After you know the contact area for the device, you can think about the design of the heatsink base. Decisions made here can significantly impact the area, performance, and cost of the thermal solution and is one that should not be overlooked. One consideration that can have significant impact on the base design is how many devices the heatsink must cool. Having a heatsink dedicated to a single device allows sizing and height tolerances to be optimized for that device often leading to both easier design and higher performance. On the other hand, a single heatsink that must touch multiple devices often must have compromises in size and height tolerance optimization that leads to less than ideal results. There are ways to compensate for this. However, for the basis of this application note, we assume the heatsink is dedicated to the Xilinx device or in cases that it is not, the Xilinx device is the most thermally critical and thus the heatsink is optimized towards the Xilinx device.