High Reliability Principles and Verifications in Solid Tantalum Capacitors. End-User’s Manufacturing Processes

This paper is companion to Y. Freeman’s and P. Lessner’s paper [1] introducing a new Flawless Technology with Simulated Breakdown Screening, (F-TECH) for manufacturing MnO2 style Tantalum (Ta) capacitors. This paper focuses on the impact that the end-user’s manufacturing processes have on reliability of Solid Ta capacitors. It demonstrates that depending on the end-user’s techniques and conditions, improvements in the capacitors quality can diminish significantly by unintended damage to the Ta capacitor dielectric during end-user’s manufacturing processes. Among the other factors affecting non-hermetic solid Ta capacitors, exposure to moisture prior to surface mounting can have a strong negative effect on the capacitor reliability. Test results will be provided to measure failure rate differences between conventional and F-TECH solid Ta capacitors. The results provide evidence that the F-TECH process along with the end-user process improvements provide the lowest component failure rates and the highest reliability. 1. Summary of industry reporting Evidence of catastrophic failure of MnO2 style Ta capacitor as a result of exposure to humidity is well documented [2,3,4]. In 1998, Devaney and Dicken [2] reported the results of testing following exposure to 85% RH at 35°C. They observed 20% failure with no subsequent bake out and a decrease to 4-5% failure with bake out at 100°C for 3 days. They concluded that the effects of humidity are not unique to one manufacturer, can be lot independent or dependent on the location of the user’s facility. In 2003, R.W. Dobson [3] observed 2.9% fallout of surface mount MnO2 style capacitors used in switching power supply applications. These parts were stored in conditions of uncontrolled humidity prior to mounting as well as uncontrolled internal manufacturing process related to aqueous wash and solder reflow. The supplier retested recently manufactured capacitors and found no failures following surge A and B and a 100 hour screen performed at 85°C and rated voltage. A subset of these same parts was subjected to 85°C/85%RH/100hours with 7.5% failure. Independent testing of parts that were initially stored in an uncontrolled environment with and without unbiased 85°C/85%RH/100hours showed a range of 1.7% to 5% failure with an undefined bake out. Continued testing of this sample under conditions of biased 85°C/85%RH/100hours showed failures 3 to 4 time higher than unbiased test results. The conclusions from this work indicate that failure mechanism is not lot or supplier specific, exposure to biased humidity is more severe than un-biased, the failure mechanism affects the entire population of parts and exhibits a wear-out characteristic given continued or repeated exposure to moisture. CARTS International 2014 March 31-April 3, 2014