By Minoru Suzuki, Thermo Electron, Yokohama, Japan; David Rohde, Dennis Masaki, Thermo Electron, Madison, Wisconsin
One area of device reliability is the physical and electrical connection of the die to the lead frame through the bond wire. Even with the emergence of new techniques for the connection of die to circuit board, the wire bond is still a mainstay of the semiconductor industry. When bonds fail, visual or even electron imaging may not provide enough information to diagnose a problem and provide a solution.
Adding energy dispersive spectroscopy (EDS) to scanning electron microscopy (SEM) analysis provides more information while new acquisition and analysis tools provide clearer answers. Using a SEM and an EDS x-ray microanalysis system, wire bonds can be analyzed to find the root cause of problems. In this example, the imaging and analysis synergy of the SEM/EDS combination was used to visualize elemental distribution and identify potential problem areas.
Elemental mapping using SEM/EDS is a proven technique for determining the distribution of elements in the micro and now nano world of device manufacturing and packaging. But there are limits to its usefulness due to elemental peak energy resolution, background noise, and the time it takes to collect and analyze the x-ray data. New software and hardware developments can improve the analysis and make the analyst more productive as well.
Modern x-ray microanalysis systems include powerful data acquisition and analysis tools to improve the quality, speed, and convenience of diagnosing and solving problems with the adhesion of wire bonds. The example in this paper is a cross-section of a faulty wire bond that was viewed in a field emission scanning electron microscope (FESEM) at 10,000x using a 7kV accelerating voltage. The electron image shows the normal-looking surface of the sectioned material without an apparent cause for the bond failure. …
Julie MacShane, Managing Editor, SST, at email: [email protected]