Let's first introduce the common drilling in PCB: through hole, blind hole and buried hole. The meaning and characteristics of these three kinds of holes.
Via, a common type of hole, is used to conduct or connect copper foil circuits between conductive patterns in different layers of a circuit board. For example (such as blind hole, buried hole), but can not insert component leg or other reinforcement of copper plated hole. Because PCB is formed by the accumulation of many copper foil layers, each layer of copper foil will be laid with a layer of insulation layer, so that the copper foil layers can not communicate with each other, and the signal link depends on the via, so it has the name of Chinese through-hole.
The characteristics are: in order to meet the needs of customers, the through hole of circuit board must be plugged. In this way, in changing the traditional aluminum sheet plug hole technology, the white mesh is used to complete the solder mask and plug hole on the circuit board surface, so that the production is stable, the quality is reliable, and the application is more perfect. With the rapid development of electronic industry, higher requirements are put forward for the process and surface mounting technology of printed circuit board. The technology of plug hole through hole is applied and should meet the following requirements: 1. There is copper in the through hole, but the solder plug can not be plugged. 2. There must be tin and lead in the through hole, and there is a certain thickness requirement (4um) and no solder resist ink is allowed to enter the hole, resulting in tin beads hidden in the hole. 3. The through-hole must be provided with solder resist ink plug hole, which is opaque, free of tin ring, solder bead and leveling requirements.
Blind hole: it is to connect the outermost circuit in PCB with the adjacent inner layer by electroplating hole. Because the opposite side cannot be seen, it is called blind pass. At the same time, in order to increase the space utilization between PCB layers, blind holes are applied. That is, the through hole to a surface of the printed circuit board.
Features: the blind hole is located on the top and bottom surface of the circuit board, and has a certain depth. It is used to link the surface circuit and the inner circuit below. The depth of the hole usually does not exceed a certain ratio (aperture). In this way, special attention should be paid to the drilling depth (Z-axis). If not, electroplating in the hole will be difficult. Therefore, it is almost not used by factories. When the circuit layers need to be connected in advance, the holes can be drilled first and then bonded together. However, precise positioning and alignment devices are required.
Buried hole refers to the connection between any circuit layers in PCB, but it does not conduct to the outer layer, and it also means that the through hole does not extend to the surface of the circuit board.
Features: in this process, it is impossible to drill holes after bonding. Drilling must be carried out at the time of individual circuit layers. First, the inner layer is partially bonded and then electroplated. Finally, all the bonding can be achieved. It takes more time than the original through-hole and blind hole, so the price is also the most expensive. This process is usually only used for high density circuit boards to increase the usable space of other circuit layers
In PCB production process, drilling is very important, not careless. Because drilling is to drill the required through-hole on the copper clad laminate to provide electrical connection and fixed device function. If the operation is not proper, there will be problems in the via process. If the device can not be fixed on the circuit board, the light will affect the use, and the whole board will be scrapped. Therefore, the drilling process is very important.
