A polymer material hardened at the time of bare-board fabrication is used in solder mask formulation the PCBs of today. Solder masks ensure the protection of surface layers of the conductor. Solder masks too have peculiar thermal properties that need to be looked into during assembly. The base material of a solder mask is polymer and it succumbs to the problems that other polymers face. Polymers and their properties are not a concern for the designers but to analyze the reflow cycles and reliability of the solder mask is nevertheless important while you're building PCBs which are to be used in high-grade tech which have to run for prolonged periods in extreme conditions and unpredictable environments. Hence the fact of the hour is that the material integrity of the solder mask has to be kept intact in order to get a desirable end result. Factors That Determine Reliability of Solder Mask: Being a complex mixture of chemically active ingredients like pigments, fillers, ...