Via hole, also known as through hole, is a conductive hole. In order to meet customer requirements, the through hole must be plugged. After a lot of practice, the traditional aluminum sheet plugging process has been changed, and the board surface resistance welding and plugging holes are completed with white mesh. Stable production and reliable quality.

The Via hole plays a role in connecting and conducting circuits, promoting the development of the electronics industry and promoting the development of PCBs. It also puts forward higher requirements for printed circuit board manufacturing processes and surface mount technology. The Via hole plugging process has emerged and should meet the following requirements:

（1） Copper can be present in the through hole, but solder resistance can be plugged or not; （2） There must be tin and lead inside the conducting hole, with a certain thickness requirement (4 microns), and there must be no solder blocking ink entering the hole, causing tin beads to be hidden inside the hole; （3） The conductive hole must have solder blocking ink plug holes, which are not transparent, and must not have tin rings, solder beads, or flatness requirements.

With the development of electronic products in the direction of "light, thin, short, and small", PCBs are also developing towards high density and difficulty, resulting in a large number of SMT and BGA PCBs. Customers require plug holes when mounting components, which mainly serve five purposes:

（1） To prevent short circuits caused by tin penetrating through the component surface through the through hole during PCB wave soldering; Especially when we place the via hole on the BGA pad, we must first make a plug hole and then gild it to facilitate BGA welding.

Implementation of conductive hole plugging process

For surface mount boards, especially BGA and IC mounting, the plug holes for the through holes must be flat, with a convex and concave positive and negative 1mil, and there must be no red or tin on the edges of the through holes; The guide hole contains tin beads. In order to meet customer requirements, the plug hole process of the guide hole can be described as diverse, with a particularly long process flow and difficult process control. Oil often falls off during hot air leveling and green oil solder resistance experiments; Problems such as oil explosion occur after solidification. Based on the actual production conditions, various PCB plug hole processes are summarized, and some comparisons and explanations are made in terms of process flow and advantages and disadvantages:

Note: The working principle of hot air leveling is to use hot air to remove excess solder from the surface and holes of printed circuit boards, and the remaining solder is evenly covered on the solder pads, unobstructed solder lines, and surface packaging points. It is one of the surface treatment methods for printed circuit boards.

1. Plug hole process after hot air leveling

This process flow is: board surface resistance welding → HAL → plug hole → curing. Production is carried out using a non plug hole process, and after hot air leveling, aluminum mesh or ink blocking mesh is used to complete the plug holes of all fortresses required by customers. Plug hole ink can be photosensitive ink or thermosetting ink, and it is best to use the same ink as the board surface to ensure consistent color of the wet film. This process flow can ensure that the guide hole does not lose oil after hot air leveling, but it is easy to cause ink pollution and unevenness on the board surface. Customers are prone to false soldering during installation (especially within BGA). So many customers do not accept this method.

2. Hot air leveling front plug hole process

2.1 Using aluminum sheets to plug holes, solidify, and grind plates for pattern transfer

This process uses a CNC drilling machine to drill aluminum sheets that need to be plugged, make a mesh plate, and plug the holes to ensure that the conductive holes are full. The plug ink can also be used to plug the holes, and its characteristics must be high hardness and resin