Flip chip assembly in air from manufacturing and reliability perspectives

Soldering in nitrogen improves assembly yields due to low oxygen levels that improve the wetting of solder and consequently provide a wider reflow process window. However, soldering in nitrogen introduces manufacturing concerns. On the other hand, soldering in air can reduce manufacturing costs and prove to be cost effective as long as both the assembly yield and reliability are not affected.; Developing a robust process window for flip chip assembly in air becomes significant when integrating flip chips with other surface mount components that are soldered without the use of nitrogen atmosphere. There were two main objectives in this research. The first was to develop a robust process window for soldering flip chips with the eutectic Sn/Pb solder alloy in air. The second objective of this research endeavor was to identify the cost implications that are associated with the nitrogen reflow process. While the cost of manufacturing without the use of nitrogen is comparatively less, the cost is addressed within the overall context of the entire assembly process (or system).; In this research endeavor, a factor that is critical to flip chip assembly in air has been identified. Soldering in air requires limitations on the reflow profile. Reflow profiles with shorter and limited soak stages are necessary to conserve flux throughout the soldering process to ensure the proper formation of solder joints. In the subsequent reliability study, there was little difference observed between the air and nitrogen reflowed flip chip assemblies.; The use of inert soldering should be carefully evaluated for the impact of nitrogen on the costs of manufacturing. Although the costs vary with each situation, the typical costs include the initial capital expenditures and the supply of nitrogen. With a controlled process in air, the cost associated with the use of nitrogen in reflow for flip chip assembly can be eliminated. The ultimate decision to adopt inert soldering for a given process should be based on a comprehensive analysis of cost and benefits. Yield and reliability that can be obtained from both the reflow processes should be evaluated, similar to what has been conducted in this research.