For surface mount boards, especially for BGA and IC, the via hole plug hole must be smooth, convex and concave plus or minus 1mil, and there should be no red tin on the edge of the through hole. In order to meet the customer's requirements, the through hole plug hole process can be described as varied, with a long process flow and difficult process control. Oil often drops during hot air leveling and green oil solder resistance test; curing After explosion oil and other problems occurred. According to the actual conditions of production, this paper summarizes various plug hole processes of PCB, compares and expounds the process flow, advantages and disadvantages: Note: the working principle of hot air leveling is to remove the excess solder on the surface and hole of printed circuit board by using hot air, and the remaining solder is uniformly covered on the pad, the non blocking solder line and the surface packaging point, which is one of the surface treatment methods of printed circuit board. 1、 The technological process of plug hole after hot air leveling is as follows: resistance welding of plate surface → Hal → plug hole → solidification. Non plug hole process is adopted for production. After hot air leveling, aluminum screen plate or ink screen is used to complete the through hole plug hole of all fortresses required by customers. Plug ink can be photosensitive ink or thermosetting ink, in the case of ensuring that the wet film color is consistent, the plug ink is best to use the same ink as the board. This process can ensure that the through hole will not drop oil after hot air leveling, but it is easy to cause plug ink pollution on the board surface. It is easy for customers to cause false soldering during mounting (especially in BGA). Therefore, many customers do not accept this method. Sendwin used this method, but it has been improved in the future, and now it is rarely used. 2、 Plug hole technology before hot air leveling 2.1 use aluminum sheet to plug hole, solidify and grind the plate, then transfer the figure. This process uses NC drilling machine to drill the aluminum sheet to make screen plate and plug hole to ensure that the through hole plug hole is full. Plug ink can also be used to plug hole ink. Its characteristics must be large hardness, small resin shrinkage change, and good adhesion with hole wall. The technological process is: pretreatment → Plug hole → grinding plate → pattern transfer → etching → plate surface resistance welding. This method can ensure that the plug hole of the through hole is flat, and there will be no oil explosion and oil dropping from the hole edge during hot air leveling. However, this process requires one-time thickening of copper, so that the copper thickness of the hole wall can meet the customer's standard. Therefore, the requirements for copper plating on the whole plate are very high, and the performance of the plate grinder is also very high, so as to ensure the trees on the copper surface The copper surface is clean and free from contamination. Many PCB plants do not have one-time thickening copper process, and the performance of the equipment can not meet the requirements, resulting in this process is not used in PCB plants. At present, this method is commonly used in the production of Sendwin. two point two The process is: pre-treatment - plug hole - screen printing - pre - drying - exposure - Development - curing, using this process Ensure that the via hole is covered with oil well, the plug hole is flat, and the wet film color is consistent. After hot air leveling, it can ensure that there is no tin on the through hole and no tin bead is hidden in the hole, but it is easy to cause ink in the hole after curing on the pad, resulting in poor solderability; after hot air leveling, the edge of the via hole blisters and drops oil, which is difficult to control by using this process, which requires special process and parameters It can ensure the quality of plug hole. 2.3 aluminum sheet plug hole, development, pre curing, grinding plate surface resistance welding. With the NC drilling machine, the aluminum sheet required to plug hole is drilled out and made into screen plate. The plug hole must be full, and the two sides are better to protrude. After solidification, the plate is ground for surface treatment. The process flow is as follows: pretreatment - plug hole - pre drying - Development - pre curing - board surface resistance welding However, after Hal, it is difficult to completely solve the problem of tin coating on vials and through holes, so many customers do not accept it. 2.4 the solder mask and plug hole shall be completed at the same time. This method uses 36t (43T) silk screen, which is installed on the screen printing machine, and uses the backing plate or nail bed to plug all the through holes while completing the board surface. The process flow is as follows: pretreatment silk screen printing pre drying exposure development curing. This process has the advantages of short time and high equipment utilization, which can ensure that the via hole does not drop oil and tin is not applied to the through hole after hot air leveling. However, due to the use of screen printing for plug hole, there is a large amount of air in the via hole. During solidification, the air expands and breaks through the solder mask, resulting in voids and unevenness. There will be a small amount of tin in the via hole after hot air leveling. At present, through a large number of experiments, the selection of different types of ink and viscosity, adjustment of screen printing pressure, etc., has basically solved the problem of via hole cavity and unevenness, and has adopted this process for mass production.