PCB News - The reason why the vias are blocked after the circuit board is mounted

The reason why the vias are blocked after the circuit board is mounted

After the circuit board After patching, many users will encounter the situation that the vias are blocked. In those cases, the via will be blocked. Based on personal past experience, share the reasons for the via failure after patching. Of course, this reason is the production of circuit board manufacturers on the one hand, and SMT on the other hand. Analyze both aspects.

1. Defects caused by the circuit board during drilling

The board produced by the circuit board is made of epoxy resin glass fiber. Referred to as FR4 fiberglass board. After the circuit board is drilled, there will be a layer of dust in the hole. Especially drilling holes above 0.3MM. If the dust is not cleaned, copper should not be deposited in dusty areas after curing, which will cause the vias to be blocked. The defects caused by drilling can be tested if the PCB has been tested. Manufacturers of such bad circuit boards can be scrapped.

2. Defects caused by copper sinking

The first choice is that the time for sinking copper is too short. The hole copper is not full. When tin is applied, the hole copper melts and causes defects. This kind of vias mostly appear below 0.3MM. The second is that the circuit board requires excessive current without thickening copper. After energizing, the current is too large to melt the hole copper, which causes defects. Therefore, if there is a PCB board that requires excessive current, you must tell the circuit board manufacturer to make thicker copper during production. For example, almost all circuit boards such as power supply boards are made of thick copper boards.

3. Defects caused by SMT tin or flux quality and technology

This type of situation mostly occurs in the vias of the plug-in. The tin used by SMT manufacturers is not pure and has too many impurities. And the flux quality is too poor. Tin and tin are not well welded. This is easy to cause false welding. The components are not working. In addition, SMT has technical problems, so that the circuit board will stop flowing for too long when it passes through the tin furnace during soldering. Caused the hole copper to melt. The resulting via is blocked.