Why PCB circuit board vias must be plugged. What is worth studying?(Part Ⅰ)

With the development of electronic products in the direction of “light, thin, short and small”, PCBs have also developed to high density and high difficulty. Therefore, a large number of SMT and BGA PCBs have appeared, and customers require plugging holes when mounting components. What is it for and why?

The conductive hole Via hole is also known as the conductive through hole. In order to meet the customer's requirements, the conductive hole of the circuit board must be plugged. After a lot of practice, the traditional aluminum chip plugging process is changed, and the white plate is used to complete the circuit board surface soldering and plugging. hole. Stable production and reliable quality.

The Via hole leads the connection of the lines to each other. The development of the electronics industry also promotes the development of pcb, and also puts higher requirements on the manufacturing process and surface mount technology of printed boards. The Via hole plugging process came into being, and the following requirements should be met:

1. There is copper in the via hole, and the solder resist can be plugged;
2. There must be tin-lead in the via hole, which has a certain thickness requirement (4 micrometers), and no soldering ink is allowed to enter the hole, resulting in the inclusion of tin beads in the hole;
3. The through hole must have a solder-proof ink plug hole, which is opaque, and must not have tin ring, tin bead and leveling requirements.

With the development of electronic products in the direction of “light, thin, short and small”, pcb is also developing to high density and high difficulty. Therefore, a large number of SMT and BGA pcbs appear, and customers require plugging holes when mounting components. Five roles:

1. Preventing the short-wave soldering of the pcb from causing a short circuit from the via hole through the component surface; especially when we place the via hole on the BGA pad, it is necessary to first make a plug hole and then gold-plated to facilitate the BGA soldering.
2. avoiding flux remaining in the via hole;
3. After the surface mounting and component assembly of the electronics factory is completed, the pcb is vacuumed on the test machine to form a negative pressure:
4. Preventing the surface solder paste from flowing into the hole to cause solder joints and affecting the mounting;
5. Preventing the soldering of the solder balls from over-wave soldering, causing a short circuit.

Implementation of conductive hole plug hole process

For surface mount boards, especially for BGA and IC mounting, the via hole must be flat, positive and negative 1 mil, no red tin on the edge of the via hole; tin beads in the via hole, in order to reach the customer The requirements of the via hole plug hole process can be described as various, the process flow is particularly long, the process control is difficult, and often there is oil drop during the hot air leveling and green oil solder resistance test; the problem of oil explosion after curing occurs. According to the actual conditions of production, we will summarize the various plugging processes of pcb, and make some comparisons and explanations on the process, advantages and disadvantages:

Note: The working principle of hot air leveling is to remove the excess solder on the surface of the printed circuit board and the holes by using hot air. The remaining solder is evenly covered on the pads and the un-resisted solder lines and surface package points, which is the way of processing the surface of the printed circuit board. one.