Discover the details of flip-chip package thermal resistance characterization using Ansys Fluent.
Flip-Chip Thermal Resistance Characterization Challenges
As electronic devices continue to scale in performance and miniaturization, effective thermal management becomes critical to ensure reliability and longevity. Flip-chip packaging is known for its high I/O density and superior electrical performance, presenting unique thermal challenges due to its compact structure, high-power density, and high heat output. Accurate thermal characterization is essential to predict temperature distribution and optimize cooling strategies to avoid overheating that can degrade performance and shorten device life span.
Engineering Solution
Flip-chip packaging technology is revolutionizing high-performance electronics, but its complex architecture presents significant thermal management challenges. With increasing power densities and compact layouts, engineers need to evaluate thermal performance early in the design process, long before the first physical prototype is built. High-power density AI packages frequently employ flip-chip package technologies, making precise thermal analysis and characterization essential for modern electronic system design.
Factors such as chip size, material distribution, interconnect type, underfill properties, and substrate thickness can all influence heat dissipation and temperature profiles. Fortunately, modern simulation tools like Ansys Fluent empower engineers to explore these variables virtually. By simulating heat transfer and airflow dynamics, Fluent helps validate thermal concepts, identify potential hotspots, and optimize cooling strategies.
In this blog, I will go through the different steps to set up the simulation for characterizing theta-JB and theta-JC thermal resistances in Ansys Fluent.
Method
Geometry
A custom-made flip chip and 2S2P PCB were used for this demonstration. The computational domain is shown in Figure 1.
Figure 1. Computational Domain Flip Chip Package Setup.
Ansys Fluent allows you to set different material properties for each of the flip chip parts. It is important to create a body that represents each of the components so we can add the required thermal properties to them. For this demonstration, a simplified version was used and is shown in Figure 2. You can add any additional details that are important for your analysis.
Figure 2. Flip Chip Package Common Material Distribution.
Material Properties
For non-isotropic material, Ansys Fluent allows the configuration of orthotropic thermal conductivity. You can create new material, go to thermal conductivity, and select orthotropic. Fluent lets you define a different coordinate system to set the orthotropic thermal conductivities. It will ask for two principal directions to form a plane, and the third direction is calculated by Fluent; then, you can assign the corresponding thermal conductivity in each direction.
Source term
To account for the thermal dissipation, a volumetric source term is applied in the cells of the die. In this demo, we used an expression that allows us to input the power in Watts, and Fluent calculates the corresponding W/m3 for the die. This configuration facilitates doing a parametric study, but you can also add a constant value in W/m3.
Another approach is to add the thermal dissipation in a thin layer at the top of the die. This approach will be discussed in a different blog.
Boundary conditions
Boundary conditions are an important part of setting up the thermal cases. For the theta-JB thermal resistance, the setup requires that all the heat generated flows through the PCB. The boundary conditions for this case are shown in Figure 3.
Figure 3. Boundary Condition Theta-JB Thermal Resistance Case.
For theta-JC thermal resistance, the setup requires that all the heat generated flows through the top of the flip chip. The boundary conditions used for this case are shown in Figure 4.
Figure 4. Boundary Condition Theta-JC Thermal Resistance Case.
Results
After the simulation finishes, you can use the built-in postprocessing tools of Ansys Fluent to explore and calculate final values; some results are shown below.
Theta-JB Thermal Resistance
To obtain the maximum temperature in the die and average temperature in the BGA-PCB connection, it is possible to use the report tool on the Results tab. For this demo, the results obtained are shown below:
Some contour plots for the case are shown below:
Figure 5. Temperature Distribution on the Package and Board Surface Theta-JB.
Figure 6. Temperature Distribution on the Board Surface Theta-JB.
Theta-JC Thermal Resistance
For this demo, the results obtained for Theta-JC are summarized below:
Some contour plots for the case are shown below:
Figure 7. Temperature Distribution on the Package and Board Surface Theta-JC.
Step-by-step video
You can download the case file here.
Ansys Solution Benefits
Ansys provides powerful thermal simulation capabilities for semiconductor design, enabling engineers to analyze geometry configurations, material distributions, interconnect types, underfill properties, and substrate thickness, all without building physical prototypes. Beyond Ansys Fluent, Ansys has specialized tools like Icepak for electronics cooling, SiWave for signal and power integrity, Maxwell and HFSS for electromagnetic analysis, Mechanical for structural and thermal simulations, and DesignXplorer and OptiSLang for design optimization and parametric evaluation, making it a comprehensive suite for multi-physics modeling and performance refinement.
Ozen Engineering expertise
Ozen Engineering Inc. leverages its extensive consulting expertise in CFD, FEA, thermal, optics, photonics, and electromagnetic simulations to achieve exceptional results across various engineering projects, addressing complex challenges like multiphase flows, erosion modeling, and channel flows using Ansys software.
We offer support, mentoring, and consulting services to enhance the performance and reliability of your hydraulic systems. Trust our proven track record to accelerate projects, optimize performance, and deliver high-quality, cost-effective results for both new and existing water control systems. For more information, please visit https://ozeninc.com.
Suggested Blogs:
- https://blog.ozeninc.com/resources/calculation-of-electronic-package-thermal-resistance-with-ansys-icepak
- https://blog.ozeninc.com/resources/ansys-icepak-and-electronic-cooling-analysis
- https://www.ozeninc.com/consulting/thermal-engineering-electronics-cooling/
- https://blog.ozeninc.com/resources/ansys-icepak-and-electronic-cooling-analysis-0
- https://blog.ozeninc.com/resources/ansys-icepak-and-electronic-cooling-analysis-1
