The QFN (quad flat pack, no leads) package can no longer be considered exotic. It was about a decade ago, but not any more. In fact, with the wafer scale BGA, it's one of the more common packages for new chip designs. Not all QFNs come with an exposed metal pad underneath, but most do, and that can still cause problems with reflow solder. The pad itself isn't the problem, but improper solder paste stencil layer design can be.