Via:It is also called through hole. It is completely opened from the top layer to the bottom layer. In a four layer PCB, through holes run through layers 1, 2, 3, and 4, which will hinder the routing of irrelevant layers. There are two main types of vias:
1. Countersunk hole PTH (Plating Through Hole) has copper on the hole wall, generally VIA PAD and DIP PAD.
2. Non countersunk copper hole NPTHNon Plating Through Hole), the hole wall is free of copper, generally positioning hole and screw hole.
Blind Via: Only one layer of the top or bottom layer can be seen, and the other layer cannot be seen. That is to say, Blind holes are drilled from the surface, but not through all layers. The blind hole may be from 1 to 2, or from 4 to 3 (advantage: I, 2 conduction will not affect 3, 4 routing); The vias run through layers 1, 2, 3 and 4, which affects the routing of irrelevant layers However, the cost of blind hole is relatively high, and laser drilling machine is required. The blind hole plate is applied to the connection between the surface layer and one or more inner layers. One side of the hole is on the -- side of the plate, and then it is connected to the interior of the plate: simply speaking, only one side of the blind hole surface can be seen, and the other side is in the plate- It is generally applied to PCB boards with four or more layers.
Buried Via:The embedded hole refers to the hole made in the inner layer, which cannot be seen after pressing, so it does not need to occupy the area of the outer layer. The upper and lower sides of the hole are in the inner layer of the board, in other words, they are embedded in the board. To put it simply, it is sandwiched in the middle. These processes cannot be seen from the surface, neither the top layer nor the bottom layer. The advantage of making buried holes is to increase wiring space. However, the process cost of making buried holes is very high. General electronic products are not used, but only in special high-end products. It is generally applied to PCB boards with six or more layers.
Almost all PCB boards use vias, which are basic and common holes. Therefore, we will not explain them here, but mainly talk about blind holes and embedded holes. First, let's start with the traditional multilayer board. The structure of the standard multilayer circuit board is composed of inner and outer circuits. The drilling and metallization process in the hole are used to achieve the internal connection function of the circuits in each layer. However, with the increase of circuit density, the packaging method of parts is constantly updated. In order to allow the limited circuit board area to accommodate more parts with higher performance, in addition to the thinner line width, the aperture of the DIP jack is also reduced from 1mm to 0.6 mm of the SMD, and further reduced to 0.4 mm or less. However, it will still occupy the surface area, so there are blind holes and buried holes.
In the four layer board, the middle two layers are mainly used to run the power supply layer (VCC) and the stratum (GND). If the board sub components have a large density, the inner layer can also run some ordinary signal lines, which can be used as the stratum in the adjacent inner layer of the main component layer (the main component layer is generally in the item layer). The whole layer is used for copper coating, and the other inner layer is used as the main wiring layer. The sub component layer (the sub component layer is generally in the bottom layer) can also run some lines.

Positives and negatives:For the four layer board, the first thing to understand is the difference between positive film and negative film, that is, between layer and plane. The positive section is the wiring method commonly used in the project layer and stratum. That is, the wiring place is copper wire, and the Polygon Pour is used for bulk copper coating filling. On the contrary, the negative film is coated with copper by default. The place of wiring is the split line, that is, after generating a negative film, the whole layer has been coated with copper. The thing to do is to split the copper coating, and then set the split copper coating network. In the previous version of PROTEL, split was used for segmentation. In the current version of Altium Designer, Line and the shortcut key PL were used for segmentation. The split line should not be too thin. I used 30mil (about 0.762mm). To split copper coating, just draw a closed polygonal box with LINE, and set the network by copper coating in the double click box. Both positive and negative sheets can be used for the internal electric layer, and the positive sheet can also be realized by wiring and copper coating. The advantage of negative film is that it is filled with large copper coating by default. Adding vias, changing copper coating size and other operations do not require rebuilding, which saves the time for copper coating calculation. When the middle layer is used for the power layer and stratum, most of the layers are large pieces of copper, so the advantage of using negative film is obvious.

Advantages of blind hole and buried hole:In the non through hole technology, the application of blind hole and buried hole can greatly reduce the size and quality of PCB, reduce the number of layers, improve electromagnetic compatibility, increase the characteristics of electronic products, reduce costs, and also make the design easier and faster. In the traditional PCB design and processing, through holes will bring many problems. First, they occupy a large amount of effective space, and secondly, a large number of densely spaced through-hole holes also create a huge obstacle to the routing of the inner layer of the multilayer PCB. These through-hole holes occupy the space required for routing. They densely pass through the surface of the power and ground layers, and also damage the impedance characteristics of the power and ground layers, making the power and ground layers invalid. And the conventional mechanical drilling will be 20 times as much as the non pilot drilling. In PCB design, although the size of pads and vias has gradually decreased, if the thickness of the board layer does not decrease proportionally, the aspect ratio of the through-hole will increase, and the increase of the aspect ratio of the through-hole will reduce the reliability. With the maturity of advanced laser drilling technology and plasma dry etching technology, it is possible to apply non penetrating small blind holes and small buried holes. If the hole diameter of these non penetrating pilot holes is 0.3mm, the parasitic parameters are about 1/10 of the original conventional holes, which improves the reliability of PCB. Due to the use of non through hole technology, there will be few large through holes on the PCB, which can provide more space for wiring. The remaining space can be used for large area shielding to improve EMI RFI performance. At the same time, more remaining space can also be used for the inner layer to partially shield devices and key network cables, so that they have good electrical performance. By using non guide holes, it is more convenient to fan out the device pins, making it easy to route high-density pin devices (such as BGA package devices), shorten the length of wiring, and meet the timing requirements of high-speed circuits.
Disadvantages of using blind hole and buried hole:The main disadvantage is that the cost of boards is high and the processing is complex. It will not only increase the cost but also cause processing risks, and it will be more difficult to test and measure during commissioning. Therefore, it is recommended not to use blind holes and embedded holes as much as possible, unless the board size is limited and it is unavoidable to use them.