Environmental etch resistance

The superior scratch and environmental etch resistance of these coatings led to their acceptance as topcoats for 8 of the top 10 sellers for 1997, including Ford Taurus, Toyota Camry and Honda Civic/Del Sol (Fig. 11). 

A new type of single package coating (pseudonym for a IK coating) has been promoted (16) for having a superior balance of flexibility, hardness, UV durability, and environmental etch resistance. This carbamate chemistry cures in the same range as MF-based crosslinkers and has been shown to exhibit excellent shelf life and application properties. 

Other characteristics of DNQ/novolac resists that have contributed to their lasting success in the semiconductor industry include their high etch resistance and the fact that they can be developed in environmentally benign aqueous base developers. In addition, the cyclized rubber/bis-azide negative tone resists did not image well at the Hg g-line, the exposure wavelength of the earliest commercially available wafer steppers, the introduction of which effectively brought about the complete and wholesale conversion of the IC industry to novolac resists from the cyclized rubber/bis-azide. ... 

The key figures of merit for a photoresist are resolution, process latitudes (dose and focus), and reactive ion etch resistance. Other important performance parameters include sensitivity, compatibility with industrial standard developer (0.263N aqueous tetramethylamoniumhydroxide (TMAH) solution), adhesion to substrates, environmental stability, and shelf life. These performance characteristics are mainly determined by the base polymer in the photoresist. It should be pointed out, however, that some of these performance parameters, such as resolution, process latitudes and etch resistance, are also tool and process condition dependent. 

Base coat-clear coat finishes for automobiles are subject to environmental etching. Small spots appear in the clear coat surface in a warm climate with acidic rain. The spots are uneven, shallow depressions from hydrolytic erosion of resin in the area of a droplet of acidic water. Several factors are involved in differences in resistance to environmental etching (51). Since urethane linkages are more resistant to acid hydrolysis than the activated ether cross-links obtained with MF resins, generally urethane-polyol clear coats are less susceptible to environmental etching. Temperature, Tg, and surface tension are also important. 

Diethyl malonate blocked diisocyanates cross-fink polyols at 120°C for 30 min. The reaction with alcohols does not srield urethanes, rather transesterification occurs (134), and reaction with amines srields amides, not ureas. Storage-stable coatings can be formulated by using monofimctional alcohol in the solvent (135). Clear coats for automobiles that have both excellent environmental etch and abrasion resistance have been formulated with a combination of a hydroxy-functional acrylic resin, malonic ester blocked HDI and IPDI trimers, and an ME resin (136). 

Another approach using carbamate-functional reactants is to react a polyisocyanate such as IPDI isocyanurate or HDI isocyanurate with hydroxypropyl carbamate (50). These carbamates are used in automotive clear coats with an MF resin that has been partially reacted with butyl carbamate to reduce its fimc-tionality. The remaining methoxymethyl groups of the melamine resin react with the carbamate groups of the isocyanurate-derived carbamate to give cross-linked films with outstanding environmental etch and mar resistance. The use of a combination of a carbamate-functional acrylic resin, a polycarbamate derived from a polyisocyanate, and an MF resin has also been patented (51). 

ED resists have been used for the protection of circuit pattern tracks and plated through-holes during subtractive etching of copper in the manufacture of printed circuit boards [15, 25]. This involves the deposition of a polymeric etch-resist in place of the traditional metallic tin or tin-lead solder, providing a faster, simpler and more environmentally acceptable process that eliminates the need for disposal of toxic wastes from the plating and stripping chemistries used. 

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