Thin-film multilayer polyimide films

Copper/Polyimide Thin Film Multilayer Interconnect Structure... 

A typical polyimide (BDTA-ODA-MPD) for thin-film multilayer interconnections... 

Figure 1. Proposed approach for multichip packaging using thin film multilayer Cu/polyimide interconnections.

With advancements in MCMs, where large chips (up to 500-mils square) are closely packed and where devices and interconnect substrates are fragile (for example, polyimide thin-film multilayer substrates used in MCM-D), new rework challenges have arisen. In these high-density circuits, spacings between the chips may be as small as 40 mils—too small... 

Figure 15.24 shows the fabrication process of the optical filter on a fluorinated polyimide substrate. First, the low-thermal-expansion-coefficient PMDA/TFDB poly(amic acid) solution was spin-coated onto a Si substrate and baked. Then alternate TiO2 and SiO2 layers were formed on the polyimide film by ion-assisted deposition. The multilayered polyimide film was diced and peeled off from the Si substrate. In this way, thin optical filters on a fluorinated polyimide substrate are easily fabricated. 

Much subsequent work has been carried out on the formation and characterisation of polyimide multilayers ([259-63] and other papers of less relevance to the theme of this book). It has been established that there is substantial orientation of the polymer axes in the direction of dipping, an effect which increased with the length of the polymer chains. Thin films consisting of ten monolayers were far more defect-free than fatty acid films of comparable thickness. Progress has also been made... 

Polvimide-Metal Interfaces. Several technological applications including semiconductor packaging and metallization demand a reliable and durable adhesion properties of the metal films. In the development of multilayer devices consist of alternating layers of metal and polyimides several reliable techniques are needed to study both thin films and their interfaces. The usefulness of the nuclear scattering techniques to study the metallization and the associated interfacial elemental diffusion processes under the effects of various temperature and humidity treatments on the metal-polyimide systems, such as Al, Cu, N, and Au on Du Pont Kapton type H have already been reported (21., 22.). Only a couple of examples are presented here to illustrate the ERD application. 

Vapour Deposition Polymerisation. This is a little studied approach but one that offers significant potential for the fabrication of very thin films and for elaborate multilayer structures. A commercial process has been developed by the Ulvac Corporation in Japan to coat magnetic relay switches with an insulating polyimide layer. A polyamic acid is sythesised by co-deposition of two reactive monomers and is then thermally imidised. The same approach can be used for the condensation polymerisation of poly(azomethine)s, ° poly(ox-adiazoles) and poly(quinoxalines) all of which have been used in LED structures. This approach to polymer synthesis is ripe for further development. 

Zhang F, and Srinivasan M. P. Multilayered gold-nanoparticle/polyimide composite thin film through layer-by-layer assembly. Langmuir. 23 no. 20 (2007) 10102-10108. 

Thin-film polyimide-based implants use the polymer as both the structural and insulation material. They have been micromachined with multilayer metallization [54] for use as acute and chronic extracellular recording electrodes, and sieve and cuff regeneration electrodes. Thin-film metal layers (approximately 200-300 nm thickness) are sandwiched between the polymer layers. Reactive ion etching in oxygen opens contacts to the electrodes. This dry etch also defines the probe shape (Fig. 7). 

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