TABLE OF CONTENTS In some cases, even the best solvent, cleaning process, and adhesive are not sufficient to produce a reliable bond. Chemically inert surfaces such as gold, other noble metals, and nonpolar plastics such as Teflon , polyolefins, and parylene are extremely difficult to bond and require additional surface treatment besides cleaning. Roughening a gold-plated bonding pad lightly using an abrasive or scuffing the surface with an electric eraser have been found to increase the adhesive strength of epoxy adhesives. Surfaces may also be sputter etched or ion milled to remove surface contaminants and to physically etch the surface providing greater surface roughness and area for adhesives to wet and adhere.
Primers recommended by the adhesives supplier are also useful. Primers are generally not necessary for epoxies because of their high polarity and affinity for most surfaces. In fact, solvent-thinned epoxies have been used as primers to improve the adhesion of other polymer types. Primers are often required for one-part and two-part RTV silicone adhesives. Primers are low-solids, solvent-based, air-drying coatings that can be applied by spraying, brushing, dipping, or spin coating. Solvent solutions of various silanes are among the best primers.
Finally, chemical alteration of surfaces can improve adhesion. Semi-crystalline materials have low polarity and low surface tension that must be increased to enable adhesives to bond. Oxidizing processes such as corona discharge, plasma, flame treatments, or UV irradiation in the presence of air or oxygen may be used to alter normally nonpolar surfaces, rendering them polar...
