Silicone soft and transparent layer for wafer-level fabrication of optical applications

Dow Corning developed a spin-on dielectric polydimethylsiloxane material suitable for wafer-level packaging in optical applications. The product is optically transparent in the visible range and has a very low Young modulus, inducing a low residual stress when applied at a wafer level. The product has been specifically designed for use as a thin protection or passivation layer of devices and it can also be used as permanent bonding adhesive. Specific attention in the formulation of the product was considered in order to minimize the amount of volatiles being released in the processing steps and a volatile-free layer over a broad temperature range is created at the end of the process. In the discussion section of this paper, a first section will explain the processing conditions of this wafer-level packaging solution and the key benefits will be exposed. A second section will present the volatile outgasing study in order to demonstrate that pending proper care is considered in the processing steps, the silicone solution can be used in a manufacturing environment and that a volatile-free layer is created at the end of the process. A third section will deal with the optical properties of this product and the stability after UV exposure will be exposed. The dielectric strength stability of the silicone layer will be investigated in a fourth section, followed by a study of the low mechanical stress induced by this product coated on a silicon wafer. A brief summary of all the benefits brought by this new technology will finally by summarized in the conclusion section.