Numerical characterization of electronic packaging solutions based on hidden dies

Innovative electronic portable products can be characterized by increasing signal frequencies and the demand on higher density of functions, which requires more space, for active components as well as for passives. One way to meet these requirements is a three-dimensional integration of components. The authors follow a so-called "chip in polymer" approach, which allows an extremely dense integration and very short interconnects. Thinned Si-components are embedded directly into the printed circuit boards, and interconnects are realized by laser drilling and galvanic metallization. In order to achieve high functionality and reliability and to minimize the number of later redesign loops, thermal and thermomechanical reliability aspects are taken into account already from the initial design phase. For this purpose, numerical studies by means of finite element (FE) analyses are very efficient to check the desired properties. The authors\´ approach for a package design, containing different types of test structures and ICs, is outlined. First, FE calculations were carried out in order to study the thermal performance. The number, positions, and dimensions of thermal vias were investigated in detail, and their influence on leading heat off could be evaluated. Beside this, the fraction of copper in the top metallization layer of the package was taken into account. In order to reduce the number of necessary real parts and the effort for the test procedures, a special test board was designed with different versions of interconnects between the hidden dies and the ambient. The thermomechanical behavior during thermal cycling was investigated numerically by a single 3d FE model in which the properties of certain material regions can be switched. This way, several design details in the vicinity of the active buried dies could be analyzed before any real parts were available. Reliable material data are necessary for reproducible numerical results, including temperature- and time-dependencies, especially for plastic materials. This way, the board material RCC (resin covered copper) has been tested in detail. The preparation of specimens, test results and the procedure of data adaptation to the FE syntax requirements are reported. This methodology enables a pre-optimization - of the thermo-mechanical properties and can be generalized and applied to many design procedures before any real parts are available. It is helpful to reduce cost and time-to-market for future products by minimizing real tests and expensive redesign.