**Abstract:** As a critical step in integrated circuit manufacturing, semiconductor packaging imposes stringent performance demands on packaging materials. Thanks to its exceptional overall properties, polyimide film stands out from a pool of candidate materials, earning its title as the "gold standard material" in the field of semiconductor packaging. This paper provides an in-depth analysis of the molecular structure and performance characteristics of polyimide film, details its application advantages across various stages of semiconductor packaging, and leverages industry data and real-world cases to reveal its crucial role in enhancing chip reliability and facilitating technological advancement within the semiconductor industry. It also offers a theoretical basis for the selection and innovation of semiconductor packaging materials.
**I. Semiconductor Packaging: The "Protective Armor" and Performance Hub of Integrated Circuits**
Semiconductor packaging is far more than simple physical encapsulation. It fulfills multiple critical functions, including mechanical support, electrical interconnection, and environmental isolation. As Moore's Law approaches its physical limits, chip integration density has increased exponentially. Current advanced process nodes have reached 3nm or even beyond, leading to a significant surge in internal chip heat generation and pushing signal transmission rates into the THz range. In this context, packaging materials must precisely withstand extreme operating conditions—such as high temperature, high frequency, and high humidity—within extremely confined spaces. For example, power amplifier chips in 5G base stations can experience surface temperatures exceeding 150°C during operation, while simultaneously requiring signal transmission delays to be controlled at the picosecond level. Traditional packaging materials often struggle to meet such demanding challenges.
**II. Polyimide Film: The "All-Round Champion" of Materials**
**2.1 Unique Molecular Structure Fosters Exceptional Properties**
Polyimide film is synthesized through a polycondensation reaction of aromatic dianhydrides and diamines. Its molecular backbone contains a large number of rigid aromatic heterocyclic structures. This unique molecular architecture endows the film with a series of extraordinary properties:
• **Thermal Stability: The "Iron Man" of High-Temperature Resistance:** The conjugated aromatic ring skeleton in the molecule possesses a bond energy as high as 520 kJ/mol. This allows polyimide film to exhibit a mere 1% mass loss at 500°C and, for short durations, even withstand extreme temperatures up to 1000°C without structural failure, far surpassing most traditional packaging materials.
• **Mechanical Properties: The "Strongman" Combining Rigidity and Flexibility:** The closely packed, ladder-like molecular arrangement within the film, with a free volume of only 0.08 nm³, gives it excellent tensile strength, reaching above 200 MPa. Simultaneously, it maintains good flexibility, capable of withstanding multiple bends without fracturing, with a bend radius as low as below 1 mm.
• **Dielectric Properties: The "High-Speed Lane" for Signal Transmission:** Thanks to π-π conjugation effects, polyimide film boasts a volume resistivity of ≥10¹⁶ Ω·cm and a dielectric constant around 3.2. Even at 200°C, its insulation property retention rate exceeds 95%. This characteristic provides a low-loss, high-fidelity transmission medium for high-frequency signals.
**2.2 Comparison of Key Performance Parameters**
Compared to other materials commonly used in semiconductor packaging, the performance advantages of polyimide film are immediately apparent: [Refer to embedded image `media/image1.png` for comparison chart.]
**III. The Diverse Applications of Polyimide Film in Semiconductor Packaging**
**3.1 Chip-Scale Packaging: Building a "Close-Fitting Protective Net"**
In Chip-Scale Packaging (CSP), polyimide film primarily serves the critical roles of chip surface passivation and stress buffering. Wrapping the chip surface with a 0.05mm thick PI film effectively blocks the intrusion of external contaminants like moisture and ions. When thermal stress is generated during chip operation, the flexibility and high mechanical strength of the PI film allow it to uniformly distribute stress, preventing cracks in the chip caused by stress concentration. Research shows that chips passivated with PI film maintain stable performance even after 1000 hours of storage under harsh conditions of 85°C and 85% RH, whereas unprotected chips exhibit a performance degradation rate as high as 30%.
