A Review of Polymer Dielectrics for Redistribution Layers in Interposers and Package Substrates.

The ever-increasing demand for faster computing has led us to an era of heterogeneous integration, where interposers and package substrates have become essential components for further performance scaling. High-bandwidth connections are needed for faster communication between logic and memory dies. There are several limitations to current generation technologies, and dielectric buildup layers are a key part of addressing those issues. Although there are several polymer dielectrics available commercially, there are numerous challenges associated with incorporating them into interposers or package substrates. This article reviewed the properties of polymer dielectric materials currently available, their properties, and the challenges associated with their fabrication, electrical performance, mechanical reliability, and electrical reliability. The current state-of-the-art is discussed, and guidelines are provided for polymer dielectrics for the next-generation interposers.

Transition Metal ß-Diketonate Adhesion Promoters in Epoxy-Anhydride Resin.

Epoxy to copper adhesion supports the reliability of numerous structures in electronic packaging. Compared to substrate pre-treatment, processing and cost considerations are in favor of adhesion promoters loaded in epoxy formulations. In this work, first row transition metal ß-diketonates present such a compelling case when added in epoxy/anhydride resins: over 30% (before moisture aging) and 50% (after moisture aging) enhancement in lap shear strength are found using Co(II) and Ni(II) hexafluoroacetylacetonate. From extensive X-ray photoelectron spectroscopy (XPS) analyses on the adhesively failed sample surfaces, increased population of oxygen-containing functional groups, especially esters, is linked to the adhesion improvement. Assisted by XPS depth profile on the fractured epoxy side and in situ Fourier-transform infrared spectroscopy (FTIR), the previously discovered latent cure characteristics endowed by the metal chelates interacting with phosphine catalysts are regarded pivotal for pacing the anhydride consumption and allowing interfacial esterification reactions to occur. Further examinations on the XPS binding energy shifts and dielectric properties of the doped epoxy also reveal metal-polymer coordination that contribute to the adhesion and moisture resistance properties. These findings should stimulate future research of functional additives targeting at cure kinetics control and polar group coordination ideas for more robust epoxy-Cu joints.

Melamine-graphene epoxy nanocomposite based die attach films for advanced 3D semiconductor packaging applications.

With the ultra-fast development of personal portable electronic devices, it is important to explore new die attach film (DAF) materials in the limited mounting area and height in order to meet the requirements of a high packaging density and a high operating speed. Graphene-based epoxy nanocomposites are becoming one of the most promising candidates for the next generation of DAFs combining the ultra-high thermal conductivity of graphene, and ultra-strong adhesion of epoxy polymers. However, poor dispersion and weak interfacial connections, due to the overly smooth surface of graphene nanosheets, are still pressing issues that limit their industrial applications. Additionally, pristine graphene nanosheets have only a small effect on improving the glass transition temperature (Tg) of epoxy composites to meet the requirements of DAFs. In this work, melamine-functionalized graphene is synthesized by using a nondestructive ball milling process, which results in greater dispersion and enhancement of the interfacial connections between graphene and epoxy resins demonstrated by both experimental and simulation results. In particular, the aromatic triazine rings of melamine increase Tg in the cured resin, thus improving the thermal stability of DAFs. The melamine-graphene (M-G) epoxy nanocomposites synthesized have a high Tg of 172 °C and an out-of-plane thermal conductivity of 1.08 W m-1 K-1 at 10 wt% loading. This is 6.4 multiples higher than that of neat epoxy. Moreover, M-G epoxy nanocomposites exhibit superb thermal stability, an effective low coefficient of thermal expansion (CTE), low moisture adsorption, and a useful high electrical resistivity. In the DAF performance test, involving experimentation and modeling, the samples present a better cooling capability and heat dissipation. This supports the idea that our findings have potential to be applied in the next generation of DAFs for high-power and high-density 3D packaging.

Enhanced permittivity and energy density in neat poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer films through control of morphology.

Polymer materials with large dielectric constants are desirable for the development of high energy density capacitors. We show that the dielectric properties of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] can be improved by the use of processing conditions that favor formation of a highly crystalline morphology of the nonpolar α-phase. Through the use of spin coating, thermal treatment above the melting temperature, and quenching, we were able to attain a highly crystalline, α-phase rich morphology that has a quite large dielectric constant of 77 ± 10 at 1 kHz. The final morphology and phase composition of the terpolymer films depend strongly on the postprocessing thermal treatment and the quality of the solvent. Evaluation of the polarization behavior of the terpolymer films as a function of electric field reveal that the polymer exhibits a relaxor-ferroelectric behavior and has a substantial energy density of 9.7 J/cm(3) at fields of up to approximately 470 V/µm. Under millisecond pulsed charge-discharge measurements a 3-fold increase in energy density (27 J/cm(3)) is obtained at high fields (∼600 V/µm). Our study demonstrates that the processing conditions and morphology of fluorinated terpolymer films are controlling factors for achievement of high dielectric permittivity and energy density that are critical for high performance capacitors.

High-energy-density sol-gel thin film based on neat 2-cyanoethyltrimethoxysilane.

Hybrid organic-inorganic sol-gel dielectric thin films from a neat 2-cyanoethyltrimethoxysilane (CNETMS) precursor have been fabricated and their permittivity, dielectric strength, and energy density characterized. CNETMS sol-gel films possess compact, polar cyanoethyl groups and exhibit a relative permittivity of 20 at 1 kHz and breakdown strengths ranging from 650 V/µm to 250 V/µm for film thicknesses of 1.3 to 3.5 µm. Capacitors based on CNETMS films exhibit extractable energy densities of 7 J/cm(3) at 300 V/µm, as determined by charge-discharge and polarization-electric field measurements, as well as an energy extraction efficiency of ~91%. The large extractable energy resulting from the linear dielectric polarization behavior suggests that CNETMS films are promising sol-gel materials for pulsed power applications.