A Microwave curing system for microelectronics assembly

An approach to curing thermosetting polymers is the use of Variable Frequency Microwave (VFM) systems, which have been shown to cure encapsulant materials in substantially shorter times than conventional methods [1]. The microwave curing of thermosetting polymer material is a complex process, with interactions between electromagnetic field intensity, temperature, polymer cure kinetics and resulting development of potential thermo-mechanical stresses. As the real-time in-situ experimental analysis of a number of these parameters is extremely challenging, a numerical model has been developed to assess this process. The integration of microwave curing into an existing assembly machine imposes the requirement of a compact microwave system, based on a solid state source. Such a system has been designed and installed into our prototype demonstrator. A series of shear tests have been performed on an electrically conductive adhesive and an encapsulation material. No major deviation between microwave-cured material and material cured in a convection oven has been witnessed. Fourier Transform Infra-Red (FTIR) experiments were carried out on uncured, conventionally and microwave cured samples. The spectra of microwave cured and conventionally cured samples were practically identical. A series of LM-2940 dies have been die- and wirebonded to a Mirror Semiconductor open cavity package. Tests have demonstrated that the encapsulation and subsequent microwave curing can be performed without evident detrimental effects.