The AMD flip-chip BGA packages exhibit a low-resistance thermal path that adequately cools devices. These packages incorporate a heat spreader lid with additional thermal interface material as shown in the following figure.
Materials with high thermal conductivity and consistent process applications deliver low thermal resistance up to the heat spreader. A parallel effort to ensure optimized package electrical return paths produces an enhanced power and ground plane arrangement in the package. A boost in copper density on the planes improves the overall thermal conductivity through the laminate. The extra density and distribution via fields in the package also increases the vertical thermal conductivity.
Lidless packages use the same substrate design and provide electrical and board thermal conductivity similar to the flip-chip BGA packages. However, removing the lid (heat spreader) and the thermal interface material allows for direct contact between the external heat sink and the die. This further reduces the thermal resistance and exhibits improved thermal behaviors.
Custom passive or active heat-sink designs benefit from incorporating two-phase cooling methods. Place heat pipe, vapor chamber, or liquid cooling directly adjacent to the source of the dissipated heat on the die. This removes heat from the device more efficiently. Consequently, the device can operate at higher ambient temperatures while in area-constrained surroundings resulting in operational power advantages.
A unique feature of lidless packages is the addition of a stiffener ring around the periphery of the package substrate. This ring increases package rigidity and improves coplanarity (flatness). It also serves as a guide for the heat sink solution applied to the device. For examples, see the VSVD1760 Mechanical—VC1802, VC1902, and VM1802 or VSVA2197 Mechanical—VC1802, VC1902, and VM1802. In the lidless packages, capacitors can be placed in the area surrounding the die. Avoid contact with electrically conductive materials because die-side capacitors, which are only slightly shorter than the die, can conduct electricity. Any thermal and mechanical solution higher than the die must not interfere with the package stiffener. Therefore, the thermal solution must have an island, see System Level Heat Sink Solutions. For further guidelines on mechanical and thermal designs of lidless packages, refer to Designing Heatsinks and Thermal Solutions for Xilinx Devices (XAPP1377).