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PHYSICAL AND CHEMICAL PROPERTIES OF THIN METAL FILMS ON POLYETHERIMIDE

IP.com Disclosure Number: IPCOM000005970D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-21
Document File: 8 page(s) / 282K

Publishing Venue

Motorola

Related People

Lynn Davis: AUTHOR [+2]

Abstract

The exceptional combination of electrical, thermal, physical and chemical pmperties found in polyetherimide (PEI) resins make them particularly suited for printed circuit board (PCB) applications. PEI resins are noteworthy for their low dissipation factor at high frequencies, which makes the material ideal for use in micmwave applications. The key to making high quality PCBs from PEI is a thorough understanding of the factors influencing metal/PEl adhesion. A strong metal/polymer interaction is desirable in order to achieve optimum metal adhesion. This study utilizes X-ray Photo- electron Spectmscopy (XPS) to characterize the chemical interactions between PEI and three metals, copper, chromium, and nichmme (80% Ni, 20% Cr.).

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MOIVROLA Technical Developments Volume 11 October 1990

PHYSICAL AND CHEMICAL PROPERTIES OF THIN METAL FILMS ON POLYETHERIMIDE

by Lynn Davis and Marc Papageorge

   The exceptional combination of electrical, thermal, physical and chemical pmperties found in polyetherimide (PEI) resins make them particularly suited for printed circuit board (PCB) applications. PEI resins are noteworthy for their low dissipation factor at high frequencies, which makes the material ideal for use in micmwave applications. The key to making high quality PCBs from PEI is a thorough understanding of the factors influencing metal/PEl adhesion. A strong metal/polymer interaction is desirable in order to achieve optimum metal adhesion. This study utilizes X-ray Photo- electron Spectmscopy (XPS) to characterize the chemical interactions between PEI and three metals, copper, chromium, and nichmme (80% Ni, 20% Cr.).

RESULTS

Copper on pblyetherimide

    XPS studies were performed on thin copper films evaporated onto the surface of cleaned PEI castings. The thickness of the copper films was roughly 50 nm. The surfaces of the clean PEI castings were free of any impurities, within the detection limits of XPS ( - 0.1% of a monolayer). Copper was found to interact weakly with PEI resulting in the formation of some copper carbides and a minor amount of polymer scissoring. Representative spectra of the Cu 2p and x-ray induced Cu Auger transitions are given in Figure 1 for the CopperlPEl interface. The location of the interfacial boundary was determined by monitoring the C 1s signal during depth profiling experiments. The C 1s spectra recorded for the CopperlPEl interfacial region is shown in Figure 2a, and the C 1s spectra for subsurface region of PEI is given in Figure 2b.

   Both the Cu 2p and x-ray induced Cu Auger transitions are characteristic of the present of metallic copper. If oxides of copper were present, they could be most easily identified by the Cu Auger spedrum. Cupric oxide (CuO) is characterized by an x-ray induced Auger transition at 566.7 eV, and a Cu 2p spectrum exhibiting strong shake-up featUreS at 942.3 and 962.1 in addition to the 2~3, and 2p,, transitions at 9336 and 9536 eV, respectively. Cuprous oxide (C&O) ex- hibits a Cu 2p XPS spectrum virtually identical to that of metallic copper, but the principle x-ray induced Auger transition of these species occurs at 569.4 eV The absence of the characteristic oxide transitions in the x-ray induced Auger spec- trum provided clear proof that copper oxidation by the PEI substrate was minimal.

   The presence of the copper layer clearly influenced the PEI substrate, as evidenced by Figure 2a. Some scissoring of the polymer backbone occurred resulting in the formation of a small amount of surface carbides, which were iden- tified by a C 1s binding energy of 264.1 eV These carbide species are clearly not due to surface contamination, as the intensity of the C 1s signal first decreased upon depth pmfiling and then incre...