There are many reasons you shouldn't use via-in-pad. It's not good practice, and those via holes act like little capillary straws and suck solder off the pad or the BGA (FIGURE 1). That said, there are some applications that may require - or seem to require - via-in-pad. Here are a few examples of why you might need to use via-in-pad: 1. There is not enough space on the board. 2. It can help with thermal management. 3. Trace routing may be easier with via-in-pad when component spacing is tight. 4. High-frequency designs benefit from the shortest possible routing to bypass capacitors, which may indicate via-in-pad.
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