Super Small VIA-IN-PAD

摘要

Via-in-pad is an old issue that still pops up far too often. Our standard answer hasn't changed: no open vias in pads. But one of the questions we get related to the subject is: What if we make the vias really small? Logically, that makes sense. In fact, in some cases, the via is so small that it's essentially closed. If it's so small that it really is closed, then it's not an open via. But look close: If it's closed with solder, that solder may melt during reflow, leading to an open via. Small vias on HASL finished boards (leaded or lead-free) often look closed, but will melt through in the reflow oven.