AVS 45th International Symposium
    Applied Surface Science Division Wednesday Sessions
       Session AS-WeA

Paper AS-WeA6
Effect of PDMS Segment Length on the Surface Composition of Polyimidesiloxane Copolymers and its Role in Adhesion

Wednesday, November 4, 1998, 3:40 pm, Room 307

Session: Polymer Surfaces, Films and Interfaces
Presenter: J. Chen, State University of New York, Buffalo
Authors: J. Zhao, State University of New York, Buffalo
S.R. Rojstaczer, Occidental Chemical Corporation
J.A. Gardella, State University of New York, Buffalo
J. Chen, State University of New York, Buffalo
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Polyimidesiloxane (SIM) copolymers are becoming increasingly important materials in the microelectronics industry in applications, such as die attach adhesives, due to their attractive properties, such as good adhesion, low dielectric constant and low stress. In this study, a series of SIM copolymers, based on @alpha@,@omega@-aminopropylpoly(dimethylsiloxane)(PDMS), 2,2-bis(4-[4-aminophenoxyl]phenyl)propane(BAPP) and 4,4'-oxydiphthalic-anhydride(ODPA) was synthesized in our laboratories. We investigated the effect of siloxane segment length on the surface composition of the SIM copolymers and its role in adhesion. The aim is to elucidate the correlation between polymer structure, surface composition, and the adhesion strength, as evaluated by peel tests. In-depth compositional profiles of the near surface region to approximately 100Å depth were simulated from the results of angle-dependent Electron Spectroscopy for Chemical Analysis (ESCA) experiments by using a deconvolution computer program. The simulated in-depth compositional profiles show that the topmost surface of the air (free) surface of the 75µm thick SIM copolymer film consists of a siloxane-rich layer, even with the shortest siloxane segment. For a given siloxane bulk content, a longer siloxane segment gives a surface richer in siloxane. The adhesion strength was determined by peel testing of SIM copolymers-Fe/Ni Alloy-42 laminates. The peel strength decreases exponentially with increasing thickness of the surface siloxane-rich layer, which corresponds to a longer siloxane segment length. However, all values of adhesion strength of SIM copolymers are higher than that of pure polyimide. This confirms our previous results that both siloxane and polyimide are essential components to rendering the high adhesion strength. The siloxane component provides a good diffusive ability, while the polyimide component interacts with the substrate to give rise to adhesion strength. Longer siloxane segments in the SIM copolymers are found to be detrimental to adhesion strength by way of interference with the polyimide-metal interaction.