Micro-mechanical characterization of solder mask materials

Mechanical properties of solder masks are critical in the reliability perfo rmance of flip-chip packages. Many recent studies show that the mechanical properties of solder mask materials have great influence on moisture absorp tion, delamination at interconnections and solder fatigue life in flip-chip packages. There are also assembly process issues related to the properties of solder masks. This article presents an experimental investigation that mechanically characterizes two polyimide solder mask materials; Type A and Type B by using a micro thermo-mechanical tester. The mask samples are prep ared as thin film specimen. Mechanical properties such as Young's modulus, failure strength and creep behaviors are determined based on the recorded d ata from the experiments. In addition, a testing procedure of measuring the coefficient of thermal expansion (CTE) is developed, which provides an alt ernative to the TMA method. It is shown that the experimental investigation is suitable in conducting such a characterization of thin-film solder mask s.