PCB News - Introduction of blind PCB and buried PCB

PCB Via: It is also called a through hole. It is opened from the top layer to the end layer. In a four-layer PCB, the via hole penetrates through the 1, 2, 3, and 4 layers.

There are two main types of PCBvias:

1. Immersion copper hole PTH (Plating Through Hole), the hole wall has copper, usually current through hole (VIA PAD) and component hole (DIP PAD).

2. NPTH (Non Plating Through Hole), the hole wall has no copper, usually positioning holes and screw holes

PCBBlind Via: It can only be seen from the top or bottom layer. The extra layer is invisible. That is to say, the blind hole is drilled from the outside, but not through the entire layer.

PCBBlind vias may be as long as from 1 to 2, or from 4 to 3 (benefits: 1, 2 conduction will not affect 3, 4 traces); and vias run through 1, 2, 3, and 4 layers. The layer routing has an impact. However, the cost of blind holes is higher, and laser drilling machines are required. The blind hole plate is used to connect the outer surface layer and one or more inner layers. One side of the hole is on one side of the wrench, and then passes to the inner side of the wrench to cut off; to put it simply, the outer surface of the blind hole can only be seen on one side, the other side It's in the wrench. Generally used in PCBboards with four or more layers.

PCBBuried Via: Buried via refers to the inner via hole. After pressing, there is no way to see it, so it does not occupy the size of the outer plane or the surface of the object. The upper and lower sides of the hole are both inside the inner layer of the wrench, In other words is buried in the wrench. To put it simply, it is sandwiched in the middle of the waist. You can't see these processes from the outside, and you can't see the top and bottom layers. The benefit of making buried vias is to increase the wiring space. However, the process cost of making buried holes is long, and ordinary electronic products are not considered suitable and used, and they will only be applied in especially high-end products. Generally used in PCB boards with six or more layers.

After reading this experience, I still felt that it was not intuitive. If you think about it, just go to a picture! Positive film and negative film: For a four-layer board, the first thing to figure out is the difference between a positive film and a negative film, which is the difference between layer and plane. The positive film is the wiring method commonly used on the top layer and the ground layer, and the wiring place is copper wire, which is supplemented by a large block of copper with Polygon Pour. The negative film is just the opposite. The copper is acquiesced, and the wiring is divided into lines, that is, a negative film is generated. After that, the entire layer has been coated with copper. The thing to do is to divide the copper and set the divided coating. Copper network. In the previous version of PROTEL, Split was used to divide, but in the current version of Altium Designer, Line and the agile key PL are used directly to divide. The dividing line is not suitable for too thin, I use 30mil (about 0.762mm). When you want to divide the copper, just use LINE to draw a closed polygonal box, and double-click the copper to set the network. Both positive and negative films can be used for the internal electrical layer, and the positive film can also be successfully implemented after routing and copper coating. The benefit of the negative film is that it acquiesces to the addition of large copper deposits, and there is no need to rebuild when adding vias, changing the copper deposit volume, etc., which saves the time for calculating the new copper deposit. The half mid-waist layer is used for the power layer and the ground layer, and most of the layer is copper-clad, so the advantage of using the negative film is more superficial.

The advantages of using blind vias and buried vias are considered appropriate. In the non-through via technology, the application of blind vias and buried vias can greatly reduce the size and quality of HDI PCB, reduce the number of layers, increase electromagnetic compatibility, and increase electronics The unique style of the product reduces the cost, and at the same time it will make the default office easier and more convenient. In traditional PCB presetting and processing, through holes can cause many problems. First of all, they occupy a large number of pipe space. The densely packed through holes in one place also cause a big stumbling block to the inner layer of the multilayer PCB. These through holes take up the space required for the wiring, and they are densely distributed. The penetration of current through the surface of the source and the ground plane will also damage the special impedance of the power ground plane and make the power ground plane ineffective. And the common sense mechanical method of drilling will be 20 times the amount of office work that is deemed appropriate and using non-through via technology. In the PCB preset, although the size of the pads and vias have gradually decreased, if the thickness of the board layer is not proportionally reduced, the aspect ratio of the through hole will increase, and the increase in 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 becomes possible to apply non-through small blind holes and small buried holes. If the diameter of these non-through vias is 0.3mm, the resulting The parasitic parameter variable is about 1/10 of the initial common sense hole, which increases the reliability of the PCB. Because it is deemed appropriate to use non-through via technology, there will be few large vias on the PCB, so more space can be provided for wiring. The remaining space can be used as a shielding field for large planes or object surfaces to improve EMI/RFI performance. At the same time, more remaining space can also be used for the inner layer to partially shield components and key network cables, so that it has the best electrical performance. Using non-through vias deemed appropriate can facilitate component pin fan-out. High-density pin components (such as BGA package components) are easy to route, reduce the length of the string, and meet the timing requirements of high speed PCB.

Defects of using blind holes and buried holes that are deemed appropriate: The main shortcomings are the high cost of HDI boards and the complexity of processing. It not only increases the cost but also the processing risk. It is very difficult to adjust the special situation for testing and surveying, because this proposal does not need blind holes and buried holes as much as possible. The fault is that the size of the wrench is limited, and it is used when the situation is helpless.