I'm designing a new board using the AD9643 at 250 MSPS. The data sheet (Rev. B) states on page 35 that the exposed paddle "...vias should be filled or plugged with nonconductive epoxy." Why nonconductive? It seems that if the fill was both electrically and thermally conductive that it would only improve grounding and heat dissipation. A second question is: Because epoxy-filled vias can add significant cost to board fab, has anyone had experience using solder mask-tented vias (tented both sides?) with this ADC at 250 MSPS?
By the way, the board will be at least 14 layers with 4 internal ground planes and an unmasked copper area on the opposite side from the ADC for additional heat dissipation.