Abstract
A few diodes from a production lot were discovered to have unacceptable current leak rates after about 5 years of storage. Inspection revealed the presence of copper sulfide deposits that bridged the external body of the diode and presumably provided a leakage path. Figure 1 shows the physical configuration of a diode. The function of this device is performed by a silicon-based semiconductor that is bonded between two cylinders of tungsten with copper headpins (Cu wire with a flat “nail-head” formed on one end) brazed to the opposite ends of the cylinders. A toroidal ring of glass protects the Si chip. All exposed metal parts are covered by an immersion plating of Ag. Then the entire assembly is coated with black epoxy and a band of green ink is applied to the cathode end. During storage, each diode was placed in a cardboard holder and secured in stacks of about ten with rubber bands.Analytical and environmental exposure studies were performed at Allied Signal and Sandia to determine the cause and potential long-term significance of this corrosion-related degradation problem. The objective of the analytical work was to characterize the corrosion product and help identify the corrosion mechanism. Tools included optical microscopy, scanning electron microscopy, electron microprobe analysis, SIMS, and x-ray diffraction.
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
