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In the domains of Advanced Driver Assistance Systems (ADAS), high-performance computing, and high-power electronics, thermal interface materials (TIMs) serve as a critical component of thermal management systems. Their long-term reliability directly determines the operational lifespan and stability of entire electronic devices. As device power density continues to increase and operational lifespan requirements extend, the performance degradation of TIMs under prolonged thermal exposure—known as material aging—has emerged as a core challenge hindering systems from achieving higher reliability. Deepening our understanding of aging mechanisms and developing effective countermeasures represent critical research topics in materials science and engineering.
Inevitable Performance Degradation: Multiple Mechanisms of TIM Aging
When exposed to thermal cycling and high-temperature operating environments over extended periods, the performance degradation of thermal interface materials unfolds as a progressive, multi-stage process. The primary mechanisms can be attributed to three aspects: physical relaxation, component migration, and chemical aging.
The initial phase involves physical relaxation inherent to polymeric materials, primarily manifested as creep.Under sustained temperature and pressure, the polymer matrix undergoes irreversible plastic deformation, reducing material elasticity and diminishing the sustained contact pressure at interfaces. This gradually increases contact thermal resistance. Compensating for lost contact pressure during this stage—through optimized packaging structures and physical locking mechanisms—falls under mechanical reliability design.
Subsequently, silicone oils or other low-molecular-weight plasticizers added to enhance processability gradually migrate out of the polymer matrix—a phenomenon termed “pump-out.” The loss of lubricants directly causes material hardening and loss of flexibility, similarly leading to a significant increase in contact thermal resistance and reduced thermal conductivity. The direct approach to counteract aging at this stage involves modifying material formulations to reduce or eliminate easily migrating small-molecule oil components, shifting toward inherently flexible materials or reactive plasticization systems.
A deeper and more fundamental form of aging is thermo-oxidative degradation. Under the combined action of heat and atmospheric oxygen, the molecular chains of organic polymers undergo chain scission, resulting in reduced polymer molecular weight. This chemical change triggers severe deterioration in macroscopic material properties: significant loss of mechanical strength, diminished elasticity, and increased brittleness. Thermal conductive filler systems may also change concurrently. For example, prolonged heat stress can cause aluminum oxide particles to collapse and clump together, worsening the overall hardening of the material. Thermo-oxidative aging cannot be completely avoided because it is a chemical degradation process that is intrinsic to polymeric materials. Consequently, the core objective of material development has shifted toward significantly delaying this process to extend the effective service life of TIMs.
Synergy and Conflict: The Performance Balance Dilemma in Traditional Material Systems
Several distinct technical approaches exist in materials engineering to achieve thermal-oxidative aging mitigation: The primary strategy involves enhancing the thermal conductivity of the TIM itself, thereby reducing the actual operating temperature at the interface between the heat-generating chip and the TIM. According to the Arrhenius equation, lowering the temperature by 10°C can halve the rate of many chemical reactions, meaning reduced operating temperatures fundamentally mitigate the thermal-oxidative aging environment. The second approach involves increasing the molecular weight and crosslinking density of polymeric organic materials. Longer, denser molecular chain networks resist segment breakage under thermal-oxidative stress more effectively. Increasing the proportion of organic polymer matrices in the material is the third tactic. Superior aging resistance is intrinsically conferred by a higher percentage of high-quality polymeric matrix.
However, in traditional silicone gasket systems using alumina as a thermal conductive filler, significant trade-offs exist between these approaches. To enhance thermal conductivity (Path 1), the filler loading of highly conductive alumina powder must be substantially increased. This inevitably reduces the polymer matrix content (Path 3) and simultaneously limits the polymer chains' ability to achieve full crosslinking (Path 2) due to excessive filler loading. Conversely, increasing polymer content or crosslinking density to improve aging resistance sacrifices space for fillers, degrading thermal conductivity. This fundamental trade-off between “thermal conductivity” and “aging resistance” represents the core bottleneck for alumina systems pursuing high-reliability applications. Typical aluminum oxide thermal pads exhibit an “oil-to-powder ratio” (which indirectly reflects the organic/inorganic phase ratio) often exceeding 1:30, featuring a low polymer matrix content and consequently higher risks of thermal-oxidative aging over extended periods.
The Revolutionary Approach: The Methodical Benefits of Boron Nitride Thermal Fillers
Adopting sophisticated fillers with intrinsically higher thermal conductivity is essential to overcoming the performance trade-offs present in conventional systems. A complete answer to this problem is provided by flake-shaped fillers, such as hexagonal boron nitride (h-BN).Thermal pads made from boron nitride demonstrate synergistic improvements across multiple dimensions:First, boron nitride constructs a more efficient three-dimensional thermal network within polymer matrices. The measured thermal conductivity of these pads significantly increases, fulfilling the primary requirement of “reducing chip operating temperatures.”More critically, the filler ratio required for high thermal conductivity in boron nitride is substantially lower than that for alumina. Data indicates the “oil-to-powder ratio” for high-performance boron nitride thermal pads can be optimized to approximately 1:3. This means that while achieving equivalent or superior thermal performance, the organic polymer content in the material system can be increased nearly tenfold compared to alumina-based systems.The material's overall flexibility, mechanical strength, and resistance to thermal-oxidative aging are all directly and significantly improved by the large increase in polymer matrix proportion.Concurrently, the reduced filler loading gives polymer chains plenty of room to move and cross-link, which promotes the development of stronger cross-linked network structures and higher molecular weight. This further reinforces the material's long-term stability.
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