1) What is the optimal thermal PCB layout? Does the evaluation board DC2327A represent the optimal thermal PCB layout?
2) The datasheet has several thermal theda values: theda_JCtop = 20.6, theda_JCbottom = 5.1, theda_JB = 6.0, theda_JA = 15.5. Which would I use for analysis of the BGA packaged soldered to the board without a heatsink? I am particularly confused about the difference between theda_JCBottom and theda_JB. I want to take advantage of the theda_JCbottom thermal resistance, but I am unsure what PCB layout and assembly configuration resulted in theda_JCbottom.