includes inner and outer lines, and uses drilling and metallization inside the holes to realize the connection function between the inner layers of lines. With the development of electronic products to high density and high precision, the same requirements are put forward for circuit boards. The effective way to improve the density of PCB is to reduce the number of through holes, and set blind holes and buried holes to meet this requirement. Therefore, HDI PCB boards are produced.

The increased wiring density on the HDI PCB board allows more functions per unit area. The advanced HDI PCB board has multilayer copper filled stacked micropores, enabling complex interconnections. Microholes are tiny laser drilled holes on multilayer circuit boards that can be interconnected between layers. In advanced smartphones and handheld electronic devices, these pores span multiple layers. Microholes are through holes in the pad that are staggered, offset, stacked, copper plated on the top, plated, or filled with solid copper.

HDI: High-Density Interconnection Technology. It is a multilayer board manufactured by using the layer adding method and the micro blind hole embedding method.

Micro holes: In PCB board, holes with a diameter less than 6mil (150um) are called micro holes.

Buried Via Hole: The hole buried in the inner layer is invisible in the finished product. It is mainly used for the conduction of the inner line, which can reduce the probability of signal interference and maintain the continuity of the characteristic impedance of the transmission line. Since the buried hole does not occupy the surface area of PCB, more components can be placed on the surface of PCB board.

Blind Via: a through hole connecting the surface layer and the inner layer without penetrating the whole plate.

HDI PCB board are generally manufactured by lamination method. The more times of lamination, the higher the technical level of boards. Ordinary HDI PCB board is basically stacked once, while high-order HDI PCB board is stacked twice or more, and advanced PCB technologies such as hole stacking, electroplating and hole filling, and laser direct drilling are also used. When the density of PCB is increased to more than eight layers, the cost of HDI manufacturing will be lower than that of traditional complex pressing process. HDI PCB board is conducive to the use of advanced construction technology, and its electrical performance and signal accuracy are higher than traditional PCB. In addition, HDI PCB board has better improvement for radio frequency interference, electromagnetic wave interference, electrostatic discharge, heat conduction, etc. Electronic products are constantly developing towards high density and high precision. The so-called "high" means not only improving the performance of the machine, but also reducing the size of the machine. High density integration (HDI) technology can make the terminal product design smaller, while meeting higher standards of electronic performance and efficiency. At present, many popular electronic products, such as mobile phones, digital cameras, laptops, automotive electronics, etc., use HDI PCB board. With the upgrading of electronic products and market demand, HDI PCB board will develop very rapidly.

How to distinguish the first, second and third order of HDI PCB

The first level is relatively simple, and the process and process are easy to control.

The second order problems began to be troublesome. One was alignment, the other was punching and copper plating. There are many kinds of second order designs. One is stagger position of each order. When it is necessary to connect the next adjacent layer, it is connected in the middle layer through wires, which is equivalent to two first order HDI. The second is that the two first order holes overlap, and the second order is realized by overlapping. The processing is similar to the two first order holes, but there are many process points to be specially controlled, that is, the above mentioned. The third method is to directly drill from the outer layer to the third layer (or N-2 layer). The process is different from the previous one, and the drilling is more difficult.

HDI high-density system method has no clear definition, but generally there is a considerable difference between HDI and non HDI. First of all, the aperture used for circuit carrier boards made of HDI should be less than or equal to 6mil (1/1000 inch). As for the ring diameter of hole ring, it should be ≤ 10mil, while the layout density of line contacts should be more than 130 points per square inch, and the line spacing of signal lines should be less than 3mil. HDI PCB board has many advantages. Because HDI circuits are highly integrated, the area of the boards used can be greatly reduced, and the higher the number of layers, the smaller the boards can be correspondingly increased. Because the size of the substrate is smaller, the area of HDI applied circuit boards can be 2 to 3 times less occupied than that of non HDI PCB board, but can maintain the same complex circuits. The weight of natural boards can be reduced accordingly. As for the design of RF, HF and other specific block circuits, multi-layer structures can be used well. Large area metal grounding layers can be set on the upper/lower layers of the main circuit to limit the EMI problems of high-frequency lines that may be caused by PCB to the interior of HDI PCB board, so as to avoid affecting the operation of other external electronic equipment. The HDI PCB board is lighter, the circuit density is higher, and the space utilization rate in the chassis is higher than that of non HDI PCB board design. The original high-frequency operating devices will shorten the transmission distance of the signal line because of the HDI PCB board, which is naturally conducive to the signal transmission quality of the new SoC or high-frequency operating devices. Because of the better electrical characteristics, the transmission efficiency is improved. In addition, if the HDI PCB board is used more than 8 layers, Basically, it can achieve better cost performance than non HDI PCB board. For terminal product design, HDI motherboard design scheme can also be used to improve product performance and specification data performance, making the product more competitive in the market.