Characterization of material adhesion in redistribution multilayer for embedded high-frequency packages

Drivers for flexible electronics solutions suitable for high frequency applications are increasing constantly. Packaging technologies enabling reliable flexible high-frequency application for communication for sensors and actuators on human, are the key to promote future human-machine collaboration. As part of this, this paper investigated adhesion properties of interfaces within the package, to study the feasibility of applying the new materials for flexible packages. Package redistribution layers (RDL) include dielectric layers and Cu traces that are manufactured following a semi-additive approach. The interfaces of these materials to the encapsulation material, here a sheet mould compound (SMC) is used, is the focus on study in this paper. This work investigates adhesion properties of interfaces of redistribution layers that are manufactured following a semi-additive approach and which are of importance for fan-out packaging of high-frequency chips. The adhesion analyses are performed by means of button shear tests considering mould compound as well as RDL dielectric (organically modified ceramics, benzocylobuthene, and polyimide) and metals. A die-shear tester is used to measure the button shear strength. Cu buttons with 200 µm diameter and a height of 50 µm on the dielectric layer span on the Si wafer are used to investigate the adhesion strength between the dielectric material and RDL. The shear test of Ormocer® button on SMC surface have been carried out additionally to demonstrate the impact of the process sequence on the reliability of embedding-first integration approach in comparison to RDL-first approach. The results indicate dielectric layers are feasible for application in chip embedding, in terms of adhesion strength, and among the tested material, BCB showed the best performance to both SMC and Cu.