Surface shaping and 3D integration of optical functions on photo detector, using an optimized reflow process of solder Bumps

Solder bumps are widely used in micro electronic devices, for electrical interconnection. The solder bumps diameter can range, from 15μm, for detector with fine pixel pitch [1] to several millimeters for BGA (Ball Grid Array) packaging. For electrical interconnection, most important parameters of solder bumps are to have low resistance and efficient contact for all connection. However, solder bumps can be used to bring other functions to electronic assemblies. This paper presents the added value of solder bumps parameter (predictable shape, reflow temperature) coupling with self alignment for device positioning. The study focuses on low temperature solder bumps materials like indium or InSn alloy and the solder shape after reflow. Taking into account these parameters, it is possible to control the solder bump interconnection to add functions to microelectronic components and therefore bring more value to them (especially for optical and MEMS-based systems). Also, such a technique is compatible with low cost manufacturing and high volume production, since it can be implemented at wafer level. Two specific applications will be presented on this paper. The first application is about surface shaping and the second application is about 3D stack assembly for height passive control.