Tin Whisker Electrical Short Circuit Characteristics—Part II

Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has an unknown probability associated with it. Note however that due to contact resistance, electrical shorts may not occur at lower voltage levels. In our first paper, we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data, we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish.

[1]  Jay Brusse,et al.  NASA Goddard Space Flight Center Tin Whisker (and Other Metal Whisker) Homepage , 2004 .

[2]  J. Downs,et al.  THE PHENOMENON OF ZINC WHISKER GROWTH AND THE ROTARY SWITCH : (OR, HOW THESWITCH INDUSTRY CAPTURED THE ABOMINABLE SNOWMAN) , 1994 .

[3]  R. H. Myers,et al.  Probability and Statistics for Engineers and Scientists , 1978 .

[4]  J. Smetana,et al.  Theory of Tin Whisker Growth: “The End Game” , 2007, IEEE Transactions on Electronics Packaging Manufacturing.

[5]  Two-Phase Grain Structures.  Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis 1 , 2004 .

[6]  R. Holm.  Electric contacts; theory and application , 1967 .

[7]  Jay Brusse,et al.  Zinc whiskers: hidden cause of equipment failure , 2004, IT Professional.

[8]  R. Schetty.  Electrodeposited tin properties & their effect on component finish reliability , 2004, Proceedings of 2004 International Conference on the Business of Electronic Product Reliability and Liability (IEEE Cat. No.04EX809).

[9]  J. Conrad,et al.  Pb-free plating for peripheral/leadframe packages , 2001, Proceedings Second International Symposium on Environmentally Conscious Design and Inverse Manufacturing.

[10]  Paul G. Slade,et al.  Electrical contacts : principles and applications , 1999 .

[11]  Simos G. Meintanis,et al.  Estimation in the three-parameter inverse Gaussian distribution , 2005, Comput. Stat. Data Anal..

[12]  S. M. Arnold,et al.  Growth of Metal Whiskers , 1953 .

[13]  S.S. Asfour,et al.  Tin Whisker Electrical Short Circuit Characteristics—Part I , 2008, IEEE Transactions on Electronics Packaging Manufacturing.

[14]  G. Galyon,et al.  Annotated tin whisker bibliography and anthology , 2005, IEEE Transactions on Electronics Packaging Manufacturing.

[15]  Henning Leidecker,et al.  Tin Whiskers: A History of Documented Electrical System Failures , 2006 .

[16]  Gary J. Ewell,et al.  TIN WHISKERS: ATTRIBUTES AND MITIGATION , 2002 .

[17]  Shinji Kumagai,et al.  Application of inverse Gaussian distribution to occupational exposure data , 1997 .

[18]  A. Mendizza,et al.  Filamentary Growths On Metal Surfaces – “Whiskers”★ , 1951 .