The soldering of the via components has always used a wave soldering process to complete the connection between the components and the PCB. The soldering of surface mount components uses a reflow soldering process. In this case, if a board incorporating a hybrid technology of through-hole components and surface-mount components requires two types of welding equipment to complete the welding operation.
Although reflow soldering is a good technique, there are some quality defect problems in the pcb manufacturing process.
When the reflow soldering is used, the vias of the board "long" out what the black mushroom-like substance is, as shown in the figure:
The solder resist is ejected, and this status quo is commonly called "elastic oil" in the pcb industry.
What causes this phenomenon:
1. Poor hole ink performance is not good
2. Insufficient ink coverage on the upper surface of the oil hole
3. Post-cure parameters are unreasonable (filler inks are not fully cured)
Circuit board process problems with this phenomenon, scrap processing, this case is rarely rare, but understanding this issue is meaningful for understanding the complexity of PCB incoming quality.