1. Defect caused by Drilling
The board produced by the circuit board is epoxy resin glass fiber material, AKA FR4. After drilling, there will be a layer of dust in the hole of the board. Especially the drilling of 0.3mm or more. If this dust is not cleaned, the dusty area can not immersion copper, which will cause a through hole failure. Defect caused by Drilling, if the PCB has been tested, this situation can be tested out. This bad circuit board manufacturers need to do scrap processing.
2. Defect caused by Copper immersion
The first possibility is the immersion copper time is too short. Copper holes are not full. When pass the wave soldering, the hole copper melted off. Most of these appear in the 0.3mm below the over-hole.
Secondly, the circuit board needs too much current when working, but did not do heavy copper. After the power is applied, the current is large, melt off the hole copper, thus causing the defect. So if there is a need for high current PCB board, before production it is necessary to tell the PCB manufacturer to do heavy copper. For example: the power supply board is almost always made by heavy copper.
3. Defect caused by SMT solder paste, flux quality or technology
This type of situation mostly occurs in the plug-in hole. SMT manufacturers use impure tin, too many impurities. And flux quality is too poor. Tin and tin fusion is not good. This is easy to cause pseudo solder. Components do not work. In addition, there are technical problems in SMT.