Development of a wafer-level burn-in test socket for fine-pitch BGA interconnect

Contact beam structures for fine pitch (0.5-mm) test socket that will mate with 95/5 lead/tin solder balls (50±5 μm in diameter) were fabricated by conventional integrated circuit processing technology. A range of dimensions for contact beam structure (cross and bridge) were tested for mechanical behavior and electrical performance. Non-linear finite element models (ANSYS 5.5) were used to predict the force and stress between the copper thin film beam structure and the solder ball. To avoid plastic deformation of the solder ball, numerical analysis suggests that the contact force on 50 μm solder balls should be lower than 17 mN. The yield strength of sputtered copper thin film (2 μm) is inferred from experimental and numerical data to be in the range of 2.80-3.09 GPa. The best cross and bridge structures are presented in addition to a new “Meander” structure which, numerically, shows the best potential