This article addresses the reactive thermal processing of locally heated intermetallic seals for micro-electro-mechanical systems (MEMS) packaging. Traditional post-packaging of MEMS involves high temperature brazing or soldering which results in degrading the quality of the thermally sensitive device. Focused laser heating of multilayer metals, therefore, serves as an attractive alternative due to a decrease in heat affected/degraded area. In this work a model is presented to decipher the dynamics of the thermal reaction and to serve as a tool for optimization and control of the multilayer sealing process. The analytical model is based on three-dimensional space- and time-dependent temperature and concentration Green’s fields and is solved numerically. The laser heat distribution is represented as a spatially varying Gaussian heat source to simulate the temperature and concentration evolution that occurs during the thermal process. The rapid heating induced by the laser source results in melting the sealing layer of lowest melting temperature, and then dissolves the layer in contact with the molten region to facilitate the nucleation and growth of an intermetallic compound. The simulation results show the model can successfully predict the temperature of the layers as well as the amount of barrier layer dissolution, which consequently determines the extent of the intermetallic compound growth in the bonding/sealing process.

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