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This paper deals with the wideband frequency molding material characterization in three dimensions stack of integrated circuits (3-D IC). This material is required as a passivation layer at the top of an element called interposer. The interposer constitutes a platform that allows to connect heterogeneous chips, for example, a radio frequency transceiver, a low-noise amplifier, and an antenna. As the molding material has been recently developed, its performance (electrical proprieties, such as permittivity and loss tangent) must be evaluated in order to predict the impact on the signals propagation. First, the process flow and fabrication steps of the 3-D stack are presented. Then, the wideband frequency characterization method based on transmission lines is described. First, this method requires high-frequency measurements using the same coplanar transmission lines with and without molding material. Second, a deembedding procedure, specifically developed for this 3-D test configuration, is performed. Next, a conformal mapping algorithm to extract the permittivity and the loss tangent of the dielectric is achieved. Finally, results are presented and discussed; for example, the molding relative permittivity is found around a value of 3.7. This value appears relatively constant up to 67 GHz. This result is promising for millimeter-wave applications, and reveals the molding as a potential good candidate for microelectronic manufacturing.