PCB board through hole plug function and process introduction

Conductive hole also known as through hole, in order to meet customer requirements, circuit board through hole must be plugged, after a lot of practice, change the traditional aluminum sheet plug process, with white mesh to complete the circuit board surface welding and plug hole. Stable production, reliable quality.

The Via hole plays the role of connecting the lines to each other, and the development of the electronics industry also promotes the development of PCB, and also puts higher requirements on the printed board production process and surface mount technology. The Via hole plug process comes into being and should meet the following requirements:

1. There is copper in the through hole, and solder resistance can be plugged or not;

2. There must be tin lead in the through hole, there is a certain thickness requirement (4 microns), there must be no solder resistance ink into the hole, resulting in tin beads in the hole;

3. The pass-through hole must have solder resistance ink plug hole, opaque, no tin ring, tin bead and flat requirements.

With the development of electronic products to the direction of "light, thin, short, small", PCB also to high-density, difficult development, so there are a large number of SMT, BGA PCB, and customers in SMT processing requirements of the plug hole, there are five main roles:

1.Prevent short circuit caused by tin penetrating through the component surface through the through hole when PCB overwave soldering; In particular, when we put the hole on the BGA pad, we must first make the plug hole and then gold-plated treatment to facilitate the welding of the BGA.

2. Avoid flux residue in the pass hole.

3. After the surface mounting and component assembly of the electronics factory is completed, the PCB should absorb vacuum to form negative pressure on the test machine.

4. Prevent the surface solder paste from flowing into the hole to cause virtual welding, affecting the mounting. 

5. Prevent the tin bead from popping out during over-wave soldering, resulting in short circuit. The realization of the plugging technology of conductive hole.

For the surface mount board, especially the mounting of BGA and IC, the through hole plug hole must be flat, convex and concave plus or minus 1mil, and the edge of the through hole must not be red and tinned; In order to meet customer requirements, the plugging process of the through hole can be described as various, the process is particularly long, the process control is difficult, and the oil is often lost during the hot air leveling and green oil soldering resistance experiment; Problems such as oil explosion occur after curing.

Now according to the actual conditions of production, various PCB plug processes are summarized, in the process and advantages and disadvantages of some comparison and description: Note: The working principle of hot air smoothing is to use hot air to remove excess solder on the surface of the printed circuit board and the hole, and the remaining solder is evenly covered in the solder pad and open solder lines and surface sealing decoration, which is one of the ways of surface treatment of the printed circuit board.