What kinds of defects may occur during the processing of PCBA?

During the processing and production of PCBA, due to some operational mistakes, the soldering process may result in defective phenomena. So, what kinds of defective phenomena may occur in the processing of PCBA? 

1. Standing upright 

The causes are as follows: Unequal sizes on both the copper and platinum sides result in uneven pulling force; The preheating and heating rate is too fast; The machine assembly is off-center; The thickness of the solder paste is uneven; The temperature distribution in the reflow oven is uneven; The solder paste printing is off-center; The clamping plates of the machine track are not tight, causing assembly offset, etc. 

2. Short circuit 

The causes are as follows: The excessive distance between the steel mesh and the PCB board resulted in too thick solder paste application, causing short circuits; The excessively low height setting for component mounting squeezed the solder paste, leading to short circuits; The rapid temperature rise of the reflow oven caused short circuits; Component mounting deviation led to short circuits; Poor hole formation of the steel mesh (too thick, excessively long pin hole, or too large hole size) caused short circuits, etc. 

3. Deviation 

The causes are as follows: The positioning reference points on the circuit board are not clear; the positioning reference points on the circuit board are not aligned with the reference points of the net board; the fixing clamps for the circuit board in the printing machine are loose, and the positioning pins are not in place, etc. 

4. Missing Components 

The causes are as follows: Poor quality of the carbon sheet in the vacuum pump results in insufficient vacuum and causes component shortage; Blockage or malfunction of the suction nozzle; Inappropriate thickness detection of the components or malfunction of the detector; Incorrect setting of the mounting height, etc. 

5. Air welding 

The causes: The solder paste is not active enough; The holes in the steel mesh are not well made; The spacing between copper and platinum is too large or there is a large copper pad for a small component; The pressure of the scraper is too high; The flatness of the component pins is poor (warping, deformation); The preheating zone of the reflow oven heats up too quickly, etc.