Why are holes not conductive after SMT

After the PCB board assembled with components, some customers encounter situations that the through holes are not conductive. In which cases will cause un-conductive? Based on our engineers’ past experiences, SysPCB want to share the reasons which caused vias opened. This can be either caused by the PCB manufacturer or by the SMT factory. We will analyze these two aspects.

1. Caused by poor drilling
Conventional Circuit board production is made from glass epoxy and copper sheet material. After drilling, there may exit few dust in the holes. Especially for the PCB holes with the drill size bigger than 0.3MM. If this dust have not been cleaned before plating Cu process, place with dust won’t be platted copper, which will cause vias can not conduct electricity. If the PCB with poor hole wall copper plating issues goes through the electrical test, this situation can be test out. This poor quality circuit board will be scrapped by Shenzhen PCB manufacturers if it was test out.

2. Defect caused in copper plating process
First, if the copper plating time is too short, the hole copper is not thick enough. When soldering the thin copper wall can be dissolved by the high temperature of reflow oven, most of this appears in the less than 0.3MM vias. Second if the board design requires a large current, without doing heave copper for actual PCB, the current is too large so hole copper wall melt away, causing defect in PCBA. So if there is a need big current PCB board, designers must tell PCB manufacturers to do the production of thick copper. For example: the power supplying boards are mostly thick copper.

3. Un-qualified SMT tin or flux or SMT technique
Most of this type of situation occurs with via plug-in. SMT manufacturers use impure tin with too many impurities and flux of poor quality. Tin and tin welding bad, Component is not working. In addition problem in SMT technology can also cause this issue.