Angle-dependent electron spectroscopy for chemical analysis (ESCA) was used to examine the air facing surface (20-100 Angstrom thick) composition of polyimidesiloxanes with different processing variations, and of varying polydimethylsiloxane (PDMS) content and block length (number of PDMS repeat unit varies from 1 to 9). Polyimide was clearly detected (due to the nitrogen content) in the 20-100 Angstrom surface regions. This shows that a small amount of PDMS and short PDMS segment lengths in polyimidesiloxanes give a surface region with both PDMS and polyimide present. The surface composition, particularly that in the ca. 100 Angstrom region, was correlated to the peel strength of polyimidesiloxane melt pressed to a metal substrate. Our results suggest that both PDMS and polyimide are essential components to rendering a needed peel strength. PDMS, having a good diffusive ability, readily reaches the substrate upon being pressed, achieving intimate contact, while imide groups interact with the substrate, presumably through chemical bonding; these two factors act synergistically to result in a high peel strength. In addition, the interaction mechanism and the failure mechanism involved in bonding polyimidesiloxane and metal substrate were also elucidated based on the ESCA results.