The humble via is just a plated hole linking copper layers, but drop one inside a component pad and you inherit one of the trickiest problems in modern board fabrication. aivonpcb As pin counts climb and pitches shrink, particularly under fine-pitch BGAs, there is simply no room to escape a trace out between the pads. The classic fix was the dogbone: offset the via slightly and bridge it to the pad with a short neck of copper. Elegant at 0.8mm pitch, effectively impossible below roughly 0.5mm. Via-in-pad drops the hole straight into the land. The geometry works, but an open plated barrel under a solder joint is a disaster in reflow. Molten solder wicks down the hole by capillary action, starving the joint and leaving voids, tombstoned parts and connections that pass inspection then fail in the field. The answer is a filled and capped structure, often called VIPPO (via-in-pad plated over): - Drill and plate the barrel as normal - Fill the bore with epoxy, conductive for thermal p...