Surface modification of polyimide film surface by silane coupling reactions for copper metallization

To improve the adhesion between copper metal and Kapton film, cyano and amino groups were introduced onto Kapton film surfaces by a combination of argon plasma treatment and coupling reactions. 3-Aminopropyltrimethoxysilane (APS-1), 3-aminopropyltriethoxysilane (APS-2), 2-cyanoethyltriethoxysilane (CES), and 3-cyanopropyltriethoxysilane (CPS) were used for the coupling reactions. The effects of the cyano and amino groups on the adhesion with copper metal were assessed from the peel strength of copper metal/Kapton systems. Cyano groups contributed to the adhesion with copper metal, but amino groups did not contribute. The peel strengths in the copper metal/CES- and CPS-modified Kapton systems were 2.2 and 2.3 N/5 mm, respectively, 2.3-2.4 times higher than the value for the unmodified Kapton film (0.94 N/5 mm). The locus of failure was found to be in a weak boundary layer (WBL) in the copper metal/CPS-modified Kapton system; the WBL could originate from the Ar plasma-treated Kapton or the original Kapton layer.