Surface chemistry adhesive bond formation

One important influence in the formation of a good adhesive bond is surface or interfacial chemistry. In the broader sense, in which two substances are held together by interfacial forces, adhesion is of importance in many technologies such as in thin films and semiconductors. It is the purpose of this paper to discuss ion beam methods of surface characterization applicable to the broad area of adhesion with emphasis on adhesive bonding. 

In the substrate preparation step involving priming, the surface chemistry of the substrate is modified to promote the adhesion between the substrate and the resist material during coating. In the exposure process proper, exquisite radiation chemistry takes place inside the radiation sources in order to generate the exposure radiation, but also because of the interaction of these radiations— be they photons, ions, electrons, X rays—with the outer-shell electrons of the radiation-sensitive compounds and molecules in the resist, leading to bond breakage and/or bond formation. 

There are relatively few well-documented examples of interfacial primary bonding in the literature but it is possible to find examples in the areas of organic coatings on steel, metallized plastics and adhesion promoters. As the following examples will show, the exact definition of the chemistry resulting from primary bond formation at the interface has only become possible with the advent of surface analysis techniques. Such investigations rely heavily on XPS and ToF-SIMS for interfacial analysis. 

In the case of the GPS organosilane adhesion promoter applied to aluminum (and used as a substrate in the data of Fig. 10.13), ToF-SIMS has established the formation of a covalent bond between the GPS molecule and the oxidized aluminum substrate (Abel et al. 2000). The chemistry leading to the formation of the diagnostic fragment (Al-O-Si at m/z = 70.9534 u) and the high resolution spectrum at a nominal mass of 71 u is shown in Fig. 10.15. The formation of the specific bond is associated with good durability of the resultant bond, and examination of the fracture surfaces of failed joints shows that the presence of the ion in the ToF-SIMS spectrum correlates well with good durability. 

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