Fine pitch area array packaging is achieved using a via-in-pad design within the area array attach portion of a printed circuit board (PCB). The limitation of the design is the wicking action, whereby solder applied to the capture pad contact surface is depleted by capillary action into the via hole...http://www.google.com/patents/US6300578?utm_source=gb-gplus-sharePatent US6300578 - Pad-on-via assembly technique
