A method for the assembly of microelectronic packages using microwave curing (Englisch)

Advanced electronic packaging continues to gain prevalence, driven by the continuous trend for miniaturization with concurrent functional integration. Processes in use today are typically efficient for mass production, but are not suitable for the purposes of low volume and prototype production. Adhesive bonding circumvents the elaborate tooling typical for mass production and provides a higher degree of flexibility. Disadvantages lie in long curing cycle times and high handling effort. To overcome these problems, a novel method for the assembly of electronic packages is proposed, one that improves the performance and efficiency of the assembly processes and reduces the handling effort between the separate process steps by integration of assembly and curing process equipment into a single machine. An analysis of the field of electronic packaging with particular respect to adhesive curing processes is performed. Then the relevant state-of-the-art is reviewed and the need of a novel method is identified. The conception and realization of a microwave curing system, based on an open-ended waveguide resonator are carried out. Different concepts for the control of the curing process are described. A machine integrating the curing system and the assembly process equipment is designed and prototypically realized. This is followed by extensive evaluation and testing of the novel method. In the course of the evaluation a representative flip-chip assembly is realized. In order to assess the influence on reliability, a series of temperature cycling tests is performed. Additionally, stress-measurement dies are packaged and the influence of the proposed method onto residual stresses is studied. The influence of the proposed method on throughput and assembly efficiency is investigated. The proposed method provides reduction of curing cycle times for three different adhesive materials and therewith an increase of the overall throughput. By reduction of handling effort, the overall process efficiency could be improved. Furthermore, by microwave curing with the proposed method, a higher reliability of the resulting electronic packages can be achieved. The experiments with the stress chips reveal lower residual stresses in the microwave-heated chips compared to convection heating.