TABLE OF CONTENTS The most important requirements in assuring good adhesion between surfaces are the cleanliness of and the chemical and physical condition of the surfaces. The adhesive chosen must be able to wet the surfaces so that a contact angle of less than 90 results, as discussed in Ch. 2. Unfortunately, the choice of solvent and cleaning process is often made hastily without considering the nature of the contaminants or how clean the part needs to be. Inadequate cleaning prevents or reduces adhesion and can cause corrosion or electrical deterioration over time, but extra cleaning, if not necessary, becomes costly. It is good engineering practice to analyze the types of contaminants that are likely to exist on a surface as a result of exposure to the ambient, handling, or previous processing such as plating, soldering, or etching. Analytical procedures such as infrared spectroscopy, energy-dispersive x-ray (EDX), scanning-electron microscopy (SEM), and ion analysis can be used to identify the residues. Once the contaminants are identified, the appropriate solvents and cleaning process for their removal can be selected.
Contaminants may be of three general types: particulates, highly polar (ionic) residues, and nonpolar (grease-like) residues. In many production environments, all three are present and several solvents and cleaning processes must be used to remove them. Both the choice of solvent or cleaning solution and the cleaning process are critical, and several theoretical principles maybe followed in their selection. Ultimately, cleaning is more an art than a science, and the procedure chosen should be...