**3.2 Wafer-Level Packaging: Creating an "Efficient Interconnection Bridge"**
In Wafer-Level Packaging (WLP) processes, polyimide film, as a key material for the Redistribution Layer (RDL), performs the dual functions of electrical interconnection and insulation/isolation. Its low dielectric constant and low dielectric loss characteristics significantly reduce signal delay and loss during transmission, ensuring high-speed data communication between chips. For example, in advanced 2.5D/3D packaging, using PI film as the RDL material can increase signal transmission rates by over 20% while reducing power consumption by 15%.
**3.3 System-in-Package: Forging a "Sturdy and Secure Fortress"**
In System-in-Package (SiP), polyimide film is used for the overall encapsulation of the package and for isolation between internal layers. Its excellent chemical corrosion resistance and thermal stability provide reliable protection for various types of chips and components, shielding them from complex working environments. Taking a smartphone SiP module as an example, after using PI film for encapsulation, the module's drop resistance improved by 50%, and its service life under high-temperature and high-humidity conditions was extended threefold.
**IV. Industry Practice and Data Support**
**4.1 The "Choice of PI Film" by Leading Enterprises**
Global leaders in the semiconductor industry, such as Intel, TSMC, and Samsung, have widely adopted polyimide film in their advanced packaging processes. Intel uses PI film as a stress buffer layer in chips manufactured at the 10nm node and below, effectively improving chip yield rates from 80% to over 90%. TSMC employs PI film to construct the RDL in its 2.5D/3D advanced packaging technology, successfully increasing inter-chip signal transmission bandwidth by 30%.
**4.2 Cost-Benefit Analysis: The "Potential Stock" with Long-Term Value**
Although the initial procurement cost of polyimide film is relatively high—approximately 10 times that of traditional PET film—its comprehensive benefits over the entire lifecycle of semiconductor packaging are significant. On one hand, the use of PI film greatly enhances chip reliability and service life, reducing after-sales repair costs due to chip failures. On the other hand, its outstanding performance helps chips achieve higher performance metrics, boosting product market competitiveness and bringing higher added value to enterprises. Estimates suggest that in high-end chip packaging, using PI film can reduce the product's overall cost by 15% to 20%.
**V. Challenges and Future Outlook**
**5.1 Industrialization Bottlenecks Awaiting Breakthrough**
Despite its bright prospects in semiconductor packaging, polyimide film currently faces several industrialization challenges. For instance, there remains a gap between domestic capabilities and international advanced levels in the preparation technology for ultra-thin PI film (thickness <12µm), with import dependency exceeding 60%. Furthermore, recycling technologies for PI film are not yet mature, making large-scale closed-loop recycling difficult, which somewhat limits its sustainable development.
**5.2 Technological Innovation Guiding Future Development**
Looking ahead, polyimide film in semiconductor packaging will evolve towards greater functionalization and integration. By incorporating nanomaterials for composite modification, it is possible to further enhance the thermal conductivity of PI film, potentially increasing it from the current 1.2 W/(m·K) to over 200 W/(m·K), thereby better addressing chip cooling requirements. Simultaneously, developing intelligent PI films with self-healing or self-monitoring functions will provide a higher level of reliability assurance for semiconductor packaging.
**VI. Conclusion**
Thanks to its unparalleled thermal stability, mechanical properties, and dielectric performance, polyimide film demonstrates irreplaceable advantages in the highly complex field of semiconductor packaging, where material performance requirements are extremely demanding. From fine protection at the chip level, to high-speed interconnection at the wafer level, and overall safeguarding at the system level, PI film has deeply integrated into every stage of semiconductor packaging. It has become a key force driving the semiconductor industry towards higher integration density, faster processing speeds, and stronger reliability. With continuous technological advancement and the gradual overcoming of industrialization bottlenecks, polyimide film is destined to continue writing the legendary chapter of a "gold standard material" in semiconductor packaging, injecting a continuous stream of innovative vitality into the development of the global semiconductor industry.
