INSTRUMENTATION • ELECTRONICS
TRENDS IN ADVANCED SEMICONDUCTOR PACKAGING
Dr Yu-Han Chang, technology analyst at IDTechEx, explores new innovations in the field
A
s semiconductor packaging techniques evolve, advanced technologies like 2.5D
and 3D Cu-to-Cu hybrid bonding have emerged as ways of achieving higher performance and power efficiency. However, manufacturing these technologies to meet standards while fulfilling client requirements is complex and challenging. Research company IDTechEx’s recent report ‘Materials and Processing for Advanced Semiconductor Packaging 2025-2035: Technologies, Players, Forecasts’ provides insight into these challenges.
2.5D INTERPOSER MATERIALS In 2.5D packaging, different chiplets are interconnected horizontally through interposers, with three main materials being considered: silicon (Si), organic, and glass. Silicon interposers are the industry standard for high-performance computing (HPC) owing to their ability to
support fine routing, but their high cost and packaging area limitations pose challenges.
LOCALISED SI BRIDGES ARE A SOLUTION Localised Si bridges have emerged as a solution, while organic interposers offer a cost-effective alternative, particularly through Fan-Out Panel Level Packaging (FOPLP), which increases area utilisation and lowers costs by up to 60%. However, achieving fine routing similar to silicon remains difficult. Glass interposers, with their tunable coefficient of thermal expansion (CTE) and high dimensional stability, also support panel-level packaging and cost reduction. Yet, despite their promise, glass interposer production is still maturing, limiting large-scale adoption.
FIVE IMPORTANT CRITERION Generally, when selecting next- generation materials for interposers
in 2.5D semiconductor packaging, five key criteria are essential: dielectric constant (Dk), elongation to failure, coefficient of thermal expansion (CTE), Young’s modulus, and moisture absorption. A low Dk is crucial to reduce capacitance and enable higher data rates, improving signal integrity. Elongation to failure ensures the material withstands mechanical stress during manufacturing. Matching the CTE of the dielectric to copper layers enhances package reliability. On the other hand, Young’s modulus is also a key factor. While a low Young’s modulus minimises stress on microvias, crucial for advanced designs with sub-5 microvias, a higher modulus offers better stability for the package. Therefore, finding the right balance between these opposing requirements is essential for advanced packaging. Finally, low moisture absorption is critical for long-term reliability, as excessive moisture can lead to delamination and degrade both mechanical and electrical performance. Balancing these parameters is vital for optimising bandwidth and power efficiency in next-generation interposer materials.
The chart shows an analysis of the performance of interposer materials 42
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CU-CU HYBRID BONDING MANUFACTURING Wafer-to-Wafer (W2W) and Die- to-Wafer (D2W) hybrid bonding are two key approaches for 3D Cu-to-Cu hybrid bonding, each has distinct advantages and challenges. W2W bonding, the more established process, involves bonding two full wafers, typically in a single, uniform step. This approach benefits from consistent surface area, making
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