The conductive hole via hole also leads the through hole. In order to meet the customer's requirement, the through hole must be plug holes. After a lot of practice, the traditional aluminum plug hole technology is changed, and the white board is used to complete the circuit board plate solder mask and plug hole. Stable production and reliable quality.

The role of Via hole in conducting connections between conductance lines and the development of the electronic industry also promotes the development of PCB manufacturing, as well as the higher requirements for printed circuit board manufacturing process and surface mount technology. The technology of Via hole plug hole arises at the historic moment and should meet the following requirements:

1. If there is copper in the through hole, the plug can be used for resistance welding;

2. There must be tin lead in the through hole. There is a certain thickness requirement (4 micron). No solder joints can be inserted into the hole, resulting in tin beads in the hole.

For the surface mounting board of circuit board, especially for the mounting of BGA and IC, the through-hole plug hole must be flat, convex and concave positive and negative 1mil, and there must be no red and tin on the edge of the through-hole; the through-hole tin bead, in order to meet the customer's requirements, the through-hole plug hole process can be described as various, the process flow is particularly long, the process control is difficult, and there is often oil drop during hot air leveling and green oil solder resistance test; After solidification, explosion oil and other problems occur. According to the actual production conditions, this paper sums up the various plug hole processes of PCB, and makes some comparison and elaboration on the process, advantages and disadvantages:

Note: the principle of hot air leveling is to remove the excess solder from the printed circuit board surface and the hole by hot air. The remaining solder is evenly covered on the pad and the solder wire and the surface package point. It is one of the ways of surface treatment of printed circuit boards.

1. After hot air leveling, plug hole technology.

The technological process is as follows: plate surface resistance welding→Hal→plug hole→solidification. Non plug hole process is adopted for production. After hot air leveling, aluminum plate or ink screen is used to complete the through hole plug holes of all fortresses required by customers. Plug ink can be light-sensitive ink or thermosetting ink, in order to ensure that the color of the wet film is the same, plug ink is best used with the same ink on the board. This process ensures that after the hot air is leveled, the through hole does not drop off oil, but it will cause contamination of the hole and ink. Customers are prone to false soldering (especially in BGA) during installation. So many customers don't accept this approach.

2. Hot air leveling before plug hole technology

2.1 use aluminum pieces to plug holes, solidify and grind the plates.

This technological process uses CNC drilling machine to drill the aluminum sheet that needs to be plugged, which is made into a screen plate to plug holes, so as to ensure that the through hole plug hole is full, and the plug hole ink plug hole ink can also be used as thermosetting ink. Its characteristics must be large hardness, small resin shrinkage change, and good binding force with the hole wall. The process flow is: pretreatment, plug hole, grinding plate, pattern transfer, etching, plate resistance welding.

This method can ensure that the through hole plug hole is flat, and there will be no quality problems such as oil explosion and oil drop at the hole edge during hot air leveling. However, this process requires one-time thickening of copper to make the hole wall copper thickness 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 that the resin on the copper surface is completely removed, and the copper surface is clean and not polluted. Many PCB factories do not have a one-time thickening copper process, and the performance of the equipment can not meet the requirements, resulting in little use of this process in PCB plant.

2.2 plug the hole with aluminum sheet and then directly solder the silk screen plate

This process uses CNC drilling machine to drill the aluminum sheet to be plugged, which is made into screen plate, installed on the screen printing machine to plug holes. After the completion of plug holes, it shall not be parked for more than 30 minutes. 36t screen is used to directly block welding on the screen. The process is: pretreatment - plug holes - screen printing - pre drying - exposure - Development - curing.

2.3 plug the hole with aluminum sheet and then directly solder the silk screen plate And parameters to ensure the quality of plug hole.

2.4 PCB aluminum sheet plug hole, development, pre curing, grinding plate after plate resistance welding.

The CNC drilling machine is used to drill out the aluminum pieces that require the plugging holes. The screen is made into a screen, which is installed on the moving screen printing machine for plugging. The plug must be full and the two sides protruding is good. Then the surface is treated by solidifying and grinding plates. The technological process is as follows: pre processing - plug hole pre drying - developing - pre curing - plate resistance welding.

As this process uses plug hole solidification to ensure that the oil will not drop or explode after Hal, but after Hal, it is difficult to completely solve the problem of tin on the through-hole tin beads and through-hole, so many customers do not accept it.

2.5 the resistance welding of circuit board surface and plug hole shall be completed at the same time.

In this method, 36t (43T) wire mesh is used, which is installed on the screen printing machine, and the base plate or nail bed is used. When the circuit board surface is completed, all the through holes are plugged. The technological process is: pretreatment - screen printing - pre drying - exposure - Development - curing.

This process has a short time and high utilization rate of the equipment, which can ensure that the through-hole will not lose oil and the through-hole will not be tinned after the hot air leveling. However, due to the use of silk screen to plug the hole, there is a large amount of air in the through-hole. When the air is solidified, the air expands and breaks through the resistance welding film, resulting in holes and unevenness. There will be a small amount of through-hole tin in the hot air leveling. At present, our company has chosen a large number of experiments, choose different types of ink and viscosity, adjust the pressure of silk screen, etc., basically solved the hole and uneven, through the process circuit board batch production.

3. through hole must have solder resist ink plug hole, opaque.