Currently, in a context of virtual product development process, information related to the entire product life cycle has to be taken into account. In order to support that product development, the scientific community so far proposed a lot of results concerning product modelling that have to be seen as complementary in order to cover the largest product life cycle activities (functional analysis, structural breakdown, CAD model, FEM, "X" assessment, etc). The synthesis of activities provides new information concerning the product and is expressed to provide new data that have not been already defined or to constraining already-defined ones by a reduction of their alternatives and of their range of values. The final solution is defined as the convergence "first the right time" by least commitments of the initial solutions space according to experts' information synthesis. The main result presented in this paper is to provide adequate tools to the designers in order to first define potential product alternatives at the earliest stage of design and then progressively reduce the space of solutions skipping non optimal or non robust ones. The initial space of solutions is therefore analysed by solving transfer functions and then to asses the product's behaviour (required functions) respect to parameters range of values. This decision making process is finally performed identifying what could be the optimal solution or the most robust one. An example based on an electrical switch illustrates the management of product models, multidisciplinary optimisation and robustness analysis.