THE EFFECTS OF CURING PROFILE, TEMPERATURE, AND AGING ON THE MECHANICAL BEHAVIOR OF SOLDER MASK MATERIALS

In this work, the mechanical behavior of a typical UV curable solder mask material has been explored as a function of ultra violet (UV) curing time, testing temperature, and isothermal aging exposure. Mechanical testing has been performed using standard tensile testing. For the tensile testing, a specimen preparation procedure has been developed to make 80 x 3 mm uniaxial tension test samples with a defined thickness (e.g. 0.30 mm), and both stress-strain and creep tests were performed. The solder mask test specimens were prepared in a unique way and no release agent is required to extract them from the mold. The mechanical behavior changes of the solder mask material were recorded for different curing profiles including various durations of UV exposure and subsequent isothermal curing. The results showed that an optimum UV exposure time was critical to provide acceptable mechanical properties. In addition, the stress-strain and creep behavior of the solder mask were recorded for various temperatures from 25 to 125 C, and the mechanical properties were found to degrade significantly at elevated temperatures as expected. The experimental results showed that variations of thermal curing profile (curing temperature and time) also change the mechanical properties significantly, so that solder masks have a very small optimum processing window. Finally, the effects of isothermal aging at 100 C on the material behavior were characterized for different aging times. Using the recorded data, the changes in the elastic modulus, strength, and creep rate were characterized as a function of aging time. Significant variations were observed in the elastic modulus (250%) and ultimate strength (150%) of the aged samples.