| 摘要 |
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 when reflowed, causing insufficient solder to be present at the contact surface to effect reliable and repeatable electrical connections. In one implementation, an initial application of solder is applied to plug the via hole with a material having a higher final melting temperature than eutectic solder, thereby providing a stable plug. This plug is formed by the initial solder application that may be either a eutectic solder containing a third metal that forms intermetallic compounds, when reflowed, that elevate the liquidus temperature or a solder having a different formulation with an inherent higher melting temperature. An alternative implementation is to plate the via hole with a material, such as nickel, which prevents eutectic solder, applied to the via capture pad contact surface, from wetting the hole surface and being drawn away from the contact surface by capillary action. Thus, the solder, applied to the via capture pad and used to establish an electrical connection is not depleted.
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