PCB Technical - What kind of knowledge is it when PCB vias are blocked?

Conductive hole via hole is also called via hole. In order to meet the requirements of users, the wire board through hole must be blocked. After a lot of practice, the traditional aluminum plate plugging process is changed, and the surface resistance welding and plugging of the printed circuit board are completed with white mesh. Stable production and reliable quality.

Via holes play the role of circuit interconnection and conduction, promote the development of the electronics industry, and also promote the development of PCB. At the same time, it also puts forward higher requirements on the manufacturing technology and surface mount technology of printed circuit boards. Through hole plugging technology came into being and should meet the following requirements:

(1) If the through hole has copper, resistance welding can be blocked or not; (2) There must be tin and lead in the through hole, and there is a certain thickness requirement (4 microns). No solder ink can enter the hole, causing the tin beads to hide in the hole.

(3) The through hole must have resistance welding ink plug hole, anti-seepage, no tin ring, tin ball and leveling requirements.

With the development of electronic products in the direction of "light, thin, short and small", printed circuit boards are also developing in the direction of high density and high difficulty. Therefore, there are a lot of PCBs with SMT and BGA. Customers need plug holes when installing components. It has five main functions:

(1) In order to prevent TiN from causing short circuits through through holes during PCB over-wave soldering, especially when placing through holes on BGA pads, plug holes must be made first and then gold-plated to facilitate BGA soldering.

(2) Avoid residual flux in the through hole;

(3) After the surface mounting and component assembly in the electronics factory are completed, the PCB must absorb vacuum before completion to form negative pressure on the testing machine:

(4) Prevent the surface solder paste from flowing into the hole to cause false soldering and affect the installation;

(5) Prevent the tin ball from spraying out during the welding process, causing short circuit.

Realization of Conductive Hole Plugging Process

For surface mounting boards, especially for BGA and IC mounting, the requirements for the via hole plug hole must be flat, with convex and concave plus or minus 1 mm, and there is no red tin on the edge of the via hole; To meet customer requirements, the via hole plugging process can be described as a variety of processes. The S flow is extremely long and process control is difficult. In the hot air leveling and green oil solder mask experiments, the oil often solidifies, causing problems such as explosion. According to the actual production, various PCB jack technologies are summarized, and the process, advantages and disadvantages of the technology are compared and explained.

Note: The working principle of hot air leveling is to use hot air to remove excess solder on the surface of the printed circuit board and in the holes. The remaining solder is evenly coated on the pads, non-resistance solder wires and surface packaging points. It is a method of surface treatment of printed circuit boards.