Photosensitive solder resist for semiconductor package is now in transition stage. Smaller flip-chip burnp and finer bump pitch lead thinner solder resist with surface flatness and uniform thickness. In addition, the thickness precision is also important in the package. The demand of film type solder resist has been increasing against conventional liquid ink type one because of its ease to give flat surface. Additional advantage of the film type solder resist is that it is easy to disperse fine particle filler and remove fine foreign matters in the varnish because of the lower viscosity of the vanish comparing with that of conventiona1 liquid ink type solder resist. The solder resist of next generation requires the following properties: (1)Compatibility with direct image exposure, (2)Thinner film, (3)Fine pitch HAST resistance (line/space ≦ 8/8 μ m), and (4)Crack resistance on various heat processes and TCT. In this paper, we introduce our approaches to satisfy these requirments such as preventing oxidation of underlying Cu which weakens the resistance to plating with thin thickness, greatly reducing contamination by Cl and Br, espetially hydrolyzable Cl, for HAST, and improving crack resistance by combination of new high Tg and low CTE resin and our elastomer technology.