Modules and Daughter Boards.
We ran across an interesting part the other day. Modular sub-components are getting more and more common. You see bluetooth radios in module form, ZigBee radios, GPSs, Power Supplies and other common building blocks showing up like this more and more.
These little modules are are non-isolated PTH05060WAS and PTH05050WAZ DC to DC converters; less than $20.00 each from Digi-Key as of this writing. One of the interesting aspects of this product is that they are multi-sourcable. In my experience, most modules of this sort are dramatically different from one manufacturer to another. These ones, though, are offered by at least three manufacturers as part of the "Point-of-Load Alliance" (POLA) with a standard footprint and functionality.
It's also interesting to note that these are essentially BGA packages. It's not quite the same as a standard BGA but the connections use solder balls like a BGA.
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Take a look at this closeup here. Rather than laying directly on a substrate as normal BGAs do, each of the solder balls is on what appears to be a little tiny round PCB on top of a short stand-off. Using this type of construction allows the module to be double sided and, presumably, helps with convection cooling.
Whomever laid out the main PC board did a good job with the CAD library part landing pad too. The individual lands look overly large at first glance, but the part manufacturer specifies a 2.03 mm to 2.16 mm solder mask defined pad. These ones are right in there.
It's also important to note that there are no open vias in the land pads. Doing so would have led to an unreliable connection with poor (or no) electrical and thermal performance. The component datasheet (page 17) specifies that the input, output and ground power pins need several vias, but it fails to mention that they shouldn't be left open in the middle of the pad. Fortunately, in this case, the designer put the vias in masked area, outside of the land pad. It would have also been fine to put the vias in the pad and plug and plate over them.
Newton says: may the net force be with you