Effect of Thermal Cycling on the Thermal and Mechanical Properties of Dielectric Materials

Photosensitive polymers or dielectric materials such as polyimides (PIs) have been used in fan-out wafer-level packaging process (FOWLP) as a redistribution layer for quite some time. In the condensed 2-D and 3-D packaging processes, the dielectric materials are applied multiple times to create as many as four or five redistribution layers. At the end of the process, the first layer may experience up to four times of heat cycles in which the polymer properties may change. However, the effect of heat cycles on properties of dielectric film as well as their contributions to the wafer-level warpage is still unclear. To understand the changes of materials’ properties after several heat cycles, the thermal and thermo-mechanical properties of negative-tone and positive-tone types of dielectric films are characterized by using the thermomechanical analysis (TMA), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). The glass transition temperature ( ${T}_{g}$ ), coefficient of linear thermal expansion (CTE), and modulus (storage, ${E}'$ , and loss, ${E}''$ ) are analyzed and compared. In addition, the morphology of the films before and after heat cycles is also analyzed.