Advanced Dielectric Polymer Development at Kayaku Advanced Materials

High frequency, 5G+ and edge computing opportunities continue to evolve towards wider adoption.  Next-generation dielectric polymeric materials remain crucial to enabling future device packaging designs. The challenge lies in creating a material that balances the necessary characteristics to withstand harsh environments and complex designs. Most importantly, the material’s stability is essential to the performance of the packaged device. Future materials must continue to offer low dielectric loss (Df), low dielectric constant (Dk), and low moisture absorption while maintaining strong mechanical and thermal properties to resist the inherent stresses in the final package. High power devices such as MOSFETs and Si-C and Si-N based transistors require performance criteria of further increased thermal stability and higher break-down voltage, simply due to higher operating temperatures and voltages. Additionally, these emerging materials must be competitively priced and/or easy to manufacture to displace current industry players and manage the complexities of assembly. The resin polymer is often the most critical component among these materials. Therefore, it is essential for suppliers to continue innovating and developing advanced polymers with an optimal balance of properties.

Kayaku Advanced Materials (KAM) has focused extensively on expanding our portfolio of permanent dielectric materials through the development of novel and superior polymers. This presentation will cover recent R&D advancements in polymers designed for permanent dielectrics with potential applications in wafer-level packaging, such as redistribution layers or stress buffer layers. For instance, the earlier release of the photo-patternable dielectric KMSF 2000 provided a product that could be coated in thicknesses ranging from 3 to 10 microns and patterned successfully with a 1:1 aspect ratio, while offering good electrical performance, thermal stability, toughness, and excellent resistance to water uptake. This was achieved through KAM’s innovative block copolymer polyester, which balances several key properties.

Building on this success, we have now demonstrated the ability to modify the polymeric composition to extend the product’s capabilities, enabling coating up to 30 microns and patterning with a 3:1 aspect ratio, all while retaining the excellent performance metrics established by KMSF 2000. We have also expanded beyond the previous composition by developing new block copolymeric compositions, including polyesters, styrenics, polyimides, polybenzoxazoles, and hybrids thereof. Regarding film loss, it is important to distinguish between loss due to development and loss due to shrinkage. We have reduced film loss during development to less than 1%. This significant reduction indicates a marked improvement in pattern fidelity and material stability during processing, ensuring the material maintains its designed thickness and properties through to the final application. Furthermore, the material exhibits minimal shrinkage during curing, preserving dimensional stability and reliability. Finally, we will report the current extent of BDV tuning through polymer composition across different polymer platforms and inherent film thickness sensitivity.

The properties of these new materials offer several benefits to target markets:

1. Wafer-Level Packaging: The high Tg (tunable from ~175°C to over 280°C) and excellent thermal decomposition temperature (Td exceeding 450°C in some cases) make these materials ideal for use in environments where thermal stability is crucial. For example, in wafer-level redistribution layers, these properties ensure that the material can withstand the thermal stresses of solder reflow processes without compromising electrical performance or dimensional integrity. 2. Stress Buffer Layers: The toughness and elasticity of the polymers, combined with low dielectric constants (Dk ranging from 2.5–3.0) and low dielectric losses (Df ranging from 0.002–0.015), make them well-suited as stress buffer layers in advanced packaging. These layers help absorb mechanical stresses, protecting sensitive underlying structures in devices subjected to frequent thermal cycling or mechanical bending, such as in flexible electronics.

These advancements have been made possible by combining new polymer discoveries with advanced formulation strategies. Importantly, these materials can be manufactured without significant changes to current processes and capabilities. Additionally, we prioritize the exclusion of chemicals of concern. All of the polymers and formulations discussed here are free from NMP and are 100% PFOS/PFOA-free.