The X-ray inspection system is most used to test the quality of a printed circuit board (PCB) soldering. BGA is the most important component of a PCB. Its soldering quality directly affects the quality and function of the PCB. So, what are the BGA soldering defects? How can it be identified as a defect?
During the BGA soldering process, affected by factors such as the amount of printed tin, temperature profile, and solder paste quality, problems such as bridging, voids (bubbles), cold soldering and insufficient solder may directly affect product quality and stability. Use the Wellman X-Ray inspection system can help improve the soldering process.
1. When the amount of tin in the solder ball is too much, it will easily cause the problem of bridging, resulting in a short circuit. When the amount of tin is too small, the BGA will not be connected well with the PCB pad.
2. Cold soldering is also a common problem. When the temperature profile is not suitable or there is a problem in the reflow oven, the temperature will not be high enough, or the heating time will not be long enough, the solder paste will not completely melt, and the shape of the solder ball will become irregular. The result of cold soldering is that the bottom of the BGA is very weak, and it is easy to crack when an external force collides, forming an insufficient solder.
3. The voids are mainly caused by the solder flux and moisture, and the voids mostly appear at the bottom of the BGA ball. If the voids are too large, it will affect the stability of the BGA, which will cause cracks and insufficient solder. Industry standards and IPC clearly state that the void area needs to be controlled within 25%.
It should be noted that the density and thickness of the solder balls are relatively high. Usually, the X-ray power (voltage and current) must be increased to penetrate the solder balls till the voids are displayed.
4. There are two kinds of insufficient solder. One is that the BGA solder ball area is too small, the other is the ball area is too large.
The small ball area is due to insufficient or no solder paste, and there is no wetting on the bottom of the BGA ball.
Then why the large area is also an insufficient solder?
If the solder paste is of poor quality or the pad is oxidized, it will be turned into solder rejection. In this way, even if the BGA ball and the solder paste are melted, the bottom does not form wetting, and then the BGA ball is squeezed, makes its area larger.