Simulation Analysis on Thermal Performance of a Lidless Fan-Out Package

As an emerging and competitive candidate, the fan-out package can meet the small form factor, high density and high electrical performance requirements of the state-of-the-art applications in mobile, 5G and AI. The fan-out package also offers high packaging flexibility for integration. While the demands in high performance of chip drive the power consumption and heat dissipation dramatically increased, the thermal management of the fan-out package is becoming a critical issue. In this paper, the thermal performance characterization of the fan-out package is performed by the 3D finite element method. A lidless structure with an integrated heatsink directly attached to the fan-out package is proposed. EMC after wafer level molding of fan-out package process can support the heatsink and control warpage as the stiffener rings attached to the package. There is a certain thickness of overmolded EMC which is often used as electrical insulation between the chip and the heatsink in the fan-out package structure for high-density system integration. Nevertheless, the poor thermal conductivity of EMC will be a bottleneck for the thermal dissipation performance. The differences in thermal performance without an EMC cap and with various thicknesses of EMC cap of the lidless fan-out package are systematically simulated. The thermal resistance models are extracted. The thermal resistance without the EMC cap is 0.25°C/W, and the thermal resistance with the cap thicknesses of 50μm, 100μm and 150μm are 1.86°C/W, 3.40°C/W and 4.89°C/W, respectively. The thermal resistance is positively proportional to the thickness of the EMC cap. The fan-out package without the EMC cap is better able to dissipate heat, while the fan-out package with the certain thickness of EMC cap wrapped on the chip results in poorer dissipation performance. The thermal simulation model of the lidded fan-out package is used for performance in comparison with the lidless. The thermal resistance of the lidless is much less than the lidded. Compared with the lidded, the lidless has a better thermal performance due to the removal of the lid and thermal interface material and the absence of their thermal interface. The heat generated by the chip can be directly dissipated to the heatsink. Therefore, the lidless structure of the fan-out package is presented as a thermal dissipation solution at package level and system level. The thermal performance of the lidless fan-out package with various height/counts/size of heatsink, air velocity and chip power is characterized.