Thermal Management Challenges in Chiplet-based Architectures

[Kieu]

Hello everyone,

As Chiplet architectures become increasingly common in high-performance computing (HPC) and AI chips, I've noticed that thermal density and heat dissipation have become critical bottlenecks for performance scaling. Compared to traditional monolithic integration, Chiplets introduce unique thermal challenges. I would like to seek your expertise on a few core questions:

1. Hotspot Density: In 2.5D/3D stacking, the high heat flux of compute dies often creates extreme thermal gradients near adjacent I/O or cache dies. What are the extreme requirements this places on the CTE (Coefficient of Thermal Expansion) matching of packaging materials, such as TIM and substrates?
2. Limitations of TIM: In 3D stacking (e.g., with TSVs), as Die-to-Die contact area decreases, does traditional TIM become insufficient for heat dissipation? What is the current industry trend for micro-scale inter-die cooling? Is the focus more on optimizing the materials themselves, or are we shifting toward microfluidic cooling or immersion solutions?
3. Simulation Modeling Accuracy: For multi-die scenarios, how can thermal-electrical co-simulation be used to more accurately predict transient thermal responses? Are there any industry-recognized standards for efficient modeling?

I look forward to hearing your insights and experiences regarding packaging design and thermal management. Thank you!

 

[Daniel Nenni]

Chiplet-based HPC and AI packages impose much tighter thermo-mechanical constraints than monolithic designs. In 2.5D and 3D stacks, localized heat flux can create steep temperature gradients, causing differential expansion between silicon, interposers, substrates, underfills, and thermal interface materials. Consequently, low and closely matched CTE values, high modulus stability, strong adhesion, and resistance to thermal cycling are essential. TIM selection must also balance thermal conductivity with compliance, because overly rigid materials can transfer stress to microbumps or TSV regions.

Traditional TIM remains useful at external heat-spreader interfaces, but it is often inadequate between tightly stacked dies where bond-line thickness, contact area, and vertical heat paths are highly constrained. Industry development is therefore proceeding along two tracks: improved materials, including sintered silver, hybrid bonding, high-conductivity polymers, and phase-change interfaces; and advanced cooling approaches such as backside cooling, embedded microchannels, direct liquid cooling, and, for some systems, immersion cooling.

Thermal-electrical co-simulation should couple power maps, temperature-dependent leakage, interconnect resistance, package parasitics, and workload transients. Reduced-order models can accelerate system-level analysis while preserving hotspot behavior. Common practices rely on JEDEC thermal characterization methods, compact thermal models, and multiphysics finite-element or computational-fluid-dynamics tools, although no single standard fully captures every heterogeneous multi-die transient scenario accurately.