Surface tension study of substrates in electronic packaging

There are many interfaces in electronic packaging, and the adhesion at those interfaces is critical to the reliability of the assembly. Surface tension of the surfaces and its three components (Lifshitz-van der Waals component, acid component, and base component) are important parameters that affect the adhesion. In order to improve the wetting and thus possibly adhesion of underfill material with substrate and passivation of flip-chip device, some techniques can be employed to modify the surfaces. In this study, the three-liquid-probe method was used to study the surface tension and its three components of various surfaces: benzocyclobutene (BCB) passivation, FR-4 board, polyimide board, and alumina board. The surface tension was changed with the treatment of UV/ozone, which was indicated by the contact angle measurement. The base component increased most after UV/O₃ treatment. It was also shown that the change in contact angle decayed as time elapsed after treatment. Different substrates showed different decay rate. Among the surfaces studied, BCB passivation showed the fastest decay rate after treatment; while, alumina showed the slowest decay rate