1. There is only copper in the hole of the circuit board, and the solder mask can be plugged or not;

　　2. The through holes of the circuit board must have solder resist ink plug holes, which are opaque, must not have tin circles and tin beads, and must be flat;

　　3. There must be tin and lead in the hole of the circuit board, and there is a certain thickness requirement (4um), so as to avoid the solder mask ink entering the hole, causing the hole to hide tin beads.

　　Blind hole circuit board is to connect the outermost circuit in the printed circuit board (PCB) and the adjacent inner layer with plated holes. Since the opposite side cannot be seen, it is called blind through. In order to increase the space utilization between the circuit layers of the board, blind vias come in handy. A blind hole is a via hole to the surface of the printed board.

　　Blind holes are located on the top and bottom surfaces of the circuit board, with a certain depth, and are used for the connection of the surface circuit with the inner circuit below. The depth of the hole generally has a specified ratio (diameter). This kind of production method requires special attention. The drilling depth must be just right. If you don't pay attention, it will cause difficulties in electroplating in the hole. Therefore, very few factories will adopt this production method. In fact, it is also possible to drill holes for the circuit layers that need to be connected in advance in the individual circuit layers, and then glue them together at the end, but it requires a more precise positioning and alignment device.

　　A buried-hole circuit board is a connection between any circuit layers inside a printed circuit board (PCB), but it is not connected to the outer layer, that is, it does not mean a via hole extending to the surface of the circuit board.

　　This can not be achieved by the way of drilling the circuit board after bonding the circuit board in the production process of the circuit board factory. The drilling operation must be performed at the individual circuit layer, and the inner layer is partially bonded first, then the electroplating treatment is performed, and finally all the bonding is performed. Since the operation process is more laborious than the original via and blind vias, the price is also the most expensive. This fabrication process is usually only used for high-density circuit boards, increasing the space utilization of other circuit layers.

　　Drilling holes are very important in the printed circuit board (PCB) production process. A simple understanding of drilling is to drill the required vias on the copper clad laminate, which has the function of providing electrical connections and fixing devices. If the operation is incorrect, there will be problems in the process of the via hole, and the device cannot be fixed on the circuit board, which will affect the use of the circuit board in the light, and the whole board will be scrapped in severe cases. Therefore, the drilling process is very important.

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